大别山碰撞造山带逆冲推覆构造运动学和动力学研究

Since the discovery of coesite-bearing eclogites in Dabie and Sulu region over ten years ago, the Dabie collisional orogen has been the "hot-spot" across the world. While many great progresses have been made for the last decade in the researches on the Dabie and Sulu UHP metamorphic rocks in the following fields, such as, petrology, mineralogy, isotope chronology, and geochemistry, the study of the structural geology on the Dabie orogen is still in great need. Thrust and nappe tectonics commonly developed in any collisional orogenic belt during the syncollisional process of the orogen. It is the same as the Dabic collisional orogen is concerned. The paper put much stress on the thrust and nappe tectonics in the Dabic orogenic belt, which have been seldom systematically studied before. The geometric features including the division and the spatial distribution of various thrust and nappe tectonics in the Dabie orogen have been first studied, which is followed by the detailed studies on their kinematic characteristics in different scales varying from regional tectonics to microtectonics. In the thesis, new deformation ages have been obtained by the isotopic methods of ~(40)Ar-~(39)Ar, Sm-Nd and Rb-Sr minerals-whole rock isochrons on the mylonites formed in three ductile shear zones which bounded three different major nappes in the Dabie collisional orogenic belt. And the petrological, geochemical characteristics of some metamorphic rocks as well as the geotectonics of their protoliths, which have also deformed in the ductile shear zone, are analyzed and discussed. In the paper, twelve nappes in the Dabie orogen are first divided, which are bounded by various important NWW or NW-strike faults and three NNE-strike faults. They are Shangcheng Nappe, Huoshan Nappe, Yuexi Nappe, Yingshanjian-Hengzhong Nappe, Huangzhen Nappe, Xishui-Huangmei Nappe, Zhoudang Nappe, Suhe-Huwan Nappe, Xinxian Nappe, Hong'an Nappe, Mulan Nappe and Hhuangpi-Susong Nappe. In the Dabie orogen, three types of thrust and nappe tectonics belonging to two stages have been confirmed. They are: (1) early stage ductile thrust -nappe tectonics which movement direction was top-to-the-south; (2) late stage brittle to ductile-brittle thrust-nappe tectonics which are characterized by double-vergence movement, including top-to-the-north and top-to-the-south; (3) the third type also belongs to the late stage which also characterized by double-vergence movement, including top-to-the-east and top-to-the-west, and related to the strike-slip movement. The deformation ages of both Wuhe-Shuihou ductile shear zone and Taihu-Mamiao ductile shear zone have been dated by ~(40)Ar-~(39)Ar method. ~(40)Ar/~(39)Ar plateau ages of biotite and mica from the mylonites in these two shear zones are 219.57Ma and 229.12Ma. The plateau ages record the time of ductile deformation of the ductile shear zones, which made the concerned minerals of the mylonites exhume from amphibolite facies to the middle-upper crustal conditions by the early stage ductile thrust-nappe tectonics. The mineral isochons of Sm-Nd and Rb-Sr dating on the same mylonite sample of the metamafic rocks are 156.5Ma and 124.56Ma respectively. The two isochron ages suggest that the mylonitic rock strongly deformed in the amphilbolite facies at 156Ma and then exhumed to the upper crustal green schist condition at 124Ma with the activities of the Quiliping-Changlinggang ductile shear zone which bounded to the southen edge of Xinxian Nappe. Studies of the petrological and geochemical characteristics of some meta-mafic rocks and discussion on the geotectonics of their protoliths indicate that their protoliths were developped in an island arc or back-arc basin or active continental margin in which calc-alkline basalts formed. This means that arc-accretion orogeny had evolved in the margins of North china plate and/or Yangtze plate before these two plates directly collided with each other during the evolution process of Dabie orogen. Three-stage evolution of the thrust-nappe tectonics in Dabie collisional orogen has been induced based on the above-mentioned studies and previous work of others. And a possible 3-stage exhumation model (Thrust-Positive Flower Structure Model) has also been proposed.

