关键词: 东北印度洋, 喜马拉雅—青藏高原隆升, 华南陆缘, 南海, 海陆对比

Abstract:

In this paper the author shares his two important scientific experiences and results on “Sea-Land Correlation”: (1) to research the Himalayan and Tibetan uplift based on data from the NE Indian Ocean, and (2) to research the closure of the “proto-South China Sea (SCS)” and the birth of the SCS based on magmatic-sedimentary records from their neighboring landmasses. The unique sea-land correlation provides an effective access on the understanding of regional evolution. In the first study of monitoring the mountain uplift based on marine deposits, two highly-distinct (in composition and origin) deep-sea sedimentary sequences are discriminated. Located on the Bengal submarine fan and Ninetyeast Ridge, respectively, each sequence has its own respond signals to the Himalayan and Tibetan uplift. By strictly sieving and correlating the proxies from those sequences, this study argues that the most important periods of the uplift of the Himalayan Mountain and Tibetan Plateau occurred since Late Miocene, at 3.6-3.2 Ma and 1.0-0.6 Ma. In the second study of approaching the seas from the continental materials, highly complicated records including magma, structure, sedimentation and logging, whose preserved condition is usually inferior to those records collected from the deep sea, need to be dealt with. The advantage of such study is that researchers are permitted to organize multidisciplinary materials in a large region, and set up the regional evolutionary framework based on land-sea integration, thereby avoiding limitations brought by a single submarine drilling hole. In the southern margin of China continent there was a subversive change from the Late Mesozoic active pattern to Cenozoic passive pattern. To reconstruct systematically a Mesozoic marginal arc,the author established a cross-shaped investigation approach: searching for the extension of arc discovered in Hainan Island in the E-W direction and finding out the arc architecture in the N-S direction. It is found that a drastic regional uplift resulting from the plate convergence occurred in the Mid Cretaceous time (110-80 Ma), and its intensity weakened northward. As compared with the contemporaneous tectono-sedimentary records outcropped in the Zhejiang-Fujian continental margin, the “proto-SCS” subducting northward during the Late Mesozoic was probably affiliated to the deceased Tethyan domain. Since the end of Mesozoic, the margin of South China has entered a completely new phase. With the largest and best-preserved Cenozoic magmatic-sedimentary records, the Sanshui basin is selected as a focus to study the rupturing of the passive margin. During the Late Paleocene (~57Ma) the alkaline bimodal volcanism, represented by alkaline basalt, trachyte and comendite, extensively developed in the study area and continued to the ending of the basin (42-38Ma). The deduction can be achieved from the experimental data: (1) magma sources were derived from the asthenospheric mantle, and both the large-scale trachyte and comendite were also resulted from the phased crystallization differentiation of mantle-derived basaltic magma, and (2) the calculated mantle thermal anomaly is indistinct. The available evidences lead to the following interpretations: There is no deeply-derived mantle plume dominating regional tectonism. The volcanic rock suites developed in the Sanshui basin actually imply that the subduction-collision occurring in the Late Mesozoic had shortened and thickened the lithosphere, and the consequent lithospheric delamination and asthenospheric upwelling occurred around the Mesozoic-Cenozoic boundary. This tectonic mechanism not only resulted in the Early Cenozoic rifting in South China but also likely had an impact on the subsequently spreading of the SCS. Ocean and land, the two largest units on the Earth, are being closely connected by modern geosciences. Collecting relevant geological signals from the ocean to study continental evolution, or vice versa, can provide us with a new and effective window to examine and solve scientific problems.

Key words: the Northeastern Indian Ocean, Himalayan and Tibetan uplift, margin of the South China, South China Sea, sea-land correlation