Late-stage evolution of the Chemehuevi and Sacramento detachment faults from apatite (U-Th)/He thermochronometry--Evidence for mid-Miocene accelerated slip

Abstract

The unique low-temperature sensitivity of the apatite (U-Th)/He (AHe) technique provides valuable new information relating to the late-stage thermal evolution of metamorphic core complexes in the southern Basin and Range Province. In all the ranges studied, the data show greater complexity than previously seen from other thermochronometers. In the Chemehuevi and northern Sacramento Mountains, a trend of decreasing ages toward the northeast applies only for the structurally shallowest parts of the footwall. This is followed by essentially age-invariant segments of 15 ± 1 Ma, refl ecting an increase in the rate of detachment fault movement. The timing of the change suggested by the data agrees with recently published AHe results from the nearby Harcuvar Mountains, located ~125 km to the southeast, suggesting that an underlying regional mechanism triggered this change. Plate reconstructions indicate that the Pioneer-Mendocino fracture zone migrated northward through the area at this time, leaving a slab window in its wake. We suggest that the additional heat applied to the base of the lithosphere from the slab window resulted in mechanical weakening of the area and that this, combined with the extensional strain regime present, resulted in an increased rate of slip within the actively extending metamorphic core complexes. This agrees well with timing constraints for extension onset in the central Basin and Range Province of southern Nevada, and suggests that weakening of the southern Basin and Range Province at 15 ± 1 Ma was partially responsible for the onset of extension in the central Basin and Range. These fi ndings demonstrate that improved constraints on changes in extension rate within the Basin and Range Province should be possible through the application of the AHe technique to other metamorphic core complex footwalls.Keywords: metamorphic core complexes, Basin and Range Province, low-angle normal faults, (U-Th)/He, low-temperature thermochronology.

Miocene extension in the East Range, Nevada: A two-stage history of normal faulting in the northern Basin and Range

“…Together, these methods can constrain the thermal history of a footwall block in detail, and, by proxy, the timing of fault slip, tilting, and exhumation (e.g., Foster et al, 1991;Fitzgerald et al, 1991;Foster and John, 1998;Armstrong et al, 2003;Stockli, 2005;Carter et al, 2006;Colgan et al, 2006b;Metcalf, 2006). To quantify the timing of faulting and extension in the southern East Range, we collected a detailed E-W transect of samples across Granite Mountain, perpendicular to the range-bounding fault (Fig.…”

“…During this period, deformation was generally focused into discrete zones of high strain separated by unextended crustal blocks. Extended domains were characterized by high strain rates; closely spaced, highly tilted fault blocks; and, locally, the development of metamorphic core complexes (e.g., Proffett, 1977;Fitzgerald et al, 1991;Faulds et al, 1995;Miller et al, 1999;Snow and Wernicke, 2000;Stockli, 2005;Carter et al, 2006). In westcentral Nevada the East Range (this study) and the adjacent Tobin Range (Gonsior, 2006) constituted a middle Miocene extensional domain that was separated from the extended Shoshone-Toiyabe Range domain to the east by the intact Fish Creek Mountains block (Fig.…”

Metamorphic core complexes: windows into the mechanics and rheology of the crust

“…Vanderhaeghe et al 2003;Gordon et al 2008;Kruckenberg et al 2008), where it has been attributed to diapiric emplacement of the migmatitic gneiss complexes, followed by motion on extensional detachments (Parrish et al 1988). There is only limited evidence for upper crustal extension south of the Snake River Plain during the early Tertiary, however (Rahl et al 2002;Druschke et al 2009;Henry et al 2011;Miller et al 2012), and Eocene exhumation appears to predate motion on the detachment faults in the central and southern Cordillera, most of which have been dated to between 25 and 16 Ma (Dokka et al 1986;Davis 1988;Miller et al 1999;Carter et al 2004Carter et al , 2006Colgan et al 2010;Henry et al 2011;Konstantinou et al 2012).…”

Supradetachment basin evolution during continental extension: The Aegean province of western Anatolia, Turkey

“…Thus, supradetachment basins commonly display a complete record of sedimentary and structural processes of core complex unroofi ng and time-progressive evolution of basin infi lling and accommodation space development in intracontinental extensional settings (Yarnold, 1994;Norton, 2011). The onset of large-scale extension leading to the exhumation of metamorphic core complexes and to the development of supradetachment basins is closely related to thermal relaxation and ductile to brittle deformation of continental crust in relatively young orogenic belts with thermally and mechanically weak lithosphere (Glazner and Bartley, 1985;Miller and John, 1988;Hill et al, 1992;Dorsey and Roberts, 1996;Dilek and Moores, 1999;Snyder and Hodges, 2000), in the upper plates of subduction zones with retreating slabs (Jolivet and Faccenna, 2000;Ring and Layer, 2003;Le Pichon and Kreemer, 2010), and in association with migrating asthenospheric slab windows and triple junctions at convergent plate boundaries (Carter et al, 2006;Groome and Thorkelson, 2009;McCrory et al, 2009).…”