新疆额尔齐斯地区裂谷火山岩的初步研究

新疆富蕴县西部上石炭统喀喇额尔齐斯组的变质火山岩,是一套多旋回双峰式古裂谷型火山岩.基性成员为玄武岩。酸性成员为流纹岩.基性岩套由拉斑玄武岩-碱性玄武岩组成.微量元素分配模式证明了地幔成分不均一性;玄武岩浆来自石榴二辉橄榄岩44％的分批熔融;证明古裂谷是在岛弧基础上演化形成。从而说明额尔齐斯断裂带经历了俯冲-碰撞-裂谷三个演化阶段.晚期的碱性玄武岩喷发,标志裂谷作用的消亡.     

攀西裂谷存在吗？

大陆裂谷以地幔上隆、岩石圈伸展、减薄、断陷和沉降为特征，伸展构造环境是大陆裂谷形成的必要条件和本质特征。中国学者以前所认为攀枝花-西昌裂谷的主要标志是海西期层状堆晶杂岩、晚二叠世峨眉山玄武岩、印支期环状碱性杂岩和晚三叠世裂谷盆地沉积。最近一系列研究成果表明攀西地区海西期-印支期构造岩浆热事件是地幔柱和岩石圈相互作用的结果，不是裂谷作用的产物。进一步对上扬子西缘二叠纪-三叠纪的沉积作用和构造特征综合分析表明攀西地区不存在裂谷盆地沉积。该区晚二叠世-中三叠世为古陆隆起遭受剥蚀，晚三叠世断陷型类磨拉石建造是前陆走滑复合盆地的产物。本文根据对攀西地区二叠纪-三叠纪的岩浆活动、沉积作用、构造特征和地球物理资料等方面综合研究对攀西裂谷的存在提出质疑，并以峨眉山地幔柱活动为主线探讨了攀西地区古生代和中生代的地质构造演化历史。     

藏东南碧土带瓦浦组火山岩形成的大地构造环境

首次对藏东南原称的瓦浦组进行系统的岩石化学研究 ,发现它包括了两套不同时代和大地构造环境下形成的火山岩。瓦浦组火山熔岩由下部的玄武岩夹玄武安山岩和上部的流纹岩组成 ,是古特提斯洋盆中的洋岛火山岩 ,其时代初定为早二叠世—晚二叠世早期。在觉马—巴格和扎西所见的岩层是以钙质浊积岩为主的火山 -沉积岩系 ,火山岩为岛弧拉斑玄武岩 ,属晚三叠世早期活动大陆边缘产物。上述发现为碧土带是复杂的造山带拼贴体、古特提斯主洋盆是开阔的多岛洋和晚三叠世活动大陆边缘可能属马里亚纳型提供了重要证据     

新疆阿吾拉勒山西段下二叠统陆相火山岩岩石地球化学特征、成因及构造背景

新疆阿吾拉勒山西段是伊犁石炭-二叠纪裂谷的重要组成部分,本文对该区下二叠统典型的双峰式玄武岩-流纹岩组合进行了系统的岩相学和岩石地球化学研究。岩石整体高Na2O、高Al2O3、低TiO2、富碱。玄武岩富集大离子亲石元素Ba、K、LREE和P,亏损高场强元素Th、U、Ta、Nb。粗面斑岩和流纹斑岩富集大离子亲石元素Rb、K、LREE、高场强元素Th、Zr、Hf,亏损Ta、Nb、Sr、Ti和P。玄武安山玢岩的蛛网图与粗面斑岩和流纹斑岩较为一致,但少量元素的特征与玄武岩相似。玄武岩浆来源于弱亏损地幔,并受到了下地壳物质的混染,而玄武安山玢岩、粗面斑岩和流纹斑岩则可能来源于地壳物质的部分熔融。双峰式火山岩的形成可能与上地幔玄武岩浆的底侵作用有关。裂谷演化导致的陆相火山活动持续到早二叠世晚期达到顶峰,中二叠世以后,构造环境由拉伸转为挤压,裂谷演化趋于终止。该区石炭纪末-早二叠世的裂谷活动与整个天山地区晚古生代的构造演化背景具有一致性。     

