Fluid Inclusions,C–H–O–S Isotope and Geochronology of the Bujinhei Pb–Zn Deposit in the Southern Great Xing'an Range of Northeast China: Implication for Ore Genesis

The Bujinhei Pb–Zn deposit is located in the southern Great Xing'an Range metallogenic belt. It is a representative medium‐ to high‐temperature hydrothermal vein type deposit controlled by fractures, and orebodies hosted in the Permian Shoushangou Formation. The hydrothermal mineralization is classified into three stages: pyrite ± arsenopyrite–quartz (Stage 1), polymetallic sulfide–quartz (Stage 2), and polymetallic sulfide–calcite (Stage 3). Fluid inclusion petrography, laser Raman analyses and microthermometry indicate that the liquid‐rich aqueous inclusions (L) and vapor‐rich CO₂ ± CH₄–H₂O inclusions (C) occur in the Stage 1 and as medium‐ to high‐ temperature and low‐ to medium‐salinity NaCl–H₂O–CO₂–CH₄ hydrothermal fluids. The liquid‐rich (L) and rare vapor‐rich CO₂ ± CH₄–H₂O inclusions (C) occur in the Stage 2 with medium‐temperature and low‐salinity NaCl–H₂O ± CO₂ ± CH₄ hydrothermal fluids. The exclusively liquid‐rich (L) fluid inclusions are observed in the Stage 3, and the hydrothermal fluid belongs to medium‐temperature and low‐salinity NaCl–H₂O hydrothermal fluids. The results of hydrogen and oxygen isotope analyses indicate that ore‐forming fluids were initially derived from the magmatic water and mixed with local meteoric water in the late stage (δ¹⁸O_H2O‐SMOW = 6.0 to 2.2‰, δD_SMOW = ?103 to ?134‰). The carbon isotope compositions (?18.4‰ to ?26.5‰) indicate that the carbon in the fluid was derived from the surrounding strata. The sulfur isotope compositions (5.7 to 15.2‰) indicate that the ore sulfur was also primarily derived from the strata. The ore vein No. 1 occurs in fractures and approximately parallel to the rhyolite porphyry; orebodies have a close spatial and temporal relationship with the rhyolite porphyry. The rhyolite porphyry yielded a crystallization age of 122.9  ± 2.4 Ma, indicating that the Bujinhei deposit may be related to the Early Cretaceous magmatic event. Geochemical analyses reveal that the Bujinhei rhyolite porphyry is high in K₂O and peraluminous, and derived from an acidic liquid as a result of strong interaction with hydrothermal fluid during the late magmatic stage; it is similar to A2‐type granites, and formed in a backarc extensional environment. These results indicate that the Bujinhei Pb–Zn deposit was a vein type system that formed in Early Cretaceous and influenced by the Paleo‐Pacific tectonic system. Bujinhei deposit is a representative hydrothermal vein type deposit on the genetic types, and occurs on the western slope of the southern Great Xing'an Range. The ore‐forming fluids were medium‐ to high‐temperature and low‐to medium‐salinity NaCl–H₂O–CO₂–CH₄ hydrothermal fluids, which became medium‐temperature and low‐salinity NaCl–H₂O hydrothermal fluids in later stages, and came from magmatic water and mixed with meteoric water, whereas the ore‐forming materials were mainly derived from the surrounding strata. The LA–ICP–MS zircon U–Pb dating indicates that the Bujinhei deposit formed at the period of late Early Cretaceous, potentially in a backarc extensional environment influenced by the Paleo‐Pacific tectonic system.     

Climatic and tectonic significance of Late Pleistocene and Holocene tufa deposits in the Mijares River canyon,eastern Iberian Range,northeast Spain

The tufa deposits developed in the Mijares River canyon at the eastern sector of the Iberian Range were studied by using geomorphological, stratigraphic, micromorphological, mineralogical and chronological (U/Th and ¹⁴C) techniques. These tufas are located along a high‐gradient river profile reach, with high water turbulence and mechanical outgassing, related to Quaternary faulting activity upstream in the regional context of an extensional tectonic regime. Two stepped and terraced fluviatile tufa structures with large phytohermal barrage frameworks and smaller dammed areas have been differentiated. The first structure, Upper Pleistocene in age (from 200 000 to 50 000 years BP ), is made up by two morphosedimentary units reaching 120 m in thickness, and the second one, Holocene in age (10 000–5000 years BP ), is 35 m in thickness. These structures record a more or less continuous tufa development with a mean deposition rate ranging between 1 and 5 mm a⁻¹ as minimum. A preferential growth with high biological activity during warm and wet palaeoenvironmental stages (isotopic stages 7, 3 and 1) can be deduced. Thus, neotectonic activity controlled the location along the Mijares River as well as the large thickness of the tufa deposits, whereas warm climatic periods favoured intense tufa activity in the fluvial system. Copyright © 2000 John Wiley & Sons, Ltd.     

