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Structural evolution of the southwestern Daqing Shan, Yinshan Belt, Inner Mongolia, China

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Structural evolution of the southwestern Daqing Shan, Yinshan Belt, Inner Mongolia, China

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STRUCTURAL EVOLUTION OF THE SOUTHWESTERN
DAQING SHAN, YINSHAN BELT,
INNER MONGOLIA, CHINA
Brian Joseph Darby
A Thesis Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree of
MASTER OF SCIENCE
(Geological Sciences)
May 1999
Copyright 1999 Brian Joseph Darby
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UNIVERSITY O F SO U TH ERN CALIFORNIA
T H E G R A D U A T E SC H O O L
U N IV E R S IT Y PA R K
L O S A N G E L E S . C A L IF O R N IA 8 0 0 0 7
This thesis, written by
Brian Joseph D a r b y ____ ____
under the direction of Ai§.----Thesis Committee,
and approved by all its members, has been pre
sented to and accepted by the Dean of The
Graduate School, in partial fulfillment of the
requirements for the degree of
Master of Science
D ate Ap.riX_2_3j_j.9iL9
THESIS COMMITTEE
^ / J f O u o rm t M
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To Kristi
ii
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ACKNOWLEDGEMENTS
Greg Davis has been an outstanding advisor and a great friend. I thank
him for his guidance, support, and encouragement over the past 2 years. He has
taught me an immense amount of geology and much about life.
Zheng Yadong at Peking University has also been of great help. He is
responsible for invitations to China, arrangement of vehicles and drivers, finding
a field assistant, and translating (without which-1 surely would have gotten into
trouble).
There are several other people in China who also deserve recognition. My
field assistant, Ma Mingbo, for his help not only in the field, but also in ordering
dinner. Thanks to Wang Jianmin of the Nei Mongol Bureau for logistical support
and the head of the Bureau, General Shao Heming for providing borehole data
and endorsing this research.
The members of my committee, An Yin (UCLA) and Jim Dolan (USC), I
thank for the time and energy that they put into this project. They both gave
thorough reviews of an earlier version of the manuscript.
Discussions with Brooks, Aaron, and Keegan as well as the rest of the
strain lab crew have “enriched” my time at USC. Thanks for making me laugh
and for the good times throwing the “B”. The map and cross-sections in this
thesis could not have been printed without the wonderful plotter run by Nikki
Godfrey and Dave Okaya. Without Scott Paterson’s scanner, the map would not
have been made.
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Special thanks to my parents for all their love, help, and support
throughout my education. My soon-to-be wife Kristi and her awesome love
always put a smile on my face. Lunch in the rose garden was always great!
Thanks for being the amazing person you are!
This research was supported by the National Science Foundation (EAR-
9627909, awarded to Gregory A. Davis), the Geological Society of America
(Darby), the American Association of Petroleum Geologists Grants-in-Aid fund
(Darby), and the University of Southern California, Department of Earth Sciences
graduate student research fund (Darby).
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TABLE OF CONTENTS
DEDICATION................................................................................................... ii
ACKNOWLEDGMENTS................................................................................. iii
LIST OF FIGURES............................................................................................ vii
LIST OF PLATES.............................................................................................. viii
ABSTRACT........................................................................................................ix
INTRODUCTION...............................................................................................1
FIELD OBSERVATIONS................................................................................ 5
Stratigraphy............................................................................................5
Archean......................................................................................5
Proterozoic (?)........................................................................... 6
Cambro-Ordovician...................................................................6
Permian.......................................................................................8
Jurassic....................................................................................... 13
Structures.................................................................................................16
Reverse and thrust faults...........................................................16
Folds........................................................................................... 19
Cambro-Ordovician-cored isoclinal anticline............19
Jurassic disharmonic folding....................................... 22
Basement-involved folding......................................... 25
Normal faults............................................................................. 29
DISCUSSION..................................................................................................... 31
Timing relationships...............................................................................31
Jurassic reconstruction.......................................................................... 36
Tectonic chronology.............................................................................. 40
Tectonics................................................................................................ 44
CONCLUSIONS................................................................................................ 47
Appendix.............................................................................................................49
Detailed description of cross-sections..................................................49
Aw Aw’.......................................................................................49
AA’.............................................................................................49
BB’ .............................................................................................50
CC’ ............................................................................................. 52
DD’............................................................................................. 53
EE’.............................................................................................. 54
v
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FF’ 54
GG7.............................................................................................55
HH7.............................................................................................56
E 7................................................................................................56
References.......................................................................................................... 58
vi
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LIST OF FIGURES
Figure 1: Location map and tectonic setting of the southwestern Daqing
Shan................................................................................................ 2
Figure 2: Foliation in the Archean gneiss....................................................... 7
Figure 3: Anticlinal fold hinge in Cambro-Ordovician
carbonates....................................................................................... 9
Figure 4: Unconformity between Permian and Cambro-
Ordovician strata............................................................................ 10
Figure 5: Photograph of Permian section.........................................................11
Figure 6: Boulder conglomerate facies in Jurassic strata............................... 14
Figure 7: Low-angle thrust juxtaposing Archean gneiss and
Jurassic strata...................................................................................18
Figure 8: Faulted Archean, Cambro-Ordovician,
and Permian units...........................................................................20
Figure 9: Disharmonic folds in Jurassic strata along section Aw Aw’.......... 23
Figure 10: Disharmonic folds in Jurassic strata along section FF’ ............... 24
Figure 11: Folded and faulted Archean and Jurassic units along
section BB’..................................................................................... 26
Figure 12: Photograph of sub-isoclinal syncline.............................................27
Figure 13: Syndepositional normal faults in the Jurassic section................. 30
Figure 14: Small fold under Permian/Cambro-Ordovician
unconformity.................................................................................. 32
Figure 15: Jurassic/Cambro-Ordovician unconformity.................................. 34
Figure 16: Jurassic basin reconstruction......................................................... 38
Figure 17: Time scale for southwestern Daqing Shan................................... 41
Figure 18: Tectonic map of Asia......................................................................45
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LIST OF PLATES
Plate 1: 1:12,500 geologic map of the southwestern Daqing Shan,
Inner Mongolia, China.............................................................map pocket
Plate 2: True-scale geologic cross-secitons, southwestern Daqing
Shan, Inner Mongolia, China.................................................. map pocket
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ABSTRACT
The southwestern Daqing Shan lie -500 km west of Beijing along the
northern edge of the North China craton and within the amalgamated North China
plate. The southwestern Daqing Shan are part of the Yinshan belt, an east-west-
trending, >1100 km-long zone of folding and thrusting mainly of Jura-Cretaceous
age. Unlike other areas of the Yinshan belt, the southwestern Daqing Shan lacks
the large scale, low-angle thrust faults and plutons that obscure and overprint
much of the belt’s early history. Thus, this area is an ideal locality to understand
how and when the belt began to form.
Detailed mapping, construction of numerous cross-sections, and analysis
of relations between structures and stratigraphic units allow for the distinction of
multiple deformational events in the southwestern Daqing Shan. The structural
chronology begins in post-Cambro-Ordovician time with the broad folding and
down-dropping of Cambro-Ordovician strata. Following deposition of a Permian
clastic sequence, Cambro-Ordovician and Permian sediments were folded into an
isoclinal anticline. Possibly during this post-Permian/pre-Early Jurassic
contractional deformation, north-directed, low-angle, basement-involved thrusts
juxtaposed Archean gneiss over Permian strata. Strata were deposited
syntectonically, in Early Jurassic time, in an east-west trending half-graben with
its master fault along the southern margin. The half-graben was inverted in the
Late Jurassic, resulting in a second generation of basement involved folds (some
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sub-isoclinal in geometry), high-angle reverse faulting, and lesser low-angle
