天山—阿尔泰地区古生代构造成矿作用

天山—阿尔泰地区古生代大地构造及其相关的内生金属成矿作用是一个重要而又有趣的研究课题。阿尔泰地区属于早古生代碰撞带,天山地区属于晚古生代早期(晚泥盆世—早石炭世,385~323 Ma)碰撞带,均为区域性近南北向(按现代磁方位)缩短-碰撞作用的结果。在晚泥盆世—早石炭世碰撞作用下,阿尔泰地区近NW向区域性断层呈现为右行走滑的特征,天山地区近东西向的区域性断层表现为逆断层的活动。然而,在晚石炭世—二叠纪(323~260 Ma)受乌拉尔碰撞带向东挤压作用的远程效应影响,该地区受到较弱的向东挤压作用,阿尔泰地区NW向断层转变成左行走滑断层,天山地区近东西向的断层则转为右行走滑断层,使该区岩石发生适度的破碎,以致在天山—阿尔泰地区形成大量世界著名的大型内生金属矿床。对于亚洲大陆来说,碰撞作用最强烈的时期并不一定是内生金属成矿作用最有利的阶段。应该审慎地对待"造山带成矿"假说。     

Structural Evolution and Hydrocarbon Potential of the Upper Paleozoic Northern Ordos Basin, North China

The hydrocarbon potential of the Hangjinqi area in the northern Ordos Basin is not well known, compared to the other areas of the basin, despite its substantial petroleum system.Restoration of a depth-converted seismic profile across the Hangjinqi Fault Zone(HFZ) in the eastern Hangjinqi area shows one compression that created anticlinal structures in the Late Triassic, and two extensions in ~Middle Jurassic and Late Early Cretaceous, which were interrupted by inversions in the Late Jurassic–Early Early Cretaceous and Late Cretaceous, respectively.Hydrocarbon generation at the well locations in the Central Ordos Basin(COB) began in the Late Triassic.Basin modeling of Well Zhao-4 suggests that hydrocarbon generation from the Late Carboniferous–Early Permian coal measures of the northern Shanbei Slope peaked in the Early Cretaceous, predating the inversion in the Late Cretaceous.Most source rocks in the Shanbei Slope passed the main gas-migration phase except for the Hangjinqi area source rocks(Well Jin-48).Hydrocarbons generated from the COB are likely to have migrated northward toward the anticlinal structures and traps along the HFZ because the basin-fill strata are dipping south.Faulting that continued during the extensional phase(Late Early Cretaceous) of the Hangjinqi area probably acted as conduits for the migration of hydrocarbons.Thus, the anticlinal structures and associated traps to the north of the HFZ might have trapped hydrocarbons that were charged from the Late Carboniferous–Early Permian coal measures in the COB since the Middle Jurassic.     

Late Paleozoic volcanic rocks of the Intra-Sudetic Basin, Bohemian Massif: petrological and geochemical characteristics

Late Paleozoic volcanic rocks in the Intra-Sudetic Basin of the Bohemian Massif in the Czech Republic can be subdivided into two series: (I) a minor bimodal trachyandesite-rhyolite series of Upper Carboniferous age with initial ⁸⁷Sr/⁸⁶Sr of ca. 0.710 and ε_Nd values of −6.1 also characteristic of volcanics of the near Krkonoše Piedmont Basin (0.707 and −6.0, Ulrych et al., 2003) and (II) a major differentiated basaltic trachyandesite-trachyandesite-trachyte-rhyolite series of Lower Permian age with lower initial ⁸⁷Sr/⁸⁶Sr of ca. 0.705-0.708 and ε_Nd values ranging from −2.7 to −3.4/−4.1/. The newly recognized volcanic rocks of trachytic composition indicate that the rocks were formed by magmatic differentiation of similar parental melts rather than constituting a bimodal mafic-felsic sequence from different sources. Both series are generally of subalkaline affinity and calc-alkaline character with some tholeiitic tint (FeO/MgO vs. SiO₂, presence of orthopyroxene). The magmatic activity occurred in cycles in a layered chamber, each starting primarily with felsic volcanics and ending with mafic ones. The mafic rocks represent mantle-melt(s) overprinted by crust during assimilation-fractional crystallization. The Sr-Nd isotopic data confirm a significant crustal component in the volcanic rocks that may have been inherited from the upper mantle source and/or from assimilation of older crust during magmatic underplating and shallow-level melt fractionation.     

