新疆准噶尔造山带多旋回开合构造特征

新疆准噶尔造山带是位于西伯利亚与塔里木两大陆壳之间的多旋回造山带，是古亚洲洋的主要部分。该造山带是在新元古代早期形成的克拉通基底上裂解、扩张成洋的，在其发展历史进程中，经历了多旋回手风琴式开合运动，此开彼合，首尾衔接，几经洋陆转化，由一系列沟弧盆体系挤压拼贴到一起，于石炭纪末最终固结成新的古亚洲大陆。成陆后并不稳定，在中-新生代时期仍有强烈的活动性与造山过程，表现为发育多时期的蛇绿岩、多时期的造山花岗岩和多种不同类型的造山作用。     

Geochemical Characteristics,Petrogenesis of the Sanukitic Dikes in the Miaoergou Area of West Junggar,Xinjiang, NW China and Their Geological SignificanceEI北大核心CSCD

NS-trending dikes which contain dioritic enclaves widely occur in the Miaoergou pluton, West Junggar, Xinjiang. The dikes are composed of quartz diorite and quartz diorite porphyrite. LA-ICP-MS zircon U-Pb ages of the quartz diorite and diorite are 298.0±3.7 Ma and 299.4±2.5 Ma, respectively, corresponding to the end of the Late Carboniferous to beginning of the Early Permian. The dikes and enclaves have similar geochemical properties with island arc features. They are calc-alkaline, with moderate SiO2 (53.58% to 57.89%), high MgO (3.09% to 4.83%, Mg# values ranging from 44.69 to 54.12), TiO2 (1.17% to 1.66%), Cr (51.24×10-6 to 126.1×10-6), Ni (35.91×10-6 to 57.55×10-6) contents and K/Na ratios (0.35 to 0.70). Moreover, all samples are enriched in large-ion lithophile elements (LILEs: e.g. K, Rb, Ba and U) and light rare earth elements, but strongly depleted in high field strength elements (HFSEs: e.g. Nb, Ta and Ti), with insignificant Eu anomalies (δEu=0.67 to 1.08). In contrast, the dikes and enclaves in the Miaoergou pluton show geochemical signatures similar to those of the Cenozoic sanukitoids in Setouchi volcanic belt of SW Japan and the sanukitoids in the Hatu area, West Junggar. The source of the dikes might be the depleted mantle previously metasomatized by fluids released from subduction slabs. These sanukitic dikes may be generated by interaction of the mantle wedge with fluids derived from dehydration of the subducting oceanic slab, resulting in 2% to 5% partial melting of amphibole-spine peridotite. The identification of the sanukitic dikes in the Miaoergou pluton, together with previous studies, suggest that the southern West Junggar region was still dominated by subduction-related island arc setting at the beginning of the Early Permian, and multi-stage subduction-accretionary orogeny may account for the difference of subduction duration between the north and the south of West Junggar. © 2018, Science Press. All right reserved.     

Unraveling one billion years of geological evolution of the southeastern Amazonia Craton from detrital zircon analyses

Despite representing one of the largest cratons on Earth, the early geological evolution of the Amazonia Craton remains poorly known due to relatively poor exposure and because younger metamorphic and tectonic events have obscured initial information. In this study, we investigated the sedimentary archives of the Carajás Basin to unravel the early geological evolution of the southeastern Amazonia Craton. The Carajás Basin contains sedimentary rocks that were deposited throughout a long period spanning more than one billion years from the Mesoarchean to the Paleoproterozoic. The oldest archives preserved in this basin consist of a few ca. 3.6 Ga detrital zircon grains showing that the geological roots of the Amazonia Craton were already formed by the Eoarchean. During the Paleoarchean or the early Mesoarchean (<3.1 Ga), the Carajás Basin was large and rigid enough to sustain the formation and preservation of the Rio Novo Group greenstone belt. Later, during the Neoarchean, at ca. 2.7 Ga, the southeastern Amazonia Craton witnessed the emplacement of the Parauapebas Large Igneous Province (LIP) that probably covered a large part of the craton and was associated with the deposition of some of the world largest iron formations. The emplacement of this LIP immediately preceded a period of continental extension that formed a rift infilled first by iron formations followed by terrigenous sediments. This major change of sedimentary regime might have been controlled by the regional tectonic evolution of the Amazonia Craton and its emergence above sea-level. During the Paleoproterozoic, at ca. 2.1 Ga, the Rio Fresco Group, consisting of terrigenous sediments from the interior of the Amazonia Craton, was deposited in the Carajás Basin. At that time, the Amazonian lithosphere could have either underwent thermal subsidence forming a large intracratonic basin or could have been deformed by long wavelength flexures that induced the formation of basins and swells throughout the craton under the influence of the growing Transamazonian mountain belt.     

