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183
time = time+dt;
% Store particle information
T_part_time(itime) = T_particle;
P_part_time(itime) = P_particle;
Time_vec(itime) = time;
% Plot solution
figure(1),clf
pcolor(x,z,T), shading interp, hold on, colorbar
contour(x,z,T,[.1:.1:2],’k’),
hold on, quiver(x,z,Vx,Vz,’w’)
plot(k0_X,k0_Z,’wo’)
axis equal, axis tight
xlabel(‘Distance [m]’)
ylabel(‘Depth [m]’)
title([‘Temperature evolution after ‘,num2str(time/
Myrs),’Myrs’])
drawnow
% Plot P-T time path
figure(2),hold on
plot(T_part_time,P_part_time/1e8,’k’)
xlabel(‘Temperature [^oC]’)
ylabel(‘Pressure [kbar]’)
title([‘P-T path after ‘,num2str(time/Myrs),’ Myrs’])
end
B3.5 Velocity field for a low-angle shear zone model
for ix = 1:nx
for iz = 1:nz
if z(iz,ix)<-x(iz,ix)*tan(45/180*pi);
Vx(iz,ix) = -1e-3/(3600*24*365.25);
Vz(iz,ix) = 1e-3/(3600*24*365.25);
else
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 198 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | 183 time = time+dt; % Store particle information T_part_time(itime) = T_particle; P_part_time(itime) = P_particle; Time_vec(itime) = time; % Plot solution figure(1),clf pcolor(x,z,T), shading interp, hold on, colorbar contour(x,z,T,[.1:.1:2],’k’), hold on, quiver(x,z,Vx,Vz,’w’) plot(k0_X,k0_Z,’wo’) axis equal, axis tight xlabel(‘Distance [m]’) ylabel(‘Depth [m]’) title([‘Temperature evolution after ‘,num2str(time/ Myrs),’Myrs’]) drawnow % Plot P-T time path figure(2),hold on plot(T_part_time,P_part_time/1e8,’k’) xlabel(‘Temperature [^oC]’) ylabel(‘Pressure [kbar]’) title([‘P-T path after ‘,num2str(time/Myrs),’ Myrs’]) end B3.5 Velocity field for a low-angle shear zone model for ix = 1:nx for iz = 1:nz if z(iz,ix)<-x(iz,ix)*tan(45/180*pi); Vx(iz,ix) = -1e-3/(3600*24*365.25); Vz(iz,ix) = 1e-3/(3600*24*365.25); else |
