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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Tethyan subducted slabs under India
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Tethyan subducted slabs under India

机译：印度的特提斯俯冲板

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摘要

Tomographic imaging of the mantle under Tibet, India and the adjacent Indian Ocean reveals several zones of relatively high P-water velocities at various depths. Under the Hindu Kush region in northeastern Afghanistan and southern Tajikistan, a regional northward-dipping slab is seen in the entire upper 600 km of the mantle and is apparently still attached to the lithosphere of the Indian plate. Under northern Pakistan this same slab shows a roll-over structure with the deeper portion overturned and dipping southward, as can also be seen in the distribution of earthquake hypocenters. Farther east-southeast (e.g., in the vicinity of Nepal), a well-resolved anomaly below 450 km depth is connected to the slab under the Hindu Kush, but seems to be separated from the lithosphere above 350 km. These upper-mantle anomalies are interpreted as the remnants of delaminated sub-continental lithosphere that went down when Greater India continued to converge northward with Asia after approx 45 Ma. The deeper high-velocity anomalies under the Indian sub-continent appear clearly separated from the shallower ones as well s from each other, and are inferred to represent remnants of oceanic lithospheric slabs that have sunk into the lower mantle and were subsequently overridden by the Indian plate. They occur at depths between 1000 and 2300 km and occasionally descend down to the core-mantle boundary. The anomalies form three parallel WNW-ESE striking zones. We interpret the two southern zones as remnants of oceanic lithosphere that was subduced when the Neo-Tethys Ocean closed between India and Tibet in the Cretaceous and earliest Tertiary. The northern deep-mantle zone under northern Afghanistan, the Himalayas and the Lhasa block in southern Tibet may represent the last-subducted remnant of the Paleo-Tethys Ocean, which is thought to have closed before the Hauterivian stage of the Early Cretaceous. The middle zone continues southeastward as a rather straight high-velocity zone towards Sumatra, where it becomes convex southward and parallel to the subduction zone under the Sunda arc. Comparison of this straight middle zone near India with the shallower (upper 600-1000 km) northern zone, which displays a cusp-like shape near the Yunnan (SW China) Syntaxis of the eastern Himalayas, supports the notion that the shallow northern zone represents later subduction that the deeper middle zone. The suggestion of a counterclockwise rotation (> 20 deg) of the Indian plate during Tertiary indentation of Asia is supported by these features. The present-day latitudes of 5 deg - 35 deg N of the deep slabs under India and adjacent areas correspond to the approximate paleolatitudes of the Cretaceous subduction zones. The slab remnants in the middle mantle occur therefore near the ancient locations where they started their downward journey, which implies that lateral movements in the deeper mantle were not large.
机译：西藏，印度和邻近印度洋下面的地幔的断层成像显示出在不同深度有几个P水速度相对较高的区域。在阿富汗东北部和塔吉克斯坦南部的兴都库什地区下方，在地幔的整个上部600公里处都可以看到一个向北倾斜的区域平板，并且显然仍附着在印度板块的岩石圈上。在巴基斯坦北部，这块平板显示出翻转结构，其中较深的部分倾覆并向南倾斜，这在地震震源的分布中也可以看出。在东南偏远的地方（例如，在尼泊尔附近），一个高度已解决的深度低于450 km的异常与兴都库什山脉下方的板块相连，但似乎与350 km以上的岩石圈是分开的。这些上地幔异常被解释为分层的次大陆岩石圈的残留物，当大印度在大约45 Ma之后继续向北与亚洲汇合时，这些残留的岩石圈下降了。印度次大陆下较深的高速异常似乎与较浅的异常以及彼此明显分开，并且被推断为代表岩石圈的残余，这些岩石圈沉没到下地幔中，随后被印度人覆盖盘子。它们发生在1000至2300 km之间的深度，偶尔下降到岩心幔边界。异常形成三个平行的WNW-ESE打击带。我们将这两个南部地区解释为大洋岩石圈的残余物，这是新特提斯洋在白垩纪和第三纪最早的印度和西藏之间封闭时产生的。阿富汗北部，喜马拉雅山脉和西藏南部的拉萨地块下方的北部深地幔带可能是古特提斯洋的最后俯冲残留物，据认为该残留物已在白垩纪早期胡特里夫期之前关闭。中部地区继续向东南延伸，成为一个向苏门答腊的相当笔直的高速区，在那里它向南凸出并平行于Sun他弧线下的俯冲带。比较印度附近的这个笔直的中部区域与北部的较浅的区域（上部600-1000 km），该区域在喜马拉雅山脉东部的云南（中国西南）句法附近显示出一个尖头状的形状，支持以下观点：后来俯冲到更深的中间带。这些特征支持了在亚洲第三纪压痕期间印度板块逆时针旋转（> 20度）的建议。目前印度和邻近地区深板块的北纬5度至35度北纬对应于白垩纪俯冲带的近似古纬度。因此，中地幔中的板状残余物出现在它们开始向下航行的古代位置附近，这意味着深地幔中的横向运动并不大。

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