晚中生代松辽盆地形成的大地构造环境及成因机制

Directed by the theory of "Collision Tectonic Facies", the tectonic setting and dynamic mechanism of the formation of Songliao basin in late Mesozoic (J_3-K_1) are studied in the present thesis with the methods of petrology, petrochemistry, geochemistry and isotopic geochronology. The research contents in this paper include as followings. Firstly, the general tectonic frame is made up of different tectonic facies formed from Mid-late Proterozoic to Mesozoic, which are Huabei plate, the Chengde-Siziwangqi melange (Pz_1), the Wenduermiao magmatic arc (Pz_1), the Hegenshan-Chaogenshan melange (Pz_2), the accretion arec (Pz_1-P), the Raohe-Hulin melange (Mz), the magmatic arc (Mz) and the pull-apart basin on the magmatic arc (Mz). Secondly, the volcanic rock assemblages of Songliao basin and its adjacent area in late Mesozoic is the typical calc-alkaline of the magmatic arc. The types of volcanic rocks in the study area include basalts, basaltic andesites, andesites, dacites and rhyolites, and basic-intermediate volcanic rocks have higher alkalinity. The volcanic rock series in this area is the high-K calc-alkaline series. Thirdly, the total REE of volcanic rocks in Songliao basin and its adjacent area is higher than that of the chondrite. The pattern of the REE normalized by the chondrite shows the characteristics similar to that of the typical island arcs or the active continental margins in the earth, that is enrichment of LREE and depletion of Eu. The spider-diagram of the trace element normalized by the primitive mantle also expresses the similar features to that of the typical island arcs or the active continental margins, it has distinctive valleies of Nb, Ta, Sr, P, and Ti, as well as the peaks of La, Ce, Th, U, and K. The incompatible elements show that the high field strength elements, such as Nb, Ta, Ti, and P, are depletion while the low field strength elements, such as K, U, Pb, and Ba, are enrichment. These features are similar to those of orogenic volcanic rocks and imply the formation of the volcanic rocks in this area is related to the subduction. The degrees of both the enrichment of the HFS elements and depletion of the LFS elements become more obvious from basic to acid volcanic rocks, which suggests crustal contamination enhances with the magmatic crystallization and fractionation. The concentration of the compatible elements is W-shape, and anomalies in Cr and Ni suggest there is the contamination during the magmatic crystallization and fractionation. Fourthly, the isotopic age data prove the volcanic activity in the Songliao basin and its adjacent area started in the early-middle Jurassic, and ended in the end of the early Cretaceous-the beginning of the Cretaceous. The volcanism summit was the late Jurassic-the early Cretaceous (100 - 150Ma). Finally, the tectonic setting of volcanism in the late Mesozoic was magmatic arc, which originated the subduction of Raohe-Hulin trench to the northwest Asian plate. The subduction began in the middle Jurassic, and the collision orogenesis between the Sikhote-Alin arc and Asian continent was completed in the end of the early Cretaceous-the beginning of the late Cretaceous. The results of above tectonic processes were finally to format Nadanhada orogenic belt symbolized by the Raohe-Hulin suture or melange belt. The violently oblique movement of the Izanagi plate toward Asian plate in the late Mesozoic was the dynamic mechanism of above tectonic processes. At the same tome, the left-lateral strike-slip shear caused by the oblique movement of the Izanagi plate produced a series of strike-slip faults in east Asian margin, and the large scale displacements of these strike-slip faults then produced the pull-apart basing or grabens on the magmatic arc. Conclusively, the tectonic setting during the formation of the grabens of Songliao basin in the late Mesozoic was magmatic arc, and its dynamic mechanism was the pull-apart. In a word, there was a good coupling relation among the oblique subduction of the oceanic plate, collisional orogene between island arc and continental plate, strike-slip shear of the faults and the formation of the grabens in Songliao basin and its adjacent area in late Mesozoic. These tectonic processes were completed in the unoin dynamic setting and mechanism as above description.

扬子板块西部大陆地幔地球化学特征及壳幔演化－有关基性岩超基性岩的地球化学研究

The continental mantle geochemical characteristics and crust-mantle evolution in the west of Yangtze Plate was discussed through the study of some within-plate basic-ultrabasic rocks from Lower Proterozoic to Later Paleozoic in this paper. In the Lower Proterozoic, the plate subduction between the pre-Tethys Proterozoic Ocean Plate and paleo-Yangtze Plate induced some basic volcanic formed in the island arc-back arc surrounding, which were represented by Ailaoshan Group-Dibadu Formation-Dahongshan Group, and there existed EM I component in the mantle source. The Middle Proterozoic Caiziyuan peridotite was formed in the epicontinental basin at the ocean-land boundary or within-continent rift basin. Its mantle source could be metasomatized by the dehydration fluid of subducted plate, and much initial radioactive ~(143)Nd was added to the source. In the Later Proterozoic, some rifts at the epicontinent or within-continent was formed due to the pre-Tethys oceanic plate subduction, and within-plate hot-spot Dahongshan diabase came into being. The whole-rock isochronal age of diabase is 1066±110Ma, and its mantle source was enriched Nd isotope and trace element which was related to the primary volatile component from asthenosphere and mantle plume. Its mantle source was included "FOZO" component representing mantle plume. The layer ultramafic rocks located at the Panxi Rift in the Middle-Later Paleozoic were resulted from different period and source. The early ultramafic indicated the incipient action of Panxi Rift, which is residue of continental lithospheric partial melting. Its mantle source involved subducted material and had distinct EM II component. The Emeishan basalt in the Later Paleozoic was typical continental flood basalt and its source also contained EM II component. The subduction of paleo-Tethys Ocean Plate provided essential dynamic condition for the large-scale opening of Panxi Rift, while the mantle plume supplied much material for Emeishan basalt. However, the plume was contaminated by the metasomatized continental mantle lithosphere in its upwelling process, which resulted in the Sr isotopic and incompatible elemental enrichment, and the Nd isotope kept down the weak-depleted character of mantle plume. The magmatic history in the west of Yangtze Plate is the tectonic process between pre-Tethys, paleo-Tethys Oceanic Plate and Yangtze Plate in a long history. Due to the subduction of oceanic plate, the crustal source material took part in the crust-mantle evolution widely. the continental mantle lithosphere in the west of Yangtze Plate was metasomatized by the fluid released by the subducted plate and the primary volatile from deeper mantle, and the mantle source include obvious enriched component.

