What underlies the Philippine island arc? Clues from the Calaton Hill, Tablas island, Romblon (Central Philippines)

We report here for the first time the occurrence of a high-temperature metamorphic/plutonic complex (amphibolites, metagabbros, hornblende pyroxenites and hornblendites) in Calaton Hill, Tablas island, Romblon, Central Philippines. The mineral assemblages and relic magmatic textures in these rocks imply apparent derivation from arc-related protoliths. Major element and trace element data are also comparable to those of gabbroic rocks in arc-related setting. Subsolidus re-equilibration under granulite to amphibolite facies is documented by the triple junctions between mineral phases in the different lithologies, the recrystallization of plagioclase and the presence of coronas around olivine with mineral assemblage of orthopyroxene + amphibole ± green spinel. The formation of hornblendite and the pervasive occurrence of amphiboles in the different lithologies are being attributed to the infiltration of a younger hydrous arc magma which also caused metamorphism and hybridization on the surrounding rocks. The characteristics of the Calaton Hill samples are comparable with those of the well-studied xenoliths from Ichinomegata, NE Honshu arc, Japan. We therefore interpret the Calaton Hill metamorphic/plutonic complex as representative of the lower crust underlying the Philippine island arc.     

Hilltop Wind Profiles Using Sodar

A Remtech PA2 sodar has been operated at two hilltop sites in New Zealand overperiods of several months. Data were lost predominantly in periods of high windspeed. Data obtained from the sodar have been used to obtain typical wind profilesat the sites for the cross-ridge direction for neutral stratification and have beencompared with model profiles.     

Simulation of the Askervein Flow. Part 1: Reynolds Averaged Navier–Stokes Equations (k ∈ Turbulence Model)

The neutrally stratified flow over the Askervein Hill was simulatedusing a terrain-following coordinatesystem and a two-equation(k - ) turbulence model. Calculations were performed on awide range of numerical grids to assess, among other things, theimportance of spatial discretization and the limitations of theturbulence model. Our results showed that a relatively coarse gridwas enough to resolve the flow in the upstream region of the hill;at the hilltop, 10 m above the ground, the speed-up was 10% lessthan the experimental value. The flow's most prominent feature wasa recirculating region in the lee of the hill, which determinedthe main characteristics of the whole downstream flow. This regionhad an intermittent nature and could be fully captured only in the caseof a time-dependent formulation and a third-order discretization ofthe advective terms. The reduction of the characteristic roughnessnear the top of the hill was also taken into account, showing theimportance of this parameter, particularly in the flow close to theground at the summit and in the downstream side of the hill.Calculations involving an enlarged area around the Askervein Hillshowed that the presence of the nearby topography affected the flowneither at the top nor downstream of the Askervein Hill.     

乔治王岛菲尔德斯半岛早第三纪植物群及其环境意义

南极乔治王岛菲尔德斯半岛化石山植物群的发现是研究该地区新生代地质历史的一件大事。通过层位对比、化石特征、植物群组合面貌的研究,认为该植物层的时代为始新世末期至渐新世早、中期,当时为温暖偏干的温带或亚热带疏林环境。     

Regional metamorphism and the alteration response of selected Silurian to Devonian mineral systems in the Nymagee area,Central Lachlan Orogen,New South Wales: a HyLogger™ case study

