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The AAPG/Datapages Combined Publications Database

Pacific Section of AAPG


The Geologic Transition, High Plateaus to Great Basin - A Symposium and Field Guide (The Mackin Volume), 2001
Pages 155-168

Thermochronologic Evidence for Footwall Deformation During Extensional Core Complex Development, Mineral Mountains, Utah

Drew S. Coleman, J. Douglas Walker, John M. Bartley, K. V. Hodges


Thermochronologic data from the Mineral Mountains extensional core complex in southwest Utah indicate that the footwall experienced a simple cooling history prior to the onset of extension and was subsequently uplifted and tilted during extension at the Colorado Plateau-Basin and Range transition zone. The ca. 18 Ma (U-Pb, zircon) Mineral Mountains batholith, which comprises most of the footwall, was unroofed along the Cave Canyon detachment fault about 11 million years ago. The batholith underwent final cooling quickly to below K-feldspar Ar and apatite fission-track closure temperatures by 8 Ma.

Biotite and K-feldspar Ar dates become progressively younger from east to west across the batholith, reflecting its pre-extensional geometry. The oldest cooling dates (18–16 Ma) come from the structurally highest parts of the batholith on the eastern and northern margins where it intrudes Paleozoic wall rocks. The youngest cooling dates (11-9 Ma) come from the structurally deepest parts of the batholith on the west-central margin where it intrudes Precambrian basement rocks. Reconstruction of pre-extensional isotherms suggests that the eastern part of the batholith is now lying on its side, with the top to the east. Tilting of the batholith and associated footwall rocks was probably the result of isostatic rebound in response to extensional denudation.

There is no evidence for thermally complicated footwall evolution, or a genetic link between formation of local mylonites associated with the Cave Canyon detachment fault, and magmatism in the Mineral Mountains. However, eExtensional deformation exposed in the Mineral Mountains may have resulted in doming of the structurally deeper Beaver Valley fault (visible only in seismic reflection profiles). If so, this fault experienced a more complex structural and thermal history than is recorded in the Mineral Mountains.

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