thrusting. Dominant tectonic vergence appears to be to the north. Minimum
Jurassic north-south crustal shortening in the southwestern Daqing Shan has been
estimated at ca. 30%. Following Late Jurassic contraction, the southwestern
Daqing Shan experienced minor extension, which may be of Cretaceous age.
Currently, the southern margin of the Daqing Shan is delineated by an active,
south-dipping, normal fault of major proportions.
The tectonics of the southwestern Daqing Shan may be related to far-field
effects of plate interaction. Post-Cambro-Ordovician/pre-Permian broad folding
and extension might be related to either Devonian collision along the southern
margin of the North China craton, or Permian back-arc spreading during south-
directed subduction along the north side of the North China craton. Accretion of
Paleozoic Mongolian arcs to the craton along this subduction boundary (the
Suolon suture) in Permo-Triassic time could be responsible for post-Permian-pre-
Early Jurassic isoclinal folding and low-angle thrusting. Late Jurassic
contractional deformation in the southwestern Daqing Shan and elsewhere in the
Yinshan belt is most likely an intraplate response to closure of the Mongolo-
Okhotsk ocean 800-1000 km to the north or, less likely, to accretion of crustal
blocks to the south along the Bangong suture.
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INTRODUCTION
The Asian continent is perhaps best described as a tectonic collage
composed mainly of several continental blocks and island arc complexes that
have been assembled over the Phanerozoic period (Yin and Nie, 1996; Sengor and
Natal’in, 1996). Currently the southwestern Daqing Shan, located -500 km west
of Beijing (Fig. 1), lie within an amalgamated North China plate, which includes
the North China craton and the Paleozoic Mongolian arcs terrane (the Altaids arcs
of Sengor and others, 1993 and Sengor and Natal’in, 1996). Located just to the
north of the southwestern Daqing Shan, the Suolon (or Suolon-Linxi) suture (Fig.
1), separates the North China craton from the Mongolian arcs terrane and is
thought to record the amalgamation of the craton and arc terrane in Late Permian
to Early Triassic time (Zhang et al., 1984; Wang and Mo, 1995; Yin and Nie,
1996; Zheng et al., 1996). The amalgamated North China plate is bordered by the
Qinling-Dabie suture zone to the south and the Mongolo-Okhotsk suture to the
north, both of which have recently received much geologic attention (Fig. 1;
Davis et al., 1998a). The Qinling-Dabie suture zone separates the North and
South China plates, with closure of the intervening ocean basin in Permo-Triassic
time (Yin and Nie, 1993, 1996). Younger closure of the Mongolo-Okhotsk ocean
and the collision from west to east of Siberia with the North China plate, in Jura-
Cretaceous time forms the Mongolo-Okhotsk suture (Nie et al., 1990; Zonenshain
et al., 1990; Ziegler et al., 1996; Yin and Nie, 1996).
1
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Siberia North.
108
V ' - ' V 0 <
v' «“ / ' > 7 V — /
. / o r - .
. • V . * •>■*
Suofun
.y c u
o C D
Otdos
Hehua
K i ometers
— _South Chmajolate — — — _
Figure 1. Location map showing the tectonic setting of the southwestern Daqing
Shan (small black box) and Yinshan belt. Dark grey shading indicates areas of
Jura-Cretaceous contractional deformation and structural trends (black lines).
Stippled pattern represents Late Mesozoic basins (Hailar/Tamsag, Erlian
Songliao, Bohai Bay, Hehaui, Ordos). Sutures from north to south include the
Jura-Cretaceous Mongolo-Okhotsk, Permo-Triassic Suolon, and the Permo(?)-
Triassic Qinling-Dabie zone (QDZ). Location of paleo-Pacific subduction zone
approximate. ★=Beijing, H= Hohhot, B= Baotou, T= Taihang Shan. Modified
from Davis et al. (1996, 1998a).
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The Yinshan belt lies within the North China plate. It is an approximately
1100 km-long, E-W-striking fold and thrust belt of mainly Jura-Cretaceous age.
Extending from north of Bohai Bay, the belt can be followed west to Inner
Mongolia where it is concealed by Cenozoic sediments. The stable Mesozoic
Ordos basin defines the southern margin of the belt in the west, while northeast-
southwest-trending structures of Mesozoic age in the Taihang Shan coalesce with
structures in the Yinshan belt just west of Beijing (Fig. 1; Davis et al., 1998a; cf.
Wang et al., in review). This paper focuses on the structural evolution of the
southwestern Daqing Shan in the western portion of the Yinshan belt.
Recent work in the central and eastern Yinshan belt has documented the
existence of several large, low-angle thrust faults of Indosinian (Triassic-Early
Jurassic?) and Yanshanian (Late Jurassic) age (Davis et al., 1996,1998a, 1998b,
in review; Zheng et al., 1998). The southwestern Daqing Shan near Baotou lack
the large low-angle thrust faults and large plutons found in more eastern parts of
the range that obscure and overprint much of the early history of the belt. This
makes the southwestern Daqing Shan an ideal locality to study the early history of
the Yinshan belt, providing insights of how and when the belt began to form.
Detailed mapping of a portion of the southwestern Daqing Shan for this study has
revealed a complicated deformational history that begins in the early Paleozoic
and includes multiple extensional and contractional events.
The original mapping of the southwestern Daqing Shan was conducted in
the 1920’s and documented the existence of several coal-bearing basins (Wang,
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1928). Regional geologic surveys conducted in the late 1960’s and early 1970’s
by mapping crews from the Regional Geologic Survey Brigade of the Nei Mongol
Autonomous region produced maps at 1:200,000 for the southwestern Daqing
Shan and in addition, they attempted to establish a regional stratigraphy while
defining the general structural trends. Although these maps are useful for
establishing general rock units, the ages assigned to units sometimes differs from
map sheet to map sheet. Wang and Yang (1986) conclude that coal-bearing
basins in the southwestern Daqing Shan are bounded by thrusts, which have the
opposite sense of vergence and no more than 10 km of displacement. More
detailed, 1:50,000 maps and/or mapping in progress by the Nei Mongol Bureau of
the southwestern Daqing Shan are not available to the author.
To the east and west of the southwestern Daqing Shan, several workers
have recently reported major Jura-Cretaceous thrust structures. In the Bei Shan
and Gobi areas, several hundred kilometers west of the southwestern Daqing
Shan, Zheng et al. (1991,1996), report the existence of Jurassic thrust sheets with
over 100 km of displacement. Closer to the southwestern Daqing Shan, but -80-
100 km to the east of the field area, the Daqing Shan thrust has recently been
identified by several workers (Zheng et al., 1998; Zhu, 1997). Minimum
displacement on the Daqing Shan thrust, which involves Precambrian basement
rocks, is -22 km, with transport to the north-northwest (Zheng et al., 1998).
In a summary of Inner Mongolian structure and tectonics, Wang Yu
(1996) suggests that deformation in the Daqing Shan is long-lived, with several
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episodes of deformation beginning in the Permian when basins formed as a result
of back-arc extension during south-directed subduction along the Suolon suture.
The Permian basins were then deformed by collision of the North China plate
with the Mongolian arcs terrane in Permo-Triassic time (ibid.). Wang Yu (1996)
reports that down-warped, coal-bearing basins, in the troughs of synclines, were
formed in Late Triassic to Early Jurassic time and were subsequently shortened in
late Early Jurassic to Middle Jurassic time.
FIELD OBSERVATIONS
This work establishes a stratigraphy for the field area and maps structures
and relations between units in order to decipher the structural chronology and
tectonic history of the southwestern Daqing Shan. The ages of rock units were
established by discussion of the field area with researchers who work in the
Yinshan belt at a May, 1998, conference in Hohhot. Mapping was carried out
with the use of a hand-held GPS unit that recorded the position of each station.
Stations and data collected were then plotted on a latitude/longitude grid, which
produced the geologic map in this thesis (PI. 1, map pocket).
Stratigraphy
Archean
Plate 1 is a geologic map that shows four pre-Cenozoic units that were
mapped in the western Daqing Shan. The oldest unit is undifferentiated Archean
gneiss (Arg, PI. 1) that boldly crops out over a large portion of the field area and
generally forms the highest peaks. This unit is the basement of the
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southwestern Daqing Shan and includes amphibolitic, granitic, and gamet-bearing
gneisses, all of which are strongly layered and foliated. Transects across the
Archean gneiss along roads between Heimaban and Yangkeleng, and Weijun and
Adaohai reveal that foliation in the gneiss typically strikes N-S (±15°) and dips
~80°E (±15°; PI. 1; Fig. 2). This trend is nearly orthogonal to the post-Archean
structural trends in the southwestern Daqing Shan and, as discussed below,
makes it difficult to explain how the basement gneiss deformed when the
overlying sedimentary cover was folded into E-W trending synclines and
anticlines of at least two generations.
Proterozoic (?)
An enigmatic, highly fissile, brown, schistose unit is found only near the
town of Yangkeleng in the northwest portion of the study area. The protolith of
this unit may have been a sandstone or siltstone but is difficult to determine due to
its highly weathered nature. This localized unit lies below unmetamorphosed
Jurassic strata and above the Archean basement. Its thickness is on the order of a
few meters to 10 meters. Its metamorphic grade is less than the Archean gneiss,
suggesting that it may be Proterozoic in age.
Cambro-Ordovician
Cambro-Ordovician age strata are preserved in the northern portion of the
field area (PI. 1). Cambro-Ordovician strata rest unconformably on the Archean
gneiss and this contact is exposed at several localities in the northwestern portion
of the field area. In contrast to areas to the east near Hohhot, Proterozoic strata
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Figure 2. View to the north of foliation in
the Archean basement. Foliation trends ~N-
S and dips ~75°E. See Plate 1 for attitudes.
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are absent in the southwestern Daqing Shan, suggesting that they may have been
eroded prior to Cambrian time. Cambro-Ordovician strata are mostly buff-to-tan-
weathering carbonates, although the base of the section has minor glauconite-
bearing sandstones, green micaceous shales, and local quartzite pebble
conglomerates along the nonconformity. The carbonates in this unit typically are
bedded on a 10-20 cm scale. Cambro-Ordovician strata within the study area are
folded into an E-W-trending, isoclinal anticline (Fig. 3; PL 1; PI. 2 CC’, F F \ GG’
and IF).
Permian
A Permian section of conglomerate, sandstone, shale, and coal rests
variably on both Cambro-Ordovician strata (Fig. 4; PI. 1; PI. 2) and Archean
gneiss. Permian strata are most abundant in the northern portions of the field area
