The complex age of orthogneiss protoliths exemplified by the Eoarchaean Itsaq Gneiss Complex (Greenland): SHRIMP and old rocks

Field studies integrated with cathodoluminescence petrography and SHRIMP U–Pb dating of zircons from >150 orthogneisses and metatonalites from the Eoarchaean Itsaq Gneiss Complex (southern West Greenland) shows that only a minority contain ≥3840 Ma zircons, whereas the majority carry only younger ones. Rocks containing ≥3840 Ma zircons vary from very rare single-phase metatonalites to more common complexly banded tonalitic migmatites. The former metatonalites have simple oscillatory-zoned ≥3840 Ma zircon with limited recrystallisation and overgrowth, whereas the more common migmatites have much more complicated zircon populations with both ≥3840 Ma and 3650–3600 Ma oscillatory-zoned zircon, more extensive recrystallisation and widespread complex core-rim multiple growth relationships.     

Monazite geochronology and geochemistry of meta-sediments in the Narryer Gneiss Complex, Western Australia: constraints on the tectonothermal history and provenance

Mt. Narryer and Jack Hills meta-sedimentary rocks in the Narryer Gneiss Complex of the Yilgarn Craton, Western Australia are of particular importance because they yield Hadean detrital zircons. To better understand the tectonothermal history and provenance of these ancient sediments, we have integrated backscattered scanning electron images, in situ U–Pb isotopic and geochemical data for monazites from the meta-sediments. The data indicate multiple periods of metamorphic monazite growth in the Mt. Narryer meta-sediments during tectonothermal events, including metamorphism at ~3.3–3.2 and 2.7–2.6 Ga. These results set a new minimum age of 3.2 Ga for deposition of the Mt. Narryer sediments, previously constrained between 3.28 and ~2.7 Ga. Despite the significant metamorphic monazite growth, a relatively high proportion of detrital monazite survives in a Fe- and Mn-rich sample. This is likely because the high Fe and Mn bulk composition resulted in the efficient shielding of early formed monazite by garnet. In the Jack Hills meta-sediments, metamorphic monazite growth was minor, suggesting the absence of high-grade metamorphism in the sequence. The detrital monazites provide evidence for the derivation of Mt. Narryer sediments from ca. 3.6 and 3.3 Ga granites, likely corresponding to Meeberrie and Dugel granitic gneisses in the Narryer Gneiss Complex. No monazites older than 3.65 Ga have been identified, implying either that the source rocks of >3.65 Ga detrital zircons in the sediments contained little monazite, or that >3.65 Ga detrital minerals had experienced significant metamorphic events or prolonged sedimentary recycling, resulting in the complete dissolution or recrystallization of monazite.     

http://www.sciencedirect.com/science/article/pii/S1674987112001065

It has been thought that granitic crust,having been formed on the surface,must have survived through the Earth’s evolution because of its buoyancy.At subduction zones continental crust is predominantly created by arc magmatism and is returned to the mantle via sediment subduction,subduction erosion, and continental subduction.Granitic rocks,the major constituent of the continental crust,are lighter than the mantle at depths shallower than 270 km,but we show here,based on first principles calculations, that beneath 270 km they have negative buoyancy compared to the surrounding material in the upper mantle and transition zone,and thus can be subducted in the depth range of 270-660 km.This suggests that there can be two reservoirs of granitic material in the Earth,one on the surface and the other at the base of the mantle transition zone(MTZ).The accumulated volume of subducted granitic material at the base of the MTZ might amount to about six times the present volume of the continental crust.Our calculations also show that the seismic velocities of granitic material in the depth range from 270 to 660 km are faster than those of the surrounding mantle.This could explain the anomalous seismic-wave velocities observed around 660 km depth.The observed seismic scatterers and reported splitting of the 660 km discontinuity could be due to jadeite dissociation,chemical discontinuities between granitic material and the surrounding mantle,or a combination thereof.     