Types,geological features and geodynamic significances of gold-copper deposits in the Kanggurtag metallogenic belt,eastern Tianshan,NW China

Occupying the middle of the central Asia Paleozoic accretionary and collisional orogenic belt, the eastern Tianshan area has a great economic potential due to Au-Cu mineralization during syn- and post- orogenic events. In the Kanggurtag Au-Cu metallogenic belt, three major types of gold deposits have been recognized: ductile-shear-zone-hosted gold deposits, magmatic hydrothermal gold deposits, and epithermal gold deposits. Four kinds of copper deposits have also been identified recently: the porphyry-type, the skarn-type, the magmatic type, and volcanic/sedimentary-type. Tectonically, the development of these late Paleozoic gold and copper deposits was closely associated with the subduction and collision of the ancient Tianshan ocean that intervened between the Tarim craton and the Siberian block. In the early to mid-Carboniferous, N-dipping subduction beneath the Dananhu arc generated magmatic intrusions, leading to formation of the porphyry Cu deposits. The magmatic front migrated southward to form the Yamansu arc upon the Kanggurtag accretionary wedge. In the latest Carboniferous to early Permian, during the closure of the ancient Tianshan ocean, large mafic-ultramafic complexes were emplaced, resulting in several magmatic copper-nickel deposits. Gold deposits of the shear-zone-type are controlled by the Kanggurtag ductile shear zone, which is related to collisional orogenesis. The epithermal gold deposits are associated with extensional tectonics and post-tectonic volcanic activity. The tectonic settings, geological features, and temporal and spatial distributions of these different types of gold and copper deposits reflect, to a great extent, the accretionary and collisional tectonics that occurred between the northern margin of the Tarim block and the southern margin of the Siberian block.     

The Saint-Georges-sur-Loire olistostrome,a key zone to understand the Gondwana-Armorica boundary in the Variscan belt (Southern Brittany,France)

In the southern part of the French Armorican massif, the Ligerian domain is located along the boundary between Gondwana and Armorica. Lithological, geochemical and structural data on the Saint-Georges-sur-Loire Unit, which is the northern part of the Ligerian domain, allow us to distinguish two sub-units. A southern sub-unit, formed by various blocks (chert, limestone, sandstone, rhyolite, mafic rocks) of Silurian to Middle Devonian age included as olistoliths in a Middle-Late Devonian terrigeneous matrix, overthrusts a sandstone-pelite northern sub-unit. Both units experienced two deformation events. The first one is a top-to-the-NW thrusting and the second one is a left-lateral wrenching. The Saint-Georges-sur-Loire Unit is an accretionary prism formed during the Late Devonian closure of the Layon rift, coeval with the main phase of the Variscan orogeny. The Layon rift, which according to the mafic olistoliths was partly floored by oceanic crust, appears as a buffer structural zone that accounts for the lack in Central Brittany of any tectonic or sedimentary echo of the closure of the Medio-European Ocean. The tectonic evolution of the Saint-Georges-sur-Loire Unit supports a polyorogenic model for this part of the Variscan Belt.     

