Small scale heterogeneity of Phanerozoic lower crust: evidence from isotopic and geochemical systematics of mid-Cretaceous granulite gneisses, San Gabriel Mountains, southern California
Article Abstract:
Granulite gneisses from San Gabriel Mountains, CA, were analyzed to identify protoliths in the lower crustal section and to compare them with upper and middle crustal arc rocks. Banded gneisses in the San Gabriel Mountains were of two types. Type 1 rocks are similar to arc basalts and andesites with high aluminum (Al) content. On the other hand, type 2 rocks have low Al content and are similar to mid-ocean-ridge basalts. Isotopic and lithologic variation among intercalated ortho- and paragneisses indicate small-scale heterogeneity in the continental crust. Further studies on the isotopic ratios show a wide range of protolith ages.
Publication Name: Contributions to Mineralogy and Petrology
Subject: Earth sciences
ISSN: 0010-7999
Year: 1992
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Role of the subducted slab, mantle wedge and continental crust in the generation of adakites from the Andean Austral Volcanic Zone
Article Abstract:
The adakitic andesites and dacites in the Andean Austral Volcanic Zone (AVZ) have been formed from subducted oceanic crust that contained residual garnet, amphiboles, and pyroxene. The subducted oceanic basalt recrystallized to form garnet-amphibolite or eclogite. The partial melting probably occurs below the Austral Andes. The materials from the overlying mantle wedge and continental crust were also incorporated into the adakites. The AVZ adakites have a low Yb and Y content, and high Sr and Nd isotopic compositions.
Publication Name: Contributions to Mineralogy and Petrology
Subject: Earth sciences
ISSN: 0010-7999
Year: 1996
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Genesis of high Mg# andesites and the continental crust
Article Abstract:
The continental crust contains Mg/(Mg+Fe) and Ni in andesites which did not originate from differentiation of basaltic magmas. The High Mg# andesite (HMA) in the crust might have formed when peridotite was depressed to mantle, melted there and metasomatised. It might have also formed by reaction of ascending melts and peridotite. HMA is not found in island arcs at present but may be common in the past, or perhaps abundant in the lower and middle crust, being formed in the specific environment.
Publication Name: Contributions to Mineralogy and Petrology
Subject: Earth sciences
ISSN: 0010-7999
Year: 1995
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