Evolution characteristics and genesis of fault-structure in the eastern Andaman Sea depression since the Oligocene
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摘要: 本文研究内容为印度洋东北部边缘海安达曼海的构造演化。利用安达曼海域东部大范围二维地震数据资料及钻井数据，结合区域地质概况以及前人研究成果，选取8条具有代表性的断层并将其划分为一级和二级断裂，运用生长指数法和古落差法对断层进行定量分析，再通过计算安达曼海东部凹陷4条主测线的构造沉降量，探讨构造演化过程。结果表明：选取的生长断层中3条属于一级断裂，跨度大，几乎切穿整个地层，属于控制安达曼海域地区沉降的大断裂；另外5条属于二级断裂，控制构造带的展布情况，属于构造带的分界线。渐新世时期，印度–澳大利亚板块与欧亚板块之间处于软碰撞阶段，断层发育缓慢，上下盘落差较小，生长指数与构造沉降量也处于低值；中新世时期，板块之间的耦合效应不断增强，断层发育速度加快，此时上下盘厚度最大，是形成多处断裂带以及多种断裂样式的关键时期，各地层生长指数和构造沉降量也达到峰值。上新世至今，安达曼海沟–弧–盆体系逐渐稳定，断层活动减弱，断裂上下盘厚度差基本一致，生长指数差异较小，构造沉降量基本稳定在 1 km 左右。Abstract: We deals with the tectonic evolution of the Andaman Sea, the northeastern margin of the Indian Ocean. Based on large-scale 2D seismic data and drilling data in the eastern Andaman Sea area, combined with regional geological survey and previous research results, eight representative faults were selected and divided into first-order and second-order faults. Growth index method and paleo-fall method were used to quantitatively analyze the faults. The tectonic evolution of the eastern Andaman Sea depression is discussed by calculating the tectonic subsidence of the four main survey lines. The results show that three of the selected growth faults are first-level faults with large span and almost cut through the whole stratum, which are large faults controlling the subsidence of the Andaman Sea area. The other five are secondary faults, controlling the distribution of the tectonic belt and belonging to the boundary of the tectonic belt. During the Oligocene, the Indo-Australian Plate and Eurasian Plate were in the stage of soft collision, with slow fault development, small overhanging and footrow drop, low growth index and tectonic subsidence. During the Miocene, the coupling effect between plates was strengthened, the fault development speed was accelerated, and the thickness of the upper and lower walls was the largest. It was the key period for the formation of multiple fault zones and various fault styles, and the growth index of various layers and the tectonic subsidence reached the peak. Since the Pliocene, the Andaman trench-arc-basin system has gradually stabilized, the fault activity has weakened, the thickness difference between the upper and lower wall of the fault is basically the same, the growth index difference is small, and the tectonic subsidence is basically stable at about 1 km.
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图 4 断层（F1–F8）二维分布（位置见图3）
Fig. 4 Typical faults (F1–F8) are distributed in two dimensions (the location is shown in Fig. 3)
图 9 典型剖面构造沉降量
图中不同颜色折线代表每隔10 km提取一道层位信息
Fig. 9 Tectonic settlement amount of typical section
The broken lines with different colors in the figure represent a layer information extracted every 10 km
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