再论印度—亚洲大陆碰撞的启动时间   总被引：39，自引：6，他引：39       下载免费PDF全文

王成善  李祥辉等 《地质学报》2003,77(1):16-24

利用沉积响应来识别印度－亚洲大陆碰撞启动时间是最直接和有效的方法之一。西藏仲巴错江顶群被甄别为碰撞型三角洲沉积，曲下组可能代表了碰撞启动时期的建造，藏南定日的海相白垩－古近系沉积演化，锶和碳同位素变化也支持两大陆碰撞启动时间大约在K／T界线时期，对比喜马拉雅西段碰撞启动时间并考虑大印度北缘失掉的宽度，提出两大陆量可能的碰撞启动时间是65Ma左右。  相似文献   

鲁东官山榴辉岩与围岩接触关系的新发现及其对年代学的启示   总被引：14，自引：2，他引：14       下载免费PDF全文

宋明春  金振民  王来明  张希道  李远友 《地质学报》2003,77(2):238-244

鲁东官山榴辉岩呈透镜状包于变质含霓石碱性花岗岩中,榴辉岩的片麻理与主岩片麻理总体呈交切关系,局部可见变质含霓石碱性花岗岩呈细小岩枝状脉贯入榴辉岩中。变质含霓石碱性花岗岩锆石U-Pb法下交点年龄为231±25 Ma,上交点年龄为818±66 Ma。发现了闪长玢岩脉斜切式侵入榴辉岩及变质含霓石碱性花岗岩的接触关系,且闪长玢岩脉中有榴辉岩捕虏体,这种现象指示:闪长玢岩侵位时榴辉岩已折返至地壳较浅部位。研究表明,榴辉岩与变质含霓石碱性花岗岩共同经历了新元古代的超高压变质作用,但变质作用发生时含霓石碱性花岗岩可能处于熔融状态,榴辉岩是其中的固相包体。  相似文献   

略阳煎茶岭铜镍硫化物矿床Re—Os同位素年龄及其地质意义   总被引：12，自引：0，他引：12  

王瑞廷  赫英  王东生  刘民武 《地质论评》2003,49(2):205-211

采用矿石Re-Os同位素方法对陕西省煎茶岭硫化镍矿床矿石进行了成矿年代学研究,获得了878士27 Ma(1σ)的等时线年龄,首次厘定了该矿床成矿时代为新元古代,成岩成矿基本同时.通过对878 Ma硫化镍矿石初始Re-Os同位素体系的γOs计算和Re/Os值分析表明,其yOs和Re/Os值变化范围大,深部条带状矿石的Re/Os值仅为0.05,yOs为-6.70;块状矿石的Re/Os值范围为4.24～24.43,γOs为-15.37～+280.65,说明成矿过程中有壳源物质的混染;两件样品的γOs为负值(-15.37,-6.70),可能指示其超镁铁质岩浆来源于Re亏损地幔.煎茶岭超基性岩体年龄及其镍矿石的Re-Os等时线年龄与扬子克拉通北缘火山岩浆活动时间相对应,它们是扬子克拉通西北缘晋宁期构造岩浆成矿作用的产物.  相似文献   

0．7Ma以来的念青唐古拉山脉隆升过程——来自冰川剥蚀作用的证据   总被引：1，自引：0，他引：1  

朱大岗赵希涛  孟宪刚吴中海邵兆刚  冯向阳杨朝斌 王建平 《地质论评》2003,49(6):630-637

通过对念青唐古拉山冰碛地层划分及冰碛物同位素测年，发现最早一期冰碛物形成于0．7～0．6MaBP，指示自中更新世以来念青唐古拉山脉开始隆升，主峰地区发生了大规模的冰川剥蚀作用，形成了大面积分布的冰碛高平台；0．2～0．14MaBP念青唐古拉山又快速隆升，并堆积了刚刚伸出各大沟谷口的高侧碛；0．07～0．03MaBP念青唐古拉山再次小规模隆起，形成各大沟谷内的侧碛和终碛垄；0．01Ma BP还有小规模冰川活动。念青唐古拉山主峰地区的冰川剥蚀作用反映出的山脉隆升过程，可较好地与青藏高原的隆起过程相对比，它应是青藏高原隆升的响应。  相似文献   

