Hydrothermal fluid flow associated to the extensional evolution of the Adriatic rifted margin: Insights from the pre- to post-rift sedimentary sequence (SE Switzerland,N ITALY)

This paper investigates the hydrothermal fluid circulation that was linked to the extensional evolution of the Adriatic rifted margin during the Jurassic opening of the Alpine Tethys. Remnants of this rifted margin are spectacularly preserved in SE Switzerland and N Italy. Five study areas were chosen ranging from the former proximal to the most distal part of the margin. We demonstrate an intimate link between Jurassic extensional tectonics and fluid activity affecting the pre- to early post-rift sedimentary sequences. Nature, composition and origin of fluids are constrained by a multidisciplinary approach based on field observations and including geochemical (O-C, Sr, He isotopes, U-Pb datings, fluid inclusion microthermometry) and petrological methods. Several fluid-related diagenetic products and processes such as dolomitization, veining, hydraulic brecciation, and silicification can be recognized. It appears that different paleogeographic settings and different stratigraphic levels document distinct phases of fluid activity. The fluids reached temperatures of up to 150°C near paleo-seafloor. They were enriched in ¹⁸O, had high ⁸⁷Sr/⁸⁶Sr and low ³He/⁴He ratios, documenting a strong interaction between seawater and a granitic basement. Many lines of evidence point to the occurrence of over-pressured fluids and long-lasting fluid circulation due to fault-valve mechanisms and high thermal gradients. Two main stages with different fluid chemistry can be recognized: (1) a carbonate-rich stage that developed during the stretching phases and was linked to high-angle normal faulting, and (2) a silica-rich stage occurring during late rift exhumation of crustal and mantle rocks in the distal domains in the presence of detachment faults and high thermal gradients. This paper provides, for the first time, a large and robust characterization of fluid–rock interactions occurring during rifting along an almost complete section across a magma-poor rifted margin.     

俯冲带深部流体:来自超高压变质锆石晶内结构和包裹物的证据

利用阴极发光和激光拉曼研究了大别山俯冲带超高压基性和长英质变质岩中的锆石。超高压变质增生锆石环带或新生锆石颗粒从不同角度反映了俯冲带地幔深度流体作用信息。其一,在超高压变质锆石生长域中存在微米级流体包裹体。由于其十分细小,组成往往难以测定。但是在变基性岩中检测到富CO2的负晶形包裹体。其二,在超高压锆石生长域中较普遍地发现富含挥发份的多硅白云母和磷灰石包裹体,其与典型的超高压变质矿物———柯石英稳定共生。副矿物研究表明,即使是在新鲜的弱退变质的榴辉岩中,富含挥发份的矿物相———磷灰石仍是含量较高的矿物,说明在俯冲带的深部(>100km),流体仍可以稳定地保存在高挥发份的矿物晶体格架中。其三,超高压变质增生锆石环带的边界呈蚕食状或港湾状,指示流体参与了锆石的变质生长过程,即通过流体与锆石之间的相互作用导致原有锆石的溶解和新生锆石的沉淀结晶。考虑到如此高的锆溶解度,认为在地幔俯冲深度,流体的成分复杂,并不是简单的富水体系,其化学组成与深熔融体相似,且赋存状态应为含水融体相。     

The relationship of mantle-derived fluids to gold metallogenesis in the Jiaodong Peninsula: Evidence from D–O–C–S isotope systematics

The largest gold district in China is the Jiaodong Peninsula, where three types of gold deposits are recognized: quartz vein, fracture-altered and breccia types. The first two developed along a group of NE-trending faults and are hosted by granitic intrusions, dated at 160 to 150 Ma (biotite granite) and 130 to 126 Ma (granodiorite), and by metamorphic rocks of the Precambrian crystalline basement. The breccia-type gold system is mainly located around the northern margin of the Jiaolai Cretaceous basin, where mineralisation is controlled by both detachment fractures and NE-trending faults. This study is based on stable isotope determinations from ten gold deposits, including Linglong, Jiaojia, Sanshandao, Cangshang, Wang'ershan, Dayigezhuang, Denggezhuang, Pengjiakuang, Fayunkuang and Dazhuangzi, as well as the Linglong Jurassic biotite granite, Guojialing Cretaceous granodiorite and Archean gneiss. The stable isotope systematics reflect the style of the three types of gold deposits, but also show that they belong to the same metallogenic system, in which the hydrothermal fluids were derived from a mantle fluid reservoir and mixed with crustal fluids. The ore-forming age is later than both the Jurassic biotite granite and Cretaceous granodiotite, but overlaps with the 121 to 114 Ma ages of lamprophyre and diabase dykes. The hydrothermal fluids that were responsible for both gold mineralisation and the retrograde alteration of the diabase and lamprophyre dykes are similar, and represent a CO₂ and potassium-rich system. This fluid system is interpreted to be the consequence of Cretaceous lithospheric thinning, asthenospheric upwelling and mantle degassing in Eastern China.     

