Journal
GEOLOGY
Volume 50, Issue 1, Pages 10-15Publisher
GEOLOGICAL SOC AMER, INC
DOI: 10.1130/G49457.1
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Funding
- National Natural Science Foundationof China [91755213, 42102268, 4191101039, 42102244]
- 111 Project [BP0719022]
- China Postdoctoral Science Foundation [2020M682512, 2021M692977]
- Open Fund from the State Key Laboratory for Geological Pro-cesses and Mineral Resources [GPMR201903, MSFGPMR29]
- Fundamental Research Funds for National Universities [CUG2106365]
- China University of Geosciences, Wuhan
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This study reports the discovery of early Paleozoic boninitic blueschists and associated greenschists from the eastern Proto-Tethyan North Qilian orogenic belt in northeastern Tibet. These rocks provide important insights into the initiation and subsequent subduction processes of an intra-oceanic subduction zone. The findings also highlight the role of former upper plate island arc/forearcs in reducing the preservation of initial subduction-related rock records in ancient orogenic belts.
Subduction of oceanic lithosphere is a diagnostic characteristic of plate tectonics. However, the geodynamic processes from initiation to termination of subduction zones remain enigmatic mainly due to the scarcity of appropriate rock records. We report the first discovery of early Paleozoic boninitic blueschists and associated greenschists from the eastern Proto-Tethyan North Qilian orogenic belt, northeastern Tibet, which have geochemical affinities that are typical of forearc boninites and island arc basalts, respectively. The boninitic protoliths of the blueschists record intra-oceanic subduction initiation at ca. 492-488 Ma in the eastern North Qilian arc/forearc-backarc system, whereas peak blueschist facies metamorphism reflects subsequent subduction of the arc/forearc complex to high pressure at ca. 455 Ma. These relations therefore record the life circle of an intra-oceanic subduction zone within the northeastern Proto-Tethys Ocean. The geodynamic evolution provides an early Paleozoic analogue of the early development of the Izu-Bonin-Mariana arc and its later subduction beneath the extant Japanese arc margin. This finding highlights the important role of subduction of former upper plate island arc/forearcs in reducing the likelihood of preservation of initial subduction-related rock records in ancient orogenic belts.
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