阿尔金蛇绿混杂带构造岩石组合及其大地构造意义

The Alytn fault is a huge left-slip fault zone within the Asian continent, and locates such zone that is linked to main tectonic units in the western China, which makes it is very important to the tectonic framework and ore distribution in the western China. Selecting two ophiolite zones (namely Hongliugou-Lapeiquan ophiolite zone and Sulamutage ophiolite zone) respectively located within the southern and northern part of the Altyn fault and based on analysis of field geology characteristics and geochemistry, this paper recognized the rock types (mainly mafic and ultramafic rocks) within the melanges and subdivided each lithological unit based on tectonic environment. At last, this paper rebuilt the paleo-tectonic framework in the Alytn region by the method of tectonic facies and discussed its tectonic evolution with the theory of collision orogens. Combining former results with hard field observation and geochemical analysis, this paper acquired such recognitions to two ophiolte zones within the Altyn fault zone as follows: To the typical regions (Hongliugou, Lapeiquan, Mangya and Sulamutage) within the two ophiolte zones in the Altyn fault zone, this paper offered the field geology profiles. Field geology characteristics show that they are composed of melange bases (mainly abyssal flysch and carbonate rocks) and melange blocks from various tectonic environments, often with fault contact among each lithological units, belonging to typical ophiolitic melange zone. The ultramafic rocks outcropped at the Altyn region are all harzburgites. Remant grains of primary minerals have melted residual texture and elastic deformation texture under high temperature and pressure. The whole-rock analyses show their low TiO_2 contents (0.01～0.04%), low Al, Ca and high MgO contents and wide Mg~# range (89.35～95.57). Rare earth patterns have two types, namely tabacco pipe-shped and LREE-shaped, of which the former is often seen. The chondrite-nomalized Yb values of these analyses are all lower than 1. The spinels have low Ti and high Cr content and most spinels have Cr# higher than 60. All of the above characteristics show that the ultramafic rocks in the Altyn fault zone are components of metmorphic peridotites of ophiolite from depleted mantle source and most ophiolites from this zone belong to supra-subduction zone (SSZ) type ophiolite with a few mid-ocean ridge basalt (MORB) type. Geochemical analyses show that the melange blocks within the Altyn ophiolitic melange zone have different characteristics from various tectonic environments. This paper recognized such tectonic-lithological assemblages as mid-ocean basalts, oceanic island basalts, oceanic island arc tholeiites, island arc calalkaline basalts and island arc granites and inferred that these tectonic-lithological units respectively belongs to such tectonic units as ophiolites, oceanic islands and/or oceanic seamounts, oceanic island arc and a~creting arcs, which show these blocks from oceanic crust and subduction zone for the most part. For the Altyn ophiolites, the chronological data show they become new from the north to the south. Combined with the study on late slip of Altyn fault and North Qilianshan orogeny, the author inferred that the Altyn region had belonged to one part of the North Qilianshan accreting wedge-arc orogeny at paleozoic, and later huge left-slip made it locate modem site.

北祁连与块状硫化物矿床有关的早古生代火山岩的地球化学研究

Different conclusions from previous work are made from the geochemical study for the early Paleozoic volcanic rocks hosting massive sulfide deposits in the north Qilian Orogen. The main points are: (1)The geochemical characteristics of the basalts and rhyolites from the Baiyin deposit are not consistent with that of the volcanic rocks in the continental rift setting, but show the relationship with subduction. The basalts and rhyolites from the Baiyin deposit are probably individual tectonic slice piled by subduction, and there is no bimodal volcanic rock suite occurred in the Baiyin deposit. Zircon U-Pb dating constrains the magmatic emplacement of basalts and rhyolites at 475±10Ma and 453±12Ma, respectively. The basalts are characterized by enriched Th and Sr, and depleted Nb, Ta and Ti. They have relatively high Th/Nb ratios between 0.9 and 1.3. Their εNd(T) values vary from -1.2 to +3.4. The chemical and isotopic compositions display a typical subduction-related signature, and they suggest that an enriched component with the isotopic composition of EMII might have contributed to the generation of the Baiyin basalts. The basalts were likely formed in a mature island-arc or a volcanic arc built on comparatively young or thin continental crust in an active continental margin. The rhyoIites have low concentrations of LILE compared to the basalts. They do not seen to have a relationship with the basalts, because of their significantly higher εNd(T) values (+4.3～+7.7). The high and positive εNd(T) values also rule out their derivation from anatexis of the continental crust. A modeling study suggests that the source.of the Zhe-Huo and Xiaotieshan rhyolites is similar to boninite and IAT (island-arc tholeiite), and hence indicating an intra-oceanic arc environment. (2) The formation of the Shangliugou volcanic rocks from .Qilian area is also related to subduction. The basaltic andesite have low TiO_2(0.45～0.63%) and P_2O_5(0.04～0.09) content, and high Th/Nb ratios (0.3～0.6). They show flat REE patterns. Their εNd(T) values vary in a narrow range from +4.8 to +6.4. The chemical and isotopic compositions indicate that they are derived from a slightly depleted mantle source and are fromed in intra-island arc setting. The rhyolites show calc-alkaline trend. They show enriched LREE and fiat HREE patterns with obvious negative Eu anomaly. They have high Th/Ta ratios (5.0 ～ 11.7) and large negative εNd(T) values (-2.6 ～ -8.4). The rhyolites are formed in active continental margin and result from a mixed process of two endmembers, or crust assimilation. (3) The metal elements of the volcanic-hosted massive sulfide deposit have two sources, the copper and zinc are derived from rhyolitic magmas whereas the lead are probably related to old sediments overlying the rhyolites. (4) It is suggested here that the volcanic rocks hosting massive sulfide deposit in the north Qilian orogen, which are previously considered as a bimodal suite of Neo-proterozoic to middle Cambrian age in a continental rift, are virtually related to subduction magmatism in Ordovician age, and there might have no continental rift magmatism of Neo-proterozoic to middle Cambrian in the north Qilian.

