西藏日土地区弗野岩体的成因——锆石U-Pb年龄及Hf同位素约束
Petrogenesis of Fuye pluton in Rutog, Tibet: zircon U-Pb dating and Hf isotopic constraints
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摘要: 班公湖—怒江成矿带西段日土—多龙地区为一条燕山期岩浆弧，已相续发现多处大、中型矿产，具有良好的成矿地质条件。弗野岩体位于该岩浆弧西侧，岩性以闪长岩和闪长玢岩为主，蚀变较强；微量元素原始地幔标准化后亏损Ba、Nb、Ta、Sr和Ti，富集 Th、U和Pb；稀土元素球粒陨石标准化后表现出整体向右缓倾，显示负Eu异常；D1046和D1049两件样品的锆石Lu-Hf同位素结果显示，εHf(t)主要集中在-5.2～-12.2区间，TDM1模式年龄介于0.98~1.28Ga之间；锆石206Pb/238U年龄加权平均值分别为119.06±0.48Ma和120.03±0.68Ma，均形成于早白垩世中期。结合岩石地球化学特征判断其属于I型花岗岩类，源区物质来源于幔源物质和下地壳物质。根据该岩浆弧带的岩体特征判断，班公湖—怒江特提斯洋至少在中侏罗世已经开始了向北的俯冲作用，且在早白垩世这种向北的俯冲作用仍在持续。Abstract: A Yanshanian magmatic arc was discovered in Rutog-Duolong area, in the western of Bangong-Nujiang metallogenic belt. It shows good ore-forming geological condition for several large and medium-size minerals had been found in recent years. Fuye pluton, locating in the west of the magmatic arc, is composed of diorite and diorite-porphyrite, with strong alteration. Primitive mantle-normalized spider diagram is loss Ba, Nb, Ta, Sr and Ti, enrichment Th, U and Pb. Chondrite-normalized REE pattern shows Slowly tilted to the right, and negative Eu anomalies. Zircon Lu-Hf isotope results of sample D1046 and D1049 show εHf(t)mainly focused at the range of-5.2 to-12.2, TDM1 model age concentrated in 0.98~1.28Ga. The 206Pb/238U weighted average age of sample D1046 and D1049 are 119.06±0.48Ma, and 120.03±0.68Ma, representing they formed in the middle age of Early Cretaceous. Combined with geochemical characteristics, it is I-type granitoid, and formed with both mantle and lower crust. According to these magmatic bodies' characteristics of this arc, Bangong-Nujiang Tethys ocean at least started northward subduction, in the Middle Jurassic. And it last to Early Cretaceous.
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Keywords:
- Rutog-Duolong magmatic arc /
- Fuye pluton /
- petrogenesis /
- LA-ICP-MS zircon U-Pb age /
- zircon Hf isotope /
- Tibet
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