Geochemical Evidence for Provenance, Tectonic Settings and Presence ofGas Hydrate in Mud Volcano Sediments of Andaman Islands

摘要

Mud volcanoes are one of the land / seafloor expressions of the expulsion of argillaceous material from deeper areas, generated by an extrusion activity involving the transfer of sediments, liquids and gas from subsurface to the land / seafloor. Eruption of mud volcano has been recorded historically in 1843, 1879, 1907, 1983, 2003, and 2004 in Bara tang in Middle and Diglipur in North Andaman Islands. Exceeding of threshold pressure of pressured gas and/ or liquid breaks upward through the overlying sediment frequently following existing zone of weakness and flow out sub aerially or subaqueous condition. Venting structure of mud volcanoes are the most important natural seepage features with fluid, gases and sediments from the earth’s surface. Most of the terrestrial mud volcanoes are located in convergent plate margin with thick sedimentary sequences as seen in Alpine-Himalayan, Caribbean and Pacific organic belts. The occurrence of mud volcanoes is controlled by several factors, such as tectonic activity, sedimentary loading due to rapid sedimentation and the existence huge thickness of fine-grained sediments and continuous hydrocarbon accumulation. Tectonic setting discrimination diagrams based on major, minor and trace elements suggest a shale provenance in an oceanic island arc. The correlation of K2O with other elements, abundance of Al2O3, Ba, Th suggest that these elements are primarily controlled by the dominant clay minerals. The compositional immaturity of the analyzed mud volcano sediments is typical of sub ducted-related environments, and their SiO2/Al2O3 and K2O/Na2O ratios reflect their oceanic island arc settings.