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1.
安徽巢县南陵湖组火山碎屑流沉积物的发现 总被引：4，自引：0，他引：4
在安徽巢县下三叠统南陵湖组上部，发育着一套火山碎屑沉积物，主要由英安质角砾岩、英安质晶屑、玻屑凝灰角砾岩和英安质玻屑、晶屑凝灰岩等组成。它厚１．８ｍ，层序清楚，分为２个布玛旋回。研究表明，它属于海底喷发、水流搬运的火山碎清流沉积（火山浊流沉积），并且可能是印支早期华北板块与扬子板块相互碰撞的一种反映。 相似文献
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太原西山太原组蚀交流纹质沉凝灰岩的发现 总被引：2，自引：0，他引：2
通过对毛儿沟灰岩中段所谓“燧石层”的研究，提出火山成因的新见解，确定该岩石为蚀交流纹质沉凝灰岩。以宏观为基础，借助镜下下鉴定及各种物理化学测试手段，揭示出岩石成分以火山玻璃为主，由火山尘、玻屑、晶清、凝灰质内功屑、非火山质沉积物及生物屑等组成。火山生及脱玻化玻屑已开始蚀变，向片状、板状、絮状粘土矿物转化。还对火山物质来源作了初浅分析。关键词 相似文献
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临澧县白土坡玻屑凝灰岩（或半固结火山灰）赋存在第四系下更新统，层状或似层状，岩石松散，镜下具典型的玻屑凝灰结构。主要由流纹质火山玻屑，少量斜长石、石英及黑云母晶屑以及粘上矿物等组成。流纹质火山玻璃的电子探针分析平均值（％）：ＳｉＯ＿２７４．９７、Ａｌ＿２Ｏ＿３１４．０４６、ＣａＯ０．３２６、ＫｚＯ６．９３３、Ｎａ＿２Ｏ２．５３６、ＦｅＯ０．５１，总量９９．５２。 相似文献
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广西合山长兴组中的火山岩和火山沉积岩 总被引：2，自引：0，他引：2
<正> 广西合山上二迭统长兴组中的火山岩,前人已有报道。最近,笔者发现合山长兴组上部晶屑玻屑凝灰岩和凝灰质砂岩中,找到生物化石,经有关同志鉴定有:(虫筵)Palaeofusulina,放射虫Flustrella,有孔虫Colaniella及棘皮类碎片。合山长兴组中的火山岩和火山沉积岩可分为三类:1.晶屑—玻屑熔结凝灰岩;2.晶屑—玻屑层凝灰岩;3.含生物晶屑凝 相似文献
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熔岩和火山碎屑岩是两类最主要的火山岩,分别代表了两种不同的火山喷发方式和成岩过程,是火山岩分类命名中首先要注意区分的。囊状体具有与浆屑很相似的形态和结构,但对其研究还相当不足,易导致富含囊状体的流纹质—英安质熔岩与富含浆屑的熔结凝灰岩相混淆,产生熔岩与火山碎屑岩分类上的错误。本文首次介绍囊状体的基本特征并分析其与浆屑之区别。囊状体由矿物集合体(结晶内带)和外围脱玻体(脱玻外带)构成,因形态总体似囊状而得名,可呈条带状、透镜状,两端呈撕裂状或须状等,有时也呈斑块状消光和脱玻褪色体;它们是火山岩中微小的高温气相或液相长英质组份结晶、并释热诱发周围玻璃质脱玻形成的一种原生岩石结构。正确区分囊状体和浆屑对火山岩的分类命名及成因研究有重要作用,并避免火山碎屑岩的人为扩大化。 相似文献
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塔里木溢流玄武岩省的巨型长英质热火山碎屑流爆发记录 总被引：1，自引：1，他引：0
在塔里木盆地西北缘的柯坪地区二叠系库普库兹满组和开派兹雷克组玄武岩之间发现厚层长英质火山碎屑岩层序。该层序包括可见含交错层理的空落火山灰层、三层含增生火山砾的火山灰、熔结凝灰岩和再沉积熔结凝灰岩。层序下部为与其准同时喷发的玄武质火山碎屑岩和玄武质熔岩流。利用锆石U-Pb法确定熔结凝灰岩层的喷发年龄为290.9±1.3Ma(MSWD=1.12),该年龄限定了库普库兹满组玄武岩喷发的截止时间。长英质火山碎屑岩层序中的增生火山砾由粒度250μm的长英质玻屑组成,且长宽比均1.5。根据形貌、结构和岩相学特征,将增生火山砾分为三类,分别对应热火山碎屑流从起始(TypeⅡ,coated ash pellet)到极盛(TypeⅠ,accretionary lapillus)再逐渐衰弱(TypeⅢ,ash pellet)的过程。由于喷发规模巨大,该火山层序很可能广泛分布于盆地内,可能是确定全盆地溢流玄武岩喷发时限的一个关键标志层。 相似文献
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松辽盆地东南隆起区下白垩统营城组三段火山岩岩性、岩相序列 总被引：1，自引：0，他引：1
通过大比例尺野外岩性岩相填图、掌子面二维岩性岩相描述和详细岩矿鉴定,研究营城组三段内幕。本区营三段自下而上岩性序列表现为2个中基性到中酸性的火山岩旋回：①下部为石英安山岩、安山岩、安山质集块熔岩、安山质集块岩、安山质角砾岩和安山质角砾凝灰岩,向上过渡为砂质凝灰岩和英安质凝灰熔岩;②上部为玄武安山岩和玄武质集块熔岩,向上过渡为英安岩、珍珠岩、英安岩、英安质凝灰熔岩、英安质沉凝灰岩和英安岩。旋回①岩相纵向序列：溢流相下部亚相、火山通道相火山颈亚相、爆发相空落亚相、火山沉积相再搬运亚相、爆发相热碎屑流亚相。旋回②岩相纵向序列：溢流相上部亚相和下部亚相、火山通道相火山颈亚相、溢流相下部亚相、侵出相内带亚相、溢流相下部亚相、爆发相热碎屑流亚相、火山沉积相再搬运亚相、溢流相下部亚相。营三段火山岩发育于松辽盆地断陷末期,是盆地断陷转为坳陷过程的重要岩石记录。 相似文献
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甘肃山丹煤田二叠系火山碎屑岩的发现及其主要特征 总被引：1，自引：1，他引：1
本文论述了山丹煤田二叠系火山碎屑岩的地质特征:(1)火山碎屑岩赋存地层层位,(2)火山碎屑岩的岩石结构特征,(3)岩石的化学成分属性,(4)火山碎屑岩的粒度特征及其沉积性质。表明,火山碎屑岩由火山角砾岩及玻屑凝灰岩组成。凝灰质碎屑物为气携,以降落灰的方式沉积于陆相浅水环境中。该火山碎屑岩的发现表明,山丹地区二叠纪曾有过重要的火山活动,它为区域地质研究提供了有意义的新资料。 相似文献
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The volcanic-sedimentary succession of the Ventersdorp Supergroup which is virtually undisturbed tectonically and of low-grade (greenschist facies) metamorphism, affords a unique opportunity for studying the interplay between volcanic and sedimentary processes. The transitional sequence between the Rietgat and Bothaville Formations consists of a number of lithofacies. These are a basal breccia representing pyroclastic and laharic deposits, an overlying breccia—arenite—conglomerate (BAC) which formed by debris flow and fluvial processes, an arenite deposited offshore during a transgression, and an upper conglomerate laid down on a beach. In the volcaniclastic BAC and arenite lithofacies the presence of thin tuff beds, deformed acid lava fragments (bombs?) and glass shards in the arenaceous matrix suggest syndepositional volcanism.Sedimentation took place along the flanks of an asymmetrical, actively volcanic, domal structure which consisted partly of unstable pyroclastic deposits in the east. Resedimentation of the pyroclastic debris by subaerial debris flows and braided streams built a volcaniclastic fan lobe at the foot of the domal structure. As volcanic activity subsided, sands derived from a granitic terrain, mixed with minor air-fall debris to subsequently cover the fan lobe during a regional transgression. 相似文献
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松辽盆地营城组古火山机构的剖析——以东南隆起区三台珍珠岩山为例 总被引：2，自引：0，他引：2
三台地区下白垩统营城组一段岩石类型有隐爆角砾岩、角砾熔岩、熔结角砾岩、珍珠岩、流纹岩和凝灰岩,所属岩相为火山通道相、侵出相、喷溢相、爆发相。厘定古火山口位置的依据主要是通过分析隐爆角砾岩和珍珠岩的岩性岩相及其分布。整个火山机构划分为中心相组、近源相组和远源相组。中心相组即火山口相,主要包括火山通道相和侵出相,近源相组主要包括喷溢相,远源相组主要包括爆发相。相序（以火山口为基点）为火山通道相隐爆角砾岩亚相-侵出相中带亚相-侵出相内带亚相-喷溢相下部亚相-喷溢相中部亚相-爆发相热碎屑流亚相。近源相组较中心相组储层物性优越。其中喷溢相上部亚相是储层物性最好的岩相带。 相似文献
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Paul A. Studemeister 《Precambrian Research》1984,24(1):85-98
A trondhjemite stock intrudes an Archean succession metamorphosed to the greenschist facies at Gutcher Lake near Wawa, Ontario, Canada. This regional metamorphism also modified the stock and its partly enveloping aureole of epidote—hornblende hornfels. Mafic metavolcanic rocks in the greenstone succession are derived from pillowed flow, amygdular flow, massive flow or sill, and minor hyaloclastites that include pillow breccia. Stratiform lenses of felsic metavolcanic rocks are derived from massive flow or tuff, crystal tuff, lapilli tuff and volcanic breccia. Chalcopyrite and native gold coexist in stringers and veins of quartz, pyrrhotite and pyrite in a layered assemblage with cherty iron-formation at the stratigraphic top of the stock. Ego Mines Ltd. reports 348 000t averaging 1.60% copper and 3.77 g t?1 gold.The deposition of pillowed and amygdular lavas on the Archean sea-floor was interrupted by the venting of felsic magma that yielded viscous flows and pyroclastic tuffs. Heat emanating from the rising stock caused seawater to convect in the volcanic sequence. Hot modified seawater debouched onto an interflow trough above the stock, mixed with ambient seawater, and precipitated aprons of sulphidic mud and chert amongst clastic sediment. Down-slope slumping culminated in a stratified assemblage with pockets of debris-flow breccia. Compaction and de-watering of this package concentrated some of the dispersed sulphide material into fractures to form veins. The stock and the intruded succession was then metamorphosed to the greenschist facies. 相似文献
