河北西北部熔积岩特征及其地质意义

熔积岩是火山碎屑岩的一种特殊类型，由熔浆和未固结的湿沉积物两种组分掺杂混合而成。熔积岩的形成主要受炽热熔浆与未固结的湿沉积物接触时引起的淬碎或蒸汽爆炸作用以及寄主沉积物流体化作用控制，通常分布于熔岩流底部或前缘，也可分布于超浅成侵人体周围。据熔浆碎屑物的结构特征，冀西北熔积岩可分为流状和块状两种类型。流状熔积岩多是熔浆与细粒沉积物混合的结果，块状熔积岩大多与粗粒沉积物相关。正确鉴别熔积岩对确定沉积作用与岩浆作用的时序、研究盆地发展演化历史具有重要意义。     

火山碎屑岩的一种重要类型--熔积岩

熔积岩(peperite)是火山碎屑岩的一种特殊类型,由熔浆和未固结的湿沉积物两种组分掺混而成,具特征的火山碎屑结构,分布在熔岩流底部、前缘和超浅成侵入体与未固结湿沉积物的接触部位。熔积岩中熔浆组分从玄武质到流纹质均有,结构上为玻璃质、隐晶质或斑状结构,沉积组分在粒度和成分上变化范围广。据岩浆碎屑的形态和结构特征可分为两种类型,即透镜状和块状熔积岩。前者由熔浆碎屑和细粒沉积物组成,岩浆碎屑以透镜状、舌状、水滴状、撕裂状     

熔积岩及其对中国几处关键构造事件的限定

熔积岩是岩浆物质(岩浆侵入体、熔岩流、热火山碎屑流)与未固结的湿冷沉积物发生同生混合的产物,以浆源(岩浆凝固裂解的浆源碎屑)-沉积物源(宿主沉积物)的二元组分为典型特征。熔积岩独特的熔积结构与其成因机制密切相关,也是鉴定熔积岩的主要依据。根据浆源碎屑的形态,熔积岩主要分为块状(多数浆屑呈多边形状)和流态(多数浆屑具曲面外形)两种类型,并分别对应着不同的熔积作用机制。块状熔积岩主要产生于淬冷、自碎裂、水汽岩浆爆发、岩浆内溢气爆发等机制,而流态熔积岩的形成则得益于岩浆表面稳定蒸汽膜的维持使岩浆碎屑缓慢凝固、免于骤冷。沉积物的流体化是熔积作用得以发生的必要条件,流体化的沉积物为岩浆的驱入腾挪空间并形成对流,因此,固结成岩的沉积岩无法与岩浆物质相互熔积。熔积岩具有重要的地质意义:精确限定岩浆活动与沉积作用的同生等时性,以及利用宿主沉积物的沉积环境精确限定火山活动时的地质背景。近年来我们在国内多处发现典型的熔积岩,并应用于中国关键大地构造问题的研究中。在中亚造山带西准噶尔晚古生代火山-沉积地层中发现熔积岩,据此限定了达拉布特—白碱滩蛇绿岩带两侧上古生界的连续性,推断达拉布特—白碱滩蛇绿岩带不是典型的板块俯冲边界的缝合带,西准噶尔晚古生代是渐浅充填的残余洋盆系统。我们还首次在大火成岩省中识别出熔积岩,如在峨眉山大火成岩省中央带下部火山碎屑层序中发现以灰岩和以橙玄玻璃角砾凝灰岩为宿主沉积的熔积岩,表明中央带早期处于海相环境,从而判定火山喷发之前不具有因地幔柱上涌而诱发的大规模地表抬升效应。在塔里木大火成岩省印干剖面中发现的熔积岩以灰质宿主,证明喷发早期并非完全为陆上环境,塔里木大火成岩省喷发期间(二叠纪早期)海进和海退频繁交替。     

