大火成岩省及地幔动力学

大火成岩省由一个体积巨大的、连续的、以富镁铁岩石占优势的喷出岩及其伴生的侵入岩组成，是一个全球现象。它包括大陆溢流玄武岩和伴生的侵入岩，火山被动边缘玄武岩，大洋高原、海岭、海山群和洋盆溢流玄武岩。Ontong Java和Kerguelen-Broken Ridge大洋高原、北大西洋火山被动边缘、德干和哥伦比亚河大陆溢流玄武岩是3个主要大火成岩省的典型代表。各种不同的大火成岩省在时空分布及组成上都具有相似性，它们具有非常大的体积、高的喷发速率，岩石类型以拉斑玄武岩为主。大火成岩省代表了地球上已知的最大的火山岩浆活动，记录了物质和能量从地球内部向外的大量转换。大火成岩省难以用板块构造来解释，可用热柱模式来解释，通常被认为是与来自下地幔的热柱“头”有关。大火成岩省是地球动力学过程在地壳的表现，因此大火成岩省参数可作为边界条件去反演地幔动力学过程。     

Flood basalts and metallogeny: The lithospheric mantle connection

Continental flood basalts, derived from mantle plumes that rise from the convecting mantle and possibly as deep as the core–mantle boundary, are major hosts for world-class Ni–Cu–PGE ore deposits. Each plume may have a complex history and heterogeneous composition. Therefore, some plumes may be predisposed to be favourable for large-scale Ni–PGE mineralisation (“fertile”).Geochemical data from 10 large igneous provinces (LIPs) have been collected from the literature to search for chemical signatures favourable for Ni–PGE mineralisation. The provinces include Deccan, Kerguelen, Ontong Java, Paraná, Ferrar, Karoo, Emeishan, Siberia, Midcontinent and Bushveld. Among these LIPs, Bushveld, Siberia, Midcontinent, Emei Mt and Karoo are “fertile”, hosting magmatic ore deposits or mineralisation of various type, size and grade. They most commonly intruded through, or on the edges of, Archaean–Paleoproterozoic cratonic blocks. In contrast, the “barren” LIPs have erupted through both continental and oceanic crustal terranes of various ages.Radiogenic isotopic signatures indicate that almost all parental LIP magmas are generated from deep-seated mantle plumes, and not from the more widespread depleted asthenospheric mantle source: this confirms generally accepted plume models. However, several important geochemical signatures of LIPs have been identified in this study that can discriminate between those that are “fertile” or “barren” in terms of their Ni–PGE potential.The fertile LIPs generally contain a relatively high proportion of primitive melts that are high in MgO and Ni, low in Al₂O₃ and Na₂O, and are highly enriched in most of the strongly incompatible elements such as K, P, Ba, Sr, Pb, Th, Nb, and LREE. They have relatively high Os contents (≥ 0.03 to 10 ppb) and low Re/Os (< 10). The fertile LIP basalts display trends of Sr–Nd–Pb isotopic variation intermediate between the depleted plume and an EM1-type mantle composition (and thus could represent a mixing of these two source types), and have elevated Ba/Th, Ba/Nb and K/Ti ratios. These elemental and isotopic signatures suggest that interaction between plume-related magmas and ancient cratonic lithospheric mantle with pre-existing Ni- and PGE-rich sulfide phases may have contributed significantly to the PGE and Ni budget of the fertile flood basalts and eventually to the mineralisation. This observation is consistent with the location of fertile LIPs adjacent to deep old lithospheric roots (as inferred from tectonic environment and also seen in global tomographic images) and has predictive implications for exploration models.Barren LIPs contain fewer high-MgO lavas. The barren LIP lavas in general have low Os contents (mostly ≤ 0.02 ppb) with high Re/Os (10–≥ 200). They show isotopic variations between plume and EM2 geochemical signatures and have high Rb/Ba ratios. These signatures may indicate involvement of deep recycled material in the mantle sources or crustal contamination for barren LIPs, but low degrees of interaction with old lithospheric-type roots.     

