辽北开原岩群蛇绿混杂岩的特征

岩石化学,地球化学资料表明,中晚元古开原岩群蛇绿混杂岩由蛇绿岩和岛弧拉斑玄武岩、钙碱玄武岩、钙碱性基性－中性火山岩、陆缘碎屑岩组成。蛇绿岩由绿泥滑石片岩,角闪岩类岩石,石英岩视肽诿古温都尔庙群蛇绿岩,吉林色洛河群同时位于古华北陆块北缘,为陆缘活动带向古华北陆块俯形,这表明古华北陆块北缘造带在中晚元古代即已出现。     

辽北开原岩群蛇绿混杂岩的特征

岩石化学、地球化学资料表明,中晚元古代开原岩群蛇绿混杂岩由蛇绿岩和岛弧拉斑玄武岩、钙碱玄武岩（斜长角闪岩、角闪石岩）、钙碱性基性—中性火山岩（变粒岩）、陆缘碎屑岩（浅粒岩）组成。蛇绿岩由绿泥滑石片岩（橄榄岩）、角闪岩类岩石（大洋拉斑玄武岩）、石英岩（远洋深海硅质岩）组成。与内蒙古温都尔庙群蛇绿岩,吉林色洛河群同时位于古华北陆块北缘,为陆缘活动带向古华北陆块俯冲形成。这表明古华北陆块北缘造山带在中晚元古代即已出现。     

内蒙古北山地区月牙山蛇绿质构造混杂岩带地质特征、形成时代及大地构造意义

月牙山蛇绿质构造混杂岩带位于红柳河—洗肠井蛇绿岩带东部的月牙山一带。月牙山蛇绿岩套出露较完整,自下而上由超基性杂岩、辉长岩、层状玄武岩、枕状玄武岩及放射虫硅质岩组成。蛇绿岩套北侧发生了强烈的构造混杂作用,形成蛇绿质构造混杂岩带,由强糜棱岩化、强蛇纹石化的辉橄岩、玄武岩基质和辉石岩、堆晶辉长岩、斜长花岗岩、橄榄岩、橄辉岩、角闪石岩、白云岩、放射虫硅质岩、蚀变玄武岩等岩块组成。通过对蛇绿岩套中辉石岩、辉长岩、斜长花岗岩、辉长闪长岩及蛇绿岩套北侧斜山——东七一山火山弧中的安山岩、花岗闪长岩等开展锆石U-Pb同位素测年研究,确定月牙山蛇绿岩套形成时代约为530Ma,相当于早寒武世;洋盆发生大规模自南向北俯冲作用的时间为421.0±15~442.4±1.5Ma,相当于志留纪。通过对蛇绿岩带两侧地层形成环境及蛇绿岩带对两侧地层单位的限定意义等研究认为,红柳河—洗肠井蛇绿岩带是代表古大洋闭合的板块缝合带,以该带为界,北侧为哈萨克斯坦板块,南侧为塔里木板块。     

内蒙古北山地区月牙山蛇绿质构造混杂岩带地质特征、形成时代及大地构造意义

月牙山蛇绿质构造混杂岩带位于红柳河—洗肠井蛇绿岩带东部的月牙山一带。月牙山蛇绿岩套出露较完整,自下而上由超基性杂岩、辉长岩、层状玄武岩、枕状玄武岩及放射虫硅质岩组成。蛇绿岩套北侧发生了强烈的构造混杂作用,形成蛇绿质构造混杂岩带,由强糜棱岩化、强蛇纹石化的辉橄岩、玄武岩基质和辉石岩、堆晶辉长岩、斜长花岗岩、橄榄岩、橄辉岩、角闪石岩、白云岩、放射虫硅质岩、蚀变玄武岩等岩块组成。通过对蛇绿岩套中辉石岩、辉长岩、斜长花岗岩、辉长闪长岩及蛇绿岩套北侧斜山——东七一山火山弧中的安山岩、花岗闪长岩等开展锆石U-Pb同位素测年研究,确定月牙山蛇绿岩套形成时代约为530Ma,相当于早寒武世;洋盆发生大规模自南向北俯冲作用的时间为421.0±15~442.4±1.5Ma,相当于志留纪。通过对蛇绿岩带两侧地层形成环境及蛇绿岩带对两侧地层单位的限定意义等研究认为,红柳河—洗肠井蛇绿岩带是代表古大洋闭合的板块缝合带,以该带为界,北侧为哈萨克斯坦板块,南侧为塔里木板块。     

