Discovery of a 1.0 Ma Yellow River terrace and redating of the fourth Yellow River terrace in Lanzhou area

Based on the aeolian loess sequence-stratigraphic division and paleomagnetic datings on terraces, we found that an undiscovered terrace with the age of 1.0 Ma BP lies between the Dunwashan terrace and Wuyishan terrace. This terrace recorded an intensive Yellow River incision event during that period. Results of paleomagnetic dating and optically stimulated luminescence (OSL) dating of the Wuyishan loess section and Zaoshugou loess section on the fourth Yellow River terrace (T4) show that the age of the fourth Yellow River terrace in Lanzhou area is 0.86 Ma BP rather than the previously believed 0. 6 Ma BP. This result answers a long-term question in the ge-omorphology community of whether there exists a 0. 8 Ma terrace in Lanzhou area. The discovery of the 1. 0 Ma Yellow River terrace and redating of the age of 0.6 Ma terrace in Lanzhou area provide new insights into further research on the evolution of Yellow River.     

Initial movement of the Karakorum Fault in western Tibet： constraints from SHRIMP U-Pb dating of zircons

The Karakorum Fault zone(KFZ)plays an important role in understanding the formation,evolvement and deformation of the Tibetan Plateau.The high-T dextral shearing metamorphic rocks,e.g.,mylonites or mylonitized gneisses-granites,locally crop out along the southeastern part of the KFZ in the Ayila Ri’gyüRange area.The SHRIMP U-Pb dating of the syn-kinematic crystallized zircons indicates that the initial age of the KFZ is~27 Ma,~10 Ma older than previous results.The extensive high-T dextral shearing along the KFZ started at least at 27-20 Ma,accompanied by the syn-kinematic emplacement of leuco-granites.Deformation and concomitant fluid circulation during shearing most likely occurred as early as at 25-13 Ma.The KFZ probably grew from southeast to northwest along the fault as a result of continuous convergence between the India plate and Eurasia plate.     

SHRIMP zircon U-Pb dating of the Gangou granitoids, Central Tianshan Mountains, Northwest China and tectonic significances

Two types of granitoids, highly deformed eugen grenitoids end undeformed fine-grained grenitoids, ere widely distributed in Gangou area, Central Tianshen Mountains, Northwest China. The augen grenitoids are high-K calc-alkaline characterized by high K20, Rb, Y and Th, and low Sr and Sr/Y. They also have high contents of large ion lithophile elements （LILE）, such as Be, Rb, K and Th, and relatively low contents of high field strength elements （HFSE）, such as Zr, Y and Nb. The fine-grained granitoids are calc-alkaline cherecterlzed by high Sr, low Y and HREE, similar to adakitic rocks, and with Na20/K20〈2 （1.76-1.91）, high/sr （0.70689--0.70981）, and negative εNd（t） （-2.4-5.3）. High-precision SHRIMP U-Pb zircon dating results indicate that the Gangou augen greniUods were formed at 428 ± 10 Me, and the fine-grained granitoids were emplaced at 361 -368 Me. These geochemical and U-Pb zircon data have significant implications for the timing of closure of the Mishigou-Gangou Ocean and the evolution of the Central Tianshan orogenic belt.     

Ages and tectonic significance of the collision-related granite porphyries in the Lhunzhub Basin, Tibet, China

The Paleocene collision-related granite porphyries are identified for the first time along the western margin of the Lhunzhub Basin, Tibet. SHRIMP U-Pb zircon analysis indicates that the granite porphyries were emplaced at 58.7±1.1 Ma (MSWD = 0.79) during the Indo-Asian continental collision. The granite porphyries are peraluminous and high in K, belonging to the calc-alkaline to high-K calc-alkaline series. They are relatively enriched in LILE, Th and LREE and depletion in Ba, Nb, P and Ti, characterized by LREE-enriched patterns with slightly to moderately negative Eu anomalies. These Paleocene granite porphyries are interpreted as the products generated by partial melting of the pre-existing arc crustal rocks caused by the increase of pressures and temperatures during the crustal shortening at the early stages of the Indo-Asian continental collision since 65 Ma. Despite inherited geochemical features and tectonic settings of the arc protoliths, they are significantly different from the volcanic rocks of the Dianzhong Formation within the Linzizong Group and the Miocene granite por- phyries in the Gangdise belt.     