Phanerozoic within-plate magmatism of North Asia: Absolute paleogeographic reconstructions of the African large low-shear-velocity province

The phanerozoic within-plate magmatism of Siberia is reviewed. The large igneous provinces (LIPs) consecutively arising in the Siberian Craton are outlined: the Altai-Sayan LIP, which operated most actively 400–375 Ma ago, the Vilyui LIP, which was formed from the Middle Devonian to the Early Carboniferous, included; the Barguzin-Vitim LIP (305–275 Ma); the Late Paleozoic Rift System of Central Asia (318–250 Ma); the Siberian flood basalt (trap) province and the West Siberian rift system (250–247 Ma); and the East Mongolian-West Transbaikal LIP (230–195 Ma), as well as a number of Late-Mesozoic and Cenozoic rift zones and autonomous volcanic fields formed over the last 160 Ma. The trace-element and isotopic characteristics of the igneous rocks of the above provinces are reviewed; their mantle origin is substantiated and the prevalence of PREMA, EM2, and EM1 mantle magma sources are shown. The paleogeographic reconstructions based on paleomagnetic data assume that the Iceland hot spot was situated beneath the Siberian flood basalts 250 Ma ago and that the mantle plumes retained a relatively stable position irrespective of the movements of the lithospheric plates. At present, the Iceland hot spot occurs near the northern boundary of the African large low shear velocity province (LLSVP). It is suggested that the within-plate Phanerozoic magmatism of Siberia was related to the drift of the continent above the hot spots of the African LLSVP.     

吉黑地区新生代船底山玄武岩正名及其意义

船底山玄武岩于1953年创名。半个多世纪以来, 由于在其创名地一直未获得该火山事件的同位素测年资料以及东北地区存在诸多与船底山玄武岩类似的新生代高位玄武岩, 导致多种相关文献对东北地区古新世-上新世众多不同的火山事件所形成的玄武岩地质体均以“船底山玄武岩”命名, 造成了该名称的使用时间跨度太大, 给东北地区新生代火山事件序列的研究带来不便。层型剖面顶部玄武岩的测年结果表明, 船底山玄武岩的全岩K-Ar年龄为(28.3 ±2.3) Ma, 结合文献资料承传, 船底山玄武岩可作为一事件地层单元, 即船底山火山事件或广义的理解为晚渐新世沉积期( 31 ～23 Ma) 火山事件所形成的火山岩石地层单元。     

峨眉山大火成岩省东区普安玄武岩系年代学、地球化学及成因研究

广泛分布于中国西南川、滇、黔三省的峨眉山玄武岩是我国最早被国际认可的大火成岩省,受到了国内外学者的广泛关注.前人对大火成岩省西区玄武岩已达成多项共识,而对东区玄武岩的岩石组合、火山活动时限、岩石成因等方面还存在诸多争议.本文以峨眉山大火成岩省东区贵州普安玄武岩系为研究对象,通过解析典型剖面,明确该区玄武岩系岩石类型从底...     

On the ages of flood basalt events

We review available data constraining the extent, volume, age and duration of all major Phanerozoic continental flood basalts (CFB or traps) and oceanic plateaus (OP), together forming the group of large igneous provinces (LIP), going from the smallest Columbia flood basalts at ～16 Ma to the as yet ill-known remnants of a possible trap at ～360 Ma in eastern Siberia. The 16 traps (CFB and OP) reviewed form a rather unimodal distribution with an initial modal volume of the order of 2.5 Mkm³. Most provinces agree with a rather simple first order model in which volcanism may have lasted of the order of 10 Ma, often resulting in continental break-up, but where most of the volume was erupted in about 1 Ma or sometimes less. This makes CFBs/OPs (LIPs) major geodynamic events, with fluxes exceeding the total output of present day hot spots and even possibly exceeding over short times the entire crustal production of mid-ocean ridges. The proposed correlation between trap ages and the ages of several geological events, including mass extinctions and oceanic anoxia, is found to have improved steadily as more data have become available, to the point that the list of trap ages may coincide with many major divisions in the geological time scale. The four largest mass extinctions in the last 260 Ma coincide to the best resolution available with four traps, making a causal connection between the two through some form of catastrophic climatic perturbations the most likely hypothesis. The time sequence of LIPs appears to have been random and there is no robust evidence for long time trends in the corresponding crustal production rate over the last 260 Ma.     

