Zircon U–Pb and Hf isotopic study of gneissic rocks from the Chinese Altai: Progressive accretionary history in the early to middle Palaeozoic     

Min Sun  Chao Yuan  Wenjiao Xiao  Xiaoping Long  Xiaoping Xia  Guochun Zhao  Shoufa Lin  Fuyuan Wu  A. Kröner 《Chemical Geology》2008,247(3-4):352-383

Gneissic rocks in the Chinese Altai Mountains have been interpreted as either Paleozoic metasedimentary rocks or Precambrian basement. This study reports geochemical and geochronological data for banded paragneisses and associated gneissic granitoids collected along a NE–SW traverse in the northwestern Chinese Altai. Petrological and geochemical data suggest that the protoliths of the banded gneisses were possibly immature sediments with significant volcanic input and that the gneissic granitoids were derived from I-type granites formed in a subduction environment. Three types of morphological features can be recognized in zircons from the banded gneisses and are interpreted to correlate with different sources. Zircons from five samples of banded paragneiss cluster predominantly between 466 and 528 Ma, some give Neoproterozoic ages, and a few yield discordant Paleoproterozoic to Archean ages. Zircon Hf isotopic compositions indicate that both juvenile/mantle and crust materials were involved in the generation of the source rocks from which these zircons were derived. In contrast, zircons occur ubiquitously as elongated euhedral prismatic crystals in the four samples of the gneissic granitoids, and define single populations for each sample with mean ages between 380 and 453 Ma. The general absence of Precambrian inheritance and positive zircon ?Hf values for these granitoids suggest insignificant crustal contribution to the generation of the precursor magmas. Our data can be interpreted in terms of a progressive accretionary history in early to middle Palaeozoic times, and the Chinese Altai may possibly represent a magmatic arc built on a continental margin dominated by Neoproterozoic rocks.  相似文献   

Evolution of subcontinental lithospheric mantle beneath eastern China: Re–Os isotopic evidence from mantle xenoliths in Paleozoic kimberlites and Mesozoic basalts     

Hong-Fu Zhang  Steven L. Goldstein  Xin-Hua Zhou  Min Sun  Jian-Ping Zheng  Yue Cai 《Contributions to Mineralogy and Petrology》2008,155(3):271-293

The ages of subcontinental lithospheric mantle beneath the North China and South China cratons are less well-constrained than the overlying crust. We report Re–Os isotope systematics of mantle xenoliths entrained in Paleozoic kimberlites and Mesozoic basalts from eastern China. Peridotite xenoliths from the Fuxian and Mengyin Paleozoic diamondiferous kimberlites in the North China Craton give Archean Re depletion ages of 2.6–3.2 Ga and melt depletion ages of 2.9–3.4 Ga. No obvious differences in Re and Os abundances, Os isotopic ratios and model ages are observed between spinel-facies and garnet-facies peridotites from both kimberlite localities. The Re–Os isotopic data, together with the PGE concentrations, demonstrate that beneath the Archean continental crust of the eastern North China Craton, Archean lithospheric mantle of spinel- to diamond-facies existed without apparent compositional stratification during the Paleozoic. The Mesozoic and Cenozoic basalt-borne peridotite and pyroxenite xenoliths, on the other hand, show geochemical features indicating metasomatic enrichment, along with a large range of the Re–Os isotopic model ages from Proterozoic to Phanerozoic. These features indicate that lithospheric transformation or refertilization through melt-peridotite interaction could be the primary mechanism for compositional changes during the Phanerozoic, rather than delamination or thermal-mechanical erosion, despite the potential of these latter processes to play an important role for the loss of garnet-facies mantle. A fresh garnet lherzolite xenolith from the Yangtze Block has a Re depletion age of ∼1.04 Ga, much younger than overlying Archean crustal rocks but the same Re depletion ages as spinel lherzolite xenoliths from adjacent Mesozoic basalts, indicating Neoproterozoic resetting of the Re–Os system in the South China Craton.  相似文献   

