The effect of rainfall and habitat on abundance and diversity of birds in a fenced protected area in the central Saudi Arabian desert

Factors influencing avian abundance and diversity in central Saudi Arabia were investigated over a 28-month period using walked belt transects in five local habitat types in a 2200 km²fenced desert protected area established in 1989. Enclosure of the protected area has resulted in the development of a mosaic of densely vegetated grassland and savanna areas amongst the sand and gravel plains which dominate the surrounding landscape. Overall bird diversity showed biannual peaks corresponding to spring and autumn passage migration, when 30–40 species were recorded; troughs occurred in summer or winter (9–12 species) following poor spring or autumn rains. Bird numbers responded dramatically to heavy rainfall (> 20 mm in a month) occurring two months earlier, with major peaks recorded in autumn 1992 and May–June 1994. Numbers of granivorous species, principally larks, fluctuated mostly in relation to rainfall, whereas largely insectivorous species tended to remain more stable. A desert locust plague in spring/summer 1993, combined with poor spring rains, resulted in the lowest numbers and species diversity recorded during the study.     

华中榴辉岩及其成因的若干问题

榴辉岩是华中高压变质带的特征岩类之一。根据其共生的矿物组合可划分出四类榴辉岩:角闪(蓝闪)榴辉岩,蓝晶石榴辉岩、柯石英榴辉岩和石英榴辉岩。其中蓝闪榴辉岩主要分布于团麻断裂以西地区;柯石英榴辉岩均出露于团麻断裂以东地区。根据矿物对地质温压计和变质矿物组合估测,西部地段榴辉岩的形成条件为p=1.1～1.5GPa,t=540～600℃,中东部地段榴辉岩为p≥2.5GPa,t=700～800℃。 根据岩石组合、矿物组合和构造环境分析,绝大多数(如果不是全部的话)榴辉岩与围岩经历了相同的高压—超高压变质作用,是同一构造运动旋回中不同构造部位的变质产物。蓝闪榴辉岩和柯石英榴辉岩的地质环境和退变质作用特征具有重要的大地构造意义。     

Premonsoonal water characteristics and circulation in the east central Arabian Sea

The hydrographic structure in the east central Arabian Sea during premonsoon period undergoes significant temporal change in the thermal field of upper 100 m, wherein temperature rises by about 0–5°C on an average from May to June. The major contribution in increasing the surface layer temperature comes from surface heat exchange processes, while the horizontal advective process tends to remove the heat from the upper layer. The geostrophic flow patterns are similar from May to June in the major part of the study area while in the coastal areas off Goa a southerly current sets in June in response to coastal upwelling.     

The higher grade metamorphic zonation of the Sambagawa metamorphic belt in central Shikoku, Japan

The higher grade metamorphic zonation of the Sambagawa (= Sanbagawa) belt is established for the first time for the whole area of central Shikoku. As discontinuous reactions to define the isograd are absent, the metamorphic grade is primarily determined by the Mg-Fe partitioning between garnet and chlorite along representative traverses. However, for regional mapping, mineralogical features of the pelitic schists, such as using mineral assemblages of more than divariant equilibrium, the modal garnet to chlorite ratio, and the optical properties of chlorite, are employed as auxiliary criteria.
The presence of the highest grade mineral zone in the middle of the structural level is confirmed, but its spatial distribution is far more complex than hitherto accepted. Thermal axes are now confirmed at three different structural levels. A model is presented in which the stacking of thrust sheets of different grade took place while metamorphic reactions were in progress. Thermal readjustment brought a continuous metamorphic temperature gradient across and within the thrust sheets. Tectonic blocks of metagabbro and ultramafic rock were emplaced synchronously with thinning and subsequently also re-equilibrated. Local anomalies of metamorphic grade, represented by mixing of schists of different metamorphic grade, exist, but they are due to a later stage event.     

吉林长安堡钼(铜)矿床成矿时代及物质来源:来自辉钼矿Re-Os同位素证据

吉林省中东部地区地处中国东北部陆缘、兴蒙造山带的东段,目前已探明大中型钼矿床十余座,矿床类型有斑岩型、矽卡岩型和石英脉型。长安堡斑岩型钼(铜)矿床是吉林中部地区新发现的一座大型斑岩型矿床,成矿年代学研究工作至今尚未开展。本文在矿床地质特征研究的基础上,对矿区辉钼矿进行了Re-Os同位素体系的定年研究,获得辉钼矿模式年龄值为167.3±2.4~168.7±2.4 Ma,加权平均值为168.0±1.0 Ma(MSWD=0.16),等时线年龄为168.0±6.2 Ma(MSWD=0.42),表明长安堡钼(铜)矿床形成于中侏罗世,属中国北方燕山期大规模钼成矿期成矿,结合已发表的钼矿床高精度年代学数据,认为吉林中东部地区的钼成矿作用发生在早-中侏罗世(167~196 Ma)。矿区辉钼矿的Re含量介于25.17~34.80μg/g,平均值为29.54μg/g,指示了成矿物质具有壳幔混源、且更偏壳源特征,为准确认识该矿床的成矿物质来源提供了进一步的制约。这些成果对于研究吉林地区钼矿资源的成矿规律提供了科学依据。     

Hyperspectral interpretation of selected drill cores from orogenic gold deposits in central Victoria,Australia