墨西哥北部拉拉米期斑岩型铜矿床时空分布及典型矿床特征

北美斑岩型铜矿集区“大集群”是世界重要铜成矿省之一; 墨西哥北部索诺拉州斑岩型铜矿带,是其在墨西哥的延伸。斑岩型铜矿床主要沿着拉拉米岩浆弧展布。拉拉米造山作用期间（80~40 Ma）,由于法拉隆板块向北美板块俯冲角度的减小,岩浆活动中心逐步向东移动,形成76~70 Ma, 63~57 Ma和46~40 Ma 三期岩浆活动高峰期,其中 63~57 Ma 岩浆活动规模最大。通过对区内已有矿床的成矿时代与岩浆活动时限及矿床分布集中程度的对比研究发现,斑岩型铜成矿高峰期主要集中在63~56 Ma期间。通过典型矿床的成矿特征梳理及区域岩浆作用综合分析,笔者等认为拉拉米造山作用是区内形成巨量铜钼富集的主要地质作用。     

Geochemistry of gold-bearing metamorphic rocks of the Natitingou area,Atacora structural unit,Northwestern Bénin (West Africa): Implications for Au genesis

The Natitingou area within the Atacora Structural Unit (ASU) of the Pan-African Dahomeyide orogenic belt, northwestern Bénin, is characterized by the monocyclic metasedimentary formations, amphibolites and orthogneisses which belong to the Internal zone of the belt. Representative samples of these different gold-bearing rocks have been analyzed geochemically to determine their petrogenesis, mode of emplacement, tectonic setting and role in the genesis of gold mineralization in the area. The orthogneisses are subalkaline, peraluminous and emplaced in a syn-collisional arc setting while the amphibolites are metaluminous, tholeiitic with an E-MORB affinity and emplaced in a rifted lithospheric setting. The metasedimentary rocks, comprising quartzites and mica schists are cross-cut by auriferous quartz veins. The metasedimentary rocks are recycled sediments varying from wackes to sublitharenite in composition and deposited in a passive margin setting. The quartz veins similar to the metasedimentary rocks are enriched in LREE, depleted in HREE and showed a negative Eu-anomaly (0.31–0.72). Their chondrite-normalised REE patterns deciphered them as Upper Continental Crustal materials which were probably derived from the reworking of their host metasedimentary rocks. Gold concentration in quartzites, amphibolites, mica schists, quartz veins and orthogneiss were 0.004–9.587, 0.26–1.76, 0.0005–0.464, 0.023–0.147 and 0.0−0.0005 ppm, respectively. Devolatilization process of the country-rocks, is the most probable mechanism for the ore-forming fluid, which could have been generated during the Pan-African Dahomeyide event. Remobilisation of gold and associated metal (As, W, Cu, Mo, Sb, and Sn) after the Pan-African Dahomeyide orogeny is suggested for enrichment of gold along shear and fault zones of the Natitingou area.     

