新疆哈尔里克山后碰撞期构造-岩浆活动特征及年代学证据

新疆地区后碰撞期构造-岩浆活动非常活跃,其同位素年龄集中在290～270Ma。天山东段的后碰撞期构造-岩浆活动研究相对薄弱,高质量的定年数据较少。在野外地质调查的基础上,笔者选择东天山哈尔里克地区的小堡花岗岩体进行了锆石的LA-ICP-MSU-Pb定年,获得两组谐和年龄,分别为297±2Ma和295±2Ma,代表哈尔里克地区后碰撞早期岩浆作用的形成时代。小堡岩体矿物组合以斜长石、石英、钾长石、角闪石和黑云母为主,副矿物有锆石、磷灰石和磁铁矿,与I型高钾钙碱性花岗岩矿物组合基本一致。与小堡花岗岩体同时发育、空间并存的还有基性岩墙群和碱性花岗岩,构成后碰撞初始阶段三组合地质标志。结合区域地质资料,认为小堡早二叠世花岗岩体是后碰撞初期碰撞造山、地壳增厚引发下地壳物质部分熔融的产物,其构造属性为板内岩浆活动。     

东准噶尔蒙西斑岩铜钼矿床脉体特征及其形成机制

蒙西斑岩铜钼矿床位于东准噶尔伊吾县琼河坝花岗岩北侧,以发育细脉、网脉状矿化为特征。脉体类型多样,包括石英脉、石英硫化物脉和硫化物脉等。根据脉体力学成因机制,其又可划分为水压破裂充填脉和构造破裂充填脉。构造破裂充填脉体按破裂形成的位错特征有正断与逆断两种。地表石英脉产状陡立,明显受断裂控制。脉体体积分数统计结果显示流体富集区呈向北缓倾的带状分布于深100～400m范围内,并与矿化富集带有较好的对应关系。脉体富集带内,脉体以共轭形式存在,一组为倾角较小的逆断破裂充填脉,另一组为倾角较大的正断破裂充填脉,他们可能为缓倾逆冲剪切带的次级破裂与充填脉,即富矿带内脉体是沿矿区低角度逆冲断裂次级破裂面充填的。矿区地表及深部(400m以下)脉体以陡立为主,矿化较弱。矿区流体的运移具先沿水压直立破裂往上运移,进入剪切带后沿剪切带次级破裂侧向和向上运移,并在剪切带中富集成矿。低温矿物组合脉体穿切高温矿物组合脉体的特征说明脉体形成过程矿区处于隆升构造环境,这对斑岩铜矿成矿有利。     

新疆东天山地区延西铜矿床的地球化学、成矿年代学及其地质意义

延西铜矿床位于新疆东天山觉罗塔格地区北部的哈尔里克-大南湖岛弧带内,是延东-土屋斑岩型成矿带的西延部分。矿床的赋矿地层主要为石炭系企鹅山群,被含矿斜长花岗斑岩侵入。矿床中的主要岩石类型为安山岩、闪长玢岩以及斜长花岗斑岩,安山岩和闪长玢岩具有同源性及岛弧火山岩的特点,是主要的赋矿围岩;斜长花岗斑岩具有埃达克质岩石的特征,与成矿作用直接相关,其形成晚于安山岩、闪长玢岩。本文测得延西铜矿床辉钼矿Re-Os年龄为326.2±4.5Ma,可以代表其成矿年龄,与土屋-延东铜矿床322.7±2.3Ma的辉钼矿Re-Os年龄基本相同;包括延西铜矿床在内的土屋-延东斑岩型铜矿带成矿时代与成岩时代基本一致或稍晚。延西铜矿床具有斑岩型铜矿床的矿化和围岩蚀变特征,与土屋-延东斑岩型铜矿带内其它矿床均为中石炭世同源岩浆演化的产物,具有相似的成矿作用过程,成矿物质均为岩浆来源,这些矿床可能为同一岩浆活动在不同部位发生矿化的产物。延西铜矿床以及土屋-延东斑岩型铜矿带形成于东天山觉罗塔格地区晚古生代的挤压岛弧背景,应与哈尔里克-大南湖晚古生代岛弧的形成相伴,可能与康古尔塔格大洋板块向北部哈尔里克-大南湖岛弧的俯冲有关。     

雅鲁藏布江大拐弯北段区域工程地质及其对地质灾害发育的影响

川藏公路然乌-鲁朗段位于雅鲁藏布江大拐弯北部,是地质灾害频发的地区,而地质灾害的发生受当地的地质、气候、水文、人类活动等多种因素的影响,其中地质条件是控制因素。研究区位于东喜马拉雅构造结北缘,是地质构造活动最强烈的地区。在地质构造上,东喜马拉雅构造结属于冈底斯、雅鲁藏布和喜马拉雅三个构造单元。区内构造的形成经历了3个时期7个阶段。川藏公路然乌-鲁朗段的地层属于冈底斯-念青唐古拉区中的拉萨-波密分区,第四纪冰碛发育。由于强烈的地质构造活动,区内断层、褶皱等构造发育,许多断裂仍在活动,尤其是嘉黎断裂。由于地质灾害的形成需要一定的条件,并受地质条件控制,因此区内地质灾害的分布具有明显的空间特征。     

