A crustal model of the ultrahigh‐pressure Dabie Shan orogenic belt, China, derived from deep seismic refraction profiling
A crustal model of the ultrahigh‐pressure Dabie Shan orogenic belt, China, derived from deep seismic refraction profiling
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DOI：
10.1029/1999jb900415
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发表时间：
2000-05
影响因子：
--
通讯作者：
Chun-yong Wang;Rong-sheng Zeng;W. Mooney;B. Hacker
中科院分区：
文献类型：
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作者：
Chun-yong Wang;Rong-sheng Zeng;W. Mooney;B. Hacker
基于400公里长的地震折射剖面，给出了穿过中国中东部的东西走向超高压大别山造山带的新的地壳剖面。我们的剖面资料表明，造山带南北克拉通地块由上、中、下三层地壳组成，厚35公里，平均地震速度分别为6.0 6~0.2公里/S、6.5~6~0.1公里/S和6.8~6~0.1公里/S，地壳在造山带北缘以下最大厚度为41.5公里，因此现今造山带下的根部厚度仅为6.5公里。剪切波模拟结果表明，泊松比由上地壳的0.24 6 0.02增加到下地壳的0.27 6 0.03。这一结果与角闪岩或麻粒岩变质相中以长英质为主的上地壳成分和镁铁质下地壳成分一致。我们的地震模型表明，造山带内地表暴露丰富的榴辉岩在中下地壳中并不是一个体积重要的成分。与大别山超高压岩石形成有关的大部分三叠纪构造已被后三叠世火成活动、伸展和大偏移走滑断层所掩盖。然而，我们可以在造山带的上地壳核心(5公里深)识别出一条高速(6.3公里/S)带，我们将其解释为超高压岩带、北倾缝合带和标志着可能的活动走滑断裂的视莫霍面错动。
We present a new crustal cross section through the east-west trending ultrahigh-pressure (UHP) Dabie Shan orogenic belt, east central China, based on a 400- km-long seismic refraction profile. Data from our profile reveal that the cratonal blocks north and south of the orogen are composed of 35-km-thick crust consisting of three layers (upper, middle, and lower crust) with average seismic velocities of 6.0 6 0.2 km/s, 6.5 6 0.1 km/s, and 6.8 6 0.1 km/s. The crust reaches a maximum thickness of 41.5 km beneath the northern margin of the orogen, and thus the present-day root beneath the orogen is only 6.5 km thick. The upper mantle velocity is 8.0 6 0.1 km/s. Modeling of shear wave data indicate that Poisson's ratio increases from 0.24 6 0.02 in the upper crust to 0.27 6 0.03 in the lower crust. This result is consistent with a dominantly felsic upper crustal composition and a mafic lower crustal composition within the amphibolite or granulite metamorphic facies. Our seismic model indicates that eclogite, which is abundant in surface exposures within the orogen, is not a volumetrically significant component in the middle or lower crust. Much of the Triassic structure associated with the formation of the UHP rocks of the Dabie Shan has been obscured by post-Triassic igneous activity, extension and large-offset strike-slip faulting. Nevertheless, we can identify a high-velocity (6.3 km/s) zone in the upper (,5 km depth) crustal core of the orogen which we interpret as a zone of ultrahigh-pressure rocks, a north dipping suture, and an apparent Moho offset that marks a likely active strike-slip fault.