Zircon U-Pb ages of granites at Changba and Huangzhuguan in western Qinling and implications for source nature

Mesozoic granitoids are widespread in the Qinling-Dabie-Sulu orogenic belt. Precise U-Pb dating on these granitoids can reveal the evolution of the continental collision orogen and thus provide information on the nature of magma sources. This study presents zircon LA-ICP-MS U-Pb dating and whole-rock geochemical analyses for two intrusions at Changba and Huangzhuguan in western Qinling. Zircon U-Pb ages for central and marginal phases of the Huangzhuguang intrusion are 214±1 Ma and 213±3 Ma, respectively. Zircons from the Changba intrusion yield a dominant cluster with an U-Pb age of 213±2 Ma. Collectively, these ages are younger than ages of 220 to 240 Ma for ultrahigh-pressure metamorphism due to the continental collision between the South China Block and the North China Block, corresponding to syn-exhumation magmatism. Some inherited zircons occur in the Changba intrusion, yielding a weighted mean of ²⁰⁶Pb/²³⁸U ages at 757±14 Ma. This indicates that the Changba intrusion has the crustal source of mid-Neoproterozoic ages and a tectonic affinity to the South China Block. Geochemically, the two intrusuons are both rich in LILE and LREE but depleted in HFSE and HREE, similar to arc-type igneous rocks. The Huangzhuguang intrusion exhibits linear correlations between SiO₂ and the other major oxides, implying chemical evolution from a cognate magma source. It contains mafic enclaves, suggesting possible mixing of felsic-mafic magmas. The Changba granite is rich in Si and K but poor in Fe and Mg as well as has a high value of Fe*, suggesting strong differentiation of granitic magma. Therefore, the two intrusions were derived from the Late Triassic anatexis of the continental crust of different compositions in the northern margin of South China Block. This process may be coupled with exhumation of the subducted continental crust in the stage of late collision.     

虎林盆地虎1井烃源岩评价及油源对比

对虎林盆地虎1井各层段泥岩地球化学指标进行评价,表明虎1井主要烃源岩层为虎林组一段和白垩系下云山组,两段源岩均为好烃源岩,源岩处于低熟到成熟阶段,具有较大的生烃潜力。通过原油与源岩的饱和烃色谱参数及生标化合物对比,发现虎1井原油为成熟原油,并具有陆相高等植物贡献生油的特点,与虎一段底部成熟烃源岩有较强的相似性,认为该井原油即来自于虎一段源岩。     

扬子地台北缘中段中上元古界中金、银矿床稳定同位素地球化学研究

本文系统地研究了扬子地台北缘中段中上元古界中金银矿床的硫、铅、碳、氢、氧同位素组成。研究表明:银洞沟Au-Ag-Pb-Zn矿床、许家坡Au-Ag-Te矿床和白岩沟Au矿床的成矿物质具深源特征,成矿流体为混有少量大气水和岩浆水的变质流体;东沟坝Au-Ag-Pb-Zn重晶石型矿床成矿物质及成矿流体皆具多来源的特征。     

黄山逍遥溪地区第四纪沉积环境研究

根据对黄山逍遥溪剖面１７个样品的分析，得出下述见解：１粒度参数和ＣＭ图象反映，该处沉积物大都未经改造就进入新环境，反映近源沉积的多变的环境。２．Ｆｅ＾３＋／Ｆｅ＾２＋含量测定表明，该处第四纪期间最低年均气温并未低于０℃，因此不具备冰发育的条件，３、该剖面ＣａＯ的淋溶强于黄土发育区，氧化和的比值反映出多数情况下较高年均气温与多雨期一致，反之亦然。４．孢粉样品揭示中更新世至多经历过从温暖→干凉→湿热     

华南某些含锡斑岩的岩石化学与地球化学特征

华南某些含锡斑岩体的化学成分以富硅、贫钙、镁、铁、富碱为特征。其分异指数(DI)一般在90％以上,固结指数低于3,属张裂性花岗岩。根据闻广提出的含锡岩体b值在1～8之间,s值在79～84之间的看法,含锡斑岩的b值和s值均位于锡矿化区间。含锡斑岩体的微量元素以高氟、富铷、贫锶、贫钡为特征。铌钽比值近于1。稀土元素分析表明:∑REE含量较高,相对富集重稀土,铕出现显著负异常。初始锶同位素比值(~(86)Sr/~(87)Sr)_i等于0.711～0.716。说明含锡斑岩体的岩浆系由下部地壳物质重熔而成。     

沃溪金锑钨矿床矿化蚀变带地球化学特征

本文结合矿床地质背景和矿化作用特征。对矿化蚀变带的地球化学规律进行了比较详细的探讨。不同的矿化蚀变作用阶段,矿化蚀变带的常量元素和微量元素、特征元素对的含量比值都是有明显区别的。钨矿化阶段热液富集W、Ca、Mg、Be、Sr、Mo,矿化指示元素为Ca、Mo;金锑矿化阶段热液富集冬Au、Sb、As、Ag、Cd、Be等,矿化指示元素为As、Ag、Cd。为矿床成因及找矿勘探提供了重要依据和重要的标型特征。     

华南花岗岩风化壳中稀土的存在形态及迁移富集模式

本文从化学形态角度，确立了一个ＲＥ形态分析流程，得出风化壳中ＲＥ化学形态可分为活性态，Ｆｅ，Ａｌ共沉淀态及有机结合态３种，全风化层样品中ＲＥ多数以活性态为主，但平远Ｃ剖面ＲＥ却以有机结合态占大多数，活性态、有机结合态ＲＥ与粘土矿物关系密切，而Ｆｅ，Ａｌ共沉淀态的ＲＥ与粘土矿物关系不大，原岩溶出试验表明，ＲＥ在有机介质中的溶出量一般高于无机介质，ＲＥ最大可能是呈有机无机混配络离子迁移，迁移、富集过程是络合、水解、沉淀和吸附反应同时出现，反应受ｐＨ控制，本文初步建立了花岗岩风化壳中ＲＥ往下迁移、富集的模式。     

337铀矿床REE地球化学特征与成矿物质来源

337铀矿床产于贵东花岗岩体东端,含矿主岩为晚期补充侵入体γ_5~(2(3)B)花岗岩,其热液铀矿脉严格地受裂隙构造密集带控制。经REE地球化学研究表明:(1)电气石化自变质作用可以促使REE,特别是HREE向热液流体中转移;(2)热液铀矿脉中的REE对γ_5~(2(3)B)花岗岩既有继承性,又有演化性:(3)含铀热液流体中的REE同U一起呈含CO_3~(2-),F~-络合物形式迁移、分异和沉淀;(4)337铀矿床中的REE和其它成矿物质主要来源于γ_5~(2(3)B)花岗岩。     

潍北凹陷孔店组烃源岩生物标志物特征及地球化学意义

通过对潍北凹陷孔店组烃源岩有机质丰度、类型、成熟度及生物标志物的研究,发现孔店组烃源岩重排甾烷含量低,C27,C28和C29规则甾烷含量较多,C29甾烷的20S/(S R)和C29ββ/(ββ αα)比值分别在0.12～0.38和0.3～0.45之间;在萜类化合物中,奥利烷含量低,γ蜡烷与C30藿烷比值在0.1～0.37之间.研究结果表明孔店组烃源岩生源以高等植物为主,混有一定比例的藻类等低等水生生物,沉积环境为含盐度低的弱还原-弱氧化湖沼相,烃源岩有机质处于低熟-成熟阶段.