Geochronology,petrogenesis, and tectonic setting of Late Triassic volcanic rocks of the Hadataolegai Formation,central Great Xing'an Range,Northeast China

In this study, new geochemical, zircon U–Pb, and Lu–Hf isotopic data are presented for volcanics from the Hadataolegai Formation of the central Great Xing'an Range (GXR) in Northeast China. These new data offer insights into the petrogenesis of the volcanics of the Hadataolegai Formation and the tectonic evolution of the Paleo–Asian Ocean (PAO) and Mongol–Okhotsk Ocean (MOO). These volcanics of the Hadataolegai Formation are divided into andesite‐trachyandesites and dacite‐trachydacites. Zircon U–Pb ages show that the volcanics of the Hadataolegai Formation erupted between 230 Ma and 228 Ma during the Late Triassic, which agrees with recently obtained data. The volcanic rocks in this study have low Y (9.9–21.1 ppm) and Yb (0.78–2.02 ppm) contents, high Sr (444–954 ppm) contents, and slight Eu anomalies (δEu = 0.82 to 0.94), similar to ‘adakite‐like’ rocks. The dacites were formed by fractional crystallization of coeval andesitic magmas. The zircons within the andesite and trachyandesite yield higher positive ε_Hf(t) values (+6.3 to +12.0) and model ages (T_DM2) between 860 Ma and 453 Ma, which indicates that the magmas were generated by a newly accreted continental crustal source. Moreover, some of the volcanics are relatively high in MgO contents. These characteristics indicate that the volcanic magmas were derived from the partial melting of delaminated lower crust and mixing with mantle materials. Combining these data with previous studies, we suggest that the magmatism in the central GXR was governed by extension due to the closure of the PAO and the back‐arc extension associated with the southward subduction of the MOO plate (western GXR, near the Erguna Block).     

近期气候变暖念青唐古拉山拉弄冰川处于退缩状态

1999和2003年在念青唐古拉山冰川考察期间,采用GPS对拉弄冰川末端位置进行了测量,并将将测量结果与1970年航摄冰川末端位置进行对比分析.结果表明:1970-1999年拉弄冰川末端退缩了285m,平均年退缩量9.8m;1999-2003年拉弄冰川退缩13m,平均年退缩量3.25m.由于冰川对气候的响应有一定滞后性,近年来气候持续变暖将使拉弄冰川继续保持退缩状态.     

南岭地区钨锡花岗岩的成矿矿物学：概念与实例

南岭地区的钨锡成矿作用与花岗岩岩浆活动有十分密切的关系。花岗岩的物源与成矿元素的初始富集、花岗岩的分异程度和花岗岩中流体性质与活动性集中体现了花岗岩对成矿的控制能力,即花岗岩的成矿能力。初步建立了南岭地区钨锡花岗岩的成矿矿物学研究体系。黑云母、榍石、锆石、锡石、金红石、黑钨矿、白钨矿和钨铁铌矿等是讨论的重点矿物,它们可用于判别花岗岩的成矿能力。首先以矿物晶体化学为基础,介绍了上述矿物在钨锡花岗岩中的岩相学特征、内部构造和矿物化学及其变化,并分别论证了花岗岩原始含矿性、花岗岩结晶演化和花岗岩中成矿元素活动性的矿物学标志;其次,系统对比了南岭地区三类钨锡花岗岩（准铝质含锡花岗岩、过铝质含锡花岗岩和过铝质含钨花岗岩）的成矿矿物学特征。以湖南骑田岭花岗岩复式岩体为实例,进行了芙蓉- 菜岭含锡花岗岩和新田岭含钨花岗岩的成矿矿物学对比研究。前者以黑云母、榍石为典型含锡矿物,它们在流体富集阶段,经热液蚀变作用,导致锡的淋滤和结晶富集作用;后者则以出现岩浆白钨矿和黑钨矿为特征。提出的钨锡花岗岩成矿矿物学研究体系有助于深化矿床学研究和矿床勘探工作,并将在今后工作中进一步完善。     

GEOLOGY OF THE NORTHERN ARUN TECTONIC WINDOW

GEOLOGY OF THE NORTHERN ARUN TECTONIC WINDOW1　BordetP .Recherchesg啨ｏｌｏｇｉｑｕｅｓｄａｎｓｌ’ＨｉｍａｌａｙａｄｕＮ啨ｐａｌ,r啨ｇｉｏｎｄｕＭａｋａｌｕ[R].EditionsduCNRS ,Paris ,196 12 75 . 2　BordetP .G啨ｏｌｏｇｉｅｄｅｌａｄａｌｌｅｄｕＴｉｂｅｔ (Himalayacentral) [J].M啨ｍｏｉｒｅｓｈｏｒｓｓ啨ｒｉｅｄｅｌａＳｏｃｉｅｔ啨ｇ啨ｏｌｏｇｉｑｕｅｄｅＦｒａｎｃｅ,1977,8:2 35～ 2 5 0 . 3　BurcfielBC ,ChenZ ,HodgesKV ,etal.TheSouthTibetanDetachmentSystem ,Hima…     