Growth and physiological responses of larch trees to climate changes deduced from tree-ring widths and δ13C at two forest sites in eastern Siberia

Tree-ring chronologies of ring width and stable carbon isotope ratios (δ¹³C) over the past 160 years were developed using living larch trees at two forest sites, each with different annual precipitation, in eastern Siberia: Spasskaya Pad (SP) (62°14′N, 129°37′E); and Elgeeii (EG) (60°0′N, 133°49′E). Intrinsic water-use efficiency (iWUE) was derived from tree-ring δ¹³C. The physiological responses of the larch trees to climate varied between these sites and over time. Ring widths correlated negatively with summer temperatures at SP, where summer precipitation is lower than at EG, probably due to temperature-induced water stress. Since the 1990s, however, the negative effect of warming has been more severe at EG, where the productivity of larch trees is higher than at SP. A greater reduction of larch tree growth and higher increase rate of iWUE at EG reflects greater temperature-induced water stress, which is incident to the larger forest biomass. Our results suggest that effect of increase in atmospheric CO₂ on larch tree growth is not sufficient to compensate for temperature-induced water stress on larch growth in eastern Siberia and differences in precipitation and forest productivity largely affect the larch tree response to changing climate in eastern Siberia.     

Trophic ecology and vertical patterns of carbon and nitrogen stable isotopes in zooplankton from oxygen minimum zone regions

The unique physical and biogeochemical characteristics of oxygen minimum zones (OMZs) influence plankton ecology, including zooplankton trophic webs. Using carbon and nitrogen stable isotopes, this study examined zooplankton trophic webs in the Eastern Tropical North Pacific (ETNP) OMZ. δ¹³C values were used to indicate zooplankton food sources, and δ¹⁵N values were used to indicate zooplankton trophic position and nitrogen cycle pathways. Vertically stratified MOCNESS net tows collected zooplankton from 0 to 1000 m at two stations along a north-south transect in the ETNP during 2007 and 2008, the Tehuantepec Bowl and the Costa Rica Dome. Zooplankton samples were separated into four size fractions for stable isotope analyses. Particulate organic matter (POM), assumed to represent a primary food source for zooplankton, was collected with McLane large volume in situ pumps.The isotopic composition and trophic ecology of the ETNP zooplankton community had distinct spatial and vertical patterns influenced by OMZ structure. The most pronounced vertical isotope gradients occurred near the upper and lower OMZ oxyclines. Material with lower δ¹³C values was apparently produced in the upper oxycline, possibly by chemoautotrophic microbes, and was subsequently consumed by zooplankton. Between-station differences in δ¹⁵N values suggested that different nitrogen cycle processes were dominant at the two locations, which influenced the isotopic characteristics of the zooplankton community. A strong depth gradient in zooplankton δ¹⁵N values in the lower oxycline suggested an increase in trophic cycling just below the core of the OMZ. Shallow POM (0–110 m) was likely the most important food source for mixed layer, upper oxycline, and OMZ core zooplankton, while deep POM was an important food source for most lower oxycline zooplankton (except for samples dominated by the seasonally migrating copepod Eucalanus inermis). There was no consistent isotopic progression among the four zooplankton size classes for these bulk mixed assemblage samples, implying overlapping trophic webs within the total size range considered.     

Tracing dissolved organic matter cycling in the eastern boundary of the temperate North Atlantic using absorption and fluorescence spectroscopy

Apparent oxygen utilization (AOU), dissolved organic carbon (DOC), coloured dissolved organic matter (CDOM) absorption spectra, and CDOM fluorescence characteristic of aromatic amino acids (excitation/emission 280 nm/320 nm; F(280/320)) and marine-humic like substances (320 nm/410 nm; F(320/410)) were measured in full depth during a cruise in the temperate Eastern North Atlantic (ENA). An optimum multi-parameter (OMP) inverse method was run to calculate water mass proportion-weighted average (archetypal) concentrations of these chemical parameters for all water masses and samples. Archetypal concentrations retain the variability due to water mass mixing and basin scale mineralization from the water mass formation sites to the study area. Conversely, the difference between measured and archetypal concentrations, retain the variability due to dissimilarities in mineralization processes within the study area. Our analysis indicates that DOC supported 26±3% of the AOU in the dark temperate ENA and that basin scale processes occurring at and from the formation area of the water masses explained 63% of the total DOC variability. Our data also suggests that DOC remineralized at the basin scale was of lower molecular weight, and with a lower proportion of fluorescent aromatic amino acids than found within the study area. The relationship between the absorption coefficient at 254 nm (a_CDOM(254)) and AOU indicates that a_CDOM(254) was consumed during organic matter remineralization in the dark ocean, with 55% of the variability being explained by basin scale processes. The relationships of F(320/410) with AOU and DOC confirmed that marine humic-like substances are produced by microbial degradation processes, at a rate of 6.1±0.9×10⁻³ mg equivalents of QS mol AOU⁻¹. Our results also indicate that basin-scale remineralization processes account for 85% of the total variability of F(320/410), emphasizing that large scale processes control the formation of humic-like substance in the dark ENA.     

