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Crustal structure of the Gulf of Kachchh, northwest India
Journal of Earth System Science ( IF 1.9 ) Pub Date : 2021-07-07 , DOI: 10.1007/s12040-021-01623-0
D Gopala Rao 1 , K S Krishna 2 , M Ismaiel 2 , T Harinarayana 3, 4 , K Veeraswamy 4 , K K Abdul Azeez 4 , A K Chaubey 5 , K Srinivas 6 , K M Sreejith 7
Affiliation  

Abstract

Analyses of the marine geophysical data collected in four oceanographic cruises during 1974–2008 inside the Gulf of Kachchh, northwest India was done, and geology and crustal structure were interpreted for the first time. Seabed topography deduced from satellite-derived bathymetry and bathymetric investigations has revealed the tide-dominated Gulf (> 6 m high) has ~50 m maximum depth along the axial part. The satellite-derived free-air gravity anomalies and their horizontal gradients together with earlier published results helped in noting major crust features like faults. Analyses of single and multi-channel seismic reflection data had enabled identifying reflection strata pattern and their continuity, wave-field and acoustic characters. 2-D model studies of ocean-bottom seismic refraction data (following ray-tracing technique), satellite-derived free-air gravity anomalies, magneto-telluric data along a profile in middle of the Gulf and magnetic anomalies near Gulf mouth have led to determine various physical properties: velocity, density, resistivity and the magnetic of the subsurface layers. They have been utilized in interpreting three-layered crust structure of the Gulf. Further, presence of ~3.0 km thick low, ~3.7 km/s velocity and 2.2 gm/cc density layer overlain by about 2.1 km thick high, 4.6 km/s velocity, and 2.55 gm/cc density layer noted. Considering the physical properties in correlation with mainland geology and crustal structure from onshore Suthri-1 and inner shelf GK-01-A1 well logs and coast parallel Mandvi–Mundra deep seismic study results, low and high-velocity layers have been noted as low velocity Mesozoic sedimentary rock formations overlain by high velocity Deccan volcanic rock formations. The volcanic rock thickness increases to the east are noted. The Tertiary sediments above them are ~1.2 km thick. The major crustal structures and geology identified contribute to understand regional geology, structure and tectonic framework of the Kachchh region and in particular, of the study area. The fractured Deccan volcanic rocks and their intervening intra-trappean sediments are possibly considered as potential hydrocarbon-bearing formations (?) in view of the underlying thick Mesozoic sediments.

Highlights

  1. 1.

    Seismic reflection, OBS, and magneto-telluric data revealed three layered crustal structure of the Gulf

  2. 2.

    We have identified fractured Deccan volcanic rocks and their intervening intra-trappeans sediments inside the Gulf

  3. 3.

    Presence of low velocity Mesozoic sedimentary rock formations overlain by high velocity Deccan volcanic rock formations



中文翻译:

印度西北部 Kachchh 湾地壳结构

摘要

对 1974-2008 年间在印度西北部 Kachchh 湾内 4 次海洋航行收集的海洋地球物理数据进行了分析,并首次解释了地质和地壳结构。从卫星测深和测深调查推导出的海底地形显示,潮汐主导的海湾(> 6 m 高)沿轴向部分的最大深度约为 50 m。卫星衍生的自由空气重力异常及其水平梯度以及早先发表的结果有助于发现断层等主要地壳特征。对单道和多道地震反射数据的分析能够识别反射地层模式及其连续性、波场和声学特征。海底地震折射数据的二维模型研究(遵循射线追踪技术),卫星衍生的自由空气重力异常、沿海湾中部剖面的大地磁数据和海湾口附近的磁异常导致确定各种物理特性:速度、密度、电阻率和地下层的磁性。它们已被用于解释海湾的三层地壳结构。此外,还注意到存在约 3.0 公里厚的低层、约 3.7 公里/秒的速度和 2.2 克/立方厘米的密度层,上面覆盖着约 2.1 公里厚的高、4.6 公里/秒的速度和 2.55 克/立方厘米的密度层。考虑到陆上 Suthri-1 和内陆架 GK-01-A1 测井和海岸平行 Mandvi-Mundra 深地震研究结果与大陆地质和地壳结构相关的物理性质,低速和高速层被认为是被高速德干火山岩层覆盖的低速中生代沉积岩层。注意到东部火山岩厚度增加。它们上方的第三纪沉积物厚约 1.2 公里。确定的主要地壳结构和地质有助于了解 Kachchh 地区,特别是研究区的区域地质、结构和构造框架。鉴于下面厚厚的中生代沉积物,断裂的德干火山岩及其中间的圈闭内沉积物可能被认为是潜在的含烃地层(?)。确定的主要地壳结构和地质有助于了解 Kachchh 地区,特别是研究区的区域地质、结构和构造框架。鉴于下面厚厚的中生代沉积物,断裂的德干火山岩及其中间的圈闭内沉积物可能被认为是潜在的含烃地层(?)。确定的主要地壳结构和地质有助于了解 Kachchh 地区,特别是研究区的区域地质、结构和构造框架。鉴于下面厚厚的中生代沉积物,断裂的德干火山岩及其中间的圈闭内沉积物可能被认为是潜在的含烃地层(?)。

强调

  1. 1.

    地震反射、OBS 和大地电磁数据揭示了海湾的三层地壳结构

  2. 2.

    我们已经确定了海湾内的断裂德干火山岩及其中间的圈闭内沉积物

  3. 3.

    低速中生代沉积岩层被高速德干火山岩层覆盖

更新日期:2021-07-08
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