Progress in Tectonic and Petrogenetic Studies in an Exposed Cross-Section of Young (~100 Ma) Continental Crust, Southern Sierra Nevada, California

Saleeby, Jason B.

doi:10.1007/978-94-009-0675-4_6

Cited by 82 publications

(88 citation statements)

References 24 publications

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“…The central region of the Sierra Nevada batholith is exposed to an average crustal depth of ---10 km [Ague and Brimhall, 1988] and has an average tonalitic composition for the upper to mid-crustal levels [Saleeby, 1990] We tentatively interpret the above relations to indicate that at •--1 GPa the primary batholithic composition graded upward from predominantly mafic (48-50 wt % SiO2) to predominantly tonalitic (55-60 wt % SiO2). The Central Sierra Nevada xenolith data further suggest that the deep mafic batholith extends or extended downward to ---65-70 km (pressures of 2 GPa).…”

Section: Before Basin and Range Extensionmentioning

confidence: 93%

Buoyancy sources for a large, unrooted mountain range, the Sierra Nevada, California: Evidence from xenolith thermobarometry

Ducea¹,

Saleeby²

1996

J. Geophys. Res.

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280

199

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Abstract. Xenoliths hosted by Cenozoic volcanic flows and plugs from the Central Sierra Nevada and Eastern Sierra Nevada, Owens Valley, and Inyo Mountains were studied for petrography and thermobarometry. The Central Sierra Nevada suite consists of abundant lower crustal feldspathic granulites, garnet clinopyroxenites, and mantle-derived peridotites and garnet websterites. Mafic crustal assemblages occur down to -65-70 km, although below 35-40 km, they are mainly in the eclogite facies. In contrast, the Eastern Sierra Region suites show peridotitic, pyroxenitic, and harzburgitic assemblages at depths of _>35-40 km. They define an adiabat in PT space (T -1180-1250øC), suggesting the presence of the asthenospheric upper mantle close to the base of the crust. The ultramafic mantle rocks from the Central Sierra Nevada also define an adiabatic slope in PT space, possibly an artifact of side heating from the east. There is xenolith evidence that the Sierra Nevada lost about half of its original crust on the eastern side of the range. Regardless of the actual mechanism of crustal thinning, the loss of the eclogitic lowermost crust and replacement by peridotite in the eastern Sierra Nevada is a process accompanied by a substantial density decrease (>100 kg/m3). Overall, if the mechanism of eclogitic lowermost crust removal is viable, there are enough buoyancy sources to explain topographic differences between the Sierra Nevada and the adjacent Basin and Range, assuming isostatic equilibrium.

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Section: Before Basin and Range Extensionmentioning

confidence: 93%

Buoyancy sources for a large, unrooted mountain range, the Sierra Nevada, California: Evidence from xenolith thermobarometry

Ducea¹,

Saleeby²

1996

J. Geophys. Res.

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280

199

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“…These density variations mimic the structure of the Sierran crust, which is dominated by the juxtaposition of silicic plutonic rocks along the Sierran crest with mafic to ultramafic rocks exposed in the western foothills [Saleeby, 1981]. Because of the large-scale vertical transport of material in the Mesozoic magmatic arc [Saleeby, 1990], it seems reasonable to assume that the gross variations in density observed at the surface extend down many kilometers into the crust. Gravity gradients associated with individual plutons in the upper crust indicate that these plutons extend down to about 10 to 13 km depth [Oliver, 1977;Oliver et al, 1987Oliver et al, , 1993.…”

Section: Lsostasy and Gravitymentioning

confidence: 99%

“…Gravity gradients associated with individual plutons in the upper crust indicate that these plutons extend down to about 10 to 13 km depth [Oliver, 1977;Oliver et al, 1987Oliver et al, , 1993. A more diffuse density contrast below 10 km between the San Joaquin crust and the Sierran crust could exist, for the deep levels of the Sierran batholith exposed in the southernmost part of the range remain fairly silicic to paleodepths approaching 30 km, and densities rarely exceed 2.8 Mg m· 3 even in these deep levels of exposure [Ross, 1989;Saleeby, 1990]. The bulk of geologic evidence along an east-west profile across the Sierra thus supports the possibility that much, or even all, of the gravity low of the Sierra comes from lateral density contrasts in the crust; the gravity data require that some of that low must be in the upper crust.…”

Section: Lsostasy and Gravitymentioning

confidence: 99%

Missing roots and mantle “drips”: Regional P_n and teleseismic arrival times in the southern Sierra Nevada and vicinity, California