新疆木纳布拉克蛇绿岩地球化学特征及形成构造背景分析

木纳布拉克蛇绿岩是新疆境内最大的蛇绿混杂岩带,由超镁铁质岩、镁铁质岩、浅色分异物和变玄武岩组成,形成时代为中元古代晚蓟县世,侵位时代为新元古代早青白口世,可能代表了阿尔金山地区中元古代的板块俯冲带.蛇绿岩可能形成于孤后或孤间有限洋盆小扩张脊;最后侵位到深海沉积物中,形成了造山带中的蛇绿岩.     

阿尔金北缘沟口泉古元古代蛇绿混杂岩(绿岩)地质特征及意义

近年经过区域地质调查,在阿尔金北缘沟口泉地区新识别出一套古元古代蛇绿混杂岩,其由洋壳岩块、上覆岩系及外来岩块等组成,洋壳岩块包括变质橄榄岩-堆晶超镁铁质岩、辉长质杂岩、斜长岩、斜长花岗岩、辉绿岩和镁铁质火山熔岩等,为一层序较完整的蛇绿岩套。根据对其各组成单元分布、岩石组合、岩石学、地球化学、同位素年代学等方面的研究以及在变质辉橄岩、斜长岩、辉长岩和玄武岩等岩石中获得锆石U-Pb SHRIMP定年加权平均值年龄(1 889±27)Ma、(1 869±27)Ma、(1 836±40)Ma、(1 818±25)Ma及数个2 200~2 600Ma单点年龄数据,证实了阿尔金北缘地区新太古宙末-古元古代存在一洋盆,并于古元古代末俯冲碰撞闭合形成了沟口泉蛇绿混杂岩,初步判定其为地幔柱型(P型)蛇绿岩。该发现为塔里木南缘阿北-敦煌地块与阿尔金造山带新太古宙末—古元古代构造演化提供了充分依据,对早前寒武纪地壳演化研究具有重要的地质意义。     

波密地区帕隆藏布残留蛇绿混杂岩带的发现及其意义

在进行1：25万墨脱幅地质调查中，笔者首次在波密地区发现和填绘出了帕隆藏布残留蛇绿混杂岩带。帕窿藏布残留蛇绿混杂岩呈串珠状产出于花岗岩类侵入岩中，其岩石组合为橄揽辉石岩、辉石岩、辉长岩、辉长辉绿岩、辉绿岩、石英岩和大理岩，局部可见条带状硅质岩。上述组分之间的相互关系表明，蛇绿岩在花岗岩类岩石侵入之前发生过构造混杂和变形。根据沉积岩所记录的盆地演化过程、蛇绿岩的Rb-Sr年龄值以及残留蛇绿混杂岩带两刨花岗岩类岩石的特征和生成时代综合分析认为：帕隆藏布残留蛇绿混杂岩带形成于石炭-二叠纪的弧间盆地中，至少在晚三叠纪之前出现洋壳，在消减过程中向北俯冲并在中侏罗世之前闭合(弧-弧碰撞)。     

