Hydrography and dynamics of the Ría de Ribadeo (NW Spain), a wave driven estuary

The Ría de Ribadeo, a small embayment in NW Spain, was observed for the first time using three months of ADCP (Acoustic Doppler Current Profiler) current meter records and three CTD (Conductivity Temperature Depth) surveys. A wave driven circulation pattern arises from the observations, instead of the shelf wind driven circulation of other Galician Rias. Based on ADCP records, a unidirectional flow in the horizontal velocity field coexists with the classic two-layer circulation (bidirectional flow). The proposed horizontal circulation pattern can then be explained as a wave driven inflow. This flow enters the ria through the west side, describes an anticlockwise gyre inside of it, and flows out through the east side. Numerical simulations run with the HAMSOM (Hamburg Shelf Ocean Model) agreed with observations, confirming the proposed pattern.     

Seasonal abundance and reproductive strategy of Tetrastemma fozensis (Hoplonemertea, Nemertea) in the Villaviciosa estuary (Asturias, Northern Spain)

The seasonal occurrence and reproductive strategy of the nemertean Tetrastemma fozensis, which inhabits the mantle cavity of the bivalve Scrobicularia plana, was studied through the analysis of the temporal diversity of a T. fozensis population. Bimonthly sampling was carried out from February 2001 to January 2002 at mudflats of Villaviciosa estuary (Asturias, Northern Spain). Nemerteans were found throughout the study period, but variations in their abundance were detected, with a maximum during winter months and a minimum during summer months. Moreover, variations in mean size of nemerteans were found, with maximal sizes at the end of the spring and the beginning of the summer and minimum size at early autumn. The annual variations in population parameters (decrease in abundance and complete disappearance of large individuals in summer) suggest that T. fozensis has a distinct reproductive season and a semelparous reproductive strategy.     

南海东北部海陆联测地震数据处理及初步结果

为开展南海东北部海陆过渡带和滨海断裂带横向深部结构研究，利用陆上流动地震台记录与海上气枪放炮相结合的方法，首次在广东汕头沿海进行了海陆联合深地震探测。详细介绍了该次海陆联测地震数据处理的主要步骤与流程，并针对海陆联测地震数据和常用地震软件编写了3个格式转换程序。应用这3个程序和SAC、SU等地震软件得到了初步的数据处理结果。在南澳台和新塘台的单台地震记录剖面中可以清晰地识别出多种震相，得到许多有用的地震信息，证明海陆联测的野外工作和第1阶段的数据处理工作是成功的，为下一步地壳深部结构的研究打下了良好的基础。     

Seasonal variation and structure of a decapod (Crustacea) assemblage living in a Caulerpa prolifera meadow in Cádiz Bay (SW Spain)

The decapod taxocoenosis living in shallow muddy bottoms with the green algae Caulerpa prolifera was studied monthly between February 1994 and January 1996 in the Inner Bay of Cádiz (SW Spain). More than 32,000 specimens belonging to 35 species were collected. Six species were dominant (representing the 85.8% of the total number of specimens), but the structure of the taxocoenosis was regulated by the Hippolyte species, Sicyonia carinata, Palaemon adspersus and Liocarcinus arcuatus. There was no significant qualitative difference between years. There was no clear change in the dominance of groups of species during the year, as happened in the outer Bay. This is probably due to the sheltered character of the area and the more stable and dense vegetal cover, but some seasonal differences were found.The benthic characteristics of the Inner Bay of Cádiz, such as shallow soft bottoms of fine and muddy sediments and the presence of macrophytes (seagrasses and seaweeds) might be key factors influencing the composition and structure of the general and seasonal decapod assemblage. In spite of human impacts on the bay (e.g. aquaculture activities, sewage), the values of the diversity, equitability and richness indexes appeared stable over time (higher than those found in outer adjacent areas) and no significant differences between years were found.     

Effects of temporal variation of the seaweed Caulerpa prolifera cover on the associated crustacean community

The aim of this study was to establish the effect of temporal variation of the alga Caulerpa prolifera cover on the composition and stability of the associated crustacean community. Forty‐five crustacean species were found, amphipods and tanaidaceans being the most abundant groups. The stations were grouped mainly based on the gradient of algal cover, independently of location or sampling period (MDS analyses). Considering separately epifaunal and infaunal species, the epifauna occurred mainly at high cover (HC) and medium–low cover (MLC) stations, while the infauna occurred at MLC and unvegetated (UV) stations. Infaunal species were predominant in all stations and sampling periods, and the abundance and numbers of epifaunal species showed a clear dependence of algal cover. To quantify the loss of biodiversity due to the plant cover variations, we applied the average and variation in taxonomic distinctness (Δ⁺ and Λ⁺, respectively). The HC stations, especially those with fewer algal cover variations along the study period, showed few fluctuations of Δ⁺,and Λ⁺ was usually located near mean; however, UV stations tended to fall in the area where the statistical power of the test is reduced and showed more oscillations of Λ⁺. The ability of these indices to test the fauna composition in function of the alga presence is discussed.     

