阿吾拉勒山西段二叠纪火山岩组合与构造环境分析     

姜常义  吴文奎  谢广成  李伍平 《地球科学与环境学报》1992,(4)

阿吾拉勒山体西段发育了厚度巨大的下二叠统火山岩,这些火山岩均属碱性玄武岩系列,以钾质类型为主,钠质类型次之,岩浆演化呈现出跨越B型趋势。这种火山活动是在大陆地壳内部产生的,代表了陆内裂谷演化的早期阶段。在早二叠世末期,由于受到新源运动的影响,这种火山活动被终止了。  相似文献   

The possible response of life zones in China under global climate change   总被引：5，自引：0，他引：5  

Xiongwen Chen  Xin-Shi Zhang  Bai-Lian Li 《Global and Planetary Change》2003,38(3-4):327-337

The response of natural vegetation to climate change is of global concern. In this research, an aggregated Holdridge Life Zone System was used to study the possible response of life zones in China under doubled atmospheric CO₂ concentration with the input climatic parameters at 0.5×0.5° resolution of longitude and latitude from NCAR regional climate model 2 (RegCM2) coupled with the CSIRO global climate model. The results indicate that the latitudinal distribution of life zones would become irregular because of the complicated climate change. In particular, new life zones, such as subtropical desert (SD), tropical desert (TDE) and tropical thorn woodland (TTW), would appear. Subtropical evergreen broadleaved forest (SEBF), tropical rainforest and monsoon forest (TRF), SD, TDE and TTW zones would appear in the northeastern China. Cool-temperate mixed coniferous and broadleaved forest (CMC) and warm-temperate deciduous broadleaved forest (WDBF) zones would appear at latitudes 25–35°N. The temperate desert (TD) in the western China would become Tibetan high-cold plateau (THP), SEBF, WDBF and temperate steppe (TS), and a large part of THP would be replaced by TRF, TDE, SEBF, TS and TTW. The relative area (distribution area/total terrestrial area) of CMC, TRF, TDE and TTW zone would increase about 3%, 21%, 3% and 6%, respectively. However, the relative area of SEBF, TS, TD and THP would decrease about 5%, 3%, 19% and 4%, respectively. In all, the relative area of forests (CCF, CMC, WDBF, SEBF, TRF) would increase about 15%, but the relative area of desert (TD, SD, TDE, and TTW) and THP would decrease about 9% and 4%, respectively. Therefore, responses of different life zones in China to climate change would be dramatic, and nationwide corridors should be considered for the conservation of migrating species under climate change.  相似文献   

The Latest Research Progress on El Nino     

CHEN Dianyou  WANG Ruiting  WANG Xudong 《世界地质(英文版)》2002,5(1)

Cold water in the deep Pacific can be drawn up to the surface (or west warm water drifts eastwards ) because strong tide increases the mixing of seawater both in vertical and horizontal. In this way greenhouse effect is decreased or increased by means of absorbing (or releasing) CO2. Therefore, La Nina cold event (or El Nino warm event) may occur,which is caused by wanning - up or cooling - down air above the ocean. Volcanic action at sea bottom is also controlled by strong tide.  相似文献   

东秦岭火山岩的地球化学特征和成因模式     

何瑞芳  段联合 《地球科学与环境学报》1993,(2)

熊耳群为玄武粗安岩-英安流纹岩组合,大红口组为粗面岩组合,属B类的过渡型拉斑玄武岩浆系列,具以太华群为岩浆房的壳幔混染型成因;秦岭群和宽坪群为变拉斑玄武岩建造,属A类拉斑玄武岩浆系列,具幔源型成因;二郎坪群和丹凤群属细碧岩-石英角斑岩建造,C类石英角斑岩浆系列与A类拉斑玄武岩浆系列共存,具壳幔双层混合型成因。  相似文献   

First seismic record for intra-arc strike-slip tectonics along the Liquiñe-Ofqui fault zone at the obliquely convergent plate margin of the southern Andes     

