Structure of the Upper Mantle and Transition Zone Beneath the South China Block Imaged by Finite Frequency Tomography
详细信息 查看全文
- 作者：Ya SUN ; Jianxin LIU ; Youcai TANG ; Jiawei CHEN ; Keping ZHOU and Bo CHEN
- 刊名：Acta Geologica Sinica - English Edition
- 出版年：2016
- 出版时间：October 2016
- 年：2016
- 卷：90
- 期：5
- 页码：1637-1652
- 全文大小：15770K
- ISSN：1755-6724
文摘
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 107°E, a significant fast S-wave anomaly is located on the southeast of Sichuan Basin. East of 107°E, 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.