Dynamics of the Leeuwin Current: Part 2. Impacts of mixing,friction, and advection on a buoyancy-driven eastern boundary current over a shelf

The boundary currents over the Western Australian continental shelf and slope consist of the poleward flowing Leeuwin Current (LC) and the equatorward flowing Leeuwin Undercurrent (LUC). Key properties of the LC are its poleward strengthening, deepening to the south, and shelfbreak intensification. The alongshore flow reverses direction below about 300 m, forming the LUC at greater depths. To investigate the processes that cause these features, we obtain solutions to an idealized, regional ocean model of the South Indian Ocean. Solutions are forced by relaxing surface density to a prescribed, meridionally varying density profile ρ^*(y) with a timescale of δt. In addition, vertical diffusion is intensified near the ocean surface. This diffusion establishes the minimum thickness over which density is well-mixed. We define this thickness as the “upper layer”. Solutions are obtained with and without a continental shelf and slope off Western Australia and for a range of values of δt and mixing parameters. Within this upper layer, there is a meridional density gradient that balances a near-surface, eastward geostrophic flow. The eastward current downwells near the eastern boundary, leading to westward flow at depth. The upper layer's meridional structure and zonal currents crucially depend on coastal processes, including the presence of topography near the eastern boundary. Kelvin waves inhibit the upper layer from deepening at the coast. Rossby waves propagate the coastal density structure offshore, hence modifying the interior currents. A comparison of the solutions with or without a continental shelf and slope demonstrate that topographic trapping of Rossby waves is a necessary process for maintaining realistic eastern boundary current speeds. Significant poleward speeds occur only onshore of where the upper layer intersects the slope, that is, at a grounding line. Its poleward transport increases when surface-enhanced vertical mixing is applied over a greater depth. When the timescale δt is sufficiently short, the poleward current is nearly barotropic. The current's spatial structure over the shelf is controlled by horizontal mixing, having the structure of a Munk layer. Increasing vertical diffusion deepens the upper layer thickness and strengthens the alongshore current speed. Bottom drag leads to an offshore flow along the bottom, reducing the net onshore transport and weakening the current's poleward acceleration. When δt is long, poleward advection of buoyancy forms a density front near the shelf break, intensifying poleward speeds near the surface. With bottom drag, a bottom Ekman flow advects density offshore, shifting the jet core offshore of the shelf break. The resulting cross-shelf density gradient reverses the meridional current's direction at depth, leading to an equatorward undercurrent.     

Agrarian stress and climate change in the Eastern Gangetic Plains: Gendered vulnerability in a stratified social formation

This paper reviews the complex impact of climate change on gender relations and associated vulnerability on the Eastern Gangetic Plains of Nepal and India. Field research has identified that gendered vulnerability to climate change is intricately connected to local and macro level political economic processes. Rather than being a single driver of change, climate is one among several stresses on agriculture, alongside a broader set of non-climatic processes. While these pressures are linked to large scale political–economic processes, the response on the ground is mediated by the local level relations of class and caste, creating stratified patterns of vulnerability. The primary form of gendered vulnerability in the context of agrarian stress emerges from male out-migration, which has affected the distribution of labour and resources. While migration occurs amongst all socio-economic groups, women from marginal farmer and tenant households are most vulnerable. While the causes of migration are only indirectly associated with climate change, migration itself is rendering women who are left behind from marginal households, more vulnerable to ecological shocks such as droughts due to the sporadic flow of income and their reduced capacity for investment in off-farm activities. It is clear that policies and initiatives to address climate change in stratified social formations such as the Eastern Gangetic Plains, will be ineffective without addressing the deeper structural intersections between class, caste and gender.     

经验模态分解和独立分量分解在航磁数据处理中的应用

以东天山1∶20万航磁数据为例,利用经验模态分解(EMD)方法对航磁数据进行分解,然后利用独立分量分析(ICA)方法对分解出的固有模态函数(IMF)数据进行重构。分解出来的从高频到低频IMF与地质体的分布具有一定的相关性,不同频率的IMF代表了一定的地质意义。经过ICA重构后的独立分量(IC)能够对异常IMF函数从盲源分离的角度进行有效的重构,其结果可以在一定程度上解释不同的地质事件对磁异常的贡献,并对构造识别和构造区域划分具有一定的指示意义。