Terrigenous Mineralogical Component in the Sediments from SCS since 30Ma and Their Geological Significance
JIANG Hengyi~ 1,2 LI Anchun ~ 1 WAN Shiming~ 1,2 (~ 1 Institute of Oceanology,Chinese Academy of Sciences, Qingdao 266071) (~ 2 Graduate School of Chinese Academy of Sciences, Beijing 100039)
Minerals are the main components of sediments, whose terrigenous parts are carried into the ocean by rivers or winds and deposit directly or indirectly. The amount of the terrigenous minerals in marine sediments indirectly indicates the source area of supply and the strength of the transport agent. Minerals in sediment are strongly affected by tectonic movement and geomorphic evolution in long time scale. Therefore, large tectonic movement must lead to change of mineral components and fluxes. The South China Sea(SCS)basin experienced two tectonic expansions in Cenozoic; the second expansion occurred between 32～15.5Ma, formed the central basin. The Palawan block moved far away from the northern continent. The Tibet Plateau experienced three accelerated uplifts at 25～17Ma.B.P, 10～8Ma.B.P and ～4Ma.B.P～present In order to determine the effective tectonic movement proxy indexes and find more evidence for the two large tectonic events in marginal sea sedimentary mineral composition and their fluxes were studied. Quartz, feldspar, clay minerals and terrigenous minerals were extracted from the sediments of site 1 148 of ODP LEG 184 by chemical dissolution method, the contents and their mass accumulation rate(MAR)were calculated. According to the chronology data in the initial report of ODP LEG 184, vertical distribution of the terrigenous minerals and their content and fluxes against age were established. Therefore, the response of content and flux of terrigenous minerals to the expansion of South China Sea floor(SCS)and the uplift of the Tibet Plateau were discussed. The results showed that the highest terrigenous mineral components between 33～27.5Ma was correlated with the start of SCS floor expansion and the ridge jump while it was affected by the uplift of Tibet Plateau after 24.5Ma. The accelerated uplift phases were very prominently revealed in the sediments, especially the rapid uplift since 4Ma ago. The provenance of terrigenous mineral components changed from southeast to northwest at about 24.5Ma as the southern source departed from the deposition site and the effects weakened with the expansion of the SCS floor, when the Tibet Plateau uplifted led to morphologic gradient increase, change of river direction and enhanced of erosion.
【Fund】： 国家自然科学基金(批准号:49732060 40576032);; 国家重点基础研究发展规划项目(GrantNo·G2000046703)资助
【CateGory Index】： P736.21
【CateGory Index】： P736.21