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581.
Trace elements and cathodoluminescence of quartz in stockwork veins of Mongolian porphyry-style deposits 总被引:1,自引:0,他引:1
Axel Müller Richard Herrington Robin Armstrong Reimar Seltmann Douglas J. Kirwin Nina G. Stenina Andreas Kronz 《Mineralium Deposita》2010,45(7):707-727
The combination of scanning electron microscope–cathodoluminescence (CL), fluid inclusion analysis and high-resolution electron
probe microanalysis of Al, Ti, K and Fe in vein quartz has yielded results permitting a greater understanding of the complex
mineralisation of the Central Oyu Tolgoi and Zesen Uul porphyry-style deposits, southern Mongolia. These data demonstrate
the relationship between quartz precipitation, dissolution and ore deposition as the mineralising fluid chemistry changed
through time. Four major quartz generations are identified in the A-type veins from the stockworks of both the Central Oyu
Tolgoi (OTi to OTiv) and Zesen Uul deposits (ZUi to ZUiv). Despite differences in the associated alteration and mineralisation
style, the observed CL textures and trace element signatures of the quartz generations are comparable between deposits. The
OTi and ZUi stage formed both the primary network of A-type veins and pervasive silicification of the host rock. Using the
Ti-in-quartz geothermometer, crystallisation temperatures for OTi and ZUi of between 598°C and 880°C are indicated. The main
stage of sulphide mineralisation was accompanied by the dissolution of pre-existing quartz (OTi and ZUi) and precipitation
of a weakly luminescent generation of quartz (OTii and ZUii) with a low Ti content, reflected in a calculated temperature
drop from approximately 700°C to 340°C in Central Oyu Tolgoi and 445°C in Zesen Uul. OTii and ZUii stage quartzes show high
and variable Al concentrations. The next stage of quartz in both deposits (OTiii and ZUiii) forms a fine network of veins
in cracks formed in pre-existing quartz. OTiii and ZUiii quartz contain measurable fluid inclusions of moderate salinity (3–17.1 wt.%
NaCl eq.), entrapped in the temperature range 256°C to 385°C. OTiii and ZUiii are not related to any sulphide mineralisation.
The final OTiv and ZUiv stages are characterised by quartz–calcite micro-breccias that penetrate the A-type veins. Based on
the calculated entrapment temperatures, the OTiv/ZUiv stage crystallised between 212°C and 335°C, and the quartz is characterised
by elevated but variable Al and Fe contents. The CL and trace element signatures of the OTi to OTiii and ZUi to ZUiii stages
of the two Mongolian porphyries show similar features to those observed in porphyry-style deposits from other regions. This
suggests that a common sequence of quartz crystallisation occurs during the formation of early veins in many porphyry copper
systems. 相似文献
582.
Shuwen Pei Xing Gao Xingwu Feng Fuyou Chen Robin Dennell 《Quaternary International》2010,211(1-2):66-74
The Jingshuiwan Paleolithic site lies in the second terrace of the Changjiang (Yangtze) River and has a complete geomorphological section. Archaeological materials from early Late Pleistocene fluvial deposits of silt and sand are dated by optically stimulated luminescence (OSL) to ca. 70 ka. The stone assemblage from layer 7 includes retouched tools (118), cores (304), flakes (281), flake fragments (101), stone hammers (four) and chunks (102). Artifacts were made from lithic sources locally available from the former riverbed. The main type used was silicarenite; quartzite, hypabyssal intrusive rock, extrusive rock and volcanic breccia were also used. The principal flaking technique was direct hammer percussion without prepared striking platforms. Major blanks for tool fabrication were complete flakes (67.0%), followed by cores and incomplete flakes. Most tools were large. Chopper-chopping tools and scrapers were the dominant tool types, followed by points and notches. Modified tools were mostly retouched unifacially on the surface of blanks by direct hammer percussion. Jingshuiwan provides evidence that South China was occupied during MIS 4. Because of the similarity of the stone tool assemblage with earlier ones associated with Homo erectus, it may also provide indirect evidence that H. erectus persisted into the early Late Pleistocene. 相似文献
583.
The paper discusses short- and long-term probability models of ocean waves. The Gaussian theory is reviewed, and nonlinear short-term probability distributions are derived from a narrow band second-order model. The nonlinearity has different impact on different measurement techniques, and this is further demonstrated for wave data from the WAVEMOD Crete measurement campaign and laser data from the North Sea. Finally, we give some examples on how the short-term statistics may be used to estimate the probability distributions for the maximum waves during individual storms as well as in a wave climate described by long-term distributions. 相似文献
584.