西藏班公湖蛇绿岩组合层序、地球化学及其成因研究

班公湖蛇绿岩带位于班公湖-怒江结合带西段,蛇绿岩均遭受了强烈挤压构造变形而形成蛇绿混杂岩带.通过对不同类型的蛇绿混杂岩片按正常蛇绿岩层序重新组合排列,恢复后的蛇绿岩层序综合剖面可与典型洋壳剖面对比,自下而上层序为：①变质橄榄岩,主要为强蛇纹石化斜辉橄榄岩和纯橄岩;②堆积岩,由层状辉长岩和层状橄榄岩组成;③辉长辉绿岩岩墙群;④镁铁质熔岩,可分为块状熔岩和枕状熔岩;⑤深海-半深海沉积,岩性为放射虫硅质岩、浊积岩、灰岩等.地质构造和地球化学特征对比综合分析表明,该区蛇绿岩主要形成于中特提斯洋中脊、洋岛环境,中特提斯洋可能为比较成熟的大洋盆地,而不是发育不完全的陆间小洋盆或边缘海盆地.     

塔里木古大陆东缘的微大陆块体群

塔里木古大陆东缘至少存在4个微大陆，自北而南分别是阿拉善、祁连、欧龙布鲁克和柴达木微大陆，它们有相近但又有一定差异的早前寒武纪变质基底和中元古代变质沉积地层。每一个微大陆边缘均有复杂的生成历史，特别是新元古代早期的热-构造事件十分发育，并在柴达木微大陆北缘形成一条长700km的花岗片麻岩带，而在多数微大陆边缘则叠加了寒武纪至奥陶纪火山弧或蛇绿混杂岩。在微大陆之间自北而南分别发育了北祁蛇绿岩混杂岩带、南祁连蛇绿岩混杂岩带、沙柳河-鱼卡河高压-超高压变质带和昆仑中部清水泉蛇绿混杂岩，它们代表了微大陆这间的结合带，其形成时代集中在寒武纪至奥陶纪。这几个微大陆总体表现出亲塔里木古大陆的特征，特别是自新元古代以来具有相似的地质演化特征。     

日喀则市幅地质调查新成果及主要进展

将原“修康群”解体为6个组级岩石地层单位。发现并确定雅鲁藏布缝合带为由雅鲁藏布蛇绿岩带、混杂岩带、高压变质带组成的一个完整而又精典的缝合带，精细刻画了各带的结构、组成及特征。蛇绿岩带厘定为“卡堆型”、“仁布型”、“白朗型”、“日喀则型”4种类型；确定混杂岩带由沉积混杂岩、构造混杂岩两大类型组成，细划并描绘出4种体态类型；识别出由蓝片岩组成的高压变质带，该带的确认使得国内外地学界长期关注的重大疑难问题得到初步解决。发现雅鲁藏布江浆混体系，发现并初步研究了冈底斯岩浆弧中的埃达克岩，新发现雅鲁藏布江流域发育数十个类似“仁布古堰塞湖”地质地貌特征的古湖泊。     

阿拉善地块北缘恩格尔乌苏地区发现志留纪侵入体

阿拉善地块北缘地区位于中亚造山带的南缘中段,连接了兴蒙造山带和北山造山带等构造单元,其古生代的构造演化对于中亚造山带南缘构造单元的对比连接具有重要的意义,是研究中亚造山带古生代构造演化的关键位置。统计归纳近年来阿拉善地块北缘地区的年代学数据发现,该地区的岩浆活动主要集中在晚古生代期间,特别是二叠期间,尚没有早古生代侵入岩的报道。恩格尔乌苏蛇绿混杂岩是阿拉善地块北缘地区出露的一条重要蛇绿岩带,本次研究在该混杂岩带中发现了早古生代的黑云母花岗岩。通过锆石LA-ICP-MS U-Pb年代学测试发现其时代为423±4.5 Ma和434±1Ma,代表了其岩浆结晶年龄,表明该侵入岩形成于志留纪期间,是阿拉善地块北缘地区最早发现的早古生代侵入体之一。该志留纪岩体的发现,表明恩格尔乌苏混杂岩在带志留纪期间已经出现岩浆活动,具有多期活动的特征。该志留纪岩体的发现,是研究、认识阿拉善地块北缘地区早古生代构造环境的重要对象,对于连接对比东、西相邻构造单元具有重要的意义。结合相邻白山组地层的碎屑锆石时代及晚泥盆世侵入岩的发现等研究成果推断,阿拉善地块北缘地区在早古生代开始就存在岩浆活动,该地区可能并非是早古生代的稳定被动大陆边缘。     

