Gas hydrates acting as cap rock to fluid discharge in the Makran accretionary prism?
Published:January 01, 2002
G. Delisle, U. Berner, 2002. "Gas hydrates acting as cap rock to fluid discharge in the Makran accretionary prism?", The Tectonic and Climatic Evolution of the Arabian Sea Region, P. D. Clift, D. Kroon, C. Gaedicke, J. Craig
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We present a numerical model of the geothermal field of the Makran accretionary prism and of the slab being subducted below it. Calculated heat flow density values for the sea floor of the abyssal plain and the shelf slope are compared with in situ measured and bottom simulating reflector (BSR)-derived heat flow density values. The result suggests a predominance of conductive heat transport within the accretionary complex. Little evidence is found to suggest that fluid flow or frictional heat modifies the observed geothermal field to any great extent. We also studied the geothermal field associated with the decay of the potential gas hydrate layers (indicated by the presence of BSRs), as gas hydrate layers are being tectonically uplifted out of the gas hydrate stability field into shallower and warmer sea water. Theoretical considerations suggest a complete disappearance of gas hydrates at a water depth of about 750 m. The observed presence of numerous gas seeps almost exclusively at water depths of less than 800 m suggests that gas hydrate layers in the Makran accretionary prism act as a very effective cap rock to upward-directed flow of fluids containing notable amounts of dissolved gas from within the prism to the sea floor.
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The Tectonic and Climatic Evolution of the Arabian Sea Region
Over long periods of time the tectonic evolution of the solid Earth has been recognized as the major control on the development of the global climate system. Tectonic activity acts in one of two different ways to influence regional and global climate: (i) through the opening and closing of oceanic gateways and its effect on the circulation patterns in the global ocean; (ii) through the growth and erosion of orogenic belts, resulting in changes in oceanic chemistry and disruption of atmospheric circulation. The Arabian Sea region has several features that make it the best area for studies of climate and palaeoceanographic responses to tectonic activity, most notably in the context of the South Asian monsoon and its relationship to the growth of high topography in the adjacent Himalayas and Tibet.
The Tectonic and Climatic Evolution of the Arabian Sea Region brings together a collection of recent studies on the area from a wide group of international contributors. The paper range from high resolution, Holocene palaeoceanographic studies of the Pakistan margin to regional tectonic reconstructions of the ocean basin and surrounding margins throughout the Cenozoic. Marine geophysics, stratigraphy, isotope chemistry and neotectonics come together in a multidisciplinary approach to the study of interactions of land and sea. while much work remains to be done to understand fully the tectonic and climatic evolution of the Arabian Sea, a great deal has been achieved since the last major review, as detailed in the 26 contributions. This volume is essential reading for palaeoceanographers, sedimentologists and geophysicists. It will also be interest to structural geologists and those working in the petroleum industry.