西秦岭中川岩体年代学、元素地球化学、Nd-Hf同位素组成及其与金成矿的关系

柯昌辉; 王晓霞; 聂政融; 杨阳; 吕星球; 王顺安; 李金宝

doi:10.12029/gc20200415

西秦岭中川岩体年代学、元素地球化学、Nd-Hf同位素组成及其与金成矿的关系

Age, geochemistry, Nd-Hf isotopes and relationship between granite and gold mineralization of Zhongchuan granitoid pluton in West Qinling

摘要

摘要: 中川岩体位于秦岭造山带西段，岩体呈同心环状产出，由外向内岩性依次为似斑状黑云二长花岗岩→含斑黑云二长花岗岩→中细粒黑云二长花岗岩，岩体边部发育岩浆暗色包体，向内逐渐减少。LA-ICPMS锆石U-Pb定年结果显示，似斑状黑云二长花岗岩、含斑角闪黑云石英闪长岩（岩浆暗色包体）、细粒黑云二长花岗岩、岩浆暗色包体（无斑）和细粒花岗岩脉的年龄分别为：（221±1）Ma（MSDW=0.26）、（220±1）Ma（MSDW=0.11）、（217±1）Ma（MSDW=0.11）、（216±1）Ma（MSDW=0.26）、（207±1）Ma（MSDW=0.29），表明岩体从边部到中心年龄逐渐变新。寄主岩石与暗色包体的里特曼指数和A/CNK值分别为2.20~3.85、0.99~1.15和2.24~9.22、0.75~1.08，两者分别为准铝质-弱过铝质、高钾钙碱系列和钾玄岩-高钾钙碱系列；稀土元素和微量元素均显示出富集LREE、Rb、Ba、K等大离子亲石元素，亏损HREE、Zr、Hf、Ta、Nb、P、Ti等高场强元素的特征，具有弱的负铕异常（δEu=0.29~0.91），无Ce异常，寄主岩显示出I型花岗岩的特征，并且中心部位的细粒黑云二长花岗岩具高分异I型花岗岩的一些特征。在哈克图解上暗色包体和寄主岩石的主要氧化物具有良好的线性关系；在同位素组成上，寄主岩石与暗色包体的ε_Nd（t）分别变化于-7.31~-8.73和-5.32~-5.69，T_DM2分别变化于1.59~1.71 Ga和1.43~1.46 Ga，ε_Hf（t）值分别为-7.02~-0.31和-3.0~0，T_DM2为1.27~1.70 Ga和1.2~1.5 Ga，显示寄主花岗岩和岩浆暗色包体分别来源于不同源区，寄主岩石主要是古老地壳物质部分熔融的结果，岩浆暗色包体可能是来自岩石圈地幔，但与寄主花岗质岩浆已发生了一定程度的混合作用。岩体外围金矿床形成略晚于岩体，与花岗质脉岩年龄相近，空间上与岩体密切相关，结合前人成矿物质来源的研究，认为成矿物质与成岩物质具有相似性。表明该岩体与其周围的金矿具有成因联系，岩浆作用不仅提供了热能，也有物质贡献。

Abstract: The Zhongchuan granitoid pluton is located in the east of the Western Qinling. Zircon LA-ICPMS dating for the porphyritic monzogranite from the Zhongchuan pluton yielded an age of (221±1)Ma (MSWD=0.26), the age of fine-grained monzogranite is (217±1)Ma(MSWD=0.107), that of magmatic enclave include phenocryst is (220±1)Ma(MSWD=0.107), that of magmatic enclave is (216±1)Ma (MSWD=0.26) and that of fine-grained granite vein is 207±1Ma(MSDW=0.29). Magmatic enclave and rock mass have the same age, and the age of granite vein is the youngest, indicating that the ages gradually become younger from the edge to the center. The rock mass and magmatic enclave are respectively of meta-aluminous or weakly peraluminous, high-K calc-alkaline and high-K calc-alkaline or shoshonite series with the Litman index(σ) being 2.20-3.85, 2.24-9.22 and A/CNK being 0.99-1.15, 0.75-1.08. Their REE and trace elements are enriched in large ion lithophile elements (LREE, Rb, Ba, K) and depleted in high-field strength elements(HREE, Zr, Hf, Ta, Nb, P, Ti), with slightly negative to positive anomalies of Eu (δEu=0.29-0.91) and no anomalies of Ce. These characteristics suggest that the granitoids have I type granite features, and the fine-grained monzogranite is located in the center with some highly fractionated I type granite features. The main oxides of rock mass and MME have a good linear relationship in Harker diagram. Nd isotopic compositions of the rock mass and MME are mainly characterized by ε_Nd(t) values of -7.31--8.73 and-5.32--5.69, and T_DM2 of 1.59-1.71 Ga and 1.43-1.46 Ga. Zircon Hf isotopic compositions of the rock mass and MME are mainly characterized by ε_Hf(t) values of-7.02--0.31 and -3.0-0, T_DM2 of 1.27-1.70 Ga and 1.2-1.5 Ga. These characteristics suggest that the rock mass was derived from partial melting of ancient crustal material and magmatic enclave was derived from the lithospheric mantle, with some mixture. The formation of gold deposits was closely related to Zhongchuan granitoid pluton in time and space, and the age of the gold deposit are slightly later than that of Zhongchuan granitoid pluton and close to that of granite vein. Mineralization data indicate that ore-forming material and lithogenous material were similar to each other. These data indicate that magmatism not only provided a thermal source for the mineralization but also offered ore-forming material.

HTML全文

参考文献(75)

施引文献

资源附件(0)