Geological and tectonic evolution of the Transantarctic Mountains,from ancient craton to recent enigma     

《Gondwana Research》2020

The Transantarctic Mountains (TAM) are one of Earth's great mountain belts and are a fundamental physiographic feature of Antarctica. They are continental-scale, traverse a wide range of latitudes, have high relief, contain a significant proportion of exposed rock on the continent, and represent a major arc of environmental and geological transition. Although the modern physiography is largely of Cenozoic origin, this major feature has persisted for hundreds of millions of years since the Neoproterozoic to the modern. Its mere existence as the planet's longest intraplate mountain belt at the transition between a thick stable craton in East Antarctica and a large extensional province in West Antarctica is a continuing enigma. The early and more cryptic tectonic evolution of the TAM includes Mesoarchean and Paleoproterozoic crust formation as part of the Columbia supercontinent, followed by Neoproterozoic rift separation from Laurentia during breakup of Rodinia. Development of an Andean-style Gondwana convergent margin resulted in a long-lived Ross orogenic cycle from the late Neoproterozoic to the early Paleozoic, succeeded by crustal stabilization and widespread denudation during early Gondwana time, and intra-cratonic and foreland-basin sedimentation during late Paleozoic and early Mesozoic development of Pangea. Voluminous mafic volcanism, sill emplacement, and layered igneous intrusion are a primary signature of hotspot-influenced Jurassic extension during Gondwana breakup. The most recent phase of TAM evolution involved tectonic uplift and exhumation related to Cenozoic extension at the inboard edge of the West Antarctic Rift System, accompanied by Neogene to modern glaciation and volcanism related to the McMurdo alkaline volcanic province. Despite the remote location and relative inaccessibility of the TAM, its underlying varied and diachronous geology provides important clues for reconstructing past supercontinents and influences the modern flow patterns of both ice and atmospheric circulation, signifying that the TAM have both continental and global importance through time.  相似文献   

An (U-Th)/He age for the small Monturaqui impact structure,Chile     

《Quaternary Geochronology》2022

Single-crystal (U-Th)/He dating of 32 apatite and zircon crystals from an impact breccia yielded a weighted mean age of 663 ± 28 ka (n = 3; 4.2 % 2σ uncertainties) for the Monturaqui impact structure, Chile. This ~350 m diameter simple crater preserves a small volume of impactite consisting of polymict breccias that are dominated by reworked target rock clasts. The small size, young age and limited availability of melt material for traditional geochronological techniques made Monturaqui a good test to define the lower limits of the (U-Th)/He system to successfully date impact events. Numerical modeling of ⁴He loss in apatite and zircon crystals shows that, for even small craters such as Monturaqui, the short-lived compressional stage and shock metamorphic stage can account for the observed partial to full resetting of (U-Th)/He ages in accessory minerals. Despite the distinctly different ⁴He diffusion parameters of apatite and zircon, the 2σ-overlapping youngest ages are recorded in both populations of minerals, which supports the inference that the weighted mean of the youngest (U-Th)/He population is the age of formation of this impact structure.  相似文献   

Wavelet-based detection of bush encroachment in a savanna using multi-temporal aerial photographs and satellite imagery     

《International Journal of Applied Earth Observation and Geoinformation》2015

Although increased woody plant abundance has been reported in tropical savannas worldwide, techniques for detecting the direction and magnitude of change are mostly based on visual interpretation of historical aerial photography or textural analysis of multi-temporal satellite images. These techniques are prone to human error and do not permit integration of remotely sensed data from diverse sources. Here, we integrate aerial photographs with high spatial resolution satellite imagery and use a discrete wavelet transform to objectively detect the dynamics in bush encroachment at two protected Zimbabwean savanna sites. Based on the recently introduced intensity-dominant scale approach, we test the hypotheses that: (1) the encroachment of woody patches into the surrounding grassland matrix causes a shift in the dominant scale. This shift in the dominant scale can be detected using a discrete wavelet transform regardless of whether aerial photography and satellite data are used; and (2) as the woody patch size stabilises, woody cover tends to increase thereby triggering changes in intensity. The results show that at the first site where tree patches were already established (Lake Chivero Game Reserve), between 1972 and 1984 the dominant scale of woody patches initially increased from 8 m before stabilising at 16 m and 32 m between 1984 and 2012 while the intensity fluctuated during the same period. In contrast, at the second site, which was formely grass-dominated site (Kyle Game Reserve), we observed an unclear dominant scale (1972) which later becomes distinct in 1985, 1996 and 2012. Over the same period, the intensity increased. Our results imply that using our approach we can detect and quantify woody/bush patch dynamics in savanna landscapes.  相似文献   

