Fluid-driven Hydrovolcanic Activity along Fracture Zones and near Seamounts: Evidence from Deep-sea Fe-rich Spherules,Central Indian Ocean Basin

An insight on occurrence of Fe-rich spherules from the Central Indian Ocean Basin (CIOB) provides an understanding of their distribution at a water depth of >5,000 m. In the present study, Fe-rich spherules are identified to occur in two different sediment types (i.e., siliceous and pelagic) and tectonic settings (i.e. near seamounts and fracture zones). These are single spheres or aggregates, of different sizes (63 to 390 μm) and show textural variability (smooth/quenched, brickwork, corkscrew, interlocking and dendritic). A comparative study based on physical morphology and chemical composition suggests a common mechanism of formation. The association of spherules with fracture zones (FZ) and seamounts signifies that morpho-tectonic features play an important role in fluid-driven hydrovolcanism. Based on the evidence and geologic conditions existing in the basin, we conclude that molten fuel-coolant interaction (MFCI) coupled with submarine hydrothermal exhalations could be an ideal mechanism for the formation of spherules and Fe-particles. The accretion of the spherules on the surface sediments could be a result of recent volcanic phenomena, while those occurring at different depths (280–355, and 460–475 cm-bsf) within the sediment core indicate two different episodes. The study provides a global implication in understanding fluid-driven magmatism in a deep-sea intraplate environment.     

Neoproterozoic U-Th-REE-bearing Pegmatites in Wadi Ibib,South Eastern Desert,Egypt:Structural and Geochemical Measures for a Syn-Tectonic Anatectic Model of Formation

The Wadi Ibib area is situated in the northern part of the Neoproterozoic Hamisana Shear Zone (HSZ), which is a high strain zone evolved during the late stages of the Pan-African orogeny, likely as a tectonic escape structure. Amphibolite facies pelitic metasedimentary windows crop out in the axial parts of the HSZ and are noticeably associated with numerous N-trending pegmatite dikes. Whole-rock geochemistry of the pegmatites reveals a peraluminous (S-type) affinity, with low K/Rb ratios and elevated concentrations of U, Th, REE, Rb, Li, Cs, Y, Nb and Ta. Structurally, the pegmatite sets intrude along the shear plane of the HSZ, corresponding to the regional N-trending tectonic fabrics, such as axial planar foliation and dextral-shearing in the metasedimentary host rock. Field relationships, including structural context, coupled with geochemical characteristics of the Wadi Ibib pegmatites, do not support their formation as a complementary part of evolved granitic magmas. Space-localized decompression-induced partial melting of peraluminous garnet-bearing metapelites was alternatively the underlying process for formation of these pegmatites. Such decompression was associated with regional escape tectonics and stress axes permutations during the late deformation stage (D3) in the evolution of the south Eastern Desert terrane, due to end-orogeny system pressure-release.     

Textural and geochemical characteristics of late Pleistocene to Holocene fine-grained deep-sea sediment cores(GM6 and GM7),recovered from southwestern Gulf of Mexico

Texture, mineralogy, geochemistry, and ~(14)C ages of two deep-sea sediment cores(GM6 and GM7) recovered in the southwestern Gulf of Mexico were investigated to infer their provenance and depositional condition. The sediments are enriched in fine-grained silt and clay and poor in sand content. Mineralogically, the sediments consist of quartz,calcite, smectite, and kaolinite. Based on the ~(14)C data, the age of the GM6 and GM7 sediment cores were calculated as23,615 cal yrs. BP and 19,007 cal yrs. BP, respectively. The weathering indices such as chemical index of alteration(CIA),chemical index of weathering(CIW), and plagioclase index of alteration(PIA) in GM6(56-69, 60-74, and 61-73,respectively) and GM7(54-69, 57-76, and 55-74, respectively) cores revealed a moderate-to-high intensity of weathering. The rare earth element(REE) patterns suggested that the sediments were derived mostly by the weathering of intermediate rocks, exposed along the coastal regions of the Gulf of Mexico. The trace elemental ratios like V/Cr(2),Ni/Co(2), and Cu/Zn(1), authigenic uranium content(1), and Ce anomaly(Ce/Ce~* ≤ 1) suggested that the sediments were deposited under an oxic condition, which was also revealed by the benthic foraminiferal assemblages throughout the GM6 and GM7 sediment cores.     

日本东北潜在大地震的规模曾被低估

自20世纪70年代以来,科学家已经把地球分为可以产生9.0级地震的板块边界和不会产生9.0级地震的板块边界.然而,2011年发生在日本东北的大地震与2004年发生在苏门答腊—安达曼的超级大地震却让科学家们震惊,因为这两个地区被认为都不可能发生震级超过8.4的大型逆冲地震.现在,地震科学家经重新研究后都承认现有的最大地震规模的预测模型不再有效.人们对这些模型已经提出疑问:苏门达腊什么时候驱动一个板块边界穿过它们的中心?日本东北又在何时驱动了另一个板块边界?     

