华北地块北缘内蒙古固阳地区早二叠世岩体的侵位深度及其构造意义

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

运用角闪石-斜长石温度计和角闪石全铝压力计估算的华北地块北缘内蒙古隆起西段固阳地区早二叠世花岗质岩体的结晶温度和侵位深度分别为679.1～728.7℃和15.6～19.8 km,表明自早二叠世以来,固阳地区至少有15.6km的地壳岩石被剥露.这一构造抬升及剥露是造成该区中—新元古代地层不连续分布及古生代—早中生代地层普遍缺失的最主要原因.岩体侵位深度与区域前二叠纪最大沉积地层厚度（13.0 kin）对比结果表明,早二叠世之前,华北地块北缘已经发生了明显的褶皱或逆冲构造变形,从而导致了地壳岩石的叠覆与加厚.这一早二叠世之前的构造变形及地壳加厚可能与晚古生代期间古亚洲洋板块向华北地块下俯冲有关.

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 kin,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 preEarly 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 PaleoAsian oceanic plate beneath the NCB during the Late Paleozoic.