Metamorphic evolution of a subduction complex, South Shetland Islands, Antarctica

A subduction complex composed of ocean floor material mixed with arc-derived metasediments crops out in the Elephant Island group and at Smith Island, South Shetland Islands, Antarctica, with metamorphic ages of 120–80 Ma and 58–47 Ma, respectively. Seven metamorphic zones (I–VII) mapped on Elephant Island delineate a gradual increase in metamorphic grade from the pumpellyite–actinolite facies, through the crossite–epidote blueschist facies, to the lower amphibolite facies. Geothermometry in garnet–amphibole and garnet–biotite pairs yields temperatures of about 350 °C in zone III to about 525 °C in zone VII. Pressures were estimated on the basis of Si content in white mica, Al₂O₃ content in alkali amphibole, Na^M4/Al^IV in sodic-calcic and calcic amphibole, Al^VI/Si in calcic amphibole, and jadeite content in clinopyroxene. Mean values vary from about 6–7.5 kbar in zone II to about 5 kbar in zone VII. Results from the other islands of the Elephant Island group are comparable to those from the main island; Smith Island yielded slightly higher pressures, up to 8 kbar, with temperatures estimated between 300 and 350 °C. Zoned minerals and other textural indications locally enable inference of P–T –t trajectories, all with a clockwise evolution. A reconstruction in space and time of these P–T –t paths allows an estimate of the thermal structure in the upper crust during the two ductile deformation phases (D₁ & D₂) that affected the area. This thermal structure is in good agreement with the one expected for a subduction zone. The arrival and collision of thickened oceanic crust may have caused the accretion and preservation of the subduction complex. In this model, D₁ represents the subduction movements expressed by the first vector of the clockwise P–T–t path, D₂ reflects the collision corresponding to the second vector with increasing temperature and decreasing pressure, and D₃ corresponds to isostatic uplift accompanied by erosion, under circumstances of decreasing temperature and pressure.     

桐柏碰撞造山带及其邻区变形特征与构造格局

桐柏碰撞造山带及其邻区可以划分为九个大地构造单元,自北向南分别是:华北克拉通南缘岩石构造单元——宽坪岩群、具弧后盆地性质的二郎坪岩石构造单元、具岛弧性质的秦岭杂岩单元、龟山岩组和南湾岩组构成的俯冲前缘楔构造带、构造混杂岩带、桐柏北部高压岩片单元、桐柏核部杂岩单元、桐柏南部高压岩片单元以及随州构造变形带。根据详细的构造解析以及新的地质年代学资料,本文将中生代以来的构造变形划分为五幕,前两幕变形主要发育在构造混杂岩带以南的各个岩石构造单元中,之后的三幕变形则波及整个研究区。第一幕变形的时间约为255～238Ma,以发育区域上透入性的片理及北西西向的拉伸线理为主,并导致了高压岩片早期自西向东的挤出。第二幕变形的时间约为230～215Ma,以自北向南的逆冲推覆构造为主,使得高压岩片进一步垂向抬升。第三幕变形应早于下侏罗统,以近北西西向的宽缓褶皱为主要特征,该幕变形期间桐柏核部杂岩及其两侧高压岩片单元发生同步的抬升。第四幕变形大致发生在140～130Ma之间,主要表现为桐柏核部杂岩两侧走滑型韧性剪切带的活动,桐柏核部杂岩表现出向东的挤出。第五幕变形发生在120～80Ma,表现为北西向及北东向的脆性断裂活动,并切割以上所有构造形迹。桐柏高压岩片的抬升剥露受多幕变形控制,呈阶段性的抬升。     

Refractory Black Carbon Results and a Method Comparison between Solid-state Cutting and Continuous Melting Sampling of a West Antarctic Snow and Firn Core

This work presents the refractory black carbon(rBC)results of a snow and firn core drilled in West Antarctica(79°55'34.6"S,94°21'13.3"W)during the 2014?15 austral summer,collected by Brazilian researchers as part of the First Brazilian West Antarctic Ice Sheet Traverse.The core was drilled to a depth of 20 m,and we present the results of the first 8 m by comparing two subsampling methods—solid-state cutting and continuous melting—both with discrete sampling.The core was analyzed at the Department of Geological Sciences,Central Washington University(CWU),WA,USA,using a single particle soot photometer(SP2)coupled to a CETAC Marin-5 nebulizer.The continuous melting system was recently assembled at CWU and these are its first results.We also present experimental results regarding SP2 reproducibility,indicating that sample concentration has a greater influence than the analysis time on the reproducibility for low rBC concentrations,like those found in the Antarctic core.Dating was carried out using mainly the rBC variation and sulfur,sodium and strontium as secondary parameters,giving the core 17 years(1998?2014).The data show a well-defined seasonality of rBC concentrations for these first meters,with geometric mean summer/fall concentrations of 0.016μg L^?1 and geometric mean winter/spring concentrations of 0.063μg L^?1.The annual rBC concentration geometric mean was 0.029μg L^?1(the lowest of all rBC cores in Antarctica referenced in this work),while the annual rBC flux was 6.1μg m^?2 yr^?1(the lowest flux in West Antarctica records so far).     