新疆东昆仑蛇绿岩岩石学、地球化学特征及其大地构造意义

The East Kunlun area of Xinjiang (briefly EKAX) is the western part of broadly speaking East Kunlun orogenic zone. The absence of geological data (especially ophiolites) on this area has constrained our recognition to its geology since many years. Fund by National 305 Item (96-915-06-03), this paper, by choosing the two ophiolite zones (Muztag and Southwestern Margin of Aqikekule Lake ophiolite zones) exposed at EKAX as the studied objects and by the analysis of thin section, electron probe, XRF, ICP-MS, SEM and Sm-Nd isotope, totally and sys ematically dealt with the field geological, petrological, minerological, petrochemical and geochemical characteristics (including trace, rare earth element and Sm-Nd isotope) and the tectonic setting indicated by them for each ophilite zone. Especially, this paper discussed the trace and rare earth element patterns for metamorphic peridotites, their implications and related them to the other components of ophiolite in order to totally disclose ophiolite origins. Besides, this paper also studied the petrological, geochemical and paleobiological characteristics for the cherts coexsisted with the Muztag ophiolite and the tectonic setting indicated by them. Based on these, the author discussed the tectonic evolution from Proterozoic to Permian for this area. For Muztag ophiolite, their field geological, petrological, minerological, petrochemical and geochemical characteristics show that: ① outcropped along the Muztag-Jingyuhu fault with west-to-east strike, the ophiolite is composed of such three components as metamorphic peridotites, cumulates and volcanic rocks; ② metamophic peridotites consist of such types as lherzolites, serpentinized lherzolites and serpentinites, only pyroxenites is seen of cumulates and volcanic rocks include basalts, basaltic andesites and andesites; ③ mineralogical data on this ophiolite suggest it formed in supra-subduction zone (SSZ)environment, and its mantle wedge is heterogeneous; ④ whole-rock TiO_2 and Al_2O_3 of metamorphic peridotites indicate their original environment with the MORB and SSZ characteristics; ⑤ metamorphic peridotites have depleted LREE and flat REE patterns and volcanic rocks have enriched LREE patterns; ⑥ trace element characteristics of metamorphic peridotites imply that they had undergone Nb and Ta enrichment event after partial melting; ⑦ trace element characteristics of volcanic rocks and their tectonic diagrams show they are formed in the spreading and developed island arc environment with back-arc basin, such as rifted island arc, which is supported by the ε_(Nd)(t) -2.11～+3.44. In summary, the above evidence implies that Muztag ophiolite is formed in SSZ environment, where heterogeneous mantle wedge was metasomatised by the silica-enriched melt from subducted sediments and/or oceanic crust, which makes the mantle wedge enriched again, and this enriched mantle wedge later partially melted to form the volcanic rocks. For Southwestern Margin of Aqikekule Lake ophiolite, their field geological, petrological, minerological, petrochemical and geochemical characteristics show that: ① it outcropped as tectonic slices along the near west-to-east strike Kunzhong fault and is composed of metamorphic perodotties, cumulates and volcanic rocks, in which, chromites are distributed in the upper part of metamorphic peridotites as pods, or in the lower part of cumulates as near-strata; ② metamorphic peridotites include serpentinites, chromite-bearing serpentinites, thlorite-epidote schists and chromitites, of which, chromitites have nodular and orbicular structure, and cumulates include pyroxenits, serpentinites, chromite-bearing serpentinites, chromites and metamorphically mafic rocks and only basalts are seen in volcanic rocks; ③ Cr# of chromites suggest that they formed in the SSZ and Al_2O_3 and TiO_2 of metamorphic peridotites also suggest SSZ environment; ④metamorphic peridotites have V type and enriched LREE patterns, cumulates have from strongly depleted LREE, flat REE to enriched LREE patterns with universally striking positive Eu anomalies and basalts show flat REE or slight enriched LREE patterns with no Eu anomalies; ⑤ trace element and Sm-Nd isotope characteristics of metamorphic peridotites imply their strikingly heterogeneous mantle character(ε_(Nd)(t)+4.39～+26.20) and later Nb, Ta fertilization; ⑥ trace element characteristics of basalts and their tectonic diagrams show they probably formed in the rifted island arc or back-arc basin enviromnent. In summary, the above evidence shows that this ophiolite formed in the SSZ environment and melts from subudcted plate are joined during its formation. Rare earth element, whole-rock and sedimentary characteristics of cherts with the Muztag ophiolite show that they formed in the continental margin environment with developed back-arc basin, and radiolarias in the cherts indicate that the upper age of Muztag ophiolite is early carboniferous. Based on the accreted wedge models of Professor Li Jiliang for Kunlunshan Mountain and combined with study on the two typical ophiolite profiles of EKAX, the author discussed the tectonic evolution of EKAX from Proterzoic to Permian.