Boron isotopic variations in tourmaline from metacarbonates and associated calc-silicate rocks from the Bohemian Massif: Constraints on boron recycling in the Variscan orogen

Various metacarbonate and associated calc-silicate rocks form minor but genetically significant components of the lithological units in the Bohemian Massif of the Variscan orogen in Central Europe.These rocks vary in terms of their lithostratigraphy,chemical composition and mineral assemblage(dolomite/calcite ratio,silicate abundance).Tourmaline is present in five paragenetic settings within the metacarbonate and calc-silicate units.TypeⅠcomprises individual,euhedral,prismatic grains and grain aggregates in a carbonate-dominant(calcite±dolomite)matrix poor in silicates.TypeⅡis characterized by euhedral to subhedral grains and coarse-to fine-grained aggregates in silicate-rich layers/nests within metacarbonate bodies whereas typeⅢoccurs as prismatic grains and aggregates at the contact zones between carbonate and associated silicate host rocks.TypeⅣis in veins crosscutting metacarbonate bodies,and typeⅣtourmaline occurs at the exocontacts of elbaite-subtype granitic pegmatite.Tourmaline from the different settings shows distinctive compositional features.Typical for typeⅠare Mg-rich compositions,with fluor-uvite>dravite>>magnesio-lucchesiite.Tourmalines from typeⅡsilicate-rich layers/nests are highly variable,corresponding to oxy-schorl,magnesio-foitite,Al-rich dravite and fluor-uvite.Typical for typeⅢtourmalines are Ca,Ti-bearing oxy-dravite compositions.The typeⅣveins feature dravite and fluor-uvite tourmaline compositions whereas typeⅤtourmaline is Li,F-rich dravite.Tourmaline is the only Bbearing phase in paragenetic typesⅠ-Ⅳ,where it is characterised by two principal ranges of B-isotope composition(δ^11B=-13‰to-9‰and-18‰to-14‰).These ranges correspond to regionally different units of the Moldanubian Zone.Thus,the Svratka Unit(Moldanubian Zone s.l.)contains only isotopically lighter tourmaline(δ^11B=-18‰to-14‰),whereas metacarbonates in the Poli?ka unit(Teplá-Barrandian Zone)and Olesnice unit(Moravicum of the Moravo-Silesian Zone)has exclusively isotopically heavier tourmaline(δ^11B=-9‰to-13‰).Tourmalines from metacarbonates in the Variegated Unit cover both ranges of isotope composition.The isotopically light end of the B isotope range may indicate the presence of continental evaporites within individual investigated areas.On the other hand,variations in the range of~8δ-units is consistent with the reported shift in B isotopic composition of metasedimentary rocks of the Bohemian Massif due to the prograde metamorphism from very-low grade to eclogite facies.In contrast to the metacarbonate-hosted settings,tourmaline of paragenetic type V from the exocontact of granitic pegmatites displays a significantly heavier range ofδ^11B(as low as-7.7‰to-0.6‰),which is attributed to partitioning of 10 B to cogenetic axinite and/or different B-signature of the source pegmatite containing tourmaline with heavyδ^11B signature.     

Geology of the 2018 Winter Olympic site,Pyeongchang, Korea

We review the geology of the Gyeonggi Massif, Gyeonggi Marginal Belt, and Taebaeksan Basin of the Korean Peninsula, which are relevant to the 2018 Winter Olympic sites. Neoarchaean–Palaeoproterozoic gneisses and schists of the Gyeonggi Massif underwent two distinct collisional orogenies at the Palaeoproterozoic (1.88–1.85 Ga) and Triassic (245–230 Ma). These basement rocks are structurally overlain by a suite of Mesoproterozoic to Early Permian supracrustal rocks of the Gyeonggi Marginal Belt, consisting primarily of medium-pressure schists and amphibolites metamorphosed at ~270–250 Ma. In contrast, sedimentary successions in the Taebaeksan Basin, commonly fossiliferous, consist primarily of Early Cambrian–Middle Ordovician Joseon Supergroup and Late Carboniferous–Early Triassic Pyeongan Supergroup. The ‘Great Hiatus’ between the two supergroups is characteristic for the North China Craton. The marked contrast in tectonometamorphic evolution between the Taebaeksan Basin and Gyeonggi Marginal Belt suggests an existence of major suture in-between, which is most likely produced by the Permian–Triassic continental collision between the North and South China cratons. Finally, recent tectonics of the Korean Peninsula is governed by the opening of East Sea/Sea of Japan during the Late Oligocene–Early Miocene. This back-arc rifting event has resulted in an exhumation of the Taebaek Mountain Range, estimated to be 22 ± 3 Ma on the basis of apatite (U–Th)/He ages. Thus, high topography in the 2018 Winter Olympic sites is the consequence of Tertiary tectonics associated with the opening of a back-arc basin.     