Relationships Between the North China Plate and the Tarim Plate1

Abstract The relationships and boundary between the North China and Tarim plates have been unclear for a long time; however, the two plates occupy a prominent position in the formation and evolution of the continental lithosphere of China. It is proposed that the Engger Us ophiolitic mélange zone discovered recently north of Alaxa is a typical suture between the two plates. The ophiolitic mélange zone is composed mainly of a mixture of fragments of ancient oceanic crust and sedimentary rocks of active and passive continental margins. The mélange may be divided into tectonic inclusions and matrix. The suture extends northeastwards into the Republic of Mongolia and probably westwards to meet the Altun fault. With the Engger Us ophiolitic mélange zone as the boundary the Alaxa area may be divided into two parts: the northern part (AN) belongs to the Tarim plate, while the southern part (AS) the North China plate. Geological evidence shows that the two plates were amalgamated in the Late Permian or a bit later.     

湘东北文家市蛇绿混杂岩带的发现及意义

在湘东北文家市首次识别出蛇绿岩套残片 ,它由变沉积岩、变玄武岩、变辉绿岩、变辉长岩、变辉石岩类及变硅质岩组成。综合其地质学、岩石学、地球化学和同位素年代学的资料 ,提出文家市蛇绿岩可能形成于有限小洋盆的构造环境。文家市蛇绿混杂岩带、前陆盆地、磨拉石建造和“S”型花岗岩等构造岩石组合记录了碰撞造山的全过程 ,证实了江南雪峰古陆属元古宙造山带。这一发现为华南前寒武纪的大地构造格架和地壳演化提供了依据 ,同时该地区也将成为研究早期华南大陆地壳演化———武陵运动的关键地带。     

西藏果芒错蛇绿混杂岩中硅质岩的地球化学特征及其形成环境

果芒错蛇绿混杂岩位于狮泉河—永珠—嘉黎蛇绿混杂岩带中段,是该带中保存较好的一套蛇绿混杂岩,其形成环境是确定狮泉河—永珠—嘉黎蛇绿混杂岩带构造属性的重要依据。对果芒错蛇绿混杂岩中的硅质岩进行了地球化学分析,为判断蛇绿混杂岩的形成环境提供新的约束条件。硅质岩通常呈几十厘米夹层产于玄武岩中,含有大量晚三叠世—白垩纪放射虫化石。硅质岩SiO2含量为71.38%~77.67%,Al2O3含量为8.62%~11.51%,MnO/TiO2值为0.28~0.35,(Ce/Ce*)SN值为0.92~0.94,(La/Ce)SN值为1.13~1.17,反映了陆源物质的影响,而V、Ni、Cu和V/Y值高于大陆边缘硅质岩,与洋中脊和大洋盆地硅质岩相似,说明果芒错硅质岩可能形成于受陆源物质影响且与大陆边缘有一定距离的环境中。结合变质橄榄岩、镁铁质岩墙和玄武岩的地球化学特征,初步认为果芒错蛇绿混杂岩的形成环境为靠近大陆边缘的弧后盆地。     

西秦岭太白地区岩湾－鹦鸽咀蛇绿混杂岩的 地质特征及形成时代

岩湾-鹦鸽咀蛇绿混杂岩是秦岭商丹蛇绿混杂岩带的重要组成部分,由变质基性火山岩(玄武岩)、蛇纹岩、变辉长岩、硅质岩、变复理石(云母石英片岩)等构造岩块组成.其中变基性火山岩具有N-MORB的地球化学特征,安山岩具有与俯冲作用密切相关的岛弧火山岩的性质.玄武岩的锆石SHRIMP U-Pb年龄为483 Ma±13Ma,与天水关子镇和丹风蛇绿混杂岩的时代相一致.对岩湾-鹦鸽咀蛇绿混杂岩的岩石组成和形成时代进行研究,可为进一步探讨商丹蛇绿混杂岩带和秦岭造山带的增生造山作用提供重要证据.     

