粤东横田花岗斑岩SHRIMP锆石U-Pb年龄、岩石地球化学和锆石Lu-Hf同位素组成及其地质意义

摘要

横田花岗斑岩位于粤东田东钨锡多金属矿床的中部.以横田花岗斑岩为研究对象,开展了SHRIMP锆石U-Pb定年、岩石地球化学、锆石Lu-Hf同位素组成特征研究.花岗斑岩多呈岩株产出,灰白色,斑状结构,块状构造,主要由斑晶(10%)和基质(90%)组成,斑晶由斜长石、钾长石、石英、黑云母组成,杂乱分布,粒度为0.6~6mm,基质由长石、石英、黑云母组成,长石粒度为0.02~0.25mm.获得花岗斑岩锆石206Pb/238U年龄加权平均值为142±1Ma,说明岩体形成于早白垩世.主量、微量元素特征显示,花岗斑岩属于高钾钙碱性强过铝质,富集Rb、U、Nd、Hf等元素,亏损Ba、Nb、Sr、P、Ti等,与高分异的S型花岗岩相似.花岗斑岩的锆石εHf(t)值均小于0,在t-εHf(t)和t-(176Hf/177Hf)i图上,所有样品点均落在球粒陨石演化线之下和华南中元古代基底演化线之上,二阶段模式年龄变化范围为1.28~1.47Ga,表明成岩物质主要来源于中元古代古老地壳变质泥岩部分熔融.%The granite porphyry related to tungsten-tin polymetallic deposits was discovered in Hengtian area, eastern Guangdong Province. In this paper, the authors reported detailed studies of SHRIMP zircon U-Pb dating, major elements ,trace elements and zir?con Hf isotopic compositions of the granite porphyry. The granite porphyries are mostly grayish white dykes with porphyritic texture and massive structure. They mainly consist of phenocrysts (10%) and matrix (90%), the phenocrysts are composed of plagioclase, K-feldspar, quartz and biotite with particle size of 0.6~6mm in mixed and disorderly distribution, whereas the matrix is composed of feldspar, quartz and biotite, with the feldspar particle size being generally 0.02~0.25mm. Zircon U-Pb age analysis for the granite porphyry yielded a weighted average 206Pb/238U age of 142 ± 1Ma, indicating that the rock was formed in Early Cretaceous. Major and trace element characteristics show that the granite porphyry belongs to high potassium calc-alkaline peraluminous series en?riched in Rb,U, Nd, HF and depleted in Ba, Nb, Sr, P, Ti, similar to features of highly fractionated S-type granites. The εHf(t) values of the granite porphyry are less than 0;in t-εHf(t)and t-(176Hf/177Hf)i diagrams, all points fall under the chondritic evolu?tion line and above the south of the Mesoproterozoic basement evolution line. Moreover, the ages are between 1.28Ga and 1.47Ga ,indicating that rock-forming materials were mainly derived from the partial melting of metamorphic mudstone in Meso?proterozoic ancient crust.