Generation of I-type granitic rocks by melting of heterogeneous lower crust

Hammerli, Johannes, Kemp, Anthony I. S., Shimura, Toshiaki, Vervoort, Jeff D., and Dunkley, Daniel J. (2019) Generation of I-type granitic rocks by melting of heterogeneous lower crust. Geology, 47 (3). e456.

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[Extract]: Granite generation is a fundamental process for the growth and evolution of Earth’s continental crust. I-type granitic rocks, nominally derived from infracrustal sources, are the most common granite type and are voluminously emplaced in convergent margin settings. A puzzling feature is that many I-type granites show isotopic evidence for reworking of older supracrustal material, in conflict with the I-type designation. How the supracrustal component was incorporated by I-type magmas is a matter of deduction, particularly given difficulties in recognizing the putative infracrustal source region in the exposed geology. We report a case study of I-type granitic magma generation by hybridization between metasedimentary-derived partial melt and intercalated mafic granulite units during extraction of silicic magma from the lower crust in the Hidaka Metamorphic Belt (HMB), Japan (Hammerli et al., 2018). Isotopic data (Nd, Hf, O) obtained by microanalysis of accessory minerals in former melt networks (leucosomes) suggest that hybridization operates on a (sub-) grain scale, where repeated injections of externally derived melt attempt to approach local equilibrium with the host mafic granulites during transfer through complex melt pathways (see our figure 3; and also Hasalová et al. [2011] and references therein).

Item ID: 61872
Item Type: Article (Short Note)
ISSN: 1943-2682
Keywords: Asia; batholiths; crust; Far East; genesis; granites; granulites; Hidaka; metamorphic belt; Hokkaido; I-type granites; igneous rocks; intrusions; Japan; leucosomes; lower crust magmas melting metamorphic rocks metasedimentary rocks; migmatites; P-T conditions; plutonic rocks
Copyright Information: © 2019 Geological Society of America. This article is Open Access via the publisher.
Date Deposited: 03 Apr 2020 05:16
FoR Codes: 04 EARTH SCIENCES > 0403 Geology > 040304 Igneous and Metamorphic Petrology @ 100%
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