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Coexisting Nb-enriched basalts and arc volcanic rocks in the northern Qiangtang Terrane, China; implications for the effects of ambient mantle on subduction zone magmatism

Zhang Ze, Chen Shengsheng, Sun Dawei and Gao Sen
Coexisting Nb-enriched basalts and arc volcanic rocks in the northern Qiangtang Terrane, China; implications for the effects of ambient mantle on subduction zone magmatism
Geological Society of America Bulletin (September 2023) 136 (5-6): 1933-1949

Abstract

The petrogenesis of Nb-enriched basalts (NEBs) is controversial. NEBs are generally considered to form by melting of either a mixed enriched and depleted mantle source or a mantle wedge metasomatized by adakitic melts. Here we present geochronological, petrological, geochemical, and Sr-Nd-Os isotope data for Early Permian volcanic rocks from the Tuotuohe area in the northern Qiangtang Terrane, China. The studied volcanic rocks can be divided into two groups: arc basalts and basaltic andesites in the lower sequence and NEBs in the upper sequence. Zircon grains from one basaltic andesite sample in the lower sequence yielded a concordia age of 302.0 + or - 1.1 Ma. The geochemical and isotopic characteristics suggest that the NEBs were derived from a mixed source consisting of enriched mid-oceanic ridge basalts (MORB)- to oceanic-island basalt-like ambient mantle and slab-derived fluids, whereas the arc basalts and basaltic andesites originated from a source made of the MORB-type ambient mantle modified by slab-derived melts. We propose for the first time that the Nb enrichment of the NEBs was most likely inherited from high-Nb ambient mantle and is independent of the addition of slab-derived components. In addition to slab-derived components, the nature of the ambient mantle is also an important factor controlling the diversity of arc magmatism. Our new findings show that the Late Carboniferous-Early Permian magmatism in the northern Qiangtang Terrane was related to northward subduction of the Paleo-Tethys Ocean, suggesting that subduction might have occurred in at least the Early Permian rather than in the previously thought Middle Permian.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: 136
Serial Issue: 5-6
Title: Coexisting Nb-enriched basalts and arc volcanic rocks in the northern Qiangtang Terrane, China; implications for the effects of ambient mantle on subduction zone magmatism
Affiliation: China University of Geosciences, School of Earth Science and Resources, State Key Laboratory of Geological Processes and Mineral Resources, Beijing, China
Pages: 1933-1949
Published: 20230912
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 129
Accession Number: 2023-064296
Categories: Igneous and metamorphic petrologySolid-earth geophysics
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sect., strat. col., 3 tables, geol. sketch map
N34°04'60" - N34°04'60", E92°19'60" - E92°19'60"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2024, 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: 202339
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