Jones¹,

Kanamori²,

Roecker³

1994

J. Geophys. Res.

134

113

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Previous seismological studies have placed the source of the uplift of the Sierra either within the crust, suggesting a Mesozoic age for the source of the uplift, or in the upper mantle, consistent with late Cenozoic creation of the buoyant material producing the uplift of the range. We deployed 16 temporary seismometers in the high part of the southern Sierra Nevada to augment the permanent Southern California Seismic Network and record arrivals from regional and teleseismic earthquakes. Arrival times of P waves from 54 teleseisms recorded at these stations are advanced by over a second by a high‐velocity body in the upper mantle west and northwest of Lake Isabella. Inversion of the arrival times indicates that this “Isabella anomaly” is of limited north‐south extent (about 40–60 km), has compressional velocities about 4–5% higher than its surroundings, and probably extends from about 100 to 200 km depth. The limited north‐south extent of the “Isabella anomaly” indicates that it is unrelated to the Sierra; we speculate that it is the downgoing part of a small scale convection system similar to that inferred beneath Southern California. This inversion does not clearly reveal either a large crustal root or a substantial low‐velocity body in the upper mantle beneath the Sierra. Although the presence of either degrades the fit to the arrival times and requires high‐velocity material beneath the low‐velocity material of either root, Bouguer gravity anomalies require low‐density material under the Sierra. Assuming that arrival times from earthquakes 150–350 km north and south from the southern Sierra come from a common refractor (the one‐layer structure), the upper mantle P wave velocity (Pn) beneath the High Sierra is about 7.6–7.65 km/s; if the arrivals from north and south are from different refractors (the two‐layer structure), material with a P wave velocity greater than ∼7.2 km/s (the “7 J.x” layer) would lie under a nearly flat interface from more normal crustal velocities and be separated by a north‐dipping interface from underlying mantle with velocities about 7.9–8.1 km/s. The Pn velocity beneath the region immediately to the east is significantly greater (7.9–8.0 km/s) than that of material at equal depths under the Sierra. For the one‐layer structure, further assuming that mean crustal velocities are uniform along north‐south lines, we find little dip on the Moho in the area; using the arrival times from earthquakes to the south, we infer a depth of 33±5 km for the Moho beneath the southern High Sierra. This structure of a thin to normal crust over a low‐velocity mantle can be reconciled with earlier observations that were used to infer a thick crust under the Sierra. By considering the Bouguer gravity anomaly, the surface geology, refraction profiles in this region, and our own observations, we suggest that 1/3 to 1/2 of the modern elevation in the range is supported by lateral (east‐west) density contrasts in the crust; the remainder is supported by density contrasts in the uppermost mantle or lateral va...

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“…6 in Saleeby et al 2003) with the level of exposure increasing from about 0.2-GPa pressure condition (about 6-km depth) at the southern region of Cretaceous-Paleogene orogenic plateau (e.g., House et al 2001) to about 1-GPa pressure condition (about 30-km depth) at western Tehachapi mountains (e.g., Malin et al 1995). This tilted crustal section has allowed direct observations of the mid-to lower-crustal batholithic rocks (Moore 1959;Saleeby 1981Saleeby , 1990Clemens-Knott 1992;Saleeby et al 2003). In Figs.…”

Section: Tehachapi Anomalymentioning

confidence: 97%

CVM-S4.26

Chen

Lee

2015

Full-3d Seismic Waveform Inversion

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Progress in Tectonic and Petrogenetic Studies in an Exposed Cross-Section of Young (~100 Ma) Continental Crust, Southern Sierra Nevada, California

Cited by 82 publications

References 24 publications

Buoyancy sources for a large, unrooted mountain range, the Sierra Nevada, California: Evidence from xenolith thermobarometry

Buoyancy sources for a large, unrooted mountain range, the Sierra Nevada, California: Evidence from xenolith thermobarometry

Missing roots and mantle “drips”: Regional P_n and teleseismic arrival times in the southern Sierra Nevada and vicinity, California

CVM-S4.26

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Progress in Tectonic and Petrogenetic Studies in an Exposed Cross-Section of Young (~100 Ma) Continental Crust, Southern Sierra Nevada, California

Cited by 82 publications

References 24 publications

Buoyancy sources for a large, unrooted mountain range, the Sierra Nevada, California: Evidence from xenolith thermobarometry

Buoyancy sources for a large, unrooted mountain range, the Sierra Nevada, California: Evidence from xenolith thermobarometry

Missing roots and mantle “drips”: Regional Pn and teleseismic arrival times in the southern Sierra Nevada and vicinity, California

CVM-S4.26

Contact Info

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Missing roots and mantle “drips”: Regional P_n and teleseismic arrival times in the southern Sierra Nevada and vicinity, California