青海南部熔积岩的发现:对寻找VMS型矿床的重要启示

熔积岩指的是侵入、混合到未固结或弱固结的湿沉积物中的熔浆分解、原位形成的一类特殊岩石。正确地认识该类岩石,有利于增进人们对岩浆-水(沉积物)相互作用过程的理解,恢复古环境。在青海南部沱沱河地区发现了一套角砾为撕片状、锯齿状及浑圆状的安山岩,胶结物为铁硅质组合的特殊熔积岩。研究表明,该熔积岩的角砾为岩浆遇水后快速淬火、裂解的产物,铁硅质组合为海底喷气沉积形成的含铁建造;且安山岩与含铁建造发生混合时,含铁建造尚未固结。该套熔积岩的发现,改变了长期以来对开心岭铁矿为火山热液交代安山岩而形成的认识,对于在矿区寻找VMS型矿床、区域内寻找海底热水喷流沉积型矿床具有重要的启示意义。     

松辽盆地东南隆起区营城组一段熔浆胶结复成分砾岩特征及其成因分析

对野外剖面实际测量及室内薄片鉴定等资料研究表明,松辽盆地营城组一段复成分砾岩共有4种胶结成岩类型：熔浆胶结、灰泥球胶结、凝灰质胶结和砂泥质胶结。其中以熔浆胶结发育最为广泛。砾岩中砾石成分复杂,以基底花岗岩及二叠系变质岩为主,原地火山岩次之。砾石整体分选性差,磨圆度中等-好,以次圆状-次棱角状最为发育。自基底向火山活动中心,砾岩中外来砾石逐渐减少,原地火山岩砾石逐渐增多。基质成分由底部的砂泥质向上过渡为凝灰质并最终完全过渡到熔浆质胶结。砾岩是冲积扇或辫状河等沉积环境下已经堆积但未固结或半固结的砂砾质沉积物,在火山活动期被火山碎屑流或熔浆流再搬运,这种碎屑流、熔浆流和水介质构成的多相混合物通过岩浆冷凝和压实复合成岩作用而形成的岩石,实质是爆发相热碎屑流亚相的另一种表现形式。由于该类砾岩主要见于断陷盆地边缘火山岩序列下部靠近基底一侧,说明其形成与构造-岩浆活动密切相关,是火山旋回早期所特有的产物。     

鄂尔多斯盆地陇东地区延长组重力流沉积特征及其模式

利用岩心、测井资料和重力流沉积理论,系统研究了鄂尔多斯盆地陇东地区延长组重力流沉积特征及其沉积模式。该区重力流沉积物可分为浊积岩、砂质碎屑流沉积物、泥质碎屑流沉积物和滑塌岩。其中,浊积岩发育正粒序;砂质碎屑流沉积物以冻结块状沉积为特征;泥质碎屑流沉积物以泥质为主,内部含少量砂质颗粒和砂质团块;滑塌岩发育包卷层理等液化构造。不同重力流沉积物发育程度差异明显,浊积岩和砂质碎屑流沉积物的钻遇井数最多,泥质碎屑流沉积物最少。在重力流单期沉积厚度方面,砂质碎屑流沉积物单期沉积厚度平均为0.986m,明显高于其他类型;浊流沉积厚度最低,平均厚度为0.414m。本区重力流是由三角洲前缘沉积物失稳滑塌所致,砂质碎屑流沉积物和浊积岩是主要的重力流沉积类型,其次为滑塌岩和泥质碎屑流沉积物。砂质碎屑流沉积物主要发育于北东向曲流河三角洲前缘前方的深水区;浊积岩主要发育于西部、西南部和南部物源形成的辫状河三角洲前缘前方的深水区域;泥质碎屑流沉积物和富含泥砾砂质碎屑流沉积物在平面分布极少,且规律不明显。     

山东惠民凹陷古近系湖泊地震涌浪记录的新发现

在陆相湖盆中,地震引起的各种作用力可以对各种先成沉积物进行改造而形成原地震积岩,同样地震可引发涌浪、浊流及碎屑流而形成地震涌浪沉积及震浊积岩.通过大量岩心观察描述和成像测井资料分析,首次提出惠民凹陷中央隆起带沙河街组含有丘状交错层理的碎屑岩与典型的原地震积岩(包括震裂岩、震褶岩、自碎屑角砾岩等)紧密共生,当属于地震作用引发涌浪的沉积产物.本区地震涌浪沉积中发育丘状及洼状层理、包卷层理、平行层理、块状层理、波痕、冲刷及截切面等沉积构造.根据沉积特征和分布位置,本区地震涌浪沉积划分为两种类型,即位于涌浪基面附近的含塑性泥砾的搅动型和涌浪基面与正常浪基面之间的回流型.垂向上地震涌浪沉积一般位于原地震积岩之上,震浊积岩之下,组成完整的原地震积岩—地震涌浪沉积—地震浊积岩序列或原地震积岩—地震涌浪沉积序列.本区地震涌浪沉积的发现和研究,将为地质学家识别陆相湖盆地震事件沉积提供对比标准.     