西秦岭晚古生代弧前盆地沉积与成矿作用

The Western Qinling Orogenie belt in the Taibai-Fengxian and Xihe-Lixian areas can be subdivided into three units structurally from north to south, which are the island-arc, forearc basin and accretionary wedge, respectively. The forearc basin developed in the Late Paleozoic mainly controls sedimentation and some larger lead-zinc and gold deposits in the western Qinling. Stratigraphically, the island arc is dissected into the Liziyuan Group, the Danfeng Group and the Luohansi Group. The metavolcanic rocks include basic, intermediate and acidic rocks, and their geochemistry demonstrates that these igneous rocks generated in an island arc. Where, the basalts are subalkaline series charactered by low-medium potassium, with enriched LREE, negative Eu anomaly, and positive Nd anomaly. Cr-content of volcanic rocks is 2-3 times higher than that of island arc tholeiite all over the world. In addition, the lightly metamorphosed accretionary wedge in the areas of Huixian, Chengxian, Liuba and Shiqun is dominated by terrigenous sediments with carbonatite, chert, mafic and volcanic rocks. The age of the wedge is the Late Palaeozoic to the Trassic, while previous work suggested that it is the Silurian. The Upper Paleozoic between the island arc belt and accretionary wedge are mainly the sediments filled in the fore arc basin. The fillings in the forearc basin were subdivided into the Dacaiotan Group, the Tieshan Group, the Shujiaba Group and the Xihanshui Group, previously. They outcropped along the southern margins of the Liziyuan Group. The Dacaotan Group, the Upper Devonian, is close to the island arc complex, and composed of a suite of red and gray-green thick and coarse terrestrial elastics. The Shujiaba Group, the Mid-Upper Devonian, is located in the middle of the basin, is mainly fine-grained elastics with a few intercalations of limestone. The Xihanshui Group, which distributes in the southern of the basin, is mainly slates, phyllites and sandstones with carbonatite and reef blocks. The Tieshan Group, the Upper Devonian, just outcrops in the southwest of the basin, is carbonatite and clastic rocks, and deposited in the shallow -sea environment. The faults in the basin are mainly NW trend. The sedimentary characteristics, slump folds, biological assemblages in both sides of and within those faults demonstrate that they were syn-sedimentary faults with multi-period activities. They separated the forearc basin into several sub-basins, which imbricate in the background of a forearc basin with sedimentary characteristics of the piggyback basin. The deep hydrothermal fluid erupted along the syn-sedimentary faults, supported nutrition and energy for the reef, and resulted in hydrothermal-sedimentary rocks, reef and lead-zinc deposits along these faults. The sedimentary facies in the basin varies from the continental slope alluvial fan, to shallow-sea reef facies, and then to deep-water from north to south, which implies that there was a continental slope in the Devonian in the west Qinling. The strata overlap to north and to east respectively. Additionally, the coeval sedimentary facies in north and south are significantly different. The elastics become more and more coarser to north in the basin as well as upward coarsing. These features indicate prograding fillings followed by overlaps of the different fans underwater. The paleocurrent analyses show that the forearc basin is composed of thrust-ramp-basins and deep-water basins. The provenance of the fillings in the basin is the island arc in the north. The lead-zinc deposits were synchronous with the Xihanshui Group in the early stage of development of the forearc basin. They were strongly constrained by syn-sedimentary faults and then modified by the hydrothermal fluids. The gold deposits distributed in the north of the basin resulted from the tectonic activities and magmatism in the later stage of the basin evolution, and occurred at the top of the lead-zinc deposits spatially. The scales of lead-zinc deposits in the south of the basin are larger than that of the gold-deposits. The Pb-Zn deposits in the west of the basin are larger than those in the east, while the Gold deposits in the west of the basin are smaller than those in the east. Mineralizing ages of these deposits become younger and younger to west.

新疆萨吾尔金矿带构造-流体地球化学及成矿作用

The Sawuer gold belt is located in the transition belt between Siberian plate and Kazakhstan-Junggar plate. Based on the geological and geochemical studies on the Kuoerzhenkuola and Buerkesidai gold deposits, in Sawuer gold mineralization belt, the time-space structure of mineralization and mineralizing factor are studied, the metallogenic regularity is concluded in thistheses. The ore bodies have the regularity that orebody are of the extensive and compressive in the sallow and depth of volcanic apparatue, respectively, and the vertical extension of orebody is more intensive than the horizontal extension. The gold deposits were controlled by the fractures of volcanic apparatus and regional faults, and featured by the hydrothermal alteration and metasomatism type disseminated mineralization and filling type vein mineralization. By virtue of the geological and geochemical studies on the two deposits that the formation of the two deposits are significantly related to the volcanic activity, we propose new ideas about their origin: (1) the two deposits are located in the same strata, and share the same genesis. (2) both of two deposits are volcanogenic late-stage hydrothermal gold deposits. Based on mapping of volcanic lithofacies and structure for the first time, it is discovered that a volcanic apparatus existed in the study area. Volcanic-intrusive activity can be divided into three cycles and nine lithofacies. where the two deposits are hosted in the same volcanic cycle, in this case, the wall-rock should belong to the same strata. The 40Ar-39Ar age method is employed in this work to analyze the fluid inclusions of quartz in the ore bodies from Kuoerzhenkuola and Buerkesidai gold deposits. The results show that the main mineralization occurred in 332.05 + 2.02-332.59 + 0.5IMa and 335.53 + 0.32Ma~336.78 + 0.50Ma for Kuoerzhenkuola and Buerkesidai gold deposits respectively, indicating that the two deposits are formed almost at the same time, and the metallogenic epoch of the tow deposits are close to those of the hosting rocks formed by volcanic activity of Sawuer gold belt. This geochronological study supplies new evidence for determining the timing of gold mineralization, the geneses of gold deposits? and identifies that in Hercynian period, the Altai developed tectonic-magmatic-hydrothermal mineralization of Early Carboniferous period, except known two metallogenic mineralization periods including tectonic-magmatic-hydrothermal mineralization of Devonian period and Late Carboniferous-Permian period respectively. The study of fluid inclusions indicates that the ore-forming fluid is a type of NaCl-HbO fluid with medium-low temperature and low salinity, Au is transported by the type of auric-sulfur complex (Au (HS)2-), the ore is formed in reduction condition. Hydrogen and oxygen isotopes of fluid inclusions in the major mineralizating stage show that the solutions mainly originated from magmatic water and meteoric water. The fluid mixing and water-rock reaction cause the deposition of Au. The helium and argon isotope compositions of fluid inclusions hosted in pyrite have been measured from Kuoerzhenkuola and Buerkesidai gold deposits in Sawuer gold belt. The results show that the ore-forming fluids of two deposits possessed the same source and is a mixture of mantle- and partial meteoric water-derived fluid, and the reliability of He and Ar isotopic compositions in Hercynian period is discussed. Isotopic studies including H, O, He, C, S, Pb and Sr reveal the same result that the ore-forming fluids of two deposits possessed the same source: the water derived mainly from magmatic water, partially from meteoric water; the mineralizers and ore materials derived mainly from mantle beneath the island arc, and partially from crust. The ore-forming fluids of two deposits are a mixture of mantle-derived fluids being incorporated by crust-derived fluid, and shallow partial meteoric water. Based on these results, it is proposed that the geneses of the two gold deposits are the same, being volcanogenic late-stage hydrothermal gold deposits that the ore-forming fluids filled in fractures of volcanic apparatus and metasomatized the host rocks in the volcanic apparatus. It is the first time we carried out the geophysical exploration, that is, the EH-4 continuous electrical conductivity image system measurement, the results show that relative large-size mineralizing anomalies in underground have been discovered.lt can confirm the law and genesis of the deposits mentioned above, and change the two abandoned mines to current large-size potenial exploration target.

