Emplacement depths of the Early Permian plutons from Guyang area in the northern margin of the North China Block and their tectonic implications

Abstract：Application of hornblende-plagioclase thermobarometry to the Early Permian plutons in Guyang area of western Inner Mongolia Paleo-uplift (IMPU) along northern North China block (NCB) provides important constraints on tectonic evolution of the NCB during the Late Paleozoic. Estimated crystallization temperatures and emplacement depths of the Early Permian plutons are 679.1-728.7 ℃ and 15.6-19.8 km, respectively. Emplacement depths of the Early Permian plutons indicate that they were emplaced at mid-crustal levels, and at least 15.6 km thickness of crustal rocks has been eroded in Guyang area since the Early Permian period. Significant uplift and exhumation of the crustal rocks in the study area resulted in discontinuous distribution of the Mesoproterozoic to Neoproterozoic sedimentary rocks and extensive absence of the Paleozoic to Early Mesozoic strata in the western part of the IMPU. Estimated emplacement depths of the Early plutons (15.6-19.8 km) are much larger than the largest thickness of the pre-Early Permian sedimentary rocks in the western part of the IMPU (13.0 km), suggesting significant crustal thickening by intense folding and thrusting along the northern margin of NCB prior to Early Permian. The above pre-Early Permian structural deformation and crustal thickening on the northern margin of the NCB was probably related to southward subduction of the Paleo-Asian oceanic plate beneath the NCB during the Late Paleozoic.