大火成岩省研新进展

大火成岩省的含义是指连续的、体积庞大的火成岩(包括镁铁质和长英质火成岩)所构成的巨型岩浆岩建造。镁铁质大火成岩省可分为:大陆溢流玄武岩、火山被动陆缘、大洋高原玄武岩、大岩墙群和大层状侵入体。镁铁质大火成岩省是地幔柱岩浆活动的直接产物,一般与聚敛板块边界无关。长英质大火成岩省主要由酸性、中酸性熔结凝灰岩及与之有成因联系的花岗岩构成,与岩石圈伸展构造和玄武岩浆底侵作用有不可分割的联系。今后研究方向包括大火成岩省的形成与地幔动力学的联系以及它与大陆增生、大陆裂解和生物绝灭的关系。此外还包括大火成岩省与成矿作用研究     

Revised definition of Large Igneous Provinces (LIPs)

Much has been learned about Large Igneous Provinces (LIPs) and their database greatly expanded since their first formal categorization in the early 1990s. This progress provides an opportunity to review the key characteristics that distinguish LIP events from other melting events of the upper mantle, and to reassess and revise how we define LIPs. A precise definition is important to correctly recognize those LIP events with regional to global effects, and to aid in refining petrogenetic models of the origin of LIPs. We revise the definition of LIPs as follows: “Large Igneous Provinces are magmatic provinces with areal extents > 0.1 Mkm², igneous volumes > 0.1 Mkm³ and maximum lifespans of ～ 50 Myr that have intraplate tectonic settings or geochemical affinities, and are characterised by igneous pulse(s) of short duration (～ 1–5 Myr), during which a large proportion (> 75%) of the total igneous volume has been emplaced.” They are dominantly mafic, but also can have significant ultramafic and silicic components, and some are dominated by silicic magmatism. In this revision, seamounts, seamount groups, submarine ridges and anomalous seafloor crust are no longer considered as LIPs. Although many of these are spatially-related features post-dating a LIP event, they are constructed by long-lived melting anomalies in the mantle at lower emplacement rates, and contrast with the more transient, high magma emplacement rate characteristics of the LIP event. Many LIPs emplaced in both continental and oceanic realms, are split and rifted apart by new ridge spreading centres, which reinforce the link with mid-ocean ridges as a post-LIP event. Three new types of igneous provinces are now included in the LIP inventory, to accommodate the recognition of a greater diversity of igneous compositions, and preserved expressions of LIP events since the Archean: 1) giant diabase/dolerite continental dyke swarm, sill and mafic–ultramafic intrusion-dominated provinces; 2) Silicic LIPs; and 3) tholeiite–komatiite associations, which may be Archean examples of LIPs. A revised global distribution of LIPs for the Phanerozoic is presented. Establishing the full extent of LIPs requires well-constrained plate reconstructions, and at present, plate reconstructions for the Precambrian are poorly known. However, the possibility of reconstructing the LIP record back to and into the Archean and using this expanded LIP record to better constrain the origins and effects of LIPs is an exciting frontier, and our revised definition is a contribution to that effort.     