and are now highly deformed (Fig. 5). The age of this unit is inferred from plant
fossils found in coal beds (Nei Mongol Bureau, 1:200,000 and 1:1,500,000 maps).
The basal portion of the Permian section consists of massive buff-colored,
quartzite cobble conglomerates interbedded with thick coal seams and sandstone.
This basal section is usually -20-40 meters thick and typically overlain by a 10-
20-meter thick coal seam. Above the coal seam, thick conglomerate beds are
interbedded with much thinner coal seams and sandstone. Above the
stratigraphically highest major thick-bedded, quartzite cobble conglomerate (a
few hundred meters from the base of the section), the Permian section changes
gradationally both in color and in Iithology - becoming pink to red and having
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Figure 3. Anticlinal fold hinge in Cambro-Ordovician (€-0) carbonates.
Anticline is isoclinal and also involves Permian strata (P).
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Figure 4. Angular unconformity between Permian (P; right side) and
Cambro-Ordovician (€-0; left side) strata. View to the west along the
northern limb of an isoclinal anticline (PI. 2, GG’). Note person inside
white circle for scale.
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Figure 5. Photo looking to the northeast of a folded Permian section. The
minimum thickness of the Permian is — 1.5 km. White beds consist of
conglomerate and sandstone.
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much more fine-grained strata. Pebble-to-cobble-conglomerate beds in the upper
portion of the section, usually several meters in thickness, are rhythmically
interbedded with red mudstones and pinkish cross-bedded sandstones. The clast
composition of the conglomerates changes upsection from quartzite to a mixture
of gneiss, quartzite, minor felsic volcanics, and rare carbonate clasts. Near the top
of some mudstone horizons, just below some conglomerate beds, carbonate
nodules can be found, which may represent paleosols. The minimum thickness of
the Permian section is >1.5 km. It’s top was not seen in the study area.
The source of the quartzite cobbles is enigmatic. The most likely source
for the large amount of quartzite is the Proterozoic section, although, Proterozoic
strata have been missing from the southwestern Daqing Shan since prior to
deposition of the Cambro-Ordovician strata. Quartzite beds can be found in the
Cambro-Ordovician section, but in only a minor amount and not nearly enough to
supply material for several hundred meters of cobble conglomerate. The quartzite
cobbles may have been derived from the north and transported south although the
direction of sedimentary transport (as indicated by sedimentary structures) was
not measured due to time constraints. A northern source is suggested because in
Permian time, the northern margin of the North China craton was an active
convergent margin, which lead to the amalgamation of the North China craton
with the Mongolian arcs terrane along the Suolon suture in Late Permian to Early
Triassic time (Fig. 1; Zhang et al., 1984; Wang and Mo, 1995; Yin and Nie, 1996;
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Zheng et al., 1996). Convergence along this zone may have produced a
topographic high that shed detritus (quartzite cobbles) to the south.
Felsic volcanic clasts found in conglomerates in the upper portions of the
Permian section may have been derived from nearby volcanic strata. The closest
possible source is 10-15 km west of the study area where undated felsic volcanics
are interbedded with sedimentary strata and intruded by a syenitic pluton. This
pluton was collected for U-Pb (zircon) dating, but its age has not been determined
as of late April 1999.
Jurassic
The Jurassic section, consisting of buff/tan/grey sandstone, conglomerate,
black shale, and coal, is wonderfully exposed and preserved in narrow synclinal
basins bordered by steeply dipping reverse faults and unconformities (the latter,
locally overturned; PL 1; PI. 2). Jurassic strata are in both fault contact with, and
rest unconformably on, all older units. Age control on the Jurassic strata is
lacking due to the terrestrial nature of the section, although an Early Jurassic age
has been assigned by the Nei Mongol Bureau (1971, 1991) based upon regional
correlation and plant fossil ages derived from coal beds.
In southern exposures of Jurassic strata, the section contains coarser-
grained strata and lacks coal and abundant shale. A boulder conglomerate facies,
with clasts as large as 2 meters, is present along the southernmost outcrops of the
Jurassic section and extends only a few hundred meters into the basin (Fig. 6).
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Figure 6. Boulder conglomerate facies in the southern exposure of Jurassic
strata. Boulders up to 2 meters can be found. Facies extends only a few
hundred meters to the north. Greg Davis (center) and Zheng Yadong (right)
for scale.
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Pebble conglomerate and sandstone dominate the rest of the southern exposure of
the Jurassic section with lesser shale and cobble conglomerate. Central exposures
in the study area of Jurassic strata contain less pebble conglomerate, more
sandstone and shale, as well as several coal beds. Jurassic sedimentary rocks
continue to fine northwards with exposures containing mostly sandstone, shale,
several coal beds, and minor pebble conglomerate. The thickness of the Jurassic
section is variable, but appears to be on the order of 500-1,000 meters, although
the original top of the section is not defined.
The clast composition of the Jurassic conglomerates and sandstones varies
slightly, but is mostly dominated by detritus derived from the Archean gneiss. In
south and southwestern exposures, cobbles and boulders of a distinctive
red/brown Permian(?) syenitic pluton can be found. A provenance for these
plutonic clasts is not known with certainty, although a pluton of this composition
lies about 10 km to the west. To the north, Jurassic strata locally contain clasts
and fragments of Cambro-Ordovician sandstone, green shale, and minor
carbonate. This is not surprising given that Jurassic strata rest along a strongly
discordant angular unconformity with the Cambro-Ordovician. Quartzite cobbles
are also locally found in the Jurassic conglomerates and may be reworked from
Permian strata.
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Structures
Reverse and thrust faults
Reverse/thrust faults in the southwestern Daqing Shan trend ~E-W. Most
contractional faults in the field area dip steeply (PL 1; PL 2) and include the
reverse faults that border Jurassic exposures as well as a fault that places Archean
gneiss over the Permian in the northern portion of the field area (PL 2, F F \ GG’,
and IF). The basement-involved faults are exposed in many localities and
typically have well-preserved striae and rare tension-cracks. The dip of the
reverse faults tends to vary along strike as shown by the southernmost reverse
fault bounding the Jurassic section (e.g. 39-85° dip variation; c.f. PL 1; PL 2). All
of the steep reverse faults cut Jurassic strata and at least some of these steep faults
may represent inversion of Mesozoic normal faults or the reactivation of pre
existing basement anisotropies.
There are two, possibly three, low-angle thrust faults in the field area, two
of which are located in the central portion of the map (PL 1; PL 2, FF’)- The
higher of these two thrust faults places Archean gneiss on top of a thin sequence
of Permian sandstone and conglomerate that has a fairly consistent thickness of
-30-40 meters. Permian strata in the lower plate of this thrust rest unconformably
on the Archean. The thrust is exposed at several places, one of which has
preserved tension cracks and striae that suggest upper plate movement to the
north. This upper thrust can be tracked to the south where it is cut by a steep
reverse fault that borders the southern belt of Jurassic strata (PL 1; PL 2 FF’).
16
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The consistent thickness of the Permian lower-plate section may be a function of
the overlying thrust following the lowest major coal seam within the Permian
section, located -30 meters from the base of the section. Minimum displacement
on this thrust fault based upon structural overlap is -1.6 km.
The lower of the two thrust faults carries the upper thrust in its upper plate
and places Archean gneiss and its Permian cover over a sequence of highly folded
Jurassic sediments (PI. 1; PL 2, FF’; Fig. 7). The thrust dips gently to the south
and is well exposed at several locations. Striae and tension cracks on the fault
surface suggest movement to ~N10°W, a direction nearly perpendicular to the
strike of fold hinges in the footwall of the thrust. The thrust can be followed to
the south until Jurassic strata in the footwall are cut out, making it difficult to
follow a thrust that juxtaposes upper and lower plate Archean gneiss. A
detachment horizon in the Jurassic section is present in the footwall of this thrust.
Above it strata have experienced strong disharmonic folding (PL 1; PL 2, FF’).
Below the detachment horizon, which is probably a coal bed, the Jurassic strata
are only broadly folded (Pl. 2, FF’). Minimum displacement along this low-angle
thrust is -1.2 km.
A third low-angle thrust fault is illustrated on cross-section II’, in the east-
central portion of the field area (PL 2). The thrust fault places Archean gneiss and
Permian conglomerates/sandstones on top of footwall Jurassic sediments, all of
which are folded into a synform. This thrust is thought to be north-directed
despite a small syncline, overturned to the south, located along the southern
17
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Figure 7. Low-angle thrust, placing Archean gneiss (Arg) over folded Jurassic
strata (Jr). View to east along Plate 2, HH’. See text for details.
18
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margin of the thrust (PI. 2, II’). The syncline is interpreted to have formed during
folding of the thrust. The complicated geometry in the hangingwall of this folded
thrust could be the result of multiple generations of thrust faulting.
Folds
Cambro-Ordovician-cored isoclinal anticline
The most dramatic example of folding in the area of Plate 1 is an isoclinal
anticline in the northern portion of the field area (see also PI. 2, C C \ FF’, G G \
IT) that involves Cambro-Ordovician and Permian strata. Disharmonic folds
occur throughout the isoclinal structure. The Cambro-Ordovician and Permian
strata are separated by an angular unconformity (< 25°) that can be followed from
the north limb of the structure, over the hinge of the fold, to the southern limb,
where it is only locally preserved and cut by a steep reverse fault (Fig. 8). A
syncline to the north is most likely related to the formation of the isoclinal
anticline (PI. 1; PI. 2, CC’, FF’, II’). It is likely that folds to the south of the
isoclinal anticline involving the Permian section are related to isoclinal fold
formation, although development related to north-directed, basement-involved
faulting is possible (PL 1; PI. 2, FF’, G G \ II’). Shortening across the isoclinal
anticline is ca. 60%, calculated by removing displacement along bordering faults
(constrained by offset unconformities) and restoring the folded Cambro-