安多地区早中侏罗世岩浆岩岩石地球化学和同位素年代学研究及其对构造演化的制约

Anduo area is located in the Central Tibet, the middle segment of the Bangonghu-Nujiang suture. Anduo Block is the northern part of Lhasa terrane. The relationships among the different geological bodies were determined during the 1: 250000 regional geological surveying. Petrography, petrologic geochemistry, isotopic geochemistry and geochronology of igneous rocks from the suture and granitoids from Anduo Block were analyzed systematically as a whole for the first time. Then, their tectonic setting and history are discussed.Anduo ophiolitic melange consists of metamorphic peridotites, cumulates, plagiogranites, sheeted dykes swarm, pillow lava and radiolarian cherts. The concentration of Cr and Ni in the metamorphic peridotites is very high, with Mg# about 0.94 ~ 0.97, higher 87Sr/86Sr and Pb isotopic ratios, and lower 143Nd/i44Nd ratio. LREE is enriched relative to HREE and positive Eu anomaly is very clear. The REE distribution curve is U shape. Nb and Ta anomalies from cumulate gabbro and sheeted dyke swarm are not clear, while that are slightly negative from pillow lava. Plagiogranite belongs to strong calc-alkaline series with high Si, middle Al, low Fe, Mg and low K contents. Eu anomaly (~ 1.23) from plagiogranites is slightly positive. The character of all components of ophiolite is similar to that of the MORB, while to some extent the ophiolite was influenced by crustal material. Anduo ophiolite formed in a mature back-arc basin. Additionally, intermediate acidity volcanic rocks within Anduo phiolite melange are island arc calc-alkline rocks related to ocean subduction.The early-middle Jurassic plutonic rocks are tonalite, granodiorite bearing-phenocryst, magaporphyritic hornblende monzogranite, magaporphyritic monzogranite, monzogranite bearing-phenocryst and syenogranite in turn. They belong to calc-alkaline series which developed from middle K to high K series temporally. REE distribution curves of all plutonic rocks are similar and parallel to each other. SREE and negative Eu anomaly values decrease. In the multi-element spider diagram, the curves of different plutons are similar to each other, but troughs of Nb, Sr, P and Ti from young plutons become more evident. This suggests that thereare some closely petrogenetic affinities among plutonic rocks which make up amagma plutonism cycle of the early-middle Jurassic. Magma source is mainly crustal,but abundant mafic microgranular enclaves within granitoids indicate that crastalmagma should be mixed with mantle-derived magma and the mantle-derived magmadecreased subsequently. Tonalite has features of I-type granite, magaporphyriticmonzogranite is transition type, and monzogranite bearing-phenocryst is S-typegranite. The characteristic of granitoids from Anduo Block suggest that the formingtectonic setting is active continental margin.Reliable zircon U-Pb SHRIMP ages are obtained in the study area firstly. Plagiogranite from the Anduo ophiolite of the Bangonghu-Nujiang suture is 175.1 Ma, and granitoids from Anduo Block is 172.6-185.4 Ma. Additionally, plagioclase from the plagiogranite dates a 40Ar/39Ar age of 144 Ma, while biotite and hornblend from granitoids of Anduo Block give a 163-165 Ma.Similar cooling ages of plagiogranite from the Anduo ophiolitic melange and granitoids from Anduo Block and the spatial distribution of the ophiolitic rocks between Anduo, Naqu, and Shainzha area suggest that bilateral subduction of the Bangonghu-Nujiang oceanic basin took place in the early-middle Jurassic. During this subduction, Anduo ophiolitic rocks were related to north subduction of the Bangonghu-Nujiang oceanic basin and Anduo back-arc basin spreading, while granitoids from Anduo Block were related to south subduction.

Structural, stratigraphic and geochemical studies of the Horwood Peninsula - Gander Bay Area, Northeast Newfoundland /