滇西昌宁—孟连地区依柳组、平掌组地层初议

<正> 滇西昌宁—孟连出露的火山岩系,1/100万普洱幅(1965)因其伏于中石炭统之下而称之下石炭统,1/20万凤庆幅(1981)、孟连幅(1982)分别创立平掌组、依柳组用以表示北部和南部的早石炭世火山岩,后被广泛采用并认为时代与地层对比问题已经解决(云南省地质矿产局,1990)。近年来有不少专事火山岩研究的工作者,如李涤辉(1989)、杨开辉(1989),也认为是一套地层并视为下石炭统。     

火山活动与气候变化研究进展

综述了火山活动对气候影响的研究进展。不同岩浆成分及喷发类型的火山活动对气候的影响不同：中酸性普林尼（Pl inian）式火山喷发主要造成气候变冷和臭氧层破坏，它导致气候变化的时间较短，但空间范围较大；大火成岩省造成气候变化的时空范围及程度均较大，它能够导致地表温度、海平面大幅度变化，最终引起生物灭绝；中小规模玄武质裂隙式喷发主要造成火山盆地内气候较大幅度变化，但对气候影响的持续时间较短，主要气候效应是导致附近地区温度快速下降和形成酸雨。简要阐述了第四纪火山活动的特点。     

21世纪初10年火山与地球内部化学研究进展

进入21世纪,我国除了在长白山天池火山、五大连池火山和腾冲火山三个主要活动火山区进行监测与研究,还开展了中国其他第四纪火山区的活动火山调查工作,发现并确定了一些新的活动火山,如镜泊湖、大兴安岭、乌兰哈达等第四纪火山区中存在的全新世火山.自峨眉山大火成岩省被确定以来,我国近10年在大火成岩省研究方面取得了重要进展,并新确定了一些新的大火成岩省,如塔里木大火成岩省和措美大火成岩省,逐渐为国际地学界所接受.     

天山石炭纪火山岩系中含有富Nb岛弧玄武岩吗?

中国西北部天山石炭纪—早二叠世裂谷火山作用代表了一个新近被认可的大火成岩省。有人认为,在天山石炭纪火山岩系中发育有富Nb岛弧玄武岩、埃达克岩和高镁安山岩组合。然而,该岩石组合具有与典型富Nb岛弧玄武岩、埃达克岩和高镁安山岩不同的化学和同位素特点,表明其并非是岛弧岩石组合。这一推断的岛弧岩石组合实际上是大陆板内火山岩组合,由未遭受地壳混染、受到地壳轻微混染和遭受地壳强烈混染的大陆火山岩组成。     

内蒙中部辉腾锡勒第四纪火山群初步研究

辉腾锡勒火山群位于内蒙古中部卓资县、察哈尔右翼中旗和后旗交界处的高山草原区。处于中国东部大同-阿尔山-诺敏河第四纪火山喷发带南段。火山群坐落在太古宙变质岩系、二叠纪花岗岩和新近纪汉诺坝玄武岩之上。平面上呈低洼的菱形台地，四周为山地，总面积约260km²。因上覆在汉诺坝玄武岩台地之上，故以往将其误归为新近纪汉诺坝玄武岩。火山群内发育近百座火山，大多数火山形貌保存基本完整。火山产物主要为一套碱性橄榄玄武岩，次为不同成因的火山碎屑物（岩）。碱性玄武岩覆盖在晚更新世坡积物和黄土之上。火山活动的时代主体为晚更新世，可进一步分为早、中、晚三期。早期为裂隙-中心式喷发，火口已剥蚀殆尽；中期主要形成"地池式"和玛珥式火山，火山形貌较完整，火口呈特征的圆形或椭圆形，大部分积水成湖，当地习称"九十九眼泉"或"海子"。晚期以熔浆的溢流为主，形成结构完整的盾片状火山。火山活动经历了沿裂隙的喷溢到中心式弱爆发、溢流-射汽岩浆爆发-溢流再到溅落堆积的演化过程。辉腾锡勒火山群是在新近纪汉诺坝玄武岩台地上新解体确定的第四纪火山群，这为研究蒙古高原南部地壳深部结构及其活动性提供了又一天然窗口，对了解新构造活动、环境及灾害预警研究都具有重要的理论和实际意义。     

Late Cenozoic Volcanism of the Vitim Depression and Its Correlation with the Vitim Lava Plateau (Western Transbaikalia) according to K–Ar Geochronology

