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祁连造山带分为南祁连、中祁连和北祁连构造带.赛支寺岩体位于中祁连与南祁连构造带的结合部位.首次发现了赛支寺花岗闪长岩及其暗色包体,然而对于暗色包体的成因机理以及与寄主岩石之间的成因联系仍存在很多争议.并对其进行了系统的锆石U-Pb年代学、Lu-Hf同位素、岩石地球化学以及Sr-Nd同位素地球化学研究,探讨赛支寺岩体及其暗色包体的成因及动力学背景.LA-ICP-MS锆石U-Pb年代学表明,赛支寺花岗闪长岩形成于446.1±1.3Ma,包体形成于446.0±1.0Ma,两者在误差范围内一致,排除了包体为捕虏体成因.暗色包体具较低的SiO2含量、较高的Na2O/K2O比值,低Sr/Y、La/Yb比值,与寄主岩稀土配分曲线基本一致,但LREE相对较低;86Sr/87Sr=0.706 4~0.706 7,εNd(t)=-7.38~-7.97;发育针状磷灰石,形成于岩浆混合作用.寄主岩SiO2=66.45%~68.12%,Na2O/K2O=0.80~0.97,A/CNK=0.91~1.03,显示准铝质-弱过铝质岩浆特点;富集大离子亲石元素Rb、Th、U、K,亏损Nb、Ta等元素,高Sr/Y、La/Yb比值,轻稀土富集,弱负Eu异常;86Sr/87Sr=0.709 3~0.709 5,εNd(t)=-1.75~-1.03,与祁连造山带I型花岗岩相似;锆石εHf(t)=1.7~6.8,TDM2=995~1 750Ma.综上所述认为,寄主花岗闪长岩形成于壳幔岩浆混合.结合区域地质背景,赛支寺花岗闪长岩形成于俯冲背景下,幔源岩浆上涌,侵入到下地壳中,造成下地壳物质熔融,由这种既有幔源物质又有古老地壳物质的花岗岩岩浆形成.
The Qilian orogenic belt is divided into the southern Qilian, the Middle Qilian and the North Qilian tectonic belt.The Xiziibei rock mass is located at the junction of the Qilian and South Qilian tectonic belts, And its dark inclusions, however, there still exist many controversies about the genesis mechanism of the dark inclusions and the genesis relationship with the host rocks, and systematical zircon U-Pb chronology, Lu-Hf isotopes, Chemistry and Sr-Nd isotope geochemistry, and discuss the genesis and kinetic background of the Sijizisi granite and its dark enclaves.The LA-ICP-MS zircon U-Pb chronology shows that the Zejisi granodiorite Formed at 446.1 ± 1.3Ma, and the inclusions formed at 446.0 ± 1.0Ma, which were consistent within the error range, and excluded the formation of xenoliths as dark inclusions with lower SiO2 content and higher Na2O / K2O The ratios of Sr, Y and La / Yb are basically the same as that of the host rock, but the LREE is relatively low; 86Sr / 87Sr = 0.706 4 ~ 0.706 7 and εNd (t) = - 7.38 ~ -7.97; Apatite formed in the magmatic mixing.The host rocks SiO2 = 66.45% ~ 68.12%, Na2O / K2O = 0.80 ~ 0.97, A / CNK = 0.91 ~ 1.03, ; Enrichment of large ion lithophile elements Rb, Th, U, K, depletion of Nb, Ta and other elements, high Sr / Y, La / Yb ratio, light rare earth enrichment, weak negative Eu anomaly; 86Sr / 87Sr = 0.709 3 ~ 0.709 5, εNd (t) = - 1.75-1.03, which is similar to the type I granite in the Qilian orogenic belt. The zircon εHf (t) = 1.7-6.8 and TDM2 = 995-1 750Ma. The granodiorite is formed in crust-mantle magmatic mixing.Based on the regional geological background, the Seljisi granodiorite formed in the subduction background, the mantle magma upwept into the lower crust, resulting in the melting of the lower crust material The formation of granite magmas, both mantle-derived and ancient crustal materials.