粤北帽峰花岗岩体地球化学特征及成因研究

Study of geochemistry and petrogenesis of the Maofeng granite, northern Guangdong province.

帽峰花岗岩体是粤北贵东复式花岗岩体中一个重要的产铀岩体。单颗粒锆石U-Pb定年结果为219．6±0．9Ma, 属于印支期岩浆活动产物。该岩体的主要元素显示富硅、富碱、强过铝质和低CaO／Na2O比值等特征。微量元素富集Rb,Th, U,Ce,Sm和Y而亏损Ba,Sr,P和Ti;LREE轻微富集(LREE／HREE=1．70-9．63,(La／Yb)N=0．41-6．25),Eu亏损明显(δEu=0．02-0．22);具有低的εNd(t)值(-12．3--10．8),变化的δ18O(4．1-11．3‰)、(87Sr／86Sr)i(0．71049- 0．73359)、206Pb／204Pb(18．345-22．019)和207Pb／204Pb(15．646-15．863)以及古老的Nd模式年龄(1879-1996Ma)。以上特征表明,帽峰岩体属于典型的壳源型花岗岩,是在地壳伸展-减薄的构造背景下,通过古元古代成分不均一的泥质变质岩低程度部分熔融的方式形成。

The Maofeng granite is of great importance because of hosting several uranium ore deposits though it is small within the Gnidong granite composite in northern Gnangdong province. Zircon U-Pb dating yields 219.6 ± 0.9Ma, which suggests that it was produced in the Indosinian magmatism event. In geochemistry it is strongly peralnminons and characterized by enrichment of silicon,alkalis, Rb, Th, U, Ce, Sm and Y, by low CaO/Na2O ratios, and by depletion of Ba, Sr and Ti. It displays slight enrichment of LREE （LREE/HREE = 1.70-9.63, （La/Yb）N =0.41 -6.25）） and strong depletion of En （δEn = 0.02-0.22）. It also has low εNd（t） values （ -12.3- -10.8） with old Nd model ages （1879-1996Ma） and has varying δ^18O values from 4.1 to 11.3‰,（^ 87 Sr/^86 Sr） i from 0. 71049 to 0. 73359 ） , ^206 Pb/^204 Pb from 18. 345 to 22. 019, and ^207 Pb/^204 Pb from 15. 646 to 15. 863. These features consistently indicate that the Maofeng granite belonged to crust sourced type of granite and was derived from partial inching of Paleoproterozoic heterogeneous sedimentary metamorphic rocks under a tectonic setting of crust extension in the late Indochina Period.