The Horwood Peninsula - Gander Bay area is located at NE Newfoundland in the Botwood Zone (Williams et a1., 1974) or in the Dunnage Zone (Williams, 1979) of the Central Mobile Belt of the Newfoundland Appalachians. The area is underlain by Middle Ordovician to possible Lower Silurian rocks of the Davidsville and Indian Islands Groups, respectively. Three conformable formations named informally : the Mafic Volcanic Formation, the Greywacke and Siltstone Formation and the Black Slate Formation, have been recognized in the Davidsville Group. The Greywacke and the Black Slate Formations pass locally into a Melange Formation. From consideration of regional structure and abundant locally-derived mafic volcanic olisto- 1iths in the melange, it is considered to have originated by gravity sliding rather than thrusting. Four formations have been recognized in the Indian Islands Group. They mainly contain silty slate and phyllite, grey cherty siltstone, green to red micaceous siltstone and limestone horizons. Repetition of lithological units by F1 folding are well-demonstrated in one of formations in this Group. The major structure in this Group on the Horwood Peninsula is interpreted to be a synclinal complex. The lithology of this Group is different from the Botwood Group to the west and is probably Late Ordovician and/or Early Silurian in age. The effects of soft-sediment deformation can be seen from the lower part of the Davidsville Group to the middle part of the Indian Islands Group indicating continuous and/or episodic slumping and sliding activities throughout the whole area. However, no siginificant depOSitional and tectonic break that could be assigned to the Taconian Orogeny has been recognized in this study. Three periods of tectonic deformation were produced by the Acadian Orogeny. Double boudinage in thin dikes indicates a southeast-northwest sub-horizontal compression and main northeast-southwest sub-horizontal extension during the D1 deformation. A penetrative, axial planar slaty cleavage (Sl) and tight to isocJ.ina1 F1 folds are products of this deformation. The D2 and D3 deformations formed S2 and S3 fabrics associated with crenulations and kink bands which are well-shown in the slates and phyllites of the Indian Islands Group. The D2 and D3 deformations are the products of vertical and northeast-southwest horizontal shortening respectively. The inferred fault between the Ordovician slates (Davidsville Group) and the siltstones (Indian Islands Group) suggested by Williams (1963, 1964b, 1972, 1978) is absent. Formations can be followed without displacement across this inferred fault. Chemically, the pillow lavas, mafic agglomerates, tuff beds and diabase dikes are subdivided into three rock suites : (a) basaltic komatiite (Beaver Cove Assemblage), (b) tholeiitic basalt (diabase dikes), (c) alkaline basalt (Shoal Bay Assemblage). The high Ti02 , MgO, Ni contents and bimodal characteristic of the basaltic komatiite in the area are comparable to the Svartenhuk Peninsula at Baffin Bay and are interpreted to be the result of an abortive volcano-tectonic rift-zone in a rear-arc basin. Modal and chemical analyses of greywackes and siltstones show the trend of maturity of these rocks increasing from poorly sorted Ordovician greywackes to fairly well-sorted Silurian siltstones. Rock fragments in greywackes indicate source areas consisting of plagiogranite, low grade metamorphic rocks and ultramafic rocks. Rare sedimentary structures in both Groups indicate a southeasterly provenance. Trace element analyses of greywackes also reveal a possible island-arc affinity.

A geochemical and petrological study of volcanic rocks in the Beardmore-Geraldton Archaean Greenstone Belt, Northwestern Ontario

Three repetitive sequences of northward youngIng, east striking, linear, volcano-sedimentary units are found in the late Archaean BeardmoreGeraldton greenstone belt, situated within the Wabigoon subprovince of the Superior Province of northwestern Ontario. The volcanic components are characterised by basaltic flows that are pillowed at the top and underlain by variably deformed massive flows which may In part be intrusive. Petrographic examination of the volcanic units indicates regional metamorphism up to greenschist facies (T=3250 C - 4500 C, P=2kbars) overprinted by a lower amphibolite facies thermal event (T=5750 C, P=2kbars) confined to the south-eastern portion of the belt. Chemical element results suggest olivine, plagioclase and pyroxene are the main fractionating mineral phases. Mobility studies on the varIOUS chemical elements indicate that K, Ca, Na and Sr are relatively mobile, while P, Zr, Ti, Fet (total iron = Fe203) and Mg are relatively immobile. Discriminant diagrams employing immobile element suggests that the majority of the samples are of oceanic affinity with a minor proportion displaying an island arc affinity. Such a transitional tectonic setting IS also refle.cted in REE data where two groups of volcanic samples are recognised. Oceanic tholeiites are LREE depleted with [La/Sm] N = 0.65 and a relatively flat HREE profile with [Sm/Yb] N = 1.2. Island arc type basalts (calc-alkaline) are LREE enriched, with a [La/Sm] N = 1.6, and a relatively higher fractionated HREE profile with [Sm/Yb] N = 1.9. Petrogenetic modelling performed on oceanIC tholeiites suggests derivation from a depleted spinel lherzolite source which undergoes 20% partial melting. Island arc type basalts can be derived by 10% partial melting of a hypothetical amphibolitised oceanic tholeiite source. The majority of the volcanic rocks in the Beardmore-Geraldton Belt are interpreted to represent fragments of oceanic crust trapped at a consuming plate margin. Subsequent post accretionary intrusion of gabbroic rocks (sensu lato) with calc-alkaline affinity is considered to result in the apparent hybrid tectonic setting recognized for the BGB.

