新疆托云火山群SHRIMP锆石U-Pb年代学及其动力学意义  

SHRIMP zircon dating of the Tuyon volcanoes group, Xinjiang, and its geodynamic implications

作　　者：梁涛[1] 罗照华[1] 柯珊[1] 魏阳[1] 李德东[1] 黄金香[1] 黄凡[1] 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,北京100083

出　　处：《岩石学报》2007年第6期1381-1391,共11页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(40472038);国家重点基础发展规划项目(2002CB412603).

摘　　要：新疆西南天山托云盆地是一个新生代火山构造盆地。盆地内火山岩主要为玄武质岩石,呈锥状岩席、熔岩被、塌陷破火山口、火山颈和岩脉产出,常见流动自碎角砾岩。锥状岩席含有大量深源岩石包体,具有原生岩浆的性质,其 SHRIMP 锆石 U-Pb 法定年结果为48.1±1.6Ma。塌陷破火山口附近熔岩层底部的锆石(样品 A015D)给出比较集中的新太古宙和古元古代年龄,最老可达2.5Ga,可能代表了塔里木地块基底的卷入;而上部岩层的锆石(样品 A015E)年龄则比较分散,几乎关贯穿整个古生代(寒武纪和泥盆纪除外),是天山古造山带演化历史的记录。火山颈锆石(样品 A-D016)的年龄时间跨度最大,包括古元古代,古生代泥盆纪和二叠纪以及中生代三叠纪。SHRIMP 测年结果证实了托云火山群开始活动的时代为古近纪,与藏北新生代岩浆活动的起始时间大致相同,揭示了天山新生代板内造山过程与印度-亚洲大陆碰撞的内在联系。不同成因与形成时间的锆石共存,显示了西南天山岩石圈演化的复杂性,托云火山群的形成与岩石圈拆沉作用有关。Tuyon basin is a Cenozoic tectono-volcanic depression located in Southwest Tien Shan, Xinjiang, NW China. The volcanic rocks are mainly of basaltic composition and occur as cone dikes, lava sheets, caldera, volcanic necks and veins. Autoclastic breccia is very prevalent in lava sheets. Many deep-seated xenoliths are occurred in the cone sheets. It indicates the cone sheets are the products of primary magma. The SHRIMP dating of zircons shows age of 48. 1± 1.6Ma of a cone sheet. The dating results of the bottom lava layer of the caldera （Sample No. A015D） can be divided distinctly into two groups： the late Archean and the early Proterozoic. The oldest age reaches 2. 5Ga, which means the Tarim block basement is probably involved in the orogenic processes of Tien Shan. The zircons from upper layer of caldera （Sample No. A015E） have shown more dispersive ages （almost distributed to the overall Paleozoic except Cambrian and Devonian） , recorded the evolution process of Tien Shan. The sample A-D016 is from volcanic neck, and its zircon SHRIMP ages imply a large time span, including early Proterozoic, Devonian, Permian and Triassic. The SHRIMP dating of the cone sheet suggests that the initial time of volcano activity in the Tuyon basin is in Paleogene, it is approximately the same as in north Tibet. It may be indicates the intrinsic relationship between Cenozoic intraplate orogenesis of Tien Shan and Indian-Asian continental collision. The coexistence of zircons of different genesis and formation time reveals the lithosphere of SW Tien Shan has undertaken complex evolution, and further suggests the formation of Tuyon volcano group is related to regional lithosphere delamination.

关 键 词：托云火山群 SHRIMP 火山机构 塔里木盆地 天山 青藏高原 

分 类 号：P588.145[天文地球—岩石学] P597.3[天文地球—地质学]