SEISMIC ANISOTROPY IN THE LOWER CRUST INDUCED BY THE LATTICE PREFERRED ORIENTATIONS OF MINERALS   总被引：2，自引：0，他引：2       下载免费PDF全文

David Mainpric 《地震地质》1989,11(4):24

To identify the physical properties responsible for the seismic reflections from the deep ductile shear zones, we have undertaken a study on the effect of lattice preferred orientation (LPO) on the seismic velocity anisotropy. LPO has been quantitatively determined by U-stage measurement for plagioclase (An 49), diopside and hornblende from an extensively deformed basic mylonite from Jotun Nappe, Norway. The typical plagioclase fabrics are produced by plastic flow on (010) [001], and  相似文献   

Fabric development in brittle-to-ductile shear zones   总被引：3，自引：0，他引：3  

Carol Simpson 《Pure and Applied Geophysics》1986,124(1-2):269-288

Brittle-to-ductile shear zones from two separate geological settings are shown to have nucleated on zones of predominantly brittle deformation. The shear zones are not simply foliated cataclasites, since they contain abundant evidence of dynamic recrystallization of constituent minerals. A small quartz diorite lens in the Borrego Springs shear zone, southern California, contains centimeter-scale cataclasite zones that exhibit a gradual transition into foliated rock. Alteration of magnesiohornblende to actinolite, feldspar to white mica plus quartz, and biotite to chlorite, produced elongate minerals that define the foliation. During the later stages of deformation, intracrystalline slip and dynamic recrystallization of quartz and feldspar were important deformation mechanisms.The widespread occurrence of mineralized dilatant cracks predated the development of meter-to-decimeter-scale ductile shear zones in the Striped Rock granite, southern Virginia. Again, important deformation mechanisms in the final stages of deformation were intracrystalline slip and dynamic recrystallization of quartz.In both field areas the role of fluids has been important from the onset of brittle deformation. Fluids may have enhanced early fracturing in addition to causing the alteration and hydrolytic weakening of host rock minerals and the introduction of new mineral species. Each of these processes is thought to have contributed to the later localization of crystal plastic deformation in the rocks.  相似文献   

海南岛东北部海岸沙丘的沉积构造特征及其发育模式   总被引：19，自引：1，他引：19  

吴正  吴克刚 《地理学报》1987,(2)

海岸沙丘沉积构造中既有大型交错层理,也具某些区别于内陆沙丘构造的特征,如厚层顶积层的保存及变形层理的普遍存在。 本区海岸沙丘形成于东北季风,沙源来自海滩砂。从海滩后滨向陆地的沙丘类型依次是海岸前丘、横向沙丘和新月形沙丘、抛物线沙丘、纵向沙丘、海岸沙席。其中海岸前丘和沙席为海岸沙丘区别于内陆沙丘的特有类型。本区海岸沙丘的发育开始于3000年前。  相似文献   

Seasonal variability of the temperature field off the south-west coast of India     

Satish R. Shetye 《Journal of Earth System Science》1984,93(4):399-411

The temperature field in the coastal region off south-west India exhibits a wellmarked annual cycle. Around March the isotherms develop an upward tilt near the coast. The magnitude of the tilt increases continuously till August, then decreases and vanishes in November. To check the hypothesis that this feature is in response to the local wind, we have used the resultant wind data to determine the annual march of the wind stress. It is found that though weak during November–March, the monthly-mean longshore component of the wind stress is always conducive to coastal upwelling and follows a pattern similar to that of the isotherm tilt. We interpret this result to indicate that coastal processes in the area during April–October are controlled by the longshore component of the local wind stress in accordance with the classical model for a coastal upwelling system. During November–March, when the wind stress is weak, it appears that the influence of the longshore density gradient, which persists at the surface during this period, dominates over the effect of the wind.  相似文献   

Seismic hazard assessment in Jordan and its vicinity     

Eid Al-Tarazi 《Natural Hazards》1994,10(1-2):79-96

The earthquake hazard in Jordan and its vicinity is assessed on the basis of probabilistic methods. For this purpose, an updated earthquake catalog is compiled which covers the period between AD 1–1989. The earthquakes lie between latitudes 27.0°-35.5° N and longitudes 32.0°-39.0° E. Thirteen seismic zones are defined on a regional seismic and tectonic map presented for the area. Point-source and line-source models are used. The seismic hazard parameters, namely, theb-parameter (of the Gutenberg-Richter relation),m ₁ (the upper bound magnitude), and ₄ (the annual rate of occurrence of earthquakes with local magnitudeM _L 4.0) are calculated for each zone. The results of the seismic hazard assessment are displayed as iso-acceleration contours expected to be exceeded during typical economic life times of structures, i.e. 50 and 100 years. For each model, two seismic hazard maps are derived. In order to determine the importance of the South-eastern Mediterranean zone and the north part of the Red Sea zone from a seismic hazard point of view for Jordan, one seismic hazard map which corresponds to 50 years' economic life for every model, excluding the seismicity of these zones, is derived.  相似文献   

