安徽南部庐枞盆地罗河-泥河铁矿田含矿辉石粗安玢岩锆石LA-ICP-MS U-Pb定年及其地质意义  

Zircon LA-ICP-MS U-Pb dating of ore-bearing pyroxene-trachyandesite porphyry and its geological significance in Luohe-Nihe iron ore field in Luzong basin,southern Anhui,China

作　　者：覃永军[1] 曾键年[1] 曾勇[2] 马振东[3] 陈津华[1] 金希[1] 

机构地区：[1]中国地质大学(武汉)资源学院,湖北武汉430074 [2]中国地质调查局南京地质调查中心,江苏南京210016 [3]中国地质大学(武汉)地球科学学院,湖北武汉430074

出　　处：《地质通报》2010年第6期851-862,共12页Geological Bulletin of China

基　　金：中国地质调查局资源评价项目(编号:1212010781014;1212010660404);中国地质大学地质过程与矿产资源国家重点实验室开放基金课题(编号:MGMR2001-1)资助

摘　　要：安徽庐枞火山岩盆地中的罗河-泥河铁矿田产有与燕山期岩浆活动有关的大型铁矿床,是长江中下游玢岩型铁矿的一个重要组成部分。对矿田的含矿岩体进行了薄片鉴定和化学分析,结果表明该类岩浆岩为超浅成的中偏基性辉石粗安玢岩。运用锆石LA-ICP-MSU-Pb定年方法进行年龄测定,测得的206Pb/238U平均年龄分别为133.3Ma±0.6Ma(LJ23)、133.2Ma±1.1Ma(LJ37)、132.8Ma±2.6Ma(NHK1-2),3个年龄在误差范围内基本一致,表明矿田内辉石粗安玢岩的形成年龄约为133Ma。这一时间正好位于区内龙门院-砖桥和双庙-浮山两大火山喷发旋回的间歇期,为砖桥火山喷发旋回后期潜火山作用的产物。结合基础地质、矿床地质分析和含矿岩体、磁铁矿单矿物化学分析结果,推测矿田的成矿时间为133～131Ma。表明成岩成矿作用与发生于中国东部140Ma左右的构造体制大转折和130Ma左右的大规模岩石圈拆沉两大地质事件相吻合。There is a Luohe-Nihe iron ore field in Luzong volcanic basin on the Lower Yangtze region ,and an important role for the porphyry iron deposits is closely related to magmatism of Yanshanian. Based on the study of petrographic thin section and chemical analysis of four ore-beating porphyry samples in Luohe-Nihe iron ore field, the results shows that these ultra-hypabyssal mgmatites are neutral-basic pyroxene-trachyandesite porphyry. Zircon LA-ICP-MS U-Pb dating for three porphyry samples yielded weighted mean age of 133.3±0.6 Ma, 133.2±1.1Ma, 132.8±2.6Ma, suggests the crystallization age is about 133 Ma. This age is between Longmenyuan-Zhuanqiao and Shuangmiao-Fushan volcanic eruption period, indicating the igneous rocks intruded followed the Longmenyuan-Zhuanqiao paroxysmal eruption. On the basis of this analysis and combined with the basic geological characteristic, we suggest that the mineralization age of the porphyrite iron ore field was between -133 Ma and -131Ma, which were coupled with the extensional geodynamical event during the later stage of tectonic system transformation occurring at about 140 Ma and the lithosphere large-scale detachment at about -130 Ma in East China.

关 键 词：锆石LA—ICP—MS U—Pb定年 辉石(玄武)粗安玢岩 罗河-泥河铁矿田 玢岩型铁矿 成矿年代学 庐枞盆地 

分 类 号：P588.134[天文地球—岩石学] P597.3[天文地球—地质学]