How the Harcuvar Mountains metamorphic core complex became cool: Evidence from apatite (U-Th)/He thermochronometry

Carter, Timothy J.; Kohn, Barry P.; Foster, David A.; Gleadow, A. J. W.

doi:10.1130/g20936.1

Cited by 43 publications

(45 citation statements)

References 16 publications

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“…Added to this is evidence that the rate of detachment-fault movement also increased at ca. 15 Ma in the nearby Harcuvar Mountains metamorphic core complex (Carter et al, 2004). This further reinforces the need for a regional mechanism that can explain an increase in slip rate for a number of core complexes in the area at the same time.…”

Section: Regional Explanations For the 15 ± 1 Ma Eventsupporting

confidence: 57%

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

Carter

Kohn

Foster

et al. 2006

Geological Society of America Bulletin

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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.

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Section: Regional Explanations For the 15 ± 1 Ma Eventsupporting

confidence: 57%

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

Carter

Kohn

Foster

et al. 2006

Geological Society of America Bulletin

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“…Although thermochronometric evidence for late Oligocene-early Miocene cooling has been described in mountain ranges of southern Arizona and southern New Mexico (Bryant et al, 1991;Kelley et al, 1992;Kelley and Chapin, 1997;Fayon et al, 2000;Carter et al, 2004), such cooling may be mostly the result of local footwall uplift and exhumation.…”

Section: Southern Basin and Range And Rio Grande Riftmentioning

confidence: 95%

Diachronous episodes of Cenozoic erosion in southwestern North America and their relationship to surface uplift, paleoclimate, paleodrainage, and paleoaltimetry

2012

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The history of erosion of southwestern North America and its relationship to surface uplift is a long-standing topic of debate. We use geologic and thermochronometric data to reconstruct the erosion history of southwestern North America. We infer that erosion events occurred mostly in response to surface uplift by contemporaneous tectonism, and were not long-delayed responses to surface uplift caused by later climate change or drainage reorganization. Rock uplift in response to isostatic compensation of exhumation occurred during each erosion event, but has been quantifi ed only for parts of the late Miocene-Holocene erosion episode. We recognize four episodes of erosion and associated tectonic uplift: (1) the Laramide orogeny (ca. 75-45 Ma), during which individual uplifts were deeply eroded as a result of uplift by thrust faults, but Laramide basins and the Great Plains region remained near sea level, as shown by the lack of signifi cant Laramide exhumation in these areas; (2) late middle Eocene erosion (ca. 42-37 Ma) in Wyoming, Montana, and Colorado, which probably occurred in response to epeirogenic uplift from lithospheric rebound that followed the cessation of Laramide dynamic subsidence; (3) late Oligocene-early Miocene deep erosion (ca. 27-15 Ma) in a broad region of the southern Cordillera (including the southern Colorado Plateau, southern Great Plains, trans-Pecos Texas, and northeastern Mexico), which was uplifted in response to increased mantle buoyancy associated with major concurrent volcanism in the Sierra Madre Occidental of Mexico and in the Southern Rocky Mountains; (4) Late Miocene-Holocene erosion (ca. 6-0 Ma) in a broad area of southwestern North America, with loci of deep erosion in the western Colorado-eastern Utah region and in the western Sierra Madre Occidental. Erosion in western Colorado-eastern Utah refl ects mantle-related rock uplift as well as an important isostatic component caused by compensation of deep fl uvial erosion in the upper Colorado River drainage following its integration to the Gulf of California.Erosion in the western Sierra Madre Occidental occurred in response to rift-shoulder uplift and the proximity of oceanic base level following the late Miocene opening of the Gulf of California. We cannot estimate the amount of rock or surface uplift associated with each erosion episode, but the maximum depths of exhumation for each were broadly similar (typically ~1-3 km). Only the most recent erosion episode is temporally correlated with climate change.Paleoaltimetric studies, except for those based on leaf physiognomy, are generally compatible with the uplift chronology we propose here. Physiognomy-based paleo eleva tion data suggest that near-modern elevations were attained during the Paleogene, but are the only data that uniquely support such interpretations. High Paleogene elevations require a complex late Paleogene-Neogene uplift and subsidence history for the Front Range and western Great Plains of Colorado that is not compatible with the regional sedimentation and er...

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“…c. 4 mm a −1 on the Buckskin-Rawhide detachment in Arizona; Brady 2002); and in some cases they substantially exceed the likely overall rate of tectonic extension in the region as a whole (e.g. 30 mm a −1 on the Bullard detachment, Arizona; Carter et al 2004). As pointed out by Wells et al (2000), hanging-wall extension will modify the pattern of cooling ages, and can lead to erroneously high estimates of slip rate.…”

Section: Core Complexes With No Breakawaymentioning

confidence: 97%

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

Platt

Behr

Cooper

2014

JGS

135

131

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Metamorphic core complexes are products of normal-fault displacements sufficient to exhume rocks from below the brittle–ductile transition. These faults (detachments) may initiate within the brittle crust at steep angles, but they sole into the ductile middle crust, and during displacement rotate to gentler dips due to hanging-wall extension. The exhumed footwall commonly adopts an arched or domed geometry owing to flexural isostatic readjustment, and may be overlain by strongly extended upper crustal rocks that slipped on gently dipping, low-friction shallow segments of the detachment. Metamorphic rocks exhumed beneath the detachment record progressively increasing flow stress, strain localization and strain-rate with decreasing temperature, providing a window into physical conditions and deformational processes in the mid-crust. The metamorphic and deformational history of the footwall rocks may reflect tectonic processes that predate formation of the detachment fault, in addition to those accompanying exhumation. These processes may include diapiric emplacement of gneiss domes, or exhumation in a subduction channel, and may not be directly related to formation of the core complex. Factors favouring core complex formation are high gravitational potential energy of the extending crust, weak rheology and a change in the tectonic boundary conditions such as a cessation or slowing of plate convergence.

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How the Harcuvar Mountains metamorphic core complex became cool: Evidence from apatite (U-Th)/He thermochronometry

Cited by 43 publications

References 16 publications

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

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

Diachronous episodes of Cenozoic erosion in southwestern North America and their relationship to surface uplift, paleoclimate, paleodrainage, and paleoaltimetry

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

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