Formation and evolution of Paleoproterozoic orogenic belt in southern Jilin, Jiao-Liao-Ji Belt, North China Craton: Constraints from geophysics

摘要

The tectonic setting and depositional environments of the Laoling and Ji'an groups in the northeastern Jiao-Liao-Ji Belt, northeastern China, are controversial. These Paleoproterozoic stratigraphic units are exposed sporadically (in Baishan and Tonghua) beneath a thick cover of Quaternary basalts, meaning that only limited information can be obtained by traditional geological methods. Therefore, using geophysical techniques in this region is pertinent. Here we present new data on the petrophysical properties (density, magnetic susceptibility, and specific resistivity) obtained from 2D cross-gradient joint inversion profiles. The results allow us to establish the relationships between the Laoling and Ji'an groups, interpret the tectonic setting of deposition, and locate the subsurface margins of the Jiao-Liao-Ji Belt. Petrophysical parameters from the Dataishan Formation (density of 2.58 g/cm(3), zero magnetic susceptibility, and specific resistance of 10(3.04)Omega m) indicate that these rocks were derived predominantly from the Longgang Block in the north. For the Zhenzhumen Formation, the petrophysical parameters (high density, weak magnetic susceptibility, and high specific resistivity) are consistent with deposition in a passive margin that received detrital material sediments from the Longgang Block and the Liaoji granitoids. The Mayihe and Huangchagou formations (intermediate to high density, strong magnetic susceptibility, and intermediate specific resistivity) were deposited closer to a magmatic arc, with the detritus derived from the Liaoji granitoids. The low to intermediate density, stronger magnetic susceptibility, and intermediate specific resistivity of the Huashan-Linjiang, Dalizi, and Dadongcha formations indicate that these rocks were deposited in a pre-orogenic setting, with the detritus derived from the Longgang Block, Liaoji granitoids, and other felsic igneous rocks. Based on the geophysical profiles, we conclude that the Jiao-Liao-Ji Belt extends under Quaternary basalt, from Linjiang to Baishan, and eastward towards North Korea. Two basincontrolling faults (F1 and F2) represent the northern and eastern boundaries between the Longgang Block and the Jiao-Liao-Ji Belt. We interpret geophysical anomalies and variations in the petrophysical parameters in the context of subduction and collision processes.