云南个旧杂岩体年代学与地球化学:岩石成因和幔源岩浆对锡成矿贡献

锡矿往往与长英质岩浆岩伴生,然而锡矿形成的热能源区尚不清楚,其可能与地幔物质相关。我国云南锡矿带中出露的中-酸性岩石及碱性岩杂岩体为研究锡矿及其周围岩浆成因提供了良好的物质条件。本文报道了云南个旧地区代表性的花岗岩、辉长-闪长岩和碱性岩类新的全岩地球化学、锆石U-Pb年代学和Hf同位素数据。LA-ICP-MS锆石U-Pb定年表明上述岩石分别形成于81.43±0.46Ma(82.89±0.58M)、81.35±0.22Ma和80.35±0.72Ma,指示它们为晚白垩世近同期岩浆活动的产物。其中闪长岩、碱性岩和花岗岩中锆石的Hf同位素组成不均一,ε_(Hf)(t)分别为-4.2~+0.8、-7.5~-1.9和-8.4~+0.4。尽管这些岩体的侵入时代一致,但它们的地球化学特征和同位素特征存在差异,表明这三类火成岩来自不同的岩浆源区,三者不是同一母岩浆相互演化的关系。个旧杂岩体中花岗岩为弱过铝质岩石,SiO_2与P_2O_5含量呈负相关的关系,排除S型花岗岩的可能。亏损Zr、Nb、Sr、Eu等大离子亲石元素的特征可能为锆石、磷灰石、长石类造岩矿物分离结晶作用的结果;Zr、Nb、Ce和Y总量较低,低的FeOT/MgO比值和低的锆石饱和温度表明,指示出个旧地区的花岗岩应为高分异I型花岗质岩石而非A型花岗岩。个旧地区形成于晚白垩世时期的中基性、碱性岩石可能为不同的幔源岩浆近同时侵入的产物,底侵的幔源熔体带来热量诱发中、下地壳岩石发生部分熔融形成含矿的花岗岩,幔源岩浆对于成矿至少在能量也可能在成矿物质上有重要的贡献。

Geochronology and geochemistry of the Gejiu complex in the Yunnan Province, SW China: Petrogenesis and contributions of mantle-derived melts to tin mineralization

Tin mineralization is generally spatially associated with felsic magmatic rocks. However, the heat source for the formation of tin mineralization is still on debate, which may be derived from the mantle material. The Gejiu complex, located in the Yunnan tin-ore belt, is mainly composed of granites, mafic and alkaline rocks. These rocks provide significant information on generation of tin mineralization and magmatic processes. In this paper, we report new zircon U-Pb ages, whole-rock major and trace elements and zircon Hf isotope data from the Gejiu complex. The results suggest that the granites (81.43±0.46Ma and 82.89±0.58Ma), gabbrodiorites (81.35±0.22Ma) and alkaline rocks (80.35±0.72Ma) emplaced contemporaneously at Late Cretaceous. Although the emplacement time of the three groups of rocks are nearly synchronous, the distinct zircon Hf isotopes (+0.8~-4.2 for gabbrodiorites, -1.9~-7.5 for alkaline rocks and +0.4~-8.4 for granites, respectively) indicate they were derived from different source regions. The Gejiu granites are weakly prealuminous and display negative correlation between SiO₂ and P₂O₅ contents, arguing against S-type granite. In addition, their negative anomalies in Zr, Nb, Sr and Eu were resulted from zircon, apatite and feldspar fractionation. The Gejiu granites show low FeO^T/MgO ratios and low zircon saturation temperatures, suggesting they are high fractionated I-type granite rather than A-type granite. The Gejiu complex was the production of the magmas from the mantle and crustal materials contemporary. Accordingly, partial melting of the continental crust induced by injection of hot mantle materials which also play an important role in tin mineralization for energy, probably metallogenic material.