The transition from continental to lithospheric breakup recorded in proto-oceanic crust: Insights from the NW South China Sea - Archive ouverte HAL Access content directly
Journal Articles Geological Society of America Bulletin Year : 2022

The transition from continental to lithospheric breakup recorded in proto-oceanic crust: Insights from the NW South China Sea

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Abstract

The formation of a new plate boundary and creation of the first oceanic crust, two of the most important processes of plate tectonics, still remains little understood. While older studies used to assumed a sharp ocean-continent boundary between continent and ocean, recent studies suggest a progressive ocean-continent transition (OCT) between unequivocal continental and oceanic crusts. In the latter view, breakup is not instantaneous but a lasting phase, which raises questions about the nature of the OCT basement and the processes operating between continental and lithospheric breakup. Based on detailed observations of high-quality and yet unpublished reflection seismic data, we describe and interpret the characteristic structures of the NW-South China Sea OCT and their relationship with overlying syn-breakup phase sediments. We show that the OCT displays a transition from fault-dominated rifting to magma-dominated seafloor spreading. On its continent-ward side, the OCT is made of hybrid crust where tectonic thinning of continental crust is compensated by syn-extensional magmatic thickening. Oceanward, the hybrid crust evolves into a fully magmatic but fault-dominated proto-oceanic crust, and finally turns into a mature Penrose-type oceanic crust. Relying on the growth structures observed in the syn-breakup sedimentary sequences and magmatic additions, we propose a kinematic restoration of the breakup phase. We suggest out-of-sequence flip-flop faulting to explain the switch from asymmetrical, fault-dominated-extension, to fully magmatic and largely symmetrical syn-extension accretion recorded in the syn-breakup sedimentary sequences overlying the OCT.
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Dates and versions

insu-03894832 , version 1 (12-12-2022)

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Cite

Peng Chao, Gianreto Manatschal, Cuimei Zhang, Pauline Chenin, Jianye Ren, et al.. The transition from continental to lithospheric breakup recorded in proto-oceanic crust: Insights from the NW South China Sea. Geological Society of America Bulletin, 2022, ⟨10.1130/B36371.1⟩. ⟨insu-03894832⟩
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