康滇裂谷带火山活动及其碱性（钠质）火山岩系特征

元古代，夹持于现今安宁河－元谋深断裂与小江深断裂之间的地区，是扬子古大陆的边缘裂谷，本文以“康滇裂谷带”命名。研究结果表明，该区广泛发育的元石代碱性火山岩系列及细碧－角斑岩类火山岩组合，是裂谷火山活动的产物，火山活动时限１９５０－９００Ｍａ，可划分为大红山群及昆阳群两个火山旋回。火山岩系多属碱性玄武岩系列，火山活动的中晚期，分异出少量亚碱性拉斑紊武岩系列和高铝玄武岩系列。裂谷带火山喷发区地壳厚度１     

藏北羌塘南部地区基性岩墙与玄武岩的岩浆同源性

青藏高原羌塘南部地区沿龙木错－双湖缝合带南侧成群分布着近东西向的基性岩墙,形成时代为晚石炭世—早二叠世,其围岩是以晚石炭世—早二叠世裂谷型沉积为主并夹有基性火山岩的浅变质岩系。基性火山岩夹层的数量和厚度有由北向南由多变少的趋势。基性岩墙的岩石类型主要为辉绿岩,火山岩以玄武岩为主,玄武安山岩次之。基性岩墙与基性火山岩在空间上密切共生,形成于大致相同的地质时期内。二者均经历了低绿片岩相变质作用,且化学成分相近,稀土元素、微量元素组成均与板内玄武岩具有相似的特点。初步判定羌塘南部地区基性岩墙群与基性火山岩来自同一岩浆源,为晚石炭世—早二叠世冈瓦纳大陆北缘裂解的产物。     

新疆于田普鲁-阿羌石炭纪裂谷地质特征及成矿意义

新疆于田普鲁—阿羌石炭纪裂谷 ,发育于塔里木板块晚古生代被动陆缘之上。裂谷发展经历了两个阶段 ,即早石炭世裂谷形成发展阶段和晚石炭世—早二叠世裂谷敛合阶段 ,形成发展阶段主要为双峰式火山岩建造 ,敛合期以钙碱性安山岩、基性玄武岩为主间夹灰岩、砂砾岩等。该裂谷为塔里木南缘晚古生代活动带的一部分。活动带内大量火山岩浆活动为以铜为主的多金属成矿提供良好条件 ,同时深大断裂活动使金刚石成矿成为可能。对该活动带的深入研究不仅对古特提斯演化研究具有重要意义 ,而且对指导找矿具有非常重要的现实意义。     

川西义敦古火山弧的火山建造

义敦古火山弧是松潘-甘孜造山带地质演化中极其重要的地质构造单元,本文对构成义敦古火山弧主体的海相火山建造进行了系统分析.按岩石地层单位的划分原则,重新厘定了火山地层的界线.这套火山建造主要由玄武岩、安山岩、流纹岩、粗面岩组成,并出现了特殊的钾玄岩组合.火山岩序列经历了由晚二叠世至早中三叠世初始裂谷的亚碱性岩系拉斑系列、碱性岩系钠质系列,到晚三叠世早期不成熟岛弧的亚碱性岩系拉斑系列、钙碱系列,再到晚三叠世晚期成熟岛弧的亚碱性岩系钙碱系列、碱性岩系钾质系列的演化过程.按照地层结构和火山喷发的自旋回单位,成熟岛弧期的火山建造可分为三个大旋回、四个大的韵律,并建立了火山岩地层模型.尝试利用层序地层学原理,把该套火山-沉积地层分为两个层序、五个准层序组,反映了海平面相对升降及沉积速率的变化.按变质矿物组合,该套火山地层的变质作用可分为三期:火山期后热液及成岩变质;区域动力变质;晚期热液及矿化热液蚀变.岩石地球化学分析表明,该火山建造总体属同源岩浆演化系列,母源有可能是石榴石或尖晶石二辉橄榄岩,并经历了早期熔融分离及围岩的长期交换.     

