The Liaonan Metamorphic Core Complex: Constitution, Structure and Evolution  

作　　者：LIU Junlai GUAN Huimei JI Mo CAO Shuyun HU Ling 

机构地区：[1]State Key Laboratory of Geological Processes and Mineral Resources, and Key Laboratory of Lithosphere Tectonics and Lithoprobing Technology of the Ministry of Education, China University of Geosciences, Beijing 100083

出　　处：《Acta Geologica Sinica(English Edition)》2006年第4期502-513,共12页地质学报（英文版）

基　　金：supported by the National Natural Science Foundation of China(Grant Nos.40472105,40510104086 and 40272084);the Specialized Research Fund for the Doctoral Program of Higher Education of China(Grant No.20040491003).

摘　　要：The Liaonan metamorphic core complex （mcc） has a three-layer structure and is constituted by five parts, i.e. a detachment fault zone, an allochthonous upper plate and an supradetachment basin above the fault zone, and highly metamorphosed rocks and intrusive rocks in the lower plate. The allochthonous upper plate is mainly of Neoproterozoic and Paleozoic rocks weakly deformed and metamorphosed in pre-Indosinan stage. Above these rocks is a small-scale supradetachment basin of Cretaceous sedimentary and volcanic rocks. The lower plate is dominated by Archean TTG gneisses with minor amount of supracrustal rocks. The Archean rocks are intruded by late Mesozoic synkinematic monzogranitic and granitic plutons. Different types of fault rocks, providing clues to the evolution of the detachment fault zone, are well-preserved in the fault zone, e.g. mylonitic gneiss, mylonites, brecciated mylonites, microbreccias and pseudotachylites. Lineations in lower plate granitic intrusions have consistent orientation that indicate uniform top-to-NW shearing along the main detachment fault zone. This also provides evidence for the synkinematic characteristics of the granitic plutons in the lower plate. Structural analysis of the different parts in the mcc and isotopic dating of plutonic rocks from the lower plate and mylonitic rocks from detachment fault zone suggest that exhumation of the mcc started with regional crustal extension due to crustal block rotation and tangential shearing. The extension triggered magma formation, upwelling and emplacement. This event ended with appearance of pseudotachylite and fault gauges formed at the uppermost crustal level. U-Pb dating of single zircon grains from granitic rocks in the lower plate gives an age of 130±2.5 Ma, and biotite grains from the main detachment fault zone have ^40Ar-^39Ar ages of 108-119 Ma. Several aspects may provide constraints for the exhumation of the Liaonan mcc. These include regional extensional setting, cover/basement contact, temporal and spatial coupling ofThe Liaonan metamorphic core complex （mcc） has a three-layer structure and is constituted by five parts, i.e. a detachment fault zone, an allochthonous upper plate and an supradetachment basin above the fault zone, and highly metamorphosed rocks and intrusive rocks in the lower plate. The allochthonous upper plate is mainly of Neoproterozoic and Paleozoic rocks weakly deformed and metamorphosed in pre-Indosinan stage. Above these rocks is a small-scale supradetachment basin of Cretaceous sedimentary and volcanic rocks. The lower plate is dominated by Archean TTG gneisses with minor amount of supracrustal rocks. The Archean rocks are intruded by late Mesozoic synkinematic monzogranitic and granitic plutons. Different types of fault rocks, providing clues to the evolution of the detachment fault zone, are well-preserved in the fault zone, e.g. mylonitic gneiss, mylonites, brecciated mylonites, microbreccias and pseudotachylites. Lineations in lower plate granitic intrusions have consistent orientation that indicate uniform top-to-NW shearing along the main detachment fault zone. This also provides evidence for the synkinematic characteristics of the granitic plutons in the lower plate. Structural analysis of the different parts in the mcc and isotopic dating of plutonic rocks from the lower plate and mylonitic rocks from detachment fault zone suggest that exhumation of the mcc started with regional crustal extension due to crustal block rotation and tangential shearing. The extension triggered magma formation, upwelling and emplacement. This event ended with appearance of pseudotachylite and fault gauges formed at the uppermost crustal level. U-Pb dating of single zircon grains from granitic rocks in the lower plate gives an age of 130±2.5 Ma, and biotite grains from the main detachment fault zone have ^40Ar-^39Ar ages of 108-119 Ma. Several aspects may provide constraints for the exhumation of the Liaonan mcc. These include regional extensional setting, cover/basement contact, temporal and spatial coupling of

关 键 词：Liaonan metamorphic core complex crustal and lithosphere thinning crustal extension late Mesozoic 

分 类 号：P588.3[天文地球—岩石学]