Emplacement Mechanisms And Deformation Characteristics Of The Early Permian Plutons From Guyang Areain The Northern Margin Of The NorthChina Block And Their Tectonic Implications

Study on the deformation characteristics and structural patterns of the Early Permian granitoid plutons in the western part of the Inner Mongolia Paleo-uplift (IMPU) along the northern margin of the North China block (NCB) enables us to understand emplacement mechanisms of the plutons and geological background during Early Permian. Emplacement depths of the two plutons imply the degree of uplift and exhumation in the IMPU since Early Permian, which facilitates us to know more about tectonic evolution of the IMPU.The main advancements of this thesis are as followings:1. Crystallization temperatures and emplacement depths of the Early Permian plutons estimated by hornblende-plagioclase thermobarometry are679℃-729℃and15.6km-19.8km, respectively.2. At least15.6km thick crustal rocks had been eroded in the Guyang area since Early Permian. Significant uplift and exhumation of the crustal rocks in the study area resulted in discontinuously distribution of the Mesoproterozoic to Neoproterozoic sedimentary rocks and widely absence of the Paleozoic to Early Mesozoic strata in the western part of the IMPU.3. Estimated emplacement depths of the Early Permian plutons (15.6km-19.8km) are much larger than the largest thickness of the pre-Early Permian sedimentary rocks in the western part of the IMPU (13.0km), which suggests significant crustal thickening caused by intense folding and thrusting along the northern margin of the NCB prior to Early Permian existed. The above pre-Early Permian structural deformation and crustal thickening along the northern margin of the NCB is likely related to southward subduction of the Paleo-Asian oceanic plate beneath the NCB during the Late Paleozoic.4. Deformation temperature of the Heleng pluton and its host rocks ranges from450℃to600℃and from300℃to400℃, respectively. Deformation temperature of the Xiyingzi pluton and its host rocks ranges from450℃to higher than700℃and from300℃to higher than700℃, respectively. Well developed parallel or sub-parallel magmatic foliations and widely distributed high temperature solid-state deformation in the two plutons, especially in the Xiyingzi pluton, provide strong evidences for syn-tectonic emplacement deformation. High crystallization temperature (679℃-729℃) and emplaced in mid-crust depth (15.6km-19.8km) of the two plutons result in the cooling rate of the plutons being slow, which maintains an advantageous temperature for magmatic flow, sub-magmatic flow, and high temperature solid state deformation to be ocurred in the two plutons and high temperature solid-state deformation in their host rocks.5. Structural patterns of the two plutons and their host rocks indicate that multiple processes, including increamental growth, ballooning, stoping and diapirism, were involved in their emplacement. Lowering the Moho or outward displacement of the Earth’s surface, ductile shortening of host rocks, stoping, material exchange among different petrous facies units and assimilation provide spaces for emplacement of the plutons.6. Structural patterns of the two plutons suggest that the Early Permian plutons were emplaced under a N-S compressional tectonic regime. The above N-S compression was likely a result of southward subduction of the Paleo-Asian oceanic plate beneath the NCB during the Late Paleozoic.