大兴安岭北段富林矽卡岩铜矿床成因:印支期含矿岩浆源区特征、蚀变矿物学及勘查意义

新近发现的印支期富林矽卡岩铜矿床位于大兴安岭北段新林区新林镇东约90km。矿区发育与成矿直接相关的花岗岩和侵入花岗岩中的花岗斑岩,矿体主要赋存于花岗岩与古元古代兴安桥组大理岩和早奥陶世黄斑脊山组钙质粉砂岩接触带内。富林矿床矿化与矽卡岩密切相关,整个矿化过程可分为两期:矽卡岩期和石英-硫化物期,5个阶段:早期矽卡岩阶段、退化蚀变阶段、氧化物阶段、早期硫化物阶段和晚期硫化物阶段,其中铜矿化主要发生在早期硫化物阶段。硫化物主要包括黄铜矿和黄铁矿,并含少量闪锌矿、方铅矿、斑铜矿等。蚀变类型包括石榴子石-透辉石矽卡岩化、阳起石-透闪石矽卡岩化、绿帘石矽卡岩化、绿泥石化、绢云母-粘土化、钾长石化和局部角岩化。电子探针分析(EMPA)结果表明:矿区内的石榴子石属钙铝-钙铁榴石系列,主要为钙铁榴石,辉石为透辉石-钙铁辉石系列,以透辉石为主,闪石主要为透闪石、阳起石以及少量镁绿钙闪石和铁浅闪石,帘石为黝帘石-绿帘石系列。黑云母以镁铁黑云母和铁叶云母为主,绿泥石主要为密绿泥石和铁叶绿泥石,长石以正长石和钠长石为主。石榴子石成分剖面显示从核部到边部,石榴子石呈现出钙铝榴石和钙铁榴石交替变化的环带特征,且Fe~(3+)含量的逐渐升高暗示后期成矿流体氧逸度升高,结合黑云母Mg-Fe~(3+)-Fe~(2+)图解,说明富林矽卡岩型铜矿床形成于较强的氧化环境。锆石LA-ICP-MS U-Pb测年结果显示花岗岩形成于~253Ma,花岗斑岩形成于~244Ma,为大兴安岭地区一期新的成矿事件。锆石原位Hf同位素测试结果表明,花岗岩εHf(t)介于-1.60~2.23,花岗斑岩εHf(t)介于-3.53~1.90,二者均具有古老的两阶段模式年龄,结合前人对区域构造背景的研究,认为富林花岗质岩石可能来自于松辽地块和兴安地块后碰撞背景下俯冲板片断离软溜圈上涌导致古老下地壳的部分熔融并卷入少量地幔物质而形成的岩浆。花岗斑岩及与斑岩有关的脉状矿化和蚀变的出现暗示富林地区可能存在印支期的斑岩型矿床,此外结合石榴子石、辉石成分特征以及辉石Mn/Fe比值与世界矽卡岩矿床对比,指出富林矿区外围找矿应综合考虑铜、钼、铁、金、铅、锌等矿化组合。     

滇西腾冲更新世粗面安山岩Ar-Ar年代学、地球化学特征及其构造意义

腾冲芒棒地区广泛发育新近纪以来的火山岩,本文首次对该区粗面安山岩进行的高精度40Ar/39Ar同位素定年,其坪年龄分别为2.1±0.1Ma和2.0±0.1Ma,代表其喷溢时代为早更新世。岩石地球化学特征研究显示,粗面安山岩属高钾钙碱性系列,富集大离子亲石元素、亏损高场强元素,具有弧火山岩与大陆板内火山岩的双重属性,推测其形成于后造山环境。综合研究表明,腾冲地块更新世火山岩的形成与印度-欧亚板块俯冲-碰撞造山隆升后的伸展垮塌、富集地幔部分熔融作用密切相关,而印支陆块向东南逃逸以及腾冲弧形走滑断裂带(龙川江断裂带、大盈江断裂带)的活化促使了该期火山岩的喷发与侵位。     

