皖南印支期石英斑岩的首次发现及其构造意义

印支时期,中国东南部地区构造运动活跃,岩浆活动较为发育。但是,皖南地区一直未发现该时期侵入岩。近期在安徽省黄山市徽州区东坑口村北约500m处x046县道旁,发现石英斑岩脉体。用LA-ICP-MS技术测得其中锆石的U-Pb年龄为245.2±2.4Ma,此年龄代表石英斑岩的结晶年龄,即形成于印支期中三叠世,而非前人一直认为的燕山期岩浆活动产物。岩石地球化学特征显示,东坑口石英斑岩富集Th、La、Ce等大离子亲石元素及轻稀土元素,亏损Ba、Sr、P、Ti等高场强元素,具有高的10000×Ga/Al值及Zr、Nb、Ce、Y含量,岩石中可见半自形的石英和斜长石,具有A型花岗岩的特征。皖南印支期A型花岗岩的发现,为区域构造-岩浆演化研究提供了新的科学依据,对理解和构建中国东南部乃至华南地区早中生代构造演化具有重要意义。

The first discovery of Indosinian quartz porphyry in Dongkengkou Village, southern An-hui Province

It is generally thought that both tectonic events and magmatic activities during the Indosinian period were intense in south-eastern China. In contrast, the Indosinian magmatic activities in southern Anhui area were generally not considered to be existent, be-cause there was not any previous reported Indosinian intrusive rock in this area. In this paper, the authors obtained LA-ICP-MS zir-con U-Pb weighted average age of 245.2±2.4Ma for the quartz porphyry dyke from the side of x046 highway, about 500m north of Dongkengkou Village, Huizhou District, Huangshan City, southern Anhui Province, which implys that the Dongkengkou quartz por-phyry (DQP) was formed during Indosinian period rather than in Yanshanian period. The bulk-rock chemical data indicate that the DQP is enriched with LILE, LREE and depleted in high field-strength elements Ba, Sr, P, Ti, and possesses high 10000×Ga/Al ra-tios and high Zr, Nb, Ce and Y values. Petrologically, the DQP has hypidiomorphic quartz and plagioclase, exhibiting A-type gran-ite characteristics. The confirmation of the Indosinian A-type granite from southern Anhui area provides new scientific evidence for understanding the regional tectono-magmatism history, and finally supplies extra evidence for remodeling the tectonic and geody-namic evolution of southeast China.