我国显生宙含金花岗岩类岩石-地球化学特征初探

赋存于花岗岩中的金矿床在我国金矿资源中的地位极其重要，并形成我国独具特色的金矿类型。我国含金花岗岩的时代，绝大多数为燕山期，其次是华力西-印支期及加里东期；含金花岗岩体分布广泛，特别集中出露在中朝板块东缘的胶东地体内和北缘广大地区，在北方陆壳增生区及华南扬子板块内亦有分布；研究表明，含金花岗岩类以Ⅰ型花岗岩为主，其次是A型和S型；在同一地区含金花岗岩的金丰度明显高于不含金花岗岩。     

Rural restructuring and social sustainability: some reflections on the Western Australian wheatbelt

Over the past three decades the Western Australian wheatbelt has undergone dramatic economic, environmental and social changes precipitated, primarily, by the process of rural restructuring. Farm amalgamation, environmental degradation, labour market adjustments and severe population decline have been consistently noted trends throughout much of the wheatbelt. The ongoing and integrated nature of these problems has led to increasing calls for a more holistic approach to sustainable rural development. This paper argues that while considerable efforts are being made to find solutions to the economic and environmental problems faced in the wheatbelt, these endeavours do not address many important problems faced by rural communities. It therefore advocates the inclusion of a social dimension in any attempt to achieve an overall goal of rural sustainability.     

Investigation on age and genesis of silcretes in Queensland (Australia)–Preliminary results

Silcretes from Queensland (Australia) were dated by means of the electron spin resonance dating technique. The results range from 1.5 to 10.8 million years; therefore, these silcretes were formed between the upper Miocene and the early Pleistocene. For a conclusive interpretation of the data geochemical and thin section analyses were also carried out. ESR dating of silcretes for the first time offers a direct approach to a chronostratigraphic framework of the genesis of these duricrusts, and of the palaeoclimatic events attributed to them.     

Thin surface soil layers attributable to rain-flow transportation on low-angle slopes: An example from semi-arid tropical Queensland,Australia

Particle-size analyses have been made on surface soils and a thin, overlying sandy pavement at 16 sites along a gently sloping transect at Torrens Creek in North Queensland. The transect is 1590 m long and has a maximum gradient of 0.018 (less than 1°). The sandy pavement is enriched in coarse components due to the sorting and differential downslope transport of the finer soil fractions. Particle movement is ascribed to the action of raindrops impacting very shallow, flowing water. The process, referred to as ‘rain-flow transportation’, is active wherever overland flow is too weak to generate rills and channels and occurs in areas of very low slope with permeable surface soils that allow rapid infiltration during storms. Rain-flow transportation is discussed with particular reference to the development of soil profiles in an old, subdued landscape of semi-arid tropical Australia.     

A study into the export of saline water from Hervey Bay, Australia

Australia's climate is one of the world's driest and locally characterised by high year-to-year rainfall variability. Due to high evaporation and low river runoff many estuaries and embayments in the region are characterised by inverse conditions with salinity increasing toward the coast and river mouths. Such conditions were also found during the first comprehensive hydrographic survey of Hervey Bay located at the east coast of Australia in early spring 2004. The survey traced a subsurface salinity maximum that was found in earlier studies within the East Australia Current, east of Hervey Bay to the shallow southwest regions of the bay. These are identified as the most likely source region for locally produced saline Hervey Bay Water. Utilising a simple box model, mean evaporation rates and historical river runoff data, it is demonstrated that inverse conditions are likely to dominate throughout the year. The negative circulation is a climatological feature of this estuary that is not limited to the dry season of the year. Due to persistent drought and declining rainfall in coastal eastern Australia, these conditions are likely to persist into the near future and need to be considered in coastal management strategies.     

Seasonal and spatial variation in the distribution of mangrove macroalgae in the Clyde River, Australia

The objective of this study was to determine whether there was significant spatial and temporal variation in macroalgae epiphytic on pneumatophores of the Grey Mangrove, Avicennia marina (Forsk.) Vierh., in the Clyde River, located 280 km south of Sydney, Australia. Three estuarine sites in the Clyde River were surveyed seasonally on four occasions over a two-year period, and algal distribution and abundance assessed in respect to temporal, inter-site, intertidal (from front to back of mangrove stand) and vertical (from bottom to top of pneumatophores) variation. Sediment and water characteristics, including nutrient levels, were also assessed in order to examine all variables of potential influence on algal distribution and abundance. The results indicated that intertidal position within sites, and vertical height along the length of the pneumatophore, were the greatest influence on algal frequency and biomass. Individual species dominated in different intertidal and vertical zones. These observations, together with the identification of three species of macroalgae that fulfil the criteria for bioindicators/biomonitors of environmental impacts are discussed.     

Does transported seagrass provide an important trophic link in unvegetated, nearshore areas?

