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Igneous Carbonatites in North China Craton: The Temporal and Spatial Distribution, Sr and Nd Isotopic Charateristics and Their Geological Significance

YAN Guo-han1, MU Bao-lei1, ZENG Yi-shan1, CAI Jian-hui2, REN Kang-xu3, LI Feng-tang1   

  1. 1. Key Laboratory of Orogenic Belts and Crustal Evolution, Ministry of Education,School of Earth and Space Sciences,Peking University, Beijing 100871, China;2.Institute of Mineral Resources, Chinese Academy of Geological Sciences,Beijing 100037, China;3.Research Institute of Exploration and Development,Tarim Oilfield Company,PetroChina,Korla 841000, Xinjiang, China
  • Received:2007-09-20 Revised:2007-09-20 Online:2007-09-20 Published:2007-09-20

Abstract: According to the research of some predecessors and the present authors, the ages of the igneous carbonatites in North China Craton are focused in three stages: the latest Paleoproterozoic-early Mesoproterozoicera, the early Mesozoic era and the late Mesozoic era, which means that these three stages are obviously extensional periods in evolution history of North China Craton. The igneous carbonatites generated in the first and the second periods are distributed in northern and southern margins of the North China Craton, and the third one is recognized in the eastern and central parts of this craton. The isotopic geochemistry of these carbonatites is characteristic of negative εNd(t ) , decreasing with formation ages. On the εNd(t )-I Sr correlation diagram, most of the samples fall within the third and the forth quadrants, near the enriched mantle evolution trendline except for those located in Laiwu-Zibo area, where the enrichment degrees become higher and higher with their ages. This paper also suggests that the deep geodynamic mechanics of these carbonatites probably be related to the hot mantle plume activities or the subduction of the blocks around the North China Block (NCB), resulting in extensional setting of NCB. With the pressure reduction, the alkaline ultramafic-mafic or intermediate magmas were generated by partial melting of the mantle, and subsequent upwelling along the regional deep faults and formation of the complexes by fractional crystallization. The igneous carbonatites are mainly the late products of above-mentioned magmatic evolution. In addition, some carbonatites are argued most likely to be the direct crystallization products of the carbonatite magma derived from the low degree partial melting of the upper mantle.