Fashion and phases of late Pleistocene aggradation and incision in the Alaknanda River Valley, western Himalaya, India

We study the aggradation and incision of the Alaknanda River Valley during the late Pleistocene and Holocene. The morphostratigraphy in the river valley at Deoprayag shows the active riverbed, a cut terrace, and a fill terrace. The sedimentary fabric of the fill terrace comprises four lithofacies representing 1) riverbed accretion, 2) locally derived debris fan, 3) the deposits of waning floods and 4) palaeoflood records. The sedimentation style, coupled with geochemical analysis and Optically Stimulated Luminescence (OSL) dating, indicate that this terrace formed in a drier climate and the river valley aggraded in two phases during 21–18 ka and 13–9 ka. During these periods, sediment supply was relatively higher. Incision began after 10 ka in response to a strengthened monsoon and aided by increase of the tectonic gradient. The cut terrace formed at ~ 5 ka during a phase of stable climate and tectonic quiescence. The palaeoflood records suggest wetter climate 200–300 yr ago when the floods originated in the upper catchment of the Higher Himalaya and in the relatively drier climate ~ 1.2 ka when locally derived sediments from the Lesser Himalaya dominated flood deposits. Maximum and minimum limits of bedrock incision rate at Deoprayag are 2.3 mm/a and 1.4 mm/a.     

铀(Ⅵ)分析中的分离富集技术

本文归纳总结了近10年来国内外铀分析中的分离富集方法.依据分离富集原理的不同,将其划分为浮选、毛细管电泳、吸附分离、萃取4类方法.着重讨论了它们的分离富集条件、吸附容量、富集倍数以及方法的检测限等主要参数,并对未来铀的分离富集技术进行了展望.     

Polyphase metamorphism in the eastern Carnic Alps (N Italy–S Austria): clay minerals and conodont Colour Alteration Index evidence

Thermal evolution of the Palaeozoic–Triassic sequences of the Carnic Alps has been characterized by b cell dimension and Kübler Index (illite “crystallinity”) of K-white micas (KI), árkai Index (AI) of chlorites, clay mineral assemblages and conodont Colour Alteration Index (CAI). Data indicate at least two metamorphic events, Variscan and Alpine. In the older event high anchizonal conditions predominated although epizonal conditions were reached over wide areas. It was characterized by low-intermediate pressure facies. The thermal peak was mainly due to an extensional regime during the Bashkirian. A younger thermal overprint generated by Alpine orogeny was of lower grade, reaching high diagenetic–anchizonal conditions characterized by high-pressure facies. Inverted metamorphic patterns are associated with middle to late Miocene thrusting. Hydrothermal alteration in the northern part of the region can be linked with emplacement of Oligocene plutons and high heat flow along the Periadratic lineament. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Alteration-weakening leading to localized deformation in a damage aureole adjacent to a dormant shear zone

Deformation adjacent to faults and shear zones is traditionally thought to correlate with slip. Inherited structures may control damage geometry, localizing fluid flow and deformation in a damage aureole around structures, even after displacement has ceased. In this paper we document a post-shearing anastomosing foliation and fracture network that developed to one side of the Mesoarchean Marmion Shear Zone. This fracture network hosts the low-grade, disseminated Hammond Reef gold deposit. The shear zone juxtaposed a greenstone belt against tonalite gneiss and was locked by an intrusion that was emplaced during the final stages of suturing. After cessation of activity, fluids channeled along fault- and intrusion-related fractures led to the pervasive sericitization of feldspars. Foliated zones resulted from flattening in the weaker sericite-rich tonalite during progressive alteration without any change in the regional NW-SE shortening direction. The anastomosing pattern may have been inherited from an earlier ductile fabric, but sericite alteration and flattening fabrics all formed post-shearing. Thus, the apparent foliated fracture network adjacent to the Marmion Shear Zone is a second-order effect of shear-related damage, distinct in time from shear activity, adjacent to an effectively dormant shear zone. This phenomenon has implications for understanding the relative timing of fault zone activity, alteration and (in this case) gold mineralization related to long-term fault zone permeability.     

论铁氧化物铜金型(IOCG)矿床地球化学岩相学填图新技术研发

在铁质苦橄岩—铁质安山岩、钛铁辉长岩—钛铁质闪长岩和二长岩—二长斑岩岩体附近,同岩浆侵入期脆韧性剪切带中构造岩相和热液角砾岩相,它们是铁氧化物铜金型(IOCG)矿床含矿岩相学类型。总体垂向蚀变分带为:上部为粘土化—绢云母化—赤铁矿蚀变带,中部钾质蚀变相带(电气石—铁质)+热液角砾岩化相带,下部钠质蚀变相(铁质)—热液角砾岩化带。围绕二长斑岩—二长闪长岩舌状侵入体形成电气石蚀变岩相带,属于汽成热液蚀变中心。大型—超大型IOCG矿床具有多期蚀变相系叠加特征,不同成因的热液角砾岩化相带发育、异时同位多期蚀变岩相叠加和汽成热液蚀变相发育等是寻找大型—超大型IOCG矿床标志。     