The Cariris Velhos tectonic event in Northeast Brazil

The Borborema Province in northeastern South America is a typical Brasiliano-Pan-African branching system of Neoproterozoic orogens that forms part of the Western Gondwana assembly. The province is positioned between the Sao Luis-West Africa craton to the north and the Sao Francisco (Congo-Kasai) craton to the south. For this province the main characteristics are (a) its subdivision into five major tectonic domains, bounded mostly by long shear zones, as follows: Medio Coreau, Ceara Central, Rio Grande do Norte, Transversal, and Southern; (b) the alternation of supracrustal belts with reworked basement inliers (Archean nuclei + Paleoproterozoic belts); and (c) the diversity of granitic plutonism, from Neoproterozoic to Early Cambrian ages, that affect supracrustal rocks as well as basement inliers. Recently, orogenic rock assemblages of early Tonian (1000-920 Ma) orogenic evolution have been recognized, which are restricted to the Transversal and Southern domains of the Province. Within the Transversal Zone, the Alto Pajeu terrane locally includes some remnants of oceanic crust along with island arc and continental arc rock assemblages, but the dominant supracrustal rocks are mature and immature pelitic metasedimentary and metavolcaniclastic rocks. Contiguous and parallel to the Alto Pajeu terrane, the Riacho Gravata subterrane consists mainly of low-grade metamorphic successions of metarhythmites, some of which are clearly turbiditic in origin, metaconglomerates, and sporadic marbles, along with interbedded metarhyolitic and metadacitic volcanic or metavolcaniclastic rocks. Both terrane and subterrane are cut by syn-contractional intrusive sheets of dominantly peraluminous high-K calc-alkaline, granititic to granodioritic metaplutonic rocks. The geochemical patterns of both supracrustal and intrusive rocks show similarities with associations of mature continental arc volcano-sedimentary sequences, but some subordinate intra-plate characteristics are also found. In both the Alto Pajeu and Riacho Gravata terranes, TIMS and SHRIMP U-Pb isotopic data from zircons from both metavolcanic and metaplutonic rocks yield ages between 1.0 and 0.92 Ga, which define the time span for an event of orogenic character, the Cariris Velhos event. Less extensive occurrences of rocks of Cariris Velhos age are recognized mainly in the southernmost domains of the Province, as for example in the Polo Redondo-Maranco terrane, where arc-affinity migmatite-granitic and meta-volcano-sedimentary rocks show U-Pb ages (SHRIMP data) around 0.98-0.97 Ga. For all these domains, Sm-Nd data exhibit Tom model ages between 1.9 and 1.1 Ga with corresponding slightly negative to slightly positive epsilon(Nd)(t) values. These domains, along with the Borborema Province as a whole, were significantly affected by tectonic and magmatic events of the Brasiliano Cycle (0.7-0.5 Ga), so that it is possible that there are some other early Tonian rock assemblages which were completely masked and hidden by these later Brasiliano events. Cariris Velhos processes are younger than the majority of orogenic systems at the end of Mesoproterozoic Era and beginning of Neoproterozoic throughout the world, e.g. Irumide belt, Kibaride belt and Namaqua-Natal belt, and considerably younger than those of the youngest orogenic process (Ottawan) in the Grenvillian System. Therefore, they were probably not associated with the proposed assembly of Rodinia. We suggest, instead, that Cariris Velhos magmatism and tectonism could have been related to a continental margin magmatic arc, with possible back-arc associations, and that this margin may have been a short-lived (<100 m.y.) leading edge of the newly assembled Rodinia supercontinent. (C) 2009 Elsevier Ltd. All rights reserved.

Petrology and geochemistry of the banded iron formation in the Eastern Sierras Pampeanas of San Luis (Argentina): Implications for the evolution of the Nogoli Metamorphic Complex

The metamorphosed banded iron formation from the Nogoli Metamorphic Complex of western Sierra de San Luis, Eastern Sierras Pampeanas of Argentina (Nogoli area, 32 degrees 55`S-66 degrees 15`W) is classified as an oxide facies iron formation of Algoma Type, with a tectonic setting possibly associated with an island arc or back arc, on the basis of field mapping, mineral and textural arrangements and whole rock geochemical features. The origin of banded iron formation is mainly related to chemical precipitation of hydrogenous sediments from seawater in oceanic environments. The primary chemical precipitate is a result of solutions that represent mixtures of seawater and hydrothermal fluids, with significant dilution by maficultramafic volcanic and siliciclastic materials. Multi-stage T(DM) model ages of 1670, 1854 and 1939 Ma and positive, mantle-like xi Nd((1502)) values of +3.8, +1.5 and +0.5 from the banded iron formation are around the range of those mafic to ultramafic meta-volcanic rocks of Nogoli Metamorphic Complex, which are between 1679 and 1765 Ma and +2.64 and +3.68, respectively. This Sm and Nd isotopic connection suggests a close genetic relationship between ferruginous and mafic-ultramafic meta-volcanic rocks, as part of the same island arc or back arc setting. A previous Sm-Nd whole rock isochron of similar to 1.5 Ga performed on mafic-ultramafic meta-volcanic rocks led to the interpretation that chemical sedimentation as old as Mesoproterozoic is possible for the banded iron formation. A clockwise P-T path can be inferred for the regional metamorphic evolution of the banded iron formation, with three distinctive trajectories: (1) Relict prograde M(1)-M(3) segment with gradual P and T increase from greenschist facies at M(1) to amphibolite facies at M(3). (2) Peak P-T conditions at high amphibolite-low granulite facies during M(4). (3) Retrograde counterpart of M(4), that returns from amphibolite facies and stabilizes at greenschist facies during M(5). Each trajectory may be regarded as produced by different tectonic events related to the Pampean? (1) and the Famatinian (2 and 3) orogenies, during the Early to Middle Paleozoic. The Nogoli Metamorphic Complex is interpreted as part of a greenstone belt within the large Meso- to Neoproterozoic Pampean Terrane of the Eastern Sierras Pampeanas of Argentina. (C) 2009 Elsevier Ltd. All rights reserved.

Occurrence and geochemistry of metamafic rocks from the Forquilha Eclogite Zone, central Ceara (NE Brazil): geodynamic implications

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Evidence for 2.35 to 2.30 Ga juvenile crustal growth in the northwest Borborema Province, NE Brazil

The c. 600 Ma Brasiliano Borborema Province of NE Brazil comprises a complex collage of Precambrian crustal blocks cut by a series of continental-scale shear zones. The predominant basement rocks in the province are 2.1-2.0 Ga Transamazonian gneisses of both juvenile and reworked nature. U-Pb zircon and Sm-Nd whole-rock studies of tonalite-trondhjemite-granodiorite basement gneisses in the NW Ceará or Médio Coreaú domain in the northwestern part of the Borborema Province indicate that this represents a continental fragment formed by 2.35-2.30 Ga juvenile crust. This block has no apparent genetic affinity with any other basement gneisses in the Borborema Province, and it does not represent the tectonized margin of the c. 2.1-2.0 Ga São Luis Craton to the NW. The petrological and geochemical characteristics, as well as the Nd-isotopic signatures of these gneisses, are consistent with their genesis in an island arc setting. This finding documents a period of crustal growth during a period of the Earth's history which is known for its tectonic quiescence and paucity of crust formation. © Geological Society of London 2009.