西藏松西地区辉绿玢岩岩石化学、地球化学特征及构造环境

青藏高原南羌塘石炭纪-二叠世地层中侵入大量的辉绿玢岩岩墙群，其侵位时代为晚古生代。区域资料显示，这一时期该地区处于冈瓦纳大陆北部边缘。岩石化学、地球化学特征表明，辉绿玢岩与洋脊型、洋岛型及典型的大陆裂谷玄武岩都有明显区别，显示出大陆拉张带（或初始裂谷）的拉斑玄武岩特征。辉绿玢岩是冈瓦纳被动陆缘在晚古生代裂解的产物。     

昌宁—孟连地区火山岩系基本特征及构造环境的认识

昌宁-孟连地区是我国研究古特提斯演化的重点地区之一，该区不同时代火山岩的性质为大地构造演化提供了重要依据。（1）变质火山岩，由玄武岩-玄武安山岩及偏碱性玄武岩所组成，时代可能为晚一中元古代，具有大洋中脊型玄武岩特征；（2）下石炭统火山岩，由橄榄玄武岩-碱性橄榄玄武岩组成，具裂谷洋盆玄武岩特征；．（3）上二叠统火山岩，为一套高镁质偏碱性的基性一超基性火山岩，具快速张裂之裂谷洋盆玄武岩特征；（4）上二叠统-三叠系火山岩，为一套碱性中基性火山岩，以爆发相为主，其喷发环境显示由浅水相向陆相的转化，具弧后裂谷火山岩特征。上列各期火山岩展示，昌宁-孟连地区大地构造发展是从残留洋盆经历过两度“打开-闭合”的过程。晚古生代（石炭纪-二叠纪）该区从被动大陆边缘裂陷逐渐发展为局部具有新生洋壳性质之裂谷系环境。     

四川龙舟山玄武岩的岩石学特征及成因探讨

龙舟山玄武岩一直被认为是与P_2峨眉山玄武岩相当的溢流玄武岩。笔者的观察和研究表明:只有龙舟山玄武岩的上部才相当于P_2峨眉山玄武岩;下部则具有分期复杂的特点。本区玄武岩的演化具典型的板内裂谷玄武岩演化特点,玄武岩的演化同攀西裂谷的构造演化是一致的。     

吉林省长白山地区新生代火山岩的特点及其成因

长白山地区新生代火山岩是一套玄武岩、粗面岩和钠闪碱流岩的双峰式火山岩组合。玄武岩类分别属于碱性玄武岩系列和拉斑玄武岩系列。奶头山期玄武岩是幔源原生岩浆直接喷发于地表的产物,其他各期玄武岩是幔源原生岩浆经历了一定程度分异作用的产物。粗面岩和钠闪碱流岩与玄武岩有成因联系,可能是玄武岩浆通过分离结晶作用而形成的。本区新生代火山岩是大陆裂谷构造环境下的产物,是在地幔增温和底辞上升过程中形成的。     

南秦岭勉略带两河弧内裂陷内火山岩组合地球化学

两河火山岩岩片位于秦岭微板块与扬子板块的分界断裂－巴山弧形构造混杂带内。岩石内亚碱性拉班系列玄武质岩石和钙碱性英安岩、流纹岩组成。基性岩和酸性岩均具有高Ｂａ,低Ｔｈ、Ｕ,显著的Ｎｂ、Ｔａ亏损和Ｔｉ的负异常等地球化学特征,玄武岩的Ｔｈ／Ｙｂ－Ｔａ和Ｔｉ／Ｚｒ－Ｔｉ／Ｙ不活动痕量元素组合特征指示这套火山岩可能产于弧间盆地环境。是勉略洋盆在古生代晚期－中生代早期发育期间洋壳俯冲及弧内裂陷的岩浆作用产物。     