Laser step-heating ^40Ar/^39Ar dating on young volcanic rocks

An attempt was made to use CO_2 laser step-heating method to date the late Pleistocene basaltic groundmass (DF-2) from Tengchong volcanic field. Among the fourteen heating steps, ten define a good inverse isochron (MSWD = 1.4) with an age of 32.2 ± 7.1 ka (2 σ).The inverse isochron also shows that the initial argon isotopic ratio is 297.1±2.0 (2σ) which is the same as the atmospheric argon at the 2σ error level. Study indicates that it is a useful means to date young volcanic groundmass with low K content by using CO_2 laser step-heating ~(40)Ar/~(39)Ar method.     

Zircon SHRIMP geochronology and geochemistry of TTG rocks in Sushui Complex from Zhongtiao Mountains with its geological implications

The tonalite-trondhjemite-granodiorite (TTG) rocks in Sushui Complex of Zhongtiao Block can be divided into two series according to their zircon U-Pb ages and geochemical characteristics: one is subduction-related (SR) and the other collision-related (CR). The SR TTG rocks, together with other Late Archean island arc magmatism, were developed as a result of oceanic subduction between the Eastern and Western blocks in Late Archean; while the CR TTG rocks formed in a thickened crustal environment, which was responding to the collision between the Eastern and Western blocks in Paleoproterozoic. All these features support a model that the Zhongtiao Block is a part of the Trans-North China Orogen in the middle of North China Craton.     

北黄海侏罗系碎屑锆石UPb定年及地质意义

对北黄海钻遇的侏罗系地层的4个变质火成岩样品进行锆石U-Pb定年分析,主要获得了2类年龄记录,一类是前寒武纪变质基底形成演化的年龄,另一类是印支期碰撞造山改造的年龄记录.变质基底的年龄区间分布在1.0Ga至2.6Ga,其中1.4Ga至1.8Ga是一个主要构造岩浆期,包括(1 792±140)Ma,(1 447±110)Ma和(1 524±68)Ma三组U-Pb谐和年龄.与华北和扬子印支期碰撞造山作用有关的定年结果为200Ma至240Ma.这2类年龄与邻区胶北地体及苏鲁造山带获得的年龄数据具有很好可比性,可为进一步认识北黄海侏罗系物源区构造演变特点提供重要依据.     

鄂尔多斯盆地东部上古生界气藏成藏史

应用生烃时限分析、储层流体包裹体以及储层自生伊利石K-Ar定年等成藏年代学方法,精细描述鄂尔多斯盆地东部上古生界不同含气组合气藏的成藏期次和成藏时间,实现了区内由传统的定性到定量或半定量研究的转变.研究表明:上古生界不同含气组合气藏从南到北、从下至上成藏时间依次变晚.中、下部含气组合主要两期充注,分别为200.0～175.0Ma和160.0～120.0Ma,后一期为天然气的主力充注期,成藏关键时刻为135.0Ma.上部含气组合属于次生气藏,为一期充注,主要成藏时间略晚,为150.0～97.5Ma,其与晚侏罗世—早白垩世构造运动密切相关.     

<Superscript>40</Superscript>Ar/<Superscript>39</Superscript>Ar geochronology constraints on hydrocarbon accumulation and destruction periods in the Bankeng paleo-reservoir in the southern margin of the middle Yangtze block

The exact determination of isotopic ages of hydrocarbon accumulation,reconstruction and destruction periods using traditional isotopic dating methods is complex because of the small numbers of minerals that correlate with hydrocarbons.The quantitative and direct study of hydrocarbon geochronology is therefore an important scientific problem for isotope geochronology and petroleum geology.This study obtains two isotopic ages from a quartz vein sample associated with bitumen in a reverse fault located in the ...     

浅析同位素测年方法及其应用

成矿年代的确认是现代矿床研究的热点,本文仅简单的介绍了几种同位素测年的方法,包括:U-Pb法、Rb-Sr法、Sm-Nd、K-Ar法和Re-Os法,并对某些方法进行了具体实例研究,找出其中的优缺点。在综合几种方法的优缺点之后又进一步对现阶段地质年代定年的方法进行了综评。