Origin of Listwanite in the Luobusa Ophiolite, Tibet, Implications for Chromite Stability in Hydrothermal Systems   总被引：1，自引：0，他引：1  

ZHANG Lan  YANG Jingsui  Paul T. ROBINSON  XIONG Fahui  CHEN Yanhong  LAI Shengmin  CHEN Mei 《《地质学报》英文版》2015,89(2):402-417

Listwanite from the Luobusa ophiolite,Tibet,forms a narrow,discontinuous band along the eastern part of the southern boundary fault. We undertook a detailed petrographic and geochemical study to understand the mineral transformation processes and the behaviour of major and trace elements during listwanite formation. Three alteration zones characterized by distinct mineral components and texture are recognized and,in order of increasing degree of alteration,these are: zoneIII is rich in serpentine minerals; zoneII is rich in talc and carbonates; and zoneI is mainly composed of carbonates and quartz. Geochemical data for the three alteration zones show significant modification of some major and trace elements in the protolith,although some oxides show linear correlations with Mg O. Gold mineralization is recognized in the Luobusa listwanite and may signify an important target for future mineral exploration. Gold enrichment occurs in both zoneI and zoneIIand is up to 0.91 g/t in one sample from zoneI. We show that CO2-rich hydrothermal fluids can modify both the occurrence and composition of chromite grains,indicating some degree of chromite mobility. Low-Cr anhedral grains are more easily altered than high-Cr varieties. The compositions of chromite and olivine grains in the listwanite suggest a dunite protolith.  相似文献   

华北陆块南缘郁山铝土矿矿物组成研究          下载免费PDF全文

焦赞超  梁会娟  张筝  刘百顺  李中明  王庆飞  董卫东 《地质找矿论丛》2015,30(4):480-491

郁山铝土矿床是2006年河南省地质调查院在豫西新安县发现的一个大型隐伏铝土矿矿床。文章通过利用显微镜、X衍射、扫描电镜、电子探针、红外光谱、热重等手段分析发现,郁山铝土矿中的矿物组成有:铝矿物,黏土矿物,铁矿物,钛矿物,非晶质,其它微量矿物(锆石、电气石、硫磷铝锶矿、明矾石、斜长石、钾长石、石英、方解石)六大类。非晶质组分的存在是华北陆块南缘铝土矿研究中物质组分方面的一个突破,为华北陆块南缘铝土矿的物质来源,成矿过程以及物质成分变化研究提供了线索和证据。  相似文献   

http://www.sciencedirect.com/science/article/pii/S1674987114000413     

Dong Feng  Hongwen Deng  Zhan Zhou  Xiaopeng Gao  Longtao Cui 《地学前缘(英文版)》2015,6(4)

Braid-delta depositional systems are widely developed in most continental basins in China. Research indicates that, for different types of braid delta, the facies sequence and association, which are cr...  相似文献   

Subbottom acoustic and sedimentary records of past surface water–groundwater exchange through sinkhole lakes in south Georgia,U.S.A     

J.?A.?HyattEmail author  R.?Gilbert 《Environmental Geology》2004,46(1):32-46

Lake Balboa is a deep sinkhole lake in south Georgia. Subbottom acoustic profiling and long sediment cores reveal four stratigraphic units within >20 m of lacustrine fill above acoustically stratified and faulted Miocene/Pliocene overburden and basement Eocene limestone which hosts the Floridan Aquifer system (FAS). Fill consists of thin, rhythmically bedded, peaty sediments (Unit I), indicative of slow sedimentation in a shallow swamp until 13,110–12,680 cal BP, a mix of desiccated and over-consolidated clay and silty sand (Unit II) implying periodic subaerial exposure of the lake bed until 9470–9025 cal BP, and gyttja associated with a rapid 8 m rise in water level by 9120–9020 cal BP (Unit III), as well as an additional rise of 10 m to modern lake levels (Unit IV). Accumulation of nearly 4.5 m of low permeability gyttja, and higher lake levels have fundamentally changed exchange between surface water and groundwater, reducing by 40% or more the rate of vertical leakage to the FAS and increasing shallow aquifer discharge to the lake.  相似文献   

Nouvelles données sur le téphra de Sarliève et le téphra CF7, marqueurs chrono-stratigraphiques de Grande Limagne (Massif central,France)     

Didier Miallier  Serge Sanzelle  Thierry Pilleyre  Gérard Vernet  Sarah Brugière  Tohru Danhara 《Comptes Rendus Geoscience》2004,336(1):1-8

A trachytic tephra, discovered in the ancient lake of Sarliève, ‘Grande Limagne’, has been dated using the thermoluminescence technique. The obtained age, 16±4 ka ($\text{2}\text{σ}$), is older than that of the trachytic volcanoes of the Cha??ne des Puys, the ashes of which have already been locally recognised in the region. Its analysis confirms its originality. In the course of the comparisons made to search for its spring, it appears that the wide-dispersion tephra CF7, beforehand correlated by hypothesis to the Puy de Clierzou, probably originates from the Kilian crater or the Puy de Vasset. To cite this article: D. Miallier et al., C. R. Geoscience 336 (2004).  相似文献   

Processes affecting deposition of sediment in a small, morphologically complex lake     