Ordovician/ Permian unconformity to horizontal.
19
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Figure 8. View to the east of folded and faulted Archean (Arg), Cambro-
Ordovician (-C-0), and Permian (P) units. On the left, Cambro-Ordovician
carbonates, which form the southern limb of an isoclinal anticline, are juxtaposed
with Permian clastic strata along a steep reverse fault. Folded Permian strata are
overridded by a thrust carrying Archean gneiss (right side of photo). Northern
portion of section 11’ (PI. 2) drawn along high ridge. Section HH’ (PI. 2) drawn in
foreground drainage.
20
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The Permian clastic sequence rests directly on the Archean basement
south of the isoclinal anticline. This suggests that Cambro-Ordovician strata
occupied a structurally low position prior to deposition of Permian sediments.
Cambro-Ordovician strata might have been preserved in the trough of a syncline
or in a graben or half-graben. A graben or half-graben requires a normal fault to
juxtapose the Cambro-Ordovician sequence and more southerly Archean
basement. This fault may be exposed in the study area along section line CC’ (PI.
2), just south of the isoclinal structure (see below for discussion). Borehole data
located at N 40° 40’ and E 110° 24’ (about 1 km north of the study area) provided
by the Nei Mongol Geological Bureau indicate that Cambro-Ordovician strata are
not present north of the isoclinal anticline. Boreholes begin in Jurassic strata and
at -150 m depth, penetrate the Archean basement without encountering Permian
or Cambro-Ordovician strata. The author, thus, favors a graben or half-graben
model to explain relations between Cambro-Ordovician strata and Archean
basement.
In the northwestern portion of the field area (PI. 1), the exposed
unconformity between the Cambro-Ordovician and Archean has not been folded
into an isoclinal anticline, as has the Cambro-Ordovician section above it (PI. 2,
BB’). This contrast in the amount of folding between the Archean basement and
the overlying Cambro-Ordovician/Permian cover implies that there must be an
accommodating structure between Cambro-Ordovician strata and the basement.
This structure, most likely a low-angle thrust that allows the basement to
21
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deform differentially from its Cambro-Ordovician cover, could dip to the north
and now be covered by Permian and Jurassic sediments. Alternatively, the low-
angle thrust could dip to the south, but was not seen because time constraints did
not allow for the detailed mapping of the Archean basement in that area. The
intense disharmonic folding of the Cambro-Ordovician carbonates might also
have been aided by slip along detachment horizons in the Cambro-Ordovician
section.
Jurassic disharmonic folding
Strongly disharmonic folding occurs in the east-central and southern
exposures of Jurassic strata (PI. 2, Aw Aw’, CC’, DD’, FF’, HET, II’; Figs. 9, 10).
Many of these structures are tight and overturned with the dominant sense of
tectonic vergence to the north and gentle plunges to the east. Some of these folds,
including some recumbent structures, may have developed as a result of
detachment along coal beds or shale horizons. It is interesting to note that an
axial (?) planar cleavage is found at only one locality in Jurassic strata in the east-
central field area, just west of cross-section line I (PI. 2) along the road between
Weijun and Adaohai (PI. I). Spacing of the weakly developed cleavage is -10
cm. The lack of cleavage in the rest of the field area may be a function of
deformation taken up in abundant small faults and shear zones (short red lines on
Plate 1) and slip along detachment horizons as discussed above.
22
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Figure 9. Disharmonic folds involving Jurassic strata. View to the west. Folds
are located along section line Aw Aw’ (PI. 2), just north of Dongyuan, a small
town along the mountain front. Field of view is — 100 meters.
23
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Figure 10. Strong disharmonic folding in Jurassic strata, near section FF’ (PL 2),
below low-angle thrust. View to the east. Folds appear to be the result of
detachment above an underlying stratigraphic horizon (coal?)..
24
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Basement-involved folding
The basement/sedimentary cover contact is clearly folded throughout the
field area (PI. 2, B B \ FF’, G G \ II’), although the strike and dip of the foliation in
the basement (~N-S, -15° E) lies at a high angle to structural trends. This
geometry complicates the deciphering of basement rock behavior during folding,
1.e., folding is at a high angle to the Archean foliation and cannot, therefore, be
facilitated by slip on favorably oriented surfaces of anisotropy in the basement
gneiss. The tight folding of the Jurassic/Archean and Permian/Archean
unconformities into narrow synclines (Fig. 11; some sub-isoclinal in geometry; PI.
2, BB’, GG’, II’) requires profound shallow level folding of the Archean gneiss as
well. Figure 12 is a photograph illustrating the extreme narrowness of a Jurassic
sequence and the vertical orientation of its strata; the southern (left hand) contact
is a nonconformity while the northern contact is a nonconformity at the lowest
topographic levels (only locally preserved) and a steep fault at higher levels.
Again, the foliation of the bordering Archean gneiss is nearly vertical and strikes
at nearly right angles to the fold hinge and parallel to the plane of the photograph
(PI. 1).
Although fabric in the basement has been shown to influence the
development, orientation, and geometry of basement involved folds in the
Laramide Rocky Mountains of western North America (e.g. Chase et al., 1993;
Miller and Lageson, 1993; and Schmidt et al., 1993), that does not seem to be the
case with folds in the southwestern Daqing Shan. Miller and Lageson (1993)
25
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Figure 11. Folded and faulted Jurassic strata (Jr) and Archean gneiss (Aug).
View to the east. Note that the basement cover contact is folded. Southern
portion of section line BB’ (PI. 2) located along ridge top.
26
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Figure 12. View to the west of faulted subisclinal syncline of Jurassic
strata (Jr) enlcosed with Archean gneiss (Arg). Picture is taken from
section line II’ (Pl. 1) in the central portion of the field area. The
foreground consists of folded Jurassic conglomerate, sandstone, and shale,
while the background shows a narrower, subvertical portion of the
syncline. Well-exposed nonconformities between Jurassic strata and
Archean gneiss are present on both limbs at lowest structural levels
shown. At higher structural levels the northen contact between clastic
rocks of the basin and Archean gneiss is a steeply dipping reverse fault.
Sub vertical foliation in the Archean gneiss strikes at right angles to the
syncline hinge and in the approximate plane of the photograph.
27
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report that when the discordance between the foliation in the basement and
overlying sedimentary cover is less than 25°, the basement folds similarly to the
overlying cover due to flexural slip along foliation planes. If the angle of
discordance between the foliation in the basement and bedding in the overlying
cover is great (similar to that in the study area), Miller and Lageson (1993)
conclude that the basement does not fold, rather it deforms as several rigid blocks
separated by steep reverse faults. This seems contrary to mapped relations in the
southwestern Daqing Shan (PI. 1)
In the southwestern Daqing Shan, little to no shear is observed along the
basement cover nonconformity where it is exposed. It seems that it is not possible
to accommodate folding by allowing for slip to occur along foliation planes.
Although steep faults can be seen in the Archean basement, the age of movement
along such structures is difficult, if not impossible, to determine because there is
no overlying sedimentary cover. Lineations in the Archean gneiss are not
abundant and therefore cannot help to constrain basement behavior and determine
if block faulting or bulk rotation plays a major role in basement deformation.
Field observations (e.g. steep folding of nonconformities; Figs. 11, 12) require
that the basement has been folded, despite the orientation of the fabric in the
Archean gneiss.
28
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Normal faults
Several normal faults can be found in the southwestern Daqing Shan,
including an active structure at the mountain front. The mountain front fault
surface is exposed at several localities, dips ~ 45-55° southward, and can be seen
truncating and offsetting Quaternary alluvium. Fault surfaces typically contain
striae that indicate pure dip-slip movement. Fault scarps cutting modem alluvial
fans can be seen at many locations along the mountain front.
Normal faults are also found at several localities in lower portions of the
Jurassic section (PI. 2, AA’, BB’, EE’). The best-exposed example of these faults
occurs in the southern exposures of Jurassic strata along section line BB’ (Fig. 13;
PI. 2). These small normal faults cut the lower 20 meters of the Jurassic section
and extend into the Archean basement. Higher Jurassic strata overlie the faults
and are not displaced. This suggests to the writer that the normal faults are
synsedimentary in nature and were active during the early depositional history of
the Jurassic strata.
Other potential normal faults include the fault in the north-central field
area that separates Cambro-Ordovician carbonates from Archean gneiss (PI. 2,
CC’). This fault has limited exposure due to cover by Jurassic strata, but may
have had normal displacement. Several small normal faults can be seen cutting
folded Jurassic and Permian strata (PI. 1). These structures tend to be small, with
limited displacement (PI. 2, CC’, FF’).
29
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Figure 13. Syndepostional normal faults in the lower portions of the Jurassic
section. Faults (black lines) offset lower 20 meters of Jurassic strata while upper
portions of the section are not effected (white line).
30
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DISCUSSION
Timing relationships
Field relations between units and structures allows for the relative timing
of folding and faulting events to be determined. Cambro-Ordovician strata rest
unconformably on the Archean basement. The lack of Proterozoic strata in the
study area suggests the existence of a Pre-Cambrian event that allowed for the
assumed erosional removal of Proterozoic strata still present -80 km to the east.
The angular unconformity (up to 25°) between the Permian and the Cambro-
Ordovician implies that the Cambro-Ordovician strata were broadly folded before
the Permian. A small overturned fold (~ 1 m across) was observed just below the
angular unconformity near section line II’ (Fig. 14; PI. 1; PI. 2). Just to the south
of Cambro-Ordovician exposures, Permian conglomerates rest unconformably on
the Archean basement (PI. 1; PI. 2, FF’, GG\ 1 1 ’). This relationship requires that
a pre-Permian structure had juxtaposed Cambro-Ordovician and Archean rock
units. The inferred structure - presently a high-angle fault - is exposed near
