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180
% Move to k3
k3_X = dt*Vx_cen2;
k3_Z = dt*Vz_cen2;
k3_X_full = k0_X+k3_X;
k3_Z_full = k0_Z+k3_Z;
% Interpolate velocity at k3
Vx_k3 = interp2(x,z,Vx_n1,k3_X_full,k3_Z_full, ‘linear’);
Vz_k3 = interp2(x,z,Vz_n1,k3_X_full,k3_Z_full, ‘linear’);
% Move to k4
k4_X = dt*Vx_k3;
k4_Z = dt*Vz_k3;
% Compute new particle location
k_X_final = k0_X + k1_X/6 + k2_X/3 + k3_X/3 + k4_X/6;
k_Z_final = k0_Z + k1_Z/6 + k2_Z/3 + k3_Z/3 + k4_Z/6;
B3.4 Advection-diffusion operator splitting code for the three tectonic models
% Physical parameters
Q_UC = 9.5e-10; % radiogenic heat production in
upper crust (W/kg)
density_UC = 2700; % density of upper crust (kg/m3)
density_LC = 2900; % density of lower crust (kg/m3)
heat_cap_UC= 1000; % heat capacity of upper crust
(J/kg/C)
heat_cap_LC= 1000; % heat capacity of lower crust
(J/kg/C)
k_UC = 2; % thermal conductivity of upper
crust (W/m/K)
k_LC = 3; % thermal conductivity of lower
crust (W/m/K)
g = 9.81; % gravitational acceleration (m/
s2)
hr = 10e3; % decay length of rad.heat
Object Description
| Title | Structural and thermobarometric constraints on the exhumation of the northern Snake Range metamorphic core complex, Nevada |
| Author | Cooper, Frances Jacqueline |
| Author email | fcooper@usc.edu; fcooper@usc.edu |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Geological Sciences |
| School | College of Letters, Arts and Sciences |
| Date defended/completed | 2008-08-27 |
| Date submitted | 2008 |
| Restricted until | Unrestricted |
| Date published | 2008-10-22 |
| Advisor (committee chair) | Platt, John P. |
| Advisor (committee member) |
Davis, Gregory A. Morrison, Jean Platzman, Ellen Thompson, Mark E. |
| Abstract | Observations from areas of large-scale continental extension, including the Basin and Range Province in western North America, have revealed the presence of regionally subhorizontal normal faults that appear to have exhumed rocks from mid- to lower-crustal levels. These detachment faults separate upper plate rocks extended on arrays of high-angle brittle normal faults from lower plate rocks exhibiting ductile mylonitic stretching and medium- to high-grade metamorphism. The origin and evolution of these detachments has been a matter of debate for decades, and yet a number of issues remain unresolved: (1) the dip of the faults when they were initiated and were active; (2) their penetration depth into the crust; (3) their role in exhuming high-grade metamorphic rocks; and (4) the origin and significance of the mylonitic deformation in their footwalls.; I explored these issues in the footwall to a classic detachment fault -- the northern Snake Range décollement (NSRD) in eastern Nevada -- using a combination of structural geology, geothermobarometry, paleomagnetism, isotope geochronology, and electron backscatter diffraction (EBSD) analysis. Garnet-biotite-muscovite-plagioclase thermobarometry suggests that the footwall to the NSRD experienced late Cretaceous peak metamorphic conditions of 6–8 kbar and 500–650°C, equivalent to a burial depth of ≤ 30 km. Calcite-dolomite thermometry indicates that Tertiary mylonitic deformation occurred under lower temperature conditions of 350–430°C, equivalent to mid-crustal levels. Structural, paleomagnetic, and EBSD data demonstrate that mylonites experienced two phases of shear (top-east and top-west), inconsistent with movement along a single throughgoing normal fault.; I conclude that exhumation of the northern Snake Range footwall was a two-step process. Initial ductile stretching and thinning of the crust exhumed footwall rocks to the middle crust beneath a discontinuity, referred to as the localized-distributed transition (LDT), that separated extension along brittle normal faults above from localized ductile shear zones below. Mylonites formed along the LDT were subsequently captured by a moderately-dipping NSRD that soled into the middle crust. The NSRD, therefore, appears to be a late-stage brittle normal fault that was responsible for only about half the total exhumation of the footwall, and is not directly related to the mylonitic deformation. |
| Keyword | continental extension; extensional tectonics; Basin and Range province; Cordillera; metamorphism; mylonite zone |
| Geographic subject | tectonic features: Snake Range décollement |
| Geographic subject (state) | Nevada |
| Geographic subject (country) | USA |
| Language | English |
| Part of collection | University of Southern California dissertations and theses |
| Publisher (of the original version) | University of Southern California |
| Place of publication (of the original version) | Los Angeles, California |
| Publisher (of the digital version) | University of Southern California. Libraries |
| Provenance | Electronically uploaded by the author |
| Type | texts |
| Legacy record ID | usctheses-m1695 |
| Contributing entity | University of Southern California |
| Rights | Cooper, Frances Jacqueline |
| Repository name | Libraries, University of Southern California |
| Repository address | Los Angeles, California |
| Repository email | cisadmin@lib.usc.edu |
| Filename | etd-Cooper-2458 |
| Archival file | uscthesesreloadpub_Volume40/etd-Cooper-2458.pdf |
Description
| Title | Page 195 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | 180 % Move to k3 k3_X = dt*Vx_cen2; k3_Z = dt*Vz_cen2; k3_X_full = k0_X+k3_X; k3_Z_full = k0_Z+k3_Z; % Interpolate velocity at k3 Vx_k3 = interp2(x,z,Vx_n1,k3_X_full,k3_Z_full, ‘linear’); Vz_k3 = interp2(x,z,Vz_n1,k3_X_full,k3_Z_full, ‘linear’); % Move to k4 k4_X = dt*Vx_k3; k4_Z = dt*Vz_k3; % Compute new particle location k_X_final = k0_X + k1_X/6 + k2_X/3 + k3_X/3 + k4_X/6; k_Z_final = k0_Z + k1_Z/6 + k2_Z/3 + k3_Z/3 + k4_Z/6; B3.4 Advection-diffusion operator splitting code for the three tectonic models % Physical parameters Q_UC = 9.5e-10; % radiogenic heat production in upper crust (W/kg) density_UC = 2700; % density of upper crust (kg/m3) density_LC = 2900; % density of lower crust (kg/m3) heat_cap_UC= 1000; % heat capacity of upper crust (J/kg/C) heat_cap_LC= 1000; % heat capacity of lower crust (J/kg/C) k_UC = 2; % thermal conductivity of upper crust (W/m/K) k_LC = 3; % thermal conductivity of lower crust (W/m/K) g = 9.81; % gravitational acceleration (m/ s2) hr = 10e3; % decay length of rad.heat |