Karl A. Aiken G. Andre Kong Stephen Smikle Robin Mahon Richard Appeldoorn 《Ocean & Coastal Management》1999,42(12):67
The history, methods, problems and regulation of fishing of the last remaining large queen conch resource in the world, located on a Jamaican fishing bank, are examined. The fishery activities for the queen conch, Strombus gigas Linnaeus are briefly described with the main activities in the industrial sector which produce the bulk of the harvest, which is exported. There are a few large producers harvesting the single major fishing ground of Pedro Bank, southwest of Kingston. These fishers harvested at least 1500 t annually between 1992 and 1998. Management is by licensing, individual quotas and a close season from July to October. Regulations related to CITES are thought to greatly assist in making licensed harvesters provide catch data to the Fisheries Division. The industrial operators have provided funding to undertake stock assessment studies in 1994 and again in 1997. We highlight the focus on management on a participatory consensual approach with meetings with all players in the industry. The conch fishery is thought to be one of the few areas of the Jamaica fishery where there is close and successful collaboration between fishers and the Fisheries Division. It provides an example of how rapid, precautionary, participatory action can provide an adequate basis for management until more definitive scientific information becomes available. The status of the conch fishery is thought to be sustainable at present, once reductions are made to the annual quota. 相似文献
585.
Ruohong Jiao Jean Braun Antoine Delaunay Cécile Robin François Guillocheau 《地球表面变化过程与地形》2023,48(1):215-229
We present a study to estimate the large-scale landscape history of a continental margin, by establishing a source-to-sink volume balance between the eroding onshore areas and the offshore basins. Assuming erosion as the primary process for sediment production, we strive to constrain a numerical model of landscape evolution that balances the volumes of eroded materials from the continent and that deposited in the corresponding basins, with a ratio imposed for loss of erosion products. We use this approach to investigate the landscape history of Madagascar since the Late Cretaceous. The uplift history prescribed in the model is inferred from elevations of planation surfaces formed at various ages. By fitting the volumes of terrigenous sediments in the Morondava Basin along the west coast and the current elevation of the island, the landscape evolution model is optimized by constraining the erosion law parameters and ratios of sediment loss. The results include a best-fit landscape evolution model, which features two major periods of uplift and erosion during the Late Cretaceous and the middle to late Cenozoic. The model supports suggestions from previous studies that most of the high topography of the island was constructed since the middle to late Miocene, and on the central plateau the erosion has not reached an equilibrium with the high uplift rates in the late Cenozoic. Our models also indicate that over the geological time scale a significant portion of materials eroded from Madagascar was not archived in the offshore basin, possibly consumed by chemical weathering, the intensity of which might have varied with climate. 相似文献
586.
Lynchets are ridges formed by erosion and sediment accumulation downstream of agricultural plots and offer valuable insights into past agricultural activity. These microtopographies cover vast areas and serve as indicators of historical changes in land use. As a result, their ubiquity across Europe makes them particularly interesting. In this study, we propose a geoarchaeological approach to analyze six lynchets, four in the Vosges Mountains and two on the Lorraine Plateau (France). The lynchets can be considered soil archives with no stratigraphic organization or chronological sequence from bottom to top, making it difficult to determine the age of the lynchets and identify changes in land use over time. To this end, we propose the analysis of historical and geo-historical archives combined with the “pedosedimentary” archives of lynchets through charcoal identification and dating combined with near-infrared spectroscopy to determine the age, vegetation, and past land use changes associated with lynchet landscapes. By combining these multiple data sources, we are better able to show the chronological development of these ancient agricultural systems and uncover valuable information on landscape history. Charcoal dating suggests a higher frequency of fires from the Middle Ages. The dating aligns with the regional dynamics of anthropogenic fires, indicating a potential use of fire for cultural purposes. We also demonstrate the difficulty of extrapolating the dating of a lynchet to the entire lynchet system. Our results highlight the difficulties of interpreting the formation and dating of lynchets and the lynchet system on the sole basis of charcoal analysis. However, we highlight the value of applying pedoanthracology to lynchets to determine the dynamics of land use change in former fields. 相似文献
587.
McKenna E. Holliday Tiffany Rivera Brian Jicha Robin B. Trayler Robert F. Biek Michael J. Braunagel W. Ashley Griffith David B. Hacker David H. Malone Danika F. Mayback 《地学学报》2023,35(1):66-72
The Markagunt gravity slide (MGS) is a large-volume landslide in southwestern Utah that originated within the Oligocene-Miocene Marysvale volcanic field. Gravity slides are single emplacement events with long runout distances and are now recognized as a new class of volcanic hazard. Accumulation of volcanic material on a structurally weak substrate along with voluminous shallow intrusive events led to collapse. Here, 40Ar/39Ar data for landslide-generated pseudotachylyte, the landslide-capping Haycock Mountain Tuff and the deformed Osiris Tuff are combined with a Bayesian age model to determine an emplacement age of 23.05 + 0.22/−0.20 Ma for the MGS. The results suggest a lag time of <200 kyr between the caldera-forming eruption of the Osiris Tuff, additional buildup of the unstable volcanic pile and subsequent mass movement. 相似文献