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Sources of the Early Cretaceous Plutons in the Turtle and West Riverside Mountains, California: Anomalous Cordilleran Interior Intrusions |
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| Authors: | ALLEN C M; WOODEN J L; HOWARD K A; FOSTER D A; TOSDAL R M |
| Institution: | 1 DEPARTMENT OF GEOLOGY, AUSTRALIAN NATIONAL UNIVERSITY CANBERRA, A.C.T. 0200, AUSTRALIA 2US GEOLOGICAL SURVEY, MENLO PARK, CA 94025, USA 3 SCHOOL OF EARTH SCIENCES, LA TROBE UNIVERSITY BUNDOORA, VIC. 3083, AUSTRALIA |
| Abstract: | Ages and initial isotopic ratios of Early Cretaceous ({smalltilde}100 Ma) plutons of the Cordilleran Interior in the southernTurtle and West Riverside mountains distinguish them from LateCretaceous plutons in surrounding ranges in the eastern MojaveDesert. Furthermore, the studied plutons have isotopic and geochemicalcharacteristics more similar to plutons of Cretaceous age inthe coastal batholiths (Peninsular Ranges and Sierra Nevada)than to most Mesozoic plutons in the Cordilleran Interior. Thestudied plutons are calcic, in contrast to the mostly cak-alkalineMesozoic plutons of the eastern Mojave Desert. Distinctive isotopicsignatures of the granitoids include lower initial 87Sr/86Srof 0•705–0•710,  18O of +6•3 to +7•7 ,208Pb/204Pb of 38•3–39•5, and higher  Nd of –3•86to –9•60 than the Late Cretaceous plutons in theregion. The distinctive characteristics of these Early Cretaceousplutons are probably both location and time specific and resultfrom: (1) emplacement in a cold, untapped ‘Mojave-type’Proterozoic upper crust, (2) a significant component of basalticmagmas partially melted from the asthenosphere or subcontinentallithosphere and (3) a magmatic component derived from Proterozoic,mafic, lower crust. They interacted less with their crustalhosts than did the later, more voluminous Late Cretaceous plutons. KEY WORDS: Cordilleran Interior; Cretaceous; Mojave; pscudothron; Turtle Mountains |
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