Geology and K-Ar Ages of the South, Huh Bulgiin Hundii, Saran Uul, Taats Gol and Han Uul deposits in the Bayankhongor Region, Mongolia

Abstract: The Bayankhongor region in central Mongolia consists of a Paleozoic subduction system including Precambrian microcontinents (Baidrag and Burd Gol zones), obducted ophiolites and accretionary sedimentary rocks (Bayankhongor and Dzag zones), and forearc sedimentary rocks (Khangay zone). Arc magmatism in the Bayankhongor region is characterized by dominance of Early Paleozoic ilmenite-series and Late Paleozoic magnetite-series granitoids. These granitoids accompany many hydrothermal deposits of such various types as porphyry, skarn and vein. K-Ar dating on four deposits in the region revealed that the South porphyry Cu-Au, Huh Bulgiin Hundii skarn Cu-Au, Han Uul shear zone-hosted Au and Taats Gol pegmatite W-Au deposits formed at 240±5 Ma, 252±5 Ma, 283±6 Ma and 329±7 Ma, respectively.
Thus the former three are related to the Permian to earliest Triassic magnetite-series granitoids, whereas the W-Au pegmatite at Taats Gol to the Early Carboniferous ilmenite-series granitoids. Porphyry and skarn Cu-Au mineralization occurred at latest Permian to earliest Triassic, when the Andean-type arc magmatism was immediately followed by the collision between the Baidrag and Tarbagatai microcontinents.     

长江流域稻田生态系统的水分和养分转换过程

田间模拟施肥进步和灌溉模式的定位试验在中国科学院桃源农业生态试验站进行。结果表明施肥制度和水分管理模式显著地影响水分和养分的转化过程和生产效益。单施N的产量效应为4.5 kg/kg,而NP或NPK配施养分总的产量效应分别为8.8 kg/kg和8.0 kg/kg;有机物料循环的增产率为56.8%,在有机物料循环的基础上配施NPK化肥最大的增产率可达到80.1%;化肥应用的进步可使水稻产量增长62.5%或通过施肥实现的水稻产量中由于化肥应用所占的贡献份额为38.4%,有机无机肥配合水稻产量增长80.1%,或通过施肥达到的产量中有机无机肥配合所占的份额为44.4%。本区双季稻年灌溉需水量为5838 m³/hm²,年变异C.V = 8.3%。晚稻灌溉占全年的71%,7~9月是灌溉需水高峰期,占全年灌溉量的68%。生产灌溉效率 (灌溉水量与产量之比)：生物量3.67 kg/m³,精谷量1.48 kg/m³。常规管理田间水分分配为：蒸散占1/2,翻耕整地占1/6,植物构成占1/21,田间渗漏占1/14,其它环境耗水 (维持) 占1/5。耕灌雨养管理翻耕整地和田间渗漏比例过高。不同灌溉处理试验表明：双季稻生产的灌溉,以早稻保持水层灌溉,晚稻按需配额灌溉的模式比较适宜。     

铟矿床研究现状及其展望

铟是一种稀有金属,它在高科技产业中的应用价值越来越受到人们的普遍关注。由于供求矛盾突出,其消费价格水平不断上涨。目前,世界矿业界在铟业投入的技术和资金支持不断增加,以寻求满足日益增长的经济发展的需求。但相对来说,与铟有关的地质工作程度较低,新探明的储量远远跟不上其消费的增长水平,因此,有必要加大地质投入,探求新的资源量,保障世界经济可持续发展的要求。文章在总结前人研究成果的基础上,综述了世界上铟矿床的分布及其地质构造背景,以及铟矿物学、矿床成因和成矿机制等方面的最新研究成果。文章指出,为了寻找潜在的铟资源,必须加强铟的基础地质研究工作,在对铟的成因矿物学、成矿机制及其成矿环境进行深入系统研究的基础上,建立铟矿床的成矿模型和找矿勘查模型。     

Rare Earth Elements in Hydrothermally Altered Granitic Rocks in the Ranong and Takua Pa Tin‐Field,Southern Thailand

