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Late‐Cretaceous construction of the mantle lithosphere beneath the central California coast revealed by Crystal Knob xenoliths

Quinn, D. P. and Saleeby, J. B. and Ducea, M. N. and Luffi, P. and Asimow, P. D. (2018) Late‐Cretaceous construction of the mantle lithosphere beneath the central California coast revealed by Crystal Knob xenoliths. Geochemistry, Geophysics, Geosystems, 19 (9). pp. 3302-3346. ISSN 1525-2027.

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The Pleistocene (1.65 Ma) Crystal Knob volcanic neck in the California Coast Ranges is an olivine‐plagioclase phyric basalt containing dunite and spinel peridotite xenoliths. Crystal Knob erupted through the Nacimiento belt of the Franciscan complex and adjacent to Salinian crystalline nappes. Its xenoliths sample the mantle lithosphere beneath the outboard exhumed remnants of the southern California Cretaceous subducting margin. This sample set augments previously studied xenolith suites in the Mojave Desert and Sierra Nevada, which linked the mantle lithosphere architecture and crustal structure of the western Cordillera. We examine six peridotite samples ranging from fertile lherzolites to harzburgite residues. Time‐corrected (ε_(Nd)) of 10.3–11.0 and ^(87)Sr/^(86)Sr of 0.702 are characteristic of underplated suboceanic mantle. Pyroxene exchange geothermometry shows equilibration at 950–1060 °C. Phase stability, Ca‐in‐olivine barometry, and 65‐ to 90‐mW/m^2 regional geotherms suggest entrainment at 45‐ to 75‐km depth. The samples were variably depleted by partial melting, and re‐enrichment of the hottest samples suggests deep melt‐rock interaction. We test the Crystal Knob temperature depth array against model geotherms matching potential sources for the mantle lithosphere beneath the Coast Ranges: (A) a shallow Mendocino slab window, (B) a young Monterey plate stalled slab, and (C) Farallon plate mantle nappes, underplated during the Cretaceous and reheated at depth by the Miocene slab window. Models B and C fit xenolith thermobarometry, but only model C fits the tectonic and geodynamic evolution of southern California. We conclude that the mantle lithosphere beneath the central California coast was emplaced after Cretaceous flat slab subduction and records a thermal signature of Neogene subduction of the Pacific‐Farallon ridge.

Item Type:Article
Related URLs:
URLURL TypeDescription ItemPostgreSQL database ItemData-reduction, modeling, and graphics-compilation code
Quinn, D. P.0000-0003-1895-3742
Ducea, M. N.0000-0002-5322-0782
Luffi, P.0000-0001-9536-5405
Asimow, P. D.0000-0001-6025-8925
Additional Information:© 2018 American Geophysical Union. Received 26 SEP 2017; Accepted 5 MAY 2018; Accepted article online 23 JUN 2018; Published online 21 SEP 2018; Corrected 21 OCT 2018. This article was corrected on 21 OCT 2018. See the end of the full text for details. We would like to thank M. Cosca and the USGS Argon geochronology laboratory for their assistance with dating the Crystal Knob basalt flow. J. Blundy and M. Gurnis were valuable resources on REE thermometry and geodynamic modeling, respectively. F. Sousa and J. Price encouraged consideration of the wider tectonic context. We would also like to thank A. Chapman, E. Nadin, and one anonymous reviewer for their excellent feedback, which greatly improved this contribution. This work was supported by the Caltech Tectonics Observatory and funded by the Gordon and Betty Moore Foundation through grant GBMF423.01. A PostgreSQL database containing analytical data and modeling results is archived with CaltechDATA at DOI 10.22002/D1.320. Data reduction, modeling, and graphics compilation code is at 10.22002/D1.321.
Errata:In the originally published version of this article, the key in Figure 17 was not rendered correctly, and there was a minor typographical error in Figure 19. These figures have since been corrected and this version may be considered the authoritative version of record.
Group:Caltech Tectonics Observatory
Funding AgencyGrant Number
Caltech Tectonics ObservatoryUNSPECIFIED
Gordon and Betty Moore FoundationGBMF423.01
Subject Keywords:xenolith; underplating; subduction; slab window; California; peridotite
Issue or Number:9
Record Number:CaltechAUTHORS:20180626-072857286
Persistent URL:
Official Citation:Quinn, D. P., Saleeby, J. B., Ducea, M. N., Luffi, P., & Asimow, P. D. (2018). Late Cretaceous construction of the mantle lithosphere beneath the central California coast revealed by Crystal Knob xenoliths. Geochemistry, Geophysics, Geosystems, 19, 3302–3346.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:87337
Deposited By: Tony Diaz
Deposited On:26 Jun 2018 19:47
Last Modified:03 Oct 2019 19:54

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