section line CC’ (PI. 2) in the northern portion of field area, just south of the
isoclinal anticline. It is most likely a normal fault, down-dropping Cambro-
Ordovician strata against the Archean basement. It is unclear if the broad folding
of the Cambro-Ordovician section, prior to deposition of the Permian is related to
displacement along this fault or to another deformational event.
31
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Figure 14. Permian (P)/Cambro-Ordovician (C-0) angular unconformity.
Note small overturned syncline in Cambro-Ordovician carbonates. Hammer
for scale.
32
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Pre-Jurassic/post-Pennian (Indosinian) contractional deformation in the
southwestern Daqing Shan can be seen in the spectacular isoclinal anticline and
related syncline in the northern mapped area (PL 1, PL 2, BB’, CC’, FF’, GG’,
II’). Along the southern edge of the isoclinal anticline, gently dipping Lower
Jurassic sandstones and shales rest unconformably on nearly vertical Cambro-
Ordovician strata on the south limb of the isoclinal anticline (Fig. 15; PL 2, CC’).
Because Permian strata (see PL 2, IT) are also folded in the anticline its age is
post-Permian and pre-Early Jurassic.
A low-angle thrust, which places Archean gneiss atop a thin section of
Permian conglomerates and sandstones above Archean basement (Pl. 2, FF’), is
interpreted to be pre-Jurassic (Indosinian?) in age. This age is based on the
unconformity between the Jurassic and the Archean units. It would seem that in
most places in the field area, the entire Permian section had been stripped by
erosion prior to deposition of Jurassic strata. If not, then we would expect to see
Jurassic strata sitting on Permian, and Permian strata resting unconformably on
Archean gneiss. The nonconformity between Permian and Archean units that is
preserved in the lower plate of the upper, low-angle thrust (PL 1; PL 2, FF’),
suggests that thrust faulting occurred prior to stripping of the Permian section
from the central and southern portions of the field area and before deposition of
Early Jurassic strata.
33
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Figure 15. Angular unconformity between Jurassic (Jr) and Cambro-Ordovician
(-C-0) strata. Broadly folded Jurassic sandstones rest on folded, vertical
Cambro-Ordovician carbonates.
34
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All high-angle reverse faults cut Lower Jurassic strata. The folded thrust
located along section II’ (PL 2) and the structurally lowest, low-angle thrust (PI. 2,
FF’) also cut Lower Jurassic strata. Portions of the pre-Permian normal fault that
juxtaposes Cambro-Ordovician carbonate strata and the Archean basement appear
to have been reactivated (see PI. 2, FF’). If displacement along the northernmost
reverse fault, which dips steeply to the north in section FF’ (PI. 2), is backed-out
until the unconformity between the Permian and Cambro-Ordovician, and
Permian and Archean is at the same structural level the steep fault appears to be a
normal fault, juxtaposing Cambro-Ordovician and Archean units. The inversion
of portions of this fault is thought to be post-Early Jurassic in age, as along strike
to the west the steep reverse fault also deforms Lower Jurassic strata.
Normal faulting in the southwestern Daqing Shan is thought to have
occurred in both Early Jurassic time as syndepositional faults, and later, following
Jurassic contractional deformation. Steeply dipping normal faults are seen cutting
folded Jurassic and Permian strata in several locations (PI. 1; PI. 2, CC’, FF’).
The age of these structures is fairly unconstrained since they involve strata no
younger than Jurassic. It is unclear if the second generation normal faults are
related to the present episode of extensional deformation seen at the mountain
front or represent collapse/ relaxation of the crust after contractional deformation;
the latter alternative is favored for reasons discussed below.
35
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North of the Daqing Shan, in Inner Mongolia and southern Mongolia,
several basins such as the Erlian basin (Fig. 1) are known to have been actively
extending in late Mesozoic and early Cenozoic time (Traynor and Sladen, 1995;
Graham et al., 1996). Zheng et al. (1991) and Webb et al. (1999) have described
a major extensional structure, the Yagan metamorphic core complex,
approximately 400 km west of the study area along the China/Mongolia border.
Extension occurred in the Yagan core complex in Early Cretaceous time (-129-
126 Ma; Webb et al., 1999). North of Beijing in the Yunmeng Shan, 500 km to
the east of the study area, Davis et al. (1996) report formation of a probable mid-
Cretaceous extensional metamorphic core complex. Near Hohhot, 80 km to the
east of the study area, normal faults down-drop the Cretaceous Lisangou
formation in grabens and cut the older Daqing Shan thrust (Zhu, 1997; Zheng et
al., 1998). These relationships combined with data from the Erlian basin of Inner
Mongolia and Mongolia, the Yagan area, and the Yunmeng Shan, suggests that
late Mesozoic extension was a regional phenomenon. On the basis of regional
relationships, normal faults that cut folded Jurassic strata within the southwestern
Daqing Shan are most likely late Mesozoic (Cretaceous) age.
Jurassic reconstruction
Geologic relations in the field area and the conceptual removal of crustal
shortening, can be used to interpret the pre-folding and pre-faulting geometry of
the Jurassic exposures. Constraints on the pre-shortening geometry include
localized syndepositional normal faulting, sediment analysis, and the location
36
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of unconformities. Normal faults of limited displacement (up to several 10’s of
meters), seen at several localities, cut only lower portions of the Jurassic section
and suggest that Jurassic strata were deposited in an extensional environment.
The presence of an unconformity along portions of all the Jurassic exposures
might suggest that now-isolated Jurassic sections in the study area were once
continuous across the Archean basement. Due to reverse faulting and anticlinal
folding, the Jurassic-Archean nonconformity between the now-separated Jurassic
exposures was at higher structural levels subsequently removed by erosion.
In an attempt to calculate shortening of Jurassic strata across the study
area the unconformity at the base of the Jurassic has been modestly projected
below and above current exposure levels of the Archean basement (e.g. PI. 2,
B B \ dashed line). Shortening can then be calculated by flattening the projected
unconformity and by estimating its original line length as compared to its present
geometry (PI. 2, BB’). Using this method, a north-south shortening of -30% was
calculated. This amount is probably a minimum because there are inadequate
controls for projecting the unconformity above the Archean.
A half-graben model has been constructed for the Jurassic sedimentation
in the study area, removing 30% of post-Jurassic crustal shortening and
considering the available structural and sedimentary data (Fig. 16). The
northernmost exposure of Jurassic strata, just south of the Cambro-Ordovician-
cored anticline was used as a pinning point, with shortening removed to the south.
This location was picked because Jurassic strata rest unconformably on nearly
37
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Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission.
Jurassic basin reconstruction in the southwestern Daqing Shan with 30% shortening removed
. ...a tm .* V r l f lu
^ ;:A r g •
Kilometers
Approximate scale
No vertical exaggeration
l . A rg i V
TK fcaJ* /
9/
7
Figure 16. North-south Jurassic basin reconstruction with 30% shortening removed. Jurassic strata (Jr)
rest unconfonnably on Archean gneiss (Arg), nearly vertical Cambro-Ordovician (€-0) carbonates (north
side) and a pre-Jurassic low-angle thrust (see text for details). Note boulder conglomerate facies along the
southern margin and coal horizons in the central and northern portions of basin. Exact location and
number of coal horizons is unknown. P= Permian. Approximately true scale.
U >
00
vertical Cambro-Ordovician strata and also because displacement along the steep
reverse fault separating the Cambro-Ordovician and Jurassic (PL 2, CC’) is
probably less than 0.5 kilometers (see PI. 2, FF’)- The isoclinal anticline in the
Cambro-Ordovician might have formed a sedimentologic barrier, or structural
high, between Jurassic strata deposited to the south and to the north in the Shiguai
basin.
The author interprets the southernmost, Jurassic-bounding fault as the
master fault controlling formation of a half-graben. This is supported by the
presence of a border conglomerate facies (boulders up to 2 meters in diameter;
Fig. 6) that only extends several hundred meters northward into the Jurassic
exposure. Boulders in this facies most likely did not travel great distances (<10
km) and were probably being eroded off a nearby mountain front. Abrupt facies
changes can be seen near some faults, such as the northern fault in cross-section
A-A’ (PI. 2). North of this fault, the Jurassic section consists mostly of sandstone
and minor pebble conglomerate, while south of the structure the section consists
mostly of cobble and small boulder conglomerate with lesser amounts of
sandstone and pebble conglomerate (not shown on Plates 1 or 2). Additional
sedimentologic evidence, such as the general fining of grain-size northward and
the restriction of coal horizons to only central and northern exposures of Jurassic
strata also supports the reconstruction of Figure 16.
39
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We use the half-graben model to explain the present architecture of
Jurassic exposures. Normal faults, active in the Early Jurassic, are presumed to
have been structurally inverted and rotated and now form the steep reverse faults
that bound the various belts of Jurassic exposures. If this is correct, preexisting
normal faults essentially controlled the geometry of late contractional structures.
The reactivation of extensional faults so that they undergo reverse-slip, i.e. the
process of inversion (Cooper and Williams, 1989), has been documented in many
orogenic belts throughout the world including the Alps (Butler, 1989), the
Canadian Cordillera (McClay et al., 1989), and the Yanshan belt (Wang G. et al.,
1996).
Tectonic chronology
Field relationships between units and structures allow the recognition of
several deformational events beginning in the Paleozoic, thus shedding light on
the early history of the Yinshan belt (Fig. 17). The timing of each event is not
specific due to lack of radiometric age control, but is bracketed by rock unit ages.
The first Paleozoic deformational event involves Cambro-Ordovician strata and is
pre-Permian in age. During this event, Cambro-Ordovician strata were broadly
folded and juxtaposed with Archean gneiss, probably during normal faulting. It is
unclear if broad folding is related to normal faulting, although folding may
represent a separate, earlier structural event. Following deposition of Permian
strata and prior to deposition of Jurassic units, the southwestern Daqing Shan
underwent major N-S shortening (present day coordinates) that led to isoclinal
40
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Unit Deformation
