The Oldest Continental Nucleus Beneath the South China Block, Constrained by Regional Lg-Wave Attenuation Tomography

Session: Seismicity and Tectonics of Stable Continental Interiors
Type: Oral
Date: 4/30/2020
Time: 09:30 AM
Room: 240
Description: 

The ancient continental nucleus witnessed long-term complex tectonic evolution during the form of the lithospheric block. Detecting the distribution of the continental nucleus can explore the tectonic structure and trace the origin of continent. The current tectonic framework of the South China Block (SCB) was inherited from early Neoproterozoic. Due to extensive reworking by Phanerozoic tectonic evolutions and obscured much of Precambrian geological record, it has great uncertainty to constrain the old nucleus only by surface exposures. Exploring the deep distribution of the continental nucleus of the SCB can constrain its early development history and delineating rework and reconstruction of the crust in the SCB. Ancient continental nucleus, survived in several stages of tectonic evolution, are characterized with high density, low temperature and often presented low attenuation. Seismic attenuation, sensitive to the crustal structure, thermal status and seldom affected by compositional variations, can give an effective constraint on nucleus distribution. The Lg wave is suitable to map the crustal structures. In order to better constrain the extension of the nucleus and understand the rework and the formation of SCB crust, we collected regional seismic data from 218 crustal earthquakes recorded at 580 regional stations; measured the 0.05-10.0 Hz broadband Lg-wave Q; and constructed a high-resolution crustal Q model for the SCB.

In the high-frequency band, there are four high-Q regions, one is located in the western Sichuan Basin and other three are located in the western Cathaysia Block. Based on the attenuation model and geophysical and geological evidence, we speculate the Archean nucleus of Yangtze Craton is located in the western Sichuan Basin; whereas three other nuclei are scattered beneath the Cathaysia Block. The latter may represent the rifted continental fragments generated during the breakup of the Rodinia supercontinent in late Neoproterozoic. This process may lead to the initial destruction of the SCB. This work was supported by the NNSF of China (41974054).

Presenting Author: Lin Shen

Authors