Crustal thickness beneath the Tanlu fault zone and its tectonic significance based on two-layer H-κ stacking

Tanlu fault zone (TLFZ) is the largest active fault zone in eastern China. It is characterized by complex tectonic evolution and multiple faults and marks the boundary between the North and South China blocks. An in-depth understanding of the distinct crustal structures of both parts of the TLFZ will provide valuable insights into the lithospheric and crustal thinning in eastern China, extensive magmatism since the Mesozoic, and formation mechanisms of metallogenic belts along the Yangtze River. In this study, a two-layer H-κ stacking approach was adopted to estimate the thicknesses of the sediment and crystalline crust as well as the corresponding v_P/v_S ratios based on high-quality teleseismic P-wave receiver functions recorded by permanent and temporary stations in and around the TLFZ. The geological units in the study region were delineated, especially the crustal structures beneath extensive sedimentary basins on both sides of the TLFZ. The following conclusions can be drawn: (1) The crustal thickness in and around the TLFZ greatly varies depending on the segment. In the northern segment, the crust is relatively thin beneath the eastern part of the Songliao Basin, a broad uplift of the Moho can be observed, and the Moho descends from south to north. The crust below the central and southern segments becomes thinner from west to east. The thickness of the crust is less than 30 km toward the eastern side of the boundary between the Jiangsu and Anhui provinces, that is, significantly thinner than in other areas. In terms of the v_P/v_S ratios, high anomalies were detected in the central-southern segments of the TLFZ, indicating the upwelling of deep mantle magma via deep faults. (2) Positive isostatic gravity anomalies were observed in the eastern part of the northern segment of the TLFZ and in the eastern part of the Suwan segment. The crustal thickness is smaller than that obtained from the Airy model of isostasy. This suggests that the lower crust in this area may have experienced intensive transformation processes, which may be related to crustal thinning (caused by crustal extension) and the strong uplift of the mantle in eastern China. The isostatic gravity anomalies between the eastern and western parts of the TLFZ indicate that the fault zone plays a dominant role in controlling the development of the deep crustal structure. (3) Significant crustal thinning was observed beneath the eastern part of the boundary between the Jiangsu and Anhui provinces in the southern segment of the TLFZ, suggesting that this area is prone to lithospheric thinning of the North China Craton. Due to the subduction, compression, and retreat of the Paleo-Pacific Plate during the Yanshanian Period as well as the dehydration of subducting oceanic crust (within subduction zones), the asthenosphere and oceanic crust in eastern China partially melted, resulting in mantle enrichment. The basic magma from the mantle is accumulated at the base of the crust, leading to magmatic underplating. In areas with weak topography toward the east of the TLFZ, magma rises to the upper crust and surface, resulting in the enrichment of multiple metal deposits in this area.