Primary volcanic structures from a type section of Deccan Trap flows around Narsingpur-Harrai-Amarwara, central India: Implications for cooling history     

Piyali Sengupta  Arijit Ray 《Journal of Earth System Science》2006,115(6):631-642

Field investigations of the Deccan Trap lava sequence along a 70 km traverse in the Narsingpur-Harrai-Amarwara area of central India indicate twenty lava flows comprising a total thickness of around 480 m. Primary volcanic structures like vesicles and cooling joints are conspicuous in this volcanic succession and are used to divide individual flows into three well-defined zones namely the lower colonnade zone, entablature zone, and the upper colonnade zone. The variable nature of these structural zones is used for identification and correlation of lava flows in the field. For twenty lava flows, the thicknesses of upper colonnade zones of eight flows are ∼5 m while those of eight other flows are ∼8 m each. The thicknesses of upper colonnade zones of remaining four flows could not be measured in the field. Using the thicknesses of these upper colonnade zones and standard temperature-flow thickness-cooling time profiles for lava pile, the total cooling time of these sixteen Deccan Trap lava flows has been estimated at 12 to 15 years.  相似文献   

苏鲁造山带超高压变质作用及其P-T-t轨迹   总被引：23，自引：25，他引：23  

张泽明张金凤  游振东沈昆 《岩石学报》2005,21(2):257-270

基于超高压变质岩的岩石学,特别是超高压矿物生长成分环带、扩散环带和蚀变作用研究,综合前人的岩石学和年代学研究成果,提出苏鲁造山带超高压变质作用峰期发生在1000-1100℃和6-7GPa条件下,俯冲深度相当于200km,形成年代为240-250Ma。在此基础上,重塑了一个包括八期变质作用的P-T-t轨迹,揭示出超高压变质岩经历了三个不同的折返阶段,即从200km到100km深度的快速折返阶段,抬升速率为5km/Ma,冷却速率为10℃/Ma;从100km到30km的快速折返,抬升速率为4km/Ma,或为近等温降压,或为缓慢降温的快速降压过程;从下地壳到近地表的缓慢折返阶段,抬升速率为1km/Ma,但为快速降温过程,冷却速率可达20℃/Ma。  相似文献   

Evolution of the fogwater composition in Strasbourg (France) from 1990 to 1999     

Pierre Herckes  Henri Wortham  Philippe Mirabel  Maurice Millet   《Atmospheric Research》2002,64(1-4)

The chemical composition of fogwater has been studied in the city of Strasbourg (France) from 1990 to 1999. During these years, fogwater samples have been collected and analysed for major ions and trace metals. This paper reports on the analysis of the collected dataset. The analysis revealed a significant decrease in acidity of approximately one pH unit over the course of the study. This decrease in acidity appears to be linked to a decrease in SO_2(g) and the resulting SO₄²⁻. Trace metal concentrations have also strongly decreased over the 10-year period. Pb concentrations, following the elimination of leaded gasoline, decreased by more than one order of magnitude.  相似文献   

Soluble organic compounds in fog and cloud droplets: what have we learned over the past few years?     

Sandro Fuzzi  Maria Cristina Facchini  Stefano Decesari  Emanuela Matta  Mihaiela Mircea 《Atmospheric Research》2002,64(1-4)

We have recently set up a new procedure for characterising the water soluble organic compounds (WSOC) in fog water, for which information is still rather limited. Fog samples collected during the 1998–1999 fall–winter season in the Po Valley (Italy) were analysed following this procedure, which allows a quantitative determination of three main classes of organic compounds (neutral species, mono- and di-carboxylic acids, polycarboxylic acids), together accounting for ca. 85% of the total WSOC. This procedure also provides information on the main chemical characteristics of these three classes of compounds (functional groups, aliphatic vs. aromatic character, etc.). The enhanced chemical knowledge on fog/cloud chemical composition opens new scenarios as far as chemical and microphysical processes in clouds and fogs are concerned.  相似文献   

Denudation and cooling of the Lake Teletskoye Region in the Altai Mountains (South Siberia) as revealed by apatite fission-track thermochronology     

Johan De Grave  Peter Van den haute 《Tectonophysics》2002,349(1-4)

Lake Teletskoye occupies a narrow graben located in the northwestern sector of the Altai fold belt in South Siberia. The lake basin is thought to have formed during the Pleistocene as a distant result of the Cenozoic collision of India and Eurasia that caused a tectonic reactivation of the Palaeozoic Gorny–Altai (GA) and West Sayan (WS) blocks.The present work reports of a pilot fission-track study performed on 13 apatite separates collected from rocks that were sampled along two profiles in close proximity of the lake. The age–length data and AFT thermochronological modelling reveal two important phases of cooling in the Altai Mountains, a first one during the Late Jurassic–Early Cretaceous and a second one that started in the Miocene–Pliocene and that persists until today. The first event is interpreted to result from uplift-induced denudation probably related to the closure of the Mongol–Okhotsk Ocean; the second event can be linked to the young Cenozoic movements that lie at the origin of the formation of the Lake Teletskoye basin.  相似文献   

An Early-Cambrian UPb apatite cooling age for the high-temperature regional metamorphism in the Piancó area,Borborema Province (NE Brazil): initial conclusions     

Bruno Dhuime  Delphine Bosch  Olivier Bruguier  Renaud Caby  Carlos Archanjo 《Comptes Rendus Geoscience》2003,335(15):1081-1089

The Borborema Province (BP) of northeastern Brazil is a complex crustal assemblage, which has undergone a polycyclic evolution during the Proterozoic. In the Piancó-Alto Br??gida belt, a metamorphosed leucosome vein inserted in amphibolites has a trace element pattern suggesting a T-MORB protolith. Apatites yield a REE pattern indicating growth in equilibrium with garnet, thus pointing to its metamorphic origin. UPb analyses yield an age of 540±5 Ma interpreted as a cooling age following amphibolite facies regional metamorphism associated with granitic emplacement at ca. 580 Ma. The resulting slow cooling rates (ranging from ca. 2.5 to 5 °C Ma^?1) are consistent with underplating of mafic magmas, or crustal thickening caused by nappe stacking, as possible processes governing the metamorphic evolution of the BP. To cite this article: B. Dhuime et al., C. R. Geoscience 335 (2003).  相似文献   

重庆雾的特点及其变化分析   总被引：16，自引：2，他引：16       下载免费PDF全文

向波  刘德  廖代强 《气象》2003,29(2):48-52

利用重庆市沙坪坝195l一2001年的资料，对重庆市区雾的生消时间、持续时间、能见度等主要特征变量及其相对湿度，温度差等相关气象要素做了较为全面的分析，认为城市热岛效应可能是造成重庆主城区雾日数减少的重要原因之一。  相似文献   

北京地区一次典型大雾天气的空气污染过程物理量分布特征   总被引：9，自引：3，他引：9       下载免费PDF全文

程丛兰李青春  刘伟东吴正华 《气象科技》2003,31(6):345-350

2002年11月30至12月4日，北京持续4天大雾天气，空气污染物在持续的稳定层结条件下，空气质量连续3天达5级以上。文中分析了大雾天气各主要污染物的变化特征，以及此次过程中天气形势的特点及演变，并对造成大雾日空气污染天气的物理量分布特征进行分析。结果表明：高空WNW气流、稳定性持续增加、逆温层结持续存在、低空风速较小、相对湿度大，导致局地污染物不能及时随大气扩散；1000～700hPa有弱的上升气流形成和维持，与500hPa高空下沉气流之间在低空的某层高度上形成稳定层结(逆温层)，导致大雾及重污染的形成；850hPa为暖区，850～500hPa为冷平流，有利于大雾的形成和加重。  相似文献   

中尺度模式MM4对高精度水汽输送#C$算法的敏感性试验   总被引：1，自引：0，他引：1       下载免费PDF全文

郑爱军  葛孝贞 《大气科学》1997,21(3):308-326

水汽输送的算法精度对中尺度模式的预报能力起有重要作用。本文在MM4的基础上用高精度的平流格式改进模式的水汽输送格式，使改进后的模式包含了对多种高精度的水汽输送格式的选择，如Prather格式和Bott格式。这些格式都是正定的，在理想风场的数值实验中几乎无数值耗散，无计算频散。我们在B网格中央差格式（原MM4中的格式）、Upstream格式和 Prather格式等模式选择项下，对1982年6月的一次梅雨期暴雨过程进行了数值对比实验。结果表明:1）模式的预报能力对水汽输送格式的精度较敏感， 2）高精度的水汽输送格式（Prather格式） 提高了模式对暴雨区、降水场结构、雨团活动的预报能力，较真实地模拟出了尺度较小的降水系统的活动。 高精度的水汽输送算法有助于提高中尺度模式的预报精度。  相似文献