Seismic evidence for multiple-stage exhumation of high/ultrahigh pressure metamorphic rocks in the eastern Dabie orogenic belt

Seismic evidence for multiple-stage exhumation of high/ultrahigh pressure metamorphic rocks in... Abstract The Dabie-Sulu orogenic belt in China contains one of the largest exposures of high and ultrahigh pressure (HP and UHP) metamorphic rocks in the world. The origin of HP/UHP metamorphic rocks and their exhumation to the surface in this belt have attracted great interest in the geologic community because the study of exhumation history of HP/UHP rocks helps to understand the process of continental-continental collision and the tectonic evolution of post-collision. However, the exhumation mechanism of the HP-UHP rocks to the surface is still contentious. In this study, by deploying 28 broadband seismic stations in the eastern Dabie orogenic belt and combining seismic data from 40 stations of the China National Seismic Network (CNSN), we image the high-resolution crustal isotropic shear velocity and radial anisotropy structure using ambient noise tomography. Our high-resolution 3D models provide new information about the exhumation mechanism of HP/UHP rocks and the origin of two dome structures. Our model reveals a slab-shaped high velocity anomaly with negative radial anisotropy in the upper crust of HP/UHP areas. Two high velocity anomalies are observed beneath the Luotian and Yuexi domes and are characterized by dome-shaped bodies, and the radial anisotropy of these two high velocity bodies appears negative in the middle crust. Our seismic observations suggest a two-stage exhumation model of HP/UHP metamorphic rocks in which the HP/UHP metamorphic rocks are first exhumed to the middle/lower crust from great depths by buoyancy and then exhumed to the surface associated with the extension related to the doming and magmatism. The negative radial anisotropy observed in the HP/UHP areas is likely caused by the vertical alignment of fossil microcracks or metamorphic foliations due to the uplift of HP/UHP rocks. The high velocities beneath the Luotian and Yuexi areas are the products of the instruction and in situ crystallization of the post-collisional mafic magma, resulting from partial melting of upper mantle or the mix of upper mantle and lower crust. The negative radial anisotropy of the two high velocity domes could be associated with the vertical alignment of anisotropic minerals that crystallized during magma intrusion. eastern Dabie orogenic belt, ambient noise tomography, crustal structure, thermal dome, exhumation © The Author(s) 2018. Published by Oxford University Press on behalf of The Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Geophysical Journal International Oxford University Press

Seismic evidence for multiple-stage exhumation of high/ultrahigh pressure metamorphic rocks in the eastern Dabie orogenic belt

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Publisher
The Royal Astronomical Society
Copyright
© The Author(s) 2018. Published by Oxford University Press on behalf of The Royal Astronomical Society.
ISSN
0956-540X
eISSN
1365-246X
D.O.I.
10.1093/gji/ggy208
Publisher site
See Article on Publisher Site

Abstract

Abstract The Dabie-Sulu orogenic belt in China contains one of the largest exposures of high and ultrahigh pressure (HP and UHP) metamorphic rocks in the world. The origin of HP/UHP metamorphic rocks and their exhumation to the surface in this belt have attracted great interest in the geologic community because the study of exhumation history of HP/UHP rocks helps to understand the process of continental-continental collision and the tectonic evolution of post-collision. However, the exhumation mechanism of the HP-UHP rocks to the surface is still contentious. In this study, by deploying 28 broadband seismic stations in the eastern Dabie orogenic belt and combining seismic data from 40 stations of the China National Seismic Network (CNSN), we image the high-resolution crustal isotropic shear velocity and radial anisotropy structure using ambient noise tomography. Our high-resolution 3D models provide new information about the exhumation mechanism of HP/UHP rocks and the origin of two dome structures. Our model reveals a slab-shaped high velocity anomaly with negative radial anisotropy in the upper crust of HP/UHP areas. Two high velocity anomalies are observed beneath the Luotian and Yuexi domes and are characterized by dome-shaped bodies, and the radial anisotropy of these two high velocity bodies appears negative in the middle crust. Our seismic observations suggest a two-stage exhumation model of HP/UHP metamorphic rocks in which the HP/UHP metamorphic rocks are first exhumed to the middle/lower crust from great depths by buoyancy and then exhumed to the surface associated with the extension related to the doming and magmatism. The negative radial anisotropy observed in the HP/UHP areas is likely caused by the vertical alignment of fossil microcracks or metamorphic foliations due to the uplift of HP/UHP rocks. The high velocities beneath the Luotian and Yuexi areas are the products of the instruction and in situ crystallization of the post-collisional mafic magma, resulting from partial melting of upper mantle or the mix of upper mantle and lower crust. The negative radial anisotropy of the two high velocity domes could be associated with the vertical alignment of anisotropic minerals that crystallized during magma intrusion. eastern Dabie orogenic belt, ambient noise tomography, crustal structure, thermal dome, exhumation © The Author(s) 2018. Published by Oxford University Press on behalf of The Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices)

Journal

Geophysical Journal InternationalOxford University Press

Published: May 24, 2018

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