大兴安岭中生代伸展造山过程中的岩浆作用

概括地介绍了大兴安岭中生代伸展造山过程,重点讨论了晚中生代火山岩、深成岩的岩石学及同位素地球化学特征：存在一套板内拉张环境下的Ａ 型花岗岩,火山岩为一套钾质粗面质岩石,大多数花岗岩和火山岩具有低的Ｎ（８７Ｓｒ）／ Ｎ（８６Ｓｒ） 值（０７０４ ～０７０８） 和正的ε（Ｎｄ ,ｔ） （１ ～４） 值,据此认为这是底侵作用形成的一套壳 幔混熔岩浆的产物,结合岩浆喷发与侵位过程中的伸展构造分析,认为这是大陆内部伸展造山的重要证据。此外,笔者还在该区发现早中生代的一套幔源镁铁质堆晶岩和侵入岩、早 中侏罗世及早白垩世的基性岩墙群、早白垩世（１３０ ～１２０ Ｍａ） 超基性的角闪岩、玻基橄辉岩和碱性橄榄玄武岩。由此可以证明,大兴安岭晚中生代的花岗岩 火山岩活动只是伸展背景下的岩浆演化的一个阶段。     

华南地台盖层褶皱及其形成时期研究

研究表明：印支运动的褶皱作用非常轻微,认为其导致华南法台盖层全面褶皱的观点是不恰当的。华南地台盖层全面褶皱是由晚三叠世以来多期次继承性造山运动形成的同步一类同步褶皱。主要褶皱时代很晚,在南北太平洋大地构造域是晚侏罗世至中始新世,在特提期大地构造域是中晚始新世之交。     

Blueschist-facies metamorphism during Paleozoic orogeny in southwestern Japan: Phengite K–Ar ages of blueschist-facies tectonic blocks in a serpentinite melange beneath early Paleozoic Oeyama ophiolite

Blueschist-bearing Osayama serpentinite melange develops beneath a peridotite body of the Oeyama ophiolite which occupies the highest position structurally in the central Chugoku Mountains. The blueschist-facies tectonic blocks within the serpentinite melange are divided into the lawsonite–pumpellyite grade, lower epidote grade and higher epidote grade by the mineral assemblages of basic schists. The higher epidote-grade block is a garnet–glaucophane schist including eclogite-facies relic minerals and retrogressive lawsonite–pumpellyite-grade minerals. Gabbroic blocks derived from the Oeyama ophiolite are also enclosed as tectonic blocks in the serpentinite matrix and have experienced a blueschist metamorphism together with the other blueschist blocks. The mineralogic and paragenetic features of the Osayama blueschists are compatible with a hypothesis that they were derived from a coherent blueschist-facies metamorphic sequence, formed in a subduction zone with a low geothermal gradient (~ 10°C/km). Phengite K–Ar ages of 16 pelitic and one basic schists yield 289–327 Ma and concentrate around 320 Ma regardless of protolith and metamorphic grade, suggesting quick exhumation of the schists at ca 320 Ma. These petrologic and geochronologic features suggest that the Osayama blueschists comprise a low-grade portion of the Carboniferous Renge metamorphic belt. The Osayama blueschists indicate that the 'cold' subduction type (Franciscan type) metamorphism to reach eclogite-facies and subsequent quick exhumation took place in the northwestern Pacific margin in Carboniferous time, like some other circum-Pacific orogenic belts (western USA and eastern Australia), where such subduction metamorphism already started as early as the Ordovician.