d
Tectonic relation
Far-field effects of
Indo-Asian collision
©
O
100
200
300
400
o
o
hS-
©
©
CL
500
Neoaene
Paleogene
Cretaceous
Jurassic
Triassic
Permian
Carboniferous
Devonian
Silurian
Ordovician
Closure of Mongolo-
.Okhotsk ocean and/or
continued convergence/
collision to the south.
suture
Cambrian
600
Proterozoic
(missing)
Break in time scale
Figure 17. Time scale showing age of strata, deformational events, and possible
tectonic relationships of structural elements in the soutwestem Daqing Shan study
area. Wavy lines represent unconformities.
41
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folding of Cambro-Ordovician and Permian strata (Fig. 17). To the south, at least
one low-angle thrust developed in the basement and propagated into the Permian
section (PI. 2, FF’). Minimum northward displacement on this thrust is 1.6 km.
Almost all of the Permian strata south of the isoclinal anticline were stripped
away during and/or after this event, because Lower Jurassic strata rest
unconformably on the basement throughout most of the study area.
Subsequently, and probably in Early Jurassic time, the southwestern
Daqing Shan of the study area experienced N-S extension and formation of a half-
graben (Figs. 16, 17). Lower Jurassic sediments, which contain local
syndepositional normal faults, have a southern boulder conglomerate border
facies. The grain-size of these strata fine to the north, in support of the writer’s
interpretation that the master fault of the half-graben lay along the southern side
of the basin.
Following deposition of the Jurassic sequence, the basin was inverted,
reactivating and rotating pre-existing normal faults as steep reverse faults and
creating the synclinal folds seen in the Jurassic section. Low-angle, north-
directed thrusting also occurred during this event as documented by two thrust
faults, one of which has a minimum northward displacement of 1.2 km (PI. 2,
FF’). The other has been folded into a synform (PI. 2, II’). Both carry evidence
of post-Permian/pre-Jurassic thrust faulting in their upper plate (PL 2, FF’, II’).
Another example of north-directed, low-angle thrust faulting can be found in the
southern Jurassic exposure, ~5 km west of the field area and just north of
42
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Dongyuan (a town at the mountain front; PI. 2, Aw Aw’). Here, a well-exposed
low-angle fault offsets the southern Jurassic-bounding fault obliquely by -0.75
km.
The basement-involved structures described here predate and now lie in
the lower plate of the NNW-directed Daqing Shan thrust (See Zheng et al., 1998;
Davis et al. 1998b; Zhu, 1997) 80 km to the east. The timing of the Daqing Shan
thrust is constrained by folded Middle Jurassic strata in its lower plate and a
Cretaceous pluton that intrudes the thrust, dated at 119 ± 2 Ma (Ub-P zircon,
Zheng et al., 1998). Folded Middle Jurassic strata in the lower plate appear to
have a structural style similar to folds in the southwestern Daqing Shan (i.e.
basement-involved). The lower plate of the thrust might also contain some Lower
Cretaceous strata on the north side of the thrust trace (Zhu Shenyu, personal
communication, 1998), which would further constrain movement along the thrust.
Based upon the above timing relations, This major thrusting event is thought to be
Late Jurassic or Early Cretaceous in age.
Following Late Jurassic time, the southwestern Daqing Shan have
experienced at least two phases of extension (Fig. 17). Major normal faults cut
the Daqing Shan thrust and offset the Cretaceous Lisangou Formation (Zhu, 1997;
Zheng et al., 1998). There are several normal faults that cut Late Jurassic reverse
faults and associated folds, although the timing of movement cannot be further
constrained. Based upon regional trends, we favor a Cretaceous age. The last
phase of extension is the active normal faulting observed at the mountain front.
43
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Tectonics
The complicated tectonics of Asia, which began in the Paleozoic (Yin and
Nie, 1996), make it difficult to ascribe each of the deformational events described
above to a unique active plate margin of the appropriate age. Plate tectonic events
called upon to account for deformational events in the southwestern Daqing Shan
become more questionable with increasing age for two reasons: (1) lack of
radiometric age control on deformational events, and (2) in general, less
information about Paleozoic plate interactions in Asia. Figure 18 is a tectonic
map of Asia showing the major crustal blocks, accretionary complexes, and the
sutures that separate them. Paleozoic and Mesozoic sutures shown on Figure 18
from oldest to youngest are the Devonian Qilian suture, the Permo/Triassic
Suolon-Tian Shan suture, the Permian (?)/Triassic/Early Jurassic (?) Qinling-
Dabie suture, the Late Triassic/Early Jurassic Jinsha suture, the Late
Jurassic/Early Cretaceous Bangong suture, the Late Jurassic/Early Cretaceous
Mongolo-Okhotsk suture, and the Early Tertiary Indus suture (Yin and Nie,
1996).
The oldest event(s) in the southwestern Daqing Shan, i.e. post-Cambro-
Ordovician/pre-Permian broad folding, may be a result of the collision of the
Qaidam block along the southern margin of the North China craton in Devonian
time (Qilian suture; Figs. 17, 18). Alternatively, down-dropping of Cambro-
44
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N Qilian suture suture
Mongolo-Okhotsk suture
Bangong suture
Suolon-Tian Shan suture
Qinling-Dabie suture
\ Jinsha suture Indus suture
Figure i8. Tectonic map of Asia showing major crustal entities and sutures.
Sutures are discussed in text. Dark grey shading indicates location of Yinshan
belt (Y) and Taihang Shan (T). Black lines in grey shading indicate Mesozoic
structural trends in the Yinshan belt (~E-W) and the Taihang Shan (~NE).
Stippled areas indicate Late Mesozoic basins (HT= Hailar/Tamsag, E— Erlian, S=
Songliao, 0=Ordos, B= Bohai Bay (latest Mesozoic and Cenozoic, H= Hehuai).
Location of paleo-Pacific subduction zone estimated. Beijing. Modified
form Yin and Nie (1996) and Davis et al. (1996; 1998a).
45
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Ordovician carbonates prior to deposition of the Permian could be a result of
subduction and back-arc extension along the northern margin of the North China
craton in late Paleozoic time
Pre-Jurassic (Indosinian) folding of the Paleozoic strata in southwestern
Daqing Shan and low-angle, basement-involved thrust faulting is likely the result
of the collision and amalgamation of the North China craton and the Mongolian
arcs terrane along the Permian/Triassic Suolon suture (Figs. 1, 17, 18). This
paleo-plate boundary is only a few hundred kilometers north of the southwestern
Daqing Shan and the east-west trend of post-Permian/pre-Jurassic structures in the
field area is compatible with that of the suture.
Late Jurassic contraction in the southwestern Daqing Shan and in the
Yinshan belt is difficult to relate to any one plate margin. Traditional Chinese
views of the Yinshan belt consider it to be an intraplate orogen with limited north-
south shortening not related to plate interactions (Wang Yu, 1996; Cui and Wu,
1997). The Jura-Cretaceous Yinshan belt may be the result of: (1) closure of the
Mongolo-Okhotsk ocean 800-1000 km to the north (Davis et al.1996, 1998a;
Zheng et al., 1998; Yin and Nie, 1996), (2) accretion of crustal blocks to the south
including continued shortening between North/South China (Yin and Nie, 1996)
or (3) possible far-field effects of the collision between the Lhasa and Qiangtang
blocks along the Bangong suture. Thermal effects related to westward subduction
of a paleo-Pacific plate (Davis et al., 1996,1998a; Yin and Nie, 1996) appear to
have influenced tectonic development of eastern (Yanshan) portions of the
46
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Yinshan belt. The distances from paleo-plate boundaries such as the Mongolo-
Okhotsk and Bangong sutures are great, but observable far-fleld effects of the
Indo-Asian collision (e.g. Molnar and Tapponnier, 1975) illustrate the possibility
of far-field Jurassic intraplate responses as well.
North of the southwestern Daqing Shan and the Yinshan belt, but south of
the Mongolo-Okhotsk suture, are several northeast-trending basins, such as the
Erlian and Songliao (Figs. 1,18), which have been interpreted as Jurassic-
Cretaceous extensional rift basins containing thick sequences of Jurassic-
Cretaceous volcanic and clastic strata (Traynor and Sladen, 1995). Graham et al.
(1996) and Webb et al. (1999) report Ar-Ar and K-Ar ages of 156-125 Ma for
syn-rift volcanic rocks in the Erlian basin, which are synchronous with
contractionai deformation in the Yinshan belt (Davis et al., in review). Jura-
Cretaceous extension north of the Yinshan belt makes it difficult to relate the
Yinshan belt contraction to the closure of the Mongolo-Okhotsk ocean.
Alternatively, Jurassic volcanics found in southern and eastern Mongolian basins
may represent pre-rift units, with extension not beginning until the Cretaceous
(e.g. Zheng et al., 1991; Davis et al., 1996, Webb et al., 1999) and related to
orogenic collapse.
CONCLUSIONS
Field studies in the southwestern Daqing Shan, in the western portion of
the intraplate Yinshan belt, have revealed a complicated structural and tectonic
history that began in the Paleozoic and includes tectonic inversion as well as
47
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basement involvement. Deformation began with post-Cambro-Ordovician and
juxtaposition of Cambro-Ordovician carbonates against Archean gneiss. Post-
Cambro-Ordovician/pre-Permian deformation might be related to Devonian
collision along the southern margin of the North China craton or to pre-Permian,
south-directed subduction along the northern margin. Contractional deformation
of post-Permian and pre-Early Jurassic age is represented by isoclinal folding of
Cambro-Ordovician carbonates and Permian strata. Low-angle, basement-
involved thrusting also occurs in this time interval. This contractional
deformation was most likely related to the collision and amalgamation of the
North China craton with the Mongolian arcs terrane along the Suolon suture to the
north.
Lower Jurassic sandstone, conglomerate, black shale and coal were
deposited across the study area in an east-west trending half-graben with the
master, graben-controlling fault along its southern margin. This basin was
segmented and inverted in Late Jurassic time, resulting in basement-involved
structures that include high-angle reverse faults, upright folds (some sub-isoclinal
in geometry), and lesser low-angle thrusting. Although some of the major folds
are more-or-less symmetrical, smaller folds suggest that the dominant transport
direction was to the north. Basement-involved folding at such shallow crustal
levels is difficult to explain, given that the orientation of the subvertical foliation
in the Archean gneiss is nearly perpendicular to the trend of fold hinges and could
not have controlled flexural slip deformation utilizing basement fabric
48
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anisotropy. The cause of Late Jurassic intraplate contraction is cryptic and could
be related to any of several east Asian plate margins converging, some of which
lie at great distances from the Yinshan belt.
APPENDIX
Description of cross-sections in the southwestern Daqing Shan (PL 2)
