Some additional observations on inclusions in the granitic rocks of the Sierra Nevada

Journal of Geophysical Research Solid Earth
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Abstract

Microgranular quartz diorite and diorite inclusions are widespread in central Sierra Nevada granitoid rocks and are almost exclusively restricted to hornblende-bearing rocks, most commonly felsic tonalites and mafic granodiorites. Strontium 87/strontium 86 values of the inclusions and host granitoids from individual plutons generally plot on single isochrons that agree closely with previously determined ages. Neodymium 143/neodymium 144 values of five inclusions ranged from 0.51229 to 0.51248 and yield εNd values that correlate closely with values of their respective hosts. The Nd-Sm and Rb-Sr systematics indicate that most inclusions were in isotopic equilibrium with enclosing materials at the time of formation. Silica contents of inclusions and granitoids are contiguous, but inclusions generally contain less than, and granitoids more than, 60% SiO2. Linear continuity of the femic oxide and H2O+ trends relative to SiO2 suggests many inclusions formed as concentrations of hydrous mafic minerals. Variation of other major element oxides and trace elements support this inference. The aforementioned data are generally inconsistent with a direct genetic link between the mafic inclusions and the mantle-derived basalt. However, many initial Sierra Nevada magmas were produced by mixing of mafic, mantle-derived melts and felsic crustal materials, resulting in isotopically varied tonalitic and granodioritic magmas. Most inclusions thus represent fragmented crystal accumulations of early-formed, near-liquidus minerals generated from these previously mixed magmas.

Publication type Article
Publication Subtype Journal Article
Title Some additional observations on inclusions in the granitic rocks of the Sierra Nevada
Series title Journal of Geophysical Research Solid Earth
DOI 10.1029/JB095iB11p17841
Volume 95
Issue B11
Year Published 1990
Language English
Publisher American Geophysical Union
Description 8 p.
First page 17841
Last page 17848
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