An Early-Cambrian UPb apatite cooling age for the high-temperature regional metamorphism in the Piancó area,Borborema Province (NE Brazil): initial conclusions     

Bruno Dhuime  Delphine Bosch  Olivier Bruguier  Renaud Caby  Carlos Archanjo 《Comptes Rendus Geoscience》2003,335(15):1081-1089

The Borborema Province (BP) of northeastern Brazil is a complex crustal assemblage, which has undergone a polycyclic evolution during the Proterozoic. In the Piancó-Alto Br??gida belt, a metamorphosed leucosome vein inserted in amphibolites has a trace element pattern suggesting a T-MORB protolith. Apatites yield a REE pattern indicating growth in equilibrium with garnet, thus pointing to its metamorphic origin. UPb analyses yield an age of 540±5 Ma interpreted as a cooling age following amphibolite facies regional metamorphism associated with granitic emplacement at ca. 580 Ma. The resulting slow cooling rates (ranging from ca. 2.5 to 5 °C Ma^?1) are consistent with underplating of mafic magmas, or crustal thickening caused by nappe stacking, as possible processes governing the metamorphic evolution of the BP. To cite this article: B. Dhuime et al., C. R. Geoscience 335 (2003).  相似文献   

Caledonian Low-Temperature Granulite-Facies Metamorphism in the West Kunlun Orogenic Belt—SHRIMP Chronological Evidence from Zircon     

Zhang Chuanlin  Shen Jialin  Wang Aiguo  Zhao Yu  Guo Kunyi  Li Chunhai 《中国地球化学学报》2003,22(4):345-351

The West Kunlun orogenic belt is located at the conjunction of the paleo-Asian tectonic system and the Tethys tectonic system. Petrological and mineralogical studies of the Early Cambrian metamorphic surface crust in this region have shown that in case the metamorphism reached low-temperature granulate facies, the typical mineral assemblage is biotite-garnet-silimanite-K feldspar-plagioclase-quartz. The peak metamorphic temperatures are within the range of 720–740°C and the pressure is 0.6 GPa ±. Three types of metamorphic zircon have been detected in the metamorphic rocks: the complex inclusion-bearing type ; the early relic zircon inclusion-bearing type; and the inclusion-free type. SHRIMP age determination of these three types of metamorphic zircon have revealed that these zircons were formed principally during 400–460 Ma, indicating that pre-Cambrian metamorphic surface crust rocks underwent low-temperature granulite facies metamorphism during the Caledonian. In combination with the geological characteristics of this region, it is considered that when the oceanic basin was closed, there occurred intense intracontinental subduction (type A), bringing part of the Early Cambrian metamorphic basement in this region downwards to the lower crust. Meanwhile, there were accompanied with tectonic deformation at deep levels and medium- to high-grade metamorphism. This study provided important chronological and mineralogical evidence for the exploration of the evolutionary mechanism and process of the West Kunlun Early Paleozoic. Part of the results from the research project “ Research on the West Kunlun pre-Cambrian tectonic events” under the program “ Research on the important geological problems of China’ s pre-Cambrian” (No. 200113900070) sponsored by the China National Geological Surveying Bureau.  相似文献   

Chemical, Isotopic, and Fluid Inclusion Evidence for the Hydrothermal Alteration of the Footwall Rocks of the BIF-Hosted Iron Ore Deposits in the Hamersley District, Western Australia     

Makoto Haruna    Takahiro Hanamuro    Kaoru Uyeda    Hirokazu Fujimaki  Hiroshi Ohmoto 《Resource Geology》2003,53(2):75-88

