ZIRCON U-Pb DATING OF THE RHYOLITE-DACITE PORPHYRY IN THE SANDAOWAN OF EAST KUNLUN MOUNTAINS AND ITS GEOLOGICAL SIGNIFICANCE
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摘要: 东昆仑格尔木河西三道湾流纹英安斑岩构成火山通道侵出相，侵入到纳赤台群哈拉巴依沟组碎屑岩系中，其形成时代对于造山带火山作用的研究和限定哈拉巴依沟组地层时代均具有重要的意义。采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，对三道湾流纹英安斑岩进行了锆石U-Pb定年，结果表明，流纹英安斑岩中25个岩浆锆石206Pb/238U加权平均年龄为425.9 ± 2.6 Ma，它被解释为流纹英安斑岩的结晶年龄，说明三道湾次火山岩所代表的火山通道为早古生代造山晚期牦牛山组火山岩形成时的火山喷发中心之一，而非晚侏罗世次火山岩。野外地质关系和次火山岩年龄可以限定哈拉巴依沟组形成于中志留世之前。Abstract: The Sandaowan rhyolite-dacite porphyry, located to the west of the Golmud River, about 55 km from south of Golmud City, is an intrusive vein of volcanic craters. It intruded into the clastic rocks, named Habalayigou group as one of the Nachitai unit in this region. A sample No. B727-1 was collected from the Sandaowan rhyolite-dacite porphyry rock. We used the LA-MC-ICPMS method of Zircon U-Pb Dating in this article. The 25 zircons from No. B727-1 yield a mean value of (425.9 ± 2.6) Ma of 206Pb/238U, which is interpreted as the age of the volcanism. The result shows that the volcanic crater was one of the eruptive center during Late collision of the Early Paleozoic in this region. Besides, it reveals a low time restrict to the Habalayigou group, implying that the Habalayigou strata formed before the Middle Silurian. These results conflict with previous 40Ar/39Ar whole rock ages of 147.96Ma for the rhyolite-dacite porphyry from the same rock.
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图 1 格尔木南地质构造图及样品点位置
1.中三叠统闹仓坚沟组; 2.下三叠统洪水川组; 3.上石炭统浩特洛洼组; 4.志留—泥盆系牦牛山组; 5.奥陶—志留系纳赤台群哈拉巴依沟组; 6.奥陶—志留系纳赤台群石灰厂组碳酸盐岩段; 7.奥陶—志留系纳赤台群石灰厂组火山岩段; 8.奥陶—志留系纳赤台群水泥厂组; 9.中新元古界万宝沟群碳酸盐岩组; 10.志留纪流纹英安斑岩(次火山岩); 11.逆断层; 12.采样点位置
Figure 1. Geological map in the south of Golmud and the sample location
图 2 三道湾流纹英安斑岩产状及岩石学特征
Figure 2. Rock occurrence and petrographic characteristics of the Sandaowan rhyolite-dacite porphyry
图 3 三道湾流纹英安斑岩锆石阴极发光图像、测点位置及年龄值
Figure 3. CL images, dating spots and ages of zircons from the Sandaowan rhyolite-dacite porphyry
图 4 三道湾流纹英安斑岩锆石U-Pb谐和图
Figure 4. Zircon U-Pb concordia diagram of the Sandaowan rhyolite-dacite porphyry
表 1 三道湾流纹英安斑岩锆石U-Pb同位素数据
Table 1. Zircon U-Pb dating results of the Sandaowan rhyolite-dacite porphyry
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