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"承德逆掩片"之商榷——来自燕山地区中元古代长城系的沉积地质证据 被引量:12

Re-inquiring of the "Chengde Thrust Plate": Evidences from theMesoproterozoic Changchengian SedimentaryFacies in the Yanshan Region
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摘要 外来岩片不但在构造变形上应具有显著的特征标志,而且在其卷入的各类地质体中也应该表现出与原地系统之间具有明显的差异。近年来,承德地区两条断裂之间所夹地质体,被部分学者认为是晚侏罗世时期从该地区南部向北推覆而来的"逆掩片",水平位移量超过40km。本文对比研究了"逆掩片"内部和"根带区"中元古代长城系原始沉积特征和相带展布以及其他证据,发现承德地区长城系各相带原始展布和格局与周边同期沉积并无显著差别,这表明晚侏罗世期间发生自南向北大规模水平位移(>40km)的可能性很小,研究结果不支持"外来岩片"的认识。 Intense tectonic deformations in Mesozoic occurred in the Yanshan area in North China, which influenced the tectonic configuration of the whole area. Some important progresses were obtained in the study of Mesozoic tectonics and their associated basin systems in recent years, and at the same time different understandings about the tectonic events of the area also appear. One of the focuses about the events is whether the movement direction of the Late Jurassic thrusting was generally from the north to the south or from the south to the north, and what its scale of displacement in horizontal is. This understanding involves the way of tectonicactivity and its geodynamic background in the Yanshan area during that time. The Chengde area is a typical location to examine the direction of the Late Jurassic structural displacement. Two conflicting understandings have been proposed for the main thrust movement direction and its scale in the Late Jurassic. One is that the direction of thrusting was generally from the north to the south, and formed piggyback basins associated with southward propagating thrusting faults. The other suggests that the direction of thrust faulting was generally from the south to the north, and a block ('thrust plate') bounded by two roughly E-W trending thrust faults, the Shuangmiao fault on the north and the Jiyuqing fault on the south, between Chengde city and Chengde county, was a Late Jurassic exotic 'Chengde thrust plate' formed in a low-angle northward thrust faulting, and its thrust distance is more than 40 km. The Shuangmiao thrust fault has been interpreted as a zone constituting the north limb of the 'thrust plate'. A study of the original sedimentary characteristic, lithofacies distribution, sequences and thickness of the Mesoproterozoic Changchengian strata shows that the strata involved in the interior of the so-call 'Chengde thrust plate' are similar to the closed outside about 2 km from the 'thrust plate', but different from a hypothetical 'root belt' in the Kuancheng area, 40, km or more southwards far away. Additional evidences that the present Mesozoic basins still keep their relatively complete outline in shape are from geological maps and our fieldwork, which indicate the continuity of Mesozoic sedimentary strata, geological boundary lines and even faults in the Chengde area. That the Changchengian lithofacies configuration was not destroyed demonstrate that no obvious change took place in the Mesozoic structural deformation, and the possibility of large-scale horizontal displacement (>40 km) from the south to the north in the Late Jurassic is very small. Therefore, this study does not support the interpretation of large-scale external 'thrust plate' in the Chengde area. We interpret that the Shuangmiao thrust fault as a back thrust played a role of accommodation fault due to the late Jurassic southward thrusting on the Jiyuqing fault, and it was reactivated again after the Jurassic.
出处 《地质论评》 CAS CSCD 北大核心 2004年第5期464-470,共7页 Geological Review
基金 中国地质调查局项目(编号DKD2001008)国家自然科学基金资助项目(编号40132020)的成果。
关键词 元古代 推覆构造 断裂带 沉积相 thrust 'Chengde thrust plate' Mesoproterozoic sedimentary fades Yanshan Mountains Hebei
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