| Session Details | |
| Section | SE - Solid Earth Sciences |
| Session Title | Accretion of Gondwana Fragments to southern Eurasia: Tectonic and Magmatic Responses in Southeast Asia |
| Main Convener | Dr. Nguyen Hoang (Institute of Geological Sciences, Viet Nam) Mr. Tuan-Anh Tran (Institute of Geological Sciences, Viet Nam) |
| Co-convener(s) | Dr. Cuong Nguyen Quoc (Institute of Geological Sciences, Vietnam Academy of Science and Technology, Viet Nam) Prof. Tran Trong Hoa (Institute of Geological Sciences, VAST, Viet Nam) Dr. Cung Thuong Chi (Institute of Geological Sciences, Viet Nam) Prof. Martin Flower (University of Illinois at Chicago, United States) Dr. Laxmidhar Behera (National Geophysical Research Institute, India) |
| Session Description | During the closure of Paleo- and Neo-Tethys the accretion of relict fragments of Gondwana to southern Eurasia produced a wide range of geodynamic and magmatic responses. As a ‘template’ for understanding such effects, the evolution of southeast Asia, especially Indochina, offers numerous examples attributable to the Early Tertiary India-Asia collision. These are particularly significant for characterizing and understanding a variety of natural hazards, and their mitigation, and yield many clues for understanding the genesis and exploitation of economic resources. Of the older accreted fragments, the Kontum Massif in central Viet Nam had long been viewed as Archean in age. However, recent U-Pb zircon and 40Ar/39Ar dating of basement facies suggest younger Paleozoic ages, quite possibly related to the closing of Paleo-Tethys. Meanwhile, the Song Ma ophiolite probably is believed to mark the Late Paleozoic collision of the Indochina and South China blocks. In general, geodynamic effects of the Early Tertiary India-Asia collision include uplift and intense erosion, crustal shortening and thickening, lateral displacement (‘extrusion’) of both lithosphere and asthenosphere, and gravitational collapse although each of these effects is controversial to varying degrees. Critical factors include the rheologic integrity of the upper and lower crust and also of the lithospheric and asthenospheric sub-continental mantle. There is also a strong likelihood that mantle convective modes, as interpreted from seismic tomography and associated magmatic activity, are linked to the rapid propagation of western Pacififc marginal basins. Perhaps the most intensively studied feature in the region is the Ailao Shan-Red River fault, which almost certainly accommodated the southeastward extrusion of Indochina and subsequent during the Late Oligocene and Miocene, followed by the eastward escape of South China. The most compelling evidence for this is a 600-560 km offset of Permo-Triassic ultramafic and related lithologies along the Song Da lineament (between Song Ma and Red River in Viet Nam), extending from the Emeishan flood basalts in southern China to the Gulf of Tonkin. Their genesis remains a puzzle, however, depending on whether or not the magmas were produced in response to a deep mantle plume. In contrast, it is well established that the voluminous intraplate basaltic magmas in Indochina and elsewhere in East and Southeast Asia erupted after c. 20 Ma coincided with the cessation of Indochina extrusion and seafloor spreading in the East Vietnam (South China) Sea. Despite the uncertainties concerning possible Paleozoic mantle plume activity it is clear that widespread Cenozoic basalt magmatism can be plausibly linked to mantle perturbations resulting from the Indian collision in turn providing a mechanism for driving lithospheric ‘escape’ and coeval opening of marginal basins such as the East Viet Nam (South China) Sea. This brief synopsis is intended to indicate the diversity of potential interpretations and the proposed special session, an opportunity for discussion from a multidisciplinary standpoint. Accordingly, we invite contributions from scientists working in structural geology, geodesy, paleomagnetism, seismology, sedimentology, petrology and geochemistry, etc., in attempting to clarify the collision’s impact with regard to key geologic features in the region, and also geologic hazards and the genesis of mineral resources. |