东昆仑南部晚新生代逆冲推覆构造系统

通过对东大滩—东温泉地区的路线地质观测与构造填图,在东昆仑南部发现晚新生代大型逆冲推覆构造系统。沿低角度逆冲断层,早二叠世大理岩和早三叠世砂板岩自北向南逆冲推覆于古新统—始新统风火山群紫红色砾岩和渐新世砖红色砂砾岩之上,形成大量不同规模的飞来峰;沿主逆冲断层发育厚层断层角砾岩与断层泥,局部形成碳酸盐质糜棱岩。东昆仑南部逆冲推覆构造的发育时代为渐新世晚期—中新世早期,主要形成、活动时期为26～13.5Ma;估算最小逆冲推覆距离为30～35km,最小逆冲推覆运动速率为2.4～2.8mm/a。东昆仑南部晚新生代逆冲推覆构造运动与现今山脉快速隆升存在着动力学成因联系。     

The Maltese Islands: climate, vegetation and landscape

The Maltese Islands, situated in the central Mediterranean, occupy an area of only some 316 km². The climate is typically Mediterranean: the average annual rainfall is c. 530 mm of which some 85% falls during the period October to March; the mean monthly temperature range is 12--26 °C, and the islands are very windy and sunny. Although small, the Maltese Islands have a considerable diversity of landscapes and ecosystems which are representative of the range and variety of those of the Mediterranean region. The islands are composed mainly of limestones, the soils are young and are very similar to the parent rocks, and there are no mountains, streams or lakes, but only minor springs; the main geomorphological features are karstic limestone plateaux, hillsides covered with clay taluses, gently rolling limestone plains, valleys which drain runoff during the wet season, steep sea-cliffs on the south-western coasts, and gently sloping rocky shores to the Northeast. The main vegetational assemblages are maquis, garigue and steppe; minor ones include patches of woodland, coastal wetlands, sand dunes, freshwater, and rupestral communities; the latter are the most scientifically important in view of the large number of endemic species they support. Human impact is significant. Some 38% of the land area is cultivated, c. 15% is built up, and the rest is countryside. The present landscape is a result of the interaction of geology and climate, coupled with the intense human exploitation of the environment over many thousands of years, which has altered the original condition of the vegetation cover, principally through the diversion of vast tracts of land to cultivation, the construction of terraces, water catchment devices, irrigation channels and drainage ditches, the grazing of animals on uncultivated land, and the development of land for buildings and industry. The scantiness of the soil, combined with the erratic rainfall and the periodic disturbance of the vegetation cover, has resulted in extensive erosion. As a consequence it is now difficult for the original vegetation to reassert itself, affecting the landscape drastically and permanently. Much of the original native flora has been lost or marginalised and the present day non-urban landscape is now dominated by vegetation consisting mainly of ruderal and introduced species. As the population increases, and human pressure on the environment mounts, such trends are likely to continue and it is only very recently that some important initiatives have been taken to manage the environment and halt the deterioration of the landscape.     

Measurement of natural stresses in a Provence mine (Southern France)

Stress measurements were carried out in the Arc syncline using drifs in a lignite mine. Eleven sites were investigated using the flat jack and hydraulic fracturing (or stimulating) methods. Two stress states were found to coexist, one isotropic, the other highly anisotropic. The orientations of the principal stresses are not homogeneous and an orientation ranging from E-W to NE-SW predominates locally. This does not accord with the regional stress field. The vertical stresses are systematically underestimated.     

Comparison of soil solution chemistry sampled by centrifugation, two types of suction lysimeters and zero-tension lysimeters

The choice of sampling method for soil solution is of great importance. In this paper soil solution chemistry sampled by centrifugation, two types of suction lysimeters and zero-tension lysimeters have been studied with the purpose of investigating systematic differences between them. The samples were taken at 4 depths from an acidified forest soil as well as from adjacent lime and ash treated soils. A centrifugation drainage method was compared with two types of suction lysimeters (‘Rhizon’ and ‘Prenart’) and zero-tension lysimeters. About half of the 27 variables measured showed a significant difference between the sampling methods used. Typically the centrifuged samples had lower pH (4.0 vs. 4.4), Ca (21 μM vs. 30 μM) and Mg (25 μM vs. 34 μM) concentrations and higher Cl (330 μM vs. 230 μM) and DOC (4.4 mM vs. 3.2 mM) concentrations than the Rhizon lysimeters. Also the other lysimeters showed significant differences compared to the centrifuged samples for about half the number of analytes. Centrifuged samples had higher concentrations of all analytes except NO₃ and PO₄ compared to zero-tension lysimeters and also for all analytes except NO₃ and Al compared to Prenart lysimeters. Among the environmental factors considered depth showed an influence to some extent, while sampling occasion had a great significant impact on the difference between the centrifugation method and the Rhizon lysimeters. Factors like individual pits or soil treatment did not show any influence on the difference between the methods.     