Serpentinized Peridotites at the North Part of the Wadi Allaqi District (Egypt): Implications for the Tectono-Magmatic Evolution of Fore-arc Crust

The Neoproterozoic Allaqi-Heiani suture （800-700 Ma） in the south Eastern Desert of Egypt is the northernmost linear ophiolitic belt that defines an arc-arc suture in the Arabian- Nubian shield （ANS）. The Neoproterozoic serpentinized peridotites represent a distinct lithology of dismembered ophiolites along the Allaqi-Heiani suture zone. The alteration of peridotites varies, some contain relicts of primary minerals （Cr-spinel and olivine） and others are extremely altered, especially along thrusts and shear zones, with development of talc, talc-carbonate and quartz-carbonate. The fresh cores of the chromian spinels are rimmed by ferritchromite and Cr- magnetite. The fresh chromian spinels have high Cr# （0.62 to 0.79）, while Mg# shows wider variation （0.35-0.59）. High Cr# in the relict chromian spinels and Fo content in the primary olivines indicate that they are residual peridotites after extensive partial melting. The studied ophiolitic upper mantle peridotites are highly depleted and most probably underwent high degrees of partial melting at a supra-subduction zone setting. They can be produced by up to -20%-22% dynamic melting of a primitive mantle source. The mineralogical and geochemical features of the studied rocks reflect that the mantle peridotites of the north part of the Wadi Allaqi district are similar to the fore-arc peridotites of a supra-subduction zone.     

Gold Deposits of the Yenisei Ridge (Russia) and Age of Its Formation

Please refer to the attachment(s) for more details     

Thermodynamic Evaluation of Mineral Balance in Water Thickness of the Soda Lake Doroninskoe(Eastern Transbaikalia,Russia)

正In recent years,lakes,including salted,attract the attention of researchers,also when reconstructing last climate changes using the bottom sediments(Solotchina et al.,2008,et al.).In this case the different geochemical     

白云鄂博稀土矿床及花岗岩类成因

<正>稀土(Rare earth elements)在现代科技领域占有举足轻重的地位,是现代工业的"维生素"。我国稀土储量占世界第一,位于内蒙古自治区包头市北部的白云鄂博矿床是世界上最大的稀土矿床,其稀土氧化物储量为4800万吨,于1927年被丁道衡教授发现。至今,国内外地质学家对该矿床作了大量的研究工作,但是其成因长期仍存在很大争议,制约了相关矿床的找矿工作。争论的焦点是该矿床同时具有火成碳酸岩的地球化学特征和典型的沉积特征,并有明显的交代作用的特点。作者在白云鄂博矿床开展了长期深入的研究,积累了丰富的标本     

Ichnology and Depositional Environment of the Cambrian Nagaur Sandstone (Nagaur Group) Along the Dulmera Section,Bikaner-Nagaur Basin,Rajasthan

Abstract: The Lower Cambrian Nagaur Sandstone (Marwar Supergroup) has yielded trace fossils Treptichnus, Cruziana, serially repeated Rusophycus, Diplichnites, Monomorphichnus, Bergaueria, arthropod swimming traces and leap frogging marks of Cruziana ichnofacies. This ichnofossils assemblage is dominantly preserved in fine to medium grained red sandstone beds of the Mohra Member (Nagaur Sandstone). The presence of graded rip-up clasts, current ripples, dune cross-stratification with mud drapes and tidal bundles indicates a subtidal paleoenvironment for the deposition of Nagaur Sandstone Formation, which is corroborated by the Cruziana ichnofacies trace fossil assemblage.     

The influence of the Po River discharge on phytoplankton bloom dynamics along the coastline of Pesaro (Italy) in the Adriatic Sea

In recent years, eutrophic phenomena have frequently been reported in the Italian coastal waters of the northern Adriatic Sea. The aim of the present study was to determine that the phytoplankton blooms occurring along the Italian coastline in the area of Pesaro are caused by the Po River waters. In fact between October and December 2000 the nutrient load flushed into the sea from local rivers is not significant (phosphorus 10 tons and nitrogen 110 tons), instead N and P load from the Po River are: 650 and 8969 tons. The bloom episodes occurred during this period, at which time hypoxia developed on the sea bottom. The phytoplankton cell concentrations were 40.0 x 10(6) cells L(-1), and a significant presence of diatoms was observed. This issue is important in analysing the anthropogenic disturbances and environmental changes. The eutrophic seawater conditions were also analysed using the eutrophic index.