Fault system and thermal regime in the vicinity of site NGHP-01-10, Krishna-Godavari basin, Bay of Bengal
Fault system and thermal regime in the vicinity of site NGHP-01-10, Krishna-Godavari basin, Bay of Bengal
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DOI：
10.1016/j.marpetgeo.2011.03.009
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发表时间：
2011-11
影响因子：
4.2
通讯作者：
P. Dewangan;G. Sriram;T. Ramprasad;M. V. Ramana;P. Jaiswal
中科院分区：
文献类型：
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作者：
P. Dewangan;G. Sriram;T. Ramprasad;M. V. Ramana;P. Jaiswal
JOIDES的钻井/取心活动用于水合物资源估计的分辨率已经确认了孟加拉湾Krishna-Godavari （KG）盆地大陆斜坡的天然气水合物，并在NGHP-01-10现场发现了裂缝填充的天然气水合物。本文对NGHP-01-10地块附近的高分辨率多通道地震（MCS）、高分辨率火花（HRS）、测深和海底剖面资料进行了分析，以了解断层系统和热状态。在NGHP-01-10点附近解释了以NNW-SSE方向为主的大型断裂系统（bbb50 ~ 5km），该断裂系统对天然气水合物的形成和分布起着重要作用。在天然气水合物稳定带（GHSZ）内，层间速度从基线速度1600 m/s增加到1750 ~ 1800 m/s可以作为天然气水合物赋存的标志，而层间速度下降到1400 m/s表明GHSZ以下存在游离气。层间速度分析表明，天然气水合物的高浓度发生在大型断裂系统附近。研究认为，NGHP-01-10点附近，乃至整个KG盆地，天然气水合物浓度主要受断裂控制，具有较高的空间变异性。利用海底深度和温度以及BSR估算了NGHP-01-10站点附近的热流和地温梯度（GTG）。在土丘顶部，GTG从38°C/km增加到45°C/km，这与土丘处（NGHP-01-10）和远离土丘处（NGHP-01-03）的温度梯度具有显著的一致性。我们分析了地形、盐度、BSR热不平衡和沿断裂系统的流体/气体平流等各种地质情景来解释GTG的增加。地球物理资料和取心结果表明，沿断层系统的流体平流是GTG增加的主要机制。根据热测量估计的对流流体通量约为十分之一毫米/年（0.37-0.6毫米/年）。
Drilling/coring activities onboard JOIDES Resolution for hydrate resource estimation have confirmed gas hydrate in the continental slope of Krishna-Godavari (KG) basin, Bay of Bengal and the expedition recovered fracture filled gas hydrate at the site NGHP-01-10. In this paper we analyze high resolution multi-channel seismic (MCS), high resolution sparker (HRS), bathymetry, and sub-bottom profiler data in the vicinity of site NGHP-01-10 to understand the fault system and thermal regime. We interpreted the large-scale fault system (>5 km) predominantly oriented in NNW-SSE direction near NGHP-01-10 site, which plays an important role in gas hydrate formation and its distribution. The increase in interval velocity from the baseline velocity of 1600 m/s to 1750–1800 m/s within the gas hydrate stability zone (GHSZ) is considered as a proxy for the gas hydrate occurrence, whereas the drop in interval velocity to 1400 m/s suggest the presence of free gas below the GHSZ. The analysis of interval velocity suggests that the high concentration of gas hydrate occurs close to the large-scale fault system. We conclude that the gas hydrate concentration near site NGHP-01-10, and likely in the entire KG Basin, is controlled primarily by the faults and therefore has high spatial variability. We also estimated the heat flow and geothermal gradient (GTG) in the vicinity of NGHP-01-10 site using depth and temperature of the seafloor and the BSR. We observed an abnormal GTG increase from 38 °C/km to 45 °C/km at the top of the mound, which remarkably agrees with the measured temperature gradient at the mound (NGHP-01-10) and away from the mound (NGHP-01-03). We analyze various geological scenarios such as topography, salinity, thermal non-equilibrium of BSR and fluid/gas advection along the fault system to explain the observed increase in GTG. The geophysical data along with the coring results suggest that the fluid advection along the fault system is the primary mechanism that explains the increase in GTG. The approximate advective fluid flux estimated based on the thermal measurement is of the order of few tenths of mm/yr (0.37–0.6 mm/yr).