Abstract. The petrography, chemical, fluid inclusion and isotope analyses (O, Rb-Sr) were conducted for the shale samples of the Mount McRae Shale collected from the Tom Price, Newman, and Paraburdoo mines in the Hamersley Basin, Western Australia. The Mount McRae Shale at these mines occurs as a footwall unit of the secondary, hematite-rich iron ores derived from the Brockman Iron Formation, one of the largest banded iron formations (BIFs) in the world. Unusually low contents of Na, Ca, and Sr in the shales suggest that these elements were leached away from the shale after deposition. The δ¹⁸O (SMOW) values fall in the range of + 15.0 to +17.9 per mil and show the positive correlation with calculated quartz/sericite ratios of the shale samples. This suggests that the oxygen isotopic compositions of shale samples were homogenized and equilibrated by postdepositional event. The pyrite nodules hosted by shales are often rimmed by thin layers of silica of varying crystallinity. Fluid inclusions in quartz crystals rimming a pyrite nodule show homogenization temperatures ranging from 100 to 240C for 47 inclusions and salinities ranging from 0.4 to 12.3 wt% NaCl equivalent for 18 inclusions. These fluid inclusion data give direct evidence for the hydrothermal activity and are comparable to those of the vein quartz collected from the BIF-derived secondary iron ores (Taylor et al, 2001). The Rb-Sr age for the Mount McRae Shale is 1,952 ± 289 Ma and at least 200 million years younger than the depositional age of the Brockman Iron Formation of ∼ 2.5 Ga in age. All the data obtained in this study are consistent with the suggestion that high temperature hydrothermal fluids were responsible for both the secondary iron ore formation and the alteration of the Mount McRae Shale.  相似文献   

冀西北地区晚太古代大陆地壳的增生和再造——同位素年代学证据   总被引：17，自引：0，他引：17  

刘敦一  耿元生  宋彪 《地球学报》1997,18(3):226-232

冀西北地区出露的太古宙变质岩系是华北地台北缘麻粒岩相带的重要组成部分。详细的同位素地质年代学研究表明，本区古老的地壳形成于２９００Ｍａ左右，为玄武质成分。古老地壳的熔融再造作用主要有两期，一期发生在２７８０～２７６１Ｍａ期间，产生了研究区西部广泛分布的英云闪长质片麻岩，另一期发生在２５６１～２５０３Ｍａ期间，形成在宣化－赤城一带广泛分布的花岗闪长质片麻岩。此后，在２５００～２４００Ｍａ期间发生了区域麻粒岩相变质改造，使部分岩石的同位素体系重新设置。  相似文献   

云开群硅质岩的40Ar/39Ar年龄及其地质意义   总被引：2，自引：0，他引：2  

劳秋元  叶真华  胡世玲  桑海清 《地球学报》1997,18(Z1):89-101

粤西云开群浅变地层年代的确定对于研究华南地壳演化有重要意义。以往的同位素年龄值多测自其中的顺层火成岩，故对其他质意义有不同的理解。本文首次测得了云开群中硅质岩的40Ar/39Ar年龄，从而提供了云开群的沉积年代。  相似文献   

激光探针质谱及单颗粒矿物^40Ar／^39Ar法年龄的测定     

蒲志平  许景荣  邱华宁  张永良  胡世玲 《岩矿测试》1997,16(1):1-6

将掺钕的钇铝榴石（Ｎｄ：ＹＡＧ）激光器与高精密ＭＭ１２００质谱计、电子倍增器联网，应用连续激光质谱对单颗粒矿物、光片样品进行微区４０Ａｒ／３９Ａｒ测年、坪年龄和等时线年龄研究。在光片上测定南极乔治王岛北海岸玄武岩等时线年龄（５２．３８±１．０５）Ｍａ和贵州绿豆岩年龄（２３９．１６±１４．１３）Ｍａ，两者与实际地质背景吻合。对两个中生代和太古代单颗粒黑云母进行连续激光质谱阶段升温４０Ａｒ／３９Ａｒ坪年龄谱测定，获得与常规法相一致的坪年龄谱  相似文献