Magma mixing in the 1100 AD Montaña Reventada composite lava flow,Tenerife, Canary Islands: interaction between rift zone and central volcano plumbing systems

Zoned eruption deposits commonly show a lower felsic and an upper mafic member, thought to reflect eruption from large, stratified magma chambers. In contrast, the Montaña Reventada composite flow (Tenerife) consists of a lower basanite and a much thicker upper phonolite. A sharp interface separates basanite and phonolite, and chilled margins at this contact indicate the basanite was still hot upon emplacement of the phonolite, i.e. the two magmas erupted in quick succession. Four types of mafic to intermediate inclusions are found in the phonolite. Inclusion textures comprise foamy quenched ones, others with chilled margins and yet others that are physically mingled, reflecting progressive mixing with a decreasing temperature contrast between the end-members. Analysis of basanite, phonolite and inclusions for majors, traces and Sr, Nd and Pb isotopes show the inclusions to be derived from binary mixing of basanite and phonolite end-members in ratios of 2:1 to 4:1. Although, basanite and phonolite magmas were in direct contact, contrasting ²⁰⁶Pb/²⁰⁴Pb ratios show that they are genetically distinct (19.7193(21)–19.7418(31) vs. 19.7671(18)–19.7807(23), respectively). We argue that the Montaña Reventada basanite and phonolite first met just prior to eruption and had limited interaction time only. Montaña Reventada erupted from the transition zone between two plumbing systems, the phonolitic Teide-Pico Viejo complex and the basanitic Northwest rift zone. A rift zone basanite dyke most likely intersected the previously emplaced phonolite magma chamber. This led to eruption of geochemically and texturally unaffected basanite, with the inclusion-rich phonolite subsequently following into the established conduit.     

勉略结合带五里坝火山岩的地球化学研究及其构造意义

五里坝火山岩位于扬子与秦岭微板块的分界断裂:巴山弧两河—饶峰—石泉—高川蛇绿构造混杂带内,岩石为一套双峰式火山岩组合,由亚碱性玄武岩和亚碱性英安流纹岩组成。基性岩和酸性岩均具有显著的Nb、Ta亏损,玄武岩的Th/Yb-Ta/Yb和Ti/Zr-Ti/Y不活动痕量元素组合特征指示这套双峰式火山岩具有岛弧火山岩的地球化学特征,形成于特殊的洋内岛弧弧内裂陷的大地构造环境。五里坝火山岩应是勉略洋盆在古生代晚期—中生代早期发育期间洋壳俯冲及裂陷的岩浆作用产物。它可能是勉略缝合带在巴山弧地区出露的重要岩石学证据。     

秦岭造山带南缘早古生代基性火山岩地球化学特征及其大地构造意义

秦岭造山带南缘早古生代基性火山岩元素地球化学特征,显示其形成于大陆板块内部构造环境,岩石稀土总量高,稀土分布模式为轻稀土强烈富集型,微量元素分布模式类似于大陆溢流玄武岩,综合主元素,微量元素地球化学研究认为,南秦岭造山带南部边缘的早古生代基性火山岩为板内伸展－初始裂谷环境的拉斑质大陆玄武岩,区域对比表明,南秦岭与扬子陆块之间的早古生代晚期是大陆板伸展裂陷环境,这种伸展扩张的动力学体制始于早古生代初     

Petrochemistry of Cenozoic basalts and associated rocks in the Baikal rift zone

The main episode of Cenozoic volcanic activity occurred simultaneously with formation of the Sayan—Baikal uplift, before the rift depressions were initiated. Volcanism and rifting in this region have developed as independent processes, connected with each other only by an ultimate primary mantle energy source. The volcanic regions do not coincide with the rift depressions, except in the Tunka graben.Chemical features of the volcanics show that during the entire period of volcanic activity there was a complex alternation of basaltic lavas of alkaline, intermediate and tholeiitic composition. Both alkaline and subalkaline lavas are distributed over the entire volcanic region, excepting the Tunka depression where tholeiitic lavas are predominant. However, there is neither mineralogical nor chemical evidence for the existence of two separate magma types within the Baikal rift zone.Judging by the presence of high-pressure, lherzolitic megacrysts of clinopyroxene, and to a lesser extent titaniferous biotite and amphibole in alkaline basalts, variations of lava chemistry are connected with high-pressure fractionation of initial melts, which was more complete for sources outside the rift zone. The predominance of tholeiitic lavas in the Tunka depression is likely to have been caused by a higher degree of partial melting and quick ascent of magma to the surface, facilitated by a high geothermal gradient under the depression where crustal extension is taking place.     