AwAw’
Section Aw Aw’ is located ~ 5 kilometers west of Plate 1, just north of
Dongyuan (a town at the mountain front). The Jurassic sediments in this section
are intensely deformed. The southernmost contact is a steep reverse fault that
places Archean gneiss on top of a boulder conglomerate facies in the Jurassic
section (Fig. 6). The steep fault is offset by a low angle thrust that has minimum
northward displacement of -0.75 km. Continuing northward, the Jurassic section
has undergone minor thrusting and strong disharmonic folding (Fig. 9), some
folds of which plunge - 60°W, and minor thrusting. The northern boundary of
this Jurassic exposure is an overturned unconformity.
AA’
Along section AA’, the northern portion of Jurassic strata includes pebble
conglomerates and sandstones that rest directly on the Archean basement. To the
south, a steep fault that presently dips to the south juxtaposes Archean gneiss to
the north and Jurassic sediments to the south. Lower portions of the Jurassic
section, south of the fault, contain cobble and boulder conglomerates consisting
49
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of Archean basement and syenite. Upper portions of this section contain pebble
conglomerates, sandstone, and minor shale. The section is interpreted to rest
unconformably on the Archean basement. The steep fault (dips 85° north) cuts a
small portion of the Jurassic section. Small folds have developed above this fault.
Facies changes across the fault, - Jurassic sandstones and pebbly conglomerate to
the north and cobble to boulder conglomerate to the south -, suggests that the fault
was active during deposition of the Jurassic section. The fault, originally a
normal fault dipping to the south, has been rotated to its present orientation and
slightly inverted causing the small folds above it. Continuing south, the Jurassic
section is overridden by a north directed thrust (variable dip) carrying Archean
basement. Jurassic strata under the fault contain numerous shear zones. The
mountain front normal fault truncates the south-dipping thrust.
BB’
The northern portion of section BB’ contains folded Permian and Cambro-
Ordovician sediments. Cambro-Ordovician strata rest unconformably on the
Archean basement. It is important to note that the basement does not appear to be
folded, which suggests that there is a detachment horizon in the Cambro-
Ordovician section. This detachment could be located in the shale-rich, lower
portions of the section. An angular unconformity separates Permian and Cambro-
Ordovician units. The folds in section BB’ are overturned to the north.
The northernmost exposure of Jurassic strata contains sandstone, shale,
minor pebble conglomerate, and coal, all of which are folded into a south-
50
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vergent syncline. A reverse fault bounds the northern exposure of Jurassic strata.
Jurassic sediments rest unconformably on the Archean basement, which is also
folded.
Central exposures of Jurassic strata are bordered by reverse faults. The
faults place Archean basement gneiss over locally overturned Jurassic sediments
that are folded into a syncline.
Southern exposures of Jurassic strata along section BB’ are highly folded
and faulted (Fig. 11). This portion of the section was constructed just east of the
road between Heimaban and Yangkeleng. Jurassic strata rest unconformably on
Archean basement along the northern margin of the exposure. At higher
structural levels, this contact develops into a steep reverse fault, placing Archean
gneiss on Jurassic strata. To the south, the Jurassic/Archean unconformity and the
lower portion (-20 meters) of the overlying Jurassic section are cut by small
normal faults, which suggests they are synsedimentary (Fig. 13). South of the
small normal faults, a north-vergent, overturned anticline appears to have
developed over a south-dipping shear zone. Areas farther south are strongly
folded and contain numerous shear zones. This southern exposure of Jurassic
strata is bounded by a south-dipping reverse fault involving the Archean
basement. The mountain front is delineated by a major normal fault.
51
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CC’
Permian and Cambro-Ordovician units are folded into an isoclinal
anticline in the northern portions of this section. Permian sediments to the north
of the isoclinal anticline are folded into a broad overturned syncline. A small
anticline has developed on the south limb of the syncline and may represent slip
along coal seams near the base of Permian section. The thickness of the Cambro-
Ordovician unit changes across the fold hinge with the southern portion having a
greater thickness (300 m vs. 500 m). The variation in thickness may be a function
of differential erosion prior to deposition of Permian sediments.
Important relations along the southern margin of the isoclinal anticline
include an angular unconformity between Jurassic and Cambro-Ordovician strata.
Cambro-Ordovician strata are nearly vertical whereas Jurassic strata are
horizontal (Fig. 15). This relationship requires that the isoclinal anticline formed
prior to deposition of Jurassic sediments.
Also found under Jurassic sediments is a fault that separates Cambro-
Ordovician carbonates and Archean gneiss. This structure might represent a
normal fault that juxtaposes Cambro-Ordovician and Archean units prior to
deposition of Jurassic sediments and most likely prior to deposition of Permian
strata (see section FF’, GG’). Small normal faults, which cut folded Jurassic
strata, can also be seen in this section.
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Central exposures of Jurassic strata are folded into a syncline bordered by
steep reverse faults that dip away from the fold hinge. There is some shearing of
Jurassic strata below the faults. This section was drawn along the road between
Heimaban and Yankeleng.
Deformation in the southern exposure of Jurassic strata along section CC’
is more intense, with strong disharmonic folding. The basic structures of the
exposure are three main folds, a syncline-anticline-syncline sequence, limited on
both sides by reverse faults. The anticlinal hinge has been sheared (shown by red
lines on PI. 2). At lower structural levels in the southern portion of this exposure,
Jurassic sediments are strongly folded.
DD’
The small section DD’, can be characterized by strong disharmonic
folding of Jurassic strata. A reverse fault along the southern flank of this
exposure places Archean gneiss atop Jurassic strata that are locally overturned.
Bounding the north side of the exposure is a steep, south-dipping reverse fault.
The basic structure is a syncline bound by reverse faults, which dip in opposite
directions.
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EE’
Jurassic strata rest unconformably on the Archean basement, with the
basement/cover contact broadly folded. Projected into the air from the east is a
north-directed, low-angle thrust. Steep faults cut folds involving Jurassic strata
and offset the basement/cover contact. Displacement on the steep faults is
unknown, but is most likely less than 0.5 km.
FF’
The northern portions of section FF’ are very similar to EE’ and GG’.
South of the isoclinal anticline, folded Permian sediments and a thrust that places
Archean basement on top of the Permian are cut by a normal fault. Displacement
on the normal fault is -400-500 meters.
The central portion of section FF’ contains two low-angle thrust faults.
The structurally lower thrust carries Archean gneiss in the upper plate, overriding
a Jurassic section. Minimum displacement on the thrust is 1.2 kilometers to the
north. Jurassic strata at higher levels are disharmonically folded possibly due to
detachment along coal horizons (Fig. 10). Below the detachment horizon,
Jurassic strata are broadly folded into a syncline. Dominant vergence as indicated
by the folds is to the north. Several steep faults cut the folded and faulted Jurassic
strata.
The upper or structurally higher thrust carries Archean gneiss in its upper
plate while the lower plate consists of a thin sequence of Permian sandstones and
conglomerates that rest unconformably on the Archean. Minimum
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displacement on the upper thrust is 1.6 kilometers. The thickness of the Permian
section may be a function of stratigraphy. Approximately 40-50 meters from the
base of the Permian sequence in other areas is a thick coal seam that may form
detachment horizon for this thrust to follow. Following the upper thrust and
lower-plate Permian sequence to the south, both are cut by the faults that bound
the southern exposure of Jurassic strata. The Jurassic sediments in this exposure
are highly sheared.
GG’
In this section, Permian and Cambro-Ordovician strata are folded into an
isoclinal anticline seen in sections to the east and west. Permian and Cambro-
Ordovician strata are separated by an angular unconformity (up to 25°; Fig. 4).
Along the southern limb of the isoclinal anticline, a steep reverse fault (-85°) with
limited displacement, juxtaposed Cambro-Ordovician and Permian units.
Displacement along the reverse fault, estimated by removing the offset of basal
Permian strata, is estimated at 0.75 km. South of the steep reverse fault, Permian
strata rest unconformably on the Archean basement, which has been folded and
overturned. This suggests that Cambro-Ordovician units occupied a structural
low (a graben? or half-graben?) prior to the deposition of Permian elastics. South
of the isoclinal anticline, Permian sediments form north-vergent folds that are
overridden by a north-directed thrust fault carrying the Archean basement.
55
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HH’
Jurassic sediments in this section (drawn near along the road) are
disharmonically folded below a north-directed low angle thrust (Fig. 7) and above
a detachment horizon in Jurassic strata (see discussion in text and description of
FF’). Below the detachment, Jurassic sediments are interpreted to be broadly
deformed, resting unconformably on the Archean basement. The northern limit of
this Jurassic exposure is delineated by a steep fault that juxtaposes Jurassic and
Archean units.
IV
Section IF is the best section to view the thickness of the Permian
sedimentary sequence. Permian strata in the northern portion of section II’ are at
least 1.5 km thick and it is important to note that the top of the sequence is not
seen. Permian strata rest on an angular unconformity with Cambro-Ordovician
strata, both of which are folded in to an isoclinal anticline. A very small
overturned fold just below the unconformity (Fig. 14), demonstrates that Cambro-
Ordovician carbonates were deformed prior to deposition of the Permian. A steep
reverse fault offsets the Permian unconformity and places Cambro-Ordovician
carbonates in a higher structural position. As previously described, south of the
isoclinal anticline the basal Permian quartzite cobble conglomerates rest
unconformably on the Archean basement. The Permian section is folded along
with the underlying Archean gneiss, a phenomena that is difficult to explain
56
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given the orientation of anisotropy in the basement is nearly perpendicular to the
strike of the folds. The basement is also thrust to the north over the Permian
