SHRIMP U-Pb zircon dating for Qiashikansayi granodiorite, the Northern Altyn Tagh Mountains and its geological implications

The Qiashikansayi granodiorite is foliated resulting in a granodioritic gneiss. Its geochemical features, such as alumina saturation index(A/CNK) of 0.81-0.99, Na2O/K2O values>1, TiO2 contents <1.0%, LREE enrichment with high fractionation factors, weakly negative or no Eu anomalies, and significant Ba and Ti negative anomalies, suggest that it is similar to a typical island arc pluton. The trace elements of the Qiashikansayi granodiorite are plotted in the island arc field in the tectonic setting discrimination diagrams as well. Cathodoluminescence images demonstrated that the zircons have clear rhythmic crystallized zoning, without any remnant core and new crystallized rim, suggesting the zircons be magmatic ones. Their U and Th contents vary in the range of 574-870 μg/g, and 279-556μg/g respectively, with the Th/U ratio in the range of 0.52-0.68. SHRIMP zircon U-Pb dating yielded the 481.5±5.3 Ma age for the intrusion of the granodiorite, which is coeval with the island arc volcanic rocks in the no     

川西坳陷断裂活动期次、热流体性质和油气成藏过程分析

川西坳陷中生代陆相地层中的众多油气藏成因,与该坳陷由持续构造沉降折向脉动性隆升的重大构造逆转事件,以及隆升过程中多期次断裂活动和流体运动密切相关。通过对充填不同期次构造裂缝和溶蚀孔洞的次生石英和方解石标型特征、ESR年龄测定、流体包裹体均一温度、盐度和密度、沥青包裹体反射率,以及氧碳同位素分析的综合研究,结合众多前人研究成果,认为：该坳陷自早白垩世至中新世的断裂活动可划分为燕山晚期早幕(I期,125～110Ma)和晚幕(Ⅱ期,94～82Ma)、喜马拉雅早幕(Ⅲ期,63～53．7Ma)、喜马拉雅中期早幕(Ⅳ期,45～21.6Ma)和晚幕(V期,14．9Ma)五个主要期次;在渐趋开放的体系中,沿各期次构造裂缝运移的热流体以继承性发展演化的载烃油田水为主,但在Ⅱ期和Ⅳ期晚时混入有深部高盐度地层水;构造裂缝为油气运移、聚集和成藏作用提供了重要通道条件;相关的成藏过程为I期石油窗阶段,Ⅱ期原始油气藏阶段,Ⅲ期原生油气藏破坏和早期次生油气藏阶段,Ⅳ期次生油气藏主要成藏阶段,V期“浅层远源次生”天然气藏阶段,Ⅳ期和V期为最重要的2个关键成藏期。     

Zircon SHRIMP U-Pb dating for the Cangshuipu volcanic rocks and its implications for the lower boundary age of the Nanhua strata in South China

Continental volcanic rocks and volcaniclastic sedi-mentary conglomerates of the Cangshuipu Formation oc- cur as wedge-shaped Neoproterozoic strata in the Yiyang region, Hunan Province. They overlie with a high-angle unconformity the Lengjiaxi Group of the Upper Meso- proterozoic Eonothem. The wedge-shaped Neoproterozoic strata of the continental clastic rocks and the Mesopro-terozoic deep marine flysch turbidites of the Lengjiaxi Group represent two distinct stages of basin-tectonic evo-…     

Determination of U-Pb age and rare earth element concentrations of zircons from Cenozoic intrusions in northeastern China by laser ablation ICP-MS

Using the in situ zircon U-Pb dating method of LA-ICPMS, we analyzed the 31 Ma old SHRIMP U-Pb age of the Yongsheng nepheline syenite from southern Jilin Province under different spot sizes. The obtained ages are comparable with that of SHRIMP in both accuracy and precision. The age is also identical to that of the Yinmawanshan gabbro from the Liaodong Peninsula within error. Both the Yongsheng nepheline syenite and the Yinmawanshan gabbro represent the youngest known exposed intrusions in northeastern and even eastern China. The results indicate the Eocene mantle-derived magmatic underplating, and the rapid crustal uplifting of this region since 30 Ma. The analyses also document extremely high LREE concentrations and relatively fiat REE patterns for the zircons from the Yongsheng nepheline syenite, which represent a new type of zircon REE pattern.     