Two periods of mineralization in Xiaoxinancha Au–Cu deposit,NE China: evidences from the geology and geochronology

The Xiaoxinancha Au–Cu deposit is located at the eastern segment of the Tianshan–Xingmeng orogenic belt in northeast China. The deposit includes porphyry Au–Cu orebodies, veined Au–Cu orebodies and veined Mo mineralizations. All of them occur within the diorite intrusion. The Late Permian diorite, Late Triassic granodiorite, Early Cretaceous granite and granite porphyry are developed in the ore area. The studies on geological features show that the porphyry Au–Cu mineralization is related to the Late Permian diorite intrusion. New geochronologic data for the Xiaoxinancha porphyry Au–Cu deposit yield Permian crystallization zircon U–Pb age of 257 ± 3 Ma for the diorite that hosts the Au–Cu mineralization. Six molybdenite samples from quartz + molybdenite veins imposed on the porphyry Au–Cu orebodies yield an isochron age of 110.3 ± 1.5 Ma. The ages of the molybdenites coeval to zircon ages of the granite within the errors suggest that the Mo mineralization was genetically related to the Early Cretaceous granite intrusion. The formation of the diorite and the related Au–Cu mineralization were caused by the partial melting of the subduction slab during the Late Palaeozoic palaeo‐Asia Ocean tectonic stage. The Re contents and Re–Os isotopic data indicate that the crustal resource is dominated for the Mo mineralization during the Cretaceous extensional setting caused by the roll‐back of the palaeo‐Pacific plate. Copyright © 2014 John Wiley & Sons, Ltd.     

Geochronology and Sr–Nd–Hf isotopes of the Mesozoic granitoids from the Great Xing'an and Lesser Xing'an ranges: implications for petrogenesis and tectonic evolution in NE China

The Great Xing′an and Lesser Xing′an ranges are characterized by immense volumes of Mesozoic granitoids. In this study, we present major and trace element geochemistry, U–Pb geochronology and systematic Sr–Nd–Hf isotopes for the representative samples, in order to constrain their petrogenesis and the tectonic evolution in NE China. The granitoids generally have high SiO₂ (66.5–78.8 wt.%) and Na₂O + K₂O (7.0–8.9 wt.%) contents and belong to high‐K calc‐alkaline to shoshonitic series. All of them show enrichment in Rb, Th, U, Pb and light rare earth elements (LREE), and depletion in Nb, Ta, P and Ti. Zircon U–Pb dating suggests that there was continuous magmatism in both the Great Xing′an Range and the Lesser Xing′an Range during the Jurassic–Early Cretaceous interval. Seven Jurassic granitoids have (⁸⁷Sr/⁸⁶Sr)_i values of 0.704351 to 0.707374, with ϵ_Nd(t) values of −3.4 to 2.4 and ϵ_Hf(t) values of 0.8 to 11.3, indicating that they originated from mixed sources involving depleted mantle and pre‐existing crustal components. One Early Cretaceous sample yields (⁸⁷Sr/⁸⁶Sr)_i value of 0.706184, ϵ_Nd(t) value of 0.6, and ϵ_Hf(t) values of 7.0 to 8.2, which is in accordance with previous studies and indicates a major juvenile mantle source for the granitoids in this period. In the Jurassic, the magmatism in the Great Xing′an Range was induced by the subduction of the Mongol–Okhotsk Ocean, while the contemporaneous magmatism in the Lesser Xing′an Range was related to the subduction of the Palaeo‐Pacific Ocean. In the Early Cretaceous, extensive magmatism in NE China was probably attributed to large‐scale lithospheric delamination. Copyright © 2014 John Wiley & Sons, Ltd.     

大兴安岭大洋山钼矿区侵入岩年代学、岩石地球化学特征及岩石成因

本文研究了黑龙江省大兴安岭东北部大洋山钼矿区中生代侵入岩的年代学和岩石地球化学特征,探讨了研究区中生代侵入岩的形成时代、岩石成因及构造背景。采用电感耦合-等离子体质谱仪（LA-ICP-MS）锆石U-Pb定年方法,获得细中粒二长花岗岩加权平均年龄分别为（177.3±2.6）Ma和（176.5±1.6）Ma, 为早侏罗世;闪长玢岩加权平均年龄为（158.0±2.7）Ma, 为晚侏罗世。岩石地球化学研究表明：细中粒二长花岗岩具高Si,富K和贫Fe、Mn、Mg等特征,大离子亲石元素Rb、K和LREE富集,高场强元素Nb、Zr、P、Th和HREE亏损,具有显著的Eu负异常（δEu =0.39）,结合其低Cr、Ni、Co质量分数和低Mg^#值（Mg^#为27.25）,指示壳源岩浆特征;闪长玢岩偏碱,富K和Na,Ca、Ti、Mg等元素质量分数中等,大离子亲石元素Rb、K、Sr相对富集,高场强元素Nb、Ta、Ti、Th和HREE相对亏损,具俯冲带弧岩浆岩的特征。综合研究表明,细中粒二长花岗岩和闪长玢岩的形成均受到北部蒙古—鄂霍茨克洋俯冲作用的影响,蒙古—鄂霍茨克洋残留部分在大兴安岭东北部俯冲闭合时间为晚侏罗世—早白垩世期间。     

