Tectonic Features and Dynamic Evolution of Bay of Bengal Basin: New Insights into Satellite-Gravity and Seismic Data
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摘要: 为了揭示孟加拉湾盆地的构造特征和中生代以来的动力学演化，对研究区卫星重力数据进行滤波、梯度和延拓等深度处理，对相关地震剖面进行标准化处理，在研究区建立了8条主干剖面.自由空气重力异常及其深度处理结果显示在盆地西部、海岭内部及盆地东部分别发育北西向破碎带、近东西向断裂和北东向线性构造，分别反映了海底北西向扩张、海岭侵位及印度洋洋壳北东向俯冲的影响.主干剖面经标准化处理后划分出上白垩统-第四系5套层系，结合重力异常与地层厚度，将孟加拉湾盆地划分为西部坳陷、85°E海岭隆起、中央坳陷、90°E海岭隆起和若开坳陷5个构造单元.85°E海岭隆起内发育的多个孤立高隆起是热点幕式喷发的响应，控制着碰撞前盆地“西厚东薄”的沉积格局，而碰撞后孟加拉扇体系在始新世至中新世期间一直向南迁移，未受到海岭的明显影响.90°E海岭南段(7°~14°N)的俯冲消减促进了安达曼增生楔的向西生长，北段(14°~20°N)的俯冲作用则控制着若开坳陷、印缅增生楔和孟加拉湾盆地沉积中心的演化.构造特征和动力学演化分析表明盆地经历了原始大洋盆地(晚白垩世-早渐新世)和残留洋盆地(晚渐新世-)2个主要演化阶段.Abstract: Based on the satellite-derived gravity data processed by applying various image enhancement methods (including filter, gradient and continuation) and processing of the standardized seismic profiles, plus the establishment of 8 major seismic cross sections, the tectonic features and dynamic evolution of the bay of Bengal basin are explored in this study. Free-air gravity anomalies and their results of enhanced processing indicate that there are NW-trending fracture zones in the west, EW-trending faults in the 90°E ridge, and NE-trending linear structures in the east of the basin, which suggest the influence of sea floor spreading, ridge emplacement and Indian Ocean crust subduction. According to the standardized seismic reflection profiling results, gravity anomalies and stratum thickness, the basin is divided into the following five tectonic units: west depression, 85°E ridge, central depression, 90°E ridge and Rakhine depression. Prior to the collision, the sedimentary framework was controlled by multiple isolated rises developed in 85°E ridge, which was the response of episodic eruption processes of the hotspot. Whereas, the post collisional sediments known as the Bengal fan sediments were not prominently affected by the ridge and the sediments kept on migrating southward during the Eocene to Miocene. The subduction of the 90°E ridge promoted the westward growth of Andaman accretionary in the south (7°-14°N) and controlled the evolution of Rakhine depression, Indo-Burmese wedge and the depocenter of the bay of Bengal basin in the north (14°-20°N). It is found that the protooceanic basin stage (Late Cretaceous to Early Oligocene) and the remnant ocean basin stage (Late Oligocene to present) are two main episodes in the bay of Bengal basin.
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Key words:
- the bay of Bengal basin /
- tectonics /
- sedimentation /
- dynamic evolution /
- satellite-gravity /
- 90°E ridge.
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图 1 孟加拉湾盆地及邻区大地构造纲要
KB.科佛里盆地; K-GB.克里斯蒂娜-戈达瓦里盆地; MB.默哈纳迪盆地; WWB.西孟加拉盆地; COB.洋-陆壳界线; SP.西隆地块; MH.米尔山; CC.F.吉大港海岸断裂; Kal.F.卡拉丹断裂; Kab.F.卡巴断裂; Sag.F.实皆走滑断裂; MB.F.主边界断裂; Dak.F.达卡断裂; Sunda.T.巽他海沟; MMB.抹谷变质带; RS.朗布尔鞍部; KGR.卡萨－甘高蛇绿岩带; Rajmahal Traps.拉杰马哈暗色岩; Sylhet Traps.锡尔赫特暗色岩; 据Maurin and Rangin, 2009; Radhakrishna et al., 2012修改
Fig. 1. Tectonic outline map of the bay of Bengal basin and adjacent region
图 2 晚中生代以来印度及邻区板块重建
AFR.非洲; ANT.南极洲; AUS.澳洲; IND.印度; MA.马达加斯加; S.中缅马苏; SI.思茅; I.印支; EM.东马来亚; SC.南中国; WB.西缅; WSu.西苏门答腊; S.塞舌尔; CIR.中印度洋洋中脊; SEIR.东南印度洋洋中脊; SWIR.西南印度洋洋中脊; Raj.T.拉杰马哈暗色岩; Dec.T.德干暗色岩; 85ER.85°E海岭; 90ER.90°E海岭; SS.约什克缝合带; IS.印度河缝合带; TS.雅鲁藏布缝合带; CR.卡尔斯伯格洋中脊; CLR.查戈斯-拉克代夫海岭; KLA.科希斯坦-拉达克岛弧; a.早白垩世(120 Ma); b.晚白垩世(80 Ma); c.早始新世(55 Ma); d.晚渐新世(28 Ma); e.晚中新世(10 Ma); f.现今(0 Ma); 据Curray and Munasinghe, 1991; Royer et al., 1992; Hall, 2012修改
Fig. 2. Plate reconstructions of India and the adjacent region since Late Mesozoic
图 3 孟加拉湾盆地重力异常与深度处理
图f黑色虚线为前人解释破碎带，白色和红色为本次解释
Fig. 3. Gravity anomaly and enhanced processing maps of the bay of Bengal basin
图 4 孟加拉湾盆地自由空气重力异常延拓处理
a.向上延拓10 km；b.向上延拓15 km；c.向上延拓20 km；d.向上延拓30 km
Fig. 4. Free-air gravity anomaly processed with methods of upward continuation in the bay of Bengal basin
图 5 孟加拉湾盆地主干剖面
1.侏罗系-下白垩统; 2.白垩系; 3.上白垩统-古新统; 4.古近系; 5.新近系; 6.始新统-渐新统; 7.中新统; 8.上新统; 9.第四系; 10.海岭; 11.火山岛弧; 12.钻井及编号; 13.断裂
Fig. 5. Cross sections of standardized seismic reflection profiling of the bay of Bengal basin
图 6 孟加拉湾盆地BODC3井地震层速度及地层厚度反演
Fig. 6. Seismic interval velocity of well BODC3 and residual stratum thickness inversion of the bay of Bengal basin
图 7 孟加拉湾盆地构造单元划分
海岭内部线条和数字显示的是埋藏深度，间隔1 km
Fig. 7. Tectonic units division of the bay of Bengal basin
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