赣南早古生代晚期花岗岩类年代学、地球化学及岩石成因

Geochronology,geochemistry and petrogenesis of the Early Paleozoic granitoids in southern Jiangxi Province,China

本文研究了赣南会同岩体花岗岩类及其闪长质包体的岩石学、锆石U-Pb定年和Hf同位素以及全岩主量、微量元素地球化学。会同岩体花岗岩年龄为425.8±6.2Ma,花岗闪长岩包体为425.0±4.1Ma,侵入年龄约为425Ma,属于早古生代晚期的志留纪。岩体总体为过铝质到强过铝质(A/CNK=1.05~1.28)、高钾钙碱性系列岩石;花岗岩和包体的微量元素和稀土元素特征一致,均富集Rb、Th、U、K、Pb,亏损Ba、Sr、P、Ti,Eu负异常明显。岩石属于S型花岗岩。花岗岩和包体εHf(t)均为负值,变化范围大(分别为-13.7^-3.3,-8.4^-3.2),Hf同位素地壳模式年龄较老(总体为1.6~2.3Ga)。结合前人资料,认为早古生代晚期赣南地区,在后碰撞伸展背景下,发生了大范围的成熟地壳的强烈再造和深熔作用,源于中、下地壳的熔体在约425Ma侵位形成中酸性岩浆,再向上侵位形成会同岩体。

This paper presents the petrologic, whole-rock geochemical, zircon U-Pb dating and Hf isotopic data of host granites and dioritic enclaves from the Huitong pluton, southern Jiangxi province. Zircon U-Pb dating results indicate that the dioritic enclave （425.0 ±4. 1Ma）, is coeval with the host granitoid （425.8 ± 6.2Ma）, which is during late stage of Early Paleozoic. The Huitong granitoids are belong to peraluminous （ A/CNK - 1.05 - 1.28 ） and high-K calc-alkaline series. They are enriched in Rb, Th, U, K, and Pb, and depleted in Ba, Sr, P, and Ti, with significant Eu negative anomaly. The rocks show S-type granite affinities. The zircon εHf（t） of host granites （ - 13.7 - -3.3） and dioritic enclaves （ -8. 4 - -3.2） are all negative values, with Hf crustal model ages ranging from 1.6Ga to 2. 3 Ga. Combined with previous data, a wide range of mature crust anatexis events took place in the southern of Jiangxi Province during Early Paleozoic. The partial melting of middle-lower crust finally formed the Huitong pluton, in a post-orogenic extension tectonic environment.