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Paper No. 15
Presentation Time: 1:30 PM-5:30 PM
A GEOCHEMICAL COMPARISON OF PLUTONIC GRANITIODS TO DEEPER SHEETED PLUTONIC ROCKS: EASTERN TRANSVERSE RANGES, SOUTHERN CALIFORNIA
The eastern Transverse Ranges is a well-exposed terrain that extends >100km across strike of the North American Cordillera in southern California. Barometric data show that this terrain constitutes a tilted cross-section of the Mesozoic arc, with the shallower eastern and central parts dominated by Mesozoic plutons intruding Proterozoic basement and Mesozoic cover, and the deeper western part dominated by a sheeted plutonic complex of Jurassic and Late Cretaceous age. In this study we compare the geochemistry of shallower plutons to contemporaneous, but structurally deeper, sheeted plutonic rocks. The central portion consists of four geochemically distinct plutons: the 151±1 Ma White Tank, 82±2 Ma Blue, 80±1 Ma Squaw Tank, and 76±2 Ma Palms plutons. The four plutons range from metaluminous hornblende biotite granodiorite to peraluminous biotite granite, with 64-76 % silica, 0.43-2.75 % Fe2O3*, and 0.07-0.46% TiO2. Volumetrically dominant components of the western sheeted plutonic complex are biotite hornblende tonalite, granodiorite, and muscovite-garnet granite sheets that are interlayered at meter to decimeter scale. Geochemically, the sheeted plutonic rocks reflect a generally more mafic character, ranging from metaluminous to peraluminous with 56-76% silica, 6 - 0.4 %wt Fe2O3, and 1.3 - 0.07 %wt TiO2. Isotopically, the central plutons and western sheeted plutonic rocks show significant overlap (Sri = 0.7086 0.7127, &epsilon Nd = -10.6 to -16.5, &delta Jerome = 3.5 to 9.3), with the more mafic components of the sheeted complex recording a less evolved character (Sri = 0.7063 0.7095). These data suggest that the deeper, sheeted plutonic complex was assembled from a greater diversity of plutonic rocks, of similar petrologic character to the relatively more homogeneous and felsic, granodioritic to granitic plutons that characterize upper crustal discordant plutons in this region of the Cordilleran arc.