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引用本文:朱彦菲,木合塔尔·扎日,赵同阳,韩琼,郑加行. 新疆阿尔泰山西段喀纳斯地区奥陶纪火山岩锆石UPb年龄和地球化学特征[J]. 中国地质, 2018, 45(3): 469-482.
ZHU Yanfei,MU Hetaer·zhari,ZHAO Tongyang,HAN Qiong,ZHENG Jiaxing. Zircon U-Pb age and geochemical characteristics of Ordovician volcanic rocks from Kanasi area in Western Altay Mountains, Xinjiang[J]. Geology in China, 2018, 45(3): 469-482(in Chinese with English abstract).
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新疆阿尔泰山西段喀纳斯地区奥陶纪火山岩锆石UPb年龄和地球化学特征
朱彦菲1,2, 木合塔尔·扎日1, 赵同阳2, 韩琼2, 郑加行2
1.新疆大学, 新疆 乌鲁木齐 830000;2.新疆地质调查院, 新疆 乌鲁木齐 830000
摘要:
喀纳斯地区发育一套火山-沉积地层东锡勒克组,因缺少可靠的年龄和地球化学数据,其形成时代及地球动力学背景长期存在争议。为探讨这一问题,文章选择区内东锡勒克组一套层状分布的糜棱岩化英安岩作为研究对象,对其进行锆石LA-ICPMS U-Pb同位素定年,得到2件样品的206Pb/238U年龄分别为(445.4±3.1)Ma和(445.7±3.7)Ma,代表火山岩结晶年龄为晚奥陶世。这表明东锡勒克组地层形成于晚奥陶世。糜棱岩化英安岩SiO2含量为53.99%~71.04%,具有富铝(Al2O3=13.83%~16.27%),贫镁(MgO=1.09%~3.53%),K2O介于1.11%~3.83%,平均为2.84%,属于高钾质火山岩系列的特征;轻稀土富集,Eu负异常(δEu=0.65~0.82);富集大离子亲石元素(Rb、Th、Ce)和亏损高场强元素(K、Nb、Ta),具有岛弧火山岩特征。结合区域地质特征,笔者认为该套火山岩形成于活动大陆边缘洋壳俯冲消减后期同碰撞的环境。晚奥陶世末古亚洲洋由南向北向西伯利亚板块之下俯冲形成具有活动大陆边缘弧性质的喀纳斯地区晚奥陶世火山岩。
关键词:  阿尔泰山  喀纳斯地区  LA-MC-ICP-MS锆石U-Pb年龄  地球化学  活动大陆边缘
DOI:10.12029/gc20180304
分类号:P597+.3;P595;P588.14+2
基金项目:中国地质调查局项目“新疆阿尔泰1:5万M45E021013等四幅区域地质矿产调查”(12120114040701)资助。
Zircon U-Pb age and geochemical characteristics of Ordovician volcanic rocks from Kanasi area in Western Altay Mountains, Xinjiang
ZHU Yanfei1,2, MU Hetaer·zhari1, ZHAO Tongyang2, HAN Qiong2, ZHENG Jiaxing2
1.Xinjiang University, Urimqi, 830000, Xinjiang, China;2.Xinjiang Institute of Geological Survey, Urimiqi 830000, Xinjiang, China
Abstract:
There is a suite of volcanic-sedimentary strata comprising Dongxileke Formation in Kanasi area; nevertheless, there is no accurate ages and geochemical study for these rocks. The genesis and geodynamical background are in controversy for a long time. To tackle these problems, the authors chose a layered mylonitic dacite in this area as the study object. LA-ICP-MS zircon U-Pb ages of(445.4±3.1)Ma and(445.7±3.7)Ma from two mylonitic dacite samples suggest that these volcanic rocks erupted in late Ordovician and that Dongxileke Formation was formed in late Ordovician. The mylonitic dacite is characterized by SiO2 content from 53.99% to 71.04%, high Al2O3 (13.83%-16.27%) and low MgO (1.09%-3.53%), with K2O between 1.11% and 3.83%, 2.84% on average, suggesting high alkline volcanic rock series. The mylonitic dacite forms a LREE-enriched distribution pattern with the existence of negative Eu anomaly (δEu=0.65-0.82). Geochemical characteristics of mylonitic dacite suggest island-arc volcanic features characterized by enrichment of LILE such as Rb, Th and Ce and depletion of HFSE such as K, Nb and Ta. Combined with regional data and the results obtained by this study, the authors consider that the volcanic rocks were generated during syn-collision of the late stage subduction in an active continental margin arc. The background was the conversion from the northward subduction of Paleo-Asia Ocean under the Siberia plate to Altay micro landmass land, which resulted in the formation of late Ordovician volcanic rocks in an active continental margin arc of Kanasi area.
Key words:  Altay Mountains  Kanasi area  LA-ICP-MS zircon U-Pb age  geochemical characteristics