Pb and Sr isotopic constraints on lithospheric magma sources during Mesozoic continental margin arc initiation, southern California

Conference · Thu Apr 01 00:00:00 EST 1993 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5292005

Barth, A P ^[1]; Tosdal, R M; Wooden, J L ^[2]

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1. Indiana/Purdue Univ., Indianapolis, IN (United States). Dept. of Geology
2. Geological Survey, Menlo Park, CA (United States)

Initiation of the Mesozoic Cordilleran arc in the southwestern US is marked by plutonism from about 241--213 Ma, exposed in the Granite Mountains in the southwestern Mojave Desert, through the Transverse Ranges to the Colorado River trough in southeastern California and southwestern Arizona. Plutons range in composition from diorite to granite, but quartz monzonite and monzodiorite predominate. Plutons intruded 1,700 to 1,100 Ma rocks of the Mojave crustal province [as defined isotopically by Wooden and Miller (1990) and Bennett and DePaolo (1987)], and episomal plutons locally intruded its deformed cratonal/miogeoclinal cover. Plutons emplaced during arc initiation overlap isotopically with local Proterozoic basement rocks, but typically have less radiogenic [sup 207]Pb/[sup 204]Pb, [sup 208]Pb/[sup 204]Pb and [sup 87]Sr/[sup 86]Sr than adjacent, more voluminous Middle-Late Jurassic and Late Cretaceous arc plutons. Among early arc plutons, an inter-suite trend toward more radiogenic Pb and [sup 87]Sr/[sup 86]Sr at similar silica contents reflects regional basement isotopic variability. Generally high Sr contents, low Rb/Sr and limited REE data suggest this inter-suite variations records heterogeneity in eclogite/garnet amphibolite facies mafic lithospheric magma sources, corresponding to mafic lower crust and/or upper mantle formed during 1,700 Ma orogenesis or rift-related magmatism at 1,100 Ma. Intra-suite trends toward less radiogenic Pb at constant or more radiogenic Sr reflect involvement of a U and Th depleted, silicic intracrustal contaminant. Distinctive magma sources and limited crustal interaction during emplacement probably reflects the relatively cool thermal structure of the nascent Cordilleran continental margin arc.

• OSTI ID: 5292005
• Report Number(s): CONF-9305259-; CODEN: GAAPBC
• Journal Information: Geological Society of America, Abstracts with Programs; (United States), Vol. 25:5; Conference: 89. annual meeting of the Cordilleran Section and the 46th annual meeting of the Rocky Mountain Section of the Geological Society of America (GSA), Reno, NV (United States), 19-21 May 1993; ISSN 0016-7592
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
CALIFORNIA
GEOLOGIC FORMATIONS
PETROCHEMISTRY
PETROGENESIS
PLUTONIC ROCKS
CHEMICAL COMPOSITION
CONTINENTAL MARGIN
GEOCHEMISTRY
GEOLOGIC HISTORY
ISOTOPE RATIO
LEAD ISOTOPES
MAGMA
MESOZOIC ERA
PLATE TECTONICS
STRONTIUM ISOTOPES
ALKALINE EARTH ISOTOPES
CHEMISTRY
DEVELOPED COUNTRIES
GEOLOGIC AGES
GEOLOGY
IGNEOUS ROCKS
ISOTOPES
NORTH AMERICA
PETROLOGY
ROCKS
TECTONICS
USA
580000* - Geosciences