某废弃煤矿有机污染场地地下水修复治理中试研究

某废弃煤矿竖井经倾倒有机废液,导致环境污染事件,造成巷道及采空区内地下水污染。本文结合场地实际情况,选取倾倒竖井(事故井)及周边区域为中试区域,采用“抽出处理+原位氧化循环”两阶段联合修复技术对污染场地开展中试研究。本文介绍了场地污染概况、地下水修复中试方案设计和实施,以及对修复效果进行评价。结果表明,中试处理后地下水中COD和二氯甲烷最高去除率分别为97.88%和99.74%。中试试验表明, “抽出处理+原位氧化循环”两阶段修复技术,对处理矿区内巷道及采空区等复杂地层结构下深层地下水中有机污染物具有较好的去除效果,可以结合现场实际情形对整个污染场区进行规模应用。     

Uptake and depuration of PAHs and chlorinated pesticides by semi-permeable membrane devices (SPMDs) and green-lipped mussels (Perna viridis)

Semi-batch seawater experiments were conducted to follow the uptake and release of selected PAHs (anthracene, fluorathene, pyrene and B[a]P) and organochlorine pesticides (α-HCH, aldrin, dieldrin, p,p′-DDT) in semi-permeable membrane devices (SPMDs) and green-lipped mussels (Perna viridis). Mathematical models were applied to describe the uptake and elimination curves of the contaminants for SPMDs, and kinetic parameters, such as uptake rate constants, and equilibrium triolein/water partitioning coefficients were calculated. SPMD data showed a good fit to estimate rate constant and partition coefficient equations, but only those contaminants which partitioned mainly in the dissolved phase (α-HCH and dieldrin) were well explained for mussels. Poor conformity of the other contaminants indicated mussels uptake by routes other than diffusion, such as ingestion of algae. An apparent equilibrium state was only noted for α-HCH in mussels. Aldrin was not detected in mussels in the first few days of exposure, indicating potential metabolism of this compound. B[a]P was not detected in the triolein of SPMDs, which suggests that the membrane may act as a reservoir. Loss of spiked B[a]P from the triolein was evident in a depuration experiment, which may indicate transfer to the membrane. Rate constants for mussels were higher than those for SPMDs, but the reverse was true for partition coefficients. Overall, mussels and SPMDs had similar uptake rates for all compounds in this study, excluding p,p′-DDT and dieldrin. Contaminant elimination took place more rapidly in mussels, implying that SPMDs are better candidates for detecting episodic discharge of organic contaminants.     

An analysis of the spectra and light curve of Nova Centauri 1995

The light curve and spectra of Nova Centauri 1995 (V888 Cen) are analysed. The spectra were obtained a few days post-maximum. The nova is found to be a very fast nova, declining by 2 mag within about 5±2 d of maximum. The light curve shows strong oscillations in the transition region, of peak-to-peak amplitude about 1.5 mag and period 12–15 d. The light curve of Nova Centauri resembles closely that of Nova Aquilae 1918 (V603 Aql).
The early blue and red spectra obtained at Mt John show broad emission lines, many with P Cygni profiles. The absorption lines are found in two velocity systems at about −1765 and −3010 km s⁻¹, in respectively the principal and diffuse-enhanced stages of spectral development, as defined by McLaughlin. Nova Centauri has many Fe  ii lines in emission, indicating that it is a member of the Williams Fe  ii class of classical novae.     

Population ecology of Sinelobus stanfordi (Crustacea: Tanaidacea) in a temperate southern microtidal estuary

Sinelobus stanfordi is a tanaidacean of worldwide distribution of considerable significance within coastal ecosystems. The aim of this research was to provide essential information on the poorly-known population biology of this species. Benthic samples were taken seasonally from winter 2005 through summer 2007 along 155?km of shoreline within the Río de la Plata Estuary, Argentina. The density of this tanaidacean was higher in vegetated than in bare sediments. The smaller individuals flourished in spring and summer, whereas the larger mature members prevailed in the cooler seasons. Females were always twice as abundant as males. Copulatory females, with 18?±?8 eggs each, were collected during all the seasons. Five cohorts were distinguished by the von Bertalanffy growth function. This research represents a baseline investigation for future studies on the population dynamics of S. stanfordi both in this estuary and in other places where this species is found.     

A physico-rheological model for the large tangshan earthquake

Space-time distributions of the epicenters of earthquakes with M_L 3 from 1966 to 1976 and of historic earthquakes with M 6 have been studied. It is suggested that they mainly occur in seismic belts running N45°E and N47°W, which form a rectangular grid, and the largest earthquakes occurred in the nodal regions of this grid. A theoretical analysis is presented to support these findings.Various types of precursors such as land deformations, changes in gravity, anomalies in the magnetic field and electrical resistivity and waterlevels in deep wells have been studied in correlation with epicenter distribution. The possibility of magma intrusion and its consequences are studied. The first author concludes that stresses must have accumulated, obviously in the regions of intersection. Two different mechanisms of stress accumulation are suggested. He presents a preliminary evaluation of the precursory data with relation to the Russian IPE (Institute of Physics of the Earth) model and the DD (Dilatancy Diffusion model) and propose a physico-rheological model for the Tangshan earthquake. In this new model an attempt is made to take account of such factors as the rheological behaviour of the crust and seismic belts, the mechanisms of stress accumulation, the local stress field, the long-term weakening of the crust, the time-dependent volume dilatancy and the possibility of magma intrusion.