Geology,geochronology and geochemistry of large Duobaoshan Cu-Mo-Au orefield in NE China: Magma genesis and regional tectonic implications

Duobaoshan is the largest porphyry-related Cu-Mo-Au orefield in northeastern(NE)Asia,and hosts a number of large-medium porphyry Cu(PCDs),epithermal Au and Fe-Cu skarn deposits.Formation ages of these deposits,from the oldest(Ordovician)to youngest(Jurassic),have spanned across over 300 Ma.No similar orefields of such size and geological complexity are found in NE Asia,which reflects its metallogenic uniqueness in forming and preserving porphyry-related deposits.In this study,we explore the actual number and timing of magmatic/mineralization phases,their respective magma genesis,fertility,and regional tectonic connection,together with the preservation of PCDs.We present new data on the magmatic/mineralization ages(LA-ICP-MS zircon U-Pb,pyrite and molybdenite Re-Os dating),whole-rock geochemistry,and zircon trace element compositions on four representative deposits in the Duobaoshan orefield,i.e.,Duobaoshan PCD,Tongshan PCD,Sankuanggou Fe-Cu skarn,and Zhengguang epithermal Au deposits,and compiled published ones from these and other mineral occurrences in the orefield.In terms of geochronology,we have newly summarized seven magmatic phases in the orefield:(1)Middle-Late Cambrian(506-491 Ma),(2)Early and Middle Ordovician(485-471 Ma and~462 Ma),(3)Late Ordovician(450-447 Ma),(4)Early Carboniferous and Late-Carboniferous to Early Permian(351-345 and 323-291 Ma),(5)Middle-Late Triassic(244-223 Ma),(6)Early-Middle and Late Jurassic(178-168 Ma and~150 Ma),and(7)Early Cretaceous(~112 Ma).Three of these seven major magmatic phases were coeval with ore formation,including(1)Early Ordovician(485-473 Ma)porphyry-type Cu-Mo-(Au),(2)Early-Middle Triassic(246-229 Ma)porphyry-related epithermal Au-(Cu-Mo),and(3)Early Jurassic(177-173 Ma)Fe-Cu skarn mineralization.Some deposits in the orefield,notably Tongshan and Zhengguang,were likely formed by more than one mineralization events.In terms of geochemistry,ore-causative granitoids in the orefield exhibit adakite-like or adakite-normal arc transitional signatures,but those forming the porphyry-/epithermal-type Cu-Mo-Au mineralization are largely confined to the former.The varying but high Sr/Y,Sm/Yb and La/Yb ratios suggest that the ore-forming magmas were mainly crustal sourced and formed at different depths(clinopyroxene-/amphibole-/garnet-stability fields).The adakite-like suites may have formed by partial melting of the thickened lower crust at 35-40 km(for the Early Ordovician arc)and>40 km(for the Middle-Late Triassic arc)depths.The Early Jurassic Fe-Cu skarn orecausative granitoids show an adakitic-normal arc transitional geochemical affinity.These granitoids were likely formed by partial melting of the juvenile lower crust(35-40 km depth),and subsequently modified by assimilation and fractional crystallization(AFC)processes.In light of the geological,geochronological and geochemical information,we proposed the following tectonometallogenic model for the Duobaoshan orefield.The Ordovician Duobaoshan may have been in a continental arc setting during the subduction of the Paleo-Asian Ocean,and formed the porphyry-related deposits at Duobaoshan,Tongshan and Zhengguang.Subduction may have ceased in the latest Ordovician,and the regional tectonics passed into long subsidence and extension till the latest Carboniferous.This extensional tectonic regime and the Silurian terrestrial-shallow marine sedimentation had likely buried and preserved the Ordovician Duobaoshan magmatic-hydrothermal system.The south-dipping Mongol-Okhotsk Ocean subduction from north of the orefield had generated the Middle-Late Triassic continental arc magmatism and the associated Tongshan PCD and Zhengguang epithermal Au mineralization(which superimposed on the Ordovician PCD system).The Middle Jurassic closure of Mongol-Okhotsk Ocean in the northwestern Amuria block(Erguna terrane),and the accompanying Siberia-Amuria collision,may have placed the Paleo-Pacific subduction system in NE China(including the orefield)under compression,and formed the granodiorite-tonalite and Fe-Cu skarn deposits at Sankuanggou and Xiaoduobaoshan.From the Middle Jurassic,the consecutive accretion of Paleo-Pacific arc terranes(e.g.,Sikhote-Alin and Nadanhada)onto the NE Asian continental margin may have gradually distant the Duobaoshan orefield from the subduction front,and consequently arc-type magmatism and the related mineralization faded.The minor Late Jurassic and Cretaceous unmineralized magmatism in the orefield may have triggered mainly by the far-field extension led by the post-collisional(Siberia-Amuria)gravitational collapse and/or Paleo-Pacific backarc-basin opening.