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引用本文:吴迪,于炳松,吴才来,雷敏,徐楠,郑坤. 安徽铜陵焦冲矿田侵入岩锆石U-Pb定年、Hf同位素特征及成因[J]. 中国地质, 2020, 47(4): 1069-1091.
WU Di,YU Bingsong,WU Cailai,LEI Min,XU Nan,ZHENG Kun. Zircon U-Pb dating, Hf isotopic characteristics and genesis of the intrusive rocks in the Jiaochong deposit, Tongling area, Anhui Province[J]. Geology in China, 2020, 47(4): 1069-1091(in Chinese with English abstract).
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安徽铜陵焦冲矿田侵入岩锆石U-Pb定年、Hf同位素特征及成因
吴迪1,2, 于炳松2, 吴才来3, 雷敏3, 徐楠3, 郑坤3,4
1.中国地质科学院地质力学研究所, 北京 100081;2.中国地质大学(北京), 北京 100083;3.中国地质科学院地质研究所, 北京 100037;4.北京大学地球与空间科学学院, 北京 100871
摘要:
安徽铜陵矿集区出露的侵入岩可划分为高钾钙碱性和橄榄安粗岩系列,作为铜陵7大矿田之一的焦冲地区是否也存在两个系列侵入岩?它们的时代及成因与整个铜陵地区的侵入岩是否相同?这些问题目前仍不清楚。本文选择铜陵焦冲矿田的侵入岩开展了岩相学、岩石地球化学、LA-ICPMS锆石U-Pb定年及原位Hf同位素地球化学研究。结果表明,焦冲矿田也存在高钾钙碱性系列和橄榄安粗岩系列侵入岩,前者的主要岩石类型为石英二长闪长岩、花岗闪长岩,后者为辉石二长闪长岩。LA-ICPMS锆石U-Pb定年结果显示,高钾钙碱性系列侵入岩年代与铜陵地区其他矿区同类岩石年代相同,约为142 Ma;而橄榄安粗岩系列侵入岩年代比铜陵地区其他矿区同类岩石年轻,约为136 Ma。总体上看,铜陵地区两个系列侵入岩具有多期次侵位的特征。焦冲高钾钙碱性系列侵入岩含有较多的老的继承性锆石,说明本区古老地壳卷入了岩浆形成过程。结合铜陵地区侵入岩的特征和焦冲矿田侵入岩岩石地球化学研究结果,笔者认为,焦冲矿田两个系列侵入岩成因与铜陵地区侵入岩相似,即橄榄安粗岩系列侵入岩是来自莫霍面附近深部位岩浆房富碱基性岩浆结晶分异后的产物,而高钾钙碱性系列侵入岩是深位岩浆房分异后的岩浆与浅位岩浆房长英质岩浆混合后的产物。
关键词:  锆石LA-CPMS U-Pb定年  岩石地球化学  侵入岩  铜陵焦冲
DOI:10.12029/gc20200412
分类号:P597;P588.12+1
基金项目:国家自然科学基金(41472063)资助。
Zircon U-Pb dating, Hf isotopic characteristics and genesis of the intrusive rocks in the Jiaochong deposit, Tongling area, Anhui Province
WU Di1,2, YU Bingsong2, WU Cailai3, LEI Min3, XU Nan3, ZHENG Kun3,4
1.Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China;2.China University of Geology(Beijing), Beijing 100083, China;3.Key Laboratory of Deep-Earth Dynamics of MNR, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;4.School of Earth and Space Sciences, Peking University, Beijing 100871, China
Abstract:
The intrusive rocks in Tongling area can be separated into a high-K calc-alkaline series and a shoshonitic series. The Jiaochong orefield is one of the seven orefields in Tongling area. The problems as to whether there are two series of intrusive rocks in the Jiaochong orefield or not and whether they have the same age and genesis as compared with the other intrusions in Tongling area are not clear. Therefore, this research was focused on the study of petrography, geochemistry, LA-ICPMS zircon U-Pb dating and in situ Hf isotopic analysis. It turns out that there are two series of intrusive rocks in the Jiaochong orefield. The high-K calc-alkaline series mainly contains quartz monzodiorite and granodiorite, and the shoshonitic series consists of pyroxene monzodiorite. The results of LA-ICPMS zircon U-Pb dating show that the age of the high-K calc-alkaline series in the Jiaochong orefield is about 142 Ma, identical with the age of the other orefields in Tongling area; the age of the shoshonitic series is around 136 Ma, which is younger than that of the other intrusive bodies in Tongling area. In general, the two series of intrusions indicate the features of the multiphase emplacement. Furthermore, lots of zircons having old inherited core in the high-K calc-alkaline series reveal the existence of the materials of old crust in the magma-forming process. Combined with the characteristics of the intrusive rocks in Tongling area and the geochemical features of Jiaochong intrusions, it is obvious that the genesis of the two series of intrusions in the Jiaochong orefield is similar to that of other intrusions in Tongling area. In other word, the intrusive rocks of the shoshonitic series were formed by the fractional crystallization of the alkali-rich basic magma that originated from the deep magma chamber near the Moho. In the meanwhile, the high-K calc-alkaline series is the product of the magma mixing between the felsic magma derived from the shallow magma chamber and the magma that suffered from the fractional crystallization and originated from the deep magma chamber.
Key words:  LA-ICPMS zircon U-Pb dating  geochemistry  intrusive rocks  Jiaochong orefield in Tongling area