Spatial and Temporal Patterns in <Emphasis Type="Italic">Thalassia testudinum</Emphasis> Leaf Tissue Nutrients at the Chandeleur Islands,Louisiana, USA

Seagrasses are submerged marine plants that are anchored to the substrate and are therefore limited to assimilating nutrients from the surrounding water column or sediment, or by translocating nutrients from adjacent shoots through the belowground rhizome. As a result, seagrasses have been used as reliable ecosystem indicators of surrounding nutrient conditions. The Chandeleur Islands are a chain of barrier islands in the northern Gulf of Mexico that support the only marine seagrass beds in Louisiana, USA, and are the sole location of the seagrass Thalassia testudinum across nearly 1000 km of the coastline from west Florida to central Texas. Over the past 150 years, the land area of the Chandeleur Islands has decreased by over half, resulting in a decline of seagrass cover. The goals of this study were to characterize the status of a climax seagrass species at the Chandeleur Islands, T. testudinum, in terms of leaf nutrient (nitrogen [N] and phosphorus [P]) changes over time, from 1998 to 2015, and to assess potential drivers of leaf nutrient content. Thalassia testudinum leaf nutrients displayed considerable interannual variability in N and P content and molar ratios, which broadly mimicked patterns in annual average dissolved nutrient concentrations in the lower Mississippi River. Hydrological modeling demonstrated the potential for multiple scenarios that would deliver Mississippi River water, and thus nutrients, to T. testudinum at the Chandeleur Islands. Although coastal eutrophication is generally accepted as the proximate cause for seagrass loss globally, there is little evidence that nutrient input from the Mississippi River has driven the dramatic declines observed in seagrasses at the Chandeleur Islands. Rather, seagrass cover along the Chandeleur Islands appears to be strongly influenced by island geomorphological processes. Although variable over time, the often elevated nutrient levels of the climax seagrass species, T. testudinum, which are potentially driven by river-derived nutrient inputs, raises an important consideration of the potential loss of the ecosystem functions and services associated with these declining seagrass meadows.     

Shape preferred orientation of object populations: automatic analysis of digitized images

An automatic technique is presented for systematic shape preferred orientation (SPO) analysis of crystal fabrics in rocks. This technique is based on digitization of an image with a CCD camera and separation of an object population from its matrix. The image is analysed globally using a rotating grid that is superimposed on the square pixel grid of the computer screen. The parametric method is based on counting intercepts in all directions. The interceps rose provides information on both the orientation and strength of the SPO. Problems of hardware-related counting noise anisotropy are avoided using an original method of filtering the intercept function with a linear, sliding mask on the counting grid. The technique was tested both on single objects of different shapes and on different populations of identical objects. A very high degree of accuracy was obtained for orientation measurements. Fabric shape parameters are introduced which are specific to this intercept technique; they compare favourably with shape parameters used in axial fabric analysis.     

Mineralogical and chemical evolution of the Ernest Henry Fe oxide–Cu–Au ore system, Cloncurry district, northwest Queensland, Australia

The Ernest Henry Cu–Au deposit was formed within a zoned, post-peak metamorphic hydrothermal system that overprinted metamorphosed dacite, andesite and diorite (ca 1740–1660 Ma). The Ernest Henry hydrothermal system was formed by two cycles of sodic and potassic alteration where biotite–magnetite alteration produced in the first cycle formed ca 1514±24 Ma, whereas paragenetically later Na–Ca veining formed ca 1529 +11/−8 Ma. These new U–Pb_titanite age dates support textural evidence for incursion of hydrothermal fluids after the metamorphic peak, and overlap with earlier estimates for the timing of Cu–Au mineralization (ca 1540–1500 Ma). A distal to proximal potassic alteration zone correlates with a large (up to 1.5 km) K–Fe–Mn–Ba enriched alteration zone that overprints earlier sodic alteration. Mass balance analysis indicates that K–Fe–Mn–Ba alteration—largely produced during pre-ore biotite- and magnetite-rich alteration—is associated with K–Rb–Cl–Ba–Fe–Mn and As enrichment and Na, Ca and Sr depletion. The aforementioned chemical exchange almost precisely counterbalances the mass changes associated with regional Na–Ca alteration. This initial transition from sodic to potassic alteration may have been formed during the evolution of a single fluid that evolved via alkali exchange during progressive fluid-rock interaction. Cu–Au ore, dominated by co-precipitated magnetite, minor specular hematite, and chalcopyrite as breccia matrix, forms a pipe-like body at the core of a proximal alteration zone dominated by K-feldspar alteration. Both the core and K-feldspar alteration overprint Na–Ca alteration and biotite–magnetite (K–Fe) alteration. Ore was associated with the concentration of a diverse range of elements (e.g. Cu, Au, Fe, Mo, U, Sb, W, Sn, Bi, Ag, F, REE, K, S, As, Co, Ba and Ca). Mineralization also involved the deposition of significant barite, K(–Ba)–feldspar, calcite, fluorite and complexly zoned pyrite. The complexly zoned pyrite and variable K–(Ba)–feldspar versus barite associations are interpreted to indicate fluctuating sulphur and/or barium supply. Together with the alteration zonation geochemistry and overprinting criteria, these data are interpreted to indicate that Cu–Au mineralization occurred as a result of fluid mixing during dilation and brecciation, in the location of the most intense initial potassic alteration. A link between early alteration (Na–Ca and K–Fe) and the later K-feldspathization and the Cu–Au ore is possible. However, the ore-related enrichments in particular elements (especially Ba, Mn, As, Mo, Ag, U, Sb and Bi) are so extreme compared with earlier alteration that another fluid, possibly magmatic in origin, contributed the diverse element suite geochemically independently of the earlier stages. Structural focussing of successive stages produced the distinctive alteration zoning, providing a basis both for exploration for similar deposits, and for an understanding of ore genesis.