新疆柯坪地区志留系柯坪塔格组的遗迹化石   总被引：2，自引：0，他引：2  

白忠凯  胡斌  齐永安  张国成 《地质学报》2008,82(9):1161-1168

通过对柯坪地区剖面志留系的研究,在柯坪塔格组中已识别出遗迹化石15属20种,它们是：Asterichnus lawrencensis,Cochlichnus anguineus, Cruziana ichnosp., Cruziana qinlingensis, Cruziana rouaulti, Diplichnites bipartibilis,Gordia molassica, Helminthopsis abeli, Helminthopsis isp., Lockeia siliquaria ,Monocraterion cf. teataculatum, Palaeophycus tubularis, Planolites isp.,Planolites montanus, Planolites punctatus, Rusophycus ramellensis,?Scolicia ichnosp., Sagittichnus lincki,Spirophycus bicornis,Taenidium cameronensis。根据这些遗迹化石的组成、产状、分布规律及其围岩的沉积特征,可以划分为2种不同沉积环境条件下的遗迹组合,即(1)Helminthopsis-Gordia遗迹组合, 主要组成分子有Asterichnus, Diplichnites,Gorida, Helminthopsis, Planolites, Rusophycus,?Scolicia和Spirophycus,等,被解释形成于低能的滨外远岸浅海陆棚环境;(2)Cruziana-Rusophycus遗迹组合,常见组成分子有Cochlichnus,Cruziana, Lockeia, Palaeophycus,Rusophycus, Monocraterion,Sagittichnus,和Taenidium等,解释它们形成于滨外近岸浅海陆棚环境。  相似文献   

Carbonate xenoliths in La Palma: Carbonatite or alteration product?     

Attila Demény  Ramón Casillas  Julio de La Nuez  Géza Nagy 《Chemie der Erde / Geochemistry》2008,68(4):369-381

Carbonate xenoliths containing olivine and rimmed by kaersutitic amphibole were collected in basaltic rocks of the Basal Complex of La Palma. The mineralogical composition and microscopic appearance may suggest a relationship with carbonatites in general, thus a major element, trace element and stable isotope study was conducted to investigate the origin of the carbonate formation. Based on electron microprobe analyses, the carbonate is calcite with up to 6.3 wt% MgO and 7.2 wt% SiO₂. The elevated SiO₂ content may suggest a melt origin for the carbonate. However, the C and O isotope compositions of the carbonate xenoliths (δ¹³C and δ¹⁸O around −1‰ and 13‰, respectively) are similar to those of calcite veins and amygdales in basaltic rocks of the Basal Complexes of La Palma and Fuerteventura and are interpreted as produced by fluid degassing and metasomatism by CO₂-H₂O fluid derived from mobilization of sedimentary material. Trace element contents determined by laser-ablation ICP-MS analyses support the assumed origin, thus, the relationship with carbonatitic melts can be excluded. Based on trace element compositions, the amphibole surrounding the xenoliths is not related genetically to the carbonate. The elevated SiO₂ content of the calcite can be attributed to submicron relics of pyroxene, thus, the use of this feature as an evidence for melt origin is questionable.  相似文献   

Trace element geochemistry by laser ablation ICP-MS of micas associated with Ta mineralization in the Tanco pegmatite,Manitoba, Canada   总被引：3，自引：0，他引：3  

Marieke Van Lichtervelde  Michel Grégoire  Robert L. Linnen  Didier Béziat  Stefano Salvi 《Contributions to Mineralogy and Petrology》2008,155(6):791-806