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Archean felsic volcanic rocks form a 2000 m thick succession stratigraphically below the Helen Iron Formation in the vicinity of the Helen Mine, Wawa, Ontario. Based on relict textures and structures, lateral and vertical facies changes, and fragment type, size and distribution, the felsic volcanic rocks have been subdivided into (a) lava flows and domes (b) hyalotuffs, (c) bedded pyroclastic flows, (d) massive pyroclastic flows, and (e) block and ash flows.Lava flows and domes are flow-banded, massive, and/or brecciated and occur throughout the stratigraphic succession. Dome/flow complexes are believed to mark the end of explosive eruptive cycles. Deposits interpreted as hyalotuffs are finely bedded and composed dominantly of ash-size material and accretionary lapilli. These deposits are interlayered with bedded pyroclastic flow deposits and probably formed from phreatomagmatic eruptions in a shallow subaqueous environment. Such eruptions led to the formation of tuff cones or rings. If these structures emerged they may have restricted the access of seawater to the eruptive vent(s), thus causing a change in eruptive style from short, explosive pulses to the establishment of an eruption column. Collapse of this column would lead to the accumulation of pyroclastic material within and on the flanks of the cone/ring structure, and to flows which move down the structure and into the sea. Bedded pyroclastic deposits in the Wawa area are thought to have formed in this manner, and are now composed of a thicker, more massive basal unit which is overlain by one or more finely bedded ash units. Based on bed thickness, fragment and crystal size, type and abundance, these deposits are further subdivided into central, proximal and distal facies.Central facies units consist of poorly graded, thick (30–80 m) basal beds composed of 23–60% lithic and 1–8% juvenile fragments. These are overlain by 1–4 thinner ash beds (2–25 cm). Proximal facies basal beds range from 2–35 m in thickness and are composed of 15–35% lithic and 4–16% juvenile fragments. Typically, lithic components are normally graded, whereas juvenile fragments are inversely graded. These basal beds are overlain by ash beds (2–14 in number) which range from 12 cm to 6 m in thickness. Distal basal beds, where present, are thin (1–2 m), and composed of 2–8% lithic and 6–21% juvenile fragments. Overlying ash beds range up to 40 in number.The climax of pyroclastic activity is represented by a thick (1000 m) sequence of massive, poorly sorted, pyroclastic flow deposits which are composed of 5–15% lithic fragments and abundant pumice. These deposits are similar to subaerial ash flows and appear to mark the rapid eruption of large volumes of material. They are overlain by felsic lavas and/or domes. Periodic collapse of the growing domes produced abundant coarse volcanic breccia. The overall volcanic environment is suggestive of caldera formation and late stage dome extrusion. 相似文献
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北京及邻区长城纪火山事件的沉积记录 总被引：6，自引：1，他引：5
北京及邻区的中元古代大红峪组中发育着与火山事件有关的沉积相,主要包括两种基本类型:火山源硅质-陆源砂-碳酸盐岩混积相和火山碎屑重力流沉积,后者又可分为火山碎屑基浪沉积相和火山-沉积角砾碳酸盐岩混积相。初步分析表明,大红峪期大量的硅质沉积主要来自同期的水下火山活动;火山碎屑基浪沉积与火山口内残余热气冲破熔岩封堵而爆发泄出,造成一定范围的海水涌浪作用有关。 相似文献
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Depositional processes of the Suwolbong tuff ring, Cheju Island (Korea) 总被引：11，自引：0，他引：11