The southern Cobar Superbasin includes the Mount Hope, Cobar and Rast troughs and adjacent Winduck, Mouramba and Kopyje shelves. These stratotectonic units host a range of mineral systems within deformed upper Silurian to Lower Devonian rocks. Despite the metallogenic importance of the terrane the regional metamorphic- and alteration-related mineral assemblages have not been systematically described until now. Here, we present a study using the HyLogger? spectral scanner to systematically map changes in both background and alteration-related mineralogy for 14 mineral systems across the Nymagee area. The study found that, with the exception of the late diagenetic zone assemblages associated with the Winduck Shelf, the mineral assemblages for zones away from mineralisation are consistent with uniform sub- to lowest-greenschist facies metamorphic conditions, with no evidence for a regional, thermal field gradient across the basin. By contrast, proximal to mineralisation, there are significant changes in alteration-related mineral abundances and species reflecting elevated fluid temperatures. For several zones, including Browns Reef, Great Central, Hera, May Day, Nymagee and Shuttleton, there is a systematic change in chlorite composition from Fe- and/or Fe–Mg-chlorites to more Mg-rich varieties towards mineralisation. In addition, talc was noted for May Day, Mineral Hill and Shuttleton. The change in chlorite composition suggests that these ore-forming fluids were undersaturated with respect to iron. Furthermore, although present in discrete zones, carbonate alteration is not a dominant alteration type. However, at Manuka and Blue Mountain, the mineralisation is associated with carbonate-rich (calcite, ankerite, dolomite) units that have been dolomitised (Mg alteration) but not all dolomite-rich zones are mineralised. For Mineral Hill, there are systematic changes to mineral species/chemistry with observed data consistent with Parkers Hill being proximal to the centre of a mineralising system. The G and H Lode area (Southern Ore Zone) is slightly more distal whereas the Pearse deposit may represent a zone more distal again.     

西金乌兰构造混杂带中基底变质岩的特征和意义

在可可西里的西金乌兰湖一带首次发现了基底变质岩。岩石组合以石英质变质岩石组成。原岩为沉积建造。出露仅限于西金乌兰构造混杂带内。根据区域对比,认为是羌塘陆块的结晶基底。说明西金乌兰构造混杂带是羌塘陆块上裂解形成的。     

最大有效力矩准则约束下的广西罗阳山地震、地质与地貌效应

使用重新调查后的1936年灵山6?级地震的烈度资料,结合罗阳山西北麓和南麓的河流地貌与地质构造考察,参考该地区裂变径迹年代学资料,探讨了罗阳山地区的地质力学环境。重新调查后的极震区等烈度区有北北西和北东2个优势方向区域,这2个区域围绕北北西向的泗州断层和北东向的寨圩断层展布。在构造与地貌调查中发现:罗阳山山体有地貌隆升表现,并得到了裂变径迹证据支持;罗阳山西北麓山前冲沟具右旋活动表现;泗州断层内部破裂面的倾向以南西向为优势方向,并具顺时针旋转和高倾角特征。地震分布显示:寨圩断层和泗州断层交汇部位的东南侧有小地震密集展布现象。经分析后认为,以上构造地貌现象是最大有效力矩准则约束下的地震、地质和地貌效应。      

The causes of forest cover loss in the hill forests in Bangladesh

The Hill Forests in Bangladesh have been depleted and degraded in volume, area, and quantity, thus requiring urgent forest protection by identifying the causes of forest loss. This study seeks to identify the fundamental causes of the shrinking forest cover in the Hill Forests in Bangladesh. The results indicate four sets of causes: (i) indigenous forest dwellers, having their own types of problems; (ii) migrants, who, because of problems in their places of origin, have decided to move to the forests; (iii) the timber industry, which, legal or not, are cutting too many trees; and (iv) the government through its Forest Department which is not able or willing to implement suitable policies to regulate the cutting trees and to prevent illegal cutting. Because it is a time consuming task to mitigate the first and second sets of factors, we recommend to involve forest dwellers in forestry practices as much as possible and taking necessary steps to alleviate the third and fourth sets and thereby reduce the rate of forest depletion. Accordingly, a number of strategies that should be adopted to halt the loss of remaining forest cover are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

新疆坡北-笔架山地区基性-超基性岩铜镍矿成矿规律

新疆坡北-笔架山位于北山裂谷带内,发育较复杂的地层、构造和岩浆岩,该地区是新疆铜镍矿重要成矿远景区.该区与基性-超基性岩型有关的铜镍矿床有:坡十铜镍矿床、坡一铜镍矿床、红石山铜镍矿床等.通过对区域成矿地质背景、典型矿床特征、成矿规律总结,建立与基性-超基性岩有关的铜镍矿矿床成矿模式及区域成矿模式.     

黄岗梁-乌兰浩特铜多金属成矿带区域综合找矿模式

在系统研究内蒙古东南部重要成矿带黄岗梁-乌兰浩特铜多金属成矿带地质、物化探特征的基础上,总结其区域成矿地质背景、物化探异常特征,建立了成矿带区域综合找矿模式。