Post-Orogenic Extension in the Pearl River Delta Region (South China): An Integrated Morphological, Structural, Geophysical and Thermochronological Study

This dissertation, "Post-orogenic Extension in the Pearl River Delta Region (South China): an Integrated Morphological, Structural, Geophysical and Thermochronological Study" by 沈文略, Wenlue, Shen, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled POST-OROGENIC EXTENSION IN THE PEARL RIVER DELTA REGION (SOUTH CHINA): AN INTEGRATED MORPHOLOGICAL, STRUCTURAL, GEOPHYSICAL AND THERMOCHRONOLOGICAL STUDY Submitted by SHEN WENLUE for the degree of Doctor of Philosophy at The University of Hong Kong in January 2008 The Pearl River Delta (PRD) region is a late Mesozoic-Tertiary basin system located on the southern margin of the Cathaysian block, South China. It follows two NW-striking faults extending into the Late Proterozoic- early Mesozoic Cathaysian orogen. It is apparently antithetic to the dominant NE to ENE-trending basement structures, including the orogen and the "South China Basin and Range Province (SCBRP)" formed due to a late Mesozoic post-orogenic collapse and the Tertiary rifting of the South China Sea (SCS). In this study, (1) the heterogeneous basin structures in the PRD are found inherited from the SCBRP basins but expanding in a NNW-SSE direction in the Tertiary. Remote-sensing image interpretation, field investigation and polyphasal paleostress inversion using fault-slip measurements suggest the major Tertiary PRD basins are consistent with the early SCS rifting, whilst a later extension exists in about the ENE-WSW direction; (2) magnetic anomaly inversion reveals the PRD region to be a crustal transition zone between the NE-trending regional structures and the E-W rifts. Both long-wavelength magnetic models for the Cathaysian block and aeromagnetic signatures over the PRD region are studied by direct map interpretation and 3-dimensional Euler deconvolution, which helps to integrate surface geology and basement structures for a 3-D estimation on the rifting system; (3) apatite fission track analysis shows a rapid exhumation of the PRD region during the late Eocene-early Miocene, representing an intensive crustal attenuation coincident with the SCS spreading. A later thermal quiet period lasting for about 10 Ma is evident followed by a fast cooling in the recent 5-10 Ma, correspondent to a possible uplift due to the collision between the Philippines and the SCB. Unroofing may reach 5 km, including 1 2 km Tertiary sediments eroded from the PRD basins. A five-stage tectonic evolution is suggested for the post-orogenic extension in the PRD region: z An initial rifting before the Late Cretaceous within the SCBRP tectonic regime as the releasing bends between the NE-striking shear zones; z A possible back-arc collapse of magmatic arc in Late Cretaceous; z A major NNW-SSE extension in the early Tertiary within the SCS rifting regime, connecting and expanding older rifts till the seafloor spreading; z A minor coast-parallel extension in between the Oligocene and late Miocene; z A general inverse of Main faults since the Pliocene, which has controlled the neotectonics in the PRD region. DOI: 10.5353/th_b3955858 Subjects: Orogeny - China - Pearl River Delta Geology, Structural - China - Pearl River Delta