阴山—燕山北麓富碱侵入岩体的岩石地球化学特征、锆石SHRIMP U-Pb年龄及构造意义

本文研究的达茂旗黄合少、察哈尔右后旗古城和河北尚义县八道沟岩体位于华北克拉通北缘阴山—燕山北麓,索伦缝合带以南,沿近东西方向展布。主要岩石类型为正长岩、二长岩和石英二长岩。岩石地球化学研究表明其SiO2含量59. 08%~66. 52%, Al2O3= 15. 34%~21. 67%,A/CNK<1。属于准铝质中性岩范畴。全碱含量（Na2O+K2O）均在8%以上,在岩石的碱度率AR—SiO2图解上大多数样品落入碱性与过碱性区域,里特曼指数σ值从3. 73~10. 83均位于碱性或过碱性系列,属于碱性岩。岩体的微量元素以富集大离子亲石元素（LILE）如Rb、Ba和Sr等,亏损高场强元素（HFSE）如Ti、P、Nb和Ta等为特征。岩石稀土元素特征显示富集轻稀土元素（LREE）,亏损重稀土元素（HREE）并且轻重稀土元素分馏比较明显的特征。除极个别样品外,岩石具有Eu负异常（δEu= 0. 35~0. 91）。通过对察哈尔右后旗古城正长岩体和河北尚义县八道沟富碱侵入岩体的高精度测年研究,获得其SHRIMP锆石U- Pb年龄分别为413. 2±3. 3~415. 0±5. 9 Ma和366. 8±5. 2~372. 3±4. 7 Ma,表明其均为古生代泥盆纪富碱侵入岩浆活动的产物。结合前人关于阴山—燕山北麓其它富碱侵入岩体（内蒙古固阳东高家村碱性正长岩体、黄合少碱性正长岩和冀北水泉沟碱性杂岩体 ）的研究成果,推断在华北克拉通北缘阴山—燕山北麓一带,可能存在一条东西方向展布的晚古生代泥盆纪富碱侵入岩带。根据该岩带岩石地球化学特征,以及Ta/Yb—Th/Yb与Zr/Nb—Zr/Nb—Y/Nb判别图推测其岩浆物质来源可能与富集地幔有关,按照成岩温压环境指示,其形成深度位置约为下地壳,岩浆上升侵位过程中明显受到地壳物质的混染。依据前人关于碱性岩特征的研究,结合本文研究岩体的岩石化学特征和及Rb—Nb+Y构造判别图解指示,推测岩体形成于张性构造环境,可能与古生代志留纪末兴蒙造山带南部发育的白乃庙岛弧带和华北克拉通发生弧—陆碰撞后的伸展背景相关。     

东天山北部古生代重大构造事件及其对中亚造山带演化的启示：基于1∶5万板房沟幅和小柳沟幅地质调查新证据

本文基于新疆哈密地区1∶5万板房沟幅和小柳沟幅区域地质调查新成果,对东天山北部古生代的重大构造事件以及演化历史进行了系统的梳理。基于下志留统与奥陶系之间角度不整合、下石炭统与泥盆系之间平行不整合以及上石炭统二道沟组与下伏岩系之间的角度不整合的确定,揭示奥陶纪与志留纪之交、泥盆纪与石炭纪之交以及晚石炭世期间存在几次重大构造事件。结合古生代不同时期沉积大地构造背景转换、岩浆活动构造环境转换以及构造变形格式转换的地质新纪录,提出奥陶纪与志留纪之交的造山事件为北部阿尔曼太洋闭合导致准噶尔—吐哈地块与阿尔泰地块碰撞的响应;泥盆纪与早石炭世之间的造陆构造事件可能是北部卡拉麦里洋盆初始汇拢碰撞的响应,其平行不整合以及下伏的志留纪—泥盆纪较稳定环境的沉积序列预示着介于卡拉麦里洋盆与南部北天山洋盆之间的准噶尔—吐哈地块为古亚洲洋盆体系中相对刚性的稳定陆块区,研究区作为准噶尔—吐哈地块的北部被动陆缘受卡拉麦里洋盆汇聚的影响较小;晚石炭世的造山事件则表现为响应卡拉麦里洋盆闭合后周缘前陆盆地的演化,是早石炭世沿卡拉麦里缝合带发生陆块碰撞以来挤压构造作用峰期的产物,其奠定了东天山北部北西-南东向构造基本格局。本文还重新界定莫钦乌拉断裂为北天山构造带(准噶尔—吐哈地块)与东准噶尔构造带的构造-地层分区界线,推断其为卡拉麦里缝合带向南东的延伸,并讨论了早石炭世受控不同构造体制的沉积和岩浆纪录的空间差异性,认为早石炭世北部莫钦乌拉山区域为与北侧卡拉麦里洋盆闭合后周缘挤压前陆盆地的发育过程,而南部博格达—哈尔里克山则总体呈现为响应南侧北天山洋盆闭合后的碰撞后伸展裂谷发育过程。     

