Craton instability induced by plume-originated magma intrusion: Inference from crustal structures of the Tarim Basin

The Tarim basin at the northwestern edge of the Tibetan plateau, having a craton core that experienced noticeable internal deformation since the formation of a Permian Large Igneous Province, is an ideal place to investigate craton-mantle plume interaction and how such interaction affects the evolution of a craton. In this study, we investigate the detailed crustal structure of the Tarim Basin based on teleseismic records from two temporary seismic arrays that largely cover the Tarim Basin. Firstly, we construct a high-resolution S-wave velocity structure image down to 15 km depth using multi-frequency receiver functions. The thicknesses and Vp/Vs ratios of the sediments and underlying crust are constrained by H-k analysis jointly using P-to-S converted phases in receiver functions and P reflected phases derived by P-wave coda autocorrelation. Then the image of the sedimentary S-wave velocity structure and the H-k result are used to establish the crustal velocity model for receiver function migration to image discontinuities. Our results in combination with drilling data, experimental rock-physics data and previous geophysical observations reveal two velocity discontinuities in the upper crust, corresponding to the top of the early Permian strata and the upper boundary of the crystalline basement. Several high-Vs anomalies in the upper crust, with an average Vs of ~ 3.4 km/s, cut the upper boundary of the basement but locate under the early Permian strata at a depth of 3 km around the Bachu Uplift. The basement at the Bachu Uplift is uplifted to 6 km depth. The Moho rises to 37 km at the southern part of the Bachu Uplift and deepens to more than 45 km in the northern basin, with an average depth of about 42 km. The most of Vp/Vs ratios between the basement and the Moho exhibit high values (>1.8) at the Bachu Uplift. The high Vs anomalies in the upper crust and high Vp/Vs values in the lower crust suggest that the crust has been modified by mafic intrusions of the Permian mantle plume around the Bachu Uplift. The mafic intrusions cause significant crustal heterogeneity in the western Tarim Basin, which may contribute to the uplift of sediments and basement around the Bachu Uplift during Cenozoic Eurasia-Indian collision, exhibiting a strong spatial correlation between the crustal deformation and the Permian magmatic intrusions. This suggests that the western Tarim Craton, compared to the east, may be weakened in strength by the Permian mantle plume and exhibits more localized Cenozoic deformation.