In the Tanco pegmatite, one of the world’s major Ta deposits, tantalum mineralization shows a complexity that reflects the complex petrogenesis of its host pegmatite. Micas are common in most of the pegmatite units and are intimately associated with the successive stages of Ta mineralization, from the wall zone to the central zones where micaceous replacement is pervasive. Different generations of micas, both primary and secondary, associated with Ta oxides, were selected for electron microprobe and laser ablation ICP-MS investigation. Their chemical trends are used to constrain the magmatic versus hydrothermal processes that played a role in their crystallization and their associated Ta mineralization. Micas range from dioctahedral muscovite to trioctahedral lepidolite through Al↔Li substitution. Unexpectedly, the most evolved compositions (low K/Rb ratios and high Li contents) occur in the wall zone; they are interpreted to reflect nonequilibrium crystallization from an undercooled melt, with or without boundary layer effects. In the central zones, the fine-grained mica–quartz assemblage hosts some coarser-grained Li-muscovite, which has the highest Ta contents (up to 400 ppm). These Li–F–a-rich micas are interpreted to originate from a magmatic metasomatic event, which was also at the origin of the MQM-style Ta mineralization at Tanco. However, the Li–Ta-poor, muscovite end-member compositions of fine-grained alteration micas suggest crystallization from an aqueous fluid, during a metasomatic (hydrothermal) event involving late pegmatitic fluids. The low Ta concentrations (around 50 ppm) of this fine-grained muscovite suggest that this fluid transported at least small amounts of Ta.  相似文献   

A micro-scale investigation of melt production and extraction in the upper mantle based on silicate melt pockets in ultramafic xenoliths from the Bakony–Balaton Highland Volcanic Field (Western Hungary)     

Enikő Bali  Alberto Zanetti  Csaba Szabó  David W. Peate  Tod E. Waight 《Contributions to Mineralogy and Petrology》2008,155(2):165-179

Mantle xenoliths in Neogene alkali basalts of the Bakony–Balaton Highland Volcanic Field (Western Hungary) frequently have melt pockets that contain silicate minerals, glass, and often carbonate globules. Textural, geochemical and thermobarometric data indicate that the melt pockets formed at relatively high pressure through breakdown of mainly amphibole as a result of temperature increases accompanied, in most cases, by the influx of external metasomatic agents. New elemental and Sr–Nd–Pb isotope data show that in several xenoliths the external agent was either a LIL-enriched aqueous fluid or a CO₂-rich fluid, whereas in other xenoliths the melt pockets were additionally enriched in LREE and sometimes HFSE, suggesting metasomatism by a silicate melt. The compositional character of the external agents might have been inherited by melting of a hydrated and probably carbonated deeper lithospheric component, which itself was metasomatized by melts with significant slab-derived components. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

Geochemical fingerprinting of oceanic basalts with applications to ophiolite classification and the search for Archean oceanic crust   总被引：61，自引：0，他引：61  

Julian A. Pearce   《Lithos》2008,100(1-4):14-48

Two geochemical proxies are particularly important for the identification and classification of oceanic basalts: the Th–Nb proxy for crustal input and hence for demonstrating an oceanic, non-subduction setting; and the Ti–Yb proxy for melting depth and hence for indicating mantle temperature and thickness of the conductive lithosphere. For the Th–Nb proxy, a Th/Yb–Nb/Yb projection demonstrates that almost all oceanic basalts lie within a diagonal MORB–OIB array with a principal axis of dispersion along the array. However, basalts erupted at continental margins and in subduction zones are commonly displaced above the MORB–OIB array and/or belong to suites with principal dispersion axes which are oblique to the array. Modelling of magma–crust interaction quantifies the sensitivity of the Th–Nb proxy to process and to magma and crustal compositions. For the Ti–Yb proxy, the equivalent Ti/Yb–Nb/Yb projection features a discriminant boundary between low Ti/Yb MORB and high Ti/Yb OIB that runs almost parallel to the Nb/Yb axis, reflecting the fact that OIB originate by melting beneath thicker lithosphere and hence by less melting and with residual garnet. In the case of volcanic-rifted margins and oceanic plume–ridge interactions (PRI), where hot mantle flows toward progressively thinner lithosphere (often becoming more depleted in the process), basalts follow diagonal trends from the OIB to the MORB field. Modelling of mantle melting quantifies the sensitivity of the Ti–Nb proxy to mantle potential temperature and lithospheric thickness and hence defines the petrogenetic basis by which magmas plot in the OIB or MORB fields. Oceanic plateau basalts lie mostly in the centre of the MORB part of that field, reflecting a high degree of melting of fertile mantle. Application of the proxies to some examples of MORB ophiolites helps them to be further classified as C (contaminated)-MORB, N (normal)-MORB, E (enriched)-MORB and P (plume)-MORB ophiolites, which may add a useful dimension to ophiolite classification. In the Archean, the hotter magmas, higher crustal geotherms and higher Th contents of contaminants all result in widespread crustal input that is easy to detect geochemically with the Th–Nb proxy. Application of this proxy to Archean greenstones demonstrates that almost all exhibit a crustal component even when reputedly oceanic. This indicates, either that some interpretations need to be re-examined or that intra-oceanic crustal input is important in the Archean making the proxy less effective in distinguishing oceanic from continental settings. The Ti–Yb proxy is not effective for fingerprinting Archean settings because higher mantle potential temperatures mean that lithospheric thickness is no longer the critical variable in determining the presence or absence of residual garnet.  相似文献   