Origin of Ore-forming Fluids Responsible for Gold Mineralization of the Pongkor Au-Ag Deposit, West Java, Indonesia: Evidence from Mineralogic, Fluid Inclusion Microthermometry and Stable Isotope Study of the Ciurug–Cikoret Veins

The Pongkor gold–silver mine is situated at the northeastern flank of the Bayah dome, which is a product of volcanism in the Sunda–Banda Arc. The hydrothermal alteration minerals in the Ciurug–Cikoret area are typical of those formed from acid to near‐neutral pH thermal waters. On the surface, illite/smectite mixed layer mineral (I/Sm), smectite and kaolinite, and spotting illite, I/Sm and K‐feldspar alteration occur at the top of the mineralized zone. Silicification, K‐feldspar and I/Sm zones are commonly formed in the wall rock, and gradually grade outwards into a propylitic zone. The mineralization of precious metal ore zone is constrained by fluid temperatures between 180 and 220°C, and with low salinity (<0.2 wt% NaCl equivalent) and boiling condition. The minimum depth of vein formation below the paleo‐water table is approximately 90–130 m for the hydrostatic column. Hydrogen and oxygen isotope data for quartz and calcite show relatively homogeneous fluid composition (?53 to ?68‰δD and ?5.7 to +0.3‰δ¹⁸O H₂O). There is no specific trend in the data with respect to the mineralization stages and elevation, which suggests that the ore‐forming fluids did not significantly change spatially during the vein formation. The stable isotope data indicate mixing between the hydrothermal fluids and meteoric water and interaction between the hydrothermal fluids and the host rock.     

稀有气体同位素地球化学研究的某些进展

稀有气体的化学惰性使其在示踪成矿流体方面具有明显的优越性,其与碳、氢、氧、硫、锶、钕、铅同位素方法,以及卤素方法等结合使用,不但可以避免单一方法的片面性,还可以相互补充,相互印证,更好地示踪成矿流体的来源与演化,进而探讨矿床的成矿机制。本文归纳了近年来稀有气体同位素与其他同位素体系联合应用的研究进展,及其存在的问题和发展趋势。     

新疆阿勒泰乌拉斯沟铅锌铜矿床的富CO_2流体及其地质意义

乌拉斯沟铅锌铜矿床位于新疆阿尔泰南缘克兰火山–沉积盆地。本矿床分为铜、铅–锌两个矿化带,矿体赋存在下泥盆统康布铁堡组上亚组,容矿岩石为大理岩、绿泥石英片岩等。矿床内角砾状铅锌矿石反映了早期海相沉积成矿作用,矿床变形变质特征明显,其矿化石英脉可分为两个阶段:早阶段顺层石英脉和晚阶段切层硫化物石英脉。石英脉中流体包裹体分为富CO_2包裹体、碳质流体包裹体和部分水溶液包裹体,含子晶包裹体。显微测温结果显示,早阶段石英脉中富CO_2包裹体,CO_2相的三相点温度(Tm,CO_2)范围在–62.3~–58.5℃,CO_2笼合物熔化温度(Tm,clath)为0.5~7.5℃,部分均一温度(Th,CO_2)集中在5.0~21.0℃,均一温度(Th,total)集中在285~378℃,所计算的盐度变化于4.9%~15.1%Na Cleqv之间,密度为0.84~0.97 g/cm~3,最低捕获压力为260~360 MPa。晚阶段石英脉中,富CO_2包裹体的CO_2三相点的温度(Tm,CO_2)为–61.9~–56.9℃,T_(m,clath)为0.4~9.5℃,Th,CO_2为9.0~28.0℃,Th,total范围为242~389℃,盐度分布于1.0%~15.5%Na Cleqv之间,密度为0.55~0.98 g/cm~3,最低捕获压力范围为180~370 MPa。激光拉曼探针测试显示包裹体除含CO_2外,还含有不定量的CH4和N2。铜矿化石英脉的流体以富CO_2为特征,为中高温、低盐度、中低密度的H_2O-NaCl-CO_2±CH_4±N_2变质流体,与造山–变质成因有关。     