Using atmospheric fallout to date organic horizon layers and quantify metal dynamics during decomposition     

James M. Kaste  Benjamin C. Bostick  Eiliv Steinnes 《Geochimica et cosmochimica acta》2011,75(6):1642-1661

High concentrations of metals in organic matter can inhibit decomposition and limit nutrient availability in ecosystems, but the long-term fate of metals bound to forest litter is poorly understood. Controlled experiments indicate that during the first few years of litter decay, Al, Fe, Pb, and other metals that form stable complexes with organic matter are naturally enriched by several hundred percent as carbon is oxidized. The transformation of fresh litter to humus takes decades, however, such that current datasets describing the accumulation and release of metals in decomposing organic matter are timescale limited. Here we use atmospheric ²¹⁰Pb to quantify the fate of metals in canopy-derived litter during burial and decay in coniferous forests in New England and Norway where decomposition rates are slow and physical soil mixing is minimal. We measure ²¹⁰Pb inventories in the O horizon and mineral soil and calculate a 60-630 year timescale for the production of mobile organo-metallic colloids from the decomposition of fresh forest detritus. This production rate is slowest at our highest elevation (∼1000 m) and highest latitude sites (>63°N) where decomposition rates are expected to be low.We calculate soil layer ages by assuming a constant supply of atmospheric ²¹⁰Pb and find that they are consistent with the distribution of geochemical tracers from weapons fallout, air pollution, and a direct ²⁰⁷Pb application at one site. By quantifying a gradient of organic matter ages with depth in the O horizon, we describe the accumulation and loss of metals in the soil profile as organic matter transforms from fresh litter to humus. While decomposition experiments predict that Al and Fe concentrations increase during the initial few years of decay, we show here that these metals continue to accumulate in humus for decades, and that enrichment occurs at a rate higher than can be explained by quantitative retention during decomposition alone. Acid extractable Al and Fe concentrations are higher in the humus layer of the O horizon than in the mineral soil immediately beneath this layer: it is therefore unlikely that physical soil mixing introduces significant Al and Fe to humus. This continuous enrichment of Al and Fe over time may best be explained by the recent suggestion that metals are mined from deeper horizons and brought into the O horizon via mycorrhizal plants. In sharp contrast to Al and Fe, we find that Mn concentrations in decomposing litter layers decrease exponentially with age, presumably because of leaching or rapid uptake, which may explain the low levels of acid extractable Mn in the mineral soil. This study quantifies how metals are enriched and lost in decomposing organic matter over a longer timescale than previous studies have been able to characterize. We also put new limits on the rate at which metals in litter become mobile organo-metallic complexes that can migrate to deeper soil horizons or surface waters.  相似文献   

Mathematical modeling of thermomechanical erosion beneath Proterozoic komatiitic basaltic sinuous rilles in the Cape Smith Belt,New Québec,Canada     

David A. Williams  Ross C. Kerr  C. Michael Lesher 《Mineralium Deposita》2011,46(8):943-958

