Structure of the Upper Mantle and Transition Zone Beneath the South China Block Imaged by Finite Frequency Tomography
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Waveform data for this study are provided by Data Management Centre of the China National Seismic Network at Institute of Geophysics, China Earthquake Administration (SEISDMC, doi:10.7914/SN/CB; Zheng et al., 2010). We thank Fenglin Niu, Min Chen for discussion and the editor Dr. Xiaodong Song for the critical review and constructive comments, which significantly improved the quality of this paper. This study is supported by National Natural Science Foundation of China (Grand No.41404042, 41504071, 41274123), Postdoctoral Science Foundation of China (Grand Nos. 2014M552147, 2015T80888) and Innovation drive Foundation of Central South University (Grand No.2016CX005). We thank Professor David Charles Nobes of University of Canterbury and James G. Keenan for help with our English expression.

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    Abstract:

    We applied the finite frequency tomography method to S wave data recorded by 350 broadband stations beneath the South China Block (SCB) and its surroundings from earthquakes occurring between July 2007 and July 2010, to better understand upper mantle deformation. Differential travel-times in the pair of stations with appropriate weighting for each station are used in the inversion. Our results are consistent with previous tomography that show a high velocity anomaly beneath the Sichuan basin and a high velocity anomaly in the transition zone beneath the Yangtze Craton. However, the resolution of mantle heterogeneity provides new insight into the tectonic framework of subduction of Burmese lithosphere in the west part of the study region and subduction of oceanic lithosphere in the east. In the subduction realm, west of 107oE, a significant fast S-wave anomaly is located on the southeast of Sichuan Basin. East of 107oE, and two narrow and discontinuous fast S-wave anomalies occur at a depth of 400–600 km beneath the middle of the South China block overlain by the pronounced low S-wave anomalies at a depth of 100 and 400 km. If the fast anomalies located in the mantle transition zone represent stagnant slabs, their fragmented nature may suggest that they could be produced by different episodes of subduction beneath western Pacific island and the above slow velocity anomaly may associated with the back-arc regions of ongoing subduction. In addition, tomography also reveals an anomalously high S-wave velocity continental root extends eastward to a depth 400 km beneath the eastern Sichuan Basin. This anomaly may be related to eastern extrusion of Indian lithosphere associated with the collision of India and Eurasia. Moreover, our results also show large slow anomalies beneath the Red River fault region connected to deeper anomalies beneath the South China Fold Belt and South China Sea. All these observations are consistent with the scenario that the South China block has been built by both of subduction of Paleo-pacific plate and eastward subduction of Burma microplate.

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SUN Ya, LIU Jianxin, TANG Youcai, CHEN Jiawei, ZHOU Keping, CHEN Bo.2016. Structure of the Upper Mantle and Transition Zone Beneath the South China Block Imaged by Finite Frequency Tomography[J]. Acta Geologica Sinica(),90(5):1637-1652

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History
  • Received:September 08,2015
  • Revised:June 06,2016
  • Adopted:
  • Online: October 20,2016
  • Published: