Subduction Within the Proto-Tethys Ocean Revealed by Recognition of the Earliest Phanerozoic Intra-Oceanic Arc, Northern Tibetan Plateau
Publication Name
Earth and Space Science
Abstract
The possibility that the Proto-Tethys Ocean may have undergone intra-oceanic subduction during ocean closure remains poorly constrained due to a lack of geological evidence for a mature intra-oceanic arc. Here we present new geochemical and geochronological data for potential arc-related volcanic rocks adjacent to the accretionary complex and forearc basin in the North Qaidam collisional belt, northern Tibetan Plateau. The volcanic rocks are dominated by foliated basalt, andesite, tuff, and minor dacite with zircon U-Pb ages ranging from 517 to 497 Ma. They show distinctive geochemical characteristics and can be subdivided into three groups: island-arc intermediate-basic volcanic rocks, back-arc basin basalts (BABB), and dacites with intra-oceanic arc affinity. The island-arc volcanic rocks have variable εNd(t) values (+1.6 to +7.5) that decrease northward and were generated by partial melting of depleted mantle wedge modified by hydrous fluid and sediment melt. The BABBs have high εNd(t) values (+5.3 to +6.6) and formed through the melting of MORB-like mantle, whereas the nearby dacites have positive εNd(t) values (+1.9 to +3.6) similar to the surrounding island-arc volcanic rocks and were derived from partial melting of intra-oceanic arc crust as a result of BABB underplating. Integrated analysis of the spatial-temporal distribution of these volcanic rocks and the reconstructed intra-oceanic arc-trench system confirms the existence of the earliest Phanerozoic intra-oceanic arc formed in response to north-directed intra-oceanic subduction. This unrecognized subduction of the Proto-Tethys Ocean in the North Qaidam belt initiated at ca. 530 Ma, matured ca. 520 Ma, and terminated by ca. 480 Ma.
Open Access Status
This publication may be available as open access
Volume
11
Issue
3
Article Number
e2023EA002985
Funding Number
41872241
Funding Sponsor
National Natural Science Foundation of China