ZIRCON U-Pb AGES FOR RHYOLITIC TUFFS OF THE NAOCANGJIANGOU FORMATION IN THE EAST KULUN OROGENIC BELT AND THEIR IMPLICATION
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摘要: 应用激光烧蚀多接收器电感耦合等离子体质谱(LA-MC-ICP MS)方法对东昆仑秀沟盆地闹仓坚沟组火山岩样品进行了锆石U-Pb定年研究。流纹质凝灰岩(DG25-4)中锆石的阴极发光图像具有振荡环带结构，属于典型的岩浆锆石。15个岩浆锆石206Pb/238U表面年龄集中在239~249 Ma之间，206Pb/238U加权平均值为243.5 ± 1.7 Ma，它记录了火山岩的形成年龄，说明该地区闹仓坚沟组形成于中三叠世早期。这一研究还在闹仓坚沟组火山岩中发现了早古生代和元古宇继承锆石，提供了昆南地体可能存在元古宇基底的信息。Abstract: By using La-Mc-ICPMC method, accurate zircon U-Pb dating has been made for volcanic rock samples from the Naocangjiangou Formation in the Xiugou basin of the East Kunlun orogenic belt. The zircons from the rhyolitic tuff (sample DG25-4) showed oscillatory girdles in its cathodeluminescence image, indicating a typically magmatic origin. The 206Pb/238U surface ages of 15 magmatic zircons are concentrated in the range of 239-249 Ma, averaging 243.5 ± 1.7 Ma, which records the forming age of those volcanic rocks, that is, the Naocangjiangou Formation was formed in the early Middle Triassic. Early Paleozoic and Proterozoic zircons were also found in volcanic rocks of the formation, suggesting the possible presence of Proterozoic basement in the Kunlun southern terrain.
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Key words:
- Naocangjiangou Formation /
- tuffs /
- U-Pb age /
- Middle Triassic /
- East Kulun orogenic belt
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图 1 东昆仑秀沟盆地一带地质略图及样品位置
1.新生界; 2.上三叠统八宝山组; 3.中三叠统闹仓坚沟组; 4.三叠系巴颜咯拉山群; 5.二叠系; 6.石炭系; 7.志留—泥盆系牦牛山组; 8.奥陶—志留系纳赤台群; 9.寒武系沙松乌拉组; 10.中元古界万宝沟群; 11.早侏罗世二长花岗岩; 12.早泥盆世花岗闪长岩; 13.蛇绿岩; 14.主要断层; 15.活动断层; 16.样品位置及编号
Figure 1. Geological map around Xiugou Basin showing location of samples
图 2 闹仓坚沟组流纹质凝灰岩露头与凝灰岩显微结构
Figure 2. Tuff occurrences of Naocangjiangou Formation and microtexture of the tuff
图 3 闹仓坚沟组流纹质凝灰岩锆石CL图像
Figure 3. CL images of zircons from rhyolitic tuffs in Naocangjiangou Formation
图 4 闹仓坚沟组流纹质凝灰岩锆石U-Pb年龄谐和曲线图
Figure 4. Zircon U-Pb concordian diagrams of the rhyolitic tuffs from Naocangjiangou Formation
表 1 凝灰岩锆石LA-MC-ICP MS U-Pb同位素年龄测定结果
Table 1. LA-MC-ICP MS U-Pb data for zircons from the tuffs in Naocangjiangou Formation
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