Crustal Structures From Receiver Functions and Gravity Modeling in Central Mongolia

3D forward gravity modeling combined with receiver function (RF) analysis characterizes the crustal structures of the southern part of the Mongolian collage. The seismic signals of the 48 stations of the MOBAL2003 and the IRIS-PASSCAL experiments were analyzed to get the RFs. This analysis revealed a significant difference between the crustal structures of the Hangay dome and the tectonic zones in the south. In addition, seismic stations south of the Hangay dome display significant signals related to the occurrence of a low-velocity zone at lower crustal level confirmed by the gravity anomalies. Finally, these seismic analysis inputs, the boundaries, the lithologies, and the density values from rock samples of the different tectonic zones constitute the starting points from the 3D forward gravity modeling. The resulting crustal density model indicates: (a) the likely absence of a Precambrian basement block beneath the Hangay dome, (b) an alternation of two low-velocity/low-density zones (LVLDZs) with high-density zones in the Baydrag microcontinent interpreted as fragments of early Tonian plutons, (c) the occurrence of an LVLDZ at the lower crustal level beneath the Lake zone, the Mongol-Altai Accretionary Wedge, and the Trans-Altai Zone. Therefore, the combination of the seismic RF with gravity analysis and modeling reveals new crustal structures of the Mongolian collage and enhances the occurrence and the extent of an LVLDZ at lower crustal level. These LVLDZ may demonstrate the existence of the relamination of a hydrous material in southern Mongolian collage. We combined geophysical data sets to obtain a 3D model of the southern part of Mongolia. We found that the relamination of continental rocks in the lower crust may explain successive contrasted layers in this accretionary domain. We used seismic data from 48 stations to create a crustal thickness map and compared it to a 3D modeling of gravity data. We discovered significant differences between the Hangay dome's crust and the rest of the area, including the likely absence of a Precambrian basement block beneath Hangay. We also found a low-velocity and low-density zone in the lower crust beneath the southern tectonic zones, which we interpret as the relamination of a previous volcanic arc beneath the younger heterogeneous upper crust. Our results demonstrate the relamination of a hydrous material in the southern part of Mongolia, and question a more regional extent for this crust composition change process. Seismic and gravity analyses confirm in 3D the relamination of a hydrous material in southern Mongolian collageWe found no evidence of a Precambrian basement block beneath the Hangay domeFragments of early Tonian plutons are imaged as an alternation of low-velocity and low-density layers with high-density material