北阿尔金恰什坎萨依沟地区早古生代构造变形特征及构造演化启示

出露在青藏高原北缘的红柳沟-拉配泉蛇绿混杂岩带一直以来为深入研究北阿尔金早古生代构造格架及演化提供了宝贵信息。经详细的野外地质填图和构造解析,文章针对红柳沟-拉配泉蛇绿混杂岩带内的构造样式、变形特征及形成时限进行研究,将北阿尔金蛇绿混杂岩带进一步细分为北侧混杂单元、中间层序单元和南侧混杂单元三个次级构造单元,南、北两侧混杂单元内以发育一系列复杂褶皱和逆冲断层为典型构造特征。卷入褶皱变形的最年轻地层岩石为中-晚奥陶世硅质岩,并被（416.8±3.7）Ma未变形的正长斑岩脉所截切;卷入逆冲断层的混杂岩中辉长岩和斜长花岗岩年龄为479~521 Ma和512.1~518.5 Ma,随后也被410.7~418.5 Ma未变形的冰沟岩体所侵位。这些基本事实表明,褶皱构造与逆冲断层均形成于中奥陶世-早泥盆世,推测其成因与北阿尔金洋俯冲作用导致的洋壳强烈缩短变形有关。在南侧混杂单元,褶皱构造样式自北向南逐渐由直立褶皱转变为斜歪褶皱,最后转变为倒转褶皱,显示出递进变形特征。褶皱所对应的应变椭球体也发生了旋转,表现出顶端指向北北东向的剪切作用,与混杂单元内逆冲断层所具有的向北北东方向逆冲、推覆特征相一致,从而推测它们与北阿尔金洋南南西向俯冲消减有密切联系。另外,在北侧混杂单元内还发育有同时期向南南东方向逆冲的断层以及轴面倾向北北东的斜歪褶皱,暗示北阿尔金洋在早古生代可能还发育有北北东方向的俯冲极性,整个北阿尔金洋俯冲消减模式可能具有双向性。      

保山地体新元古代——早古生代沉积岩碎屑锆石年代学及其构造意义

滇西潞西地区位于青藏高原东南缘,大地构造位置上属于保山地体。由于新生代强烈的陆内变形作用,保山地体与青藏高原腹地体的对应关系难以确定。野外观察及LA-ICP-MS锆石U-Pb测年结果表明,潞西新元古代—早古生代地层(震旦系—寒武系蒲满哨群及下奥陶统大矿山组)大部分碎屑锆石Th/U0.1,说明其大多为岩浆成因。U-Pb年龄跨度较大,太古宙—早古生代都有分布,且具有明显的562Ma、892Ma及2265Ma年龄峰,以及较弱的1680Ma和2550Ma年龄峰。保山地体潞西地区沉积岩碎屑锆石年龄分布特征与特提斯喜马拉雅、南羌塘沉积地层碎屑锆石年龄分布特征相似,说明其具有相同的物源——冈瓦纳大陆北部的印度大陆。在新元古代晚期—早古生代,保山地体位于印度大陆北缘,与南羌塘、喜马拉雅地体相邻。伴随着俯冲相关的增生造山过程,保山地体形成相应的新元古代末期—早古生代沉积地层。     

科马提岩与苦橄岩的区别及对若干晚古生代“科马提岩”的质疑

以往学术界更多的关注科马提岩和苦橄岩的相似性,忽略其差异。通过全数据模式,采集数据库内全球的太古宙科马提岩、后太古宙低/高钛苦橄岩数据,对比三者之间的差异发现,科马提岩更富MgO、Cr、Ni、Cs、Pb、Co和Zn,其次为低钛苦橄岩(除Co和Zn),其余主量、微量元素的含量由高至低依次为高钛苦橄岩、低钛苦橄岩、科马提岩。依据元素间的差异(如Cr/Ga、MgO/Ga、MnO/Zr、Cr/Zr等),采用密度分布函数(Density Distribution)在Matlab软件中绘制出可有效区分3类岩石的等密度判别图,并用该图对若干晚古生代"科马提岩"的岩性重新厘定。结合岩相学和地球化学特征研究表明,晚古生代"科马提岩"中,印度东部为高钛苦橄岩,越南为化学成分与科马提岩类似的低钛苦橄岩,印度拉达克地区为低钛苦橄岩。