HR: 1400h
AN: V23A-12    [Abstracts]
TI: Andaman Mud Volcanoes: Low Temperature Geochemistry of Eruptive Fluids and Potential Hydrocarbon Source
AU: * Datta, S
EM: saugata.datta@gcsu.edu
AF: Georgia College & State University, Department of Biological and Enviromental Sciences, Campus Box 081, Milledgeville, GA 31061, United States
AU: * Datta, S
EM: saugata.datta@gcsu.edu
AF: University of Calcutta, Department of Geology 35 Ballygunj Circular Road, Calcutta, WB 700019, India
AU: Haldar, D
EM: haldar2115@yahoo.com
AF: Presidency College, Department of Geology 86/1 College Street, Calcutta, WB 700073, India
AB: Mud volcanoes are a common feature, reported by several workers, in the Baratang Island of Middle Andamans, India. The association of methane gas and adsorbed hydrocarbons in the mud has been cited well by scientists working in Andamans and also by others working on other eruption areas around the world. Our intended work centres around delineating the nature of such mud volcanoes in the above terrain, their chemical composition with special reference to the clay minerals formed under this sedimentary volcanism environment and exploiting such volcanic deposits towards potential hydrocarbon reserves (if any). The analysis suggests that, at any instant of time, gas vents at variable rates in different gas channels at the same site, and that the compositional differences in these vent gases are nearly as large as can be produced by hydrate crystallization. Almost two orders of magnitude differences in venting rate between individual gas channel ways are suggested. Our hypothesis is compatible with geologic generalizations that venting evolves from fast (mud volcano), to intermediate (hydrate crystallization), to slow (carbonate precipitation) if venting organized into more discrete vents with time. The most realistic agent that explains the observed effects is a rapid local emission of mud and/or water. Stable isotopes of the separated clay minerals (smectite- and illite-rich extruded mud) from the mud volcanoes will be utilized towards the knowledge of nature of volcanism in the Andaman areas. The most likely mechanism believed is re-hydration of shales by both hydrocarbons and a geochemically mature fluid from greater depth within the wedge. Deep fluid source studies supported by our results from gas analyses, includes He-3, thermogenic C-13 in methane as well as 'ultraheavy' C-13 in CO2. Trace element and REE studies of the muds are being conducted to attest to the above hypothesis. The overall results attest active local flow of geochemically different fluids along deep-seated faults penetrating the wedge, with the waters as well as the gases coming from below. Pore water chemistry of mud volcanoes in Andamans reveal that a distinct correlation between the chloride and the isotopic composition of the water exists. O2 gets heavier and H gets lighter with decreasing chloride concentration and increasing gas hydrate content. Data of pore water isotopic composition from gas hydrate-bearing volcanoes might testify, in addition to isotopic composition by gas hydrate formation, that there are other geological processes affecting the isotopic composition.
DE: 1000 GEOCHEMISTRY
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1043 Fluid and melt inclusion geochemistry
DE: 1051 Sedimentary geochemistry
DE: 1065 Major and trace element geochemistry
SC: Volcanology, Geochemistry, and Petrology [V]
MN: 2007 Joint Assembly