D. Lange  J. Cembrano  A. Rietbrock  C. Haberland  T. Dahm  K. Bataille 《Tectonophysics》2008,455(1-4):14-24

A temporal seismic network recorded local seismicity along a 130 km long segment of the transpressional dextral strike-slip Liquiñe-Ofqui fault zone (LOFZ) in southern Chile. Seventy five shallow crustal events with magnitudes up to M_w 3.8 and depths shallower than 25 km were observed in an 11-month period mainly occurring in different clusters. Those clusters are spatially related to the LOFZ, to the volcanoes Chaitén, Michinmahuida and Corcovado, and to active faulting on secondary faults. Further activity along the LOFZ is indicated by individual events located in direct vicinity of the surface expression of the LOFZ. Focal mechanisms were calculated using deviatoric moment tensor inversion of body wave amplitude spectra which mostly yield strike-slip mechanisms indicating a NE–SW direction of the P-axis for the LOFZ at this latitude. The seismic activity reveals the present-day activity of the fault zone. The recent M_w 6.2 event near Puerto Aysén, Southern Chile at 45.4°S on April 21, 2007 shows that the LOFZ is also capable of producing large magnitude earthquakes and therefore imposing significant seismic hazard to this region.  相似文献   

The role of heterogeneous strain in the development and preservation of a polymetamorphic record in high-P granulites, western Canadian Shield   总被引：1，自引：0，他引：1  

K. H. MAHAN  P. GONCALVES  R. FLOWERS  M. L. WILLIAMS  D. HOFFMAN-SETKA 《Journal of Metamorphic Geology》2008,26(6):669-694

Mafic rocks in the Chipman domain of the Athabasca granulite terrane, western Canadian Shield, provide the first well‐documented record of two distinct high‐P granulite facies events in the same domain in this region. Textural relations and the results of petrological modelling (NCFMASHT system) of mafic granulites are interpreted in terms of a three‐stage tectonometamorphic history. Stage 1 involved development of the assemblage Grt + Cpx + Qtz ± Pl (M₁) from a primary Opx‐bearing igneous precursor at conditions of 1.3 GPa, 850–900 °C. Field and microstructural observations suggest that M₁ developed synchronously with an early S₁ gneissic fabric. Stage 2 is characterized by heterogeneous deformation (D₂) and synkinematic partial retrogression of the peak assemblage to an amphibole‐bearing assemblage (M₂). Stage 3 involved a third phase of deformation and a return to granulite facies conditions marked by the prograde breakdown of amphibole (Amph₂) to produce matrix garnet (Grt_3a) and the coronitic assemblage Cpx_3b + Opx_3b + Ilm_3b + Pl_3b (M_3b) at 1.0 GPa, 800–900 °C. M₁ and M_3b are correlated with 2.55 and 1.9 Ga metamorphic generations of zircon, respectively, which were dated in a separate study. Heterogeneous strain played a crucial role in both the development and preservation of these rare examples of multiple granulite facies events within single samples. Without this fortuitous set of circumstances, the apparent reaction history could have incorrectly led to an interpretation involving a single‐cycle high‐grade event. The detailed P–T–t–D history constructed for these rocks provides the best evidence to date that much of the east Lake Athabasca region experienced long‐term lower crustal residence from 2.55 to 1.9 Ga, and thus the region represents a rare window into the reactivation and ultimate stabilization processes of cratonic lithosphere.  相似文献   

西天山达巴特火山岩的形成环境及对斑岩型矿化的制约     

张作衡 《地质学报》2008,82(11):1494-1503

本文通过对西天山地区比较典型的达巴特斑岩铜钼矿床矿区范围内出露上的英安岩和花岗斑岩进行了系统的岩石地球化学分析,对英安岩和流纹斑岩中的锆石进行了SHRIMP U-Pb定年研究,分别获得了315.9±5.9Ma和278.7±5.7Ma。岩石化学、微量以及稀土元素特征表明从英安岩到花岗斑岩,岩体具有明显的分异演化特征和很好的继承性。火山岩和次火山岩的精确定年为准确厘定火山岩形成的时限和地球动力学背景提供了依据。结合已有的Re-Os法获得的矿化年龄,表明晚石炭世末-早二叠世初（278.7±5.7Ma）,西天山地区进入板块碰撞-板内伸展阶段,由于板内幔根的部分熔化,造成深源斑岩岩浆侵位,在达巴特矿区形成了由花岗斑岩、流纹斑岩和流纹质凝灰熔岩组成的椭圆形火山机构,并导致相关矿床的形成。  相似文献   