New data on the geology, age, and composition of the Late Cenozoic volcanic rocks of the Vitim Depression, a satellite of the Vitim Lava Plateau (VLP), have been obtained. Two-stage volcanic activity has been revealed. In the Middle Miocene (14–13 Ma), a basalt and trachybasalt (hawaiite) lava covers were formed. In the Pleistocene (1.6–0.7 Ma), basanite erupted from scoria cones. Both stages of volcanism were coeval to similar pulses of volcanism within the VLP. However, unlike the latter, there were no Pliocene and Late Miocene eruptions within the Vitim Depression. Additionally, the Vitim Depression basalts have depleted geochemical characteristics comparative to those of the VLP. These features of the Vitim Depression volcanics imply their autonomous formation, whereas the synchroneity of the initial and final stages of volcanism in the depression and in the VLP reflects the existence of a common regulating mechanism of igneous activity.     

From initiation to termination: a petrostratigraphic tour of the Ethiopian Low-Ti Flood Basalt Province

Continental flood basalts (CFBs), thought to preserve the magmatic record of an impinging mantle plume head, offer spatial and temporal insights into melt generation processes in large igneous provinces (LIPs). Despite the utility of CFBs in probing mantle plume composition, these basalts typically erupt fractionated compositions, suggestive of significant residence time in the continental lithosphere. The location and duration of residence within the lithosphere provide additional insights into the flux of plume-related magmas. The NW Ethiopian plateau offers a well-preserved stratigraphic sequence from flood basalt initiation to termination, and is thus an important target for study of CFBs. This study examines modal observations within a stratigraphic framework and places these observations within the context of the magmatic evolution of the Ethiopian CFB province. Data demonstrate multiple pulses of magma recharge punctuated by brief shut-down events, with initial flows fed by magmas that experienced deeper fractionation (lower crust). Broad changes in modal mineralogy and flow cyclicity are consistent with fluctuating changes in magmatic flux through a complex plumbing system, indicating pulsed magma flux and an overall shallowing of the magmatic plumbing system over time. The composition of plagioclase megacrysts suggests a constant replenishing of new primitive magma recharging the shallow plumbing system during the main phase of volcanism, reaching an apex prior to flood basalt termination. The petrostratigraphic data sets presented in this paper provide new insight into the evolution of a magma plumbing system in a CFB province.     

A petrologist in South Africa: Frederick Henry Hatch and the Witwatersrand Goldfield

The English geologist, Frederick Henry Hatch (1864–1932), today mainly recalled for a textbook on igneous petrology, emigrated to South Africa, where, in the years between 1892 and 1906, he became one of the pioneers of the geology of the Transvaal and the Witwatersrand Goldfield. This article reviews his life and, in particular, his work during this period which led to his becoming a mining geologist with connections to many of the world's goldfields, set against the political background of the Boer War which influenced the course of his work.     

冀中坳陷火成岩岩石学及地球化学特征

冀中坳陷发育大量隐伏玄武质岩石,尤其是坳陷北部的廊固凹陷和霸县凹陷,岩石类型以玄武岩为主,辉绿岩次之,凝灰岩分布较少,火山角砾岩极少。通过岩心、镜下薄片及铸体薄片观察,主量和微量元素测试分析,表明该区火成岩为碱性玄武岩和拉斑玄武岩系列;REE配分曲线呈轻稀土元素富集型,Eu异常不明显;火成岩微量元素原始地幔标准化曲线呈强不相容元素富集。该区玄武岩的喷发环境为水下喷发;火成岩微量元素构造环境判别图解、岩石组合、岩石系列、稀土元素和微量元素特征表明该区火成岩形成于板内大陆裂谷构造环境。通过冀中坳陷玄武岩与邻区对比发现,冀中坳陷及邻区玄武岩岩浆活动具有随时代变化往北迁移的趋势,SiO2含量显示从南往北略为增加的趋势,北部稀土元素总量变化范围相对较大,轻稀土元素富集程度较南部低。     

