Evidence of low flexural rigidity and low viscosity lower continental crust during continental break-up in the South China Sea

Author(s): Clift, Peter; Lin, Jian; Barckhausen, Udo
Author Affiliation(s): Primary:
Woods Hole Oceanographic Institution, Department of Geology and Geophysics, Woods Hole, MA, United States
Bundesanstalt für Geowissenschaften und Rohstoffe, Federal Republic of Germany
Volume Title: Marine and Petroleum Geology
Source: Marine and Petroleum Geology, 19(8), p.951-970. Publisher: Elsevier, Oxford, United Kingdom. ISSN: 0264-8172
Note: In English. 46 refs.; illus., incl. sects., geol. sketch maps
Summary: The South China Sea was formed by seafloor spreading in the Late Oligocene at ∼30 Ma following a series of extensional events within crust formed by a Mesozoic continental arc. In this study, we interpreted faults along seismic reflection profiles from both the northern and southern conjugate margins of the South China Sea and forward modeled these using a flexural cantilever model to predict modern basin geometries. When compared with the observed structure, the models based on upper crustal faulting consistently underpredicted the amount of subsidence, especially towards the continent-ocean transition (COT). We interpret this to indicate preferential extension of the continental lower crust along the COT on both margins, extending up to ∼80 km landward from COT. The regional slope of the South China continental shelf indicates lower crustal viscosities of 1019-1018 Pa s, representing an offshore continuation of the weak crust documented onshore on the eastern flanks of the Tibetan Plateau. Only in the region of Hainan Island in the western South China Shelf does lower crustal viscosity increase (1021-1022 Pa s) and the preferential loss of lower crust become less pronounced and limited to <40 km from COT. This western area represents a rigid block analogous to the Sichuan Basin onshore. Forward models based on upper crustal faulting support the idea of a very weak continental crust because models where the effective elastic thickness of the plate (Te) exceeds 5 km fail to reproduce the geometry of the sub-basins within the Pearl River mouth basin (PRMB) of the South China Margin. The observed basins are too deep and narrow to be consistent with models invoking high flexural rigidity in the upper crust or mantle lithosphere. The fact that rifting and seafloor spreading seem to co-exist for ∼5 my. adjacent to the PRMB is consistent with very weak continental crust during break-up. Abstract Copyright (2002) Elsevier, B.V.
Year of Publication: 2002
Research Program: ODP Ocean Drilling Program
Key Words: 18 Geophysics, Solid-Earth; Cenozoic; Continental crust; Crust; Flexure; Flexure folds; Folds; Leg 184; Lower crust; North Pacific; Northwest Pacific; Ocean Drilling Program; Oligocene; Pacific Ocean; Paleogene; Plate tectonics; Rigidity; Seismic anomalies; South China Sea; Tertiary; Upper Oligocene; Viscosity; West Pacific
Coordinates: N050000 N240000 E1210000 E1080000
Record ID: 2003044611
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands