The Yushugou terrain of high-pressure granulite fades in southern Tianshan Mountain is composed mainly of an ophiolite suite. Most selected zircons are round or elliptical in shape, and some are of tetragonal prism with round edges. The granulometric analyses showthat they are well sorted in sedimentation. ZrO2/HfO2 ratios in zircons range from 45 to 57. These characters, together with the petrologic and geochemical characters of plagioclase-garnet-orthopyroxenite bearing zircons, indicate that the protolith of plagioclase-garnet-orthopyroxenite may be derived mainly from volcanic base surge sedimentary debris in oceanic islands and from clays formed by seafloor weathering. Zircons are simply of pyroclastic debris. The ophiolite formation age of (440±18) Ma and the first-stage metamorphic age (amphibolite or granulite facies) of (364±5) Ma were obtained with a method of multiple grains in different groups and a method of concordia plot. These ages provide important information on the temporal and spatial occurrence of southern Paleozoic Tianshan Ocean, the subduction rate of the oceanic crust and the formation mechanism of ophiolite of granulite facies. 相似文献
Based on the Coupled Ocean-Atmospheric Response Experiment(COARE)bulk algorithm and the Naval Postgraduate School(NPS)model,a universal evaporation duct(UED)model that can flexibly accommodate the latest improvements in component(such as stability function,velocity roughness,and scalar roughness)schemes for different stratification and wind conditions,is proposed in this paper.With the UED model,the sensitivity of the model-derived evaporation duct height(EDH)to stability function(Ψ),ocean wave effect under moderate to high wind speeds,and scalar roughness length parameterization,is investigated,and relative contributions of these factors are compared.The results show that the stability function is a key factor influencing the simulated EDH values.Under unstable conditions,the EDH values from stability functions of Fairall et al.(1996)and Hu and Zhang(1992)are generally higher than those from others;while under stable conditions,unreasonably high EDHs can be avoided by use of the stability functions of Hu and Zhang(1992)and Grachev et al.(2007).Under moderate to high wind speeds,the increase in velocity roughness length z0 due to consideration of the true ocean wave effect acts to reduce modeled EDH values;this trend is more pronounced under stable conditions.Although the scalar roughness length parameterization has a minor effect on the model-derived EDH,a positive correlation is found between the scalar roughness length z0qand the model-derived EDH. 相似文献
Based on a series of experiments conducted by two regional climate models (RCA4 and LMDZ) with and without soil moisture-atmosphere coupling, we investigate the role of soil moisture on the occurrence of surface air temperature extremes and its persistence in Southeastern South America. Our analysis reveals that both factors, soil moisture-atmosphere coupling and relatively drier soil conditions, enhance the temperature extremes. In addition, the existence of soil-atmosphere coupling and the associated soil moisture variability is crucial for the development of the extremes in SESA. The key role of soil-atmosphere coupling is also reflected in the intrinsic persistence of hot days, which is greater in simulations with interactive soil moisture than in those with prescribed soil conditions. In the absence of soil-atmosphere coupling, the imprint of the anomalous dry (and also wet) soil conditions on the intensity and persistence of hot days is weaker.
Variogram-based methods are not capable of capturing high (>2) order statistics since the variogram measures the relationship between two points at a time only. Multiple-point geostatistics (MPS) has brought new insights into many geological modeling problems. The application of MPS methods has been well documented in realizing complex geological patterns. These methods have often been used in reservoir characterization since their advent in recent decades. The frequent non-linear behaviors of geologic continuity are not limited to reservoirs, but mineral deposits bear complicated formations in many cases. Relying on the power of MPS methods and considering the complexity of geological scenarios in mineral deposits, we have applied MPS in the modeling of mineral deposits. A training image (TI) is produced using geological data from upper horizons of a porphyry copper ore deposit which have been mined out during the previous mining operations. In this study, the SNESIM algorithm has been used. A number of realizations are produced using this multiple-point geostatistical method. Extensive validation steps are performed considering the TI as the reference model. These validations first show that the TI is representative for the domain under study and also illustrates some degrees of similarity between the TI and the realizations. Despite simplifications made to the problem, the application of MPS in mineral deposit modeling still faces many challenges. 相似文献
Wildfires are an integral part of Mediterranean ecosystems; humans impact on landscapes imply changes in fuel amount and continuity, and thus in fire regime. We tested the hypothesis that fire regime changed in western Mediterranean Basin during the last century using time series techniques. We first compiled a 130-year fire history for the Valencia province (Spain, Eastern Iberian Peninsula, Western Mediterranean Basin) from contemporary statistics plus old forest administration dossiers and newspapers. We also compiled census on rural population and climatic data for the same period in order to evaluate the role of climate and human-driven fuel changes on the fire regime change. The result suggested that there was a major fire regime shift around the early 1970s in such a way that fires increased in annual frequency (doubled) and area burned (by about an order of magnitude). The main driver of this shift was the increase in fuel amount and continuity due to rural depopulation (vegetation and fuel build-up after farm abandonment) suggesting that fires were fuel-limited during the pre-1970s period. Climatic conditions were poorly related to pre-1970s fires and strongly related to post-1970s fires, suggesting that fire are currently less fuel limited and more drought-driven than before the 1970s. Thus, the fire regime shift implies also a shift in the main driver for fire activity, and this has consequences in the global change agenda. 相似文献
Mathematical Geosciences - The task of optimal sampling for the statistical simulation of a discrete random field is addressed from the perspective of minimizing the posterior uncertainty of... 相似文献
It is uncertain whether the solar cycle 24 will have a high or a low sunspot maximum number. In its last revision the Solar Cycle 24 Prediction Panel indicates that the low prediction is the most likely. Also, solar cycle 25 is considered to present an equal or lower activity than cycle 24. In order to assess the possible effect of the solar activity on temperature, in the present work we attempt to model the tendency of the Northern Hemisphere temperature for the years 2009–2029, corresponding to solar cycles 24 and 25, using a thermodynamic climate model. We include as forcings the atmospheric carbon dioxide (CO2) and the solar activity by means of the total solar irradiance, considering that the latter has not only a direct effect on climate, but also an indirect one through the modulation of the low cloud cover. We use two IPCC-2007 CO2 scenarios, one with a high fossil consumption and other with a low use of fossil sources. Also we consider higher and lower solar activity conditions. We found that in all the performed experiments the inclusion of the solar activity produces a noticeable reduction in warming respect to the IPCC-2007 CO2 scenarios. Such reduction goes between ~14% and ~44%. In order to evaluate the efficiency of the TCM, we use the root mean square (RMS) between the observed and model temperatures for the period 1980–2003. We find that the RMS for the experiment using the CO2 as the only forcing is 0.06 °C,while for the experiment that includes also the solar activity it is higher, 0.13 °C. 相似文献