西藏安多县东巧晚侏罗世生物礁的发现

首次发现西藏安多县东巧地区晚侏罗世生物礁,造礁生物以层孔虫和六射珊瑚为主,其中,层孔虫可分为枝状、筒状和块状三种类型,它们多以原地生长状态保存.礁岩石学特征研究表明,礁岩可分为筒状-枝状层孔虫障积岩、枝状层孔虫障积岩、筒状层孔虫障积岩、筒状-块状层孔虫障积-骨架岩和筒状层孔虫-六射珊瑚障积-骨架岩.礁体类型可分为筒状-枝状层孔虫障积岩隆礁、枝状层孔虫障积岩隆礁、筒状层孔虫障积岩隆礁、筒状-块状层孔虫障积-骨架岩隆礁和筒状层孔虫-六射珊瑚障积-骨架岩隆礁,礁体的演化均经历了奠基阶段、发育阶段和衰亡阶段.     

川北下寒武统仙女洞组台缘斜坡碳酸盐岩重力流沉积

基于重力流剖面的野外观察、露头解剖及镜下鉴定等分析手段,对四川盆地北部下寒武统仙女洞组台缘斜坡碳酸盐 岩重力流沉积及发育机制进行了研究。研究区位于仙女洞组,主要沉积粉砂质泥岩、生屑泥晶灰岩、藻灰岩等3种岩石类 型;根据层面上产出形态的不同,将该区碳酸盐岩重力流沉积分为似瘤状碳酸盐岩重力流沉积和角砾型碳酸盐岩重力流沉 积2类。结合露头区重力流沉积物粒度及岩性变化,将碳酸盐岩重力流沉积由下至上划分出5个发育期次,期次内部重力流 沉积物由细变粗,纵向上呈现出明显的叠置关系,与仙女洞组时期所经历的海退环境大致吻合。地震、风暴浪等触发机制 导致台缘斜坡上部松散沉积的灰泥丘块体发生破碎并沿斜坡发生滑塌,伴随水体注入,大块砾石在沉积物-水体混合的环 境中发生破碎搅动,形成大小不等的块体,深水底流等作用对未固结或弱固结的砾屑灰岩进行溶蚀、改造,最终形成了层 面形态特征不同的2类似瘤状碳酸盐岩重力流沉积。角砾型碳酸盐岩重力流沉积则主要是未破碎的巨型灰泥丘块体经搬运 和短距离滑塌,最终与似瘤状砾屑灰岩共同沉积而成。     

咸化湖盆混积岩成因机理研究

关于海相及淡水湖盆混积岩的研究已相对完善,而针对咸化湖盆混积岩理论的形成及实践应用却鲜有报道,本文旨在系统地阐述咸化湖盆混积岩的成因机理、沉积模式、分布规律,对比其与一般混积岩沉积特征的异同点,并探讨其与油气富集特征的相关性。本文采用矿物学、微观岩石学分析方法进行混积岩矿物组成、沉积特征、储集空间类型研究,采取地质统计分析方法明确混积岩分布规律,并运用物性分析方法对比不同类型混积岩的储集性能。结合柴达木盆地西北区新近系混积岩研究实例,本文创新性地提出了欠补偿咸化湖盆的混积岩成因类型：机械成因的相混合混积岩和生物成因的藻混合混积岩。相混合又可划分为两种亚类：互层型混合、组构型混合;藻混合亦可划分为两种亚类：藻粘结混合、滑塌再混合。建立了咸化湖盆混积岩的沉积模式：混积岩主要发育于三角洲、水下扇、滩坝等碎屑岩沉积体系与湖相碳酸盐岩沉积体系的过渡相带以及藻灰岩发育区。明确了混积岩的分布规律,可归纳为“盆缘互层型、盆内组构型、藻混合局限分布”。混积岩沉积特征对比分析结果表明,任何环境下混积岩形成的先决条件均为碳酸盐岩的生长和聚集,而不同于淡水湖盆及海相混积岩沉积厚度大,生物含量高等特点,咸化湖盆混积岩单层厚度极薄,并发育特殊的藻混积岩类。综合研究认为,藻混合混积岩与油气储层的相关性要大于相混合混积岩。以上成果可为咸化湖盆混积岩,乃至陆相湖泊混合沉积物的成因类型及油气地质意义研究提供借鉴与参考。     