东昆仑东段香加南山花岗岩基中加鲁河中基性岩体形成时代、成因及其地质意义

东昆仑东段香加南山花岗岩基中加鲁河中基性岩体主要岩石类型包括角闪辉长岩和石英闪长岩。LA-ICP-MS锆石U-Pb同位素定年结果显示加鲁河中基性岩体的结晶年龄为220 Ma。岩体SiO_2含量较低,为47.91%~58.92%,Al_2O_3含量为15.54%~18.35%,Na2O为1.70%~3.34%,K_2O为0.58%~1.92%,Na_2O/K_2O比值为1.34~2.93,平均1.92,MgO含量为3.69%~8.24%,Mg~#为46~61,铝饱和指数A/CNK介于0.70~0.90之间,主体属于准铝质中钾钙碱性系列。岩体富集轻稀土元素,亏损重稀土元素,具明显的Eu负异常(δEu=0.40~0.59);微量元素富集Rb、Th、Ba等大离子亲石元素(LILE),亏损Nb、Ta、Ti等高场强元素(HFSE)。岩石学和地球化学研究显示岩体在地壳深部和浅部经历了两次岩浆混合作用。在深部,幔源岩浆底侵作用使下地壳部分熔融形成长英质岩浆,两种岩浆不同比例混合,经过化学扩散均一化,从而具有相似的同位素特征和岩石地球化学特征。在地壳浅部,经深部混合的岩浆注入花岗质岩浆,岩浆边部同花岗岩完全混合形成加鲁河岩体中石英闪长岩,不完全混合则形成暗色微粒包体。对加鲁河中基性岩体研究表明,东昆仑东段在晚三叠世处于古特提斯演化的后碰撞阶段,在这一时期存在岩浆底侵事件。     

贵德盆地热结构及地热成因机制

贵德盆地位于青藏高原东北缘黄河谷地之中, 四周环山, 为新生代断陷盆地, 地貌单元位于青藏块体, 地处祁连、昆仑和秦岭三大褶皱系交汇地带; 新构造活动强烈, 发育一系列NWW向、NW向及NNW向断裂, 为区内高温地热系统提供了较好的地热地质条件。区内地热显示类型多样, 水热活动剧烈, 尤其是盆地西部的扎仓寺热田, 水温高达 93℃, 蕴藏着丰富的地热资源。但是由于客观条件限制, 区内地热资源的开发利用及相关研究尚有不足之处。     

吐哈盆地硫磺山铜多金属矿床表生黄钾铁矾~(40)Ar/~(39)Ar定年及对风化、地貌演化及古气候的启示

黄钾铁矾是干旱—半干旱地区硫化物矿床氧化带中一种常见表生含钾硫酸盐矿物,对其进行~(40)Ar/~(39)Ar年代学研究,不仅可以直接限定硫化物矿床次生富集的时间,还可以为区域地貌形成演化和古气候演变等重大地质事件提供关键的年代学信息。本文对中国新疆吐哈盆地硫磺山铜多金属矿床氧化带中三个表生黄钾铁矾样品进行了~(40)Ar/~(39)Ar定年,第一次获得了始新世的风化矿物的年龄。结合已发表的年龄数据显示:在吐哈盆地,海拔较高的矿床氧化带剖面(如硫磺山矿床)记录了基岩的持续和较完整的区域风化事件,这些老的风化年龄的存在证明了剥蚀并不是均匀的,即其地貌演化遵循的是斜坡后退模型。对于吐哈盆地的古气候,这些表生硫酸盐的年龄表明:始新世以来吐哈盆地曾多次出现过有利于化学风化和硫化物矿床次生富集的干旱—半干旱气候,且主要集中在以下几个时期:27.7~23.3 Ma、16.4~14.7 Ma、11~7.8 Ma,之后气候开始向极端干旱气候转变,4.1~3.3 Ma之后吐哈盆地可能已经流行大规模的极端干旱气候。     

Tracing sediment redistribution across a break in slope using rare earth elements

