【摘要】 天湖花岗岩体由六个侵入体组成,按岩石谱系划分为三个岩相单元,归并为一个超单元,其为同一次岩浆熔融事件过程中曾经发生过三次岩浆侵入活动而形成的圆形深成岩体。LA-ICP-MS锆石U-Pb定年结果表明,天湖岩体侵位于早三叠世（241²43Ma）,为印支早期的产物。来自岩体的锆石原位Hf同位素测定结果表明,ε_Hf（t）值变化于-2.6⁵.5之间,二阶段Hf模式年龄(t_DM2)变化于941¹435Ma之间,表明其岩浆源区均为来源于亏损地慢的新生地壳岩石。该岩体总体富硅（SiO₂为69.14%⁷6.62%）,富碱（K₂O+Na₂O为7.39%⁸.83%）,而Ti,Ca,Fe和Mg含量较低,A/CNK为0.95¹.04,（K₂O+Na₂O）/Al₂O₃为0.69⁰.82,属于钙碱性花岗岩。总体上富集大离子亲石元素（LILE）K、Rb和高场强元素（HFSE）Ba、Th,但贫Ta、Nb、Ce、Hf、Zr、Sm、Y及Yb。稀土元素的球粒陨石标准化配分曲线呈右倾型,轻重稀土分馏明显,重稀土分异不显著,而轻稀土分异明显,铕呈现弱负异常（δEu=0.24⁰.78）。岩石学及地球化学特征研究表明,天湖岩体形成与幔源岩浆的底侵和内侵使得中-新元古代新生的地壳物质发生部分熔融有关。岩浆侵入活动的动力来源于海西晚期至印支早期古特提斯洋向北俯冲和碰撞及随后的板内伸展作用。更多还原

【Abstract】 The Tianhu granite pluton consists of six intrusive rocks,which can be divided into three lithofacies units but belong to one superunit.The round-shaped plutonic body was the product of three intrusive actitites of the same magma.Zircon LA-ICP-MS U-Pb dating result shows that the Tianhu pluton intruded in early Triassic between 241 Ma and 243 Ma and the product of early Indosinian period.Zircon in-situ Hf isotopic composition analysis yields the ε_Hf（t）and t_DM2 values of-2.6⁵.5and two-stage mode age of 941¹435Ma for the Tianhu pluton,suggesting that the magma originated from depleted mantle-derived juvenile crustal rock.Geochemically,the pluton is characterized by the high content of SiO₂（69.14%⁷6.62%）,and high K₂O+Na₂O value（7.39%⁸.83%）,low contents of Ti,Ca,Fe and Mg,with the ratios of（K₂O+Na₂O）/Al₂O₃ varying between 0.69 and 0.82,and the ratios of A/CNK between 0.95 and 1.04.All these features indicate that the pluton belongs to calc-alkaline granite.The pluton is also rich in LILE（K,Rb）,HFSE（Ba,Th）and depleted in Ta,Nb,Ce,Hf,Zr,Sm,Y and Yb.Chondritenormalized REE distribution pattern of the Tianhu pluton displays right skewed shapes,distinct fractionation between LREE and HREE,with slightly negative Eu anomalies（δEu=0.24⁰.78）.Petrological and geochemical studies of the Tianhu pluton indicate that the pluton resulted from mantle magma underpalting and intraplating induced partial melting of the Meso-neoproterozoic new-born lower crust.Magma intrusion was driven by northward subduction of the Tethys Ocean from late Hercynian to early Indosinian and subsequently intense intra-continental extension in the eastern Tianshan Mountains.更多还原