Clast shape and textural associations in peperite as a guide to hydromagmatic interactions: Upper Permian basaltic and basaltic andesite examples from Kiama,Australia

Upper Permian shallow marine siltstone and sandstone units of the Broughton Formation are intercalated with basaltic and basaltic andesite sheets at Kiama, New South Wales. Parts of the two sheets examined in this study display peperite texture. The lower example (Blow Hole Latite Member) can be divided into two units with peperitic contacts suggesting their intrusion into wet unconsolidated sediments of the overlying Kiama Sandstone Member. The Bumbo Latite Member overlies the Kiama Sandstone Member and has been interpreted by previous workers as a lava. Well‐developed columnar joints cut the interior of the sheets. Along contacts with sedimentary facies and peperitic dykes which penetrate the sheets, columnar joints merge into a several metre‐wide zone of blocky jointing, pseudo‐pillows and hyaloclastite. In peperitic facies, sandstone or siltstone fills joints and fractures that define pseudo‐pillows, polyhedral joint blocks and columns (closely packed fabric) or sediment matrix‐rich breccia contains fragments and apophyses of basalt and basaltic andesite (dispersed fabric). Along some contacts, peperite with dispersed fabric passes through a zone of closely packed peperite into coherent facies. Alternatively, closely packed peperite passes directly into coherent facies. Examples of peperite with more than one clast type (globular, blocky, platy), and involving sedimentary matrix of constant grain‐size, are common. In some examples, globular surfaces formed during an early, low‐viscosity phase of magma emplacement into wet sediment. Planar and curviplanar fractures cut some globular surfaces suggesting that these formed slightly later as the magma became more viscous (cooler) and/or vapour films at the magma‐sediment interface broke down. However, the complexities of peperite, in respect to clast types, abundances and distribution, as well as grainsize and structures in the sedimentary component, suggest that a spectrum of fragmentation and mixing processes were involved in fragmenting the sheets. Many peperitic domains include poorly and strongly vesicular parts, resulting in apparent polymictic breccias. Vesiculation of the sheets is interpreted to have occurred in two phases: an early degassing of primary magmatic volatiles and a later, scoria‐forming event, both of which progressed as the magma mixed with unconsolidated sediment. During the later phase, magma incorporated limited amounts of steam from the wet sediment and a vesicular front propagated out into the magmatic component. Confining pressures were insufficient to prevent vesiculation of the magma or to suppress fluidisation of the host sediment along magma‐sediment contacts, but large enough to inhibit large‐scale steam explosivity. Displacement of sediment along contacts may have reduced confining pressures sufficiently to promote vaporisation of pore water, and induce local vesiculation of the magma.     

Mafic peperite from the Gold Creek Volcanics in the Middle Proterozoic McArthur Basin,Northern Territory

Peperite is a non‐genetic term used to describe volcanic breccia in which a texture of dark blocks in a light matrix resembles a mixture of salt and pepper. In the Gold Creek Volcanics, peperite is a mixture of partly vesiculated basalt clasts in a mudstone‐sandstone matrix. It is formed by the buoyant intrusion of basaltic magma into wet unconsolidated sediment. The intruding bodies deform and quench, giving rise to discordant masses of hyaloclastic breccia, confined largely to the subsurface. These basalt masses may remain hot enough to locally superheat pore water and produce convective systems where the basalt clasts and fluidized sediment become mixed, forming the distinctive peperite.     