大火成岩省与大规模黑色页岩沉积的成因联系及其意义

大火成岩省对全球性大气-海洋环境的巨变及生物灭绝有非常重要的影响。已有研究结果表明,显生宙（即寒武纪以来）大火成岩省与全球大洋缺氧与生物灭绝有明显的成因联系,显生宙国际地质年代表中多个金钉子均与以大火成岩省、黑色页岩及生物灭绝为代表的全球性地质事件相对应。但由于对前寒武纪,特别是"地球中年期"（18~8亿年,"枯燥的10亿年"）大气氧浓度、海洋的氧化-还原状态及生物门类及演化认识的局限性,关于前寒武纪大火成岩省与环境的影响及其与黑色页岩沉积的成因联系一直很不清楚。通过对全球哥伦比亚（奴那）超大陆中约13.8亿年全球性大火成岩省及黑色页岩沉积时空分布的研究,发现这些大火成岩省及黑色页岩的分布有明显的规律。约13.8亿年大火成岩省广泛分布在北美、格陵兰、西伯利亚、波罗地、卡拉哈里、刚果、西非、亚马逊、南极及西澳大利亚等大陆上;而同期的黑色页岩在华北及北澳大利亚克拉通广泛分布,在西伯利亚、巴西及印度等克拉通也有分布。根据这些黑色页岩在超大陆重建图中的空间分布,提出了哥伦比亚（奴那）超大陆中这些广泛分布的约13.8亿年黑色页岩可能沉积于连通的大型海相盆地,而不是以往所认为的局部封闭的小盆地。通过约13.8亿年大火成岩省与黑色页岩内火山灰（斑脱岩）年龄的对比,进一步提出约13.8亿年存在一次与全球性大火成岩省有关的大洋缺氧事件,以此期大火成岩省与黑色页岩为代表的全球性地质事件为中元古代盖层系与延展系提供了精确的界限年龄为1383 Ma。初步的研究结果还显示,"地球中年期"可能还有多期的大火成岩省与黑色页岩沉积有时空联系,有望为晚前寒武纪地质年代表划分提供新的事件约束。      

Geochemical discrimination of the geotectonic environment of basaltic-andesitic volcanic rocks associated with the Laochang polymetallic ore deposit at Lancang, Yunnan

1 Introduction The Laochang polymetallic ore deposit at Lancang is located about 30 km northwest of Lancang County seat, Yunnan Province, it is an ancient ore deposit with a history of nearly 600 years of exploitation. Regionally, this deposit belongs t…     

北山石炭纪-二叠纪火山岩成因及构造背景

北山古生代火山岩尤其是石炭纪-二叠纪火山岩的形成环境及成因备受学者关注且长期以来存在争议。本文收集了近年来发表的关于北山石炭纪-二叠纪火山岩研究的地球化学数据,岩石地球化学特征显示北山石炭纪玄武岩主要为安山玄武岩,属拉斑系列,二叠纪火山岩主要为安山玄武岩和亚碱性玄武岩,落入拉斑系列及过渡区;石炭纪玄武岩和二叠纪玄武岩均具有LREE富集的球粒陨石标准化稀土元素配分模式,轻重稀土元素分馏程度均较低。在微量元素蛛网图上,石炭纪-二叠纪遭受地壳混染的玄武岩呈现出明显的Nb-Ta亏损和微弱的Ti亏损特征,而未遭受地壳混染作用的绝大多数石炭纪-二叠纪玄武岩主要呈现出与OIB相似的"隆起"状不相容元素标准化配分模式。岩石成因分析认为,石炭纪-二叠纪玄武质岩浆可能主要来源于地幔柱,部分石炭纪-二叠纪玄武岩在形成演化过程中遭受了明显的大陆地壳混染作用,导致其出现十分相似于岛弧或活动大陆边缘的地球化学特征。结合区域构造演化分析及构造环境判别,认为石炭纪-二叠纪玄武岩均形成于大陆板内环境。