安徽安庆地区成矿岩体成因：年代学和地球化学制约.doc

  Geochronological and geochemical constraints on formation of the ore-forming intrusive rocks in Anqing region, Anhui 5 10 15 20 25 30 35 40 45 Province, eastern China# XIE Jiancheng, FENG De, CHEN Si* (School of Resource and Environmental engineering, Hefei University of Technology) Abstract: Anqing region is one of the important non-ferrous metal producers where the formation of Cu-Au deposits has closely genetic relations with dioritic intrusions. However, petrogenesis of dioritic intrusions has been hotly debated in the past decade. Here we report new U-Pb dating of zircon and element data in Anqing region. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon analyses indicate a crystallization age of 142.8± 1.6 Ma for the intrusive rocks. The Anqing intrusive rocks (SiO2 contents 57%~64%) exhibit adakite-like geochemical features, including light rare earth element (LREE) enrichment, heavy REE (HREE) depletion, high Al 2O3 and Sr contents, high Sr/Y and La/Yb, and Mg# (41-67), but low Y and Yb contents. They have relatively enrichment of large ion lithophile elements, and depletion of Ti, Nb and Ta. These geochemical data from the Anqing area suggest that the Cretaceous Anqing adakitic rocks were most probably produced by fractional crystallization, and most plausibly derived from partial melting of lithospheric mantle with the material contribution of ancient subducted ocean crust and experienced assimilation of a little lower crustal material. Key words: Adakite; Fractional crystallization; Ce anomaly; Cu-Au mineralization; Anqing regionkey 0 Introduction The Anqing metallogenic district is situated near Anqing city in southern Anhui Province in the Lower and Middle Yangtze River metallogenic belt (Fig. 1) [1, 2]. Many researchers have proposed that the metal deposits are closely related to the intrusive rocks in the region and contributed to a better understanding of the genesis of these deposits. The petrogenesis of these int