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SHRIMP U-Pb geochronology of the zircons from the Precambrian basement of the Qilian Block and its geological significances 被引量:44
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作者 Kuoan TUNG Huai-Jen yang +4 位作者 houng-yi yang LIU DunYi ZHANG JianXin WAN YuSheng Chien-Yuan TSENG 《Chinese Science Bulletin》 SCIE EI CAS 2007年第19期2687-2701,共15页
Origin and tectonic evolution of the Qilian Precambrian basement on NW China were investigated using zircon U-Pb ages with collaborating stratigraphic and paleontological evidence. Zircon grains were separated from tw... Origin and tectonic evolution of the Qilian Precambrian basement on NW China were investigated using zircon U-Pb ages with collaborating stratigraphic and paleontological evidence. Zircon grains were separated from two schists, two granitic gneisses and one mylonized gneiss and dated with SHRIMP. Seventy percent of sixty-one detrital zircon ages from two schists ranges from 0.88 Ga to 3.09 Ga, mostly within 1.0 Ga to 1.8 Ga with a peak at 1.6 Ga to 1.8 Ga, and twenty percent varies from 2.0 Ga to 2.5 Ga. A few falls in the Archean and Neoproterozoic periods. The two granitic gneisses were dated 930±8 Ma and 918±14 Ma, whereas the mylonized granitic gneiss was dated 790±12 Ma. These ages represent two periods of magmatisms, which can be correlated with the early and late stages of magmatisms associated with the Jinningian movement on the Yangtze Blocks. The results from this and previous studies indicate that the ages of the Precambrian detrital zircons from the Qilian Block are widely distributed in the Proterozoic era, distinct from the North China Block which was stable in the Neo-Mesoproterozoic era. By contrast, the age histograms of the detrital zircons from the Qilian Block is similar to those from Precambrian basement of the Yangtze Craton. Therefore, it is suggested that the Qilian Block had a strong affinity toward the Yangtze Craton and might belong to the supercontinent Gondwana in the Neoproterozoic time. This inference is supported by Nd model age (TDM), stratigraphic, and paleontological evidence. It is further considered that the Qilian Block was rifted from the supercontinent Gondwana during late Sinian to form an isolated continent in the Proto-Tethyan Ocean, moving towards the Alaxa Block in the North China Craton. The part of Proto-Tethyan Ocean between the Qilian and Alaxa Blocks should correspond to the so-called Paleo-Qilian Ocean. Following the closure of the Paleo-Qilian Ocean in the early Paleozoic, the Qilian Block collided with the Alaxa Block to form the North Qilian Orogenic Belt. Based on this tectonic explanation, the North Qilian ophiolites should represent parts of lithosphere from the Proto-Tethyan Ocean. Lithological and geochronological evidence also indicates that the Qilian Block underwent continental reactivation possibly induced by the deep northward subduction of the North Qaidam Block in early Paleozoic time. 展开更多
关键词 地球年代学 锆石 前寒武纪 古地中海 特提斯海
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The Dongcaohe ophiolite from the North Qilian Moun-tains: A fossil oceanic crust of the Paleo-Qilian ocean 被引量:40
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作者 Chien-Yuan TSENG Huai-Jen yang +4 位作者 houng-yi yang LIU DunYi Ching-Lang TSAI WU HanQuan ZUO GuoChao 《Chinese Science Bulletin》 SCIE EI CAS 2007年第17期2390-2401,共12页
The Dongcaohe ophiolite, located at the south of the North Qilian subduction complexes, is a tectonic block with an exposed area of about 3 km×6 km. It consists of an intrusive section overlain by an ex- trusive ... The Dongcaohe ophiolite, located at the south of the North Qilian subduction complexes, is a tectonic block with an exposed area of about 3 km×6 km. It consists of an intrusive section overlain by an ex- trusive section. The lower part of the intrusive section consists of cyclic layers of cumulate dunites, troctolites, anorthosites, anorthositic gabbros, and gabbros with small discordant dunite and troctolite bodies. This layered sequence grades upward to isotropic gabbros and gabbronorites, which are overlain by the extrusive sequence of diabasic sheeted dikes and basaltic lavas. The overall mineral crystallization sequence was olivine±Cr-spinel, plagioclase, clinopyroxene, orthopyroxene, and Fe-Ti oxides. The Cr-spinel (Mg#: 42-66, Cr#: 41-57) in these layered cumulates and present-day abyssal peridotites have similar compositions. Also, the compositional variations of the plagioclase and cli- nopyroxene in the intrusive section reflect crystallization from melts compositionally similar to the present-day ocean basalts. Moreover, the rare earth element (REE) and multi-element distribution pat- terns of the intrusive and extrusive lithologies in the Dongcaohe ophiolite are consistent with crystal- lization of mid-ocean ridge basalts. The zircon grains separated from the gabbronorite have an SHRIMP average 206Pb/238U weighted age of 497 ± 7 Ma, which is considered as the tectonic emplacement age of the Dongcaohe ophiolite. The field occurrence, mineral and whole-rock compositions indicate that the Dongcaohe ophiolite represents a well-persevered oceanic crustal fragment composed of a complete oceanic crustal section of layered cumulates at bottom upgrading through isotropic cumulates to sheeted dikes and lava flows. 展开更多
关键词 蛇绿岩 祁连山 海洋底壳 化石
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Finding of Neoproterozoic (~775 Ma) magmatism recorded in metamorphic complexes from the North Qilian orogen: Evidence from SHRIMP zircon U-Pb dating 被引量:26
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作者 Chien-Yuan Tseng houng-yi yang +4 位作者 WAN Yusheng LIU Dunyi Da-Jen Wen Tzung-Chi Lin Kuo-An Tung 《Chinese Science Bulletin》 SCIE EI CAS 2006年第8期963-970,共8页
标明日期的虾 U-Pb 从 Niuxinshan 片麻岩的花岗石和 Leigongshan 在锆石上被执行在北方 Qilian orogen 的片麻岩的吨子盐, NW 中国。结果分别地产出 776+-10 妈和 774 +-23 妈的加权的平均 ~(206 )Pb/~(238 ) U 年龄。Igneousmorphol... 标明日期的虾 U-Pb 从 Niuxinshan 片麻岩的花岗石和 Leigongshan 在锆石上被执行在北方 Qilian orogen 的片麻岩的吨子盐, NW 中国。结果分别地产出 776+-10 妈和 774 +-23 妈的加权的平均 ~(206 )Pb/~(238 ) U 年龄。Igneousmorphology,摆动的 zonings,和为这些锆石的相对高的 Th/U 比率建议 magmaticorigin。这些年龄作为岩浆炮兵阵地预定并且因此代表 aNeoproterozoic (约 775 妈) 被解释在北方 Qilian 区域的 magmatic 事件。thismagmatism 可能与超级大陆 Rodinia 的决裂有关,这被建议。这发现,和 750 ~ 800 妈的类似的年龄为南方中央的 Qilian 和北方 Qaidam 的附近的岩层报导了,具有到在韦斯特中国的 Rodinia 进化的理解的意义。 展开更多
关键词 岩浆 造山带 SHRIMP 锆石 年代测定
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