POLYPHASE METAMORPHISM AND INVERTED THERMAL GRADIENT IN THE LESSER HIMALAYA OF CENTRAL NEPAL: CONSTRAINTS FROM WHITE MICA COMPOSITIONS

POLYPHASE METAMORPHISM AND INVERTED THERMAL GRADIENT IN THE LESSER HIMALAYA OF CENTRAL NEPAL: CONSTRAINTS FROM WHITE MICA COMPOSITIONS     

The synrift phase of the early Domeyko Basin (Triassic,northern Chile): Sedimentary,volcanic, and tectonic interplay in the evolution of an ancient subduction‐related rift basin

The geodynamic setting along the SW Gondwana margin during its early breakup (Triassic) remains poorly understood. Recent models calling for an uninterrupted subduction since Late Palaeozoic only slightly consider the geotectonic significance of coeval basins. The Domeyko Basin initiated as a rift basin during the Triassic being filled by sedimentary and volcanic deposits. Stratigraphic, sedimentological, and geochronological analyses are presented in order to determine the tectonostratigraphic evolution of this basin and to propose a tectonic model suitable for other SW Gondwana‐margin rift basins. The Domeyko Basin recorded two synrift stages. The Synrift I (~240–225 Ma) initiated the Sierra Exploradora sub‐basin, whereas the Synrift II (~217–200 Ma) reactivated this sub‐basin and originated small depocentres grouped in the Sierra de Varas sub‐basin. During the rift evolution, the sedimentary systems developed were largely controlled by the interplay between tectonics and volcanism through the accommodation/sediment supply ratio (A/S). High‐volcaniclastic depocentres record a net dominance of the syn‐eruptive period lacking rift‐climax sequences, whereas low‐volcaniclastic depocentres of the Sierra de Varas sub‐basin developed a complete rift cycle during the Synrift II stage. The architecture of the Domeyko Basin suggests a transtensional kinematic where N‐S master faults interacted with ~NW‐SE basement structures producing highly asymmetric releasing bends. We suggest that the early Domeyko Basin was a continental subduction‐related rift basin likely developed under an oblique convergence in a back‐arc setting. Subduction would have acted as a primary driving mechanism for the extension along the Gondwanan margin, unlike inland rift basins. Slab‐induced dynamic can strongly influence the tectonostratigraphic evolution of subduction‐related rift basins through controls in the localization and style of magmatism and faulting, settling the interplay between tectonics, volcanism, and sedimentation during the rifting.     

Integration of Range Split Spectrum Interferometry and conventional InSAR to monitor large gradient surface displacements

Incorrect unwrapping of dense interferometric fringes caused by large gradient displacements make it difficult to measure mining subsidence using conventional Interferometric Synthetic Aperture Radar (InSAR). This paper presents a Range Split Spectrum Interferometry assisted Phase Unwrapping (R-SSIaPU) method for the first time. The R-SSIaPU method takes advantage of (i) the capability of Range Split Spectrum Interferometry of measuring surface displacements with large spatial gradients, and (ii) the capability of conventional InSAR of being sensitive to surface displacements with limited spatial gradients. Both simulated and real experiments show that the R-SSIaPU method can monitor large gradient mining-induced surface movements with high precision. In the case of the Tangjiahui mine, the R-SSIaPU method agreed with GPS with differences of approximately 4.2 cm, whilst conventional InSAR deviated from GPS with differences of nearly 1 m. The R-SSIaPU method makes phase unwrapping less challenge, especially in the cases with large surface displacements. In addition to mining subsidence, it is believed that the R-SSIaPU method can be used to monitor surface displacements caused by landslides, earthquakes, volcanic eruptions, and glacier movements.     

Comparative review of marine mammal guidance implemented during naval exercises

This article reviews the types and effectiveness of marine mammal mitigation measures used during some naval activities worldwide. The three main standard methods used to mitigate the potential impacts of naval sonar sound on marine mammals are (1) time/area planning (of exercises/active sonar use) to avoid marine mammals; (2) implementation of operational procedures (e.g. ‘soft start’ - where sound levels are gradually increased over time); and (3) monitoring of animals for the purpose of maintaining an ‘exclusion zone’ around the sound source. Suggestions towards a minimum worldwide mitigation standard are made.