The contribution of detritus from seagrass and other primary producers to faunal production in unvegetated nearshore areas was examined primarily using stable isotopes. Fish, macroinvertebrates, meiofauna and primary producers (seagrasses, macroalgae, seston and benthic microalgae) were sampled from sites in south-western Australia. All samples were analysed for δ¹³C and δ¹⁵N values and fish gut contents were determined. δ¹³C values for seagrasses in the region were high compared to other macrophytes, ranging from 49.9 to −8.2‰ compared to −19.8 to −12.6‰ for macroalgae. The δ¹⁵N values ranged between 4.0 and 7.7‰ for the red, brown and green algae, and between 3.2 and 5.9‰ for seagrasses. Seston and benthic microalgae samples had a mean δ¹³C value of −12.8 and −14.0‰, respectively, and their δ¹⁵N values were comparable to the macroalgae. All invertebrate fauna had mean δ¹³C values considerably lower than seagrasses. However, individual samples harpacticoid copepods and polychaetes had a value as high as −11.7‰. δ¹⁵N values for consumers were higher than those of the primary producers, except for copepods and amphipods. The δ¹³C values for fish had a relatively small range, between −16.6 and −13.1‰, and the δ¹⁵N values of fish were elevated compared to the invertebrates and primary producers, ranging mostly between 10.0 and 12.6‰. Mixing model analysis based on δ¹³C values indicated that seagrass ranked low as a likely carbon source for all invertebrates other than harpacticoid copepods at a single site and some samples of polychaetes. The δ¹³C values for fish were similar to those of a combination of harpacticoid and calanoid copepods, amphipods and polychaetes. The consumption of harpacticoid copepods by some fish species indicates that Amphibolis and Posidonia species in south-western Australia can contribute to the food web of unvegetated nearshore areas as detritus, but brown algae is likely to make a greater contribution. At least for the time of year that was sampled, the flow of detrital seagrass material into the foodweb may be mediated by specific detrivores, in this case harpactacoid copepods, rather than by all detritivores.     

Seismic images grounded zone wedge in Neoproterozoic glacials,Amadeus Basin,central Australia

Recently acquired seismic data in the eastern portion of the Amadeus Basin of central Australia have enabled disconformities at the base of both the Sturt and Elatina glaciogenic sequences within the Neoproterozoic succession to be mapped on a semi-regional scale. On a more detailed scale, along the shallowly shelving eastern flank of the basin, seismic data have revealed features that demarcate the transition from a grounded to floating, or possible absent, Sturt ice-sheet. Coincident with this transition is an extensive mound-like accumulation of glacial debris, some 10 to 15?km wide, 300 m high and extending at least 150?km subparallel to the northeast–southwest-oriented basin margin. This glacial debris entered the basin subglacially through meandering tunnel valleys, one of which can be mapped seismically.     

Rocky relationships: the petroglyphs of the Murujuga (Burrup Peninsula and Dampier Archipelago) in Western Australia

The petroglyphs of the Murujuga (Burrup Peninsula and Dampier Archipelago) in Western Australia are of exceptional cultural value for the nation. It is Australia’s largest and most significant collection of aboriginal rock art essentially as petroglyphs, with the number estimated at more than one million engravings. The Murujuga is a textbook example of ancient and modern times colliding as it also hosts potentially polluting, major industrial complexes such as iron ore and salt ports; liquefied natural gas, liquid ammonia and ammonium nitrate plants; railway lines, pipelines and rock quarries. The work presented in this paper is underpinned by an annual monitoring study of 10 selected sites including two control sites located on Dolphin and Gidley islands and eight test sites located closer to the industrial areas. The main rock types of the Murujuga, gabbro and granophyre, have been affected by weathering consisting of a cm-thick leached zone capped by a skin of orange and red iron and manganese oxides. The petroglyphs were engraved by removing the few top millimetres of the iron oxide-rich layer and the contrast with the paler leached zone clearly showing the carved motifs. Phosphorus is abnormally enriched in the leached zone and the surface coating, with manganese exclusively on the surface coating, demonstrating the impact of bird droppings and ‘desert varnish’ on the rocks. The colour difference and the hematite–goethite ratio, measured with a field portable reflectance spectrometer, between the background and engraving provides a tool to estimate the relative age of the petroglyphs and the selection of the backgrounds. As the fine-grained granophyres were preferentially chosen from the coarser-grained gabbros to host the petroglyphs, the goethitic (or yellower) backgrounds were prepared as canvas before being engraved. Many petroglyphs register the food items of the area, which changed as the last ice age ended and sea levels rose. We hypothesise that based on their locations and colour difference the constraint for the oldest age of the petroglyphs exceeds 17 000?years BP.     

川东—武陵地区构造格局及其演化

陆内变形是现今大陆动力学研究的重要内容之一。川东-武陵地区位于扬子地块的内部,远离板块边界,是研究陆内变形的绝佳场所。通过野外断裂构造详细的解析、褶皱构造的形态分析以及沉积地层接触关系的研究,建立了川东-武陵地区显生宙构造格局,探讨了多期构造演化过程。晚中生代以来的两次构造作用奠定了研究区的构造格架,认为滑脱层的深度及数量从根本上控制了川东-武陵地区侏罗山式褶皱变形的差异,褶皱与断裂构造几乎同时形成,川东地区的隔挡式褶皱为单层滑脱变形的结果,而武陵地区的褶皱构造是由于多层次滑脱背景下、差异隆升剥蚀造成的不同构造层次褶皱出露的结果。结合区域地质演化,提出川东-武陵地区显生宙时期主要经历了五期构造演化。晚志留-中泥盆世、石炭纪末和中、晚三叠世之交,研究区均以整体的抬升作用为主,不发育任何褶皱构造;晚侏罗-早白垩世发生大规模褶皱-逆冲作用;新生代晚期,受印度与欧亚大陆汇聚作用的影响,区内断裂带走滑方向发生反转,早期构造被强烈改造。