Anthropogenic affects on lake sedimentation process: a case study from Lake Sapanca, NW Turkey     

Alper Gürbüz  Ömer Feyzi Gürer 《Environmental Geology》2008,56(2):299-307

Lake Sapanca in NW Turkey is a fault originated freshwater basin fed by seasonally variable flows of 15 streams. Considerations of lake–river interaction, supported by statistical measures of 47 bottom samples, suggest that sediment transport and deposition within the lake is controlled by two types of human constructed structures in addition to natural factors: (1) the dykes constructed in the front of streams, which feed the lake by strong flows, to prevent the filling of lakebed by coarse-grained sediments; (2) the constructed regulator on the outflowing Çarksuyu stream results in a higher sedimentation rate of clay-sized material on the NE corner of the lake, which is extraordinary in the shelf environment.  相似文献   

Structural elements of the Makran region, Oman sea and their potential relevance to tsunamigenisis     

Mohammad Mokhtari  Iraj Abdollahie Fard  Khaled Hessami 《Natural Hazards》2008,47(2):185-199

The character of convergence along the Arabian–Iranian plate boundary changes radically eastward from the Zagros ranges to the Makran region. This appears to be due to collision of continental crust in the west, in contrast to subduction of oceanic crust in the east. The Makran subduction zone with a length of about 900 km display progressively older and highly deformed sedimentary units northward from the coast, together with an increase in elevation of the ranges. North of the Makran ranges are large subsiding basins, flanked to the north by active volcanoes. Based on 2D seismic reflection data obtained in this study, the main structural provinces and elements in the Gulf of Oman include: (i) the structural elements on the northeastern part of the Arabian Plate and, (ii) the Offshore Makran Accretionary Complex. Based on detailed analysis of these data on the northeastern part of the Arabian Plate five structural provinces and elements—the Musendam High, the Musendam Peneplain, the Musendam Slope, the Dibba Zone, and the Abyssal Plain have been identified. Further, the Offshore Makran Accretionary Complex shown is to consist Accretionary Prism and the For-Arc Basin, while the Accretionary Prism has been subdivided into the Accretionary Wedge and the Accreted/Colored Mélange. Lastly, it is important to note that the Makran subduction zone lacks the trench. The identification of these structural elements should help in better understanding the seismicity of the Makran region in general and the subduction zone in particular. The 1945 magnitude 8.1 tsunamigenic earthquake of the Makran and some other historical events are illustrative of the coastal region’s vulnerability to future tsunami in the area, and such data should be of value to the developing Indian Ocean Tsunami Warning System.  相似文献   

The effect of naturally acidified irrigation water on agricultural volcanic soils. The case of Asembagus, Java, Indonesia     

A.M.D. van Rotterdam-Los  S.P. Vriend  M.J. van Bergen  P.F.M. van Gaans   《Journal of Geochemical Exploration》2008,96(1):53-68

Acid water from the Banyuputih river (pH  3.5) is used for the irrigation of agricultural land in the Asembagus coastal area (East Java, Indonesia), with harmful consequences for rice yields. The river water has an unusual composition which is caused by seepage from the acidic Kawah Ijen crater lake into the river. This unique irrigation setting allows the study of soil acidification in situ. This paper assesses the effects of volcanogenically contaminated irrigation water on the chemical properties of the agricultural soils.The changes in soil properties were evaluated by comparing samples taken from the topsoil and sub-soil (1–3 m depth) from areas irrigated with acid water and areas irrigated with neutral water. The field survey thus resulted in four soil categories. Bulk soil composition, organic matter content, moisture content and particle size distribution were determined. Reactive phases were quantified with the selective extractions 1 M KCl, 0.1 M Na-pyrophosphate and 0.2 M acid ammonium oxalate (AAO).By comparing the four soil categories it is shown that the use of the naturally polluted irrigation water has had a large influence on the chemical composition of the topsoil. The composition of the soil solution has changed over the entire investigated soil profile. Furthermore the acid irrigation water has strongly modified the composition of the reactive phases, extracted as KCl, pyrophosphate, and AAO extractable elements, and also the bulk soil composition has been significantly modified. Overall this has resulted in the net dissolution of some elements and the net precipitation of others. The changes in the reactive phases and bulk soil composition are only apparent in the topsoil (0–20 cm) but not in the deeper soil.  相似文献