clasts.
The only Jurassic strata exposed along section II’ are folded and faulted
into impressive geometries. A low-angle thrust carrying both Archean basement
and Permian sediments has been placed atop the Jurassic sequence. The thrust is
thought to be north-directed despite the presence of a small, south vergent fold
along the southern edge of the Jurassic exposure. The thrust sheet and underlying
Jurassic sediments have been folded into a sub-isoclinal synform. Jurassic
sediments rest unconformably on Archean basement gneiss, which have also been
folded despite the orientation of their foliation. The north limb of the synform is
highly sheared, containing at least one pod of Archean gneiss between Jurassic
and Permian sediments. A steep fault is the northern margin of this exposure of
Jurassic sediments. The folded thrust is thought to root to the south, although a
root zone has not been identified.
57
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Major thrust system in the Daqing Shan, Inner Mongolia, China: Science
in China (Series D), v. 41, no. 5, p. 553-560.
Zheng Yadong, Zhang, Q., Wang, Y., Liu R., Wang S.G., Zuo G., Wang S.Z.,
Lkaasuren, B., Badarch, G., and Badamgarav, Z., 1996, Great Jurassic
thrust sheets in Beishan (North Mountains) -Gobi areas of China and
southern Mongolia: Journal of Structural Geology, v. 18, p. 1111-1126.
Zhu Shenyu, 1997, Nappe tectonics in Sertenshan-Daqingshan, Inner Mongolia:
Geology of Inner Mongolia, v. 84, no. 1, p. 41-48 (in Chinese with
English abstract).
Ziegler, A.M., Rees, P.M., Rowley, D.G., Bekker, A., Li Qing, and Hulver, M.L.,
1996, Mesozoic assembly of Asia: Constraints from fossil floras,
tectonics, and paleomagnetism, in Yin An, and Harrison, T.M., eds., The
tectonic evolution of Asia: Cambridge University Press, p. 371-400.
Zonenshain, L.P., Muzmin, M.I., and Natapov, L.M., 1990, Mongol-Okhotsk
foldbelt, in Page, B.M., ed., Geology of the USSR: a plate tectonic
synthesis: AGU Geodynamic series, v. 21, p. 97-108.
61
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U IY li
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Plate 1
Geologic Map of the southwest<
Brian J. Darby
Department of Earth Science
University of Southern Califorr
Explanation
Q ! Undifferentiated Quaternary alluvium.
j
Jurassic sandstone, conglomerate, black shale, and coal. Conglomerates and sandstone
color containing angular to sub-rounded clasts. Clasts are mostly composed of gneiss an
Som e clasts of Cambrian strata near Cambrian outcrops. In general, the Jurassic section
north. Boulder conglomerates and sedimentary breccias can be found along the southerr
strata. Northern exposures contain mostly sandstone and black shale with lesser pebble
exposures and mines are confined to central and northern outcrops of Jurassic strata and
the section. Orange-colored sandstone and conglomerate beds are locally present in mid
Jurassic section.
Jr
Permian conglomerate, sandstone, shale, and coal. Base of section usually consists of te
rounded quartzite cobble conglomerate and locally thick coal seam s. Conglomerate usua
or ridges. Middle and upper parts of the Permian section consist of nearly rhythmically ini
— - « ■ » i t _ _ i_ I. * _ _ ______i i _______
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;tern Daqing Shan
ces
ornia
jtones are usually grey/buff/tan in
3S and quartz vein material,
sction fines from the south to the
ithern-most exposures of Jurassic
bble conglomerate. Coal
i and middle to upper portions of
i middle to upper portions of the
; of tan, massively bedded,
usually outcrops well forming ribs
lly interbedded red mudstones,
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40*39.5'
39
45
/ /
47
X
rounded quartzite cobble conglomerate and locally thick coal seam s. Conglomerate usually
or ridges. Middle and upper parts of the Permian section consist of nearly rhythmically intert
pinkish sandstone and conglomerate. Conglomerate clasts are usually pebble to small cobb
quartzite, gneiss, red mudstone rip-up clasts, and felsic volcanics. Clasts are sub-angular to
nodules are commonly found in mudstones and may represent paleosols.
Cambro-Ordovician carbonates, lesser sandstone, and very minor shale. Carbonates, mostl
recrystallized, weathering buff/tan in color, and bedded on a -1 0 cm scale. Recrystallized ss
glauconite are typically found at the base of the section. Local pebble conglomerate is also [
micaceous shales locally overlie the basal sandstones.
J Proterozoic (?) quartz-bearing schistose unit, highly weathered. Unit is found near the town i
J Jurassic strata and above the Archean gneiss. This unit is highly fissile and has a lower me
underlying Archean basement.
Arg
Undifferentiated Archean Gneiss; includes amphibolitic, granitic, and garnet-bearing varieties
J55^
-sT
r"5 § ~ r
r64
32
Bedding in sedimentary strata
Overturned bedding
Cleavage in sedimentary strata
Foliation in Archean Gneisses
Unconformities (dashed where
approximate)
Thrust/reverse fault (dashed where
approximate); teeth on upthrown
block.
Detachment surface (dashed where
approximate).
Normal fault (dashed where approximate);
ball on down-dropped block
Dip direction of faults and unconformities.
Anticline; arrow indicates direction
* of plunge.
— Overturned anticline
Syncline; arrow indicated direction
of plunge
Overturned syncline
4j ^ Small fold
. • Peak elevations (meters)
1693
IW ep tp Towns/Villages
\ Striae on fault surfaces
19
k u a u
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sists of tan, massively bedded,
ate usually outcrops well forming ribs
lically interbedded red mudstones,
small cobbles consisting of
>-angular to rounded. Carbonate
lates, mostly limestones, are
fstallized sandstones with minor
ate is also present, and minor green
ir the town of Yangkeleng under
a lower metamorphic grade than the
ng varieties.
ction
ction
'36
5-
55
28
Arg
40°37.5
/ /
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[60
V2
(53
Jr
► 5 5
7*
— — ?
y
15
J r
69,
.46
35
<\26
22
W
34;
h
1794
\77
65
21
\ *
/
^55
54
77
Ara
rso
1693
.77
8 3 1
A
% , r — &
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\ Striae on fault surfaces
19
North
o 1.0
1 ----------
Kilometers
-1:12500
1.5
2.0
E110°20'
71
70
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2.0
,40°36.5'
Not mapped,
this study
.___40°36'
40°35.5'
/
1541
1345
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‘ 74
Arg
• 1551
71 50
49
58
40
55
44
22
•74
1629
Arg
75
1477
Arg
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1465
Arg
1515
83
A rg
54
Arg
1518
45
85
74
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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
'45
Break in section
Arg
.42 55 ,85
1548
Arg
Arg
-7b
1425
84
[66
1570
k 77
Arg
40°35.5
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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
110 *2 1 ' 110*22 '
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110°24
To B aotou
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110^25' 110*26'
t
110 °26 ' 110"2r
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Arg
40°35.5
W eijun
N40°34.5
110*28
110*27
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NOTE TO USERS
Oversize maps and charts are microfilmed in sections in the
following manner:
LEFT TO RIGHT, TOP TO BOTTOM, WITH SMALL
OVERLAPS
The following map or chart has been microfilmed in its entirety at
the end of this manuscript (not available on microfiche). A
xerographic reproduction has been provided for paper copies and is
inserted into the inside of the back cover.
Black and white photographic prints (17”x 23”) are available for an
additional charge.
UMI
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C /)
C O -
LU
North
Break in sectioi
South
South
S15W
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Ay
/ \ v
i \ '
I \
V .
> i
X
I
/ /
/ /
/ /
Geologic cross-secti
i
Departrr
University
> n
Break in secti
-►
South
Arg
\
Arg
A rg
/
i
/
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Plate 2
ctions, southwestern Daqing Shan
Brian J. Darby
irtment of Earth Sciences
rsity of Southern California
I n section
— ►
outh
A rg
Arg
H H
S20E
Y
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an
i '
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S o u th ►
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South
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A r<
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A rg
Arg
Break in section
XX x
Arg
Arg
Arg
Arg
t
South
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N10W
A rg
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S28W
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Jr
Break in Section
V
South
V pf 1 1 ^
P r(? ) A rg
m Ar9
%
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South
A rg
Arg
Bend in section
S10E
Bend in section
S30E
A rg
A rg
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
D
S20E
A rg
Arg
C '
N30W j
t
1
I
i
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C '
N30W
I
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Bend in section
i----- ►
South
S40W
A rg
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Bend in section
/
/
Explanation
S ee Plate 1 for detailed unit descriptions
Q Undifferentiated Quaternary alluvium
Jr Jurassic sandstone, conglomerate, shale, and coal
Permian conglomerate, sandstone, shale, and coal
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Bend in section
Sooth
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Bend in section
\ /
V
/
/
/
Arg
Arg
A rg
Arg
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
A'
Mountain front
normal fault
A rg
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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Explanation
S e e Plate 1 for detailed unit descriptions
Q | Undifferentiated Quaternary alluvium
Jurassic sandstone, conglomerate, shale, and coal
! Jr
Permian conglomerate, sandstone, shale, and coal
Cambro-Ordovician carbonates and lesser sandstones
Proterozoic (?) schistose unit
Arg
Undifferentiated Archean gneisses
* Arrows indicate relative movement along faults
Unconformity
0 .5 1-0
I --------------------------- 1 --------------------------- 1
Kilometers
No vertical exaggeration
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A
A rg
Arg
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A
A '
Mountain front
normal fault
A rg
Topography estimated
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IMAGE EVALUATION
TEST TARGET (Q A -3 )
/
✓
&
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Asset Metadata

Creator Darby, Brian Joseph (author)

Core Title Structural evolution of the southwestern Daqing Shan, Yinshan Belt, Inner Mongolia, China

Degree Master of Science

Degree Program Geological Sciences

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag Geology,OAI-PMH Harvest

Language English

Contributor Digitized by ProQuest (provenance)

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c16-30828

Unique identifier UC11337216

Identifier 1395138.pdf (filename),usctheses-c16-30828 (legacy record id)

Legacy Identifier 1395138.pdf

Dmrecord 30828

Document Type Thesis

Rights Darby, Brian Joseph

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the au...

Repository Name University of Southern California Digital Library

Repository Location USC Digital Library, University of Southern California, University Park Campus, Los Angeles, California 90089, USA