Metasomatic interactions between slab-derived melts and depleted mantle: Insights from xenoliths within Monglo adakite (Luzon arc, Philippines)   总被引：1，自引：0，他引：1  

M. Gregoire  S. Jego  R.C. Maury  M. Polve  B. Payot  R.A. Tamayo Jr.  G.P. Yumul Jr.   《Lithos》2008,103(3-4):415-430

The Monglo adakite contains mafic and ultramafic xenoliths, which probably originated from the mantle section of an Early Cretaceous supra-subduction zone ophiolitic complex located within the Luzon arc crust. Spinel-bearing dunites are dominant among this xenolith collection and display evidence for three episodes of subduction-related melt percolation. The first one is evidenced by an undeformed clinopyroxene characterized by convex-upwards REE pattern. This clinopyroxene crystallized from a calc-alkaline basaltic magma, likely formed in the Cretaceous supra-subduction setting of the ophiolite. Then, two metasomatic events, evidenced by orthopyroxene-rich and amphibole-rich secondary parageneses, respectively, affected most of the spinel dunites. The opx-rich paragenesis is related to the circulation within the dunitic upper mantle of hydrous slab-derived melts similar to those affecting the mantle peridotite xenoliths from Papua New Guinea and Kamchatka. Finally the amphibole-rich veins are related to the interaction between the studied dunite xenoliths and the host adakite or an adakitic melt similar to it.  相似文献   

滇西沧源铅锌多金属矿集区成矿地球化学特征   总被引：2，自引：1，他引：1  

肖晓牛  喻学惠  杨贵来  杨伟光  莫宣学  曾普胜 《岩石学报》2008,24(3)

滇西沧源铅锌多金属矿集区位于中缅边境的金腊-金厂一带,是云南省地矿资源股份有限公司新近开发的一个资源产地.本文重点提供了流体包裹体中稀土微量元素和矿石的S、Pb同位素的分析结果,并对成矿流体性质,成矿物质来源等进行了讨论.研究表明,本区流体包裹体中∑BEE变化较大,在0.371～212.1×10-9之间.反映轻重稀土分馏程度的LREE/HREE比值和(La/Yb)N比值变化也比较大,分别落在1.23～31.47和2.87～505之间.矿石的硫同位素除一个重晶石的δ34S偏高,达20.8～22.1‰,其它硫化物的δ34S均落在-0.6～5.1‰范围内,具幔源硫值特征.矿石的铅同位素208Pb/204Pb、207Pb/204Pb和206Ph/204Pb分别变化在38.621～38.993,15.584～15.738和18.568～18.800之间,不同矿段、不同硫化物矿物(方铅矿、闪锌矿、黄铁矿、辉锑矿)之间,Pb同位素组成范围非常相近,表明研究区各矿段,铅的来源和成因是均一的、相同的,而且具有造山带Pb同位素特征.结合区域成矿地质背景及流体包裹体c、H、0同位素研究结果,推测本区成矿流体是以浅部流体为主,并有深源流体参与的一种混合流体.矿石S、Pb同位素组成表明,成矿物质也具有壳幔混合源的特征.  相似文献   

Spatial variability of heavy metals in soils across a valley plain in Southeastern China   总被引：1，自引：0，他引：1  

