Review of Late Proterozoic sutures,ophiolitic mélanges and tectonics of eastern Egypt and north-east Sudan

The distribution, structural relations and ages of ophiolites and ophiolitic melanges in the Eastern Deserts of Egypt and north-east Sudan, and their relation to arc and post-arc magmatism, are used to infer the probable positions of sutures and the directions of obduction and subduction. The ages of the successive tectonic stages in the terranes decrease northwards, by about 100 Ma in the region discussed. Obduction was north-westwards. The obducted sheets of ophiolite and ophiolitic melange, extending about 500 km north from the Onib-Sol Flamed suture, may all represent a single back-arc basin. The direction of subduction is still not clearly proved: more geochemical evidence of arc-magmatic polarity is needed. The late tectonic north-westward thrusting, the NW - SE stretching lineation, the transpressional north-south Hamisama Shear Zone and the NW-SE sinistral Najd faults are all attributed to north-westward movement (present coordinates) of terranes towards the older craton west of the Nile. The Najd faults are interpreted as intracontinental transform faults.     

Magma mixing model for the genesis of middle crust in the Izu–Bonin–Mariana arc: evidence from plutonic rocks in the Mineoka-Setogawa ophiolitic mélange,central Japan

ABSTRACT

A Paleogene accretionary complex, the Mineoka–Setogawa belt is distributed adjacent to the northern portion of the collision zone between Honshu and Izu–Bonin–Mariana (IBM) arcs in central Japan, comprising a mélange of ophiolitic fragments of various sizes. The Eocene-Oligocene plutonic rocks in this belt (gabbro, diorite, and tonalite) have been interpreted as fragments brought from the deep crust beneath the IBM arc through tectonic collisions. The geochemical characteristics of the gabbro and associated basaltic dike are similar to those of the Eocene IBM tholeiitic basalt; thus, the gabbro was likely formed via the crystallization of the Eocene tholeiitic basaltic magmas, which was produced by the partial meltings of a depleted mantle wedge. A comparison with experimental results and geochemical modeling indicates that the tonalite was generated by 10–30% dehydration melting of the gabbro. Actually, Eocene–Oligocene felsic veins, which are coeval with the plutonic rocks, occur in the Mineoka–Setogawa gabbro. Plagioclase crystals in the diorite comprise Ca-rich and -poor parts in a single crystal. Their compositional characteristics are consistent with those of plagioclase in the gabbro and tonalite, respectively. The textures and chemical composition of plagioclase indicate that the diorite was formed by the mixing between mafic and silicic magmas. The whole-rock composition of the diorite also indicates the evidence for the mixing between basaltic magmas which were fractionated to variable degrees and homogeneous silicic magma. The mixing model proposed from the first direct observations of the IBM middle crust exposed on the Mineoka–Setogawa belt is applied to the genesis of the Eocene to present intermediate rocks in the IBM arc. If the continental crust were created at intra-oceanic arc settings such as the IBM arc, the magma mixing model would be one of the most likely mechanisms for the genesis of the continental crust.     

青藏高原北部盆地构造沉积演化与高原向北生长过程

从可可西里到河西走廊的青藏高原的北部地区,地貌具有独特的"盆-岭"相间的特征,是青藏高原隆升增长过程中长期地质作用的产物,沉积盆地记录了这一过程的演化历史。对可可西里盆地、柴达木盆地和酒泉盆地新生代的沉积充填与盆地动力学背景的研究发现,3个盆地的演化序列具有相似性,盆地的早期为走滑盆地或伸展盆地性质,中期发育前陆盆地,最后以山间盆地结束。以南北向挤压短缩为动力背景的前陆盆地是高原北部造山带运动的直接响应。高原北部前陆盆地的发育时序为：可可西里前陆盆地（53～23Ma）、柴达木前陆盆地（46～2．45Ma）和酒泉前陆盆地（29．5～0．13Ma）,反映了青藏高原北部在新生代具有向北阶段性生长的特征。     

Palinspastic Reconstruction for Tectonics of Northeast China and Its Vicinity

ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅＮｏｒｔｈｅａｓｔＣｈｉｎａａｎｄｉｔｓａｄｊａｃｅｎｔｒｅｇｉｏｎｐｒｅｓｅｎｔａｕｎｉｑｕｅｔｅｃｔｏｎｉｃｐａｔｅｒｎ,ｗｈｉｃｈｉｓｄｉｓｔｉｎｇｕｉｓｈｅｄｂｙｌａｒｇｅｓｃａｌｅＮＥｔｒｅｎｄｉｎｇｇｒａｎｉ...     