大陆地幔研究现状

本文主要介绍大陆地幔岩石圈的年龄、大陆地幔演化和地幔流体等三个近年来引人注目的问题。地幔捕虏体的年龄范围２００～３４００Ｍａ，一般认为它可以代表地幔的年龄。澳大利亚二辉橄榄岩捕虏体的Ｐｂ－ｐｂ年龄为２０００～２５００Ｍａ，南非Ｖｉｃｔｏｒ岩管的捕虏体为１７００～２４００Ｍａ。橄榄岩型金刚石的石榴石包裹体Ｓｍ－Ｎｄ年龄为３２００～３３００Ｍａ，榴辉岩型金刚石的年龄为１２００～１５００Ｍａ。这些数值可与橄榄岩及榴辉岩捕虏体的全岩年龄数据相对应。太古代岩石圈地幔以南非为代表，经历了从地壳物质提取的亏损过程到与软流圈反应和与深部热点物质作用的富集过程。以美国西部为代表的元古代岩石圈地幔则经历了元古－显生宙的俯冲作用、地体增生过程以及与热点反应的作用。以澳大利亚东部为代表的显生宙岩石圈地幔经历了元古代的部分熔融、显生宙的俯冲或与ＤＵＰＡＬ的反应以及具ＤＭＭ特征的软流圈的上隆。钾质熔体、碳酸盐熔体、Ｈ＿２、ＣＨ＿４、Ｎ＿２Ｏ、Ｎ、ＣＯ、ＣＯ＿２、Ｓ、Ｆ、Ｃｌ等都是地幔流体的主要组分，它们的类型与所处的深度和氧逸度有关。     

兰坪盆地西缘沉积岩容矿脉状Cu-Ag(±Pb-Zn)多金属矿床成矿流体特征

兰坪盆地西部发育大量沉积岩容矿的Cu-Ag-Pb-Zn多金属矿床,矿体的分布受逆冲推覆系统控制。逆冲推覆系统根部带主要发育脉状Cu-Ag(Mo)矿床(包括金满Cu-Ag、连城Cu-Mo及一系列脉状Cu矿床);前锋带主要发育Pb-Zn-Ag(±Cu)矿床(包括白秧坪Pb-Zn-Ag-Cu多金属矿集区及一系列小型的Pb-Zn矿床)。文章系统分析了盆地西缘Cu-Ag(±Pb-Zn)多金属矿床流体包裹体及C、H、O同位素特征进行了根部带Cu和前锋带Pb-Zn矿床成矿流体的对比研究,探讨了盆地西缘Cu-Ag(±Pb-Zn)多金属矿床成矿流体的性质、来源及演化。研究表明,根部带的CuAg(Mo)多金属矿床成矿流体主要为与围岩充分交换的深循环大气降水,具有富CO2、中高温(集中在280~340℃)、中低盐度w(Na Cleq)(1%~4%)的特点;前锋带Pb-Zn-Ag(±Cu)多金属矿床成矿流体则主要为源于大气降水的盆地卤水,具有贫CO2、中低温(集中在160~240℃)、中高盐度w(Na Cleq)(集中于22.0%~24.0%)的特点。     

湖南瑶岗仙钨矿床成矿流体演化特征研究

瑶岗仙矿床位于湖南省郴州市瑶岗仙镇,是世界著名的钨矿床。近几年,随着云英岩析离体的发现,对于成矿流体的演化过程有了新的认识。文章通过对瑶岗仙石英脉型黑钨矿矿床的中粒碱长花岗岩、云英岩析离体和石英脉3个阶段地质体的石英中的流体包裹体进行显微测温和激光拉曼光谱分析,并对云英岩析离体中的熔流包裹体进行加热熔化实验,初步证明了瑶岗仙矿床石英脉型黑钨矿阶段成矿流体的演化是由花岗质岩浆→浆液过渡态岩浆→岩浆热液的一个完整连续的过程,而且成矿流体以富含挥发分为特征。并结合地质现象,提出浆液过渡态流体与成矿作用具有直接联系。     

改进的经验正交函数分析方法及其效果验证

基于中国站点网气候资料,简要介绍了经验正交函数(empirical orthogonal function,EOF)与改进的经验正交函数(adjusted EOF,AEOF)分析方法的关系,给出了验证其分析效果的方案;并将EOF、AEOF分析方法应用于中国160站60 a(1951—2010年)夏季气温距平场序列的分析。结果表明:AEOF分析方法前6个模态的模方拟合率和累积模方拟合率均高于EOF分析方法的相应量;AEOF分析方法前3个模态的典型场对夏季气温距平场序列的模方场的拟合效果明显优于EOF分析方法。由此论证了EOF分析方法中资料均匀化订正的必要性,验证了实际分析中AEOF分析方法的较优效果。