Geochemical studies were conducted on the hydrothermally altered granitic rocks in the Ranong and Takua Pa tin‐fields in southern Thailand in order to investigate the mode of occurrence of REE (rare earth elements), with emphasis placed on a potential REE resource associated with granitic rocks in the Southeast Asian Tin Belt. The total REE (ΣREE) content of altered granitic rocks ranges from 130 to 350 ppm at Haad Son Paen (which is presently mined for kaolin clay) in the Ranong tin‐field, and that of altered granitic rocks and kaolinite veinlets reaches up to 424 ppm and 872 ppm, respectively, at Nok Hook in the Takua Pa tin‐field. Rare earth elements in the altered granitic rocks and kaolinite veinlets show a relatively flat chondrite‐normalized pattern, thus enriched in heavy REE compared with the original granitic rocks and their weathered crusts. At Nok Hook (Takua Pa), the ΣREE content of kaolinite separated from an altered granitic rock by elutriation is 1313 ppm, a ΣREE amount about four times higher than that of whole‐rock composition of the altered granitic rock. Chondrite‐normalized REE patterns of the elutriated kaolinite and of the altered granite are relatively flat. Sequential extraction experiments suggest that 41 and 85 percent of REE are present as ion exchangeable‐form in the altered granitic rock, and in the kaolinite veinlets, respectively. In addition, more than 90% of REE in the kaolinite veinlets are present as the acid‐soluble state. On the other hand, the ΣREE content of kaolinite veinlets and of the kaolinite concentrated by elutriation from an altered granitic rock at Haad Som Paen (Ranong) is 70 ppm and 75 ppm, respectively, thus enrichment of REE in kaolinite was not confirmed. In addition, by the sequential extraction experiments, 23% and 4% of REE were extracted from the altered granitic rock and the kaolinite veinlets at Haad Som Paen. In the altered granitic rocks at Haad Som Paen, REE are present as refractory phases, and REE in the acid‐soluble states had been leached by hydrothermal fluid.     

Role of Iron(III) and Aluminum Hydroxides in Concentration/reduction of Au(III) Complexes

Abstract: The adsorption of gold on iron(III) and aluminum hydroxides from solutions containing Au(III) complexes has been studied as a function of pH and chloride concentration at 30C. Iron(III) hydroxide was more effective in adsorbing gold from solution than aluminum hydroxide. However, both hydroxides controlled the behavior of Au(III) complex with very similar manner. The most effective gold adsorption occurred in aqueous solution with near neutral pH and low Cl concentration. In this solution condition, Au(III) complexes were mainly dissolved as AuCl₂(OH)₂^- and AuCl(OH)₃^-, and the surface charge for both hydroxides was positive. In addition, the adsorbed Au(III) complexes were spontaneously reduced to elemental gold in spite of the absence of a specific reducing agent.
The results of this study suggest that adsorption and spontaneous reduction of gold complexes on the surface of hydrous metal oxides with positive charge play an important role in gold precipitation in subsurface environment.     

东海和冲绳沉积物中自生铀蓄积过程及控制机理

采用同位素稀释ICP-MS测定法,对中国东海陆架及日本冲绳海槽的6个沉积物芯中U和Th的同位素地球化学行为进行了研究,以了解氧化还原敏感元素U在近海次氧化性沉积物中的蓄积行为,并评价其在全球海洋铀平衡中的意义。东海沉积物芯中,238U浓度及238U/232Th比值随深度变化不明显。但是在冲绳海槽沉积物芯中,238U浓度及238U/232Th比值在沉积芯表层氧化带显示较低值,然后在次氧化层随深度增加而增加。230Th和232Th浓度在所有沉积物芯中基本不随深度变化。这些结果说明,冲绳沉积物中有“自生铀”的蓄积过程发生,蓄积速率约为(47±5)～(90±8)ng/(cm2·a),与文献报道的世界其他海域次氧化性沉积区大致相当。进一步证明了U在近海次氧化性沉积区的蓄积对于全球海洋铀平衡有重要意义。“自生铀”的主要蓄积机制是海水U(Ⅵ)向沉积物迁移,在还原条件下被还原为惰性的U(Ⅳ)并被吸附在沉积物固体相上。