Mesoproterozoic ophiolitic mélange from the SE periphery of the Indian plate: U–Pb zircon ages and tectonic implications

The Kanigiri mélange within the Proterozoic Nellore–Khammam schist belt in southern Peninsular India includes ophiolitic fragments that represent the remnants of an oceanic plate. The ophiolitic units were accreted along a NE-trending suture that juxtaposes the Proterozoic Eastern Ghats Granulite Belt (EGGB) against the Archean Nellore Schist Belt of the Dharwar craton. The ophiolite components in the Kanigiri mélange include plagiogranites and gabbros which show mutually intrusive relations indicating their coeval nature. We report laser ablation-ICP-MS age data and REE geochemistry of zircons from the gabbro and granite. The zircons from both gabbro and granite show high REE contents, prominent HREE enrichment and a conspicuous negative Eu anomaly, suggesting a common melt source. Zircon REE abundances and normalized patterns show little intersample and intrasample variations. U–Pb dating of the zircons reveals prominent Mesoproterozoic ages for the plagiogranite, with the ca.1.33 Ga age of the Kanigiri ophiolitic mélange offering important clues for arc–continent collision during the final stages of amalgamation of the Columbia-derived fragments within the Neoproterozoic supercontinent assembly.     

Geochemical constraints on Carboniferous volcanic rocks of the Yili Block (Xinjiang,NW China): Implication for the tectonic evolution of Western Tianshan

The Yili Block is important for understanding the Late Paleozoic geodynamic evolution of Central Asia. It is bounded to the north by the Northern Tianshan Carboniferous flysch and ophiolitic mélange. The center of the Block is dominated by Carboniferous sedimentary rocks with intercalation of volcanic rocks. Petrological and geochemical features of these Carboniferous volcanic rocks show that: (1) they belong to the calc-alkaline series, (2) they display prominent Nb–Ta negative anomalies consistent with subduction-related magmas, and (3) HFSE-based discriminations place these volcanic rocks in the field of continental arcs. The depositional evolution of the sedimentary series shows evidence for Carboniferous sedimentation in a basin instead of rifting as previously proposed. All these evidences, together with the occurrence of contemporaneous turbidites and ophiolitic mélange along the northern boundary of the Yili Block, allow us to infer that the northern border of the Yili Block was a continental active margin during the Carboniferous. The Late Carboniferous southward subduction that finally closed the Late Devonian to Early Carboniferous North Tianshan oceanic basin was followed by Permian–Mesozoic polyphase transcurrent faulting.     

Geology,Geochemistry, and Evolution of the Divrigi and Kuluncak Ophiolitic Melanges,with Reference to Serpentinites in East-Central Turkey

The Divrigi and Kuluncak ophiolitic mélanges are located in central Anatolia in the Tauride ophiolite belt. The stratigraphic sequence in the Divrigi ophiolitic mélange includes, from bottom to top, the Upper Jurassic-Lower Cretaceous Akdag limestone, Upper Cretaceous Çalti ultramafic rocks, and the Curek listwaenite. The Divrigi ophiolitic mélange is intruded by the Late Cretaceous-Eocene Murmano pluton. The above stratigraphic sequence is followed by the Eocene-Paleocene Ekinbasi metasomatite and the Quaternary Kilise Formation.

