Structural characteristics of the Chiwei Platform and their implications for the back-arc rifting of the Okinawa Trough, East China Sea

摘要

The Chiwei Platform is an isolated submarine topographic high located on the northwestern slope of the southern Okinawa Trough. It is separated from the East China Sea Shelf by a wedge-shaped submarine valley corresponding to a deep basin (Chiwei Depression). Newly acquired seismic reflection profiles and P-wave velocity models demonstrate that the acoustic basement of the platform is shallow and only covered by thin sediments or is even exhumed. Similarities in seismic reflection and P-wave velocity structures between the Chiwei Platform, East Chiwei Seamount and Diaoyudao Uplift suggest that the Chiwei Platform is a high-standing relict basement high formed during the back-arc rifting of the Okinawa Trough. It lies in the transition zone in which the directions of the back-arc rifting centers clockwise rotated from the NE-SW to E-W southwestwardly. Southwest of the transition zone, the southern Diaoyudao Uplift is left-laterally shifted relative to the middle Diaoyudao Uplift and might be disconnected from the latter due to the presence of the Chiwei Depression. The original southern Diaoyudao Uplift exhibited a basement high resembling the middle and northern Diaoyudao Uplift. However, this NE-SW-trending basement high was destroyed and collapsed due to oblique dissections of the E-W-trending rifting centers along with westward propagation of the southern Okinawa Trough. Since nonmagnetic prerifted basement rocks have not been drilled on the Diaoyudao Uplift, the Chiwei Platform is a preferential drilling site where the prerifted basement rocks can readily be obtained due to its high-standing position and thin sedimentary cover. This work can provide supplementary constraints on the basement properties of the Ryukyu back arc region and help to better understand the evolution of the southern Okinawa Trough.

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