Origin and Emplacement of Archean Ophiolites of the Central Orogenic Belt, North China Craton  

作　　者：Timothy M Kusky 李江海 

机构地区：[1]State Key Laboratory for Geological Processes and Mineral Resources, China University of Geosciences [2]Three Gorges Research Center for Geohazards, Ministry of Education, China University of Geosciences [3]School of Earth and Space Sciences, Peking University

出　　处：《Journal of Earth Science》2010年第5期744-781,共38页地球科学学刊（英文版）

基　　金：supported by the US National Science Founda-tion (Nos. 02-07886, 01-25925);awarded to Timothy M Kusky, the National Natural Science Foundation of China (Nos. 49832030, 40821061);the Peking University Project (No. 985);the Ministry of Education of China (No. B07039) awarded to Li Jianghai

摘　　要：Understanding Archean crustal and mantle evolution hinges upon identification and characterization of oceanic lithosphere. We report and update here more than 10 years work on a complete, yet dismembered and metamorphosed Archcan ophiolite sequence in the North China craton, in the Dongwanzi （东湾子）-Zunhua （遵化） structural belt and correlatives in the Wutaishan （五台山） area. Banded iron formation structurally overlies several tens of meters of variably deformed pillow lavas, mafic flows, and picritic amphibolites. These are in structural contact with a 2 km thick mixed gabbro and dike complex with gabbro screens, exposed discontinuously along strike for more than 20 km. The dikes consist of metamorphosed diabase, basalt, Hb-Cpx-gabbro, and pyroxenite. The dike/gabbro complex is underlain by several kilometers of mixed isotropic and foliated gabbro, which preserve compositional layering approximately 2 km below the dike complex, and then over several hundred meters merge into strongly compositionally layered gabbro and olivine-gabbro. The layered gabbro becomes mixed with layered pyroxenite/gabbro marking a transition zone into emulate ultramaflc rocks including serpentinzed dunite, pyroxenite and wehrlite, and finally into strongly deformed and serpentinized olivine and orthopyroxene-bearing ultraInafic rocks interpreted as depleted mantle harzburgite tectoultes. A U/Pb zircon age of 2.505 Ga from gabbro of the Dongwanzi ophioUte makes it one of the world＇s oldest recognized, laterally. extensive complete ophiolite sequences, though older dismembered ophiolites are recognized in South Africa and Greenland, extending back to 3.8 Ga. This age is confirmed by a ca. 2.6 Ga Re-Os isochron from chromites from the belt, and a number of dated 2.5-2.4 Ga cross-cuttlng younger igneous units. The Dongwanzi ophiolite is one of the largest well-preserved greenstone belts in the central orogenic belt that divides the North China craton into eastern and western blocks. More than 1 000 other fragments oUnderstanding Archean crustal and mantle evolution hinges upon identification and characterization of oceanic lithosphere. We report and update here more than 10 years work on a complete, yet dismembered and metamorphosed Archcan ophiolite sequence in the North China craton, in the Dongwanzi （东湾子）-Zunhua （遵化） structural belt and correlatives in the Wutaishan （五台山） area. Banded iron formation structurally overlies several tens of meters of variably deformed pillow lavas, mafic flows, and picritic amphibolites. These are in structural contact with a 2 km thick mixed gabbro and dike complex with gabbro screens, exposed discontinuously along strike for more than 20 km. The dikes consist of metamorphosed diabase, basalt, Hb-Cpx-gabbro, and pyroxenite. The dike/gabbro complex is underlain by several kilometers of mixed isotropic and foliated gabbro, which preserve compositional layering approximately 2 km below the dike complex, and then over several hundred meters merge into strongly compositionally layered gabbro and olivine-gabbro. The layered gabbro becomes mixed with layered pyroxenite/gabbro marking a transition zone into emulate ultramaflc rocks including serpentinzed dunite, pyroxenite and wehrlite, and finally into strongly deformed and serpentinized olivine and orthopyroxene-bearing ultraInafic rocks interpreted as depleted mantle harzburgite tectoultes. A U/Pb zircon age of 2.505 Ga from gabbro of the Dongwanzi ophioUte makes it one of the world＇s oldest recognized, laterally. extensive complete ophiolite sequences, though older dismembered ophiolites are recognized in South Africa and Greenland, extending back to 3.8 Ga. This age is confirmed by a ca. 2.6 Ga Re-Os isochron from chromites from the belt, and a number of dated 2.5-2.4 Ga cross-cuttlng younger igneous units. The Dongwanzi ophiolite is one of the largest well-preserved greenstone belts in the central orogenic belt that divides the North China craton into eastern and western blocks. More than 1 000 other fragments o

关 键 词：North China craton Archcan ophiolite Proterozoic MELANGE podiform chromite. 

分 类 号：P588.323[天文地球—岩石学]