塔里木西部地区古生代断裂活动的方式和机制   总被引：15，自引：2，他引：13       下载免费PDF全文

李曰俊  吴根耀  孟庆龙  师骏  冯晓军  郑民 《地质科学》2008,43(4):727-745

基于系统的地震剖面解释及其与塔中地区的对比,本文探讨了塔里木西部地区古生代断裂活动的方式和机制。玛东断裂带是一条宽阔的北东向盖层滑脱型褶皱冲断带,前展式向东南扩展,冲断作用发生在奥陶纪末。巴东断裂(吐土休克Ⅱ号断裂)为北西向基底卷入型冲断带,奥陶纪末和中二叠世末发生冲断。巴西断裂和塔参2井南断裂是海西期的正断层。塔里木古板块古生代的发育受邻侧的造山带演化制约,近东西向和北东向断裂奥陶纪末的冲断是继承基底构造发育的。塔中地区的近北西向断裂是晚寒武世的新生断裂,加里东运动可分为两幕:奥陶纪末的冲断(艾比湖运动)和晚志留-中泥盆世的冲断-走滑,后者向西明显减弱。塔里木西部的部分北西向断裂(如康西断裂)可归入塔中北西向断裂系。北东向的玛东断裂带是其西的向北(东)冲断的吐木休克断裂带与其东的向南偏东冲断的塔中8-1井——塔中5井断裂带之间的调节断层。  相似文献   

北疆阿尔泰南缘泥盆系浅变质碎屑沉积岩地球化学特征及其形成环境   总被引：12，自引：4，他引：8  

龙晓平  袁超  孙敏  肖文交  林寿发  王毓婧  蔡克大 《岩石学报》2008,24(4)

对于北疆阿尔泰地区泥盆纪所处的大地构造环境,目前仍旧存在不同观点。前人基于阿尔泰南缘泥盆纪火山岩地球化学研究,分别提出了活动大陆边缘和被动大陆边缘裂谷等不同构造观点。阿尔泰造山带南缘的泥盆纪浅变质碎屑沉积岩地球化学研究表明,该套浅变质碎屑沉积岩原岩主要为泥质或砂质沉积岩。尽管不同岩性样品主量元素含量不同,但其化学蚀变指数(CIA)小于75,成分变异指数(ICV)接近或小于1.0,斜长石蚀变指数(PIA)平均70,说明其源区物质比较新鲜,成熟度相对较低,化学风化作用较弱。同样,不同岩性样品微量元素含量差别较大,但表生过程中不活泼的微量元素比值却比较一致,轻稀土(LREE)中度富集(La_N/Yb_N=2.88～9.90),重稀土(HREE)比较平坦,并伴有明显的Eu负异常(Eu/Eu~*= 0.45～0.89)。绝大多数样品具有高的La/Sc(1～3)、La/Y(0.5～1)和Ti/Zr(10～35),以及较低的Sc/Cr(0.1～0.3)比值,类似于大陆岛弧相关环境碎屑沉积物。在La-Th-Sc和Th-Sc-Zr/10构造环境判别图解中,除一千枚岩样品外,其他所有样品均落入大陆岛弧区。以上地球化学特征明显不同于大洋岛弧和被动陆缘沉积物,说明该套浅变质碎屑沉积岩可能沉积于活动大陆边缘的大陆岛弧相关环境,为认识阿尔泰造山带泥盆纪岛弧增生构造演化过程提供了一个重要证据。  相似文献   

黑龙江省金厂金矿床J0矿体流体地球化学研究   总被引：7，自引：6，他引：1  

张宇  赖勇  卿敏  王艳忠  徐佳佳 《岩石学报》2008,24(5)

黑龙江省东宁县金厂金矿床是最新发现的特大型金矿床,目前探获黄金资源量86吨,它位于中亚造山带东端的吉黑成矿带,是与中生代中酸性岩浆活动有关的复杂成矿系统,矿化类型可能包括了斑岩型、爆破角砾岩型、浅成低温热液型.研究表明,高丽沟J0号矿体为爆破角砾岩型,热液成矿过程经历了早、中、晚3个阶段,分别形成以石英-黄铁矿、多金属硫化物-石英和碳酸盐为代表的矿物组合,中阶段矿物含自然金最多,次为早阶段矿物.初始成矿流体系统为高温、高盐度、高氧逸度、富CO2的岩浆热液;经减压沸腾,CO2等挥发分大量逸出,流体温度、盐度和氧逸度下降,导致大量金属硫化物及自然金快速沉淀;大气降水混入导致晚阶段流体低温、低盐度、贫CO2,对成矿贡献甚微.总体而言,成矿流体盐度高(11.70%～37.81%NaCl.eq),成矿作用发生在中-高温(238.3～425.7℃)的浅成环境(深633m～2736m).岩浆-流体成矿系统富CO2应发育于大陆碰撞造山带的伸展构造背景,而非大洋板块俯冲诱发的岩浆弧背景.  相似文献   