滇西南昌宁—孟连构造带火山岩地层学研究

昌宁—孟连构造带火山岩非常发育,是重要的含矿岩系。在构造带南段,火山岩统称为依柳组,北段统称为平掌组下段,以往时代均归属早石炭世。本文工作表明,该区火山岩可分为两套:一套为早石炭世火山岩,分布于该构造带西部,以拉斑玄武岩系列为主,代表大洋中脊、洋岛残留物,仍称为依柳组;另一套为晚二叠世火山岩,分布于构造带中、东部,以碱性玄武岩系列为主,可能属亚速尔型洋岛火山岩范畴,而非大洋蛇绿岩套,新命名为老厂组。     

Geochemistry of the Caledonian basic volcanic rocks at the south margin of the Qinling orogenic belt, and its tectonic implications

The geochemistry of the basic volcanic rocks at the south margin of the Qinling orogenic belt(SMQOB) suggests that they were formed in an intraplate tectonic setting.The REE distribution patterns show these rocks are strongly enriched in LREE with high ∑REE, and their trace elements geochemistry is similar to that of contimental flood basalt.All the above evidence suggests that the Caledonian basic volcanic rocks in the SMQOB were tholeiitic basalts formed in an intraplate spreading-initial rift tectonic setting.The characteristics of regional geology and geochemistry indicate that there was an intraplate spreading-rift tectonic setting between the South Qingling block and the Yangtze block in the Caledonian epoch.The dynamic spreading in this district began in the Early Caledonian and then the intraplate spreadinginitial rifts were formed in the Late Caledonian.As a result of spreading of the Tethys and geodynamic processes in deep mantle ,the Mianlue-Huashan oceanic basin was formed between the Qinling block and the Yangtze block in Devonian,and the Qinling microplate was separated from the northern part of the Yangtze plate.     

Indian Continental Crust Recovered from Elan Bank, Kerguelen Plateau (ODP Leg 183, Site 1137)

At Site 1137 on Elan Bank of the Kerguelen Plateau, a largeigneous province in the southern Indian Ocean, a fluvial, volcaniclastic,polymict conglomerate and a fluvial sandstone are intercalatedwith subaerially erupted tholeiitic basalt flows. Clasts recoveredfrom the conglomerate have highly variable lithologies, includingalkali basalt, rhyolite, trachyte, granitoid and gneiss. Majorand trace element abundances and whole-rock isotopic data forthe sandstones, the conglomerate matrix and representative clastsfrom the conglomerate are used to infer the origin of thesediverse rock types. The gneiss clasts show an affinity to crustalrocks from India, particularly those of the Eastern Ghats Beltand its possible East Antarctic corollary, the Rayner Complex.The felsic volcanic clasts are not genetically related to theintercalated basalt flows, despite being erupted contemporaneouslywith these basaltic magmas. These felsic volcanic clasts probablyformed from partial melting of evolved upper continental crust.The granitoid also probably formed by partial melting of continentalcrust and could be an intrusive equivalent of the felsic volcanicrocks. In contrast, the alkali basalt clasts have isotopic compositionsthat are more similar to those of the tholeiitic basalt flowsrecovered at Site 1137; however, these clasts are highly alkalic(tephrite to phonotephrite) and have a distinct petrogenesisfrom the tholeiitic basalt flow units. KEY WORDS: geochemistry; Indian Ocean; Kerguelen Plateau; large igneous provinces; Ocean Drilling Program