The Suwolbong pyroclastic sequence in the western part of Cheju Island, Korea, comprises partly preserved rim beds of a Quaternary basaltic tuff ring whose vent lies about 1 km seaward of the present shoreline. The sequence consists of breccia, lapillistone, lapilli tuff and tuff. Eighteen sedimentary facies are established and organized into six lateral facies sequences (LFS) and seven vertical facies sequences (VFS). The LFS 1, 4 and 5 begin with massive lapilli tuff which transforms downcurrent into either planar-bedded (LFS 1), undulatory-bedded (LFS 4) or climbing dune-bedded (LFS 5) (lapilli) tuff units. They are representative of relatively ‘dry’ base surge whose particle concentration decreases downcurrent with a progressive increase in both tractional processes and sorting. The LFS 2 begins with disorganized and massive lapilli tuff and transforms into crudely stratified units downcurrent. It results from relatively ‘wet’ base surge in which sorting is poor due to the cohesion of damp ash. The LFS 3 comprises well-sorted lapilli tuff and stratified tuff further downcurrent, suggestive of deposition from combined fall and surge of relatively ‘dry’ hydroclastic eruption. All seven vertical facies sequences generally comprise two facies units of coarse-grained fines-depleted lapilli tuff and an overlying fine-grained tuff. These sequences are suggestive of deposition from base surge that consists of a turbulent head and a low-concentration tail. Depositional processes in the Suwolbong tuff ring were dominated by a relatively ‘dry’ base surge. The base surge comprises turbulent and high-concentration suspension near the vent whose deposits are generally unstratified due to the lack of tractional transport. As the base surge becomes diluted downcurrent through fallout of clasts and mixing of ambient air, it develops large-scale turbulent eddies and is segregated into coarse-grained bedload and overlying fine-grained suspension forming thinly stratified units. Further downcurrent, the base surge may be either cooled and deflated or pushed up into the air, depending on its temperature. The Suwolbong tuff ring comprises an overall wet-to-dry cycle with several dry-to-wet cycles in it, suggestive of overall decrease in abundance of external water and fluctuation in the rate of magma rise. 相似文献
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The Ilchulbong tuff cone, Cheju Island, South Korea 总被引：3，自引：0，他引：3
The Ilchulbong mount of Cheju Island, South Korea, is an emergent tuff cone of middle Pleistocene age formed by eruption of a vesiculating basaltic magma into shallow seawater. A sedimentological study reveals that the cone sequence can be represented by nine sedimentary facies that are grouped into four facies associations. Facies association I represents steep strata near the crater rim composed mostly of crudely and evenly bedded lapilli tuff and minor inversely graded lapilli tuff. These facies suggest fall-out from tephra finger jets and occasional grain flows, respectively. Facies association II represents flank or base-of-slope deposits composed of lenticular and hummocky beds of massive or backset-stacked deposits intercalated between crudely to thinly stratified lapilli tuffs. They suggest occasional resedimentation of tephra by debris flows and slides during the eruption. Facies