L. Wang  J. Wu 《Environmental Geology》2008,55(6):1207-1217

An investigation was carried out to survey the magnitude and spatial distribution of heavy metals, as well as their relation with soil series, in a valley plain in Southeastern China. Soil was sampled at 159 sites by combining a squared grid and nested sampling strategies along the transect perpendicular to the Qujiang River in Zhejiang Province, China. Total concentrations of six metals, namely Cu, Fe, Mn, Ni, Pb and Zn, were measured. Classical statistics and geostatistics were used to quantify their spatial characteristics. There was a considerable variation in many of these parameters. The total concentrations ranged from 6.8 to 29.3 mg kg⁻¹ for Cu, 6,784 to 18,678 mg kg⁻¹ for Fe, 94 to 385 mg kg⁻¹ for Mn, 6.1 to 20.3 mg kg⁻¹ for Ni, 25.0 to 49.5 mg kg⁻¹ for Pb, and 12 to 160 mg kg⁻¹ for Zn. Pearson correlation coefficients among total metal concentrations and selected soil properties showed a number of strong associations. By virtue of analysis of variance, a predominant influence of soil series on the spatial variability of metal concentrations was observed. All metals were spatially correlated. The semivariograms of Cu, Fe, Mn, Ni and Zn were dominated by short range correlation (600 or 700 m), and that of Pb by long range (1200 m). Block kriging maps of total metal concentrations and soil properties showed strip distributions, perpendicular to the river, in the manner similar to the soil series. Principal component analysis was run to identify common distribution patterns of heavy metals and soil properties. These results illustrate that soil series information of valley plain may be useful for developing management zones for site-specific agriculture.  相似文献   

Heavy metal pollution assessment in various industries of Pakistan   总被引：1，自引：0，他引：1  

Wajid Rehman  Akif Zeb  Nayyara Noor  Mohsan Nawaz 《Environmental Geology》2008,55(2):353-358

Water pollution is a source of danger to the health of people living in developing countries such as Pakistan. The main industries located at various industrial zones of Pakistan cause water pollution, which ultimately result in various diseases. The aim of the present study was to study the concentrations of essential and toxic metals (Na, K, Cu, Zn, Fe, Ca, Pb and As) in the drained water of three main industrial estates of Pakistan, i.e., Industrial Estate No. 1 Peshawar, Small Industrial Estate No. 2 Gujranwala, Industrial Estate Hattar Haripur, and in Warsak Canal (industrially pure water) with the help of atomic absorption spectroscopy and flame emission spectroscopy. The study showed high Pb and As levels originating from industries. The concentrations of Pb and As ranged from 0.04 to 0.942 mg/L in all the samples. These have been extensively used for irrigation since the last five decades. The elevated concentrations of heavy metals are continuously entering into the food chain through agriculture leading to serious health hazards and a threat to the sustainability of local ecosystem.  相似文献   

安徽铜陵冬瓜山铜金矿床流体包裹体微量元素地球化学特征及其地质意义   总被引：9，自引：3，他引：6  

徐晓春  陆三明  谢巧勤  楼金伟  褚平利 《岩石学报》2008,24(8)

安徽铜陵冬瓜山铜金矿床是狮子山矿田中埋藏深度和地质储量最大的矿床,同时发育层控矽卡岩型和斑岩型矿体.该矿床流体成矿从早期到晚期经历了多个矿化阶段.本文选取了钾长石化阶段、矽卡岩化阶段、早石英硫化物阶段和晚石英硫化物阶段矿石中石英的原生流体包裹体进行了ICP-MS分析,结果表明,各成矿阶段石英流体包裹体微量元素的陆壳标准化分布曲线具有较好的一致性,显示成矿流体具有统一的来源和演化;流体包裹体的REE配分曲线与岩浆岩的稀土元素配分曲线相似,均为平缓右倾型,轻稀土明显富集,LREE/HREE比值与岩浆岩接近,显示成矿热液具有深部岩浆来源的特征.流体包裹体微量元素的直接分析显示成矿流体为矿质富集的热液流体,且各成矿阶段热液流体中的成矿元素含量高低的变化与相应阶段的矿化强度及矿石品位高低变化相一致,早石英硫化物阶段是矿质集中富集的最佳阶段,至晚石英硫化物阶段可能有浅部热液流体的混入.  相似文献