HyLogger hyperspectral data obtained from seven orogenic gold deposits in central Victoria, including Bendigo, Ballarat, Maldon, Fosterville, Costerfield, Castlemaine and Wildwood, are presented. The data demonstrate that fresh diamond drill core displays substantial mineralogical variation that can be attributed to the effects of cryptic hydrothermal alteration that might not otherwise be recognised. The most significant hyperspectral response lies in the white mica compositions, which vary in a systematic manner between high-Al muscovitic zones (Al–OH absorption around 2208 nm) that define a phyllic alteration halo around mineralised structures, and low-Al phengitic–chlorite zones (Al–OH absorption >2014 nm) inferred to represent either more distal alteration or possibly regional metamorphic background. An extensive ferroan dolomite alteration halo overlaps the phyllic and sulfidic alteration zones and extends beyond the sampled core in most instances. This ferroan dolomite halo has previously been defined petrographically, geochemically and using carbonate staining techniques, and is further characterised using thermal infrared hyperspectral data in drill core from the Ballarat goldfield. The mineralogical trends identified by the hyperspectral data are best developed in diamond drill core from the Costerfield, Fosterville and Ballarat goldfields, and are less pronounced at the other deposits. At Bendigo and Castlemaine the reasons for this are not immediately clear, but may be related to the close timing of gold mineralisation relative to peak metamorphism. The Maldon area lies within the contact aureole of the Harcourt Batholith and so has been thermally overprinted leading to the recrystallisation of earlier hydrothermal assemblages. The Wildwood deposit is similar to the Magdala deposit at Stawell and differs from the other goldfields in its geological setting, host rock lithologies and style of hydrothermal alteration, with the development of Fe-rich chlorite closely associated with gold mineralisation. The results demonstrate how hyperspectral data can be used to define large hydrothermal alteration footprints associated with orogenic gold mineralisation in central Victoria that are of direct benefit to mineral explorers, as well as independently characterising lithological variations in drill core.     

喜马拉雅造山带晚中新世麻迦淡色花岗岩的构建机制

在北喜马拉雅萨迦片麻岩穹窿西南侧发育有麻迦淡色花岗岩体,出露于南北向申扎—定结裂谷正断层的下盘,属一处较大规模的晚中新世淡色花岗岩体。该岩体具有较均一的元素和同位素(Sr和Nd)组成,但与多数喜马拉雅淡色花岗岩相比,具有异常高的(~(87)Sr/~(86)Sr)_i比值(0.85033~0.85034)和异常低的_(εNd)(t)值(-19.26~-18.30)组成,指示其部分熔融源区有更成熟古老地壳物质的参与。麻迦淡色花岗岩SHRIMP锆石U-Pb定年结果显示:1该岩体主要记录了至少两阶段岩浆结晶作用,分别发生在11.6±0.2 Ma和9.6±0.2 Ma;2个别13.8~16.0 Ma的岩浆作用年龄;3多数锆石继承核年龄分布于泛非期,少数年龄为中元古代(1558~1584 Ma)。在麻迦淡色花岗岩体南侧约40km处的日玛那穹窿,同位于申扎—定结南北向正断层的下盘,出露有大量原岩年龄为古元古代的日玛那糜棱岩,元素地球化学特征上类似于变泥质岩,显示高SiO_2(70.6%~74.6%),Al_2O_3(12.3%~14.0%),K_2O(4.22%~4.93%),A/CNK(1.50~1.58)和K_2O/Na_2O(1.42~2.18),代表了部分熔融源区可能存在的古老地壳物质岩石单元。因此,以麻迦淡色花岗岩为代表的北喜马拉雅晚中新世地壳深熔作用可能与青藏高原后碰撞阶段东西向伸展作用相关,泛非期变泥质岩及少量日玛那糜棱岩所代表的更古老岩石单元在16.0 Ma开始发生部分熔融,并在11.6 Ma至9.6 Ma之间达到深熔作用峰期,熔体活动可能持续了~2myr,以岩脉汇聚的形式延南北向正断层上升,构成侵位至北喜马拉雅特提斯沉积岩系之中的晚中新世麻迦淡色花岗岩体。     

琼东南盆地深水区中央峡谷黄流组储层特征及主控因素

在利用钻井和岩心资料基础上,结合铸体薄片、常规物性、压汞实验等分析测试手段,对琼东南盆地深水区中央峡谷黄流组储层特征及其影响因素进行了分析。研究表明,中央峡谷黄流组砂岩以岩屑石英砂岩为主,砂岩粒级较细且分选好,成熟度较高。原生粒间孔为主要孔隙类型,孔隙结构普遍为中孔细喉型。储层物性总体表现为中孔-特高孔、中渗-特高渗的特征。沉积微相和成岩作用是影响黄流组储层物性的主要因素,深水浊流沉积的水道砂岩是发育优质储层的前提,同时中央峡谷特殊的水深和温压条件是影响储层成岩作用的重要因素。海水深度大,而实际地层埋深浅,储层总体处于低温常压环境中,以致成岩作用程度普遍不强,但中央峡谷黄流组储层物性的内在差异仍主要受控于压实作用,中央峡谷自西向东,水深增加,实际地层埋深变浅,压实作用减弱,储层孔隙度和渗透率较好,总体上峡谷东部气层含气饱和度也较西部高。