Triassic Granitic Magmatism at the Northern Margin of the North China Craton: Implications of Geochronology and Geochemistry for the Tectonic Evolution of the Central Asian Orogenic Belt  

作　　者：CHEN Jingsheng TIAN Dexin YANG Hao LI Weiwei LIU Miao LI Bin YANG Fan LI Wei WU Zhen 

机构地区：[1]Shenyang Geological Survey Center of China Geological Survey,Shenyang 110034,China [2]Non-Ferrous Metals Geological Exploration Bureau of Zhejiang Province,Shaoxing,Zhejiang 312000,China [3]College of Earth Sciences,Jilin University,Changchun 130061,China [4]Institute of Geology and Mineral Resources of Liaoning Co.,Ltd.Shenyang 110029,China

出　　处：《Acta Geologica Sinica(English Edition)》2019年第5期1325-1353,共29页地质学报（英文版）

基　　金：financially supported by the National Key Research and Development Program (Grant Nos. 2018YFC0603804);the China Geological Survey (Grants DD20190042, DD20190039 and DD20160048-05)

摘　　要：The early Mesozoic marked an important transition from collisional orogeny to post-orogenic extension at the northern margin of the North China Craton(NCC). In this study, we undertook zircon U-Pb dating and whole-rock majorand trace-element geochemical analyses of early Mesozoic granitic rocks in the Chifeng area to establish their geochronological framework, petrogenesis, and implications for the tectonic evolution of the eastern Central Asia Orogenic Belt(CAOB). Zircon U-Pb dating results show that these rocks were emplaced in three stages during the Triassic:(1) syenogranites during 250-248 Ma,(2) granodiorites during 244-243 Ma, and(3) monzogranites and granodiorites during 232-230 Ma. These Triassic granitoids belong to the high-K calc-alkaline series and are evolved I-type granites. They have high SiO2 and low Mg O contents with enrichments in light rare-earth elements, Zr, Hf, Rb, Th, and U, and depletions in Ba, Nb, Ta, Sr, and Eu. These geochemical data indicate that the granitoids were derived from partial melting of a lower-crustal source under relatively low-pressure conditions and subsequently underwent extensive fractional crystallization. Considering both the geochemical data and regional geological information, we propose that the 250-248 Ma syenogranites were emplaced in an extensional environment linked to slab break-off after closure of the Paleo-Asian Ocean(PAO) along the Solonker-Xra Moron-Changchun suture zone. The 244-243 Ma granodiorites were formed in a compressional orogenic setting during collision between the Erguna-Xing’an-Songliao composite block and the NCC. The 232-230 Ma granodiorites and monzogranites were emplaced during the transition from compressional orogeny to post-orogenic extension. Overall, the early Mesozoic tectonic evolution of the Chifeng area can be divided into three main stages:(1) closure of the Paleo-Asian Ocean and extension related to slab break-off during the Early Triassic;(2) continuous collisional compression during the Middle Triassic after closure of The early Mesozoic marked an important transition from collisional orogeny to post-orogenic extension at the northern margin of the North China Craton（NCC）. In this study, we undertook zircon U-Pb dating and whole-rock majorand trace-element geochemical analyses of early Mesozoic granitic rocks in the Chifeng area to establish their geochronological framework, petrogenesis, and implications for the tectonic evolution of the eastern Central Asia Orogenic Belt（CAOB）. Zircon U-Pb dating results show that these rocks were emplaced in three stages during the Triassic:（1） syenogranites during 250–248 Ma,（2） granodiorites during 244–243 Ma, and（3） monzogranites and granodiorites during 232–230 Ma. These Triassic granitoids belong to the high-K calc-alkaline series and are evolved I-type granites. They have high SiO2 and low Mg O contents with enrichments in light rare-earth elements, Zr, Hf, Rb, Th, and U, and depletions in Ba, Nb, Ta, Sr, and Eu. These geochemical data indicate that the granitoids were derived from partial melting of a lower-crustal source under relatively low-pressure conditions and subsequently underwent extensive fractional crystallization. Considering both the geochemical data and regional geological information, we propose that the 250–248 Ma syenogranites were emplaced in an extensional environment linked to slab break-off after closure of the Paleo-Asian Ocean（PAO） along the Solonker-Xra Moron-Changchun suture zone. The 244–243 Ma granodiorites were formed in a compressional orogenic setting during collision between the Erguna-Xing’an-Songliao composite block and the NCC. The 232–230 Ma granodiorites and monzogranites were emplaced during the transition from compressional orogeny to post-orogenic extension. Overall, the early Mesozoic tectonic evolution of the Chifeng area can be divided into three main stages:（1） closure of the Paleo-Asian Ocean and extension related to slab break-off during the Early Triassic;（2） continuous collisional compression

关 键 词：TRIASSIC GRANITOIDS zircon U-Pb GEOCHRONOLOGY GEOCHEMISTRY tectonic evolution northern margin of the North China CRATON 

分 类 号：P59[天文地球—地球化学]