Carbonate melting and peperite formation at the intrusive contact between large mafic dykes and clastic sediments of the upper Palaeozoic Saint‐Jules Formation,New‐Carlisle,Quebec

The base of an upper Palaeozoic graben‐fill in eastern Canada was affected by mafic dyke intrusions shortly after deposition, resulting in the formation of peperite. Complex magma–sediment interactions occurred as the melts mingled with the wet and poorly consolidated clastic material of this sedimentary basin, which is separated from underlying rocks by the Acadian unconformity (Middle Devonian). As a result of these interactions, the mafic rocks are strongly oxidized, albitized and autobrecciated near and above the unconformity, where blocky juvenile clasts of mafic glass and porphyritic basalt have mingled with molten or fluidized sediments of the upper Palaeozoic Saint‐Jules Formation, forming a peperite zone several metres thick. In contrast to most peperite occurrences, the New‐Carlisle peperites are associated with the tip of dykes rather than with the sides of sills or dykes. We argue that more heat can be concentrated above a dyke than above a sill, as the former provides a more efficient and focused pathway for heated waters to invade the poorly consolidated host sediments. Superheated groundwaters that issued from the sides of the dykes appear to have promoted melting of carbonate components in calcareous sedimentary rock clasts of the Saint‐Jules Formation, locally generating carbonate melts that contributed to the mingling of juvenile and sedimentary clasts in the peperite. Copyright © 2005 John Wiley & Sons, Ltd.     

Peperite occurrence and its implications on origin and temporal development of the Proterozoic Dhala basin,Mohar area,Shivpuri district,Madhya Pradesh

In the western part of Bundelkhand massif, a caldera with intra-caldera sediments, known as Dhala Formation, occurs as an outlier in and around Mohar village of Shivpuri district, Madhya Pradesh. For the first time, occurrence of peperite is being reported from the basal part of the Dhala sediment. Two types of peperites have been recognized: blocky and fluidal or globular with variable morphology. In peperitic zones, features like soft sediment deformations, presence of sediment into the rhyolite along cracks, vesiculation of the sediments and other evidences suggestive of sediment fluidization are some definite characteristics of interaction of hot magma with wet sediments forming peperite. The occurrence of peperites reflects the contemporaniety of deposition of the Dhala sediments and volcanism, which is well in accordance to the volcanic origin of Dhala structure. Further, the nature of unconformity between the Dhala and overlying Kaimur which is characterized by merely a few centimeter thick pebbly/conglomeratic bed does not appear to represent a large hiatus as expected between the Semri and Kaimur of Vindhyan Supergroup. So, the contemporaniety of the Dhala Formation (at least the lower part) as reflected by occurrence of peperites, coupled with the available age of the rhyolite and the nature of the unconformity between the Dhala and overlying Kaimur provide convincing evidence to correlate the Dhala Formation with the Lower part of the Kaimur and unlikely with the Semri Group or Bijawar as proposed earlier.     

The Tennant Creek porphyry revisited: A synsedimentary sill with peperite margins,Early Proterozoic,Northern Territory

Isolated outcrops of coarse‐ and medium‐grained, quartz‐feldspar porphyry occur for some 60 km from Nobles Nob to near Warrego in the Early Proterozoic Tennant Creek Block of the central Northern Territory. The outcrops appear to be part of an approximately conformable sheet of variable thickness (several tens to a few hundred metres), enclosed by sedimentary rocks of the Warramunga Group. The porphyry is characterized by euhedral, complete, evenly distributed crystals up to 2 cm across, in a microcrystalline groundmass. In some samples the groundmass shows relict perlitic cracks and was formerly coherent glass. In detail, upper and lower contacts of the porphyry sheet are highly irregular: porphyry contains wisps, blocks and large rafts of sandstone, and sandstone encloses single euhedral crystals and blebs, tongues and lobes of porphyry. Clasts of each rock type commonly have fluidal shapes. Sedimentary rocks at both the upper and the lower contacts are indurated and silicified. Close to the contacts, bedding is not easily identified, or else is disturbed. The quartz‐feldspar porphyry is interpreted to have cooled and solidified from phenocryst‐rich magma that intruded approximately parallel to bedding in the enclosing sedimentary sequence. The peperite margins of the sill suggest that the porphyritic magma invaded relatively weak, poorly consolidated, wet sediments rather than solid sedimentary rock. Rapid expansion and movement of heated pore fluid would have temporarily disrupted particle packing in the sediments at the contacts, and allowed intricate penetration of magma accompanied by quenching and fragmentation. In addition to relatively short‐term and local effects on the pore fluid chemical and physical properties, the intrusion was probably responsible for premature and permanent dewatering of the adjacent sediments. The sill together with its bordering zone of peperite and indurated sedimentary rocks may have constituted a significant physical barrier to any subsequent fluid transport in the enclosing sedimentary sequence.     

