Shallow structure of the Yadong‐Gulu rift, southern Tibet, from refraction analysis of Project INDEPTH common midpoint data
Shallow structure of the Yadong‐Gulu rift, southern Tibet, from refraction analysis of Project INDEPTH common midpoint data
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DOI：
10.1029/97tc03025
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发表时间：
1998-02
期刊：
影响因子：
4.2
通讯作者：
M. Cogan;K. Nelson;W. Kidd;Changde Wu
中科院分区：
文献类型：
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作者：
M. Cogan;K. Nelson;W. Kidd;Changde Wu
西藏和喜马拉雅国际深剖面（INDEPTH）共同中点（CMP）数据的折射到达提供了对西藏南部亚东-古鲁裂谷浅层结构的深入了解。这是青藏高原新近纪-第四纪裂谷的第一个此类信息。根据这些数据和现有的地表地质信息，绘制了裂谷内三个独立山谷的地质剖面图。在每种情况下，山谷都被厚度从100米到1.5公里不等的不对称低速沉积充填物包围。在这三个地方之下，基底似乎向东倾斜（0.55 °）。来自其中一个山谷（宁中）的地震反射数据显示，在山谷下方的基底内有一个向东倾斜30°的反射层，向上突出到紧邻西部范围内暴露的正常方向念青唐古拉拆离体。INDEPTH人员的实地调查还表明，在其他两个山谷的边界存在以前未被识别的正向剪切带。新发现的剪切带厚度为200至>500 m，在这两种情况下，其特征是具有自上而下剪切方向的适度至陡峭的西倾糜棱岩。剪切带内的变质矿物至少指示角闪岩级变质作用，且变质程度随剖面的下降而增加。地震数据，再加上新的地质信息和地貌数据从陆地卫星图像，表明，结构的北方亚东-古鲁裂谷是可比的其他有据可查的裂谷系统，其中陡峭的范围前的正断层终止于，或唯一的深度，适度倾斜的正向determination已经历了大量的下盘隆起和旋转在扩展。这种几何形状意味着青藏高原地壳的伸展在深部被中地壳内部的侧向流动所容纳。它还表明，高原的E-W延伸可能比通常假设的要大得多。
Refracted arrivals on International Deep Profiling of Tibet and the Himalaya (INDEPTH) common midpoint (CMP) data provide insight into the shallow structure of the Yadong‐Gulu rift in southern Tibet. This is the first such information available for the Neogene‐Quaternary rifts on the Tibetan Plateau. Geologic cross sections across three separate valleys within the rift have been constructed from these data and available surface geological information. In each case, the valleys are floored by asymmetric, low‐velocity sedimentary fills ranging from ∼100 m to ∼1.5 km in thickness. Beneath all three, the basement appears to dip gently to the east (∼ 5°). Seismic reflection data from one of these valleys (Nyinzhong) show a ∼30° east dipping reflector within the basement beneath the valley that projects upward to the normal‐sense Nyainqentanglha detachment exposed in the range immediately to the west. Field investigations by INDEPTH personnel have additionally shown the existence of previously unrecognized normal‐sense shear zones bordering the other two valleys. The newly discovered shear zones are 200 to >500 m thick and in both instances are characterized by moderately to steeply west dipping mylonites with top‐to‐west shear sense. Metamorphic minerals within the shear zones indicate at least amphibolite grade metamorphism with increasing metamorphic grade down section. The seismic data, coupled with the new geologic information and geomorphologic data from Landsat imagery, suggest that the structure of the northern Yadong‐Gulu rift is comparable to other well‐documented rift systems in which steep range‐front normal faults terminate at, or sole into, moderately dipping normal‐sense detachments at depth that have undergone substantial footwall uplift and rotation during extension. This geometry implies that the extension of the Tibetan Plateau crust has been accommodated at depth by lateral flow within the middle crust. It also suggests that E‐W extension of the plateau may have been substantially greater than has generally been presumed.