祁东县清水塘矿区周家岭花岗岩形成时代及物质来源

Forming Age and Material Source of the Zhoujialing Granite in Qingshuitang Orefield,Qidong County,Hunan Province

本文通过岩石化学、锆石U-Pb定年和锆石Hf同位素等研究探讨了祁东县清水塘矿区周家岭花岗岩的岩石化学性质、形成时代和物质来源。研究表明,岩石以富碱,富集LREE和LILE(Rb、Th、U),亏损HREE和HFSE(Nb、Ta、Ti)和Ba、Sr等元素为特征。LA-ICP-MS锆石U-Pb加权平均年龄为203.0±1.4 Ma(MSWD=0.49,2σ,N=19),属于印支晚期产物。具有较低的Hf同位素初始比值εHf(t)=-10.69^-6.31和老的二阶段模式年龄TC DM(TC DM=1.59~1.85Ga),表明周家岭花岗岩成岩物质主要来自古元古界下地壳。印支晚期,华南地区处于同造山阶段的后碰撞构造环境挤压峰期之后,应力减弱或挤压松弛体制之下,古元古界加厚的下地壳在高温熔融环境下形成的花岗岩岩浆,沿着断裂构造上侵形成周家岭花岗岩体。

Based on geological investigation, with petrochemical, zircon U-Pb geochronological and in situ zircon Hf isotope geochemical method, in this paper, we studied the Zhoujialing granite in Qingshuitang orefield, Qidong County, Hunan Province, discussed its petrochemical property, forming age, material sources. The study shows that, the Zhoujialing granite is characterized by high potassium, rich in light rare earth elements（LREEs） and large ion lithophile elements （LILEs, i.e. Rb, Th, U ）, while depletions in heavy rare earth elements （HREEs） and high field-strength elements（ HFSEs, i.e. Nb, Ta, Ti） , Ba and Sr. LA-ICP-MS single-zircon U- Pb dating indicates that the granite formed during the late Indosinian, whose zircon average age weighted 203.0±1.4Ma （ MSWD = 0.49, 2σ, n = 19）. The Hf isotopes of zircon show that the Zhoujialing granite exhibited low εHf（t） values [εHf（t） = --10.69 ～ --6.31] and old two stage nf model ages（TCDM = 1. 59 ～ 1. 85Ga）, indicating that diagenetic substance of the Zhoujialing granite mainly derives from the lower crust of Paleoproterozoic. During the late Indosinian, South China was in the environment of post-collisinonal tectonic setting of syn-orogenic stage. With the stress receding or extrusion eased, the thickening of Paleoproterozoic lower crust in primary-defomation stage caused the rise of the temperature, causing the melting of lower crust. The granitic magma transported along the tectonic faults, then emplaced in relative open environment and formed the Zhoujialing granite.