Experimentally determined spatial patterns of soil redistribution across a break in slope derived using 10 rare earth element (REE) oxides as sediment tracers are presented. An erosion experiment was conducted using simulated rainfall within a laboratory slope model measuring 2·5 m wide by 6 m long with a gradient of 15° declining to 2°. Soil was tagged with multiple REE and placed in different locations over the slope and at the end of the experiment REE concentrations were measured in samples collected spatially. A new method was developed to quantify the erosion and deposition depths spatially, the relative source contributions to deposited sediment and the sediment transport distances. Particle‐size selectivity over an area of net deposition was also investigated, by combining downslope changes in particle‐size distributions with changes in sediment REE composition within a flow pathway. During the experiment, the surface morphology evolved through upslope propagation of rill headcuts, which gradually incised the different REE‐tagged zones and led to sediment deposition at the break in slope and the development of a fan extending over the shallow slope segment. The spatial patterns in REE concentrations, the derived erosion and deposition depths, the relative source contributions to deposition zones and the sediment transport distances, corroborate the morphological observations and demonstrate the potential of using REE for quantifying sediment transport processes. Copyright © 2010 John Wiley & Sons, Ltd.     

A new series solution method for two-dimensional elastic wave scattering along a canyon in half-space

This paper presents a semi-analytical method for studying the two-dimensional problem of elastic wave scattering by surface irregularities in a half-space. The new method makes use of the member of a c-completeness family of wave functions to construct the scattering fields, and then applies equal but opposite tractions to those of the foregoing constructed scattering fields on the horizontal surface of the half-space to produce additional scattering fields. These additional scattering fields are a series of Lamb's solutions. Thus the whole scattering field constructed in the series automatically satisfies the Navier equations, the condition of zero traction on the half-space surface, and the radiation boundary conditions at infinity. Using the traction-free conditions along the canyon surface, the coefficients of the series solutions are determined via a least-squares method. For incident P, SV, and Rayleigh waves, the numerical results are presented for the scattering displacements in the vicinity of a semi-circular canyon in the half-space.     

Contested and congested spaces: Exploring authenticity in New Zealand farmers' markets

This paper considers issues of authenticity as they apply to the evolution of farmers' markets in New Zealand. Following a discussion of the nature of authenticity and its deployment by farmers' market organisations in several jurisdictions, a two‐part case study is presented. An analysis of the strategies adopted by Farmers' Markets New Zealand to ‘protect its brand’ nationally and an examination of the disputation of authenticity in the Marlborough Farmers' Market reveals the potential of the ‘authenticity project’ to be a lightning rod for heightened tension and the fracturing of the relationship between competing interests in New Zealand farmers' markets.     

Undocumented Students’ Narratives of Liminal Citizenship: High Aspirations,Exclusion, and “In-Between” Identities

This study illustrates how national immigration policy relegates undocumented immigrant children to spaces of liminal citizenship, which shape their aspirations for higher education. Recognizing the power of migrant narratives, and the importance of privileging youths’ voices through children's geographies, we present the narratives of undocumented high school students from several rural North Carolina communities. Despite various barriers facing undocumented students, most have high academic aspirations. Students construct new forms of citizenship, legitimating their claims to higher education access through their achievement. Their liminal status, however, contributes to the formation of conflicted, “in-between” identities.     

Constructing Alterity in Ile De France?

Abstract

The aim of the article is to determine whether the Walt Disney Company has manufactured a landscape “other” to French culture around its parks in the Eastern Paris Basin. Val d'Europe is contentiously constructed by three main groups, not just one enterprise: the French state, the Walt Disney Company and local and regional governments, as well as by present and future residents, within the constraints of a contract based on French laws. The Company's investment has been a tremendous boost to the French state's project but did not lead to Disneyfication of the Briard landscape of agricultural lands in the Eastern Paris basin. In Val d'Europe the French state did not abdicate its authority in favor of commoditization of Paris as a global metropolis. The French state and French culture were never “weak” and overwhelmed.