Genetic classification of tectonic platform structures and paleotectonic reconstructions,from geophysical data on basement block structure

Geophysical expressions of the relatively mobile Cambrian-Sinian blocky layer of the platform, underlain by the relatively stable Precambrian base and overlain by sediments containing structures created by transfers of tensions from the blocky layer, are particularly well suitedfor structural regionalizations in Latvian Lithuanian territories and possibly elsewhere in the platform. Further testing and applications of the method are recommended. — V. P. Sokoloff.     

流体构造动力学与成矿作用

流体是地球的重要物质组成,其构造作用与动力学是地质力学与构造学重要的研究方向。流体构造动力学是介于流体地质学、地质力学和构造地质学之间的一个交叉学科。文章介绍了流体构造动力学的概念、主要研究内容、流体的构造作用方式及构造类型与特征,总结了近年来在流体构造动力学与成矿研究过程中取得的一系列重要进展。主要有提出液压致裂的新动力学机制、发现斑晶堆积构造并指出斑岩是岩浆房中部分结晶残余岩浆再侵位的产物及发现并厘定构造混积岩等多个方面,总结了存在的问题并指出了进一步研究的方向;指出流体作为构造作用的主要参与者和重要组织者,不仅对成矿流体的运移通道及其沉淀与就位的空间进行开拓,更重要的是作为载体运移、富集成矿元素并为最终成矿奠定基础。      

Cave stratigraphy in western Norway; multiple Weichselian glaciations and interstadial vertebrate fauna

Skjonghclleren is a marine-cut cave with 15–20. m thick pre-Holocene sediments. Corings and excavations reveal three beds of extremely fine-grained, laminated sediments alternating with blocky sediments. The laminated beds are interpreted as glaciolacustrine sediments deposited subglacially at times when ice sheets covered the area, suggesting at least three glaciations after the cave was formed. The blocky/diamictic sediments were formed by frost-shattered blocks from the roof of the cave during ice-free periods, and mixing with the fines through slow mass movements along the floor of the cave. In the diamictic sediment beneath the uppermost laminated bed, almost 7,000 bone and teeth fragments of birds, mammals and fish were found. Birds dominated, with little auk and brunnich's guillemot as the most frequently occurring species. Arctic fox was the dominating mammal. During climatic optimum of the interstadial, conditions seem to have been similar to present-day coastal Finnmark, with North Atlantic warm water entering the Norwegian Sea. Two radiocarbon dates on bones and three Uranium series dates on speleothems from this bed all cluster around 30,000 B.P., i.e., the end of the Ålesund interstadial. Above the uppermost laminated bed, bone fragments of birds, fish and mammals, deposited between c . 12,000 and c . 10,000 B.P., were found. Little auk dominate. The occurrence of squirrel is worth noting since it is limited mainly to areas with coniferous forest today. The beds below the 30,000B.P. bed are poorly dated or undated, but it is tentatively concluded that the entire sediment sequence was deposited during the Weichselian stage. It seems that the cave was formed at a high relative sea-level stand sometime during the Early Weichsclian. Two recorded palaeomagnetic excursions seem to correlate with the Laschamp/Olby and the Lake Mungo events, respectively.     

滦平盆地上白垩统九佛堂组中的熔积岩及地质意义

通过对滦平盆地沉积地层的野外观察,系统分析了九佛堂组的沉积特征及其变化规律,鉴别出特殊的岩石类型——熔积岩;较详细的描述了熔积岩所在剖面的沉积特征,最后结合盆地的区域地质背景,初步认为滦平盆地为火山—沉积盆地,强烈的同沉积构造运动伴随岩浆活动,致使盆地九佛堂组沉积地层内发育熔积岩。