U-Pb dating of zircon grains from the ore-bearing plagioclase amphibolite in the Dashuigou Te deposit

The Dashuigou Te deposit is a unique independent one found in the world, and hosted in the plagioclase arnphibolite. The upper intercept age of single zircon from the arnphibolite can be considered to be the crystallization age of the source-rock of the amphibolite (tholeiitic basalt), while the lower intercept is nearly consistent with the time of the tectono-thermal event.     

AMS dating on glacial tills at the source area of the Urumqi River in the Tianshan Mountains and its implications

Using accelerating mass spectrometry (AMS) dating method, a dating has been made on the primary calcium carbonate in tills and secondary calcium carbonate coating on till gravel and the roche moutonnee formed since the Last Glaciation at the source area of the Urumqi River valley in the Tianshan Mountains, northwestern China. The results reveal that the carbonate content in the tills in this noncarbonate area is high enough to date by AMS, that the carbon in the coatings on the newly exposed roche moutons and in the modern till is modern carbon and so the¹⁴C dating results in the ancient till can represent the actual ages of the till formation, and that the warm period during the Holocene began as early as 6 500 a B. P. and lasted to 1 800 a B. P.     

Zircon U-Pb SHRIMP ages of high-pressure granulite in Yushugou ophiolitic terrane in southern Tianshan and their tectonic implications

Zircons from two high-pressure granulite samples from the Yushugou ophiolitic terrane, southern Tian shan have been investigated by cathodoluminescence, LA ICPMS and ion microprobe (SHRIMP) for their internal textures, trace elemental compositions and in situ dating. The weighted mean ages of these two samples are 392±7 and 390±11 Ma, respectively, representing the granulite-facies meta morphic age of the ophiolitic terrane, and indicating that the southern Tianshan ocean initiated its northward subduction since the early Devonian.     

Multi-stage evolution of gneiss from North Dabie： evidence from zircon U-Pb chronology

TTG gneiss is a common rock to outcrop in the northern part of the Dabie orogen, a few of which are closely associated with eclogites that experienced the Triassic ultrahigh pressure metamorphism. Although they were thermally metamorphosed by a large-scale magma activity in this region at the Early Cretaceous, it is unclear whether or not they are also affected by the Triassic metamorphism during continental subduction and exhumation. In order to resolve this issue, SHRIMP zircon U-Pb dating was carried out for the host gneiss of eclogites in North Dabie. The results show that cores from the gneiss have an age of 746~.31 Ma, consistent with the protolith ages of granitic gneisses in the Dabie orogen. Zircon overgrowing with different U and Th concentrations give concordant ages of 212~21 and 120~11 Ma, respectively. Th/U ratios of overgrown zircons are both lower than 0.1, suggesting a metamorphic genesis. The present resuits suggest that the gneiss in North Dabie has the similar protolith ages of Neoproterozoic to those granitic gneisses elsewhere in the Dabie orogen, and experienced not only the Triassic metamorphism but also the thermal metamorphism due to the Early Cretaceous magmatism. This provides an important insight into the geodynamic evolution of gneissic rocks in the Dabie orogen.     

北秦岭罗汉寺岩群锆石年龄及地质意义

目的准确测定北秦岭罗汉寺岩群辉长岩脉的形成时代,探讨其地质意义。方法采用激光剥蚀等离子质谱法,对辉长岩中锆石进行U-Pb同位素定年。结果辉长岩形成年龄为475 Ma±4 Ma。结论罗汉寺辉长岩脉的形成时代与北秦岭两条高压—超高压变质带和富水杂岩成岩时代接近或一致,它的形成很可能与北秦岭早古生代岛弧体系碰撞有关。