新疆延东斑岩铜矿床火山机构、容矿岩石及热液蚀变

延东斑岩铜矿床位于新疆东天山晚古生代大南湖岛弧中。延东矿区出露地层是石炭纪企鹅山组火山-沉积岩,我们研究提出延东矿区出露的火山-沉积岩以及浅成侵入岩为石炭纪火山喷发-岩浆侵入产物,并将其划分成两个旋回五个岩相:第一旋回包括溢流相(玄武岩和安山岩)、爆发相(集块角砾熔岩)和爆发-沉积相(凝灰岩);第二旋回包括次火山相(闪长玢岩和闪长岩)和浅成侵入相(斜长花岗斑岩)。容矿岩石是次火山相的闪长玢岩和闪长岩以及浅成侵入相的斜长花岗斑岩。闪长玢岩发育中性斑岩蚀变系统,包括内部的绢云母-绿泥石蚀变带和绿泥石-绢云母蚀变带和外围的青磐岩化带,其中绢云母-绿泥石蚀变带控制本区部分富矿体的形成和分布;斜长花岗斑岩发育酸性斑岩蚀变系统,从中心向外依次为黄铁绢英岩化带、强绢云母化带和弱绢云母化带,黄铁绢英岩化带控制本区部分富矿体的形成和分布。这两个蚀变系统以钾硅酸盐化蚀变不发育和绢云母化广泛发育为特点。     

安徽池州马头铜钼矿地质特征及蚀变分带

安徽池州马头铜钼矿是长江中下游成矿带中安庆—贵池矿集区内一个典型的铜钼矿床。通过野外地质祥查和系统的岩相学、矿相学工作,对该矿床的蚀变特征及分带进行了深入研究。识别出马头铜钼矿的蚀变类型主要有硅化、绢云母化、钾长石化,其次为黏土化、绿泥石化和碳酸盐化等。矿区围岩蚀变在空间上往往重叠,但具有一定的水平及垂向分带特征,自岩体深部至浅部、自内向外总体表现为面型石英钾长石化带、线型石英钾长石化带和石英绢云母化带。矿（化）体以脉状矿化为主,其中分布较广的石英脉带矿化主要产在石英绢云母化带中,以石英细（网）脉为主,受节理和裂隙控制;而品位较富的细脉浸染状矿化则主要产在面型钾长石化带中。通过研究认为,马头铜钼矿在成矿过程的早期阶段,由于高温、富钾和高pH值的热液流体作用,形成大面积的钾长石化,伴生与面型钾长石化有关的细脉、浸染状矿化;热液演化中期阶段,随着温度持续下降、K＋活度和流体pH值的降低,形成硅化、绢云母化等蚀变类型,并伴随范围较大的细脉-网脉状矿化;热液演化晚期阶段,主要形成碳酸盐化,而相应的矿化作用不显著。通过与部分典型斑岩型铜钼矿床的对比研究认为,马头铜钼矿在蚀变类型等方面与斑岩型铜钼矿大体相同,可归至斑岩型成矿体系。     

云南禄劝付腥田铁矿地质特征

通过对云南禄劝付腥田铁矿区的地质普查工作,发现了2个赤铁矿体、2个磁铁矿体和3个铁矿化点,铁矿体受控于中元古界美党组五段、三段,矿床成因为美党组高含铁质碎屑沉积再经后期热液改造的沉积变质型铁矿床.     

Petrography,mineralogy and geochemistry of Cretaceous sediment samples from western Khorat Plateau,Thailand, and considerations on their provenance

At Mo Hin Khao on the western flank of Khorat Plateau, Thailand, the Phra Wihan Formation reveals litharenite and sublitharenite with some subarkose and arkose. A cuesta in the eroded sedimentary sequence exhibits spectacular rock pillars of considerable geotourist potential. The rock sequence is high in silica (SiO₂ 67–98 wt%) and contains quartz, mica, magnetite, chert fragments and accessory minerals such as zircon and tourmaline and amphibole species. These accessory minerals suggest felsic rocks, such as granite, granodiorite and pegmatite, were sources for the sandstones. Geochemical analyses of the sedimentary sequence suggest that source rocks may lie in the passive continental margin, before sediment transport and deposition in the Khorat Basin by rivers flowing across a large flood plain. Many depositional sequences/episodes formed thick beds of cross bedded clastic rocks. A high average maturity index (>5) indicates sedimentary reworking/recycling. Chemical Index of Alteration (CIA) values range from 47 to 98, suggesting variable chemical weathering within the source area rocks, largely representing moderate to high degrees of weathering. The average CIA value of these sediments (78) suggests that relatively extreme alteration factors were involved.     

斑岩铜矿床研究进展

斑岩铜矿不但形成于环太平洋成矿域,还形成于特提斯成矿域和中亚成矿域（古亚洲洋成矿域）。成矿物质来源于深部,经过“洋壳一地幔熔岩流”、“原始岩浆”、“浅部富矿岩浆”和“岩浆结晶一成矿”4个阶段,其中在“原始弧岩浆”阶段,通过MASH过程,有大量成矿物质和能量的聚集。成矿流体为富H2O、高温、高压、高盐度、强氧化性、高氧逸度的富矿气液相流体,这些特点有利于成矿物质在岩浆一热液分离过程中向流体富集,并以氯络合物的形式运移。随着成矿流体的上侵,温度和压力的降低是成矿物质沉淀的主要影响因素。磁铁矿的结晶为成矿流体提供了大量的S2-离子,也是导致成矿物质沉淀的主要因素。斑岩型蚀变带从里向外为石英内核、钾化带、SCC带和泥化带,铜矿化主要发育在矿化带外围以及SCC带。目前,斑岩铜矿成矿模型主要有经典模型、系统模型和多阶段叠加模型。