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Pb-Sr-Nd-O isotopic characterization of Mesozoic rocks throughout the northern end of the Peninsular Ranges Batholith; isotopic evidence for the magmatic evolution of oceanic arc-continental margin accretion during the Late Cretaceous of Southern California

Ronald W. Kistler, Joseph L. Wooden, Wayne R. Premo and Douglas M. Morton
Pb-Sr-Nd-O isotopic characterization of Mesozoic rocks throughout the northern end of the Peninsular Ranges Batholith; isotopic evidence for the magmatic evolution of oceanic arc-continental margin accretion during the Late Cretaceous of Southern California (in Peninsular Ranges Batholith, Baja California and Southern California, Douglas M. Morton (editor) and Fred K. Miller (editor))
Memoir - Geological Society of America (January 2014) 211: 263-316

Abstract

Within the duration of the U.S. Geological Survey (USGS)-based Southern California Areal Mapping Project (SCAMP), many samples from the northern Peninsular Ranges batholith were studied for their whole-rock radioisotopic systematics (rubidium-strontium [Rb-Sr], uranium-thorium-lead [U-Th-Pb], and samarium-neodymium [Sm-Nd]), as well as oxygen (O), a stable isotope. The results of three main studies are presented separately, but here we combine them (>400 analyses) to produce a very complete Pb-Sr-Nd-O isotopic profile of an arc-continent collisional zone--perhaps the most complete in the world. In addition, because many of these samples have U-Pb zircon as well as argon mineral age determinations, we have good control of the timing for Pb-Sr-Nd-O isotopic variations. The ages and isotopic variations help to delineate at least four zones across the batholith from west to east--an older western zone (126-108 Ma), a transitional zone (111-93 Ma), an eastern zone (94-91 Ma), and a much younger allochthonous thrust sheet (ca. 84 Ma), which is the upper plate of the Eastern Peninsular Ranges mylonite zone. Average initial (super 87) Sr/ (super 86) Sr (Sr (sub i) ), initial (super 206) Pb/ (super 204) Pb ( (super 206) Pb (sub i) ), initial (super 208) Pb/ (super 204) Pb (average (super 208) Pb (sub i) ), initial epsilon Nd (average epsilon (sub Ndi) ), and delta (super 18) O signatures range from 0.704, 18.787, 38.445, +3.1, and 4.0 per mil-9.0 per mil, respectively, in the westernmost zone, to 0.7071, 19.199, 38.777, -5, and 9 per mil-12 per mil, respectively, in the easternmost zone. The older western zone is therefore the more chemically and isotopically juvenile, characterized mostly by values that are slightly displaced from a mantle array at ca. 115 Ma, and similar to some modern island-arc signatures. In contrast, the isotopic signatures in the eastern zones indicate significant amounts of crustal involvement in the magmatic plumbing of those plutons. These isotopic signatures confirm previously published results that interpreted the Peninsular Ranges batholith as a progressively contaminated magmatic arc. The Peninsular Ranges batholith magmatic arc was initially an oceanic arc built on Panthalassan lithosphere that eventually evolved into a continental margin magmatic arc collision zone, eventually overriding North American cratonic lithosphere. Our Pb-Sr-Nd data further suggest that the western arc rocks represent a nearshore or inboard oceanic arc, as they exhibit isotopic signatures that are more enriched than typical mid-ocean-ridge basalt (MORB). Isotopic signatures from the central zone are transitional and indicate that enriched crustal magma sources were becoming involved in the northern Peninsular Ranges batholith magmatic plumbing. As the oceanic arc-continental margin collision progressed, a mixture of oceanic mantle and continental magmatic sources transpired. Magmatic production in the northern Peninsular Ranges batholith moved eastward and continued to tap enriched crustal magmatic sources. Similar modeling has been previously proposed for two other western margin magmatic arcs, the Sierra Nevada batholith of central California and the Idaho batholith. Calculated initial Nd signatures at ca. 100 Ma for Permian-Jurassic and Proterozoic basement rocks from the nearby San Gabriel Mountains and possible source areas along the southwestern Laurentian margin of southern California, southwestern Arizona, and northern Sonora strongly suggest their involvement with deep crustal magma mixing beneath the eastern zones of the Peninsular Ranges batholith, as well as farther east in continental lithospheric zones. Last, several samples from the allochthonous, easternmost upper-plate zone, which are considerably younger (ca. 84 Ma) than any of the rocks from the northern Peninsular Ranges batholith proper, have even more enriched average Sr (sub i) , (super 206) Pb (sub i) , (super 208) Pb (sub i) , and epsilon (sub Ndi) signatures of 0.7079, 19.344, 38.881, and -6.6, respectively, indicative of the most-evolved magma sources in the northern Peninsular Ranges batholith and similar to radioisotopic values for rocks from the nearby Transverse Ranges, suggesting a genetic connection between the two.


ISSN: 0072-1069
Coden: GSAMAQ
Serial Title: Memoir - Geological Society of America
Serial Volume: 211
Title: Pb-Sr-Nd-O isotopic characterization of Mesozoic rocks throughout the northern end of the Peninsular Ranges Batholith; isotopic evidence for the magmatic evolution of oceanic arc-continental margin accretion during the Late Cretaceous of Southern California
Title: Peninsular Ranges Batholith, Baja California and Southern California
Author(s): Kistler, Ronald W.Wooden, Joseph L.Premo, Wayne R.Morton, Douglas M.
Author(s): Morton, Douglas M.editor
Author(s): Miller, Fred K.editor
Affiliation: U. S. Geological Survey, Menlo Park, CA, United States
Affiliation: U. S. Geological Survey, Riverside, CA, United States
Pages: 263-316
Published: 201401
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 83
Accession Number: 2014-024227
Categories: Isotope geochemistryIgneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sects., 5 tables, geol. sketch map
N33°00'00" - N34°00'00", W118°00'00" - W116°00'00"
Secondary Affiliation: Stanford University, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201415
Program Name: USGSOPNon-USGS publications with USGS authors
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