Robert Gilbert  Scott Lamoureux 《Journal of Paleolimnology》2004,31(1):37-48

Devil Lake is morphologically complex as a result of Pleistocene glacial erosion of the Frontenac Axis of the Canadian Shield. In order to assess the processes causing highly variable sedimentation in the lake, we monitored currents, suspended sediment and temperature in the lake before and during autumn overturn in 2002. Strong summer thermal stratification (stability number to 0.11 s^–1 declining with the approach of overturn) was insufficient to prevent a dynamic response in the hypolimnion to wind forcing. Superimposed on a gradual increase in suspended sediment concentration in the last weeks of stratification from less than 2 g/l to about 30 g/l were shorter-term rises lasting up to several days. Associated with these events was an increase in particle size of the sediment from a mode of 40–50 to 150–200 m ascribed to flocculation from primary particles. These events culminated in rapid (<1 h) clearing of the water associated with strong, sustained winds over the lake, especially from the southwest. After overturn, the events were more frequent, and flocculation was unable to develop as well in the more vigorous circulation. However, currents in the hypolimnion occurred throughout the period before, during and after overturn with speed related to wind speed, but direction largely independent of wind direction. The results represent an approach to understanding the nature of sedimentary processes and thus to strengthening the use of sedimentary records as proxy in environmental and paleoenvironmental assessment.  相似文献   

A test of Sporormiella representation as a predictor of megaherbivore presence and abundance     

Diana Raper  Mark Bush 《Quaternary Research》2009,71(3):490-496

Spores of the dung fungus Sporormiella have been suggested to indicate the presence, perhaps also the abundance of past megaherbivore populations. Nonetheless, basic studies demonstrating a correlation between Sporormiella concentration in lacustrine sediments and modern herbivore abundance are lacking. This study of Sporormiella representation in grazed and ungrazed landscapes provides supporting evidence for the application of Sporormiella as an indicator of megaherbivore presence and abundance in ancient landscapes. However, Sporormiella representation is spatially sensitive to the distance from the dung source. In lakes where Sporomiella are abundant in shoreline sediments, they decline sharply with increasing distance from the lake edge. Although this study provides supporting evidence for the application of Sporormiella as a proxy for herbivore presence and abundance, independent proxies should be applied in conjunction with Sporormiella to control for changes in lake size.  相似文献   

Stratigraphy, depositional environments and level reconstruction of the last interglacial Lake Samra in the Dead Sea basin   总被引：1，自引：0，他引：1  

N. Waldmann  M. Stein  A. Starinsky 《Quaternary Research》2009,72(1):1-185

In this paper we describe the stratigraphy and sediments deposited in Lake Samra that occupied the Dead Sea basin between ∼ 135 and 75 ka. This information is combined with U/Th dating of primary aragonites in order to estimate a relative lake-level curve that serves as a regional paleohydrological monitor. The lake stood at an elevation of ∼ 340 m below mean sea level (MSL) during most of the last interglacial. This level is relatively higher than the average Holocene Dead Sea (∼ 400 ± 30 m below MSL). At ∼ 120 and ∼ 85 ka, Lake Samra rose to ∼ 320 m below MSL while it dropped to levels lower than ∼ 380 m below MSL at ∼ 135 and ∼ 75 ka, reflecting arid conditions in the drainage area. Lowstands are correlated with warm intervals in the Northern Hemisphere, while minor lake rises are probably related to cold episodes during MIS 5b and MIS 5d. Similar climate relationships are documented for the last glacial highstand Lake Lisan and the lowstand Holocene Dead Sea. Yet, the dominance of detrital calcites and precipitation of travertines in the Dead Sea basin during the last interglacial interval suggest intense pluvial conditions and possible contribution of southern sources of wetness to the region.  相似文献   

粉晶X射线衍射法在岩石学和矿物学研究中的应用   总被引：14，自引：7，他引：7  

庞小丽  刘晓晨  薛雍  江向锋  江超华 《岩矿测试》2009,28(5):452-456

X射线衍射是测定物质结构的主要分析手段,广泛应用于物理学、化学、医药学、金属学、材料学、工程技术学、地质学和矿物学。文章综述了粉晶X射线衍射法在造岩矿物、黏土矿物、岩组学、类质同象和结晶度的测定等领域发挥的重要作用。随着测量技术的发展,粉晶X射线衍射在矿物结晶过程中的研究、矿物表面研究、矿物定量相分析和矿物晶体结构测定方面均有新的应用。  相似文献   

冀南綦村岩体斑状黑云母角闪闪长岩的成因矿物学研究     

高新宇  张聚全  王一奇  孙天琦  赵改超  王琳萱  李亚琦  徐翠 《现代地质》2019,33(4):738-750

綦村岩体是冀南邯邢地区典型的中生代高镁闪长岩杂岩体,主要由斑状黑云母角闪闪长岩、角闪闪长岩、闪长岩、二长岩和少量辉长岩组成。对綦村斑状黑云母角闪闪长岩进行了较为详细的成因矿物学研究,探讨了其成因及其地质意义。研究发现,綦村斑状黑云母角闪闪长岩中的角闪石多为镁铝钙闪石和镁角闪石;黑云母主要为富镁黑云母;斜长石发育环带结构,核部以中长石和拉长石为主,边部多为更长石。角闪石矿物温压计估算结果显示,角闪石斑晶的形成温度为930~970 ℃,压力介于300~340 MPa之间,深度10~15 km,氧逸度为ΔNNO+0.1~+2.3,平衡熔融体中的水含量4.8%~5.5%;与黑云母平衡的角闪石形成温度为684~760 ℃,压力降低至42~61 MPa,熔体中水含量降至3.1%~4.3%,氧逸度为ΔNNO+0.7~+2.4。黑云母温度计和氧逸度计获得的结果与角闪石温压计估算结果一致。该结果表明,研究区高氧逸度的铁镁质岩浆在中地壳曾经驻留,并发生了以角闪石为主的结晶分异,富含挥发分的分异岩浆在后期快速侵位形成高镁闪长岩和矽卡岩型铁矿。  相似文献