Diatom paleoecology of the Mar Chiquita lagoon delta,Argentina   总被引：1，自引：0，他引：1  

Marcela A. Espinosa 《Journal of Paleolimnology》1994,10(1):17-23

A 68 cm thick outcrop of diatomaceous sediments at the head of Mar Chiquita Lagoon on the Argentine coast near Buenos Aires provides evidence of Holocene paleoenvironmental changes related to sea level changes and freshwater input to the lagoon system. Salinity tolerances of extant diatom taxa were used for the reconstruction and multivariate analytical techniques were applied to reduce subjective interpretations of the diatom percentage data.The basal half of the record was deposited before 3000 years ago and fossil diatoms indicate generally freshwater conditions with one fluctuation in mesohalobous diatoms suggesting brackish water conditions at a depth of about 60 cm. Polyhalobous (marine) diatoms characterize the record after 3000 years ago and large numbers of epiphytic diatoms indicate salt marsh environments with episodic seawater fluctuations to supratidal levels. Freshwater diatoms returned at the top of the outcrop, presumably as a result of the restriction of the historic marine inlet to the lagoon and the effects of freshwater inflow to the basin.This is the second in a series of papers published in this issue on Paleolimnology in Southern South America. Dr. C. A. Fernández served as guest editor for these papers.  相似文献   

江苏沿海地区深层地下水开发利用现状及环境地质问题   总被引：8，自引：0，他引：8  

黄敬军  陆华 《水文地质工程地质》2004,31(6):64-68

江苏沿海地区深层地下水在开发利用过程中，由于开采布局不合理和存在“三集中”(开采层次集中、开采地段集中、开采时间集中)以及水文环境地质条件脆弱等因素，出现水位逐年下降，并形成区域性降落漏斗，致使部分地段地下水资源枯竭、水质成化和诱发地面沉降等诸多环境地质问题。本文着重分析沿海地区深层地下水开发利用的6个阶段(初级、城市开采、城市超采、区域超采、区域控制开采和区域压缩开采阶段)、区域降落漏斗的3个发展过程(1986年、1995年和2002年)和因深层水超量开采诱发的水资源枯竭、水质成化和地面沉降等环境地质问题的发育特征及演化趋势，从地下水资源管理和可持续发展的角度，提出深层水的保护规划、浅层咸水、海水资源的开发利用、实行强制节水、污水资源化和发展海洋性产业的对策建议。  相似文献   

The role of socio-environmental networking in the sustainability of rain-fed agriculture in the coastal savanna of Ghana     

Michael ONeal Campbell 《GeoJournal》2004,61(1):79-88

  相似文献   

Partial Crystallization of Mid-Ocean Ridge Basalts in the Crust and Mantle   总被引：2，自引：2，他引：2  

HERZBERG  CLAUDE 《Journal of Petrology》2004,45(12):2389-2405

Pressures at which partial crystallization occurs for mid-oceanridge basalts (MORB) have been examined by a new petrologicalmethod that is based on a parameterization of experimental datain the form of projections. Application to a global MORB glassdatabase shows that partial crystallization of olivine + plagioclase+ augite ranges from 1 atm to 1·0 GPa, in good agreementwith previous determinations, and that there are regional variationsthat generally correlate with spreading rate. MORB from fast-spreadingcenters display partial crystallization in the crust at ridgesegment centers and in both mantle and crust at ridge terminations.Fracture zones are likely to be regions where magma chambersare absent and where there is enhanced conductive cooling ofthe lithosphere at depth. MORB from slow-spreading centers displayprominent partial crystallization in the mantle, consistentwith models of enhanced conductive cooling of the lithosphereand the greater abundance of fracture zones through which theypass. In general, magmas that move through cold mantle experiencesome partial crystallization, whereas magmas that pass throughhot mantle may be comparatively unaffected. Estimated pressuresof partial crystallization indicate that the top of the partialmelting region is deeper than about 20–35 km below slow-spreadingcenters and some ridge segment terminations at fast-spreadingcenters. KEY WORDS: MORB; olivine gabbro; partial crystallization; partial melting; ridge segmentation; fracture zones; crust; mantle; lithosphere  相似文献   

A Study on Soil Erosion in Pasighat Town (Arunachal Pradesh) India   总被引：1，自引：1，他引：1  

Tewari  Prakash 《Natural Hazards》2004,32(2):257-275

Pasighat which lies on the foothills of the Himalayas is one of the important townsof Arunachal Pradesh. A very turbulent river named Siang flows through the townand causes frequent flash floods, inundating the low-lying areas. This river and townis also under threat due to continuous soil erosion. This soil erosion affects theneighbouring state of Assam as well. Due to the soil erosion this river known asBrahmaputra in Assam is constantly changing its course making a large numberof water channels with sand bars thus inundating vast cultivable land every year.The study analyses the cause of the problem at Pasighat in the backdrop of theexisting river system, morphology and the geographical evolution of the TransHimalayas.  相似文献