Devonian Nb-enriched basalts and andesites of north-central Tibet: Evidence for the early subduction of the Paleo-Tethyan oceanic crust beneath the North Qiangtang Block

Zhang, Hongrui, Yang, Tiannan, Hou, Zengqian, and Bian, Yeke (2016) Devonian Nb-enriched basalts and andesites of north-central Tibet: Evidence for the early subduction of the Paleo-Tethyan oceanic crust beneath the North Qiangtang Block. Tectonophysics, 682. pp. 96-107.

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Abstract

The early evolution of the Tethyan Ocean in north-central Tibet is currently poorly constrained. A sequence of volcanic rocks ranging from basic to intermediate in composition has been identified in the Zaduo area of the North Qiangtang Block. SHRIMP U–Pb dating of zircons from a sample of Zaduo andesite suggests an eruption age of Late Devonian (~ 380 Ma). The Zaduo volcanic rocks exhibit geochemical characteristics similar to those of typical Nb-enriched basalts, with relatively high Nb, Ta, and Zr contents, resulting in high Nb/La ratios (0.70–1.08) and Nb/U ratios (10.57–34.37). The relative enrichment in high field strength elements, together with positive εNd(t) values of + 4.6 to + 5.8 and low (87Sr/86Sr)i ratios of 0.70367–0.70532, indicates the Zaduo volcanic rocks were derived from a depleted mantle source metasomatized by silicate melts of a subducted oceanic slab. The occurrence of Nb-enriched volcanic rocks in the North Qiangtang Block suggests that the subduction of Paleo-Tethyan oceanic crust was initiated in the Late Devonian. Available geochronological data from ophiolites surrounding the North Qiangtang Block suggest that the subducted slab is most likely the Longmucuo–Shuanghu Paleo-Tethyan oceanic crust.

Item ID: 48056
Item Type: Article (Research - C1)
ISSN: 0040-1951
Keywords: Nb-enriched basalt; Late Devonian; subduction; Paleo-Tethyan; North-Central Tibet
Funders: State Key Research Development Program of China (SKRDPC), National Natural Science Foundation of China (NNSFC), International Geological Correlation Program (IGCP)
Projects and Grants: SKRDPC 973, No. 2015CB452601, NNSFC 41472067, NNSFC 41320104004, IGCP IGCP/SIDA-600
Date Deposited: 23 Mar 2017 22:57
FoR Codes: 04 EARTH SCIENCES > 0402 Geochemistry > 040202 Inorganic Geochemistry @ 30%
04 EARTH SCIENCES > 0403 Geology > 040304 Igneous and Metamorphic Petrology @ 40%
04 EARTH SCIENCES > 0403 Geology > 040313 Tectonics @ 30%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970104 Expanding Knowledge in the Earth Sciences @ 100%
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