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Tectonic transition from oceanic subduction to continental collision; new geochemical evidence from Early-Middle Triassic mafic igneous rocks in southern Liaodong Peninsula, east-central China

Fang Wei, Dai Liqun, Zheng Yongfei, Zhao Zifu and Ma Litao
Tectonic transition from oceanic subduction to continental collision; new geochemical evidence from Early-Middle Triassic mafic igneous rocks in southern Liaodong Peninsula, east-central China
Geological Society of America Bulletin (November 2019) 132 (7-8): 1469-1488

Abstract

In contrast to the widespread occurrence of mafic arc magmatism during oceanic subduction, there is a general lack of such magmatism during continental subduction. This paradigm is challenged by the discovery of Early-Middle Triassic mafic igneous rocks from the southeastern margin of the North China Block (NCB), which was subducted by the South China Block (SCB) during the Triassic. Zircon U-Pb dating for these mafic rocks yields 247+ or -2-244+ or -5 Ma for their emplacement, coeval with the initial collision between the two continental blocks. These Triassic mafic rocks generally exhibit ocean island basalt (OIB)-like trace element distribution patterns, intermediate ( (super 8) 7Sr/ (super 86) Sr)i ratios of 0.7057-0.7091, weakly negative epsilon (sub Nd) (t) values of -1.2 to -3.8, and epsilon (sub Hf) (t) values of -1.3 to -3.2. Such geochemical features indicate origination from a metasomatic mantle source with involvement of felsic melts derived from dehydration melting of the previously subducting Paleo-Tethyan oceanic crust. The syn-magmatic zircons of Triassic age show variable Hf-O isotopic compositions, indicating that the crustal component was composed of both altered basaltic oceanic crust and terrigenous sediment. High Fe/Mn and Zn/Fe ratios suggest that the mantle source would mainly consist of ultramafic pyroxenites. The melt-mobile incompatible trace elements were further fractionated relative to melt-immobile trace elements during partial melting of these pyroxenites, giving rise to basaltic melts with OIB-like geochemical signatures. The mafic magmatism may be caused by tectonic extension due to rollback of the subducting Paleo-Tethyan oceanic slab in response to the initial collision of the NCB and SCB in the Early Triassic. Therefore, the syn-subduction mafic magmatism provides new geochemical evidence for tectonic transition from oceanic subduction to continental collision in east-central China.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: 132
Serial Issue: 7-8
Title: Tectonic transition from oceanic subduction to continental collision; new geochemical evidence from Early-Middle Triassic mafic igneous rocks in southern Liaodong Peninsula, east-central China
Affiliation: University of Science and Technology of China, School of Earth and Space Sciences, CAS Key Laboratory of Crust-Mantle Materials and Environments, Hefei, China
Pages: 1469-1488
Published: 20191118
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 174
Accession Number: 2020-000563
Categories: Solid-earth geophysicsGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: GSA Data Repository item 2020014
Illustration Description: illus. incl. geol. sketch maps
N38°30'00" - N41°00'00", E122°00'00" - E125°00'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2020, 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: 202001
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