| 西太平洋侏罗纪海洋地壳断裂特征及其成因机制* |
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| 引用本文： | 张锦昌,杨晓东,林婧雪,曲梦,罗怡鸣.西太平洋侏罗纪海洋地壳断裂特征及其成因机制*[J].热带海洋学报,2022,41(3):1-15. |
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| 作者姓名： | 张锦昌 杨晓东 林婧雪 曲梦 罗怡鸣 |
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| 作者单位： | 1.中国科学院边缘海与大洋地质重点实验室, 中国科学院南海海洋研究所, 南海生态环境工程创新研究院, 广东 广州 5114582.南方海洋科学与工程广东省实验室(广州), 广东 广州 5114583.中国-巴基斯坦地球科学研究中心, 中国科学院-巴基斯坦高等教育委员会, 巴基斯坦 伊斯兰堡 453204.中国矿业大学(北京)地球科学与测绘工程学院, 北京 1000835.中山大学海洋工程与技术学院, 广东 珠海 5190826.南方科技大学海洋科学与工程系, 广东 深圳 518055 |
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| 基金项目： | 国家重点研发计划(2018YFC0309800);广东省自然科学基金杰出青年项目(2021B1515020098);南方海洋科学与工程广东省实验室(广州)人才团队引进重大专项(GML2019ZD0205);国家自然科学基金项目(41776058);国家自然科学基金项目(41890813);中国科学院项目(133244KYSB20180029);中国科学院项目(131551KYSB20200021);中国科学院项目(Y4SL021001);中国科学院项目(QYZDY-SSW-DQC005);中国科学院项目(ISEE2021PY03);中国科学院项目(E1SL3C02);广东省重点领域研发计划项目(2020B1111520001) |
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| 摘 要： | 侏罗纪洋壳为现存最古老的海洋地壳, 残留在地球表面上很少, 目前对于侏罗纪洋壳的断裂特征和构造变形了解很少。本文利用高分辨率的反射地震剖面精细解释了位于西太平洋的侏罗纪洋壳基底、沉积地层和断裂结构, 发现在研究区存在基底断层、沉积断层和垮塌断层三种类型的断裂构造, 并对其走向、倾角、断距等几何参数与变形特征进行了推测和定量研究。研究还发现, 基底断层是洋壳受到板块伸展拉张而产生的, 在后期海底沉积过程中持续发育并错断上覆沉积物, 在海底形成明显的断层陡坎。沉积断层是沉积地层自身重力作用的产物,受到沉积地层岩石性质的控制。垮塌断层是岩浆侵出或者侵入形成海山, 导致洋壳及其上覆沉积局部抬升并向两侧推移, 引起先存的基底断层和沉积断层重新错动产生的。研究区内切断洋壳基底和上覆沉积的活动断层的推测走向大体符合侏罗纪洋壳基底面起伏、重力异常骤变界面以及地磁异常条带等的走向, 表明这些断裂从侏罗纪洋中脊的海底扩张中演变而来, 并且持续活动至今。这些发育在古老洋壳上的断层能够长时间让水进入岩石圈并进入俯冲带及地球内部, 从而促进地球水循环。尽管目前尚未发现这些断裂产生大地震, 但这些断层可能随着板块俯冲而演变成俯冲带地震大断裂, 今后研究应该关注这类断层在靠近海沟之前的演化规律和潜在地震风险。
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| 关 键 词： | 海洋地壳 侏罗纪 断层作用 水循环 地震 |
| 收稿时间： | 2021-09-26 |
| 修稿时间： | 2021-12-10 |
Characteristics and formation mechanisms of faults on the Jurassic oceanic crust in the western Pacific Ocean* |
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| ZHANG Jinchang,YANG Xiaodong,LIN Jingxue,QU Meng,LUO Yiming.Characteristics and formation mechanisms of faults on the Jurassic oceanic crust in the western Pacific Ocean*[J].Journal of Tropical Oceanography,2022,41(3):1-15. |
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| Authors: | ZHANG Jinchang YANG Xiaodong LIN Jingxue QU Meng LUO Yiming |
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| Abstract: | The Jurassic crust is thought to be the oldest existing oceanic crust, with a very sparse distribution on Earth. The fault characteristics and structural deformation of the Jurassic crust remain poorly understood. In this study, we took full advantage of high-resolution reflective seismic profiles to examine the basement of Jurassic oceanic crust, sedimentary stratigraphy, and fault structures in the western Pacific. Our new results revealed three types of faults in the Jurassic crust, namely, basement fault, sedimentary fault, and collapsing fault. Geometric parameters and deformational characteristics of these faults were quantitatively studied in unprecedented detail, such as strike, dip, and displacement. Basement fault is formed by the bending and extending of oceanic crust, which continues to evolve to cut off the overlying sedimentary units and break through the seafloor to form distinct fault scarps during subsequent submarine sedimentation. Sedimentary fault is resulted from the gravity loading of sediment itself, with effect from the material properties of sedimentary layer. Collapsing fault is caused by the lateral movement of sediment above the intrusive magmatic body. The intrusion of magmatic body uplifts the existing oceanic crust and its overlying sediment, causing the existing basement fault and sedimentary fault to reactivate. Inferred strikes of active faults that cut through the basement and sediment are basically in agreement with the orientations of the Jurassic basement undulation, gravity anomaly abrupt-change boundaries, and magnetic lineations, implying that these faults were formed during the seafloor spreading at the Jurassic mid-ocean ridges and had been active till now. These faults developed on such old oceanic crust allow water to enter the lithosphere for a long time and enhance water cycling through plate subduction. Despite being absent of great earthquakes on these normal faults, they have the potential to evolve into giant seismogenic faults on the subducting plate. Here, we call for attention to tectonic evolution and geologic risk of these faults when they approach subduction zone. |
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| Keywords: | oceanic crust Jurassic faulting water cycling earthquake |
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