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Heat- and melt-fluxed melting of lower continental crust; insights from two types of subduction-related granitoids in northeastern China and the implications for crustal reworking and growth

Ma Xinghua, Qiao Shilei, Xiang Peng, Andrei V. Grebennikov and Renjie Zhou
Heat- and melt-fluxed melting of lower continental crust; insights from two types of subduction-related granitoids in northeastern China and the implications for crustal reworking and growth
Lithosphere (April 2019) 11 (4): 488-506

Abstract

Convergent plate boundaries are the primary location for the formation of continental crust by the intrusion of arc batholiths that contain essentially mantle-derived magmas. This paper presents two types of arc granitoids (enclave-free monzogranites and enclave-bearing granodiorites) in northeastern (NE) China to understand crustal evolution and growth in the eastern Asian continental margin. The monzogranites (189 Ma) show characteristics typical of upper continental crust, with high SiO (sub 2) contents and enrichment of K, Rb, and Pb. These monzogranites have low I (sub Sr) ( (super 87) Sr/ (super 86) Sr) ratios (0.70378-0.70413) and positive epsilon Nd (t) (+2.2 to +2.3) and epsilon Hf (t) (+7.3 to +10.2) values. These features, combined with high zircon saturation temperatures (TZr > 800 degrees C), suggest that the monzogranites were generated by the heat-fluxed melting of juvenile lower crust. In contrast, the granodiorites (171 Ma) contain abundant coeval mafic enclaves and show relatively low silica contents, low TZr (748-799 degrees C), and particularly wide variation in epsilon Hf (t) (-3.5 to +5.6), implying a hybrid origin involving both mantle- and crust-derived components. Isotopic modeling indicates that mantle material accounts for around 60%-70% of the hybrid magmas by volume. The granodiorites have adakite-like signatures (e.g., Sr/Y > 21 and [La/Yb]N > 15), which may have been primarily caused by a process of magma mixing and hornblende-dominated fractional fractionation, rather than through melting of a subducting slab or thickened lower crust. The two distinct granitoids (monzogranites and granodiorites) represent continental crustal reworking and growth, respectively, related to the subduction of the Paleo-Pacific Plate beneath the eastern Asian continental margin during the Jurassic.


ISSN: 1941-8264
EISSN: 1947-4253
Serial Title: Lithosphere
Serial Volume: 11
Serial Issue: 4
Title: Heat- and melt-fluxed melting of lower continental crust; insights from two types of subduction-related granitoids in northeastern China and the implications for crustal reworking and growth
Affiliation: Chinese Academy of Geological Sciences, Institute of Mineral Resources, China
Pages: 488-506
Published: 20190418
Text Language: English
Publisher: Geological Society of America, Boulder, CO, United States
References: 60
Accession Number: 2019-036122
Categories: General geochemistryIgneous and metamorphic petrologySolid-earth geophysics
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 4 tables, geol. sketch maps
N42°19'60" - N42°40'00", E129°00'00" - E129°30'00"
Secondary Affiliation: China University of Geosciences at Beijing, CHN, ChinaRussian Academy of Sciences, Far Eastern Branch, Far East Geological Institute, RUS, Russian FederationUniversity of Queensland, AUS, Australia
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201919
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