A Caltech Library Service

Deep lithospheric dynamics beneath the Sierra Nevada during the Mesozoic and Cenozoic as inferred from xenolith petrology

Lee, Cin-Ty and Rudnick, Roberta L. and Brimhall, George H., Jr. (2001) Deep lithospheric dynamics beneath the Sierra Nevada during the Mesozoic and Cenozoic as inferred from xenolith petrology. Geochemistry, Geophysics, Geosystems, 2 (12). 2001GC000152. ISSN 1525-2027. doi:10.1029/2001GC000152.

See Usage Policy.


Use this Persistent URL to link to this item:


Peridotite xenoliths erupted in late Miocene basalts (~8 Ma) in the central Sierra Nevada sample a lithosphere that is vertically stratified in terms of age and thermal history. The deeper portions (~45-100 km) have asthenospheric osmium isotopic compositons and possess textural and chemical evidence for cooling from >1100° to 700-820°C. The shallower portions (<60 km) have unradiogenic Os isotopic compositions, which yield Proterozoic model ages, and contain orthopyroxenes that record temperatures as low as 670°C in their cores and heating up to 900°C on their rims. These observations suggest that the deeper xenoliths represent fragments of hot asthenosphere that upwelled to intrude and/or underplate the overlying Proterozoic lithosphere represented by the shallower xenoliths. The contrasting thermal histories between the shallow and deep xenoliths suggest that hot asthenosphere and cold lithosphere were suddenly juxtaposed, a feature consistent with the aftermath of rapid lithospheric removal or sudden intrusion of asthenospheric mantle into the lithosphere rather than passive extension. On the basis of regional tectonics and various time constraints, it is possible that this lithospheric removal event was associated with the generation of the Sierra Nevada granitic batholith during Mesozoic subduction of the Farallon plate beneath North America. Pleistocene basalt-hosted xenoliths record a different chapter in the geodynamic history of the Sierras. These xenoliths are relatively fertile, come from depths shallower than 45-60 km, are characterized by asthenospheric Os isotopic compositions, record hot equilibration temperatures (1000°-1100°C), and show no evidence for cooling. The strong contrast in composition and thermal history between the Pleistocene and late Miocene suites indicate that the post-Mesozoic lithospheric mantle, as represented by the latter, was entirely replaced by the former. The hot Pleistocene peridotites may thus represent new lithospheric additions associated with a post-Miocene lithospheric removal event or extension. High elevations, low sub-Moho seismic velocities, and the presence of fast velocity anomalies at 200 km depth may be manifestations of this event. If lithospheric removal occurred in the Mesozoic and Cenozoic, the observations presented here place constraints on the styles of lithospheric removal. In the Mesozoic, the lithospheric mantle was only partially removed, whereas in the Pliocene, the entire lithospheric mantle and probably the mafic lower crust were removed.

Item Type:Article
Related URLs:
URLURL TypeDescription
Additional Information:Copyright 2001 by the American Geophysical Union Received February 22, 2001; Revised August 2, 2001; Accepted August 31, 2001; Published December 18, 2001. Discussions with C. Conrad, P. F. Hoffman, M. Jull, and P. Molnar were valuable in honing our ideas regarding "delamination." We also thank M. Ducea, R. W. Carlson, J. T. Chesley, M. Handler, D. Hassler, S. B. Jacobsen, R. Kistler, A. Maloof, T. Plank, K. Yamashita, and Q.-Z. Yin for helpful discussions. M. Ducea and P. Molnar are thanked for insightful reviews, and M. Gurnis is thanked for efficient editorial handling. D. Lange (Harvard) and J. Donovan (U.C. Berkeley) are appreciated for help in electron microprobe analysis. S. Sorensen (Smithsonian) and R. Kistler (USGS) are thanked for donating portions of previously studied samples. This work was funded by the NSF. C.-T. Lee's fieldwork was supported by an NSF graduate fellowship, a Mineralogical Society of America Grant, and an ARCS Foundation Scholarship.
Subject Keywords:Peridotite; delamination; Sierra; xenolith; osmium; lithosphere; Chemical evolution; Composition of the crust; Igneous petrology; Dynamics of lithosphere and mantle—general
Issue or Number:12
Record Number:CaltechAUTHORS:LEEggg01
Persistent URL:
Official Citation:Lee, C.-T., R. L. Rudnick, and G. Brimhall, Deep lithospheric dynamics beneath the Sierra Nevada during the Mesozoic and Cenozoic as inferred from xenolith petrology, Geochem. Geophys. Geosyst., 2, 10.1029/2001GC000152, 2001.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:1144
Deposited By: Archive Administrator
Deposited On:23 Dec 2005
Last Modified:08 Nov 2021 19:07

Repository Staff Only: item control page