Footwall Rotation in a Regional Detachment Fault System: Evidence for Horizontal‐Axis Rotational Flow in the Miocene Searchlight Pluton, NV. Issue 7 (31st July 2019)

• Record Type: Journal Article
• Authors: Zuza, Andrew V.; Cao, Wenrong; Hinz, Nicholas H.; DesOrmeau, Joel W.; Odlum, Margaret L.; Stockli, Daniel F.
• Is Part Of: Tectonics. Volume 38:Issue 7(2019)
• Page Start: 2506
• Page End: 2539
• Publication Date: 2019-07-31
• Subjects: Searchlight pluton -- Extension -- Colorado River Extensional Corridor -- Crustal cooling -- Rheology; Geology, Structural -- Periodicals; 551.8
• DOI: 10.1029/2019TC005513
• Languages: English
• ISSNs: 0278-7407

Abstract

Abstract: The Miocene Searchlight pluton, exposed in the Colorado River Extensional Corridor of southern Nevada, tilted up to 90° on its side in the footwall of the east‐directed Dupont Mountain detachment fault system. Rapid extension and rotation occurred immediately after the ca. 17–16‐Ma emplacement of this 10 × 10‐km granite‐monzogranite body. To constrain the mechanism and timing of rapid footwall exhumation, we conducted detailed field, microstructural, electron backscatter diffraction, and zircon (U‐Th)/He (ZHe) and 40 Ar/ 39 Ar hornblende thermochronological analyses. Steeply dipping fabrics across this pluton formed over a range of temperature conditions, from magmatic to high‐ to low‐temperature subsolidus strain, and display distributed eastside‐up shear. ZHe cooling ages are consistent with constraints from tilted volcanic strata and crosscutting dikes that suggest initial rapid rotation (~75°/Myr) at 16.2–15.7 Ma followed by more modest exhumation rates until ca. 13 Ma. Our observations are used to test tilting models for the Searchlight pluton, including rigid‐body rotation, antithetic imbrication, or flow‐like rotation. Available observations are most consistent with a flow‐like tilting mechanism. We present scaling analyses that highlight how footwall tilting‐dominated extension more effectively cools the upper crust than pure‐shear extension because the hottest deep materials exhumed rapidly toward the cooler surface. This extensional mechanism efficiently cools the upper crust, causing a negative feedback whereby the rapidly cooled crust becomes strong enough to halt further fast simple‐shear extension. This may explain why rapid extension was transient and further extension is mostly accommodated by high‐angle low‐offset magnitude normal faults that developed in a colder stronger crust. Key Points: The Searchlight pluton, Colorado River Extensional Corridor, was exhumed to the surface via footwall tilting shortly after intrusion This exhumation was facilitated by flowing of the hot low‐viscosity pluton during hanging wall removal Rapid footwall advection effectively cools the crust, thus strengthening it and halting fast extension