Virtually all of the economic Ni–Cu–(platinum group element (PGE)) mineralization in the central part of the Cape Smith Belt of New Québec is hosted by thick olivine cumulate units in the Katinniq Member of the Raglan Formation at the base of the 1.9 Ga Chukotat Group. These units transgress underlying gabbros and pelitic metasediments, forming 50–200-m deep and 300–1,000-m wide V-shaped embayments and have been interpreted on the basis of surface geology, deep diamond core drilling, and magnetic inversion models to represent the remnants of one or more large, long (at least 20 km, possibly ≥50 km), sinuous, komatiitic basalt lava channels that formed by thermomechanical erosion of their substrates. We have used a mathematical model to test these hypotheses regarding komatiitic lava emplacement and erosion by lava. Our modeling predicts that an initially 10-m thick komatiitic basalt flow should have flowed turbulently near the vent and should have thermomechanically eroded unconsolidated pelitic sediment during emplacement to reach the observed degree of contamination of ≤10% at distances of ~30–60 km downstream from the source. Furthermore, our models predict that, at these distances downstream, a fully inflated 100-m thick komatiitic basalt flow would have had thermal erosion rates over consolidated gabbroic substrate of ~0.7–1.5 m/day, requiring ~70–140 days to incise a 100-m deep channel, depending on the initial temperature of the lava, the paleoslope, and the initial temperature and solidus temperature of the gabbro. These erosion rates would have been associated with volumetric flow rates of >10⁵–10⁶ m³/s and eruption volumes of >10³–10⁴ km³. Although these flow rates are orders of magnitude larger than those of most modern terrestrial basaltic flows, they are of the same order as those estimated for the largest terrestrial flood basalt flows and with those inferred for some of the largest extraterrestrial flows. Our predicted flow volumes are also of the same order as those of the largest terrestrial flood basalt units, consistent with the great thickness and widespread distribution of the Chukotat Group. Our modeling of thermomechanical erosion of gabbro by komatiitic basalt results in negligible contamination (<1%), and geochemical studies show that the spatially and petrogenetically related Chukotat basalts are uncontaminated, suggesting that the observed enrichments in U–Th–Light Rare Earth Elements (REE) > Middle REE–Heavy REE > Nb–Ta–Ti represent contamination by underlying Povungnituk semipelites. This result is consistent with present models for the genesis of the Ni–Cu–(PGE) mineralization in the Raglan Formation that involve thermomechanical erosion of unconsolidated, sulfidic semipelitic sediments, and decoupling of the miscible silicate and immiscible sulfide components.  相似文献   

Assessment of Constraint Factors of Resources and Environment of Sustainable Development in the Beijing-Tianjin-Hebeiregion: Based on the Framework of Landscape Sustainability Science     

Zhang Da  He Chunyang  Wu Jianguo  Huang Qingxu 《地球科学进展》2015,30(10):1151-1161

The Beijing-Tianjin-Hebei (BTH) region is an important engine for China’s socioeconomic development. Timely and effectively assessing constraint factors of resources and environment is of great significance for the sustainability assessment and the sustainable development of this region. However, comprehensive assessment research considering key resource and environmental constraints are still lacking. In this study, therefore, the limiting factors of resources and the environment in the BTH region were assessed based on the framework of landscape sustainability science. First, we chose five limiting factors, including topographic condition, geological environment, water resource, land resource, and atmospheric environment, to assess the constraints of resources and the environment using the single-factor evaluation method and the multi-factor comprehensive evaluation method. Based on the results, we divided the whole region into five subregions, i.e., the ecological conservation subregion, the geological disaster subregion, the water resource scarcity subregion, the atmospheric pollution subregion, and the cropland protection subregion. The results revealed that the northern BTH region was highly constrained by topographic conditions, the central BTH region was strongly constrained by geological environment and water resources, whereas the southern BTH region was constrained mainly by land resources and atmospheric environment. In addition, water resource was the main limiting factor for regional population growth and economic development. In 2010, the water resource scarcity subregion had a total population of 39.59 million, an urban population of 76.90%, and a gross domestic product of 2 455.57 billion yuan. We argue that the sustainable development of the BTH region should explicitly consider the resource and environmental limiting factors, implement land use optimization according to local conditions, maintain multiple land use types and diverse management strategies, based on the perspective of “strong sustainability”, so as to promote the regional sustainable development.  相似文献   

淮河流域水文非线性多水源时变增益模型研究与应用          下载免费PDF全文

万蕙  夏军  张利平  宋霁云  佘敦先 《水文》2015,35(3):14-19

基于传统时变增益模型(TVGM),进一步考虑地下径流退水,在传统TVGM只考虑单一地表水源的基础上,添加地下水源模块,对地表地下径流分别进行产、汇流计算,改进并提出了多水源TVGM,并将其应用于淮河流域蚌埠闸以上13个水文站控制的代表性子流域。结果表明:多水源TVGM既继承了传统TVGM以简单结构描述复杂水文非线性系统关系的优点,同时通过增加地下水源模块,大大提高了洪水预报的精度。13个子流域参数率定期和模型验证期中,传统TVGM分别有9个和7个子流域达到乙级洪水预报标准,而多水源TVGM分别提高到12个和8个,其中以大型流域和大水年改进效果尤佳。传统TVGM水量平衡系数为0.88,多水源TVGM提高到0.95,平均提高了7%。洪峰模拟相对误差也由传统TVGM的50%达标率提高到多水源TVGM的92.3%,整体提高了42.3%。因此,多水源TVGM能更好的应用于淮河流域洪水预报工作。  相似文献   

Social identity, perception and motivation in adaptation to climate risk in the coffee sector of Chiapas, Mexico   总被引：1，自引：0，他引：1  

Elisa Frank  David López-Carr 《Global Environmental Change》2011,21(1):66-76

Most investigation into climate adaptation to date has focused on specific technological interventions and socio-economic aspects of adaptive capacity. New perspectives posit that socio-cognitive factors may be as or more important in motivating individuals to take adaptive actions. Recent research indicates that incorporating insights from motivation theory can enhance theorization of adaptive capacity. Yet unexplored, and what we propose here, is the addition of social identity to models of adaptive capacity and adaptation. To apply this conceptual framework, the first author undertook in-depth interviews with a sample of farmers who had participated in broader surveys the previous year to explore their perceptions of their social identity, climate-related information and its sources, and climate risk. These interviews elicited compelling evidence that social identity mediates between risk perception and adaptation through its influence on motivation. Interviews revealed significant links between social identity and perception of information, risk perception and adaptation, of which the most salient were the relative credibility and legitimacy of information sources (related to us vs. them social group differentiation); the role of coffee organizations; and ethnicity and geographic marginalization. Strong in-group identity and perceptions of potentially influential out-groups such as the scientific community appear to particularly influence perception and use of information. These findings have rich policy implications for adaptation management and merit further investigation to identify how, where and why social identity plays a role in climate-risk perception, motivation and adaptation in other geographic areas of vulnerability worldwide.  相似文献   

Mid Holocene origin of the sea-surface salinity low in the subarctic North Pacific     

《Quaternary Science Reviews》2004,23(20-22):2089-2099

IMAGES core MD01-2416 (51°N, 168°E) provides the first centennial-scale multiproxy record of Holocene variation in North Pacific sea-surface temperature (SST), salinity, and biogenic productivity. Our results reveal a gradual decrease in subarctic SST by 3–5 °C from 11.1 to 4.2 ka and a stepwise long-term decrease in sea surface salinity (SSS) by 2–3 p.s.u. Early Holocene SSS were as high as in the modern subtropical Pacific. The steep halocline and stratification that is characteristic of the present-day subarctic North Pacific surface ocean is a fairly recent feature, developed as a product of mid-Holocene environmental change. High SSS matched a salient productivity maximum of biogenic opal during Bølling-to-Early Holocene times, reaching levels similar to those observed during preglacial times in the warm mid-Pliocene prior to 2.73 Ma. Similar productivity spikes marked every preceding glacial termination of the last 800 ka, indicating recurrent short-term events of mid-Pliocene-style intense upwelling of nutrient-rich Pacific Deepwater in the Pleistocene. Such events led to a repeated exposure of CO₂-rich deepwater at the ocean surface facilitating a transient CO₂ release to the atmosphere, but the timing and duration of these events repudiate a long-term influence of the subarctic North Pacific on global atmospheric CO₂ concentration.  相似文献   

Advances in location modeling: GIS linkages and contributions   总被引：4，自引：1，他引：3  

Alan T. Murray 《Journal of Geographical Systems》2010,12(3):335-354

Geographic information systems (GIS) have matured and proven to be an enabling technology, one that is important to many disciplines. Location analysis is also a field that has matured and continues to evolve. In fact, the combination of GIS and location science is at the forefront of advances in spatial analysis capabilities, offering substantial potential for continued and sustained theoretical and empirical evolution. This paper provides an overview of location analysis and discusses GIS. The paper highlights how GIS has contributed to location science in terms of data input, visualization, problem solution and theoretical advances. The significance of GIS in this context is that it is far more than a mere spatial data input mechanism, which is a commonly held misconception within geography, operations research and other allied disciplines. In contrast to other reviews, the focus in this paper is to highlight the theoretical foundations of location analysis and modeling and how GIS is contributing to important advancements in this field. An overall contribution of the paper is providing a perspective on spatial analysis and how associated specialty areas are evolving and thriving, particularly as a component of GIScience.  相似文献