新疆北天山晚古生代蛇绿混杂岩带的变形研究

运用有限应变测量、磁组构和岩石组构等方法，对北天山存在着的一条晚古生代蛇绿混杂岩带进行了详细的构造变形研究。各种方法的研究结果互相吻合，与野外实际地质现象也相一致。混杂岩带属压扁变形，压缩量５１％，应变强度０．８３．３个主应变轴的平均产状分别是Ｘ＝１２６°∠４４°，Ｙ＝２５７°∠３３°，Ｚ＝８°∠２５°。文中最后讨论了该混杂岩带的形成机制、时代、运动学和动力学特征。     

青藏高原可可西里地区现代冰川发育特征

经野外考察和室内分析计算，青藏可可西里地区发育现代冰川４３７条，覆盖面积达１５５２．３９ｋｍ＾２，冰储量为１６２．８３４９ｋｍ＾３，成为本区众多河湖泊水体的重要补给源泉。     

新疆黄山地区蛇绿岩块的地质、地球化学特征及构造意义

黄山地区镁铁-超镁铁堆积杂岩,岩体小而分异好,岩体边部受构造作用强烈,属蛇绿岩中的堆积杂岩,过渡元素的配分曲线为较明显的“W”型。稀土元素配分曲线为LREE弱富集的平坦型。其中辉长岩单元为高钛型(TiO_2最大值为5.20％),这些均反映了堆积杂岩形成环境为洋中脊,分布于现在的位置是板块运动的结果。结合上述事实,通过沉积建造分析,该区在中石炭统曾存在沟弧盆体系。     

山东仰口地区超高压变质岩混杂带的组成及其构造变形

从构造岩石角度将山东青岛仰口地区发育的超高压变质岩混杂带划分为构造整合单元和构造混杂单元两个组成部分，对不同单元的岩性组成及其超高压变质特征进行了描述。着重对不同构造单元中的构造变形期次进行了划分。总结了不同期次构造变形的宏观及微观特征。结合苏鲁超高压变质带在区域上构造变形期次的研究情况，初步提出形成仰口地区超高压变质岩中各种构造形迹的构造模式，并对它们所反映的仰口超高压带形成和折返的构造意义进行了探讨。     

川西雅江-道孚地区三叠系西康群若干地质问题研究进展与分歧

对川西雅江-道孚地区三叠系西康群含义及层序重新作了厘定;对杂谷脑组解体,重新定义认识的分歧,如年各组碳酸盐岩块砾混积层在西康群地层柱中的位置,进行了探讨命名地罗空松多组和新都桥组层位关系的新认识,双壳类(Pergamidia)在西康群中的分布及意义等若干地质问题进行了探讨,并作了总结与评述.     

Geological setting and tectonic subdivision of the Neoproterozoic orogenic belt of Tuludimtu, western Ethiopia

The N–S trending Tuludimtu Belt in the extreme west of Ethiopia has been subdivided into five lithotectonic domains, from east to west, the Didesa, Kemashi, Dengi, Sirkole and Daka domains. The Kemashi, Dengi and Sirkole Domains, forming the core of the belt, contain volcano-sedimentary successions, whilst the Didesa and Daka Domains are gneiss terranes, interpreted to represent the eastern and western forelands of the Tuludimtu Belt. The Kemashi Domain, which consists of an ophiolitic sequence of ultramafic and mafic volcanic and plutonic rocks together with sedimentary rocks of oceanic affinity, is interpreted as oceanic crust and is considered to represent an arc-continent suture zone. The Dengi Domain, composed of mafic to felsic volcanic and plutonic rocks, and a sequence of volcanoclastic, volcanogenic, and carbonate sediments, is interpreted as a volcanic arc. The Sirkole Domain consists of alternating gneiss and volcano-sedimentary sequences, interpreted as an imbricated basement-cover thrust-nappe complex. All the domains are intruded by syn- and post-kinematic Neoproterozoic granitoids. Structural analysis within the Didesa and Daka Domains indicate the presence of pre-Pan African structures, upon which Neoproterozoic deformation has been superimposed. The gneissic rocks of these two domains are regarded as pre-Pan African continental fragments amalgamated to West Gondwana during Neoproterozoic collision events. Unconformably overlying all of the above are a series of tilted but internally undeformed conglomerate–sandstone–shale sequences, regarded as post-accretionary molasse-type deposits, formed during gravitational collapse of the Tuludimtu Belt. The Tuludimtu Belt is interpreted as a collision orogenic belt formed during the assembly of West Gondwana prior to final closure of the Mozambique Ocean.