长岭凹陷白垩系火山岩的锆石LA-ICP-MSU-Pb定年及其地质意义  

ZIRCON LA-ICP-MS U-Pb DATING FOR THE VOLCANIC ROCKS IN CHANGLING DEPRESSION,AND ITS GEOLOGICAL IMPLICATION

作　　者：吴群[1,2] 蒲仁海[1] 韩敏强[1] 曹海虹[1,2] 李强[1] 

机构地区：[1]西北大学地质学系大陆动力学国家重点实验室,陕西西安710069 [2]中国石油化工华东分公司研究院,江苏南京210031

出　　处：《矿物岩石》2010年第2期111-119,共9页Mineralogy and Petrology

基　　金：中国石油化工2007年勘探先导项目

摘　　要：对长岭凹陷营城组流纹岩和泉头组火山角砾岩中的锆石进行U-Pb同位素分析,并利用阴极发光和LA-ICP-MS(激光剥蚀等离子体质谱)微区定年分析方法结果表明:锆石颗粒不同程度保留了原始岩浆振荡环带结构,测年共获得3期年龄,分别是102.23Ma±0.55 Ma(等时线拟合品质参数MSWD=1.7)、104.97 Ma±0.74 Ma(MSWD=1.15)和156.5 Ma±2.4 Ma(MSWD=0.42),置信度95%。经与松南区域地层和徐家围子火山岩年龄对比认为,102 Ma和105 Ma分别代表长岭凹陷泉头组和营城组火山活动的时间,156 Ma则为火石岭组早期岩浆冷凝时形成的锆石在营城组岩浆活动时混入所致。与他周边地区营城组年龄(125 Ma^131 Ma)相比,时间偏新。徐家围子升平、兴城区块营城组锆石年龄则为113 Ma至111 Ma,长岭凹陷的营城组火山岩与徐家围子营城组火山岩岩石类型和化学成分大致相同,但年龄前者却比后者小6 Ma。本次年龄测试结果还表明,长岭凹陷0~800 m登娄库组碎屑岩沉积只持续了3百万年,沉积速度高达0.27mm/y。The cathode luminescence and LA-ICP-MS dating technique was applied to the U-Pb isotope analysis of zircon in the rhyolite from Yincheng Group and in the volcanic breccia from Quantou Group in Changling depression.Zircon particles remained the primary oscillation ring structure of magma.Dating of zircon revealed 102.23 Ma±0.55 Ma（Isochron fitting quality parameters MSWD=1.7）,104.97 Ma±0.74 Ma（MSWD=1.15） and 156.5 Ma±2.4 Ma（MSWD=0.42）,respectively with the confidence of 95%.Correlation of ages of volcanic rock with regional Songnan basin and Xujiaweizi area showed that 102 Ma and 105 Ma represented the time of volcanic activity of Quantou and Yingcheng Formation in Changling depression,while the age of 156 Ma was dues to the mix of zircon during magmatic activities of the Yingchen Formation.The dated age is a little younger compared to the age of 125 Ma^131 Ma measured by Wang Pujun,Yingcheng in the adjacent areas.The rock types and chemical compositions of volcanic rocks of Yingcheng Formation in Changling and Xujiaweizi Depression are similar,but the age of the former is 6Ma younger than the later.The age measurement result showed that the deposition of 0～800 m Denglouku Group clastic rocks in Changling depression only lasted for 3 million years,and the deposition speed is up to 0.27 mm/y.

关 键 词：长岭凹陷 火山岩 LA-ICP-MS(激光剥蚀等离子体质谱) 锆石U-PB定年 

分 类 号：P597.3[天文地球—地球化学] P588.14[天文地球—地质学]