伊通盆地梁家地区奢岭组混源扇三角洲内幕结构   总被引：1，自引：0，他引：1  

石万忠  孔敏  宋志峰 《地球科学》2008,33(3):365-371

伊通盆地梁家地区(二号断层上盘)钻井揭示奢岭组是该区主要的油气富集层,目前研究结果认为奢岭组储集层是由两个方向的扇三角洲混合沉积形成,但由于资料有限,应用常规方法无法清楚地认识两个不同方向的物源混合沉积的扇三角洲的内幕特征以及这两个物源如何动态地控制着砂体的分布,影响了对该区油气储集层的深入认识.应用地震和地质资料,在波阻抗反演结果二次解释的基础,解析了这两个混合物源扇三角洲的内幕特征和演化特征,得出3个结论:(1)伊通盆地梁家地区奢岭组至少有4期扇三角洲沉积,每期扇三角洲的沉积范围由下向上逐渐扩大,反映了基准面逐渐下降的过程;(2)奢岭组的4期扇三角洲是由两个物源混合沉积形成,这4期扇三角洲逐渐由受从二号断层来的物源控制为主,变为由受从北东方向来的物源控制为主;(3)基于波阻抗体进行的砂层组解释和分析,能够清楚地分析扇三角洲沉积体的内幕结构,是应用波阻抗进行高分辨率地震分析和应用的一种新的分析方法.  相似文献   

岩矿显微组构对水银洞金矿成因的指示   总被引：1，自引：0，他引：1  

张敏  谢飞  谭月  张竹如 《矿物学报》2008,28(3)

黔西南水银洞金矿为产于上二叠统龙潭组中的超大型、高品位金矿床,矿床由多个金矿体组成.工业金矿体顺层产于龙潭组含煤地层所夹的玄武质、硅质、生物碎屑碳酸盐岩中.对水银洞金矿赋矿地层岩石以及矿石显微组构进行了研究,矿石中主要载金矿物为细粒黄铁矿,具再生边、粒内孔隙、铸模孔隙结构及镶边生物矿化构造、铸模式生物矿化构造,是一典型的具沉积一成岩组构.金矿化与硅化有密切的成因联系,金与SiO2来源于峨嵋山玄武岩的喷溢活动,主要金矿体更多显示与峨嵋山玄武岩准同生特征.矿床为沉积一成岩弱改造成囚金矿床.  相似文献   

A combined numerical tidal model for the Hangzhou Bay and Qiantang River   总被引：2，自引：0，他引：2  

Cao Deming  Fang Guohong 《海洋学报(英文版)》1989,8(4):485-496

-In order to avoid prescribing open boundary condition on the upstream side of the Hangzhou Bay, in numerical simulation of the tides and residual currents of the Bay, a 1-D model for the Qiantang River is connected to the 2-D model for the Hangzhou Bay. The harmonic constants of diurnal constituent [ (K1 O1)/2],semidiurnal constituent (M2) and shallow water constituent (M4) are obtained. The results produced by the combined model are in better agreement with the observed ones than those produced solely by the original 2-D model. The combined model gives much more reliable results for tide-induced residual water level and current.  相似文献   

秦山核电站邻近水域环境化学要素特征     

王正方  龚敏 《海洋学研究》1991,9(2):16-21

本文根据1989年4、7、10月和1990年1月(春、夏、秋、冬)秦山核电站邻近水域零点生态调查和水质监测结果的资料整理而成。经研究证明,该海域是河-海混合水域,盐度从小于3至12之间变化,受杭州湾的涌潮、风浪的影响,水体混合比较强烈,悬浮颗粒物质的含量比长江口高。由于该测区所处的海岸、海底地形,生态系统、径流输入以及水体交换状况不同,故其海洋学特征也不相同。  相似文献   

海水中234Th的超低水平液闪谱仪测定   总被引：2，自引：1，他引：2  

李鸿宾  黄奕普  陈敏  刘广山  邱雨生 《台湾海峡》2004,23(2):199-207

本文提出了利用超低水平液闪谱仪测定海水中234Th的方法.海水经氢氧化铁吸附共沉淀富集后,接着用阴离子交换和TBP/煤油萃取进行Th同位素的分离与纯化.对一系列测定条件进行了详细的研究,提出了测定海水中234Th的适宜程序,即在含有234Th和产额示踪剂230Th的纯化后的5mol/dm3HNO3溶液中加入TBP/煤油进行萃取,然后用0.1mol/dm3HNO3反萃取,后者是先用契伦柯夫计数法测量234Th(通过234mPa),后加入闪烁液Hisafe 3用α/β模式测量α放射体230Th.对于α和β放射体液闪谱仪的计数效率分别为100%和55.7%±2.7%.234Th的化学回收率和总探测效率分别为70%～80%和30%～45%.该法测定海水中的234Th快速、简便和高效.  相似文献