association III comprises thin, gently dipping marginal strata, composed of thinly stratified lapilli tuff and tuff. This association results from pyroclastic surges and cosurge falls associated with occasional large-scale jets. Facies association IV comprises a reworked sequence of massive, inversely graded and cross-bedded (gravelly) sandstones. These facies represent post-eruptive reworking of tephra by debris and stream flows. The facies associations suggest that the Ilchulbong tuff cone grew by an alternation of vertical and lateral accumulation. The vertical buildup was accomplished by plastering of wet tephra finger jets. This resulted in oversteepening and periodic failure of the deposits, in which resedimentation contributed to the lateral growth. After the eruption ceased, the cone underwent subaerial erosion and faulting of intracrater deposits. A volcaniclastic apron accumulated with erosion of the original tuff cone; the faulting was caused by subsidence of the subvolcanic basement within the crater. 相似文献
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Depositional mechanics and sequences of base surges, Songaksan tuff ring, Cheju Island, Korea 总被引：6，自引：0，他引：6
The Songaksan mount in the southwestern part of Cheju Island, Korea, is a Taalian tuff ring produced by phreatomagmatic explosions at an aquifer. A detailed analysis of proximal-to-distal facies changes reveals that the tuff ring sequence can be represented by 21 sedimentary facies; one lateral facies sequence (LFS) and three vertical facies sequences (VFS). The VFS 1 and 2 are representative of facies relationships in horizontal near-vent deposits. The VFS 1 comprises scour-fill bedded tuff, inversely graded tuff, massive tuff and laminated tuff from base to top. The VFS 2 is a variant of the VFS 1, replaced by an inversely graded lapilli tuff unit at the base. The sequences suggest traction carpet, suspension and minor traction sedimentation from a high-concentration near-vent base surge. The LFS 1 and the VFS 3 are distilled from outward-dipping flank deposits. Both sequences begin with disorganized lapilli tuff, followed successively by stratified (lapilli) tuff, dune-bedded (lapilli) tuff, very thinbedded tuff and accretionary lapilli. They are suggestive of waning base surge which decreases in particle concentration, suspended-load fall-out rate and flow regimes with an increase in traction and sorting. These facies sequences suggest that a base surge experiences flow transformation with its flow characters changing with time and space. A near-vent base surge is turbulent, uniformly mixed and highly concentrated and produces scour-fill bedded tuff. As capacity decreases, the surge transforms into a dense and laminar underflow and a dilute and turbulent upper part (gravity transformation), depositing inversely graded, massive and normally graded (lapilli) tuff. Ensuing loss of sediment load and mixing of ambient air result in flow dilution (surface transformation). Stratified and dune-bedded units are produced by tractional processes of turbulent and low-concentration surge. Further dilution causes deceleration and cooling and results in precipitation of moistened ash and accretionary lapilli from suspension. 相似文献