大兴安岭东坡小奎勒河中基性侵入岩成因及地球动力学意义:锆石U-Pb年代学、元素和Hf同位素地球化学证据

Petrogenesis and Geodynamic Significance of Intermediate-Basic Intrusive Rocks in Xiaokuile River,Eastern Slope of the Great Xing'an Range:Evidences of Zircon U-Pb Geochronology,Elements and Hf Isotope Geochemistry

大兴安岭地区以发育显生宙花岗岩和火山岩为特征,基性和中性侵入岩不是十分发育,仅在塔河、塔源、富西里、乌拉山、碧流台等地有所报道,且规模相对较小,它们在形成时代和成因上的差别为我们深入揭示大兴安岭地区壳幔过程提供了重要依据和线索。近期我们在大兴安岭东坡北部红花尔基地区开展了基础地质调查,在小奎勒河中游花岗杂岩体内部发现并确定了两处不规则中基性岩体,经系统的岩相学、年代学、元素和Hf同位素地球化学研究揭示:两处中基性岩体由细粒角闪辉长岩岩相和辉长闪长岩岩相构成;LA-ICP-MS单颗粒锆石U-Pb同位素定年结果显示,其成岩作用于310~293 Ma;岩石系列为准铝质、钾质-钠质、拉斑玄武质-钙碱性过渡岩系;初始岩浆为来自熔体-流体交代作用的富集地幔低程度(<5%)部分熔融作用,源区主要残留矿物相为辉石和石榴石、钙钛矿等;岩浆演化过程以结晶分离作用为主,伴随堆晶作用;形成于松嫩地块-兴安地块碰撞拼合晚期向初始大洋岛—晚期大洋弧初始环境。

The most rock types are Phanerozoic granites and volcanic rocks in the Great Xing’an Range,with small amount of basic and intermediate intrusive rocks which have been reported in Tahe,Tayuan,Fuxili,Wula Mountain and Biliutai.The differences of the formation ages and petrogenesis between those rocks provide the major basis and clues in the study on the evolution of crust and mantle in the Great Xing’an Range.We observed two irregular basic masses in the granitic complexes during the basic geologic surveys in the middle of Xiaokuile River,the Honghuaerji region,the north of east slope of the Great Xing’an Range.We obtained five points by systematical researches in petrography,chronology,elements,and Hf isotopes geochemistry.The two basic rocks are composed of fine-grained bojite and gabbro diorite.We collated the single grain zircon LA-ICP-MS U-Pb dating,and concluded that the age of diagenesis is 310-293 Ma.Rocks are the transitional series of metaluminous potassicsodium and tholeiitic-calcalkalic.The main residual minerals of the initial magma that originated by low-degree（less than 5%）partial melting of the EM derived from the metasomatism of melt-fluid are pyroxene,garnet and perovskite.The evolution of magma was mainly of fractional crystallization followed by accumulation.The basic rocks were formed in the initial environment which was under the late collision between the Songnen massif and the Xing’an plot or the initial oceanic island-late oceanic arc.