The oldest sequence of rocks in Kuluncak ophiolitic mélange in the GuvenÇ area is the Karadere serpentine/ultramafic body overlain successively by the Kurtali gabbro, Gundegcikdere radiolarite, the GuvenÇ listwaenites, and the Buldudere Formation. All of these units are Late Cretaceous in age. The Karamagra siderite deposit in the Hekimhan area probably was formed in the Lower Cretaceous at the contact between Çalti ultramafic rocks and the Buldudere Formation. The Kuluncak ophiolitic mélange was intruded by a subvolcanic trachyte in the Late Cretaceous. The Eocene-Paleocene Konukdere metasomatite, the Miocene Yamadag volcanic rocks, and Quaternary slope deposits are late in the stratigraphic sequence in the GuvenÇ area.

The Kuluncak ophiolitic mélange in the Karakuz area is similar to that at GuvenÇ; however, gabbro, radiolarite, and Miocene volcanic rocks are not present. The Miocene is represented by the Ciritbelen Formation at Karakuz and the Karakuz iron deposit is hosted by a Late Cretaceous subvolcanic trachyte.

The rareearth and trace-element concentration of serpentinite in the Divrigi and Kuluncak ophiolitic mélanges indicate that all of the ultramafics and their alteration products were derived from a MORB, which was depleted in certain elements and oxides. The results expressed in this study support the idea that the Divrigi and Kuluncak ophiolitic mélanges within the Tauride ophiolite belt originated from Northern Tauride oceanic lithosphere (Poisson, 1986), instead of a northern branch of Neo-Tethys (Sengor and Yilmaz, 1981).     

Geologic and Tectonic Setting of the Yozgat Batholith,Northern Central Anatolian Crystalline Complex,Turkey

The Yozgat Batholith lies along the northern edge of the Central Anatolian Crystalline Complex in Central Anatolia, Turkey. The batholith intruded the Paleozoic-Mesozoic metamorphics and Cretaceous ophiolitic mélange, and was nonconformably overlain by latest Maastrichtian-Paleocene and/or Eocene clastics, carbonates, and volcanics. The batholith itself may be subdivided into several mappable subunits bounded by Cretaceous ophiolitic mélange, Eocene cover, and/or faults.

Major- and trace-element as well as REE analyses of the subunits indicate that the granitoids of the Yozgat Batholith are principally metaluminous monzogranites, of subalkaline-calc-alkaline character, except for the peraluminous leucogranitoids of the Yozgat subunit. The granitoids were derived by thickening of the continental crust and related partial melting; the thickening was caused by emplacement of ophiolitic nappes during collisional events.     

The Petrology, Geochemistry, and Petrogenesis of E-MORB-type Mafic Rocks from the Guomangco Ophiolitic Mélange, Tibet

The Guomangco ophiolitic melange is situated in the middle part of the Shiquanhe- Yongzhu-Jiali ophiolitic melange belt （SYJMB） and possesses all the subunits of a typical Penrose- type ophiolite pseudostratigraphy. The study of the Guomangco ophiolitic melange is very important for investigating the tectonic evolution of the SYJMB. The mafic rocks of this ophiolitic melange mainly include diabases, sillite dikes, and basalts. Geochemical analysis shows that these dikes mostly have E-MORB major and trace element signatures; this is the first time that this has been observed in the SYJMB. The basalts have N-MORB and IAB affinities, and the mineral chemistry of harzburgites shows a composition similar to that of SSZ peridotites, indicating that the Guomangco ophiolitic melange probably originated in a back-arc basin. The Guomangco back-arc basin opened in the Middle Jurassic, which was caused by southward subduction of the Neo-Tethys Ocean in central Tibet. The main spreading of this back-arc basin occurred during the Late Jurassic, and the basalts were formed during this time. With the development of the back-arc basin, the subducted slab gradually retreated, and new mantle convection occurred in the mantle wedge. The recycling may have caused the metasomatized mantle to undergo a high degree of partial melting and to generate E- MORBs in the Early Cretaceous. E-MORB-type dikes probably crystallized from melts produced by about 20%-30% partial melting of a spinel mantle source, which was metasomatized by melts from low-degree partial melting of the subducted slab.