福建戴云山巨型环状体的成因探讨     

王文革  章振国 《福建地质》2002,21(4):187-194

通过对戴云山巨型环状体西南端上涌地区4幅1：5万区域地质调查，结合区域地质资料综合研究，从火山产物及火山构造空间分布格局分析，初步认为它是以石牛山地区为中心的大型破火山组合群体，其中包括不同时期，不同级别，不同类型的火山构造，是大型破火山经过多期，多旋回，继承性和迁移喷发，同一时期，旋回火山构造多呈同心环状（卫星式）分布，不同时期，旋回火山构造往中心迁移叠置或继承套叠构成巨型环状火山构造面貌。  相似文献   

安徽庐枞中生代富钾火山岩成因的地球化学制约   总被引：74，自引：7，他引：74  

刘洪  邱检生  罗清华  徐夕生  凌文黎  王德滋 《地球化学》2002,31(2):129-140

庐枞中生代火山岩产于下扬子断裂坳陷带的继承式火山盆地中，主要为一套以粗面玄武岩－玄武粗安岩－安粗岩－粗面岩为主体的偏碱质中基性岩石组合。化学成分上具有富碱、富钾、富轻稀土及大离子亲石元素（如Rb、Th、Pb)和贫高场强元素（如Nb、Ti)等特点。在郯庐断裂中南段及其邻近地区的中生代火山岩中，庐枞盆地火山岩的特征最接近钾玄岩系火山岩。这套火山岩具有较高的ISr值（0.70570-0.70653)及偏低的εNd(t)值（－5.01～-9.96)。火山岩产出地质背景的全面分析及元素－同位素的综合示踪，排除了岩浆上升过程中存在强烈的地壳物质的混染，富钾火山岩的岩浆源区应为受俯冲板片析出流体交代作用所形成的富集地幔（EMI），岩石主要起源于富集型地幔的部分熔融。  相似文献   

Possible mechanisms of magma redistribution under Mt Etna during the 1994–1999 period detected through microgravity measurements     

D. Carbone  G. Budetta  F. Greco 《Geophysical Journal International》2003,153(1):187-200

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A 3-D gravity model for a volcanic crater in Terceira Island (Azores)   总被引：1，自引：0，他引：1  

F. G. Montesinos  A. G. Camacho  J. C. Nunes  C. S. Oliveira  R. Vieira 《Geophysical Journal International》2003,154(2):393-406

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Glacial erosion and geomorphology in the northwest Sierra Nevada, CA     

L. Allan James   《Geomorphology》2003,55(1-4):283

Pleistocene glacial erosion left a strong topographic imprint in the northwestern Sierra Nevada at many scales, yet the specific landforms and the processes that created them have not been previously documented in the region. In contrast, glaciation in the southern and central Sierra was extensively studied and by the end of the 19th century was among the best understood examples of alpine glaciation outside of the European Alps. This study describes glacially eroded features in the northwest Sierra and presents inferred linkages between erosional forms and Pleistocene glacial processes. Many relationships corroborate theoretical geomorphic principles. These include the occurrence of whalebacks in deep ice positions, roches moutonnées under thin ice, and occurrence of P-forms in low topographic positions where high subglacial meltwater pressures were likely. Some of the landforms described here have not previously been noted in the Sierra, including a large crag and tail eroded by shallow ice and erosional benches high on valley walls thought to be cut by ice-marginal channels.  相似文献   

长白山天池火山区及邻近地区壳幔结构探测研究   总被引：10，自引：2，他引：10       下载免费PDF全文

张成科  张先康  赵金仁  刘宝峰  张建狮  杨卓欣  海燕  孙国伟 《地球物理学报》2002,45(6):812-820

对长白-敦化深地震测深剖面资料利用二维射线追踪程序包进行走时拟合及地震图计算,得到了长白山天池火山区及邻近地区地壳上地幔速度结构和深部构造. 结果表明,以C2界面为标志,研究区地壳可分为上部地壳和下部地壳. 上部地壳厚1-23km,P波速度为6.00-6.25km/s;下部地壳厚12-17km,它是由一个较均匀的速度层和一个厚6-km的壳幔过渡层构成. 地壳厚度由敦化一带31-33km向东南逐渐增厚,至天池火山区最深达3km. 在天池火山区地壳存在低速体,其速度较周围介质低约为0.15km/s. 利用地震剖面探测、地震CT和大地电磁测深等结果显示,在天池火山区地壳内存在低速、低密度及低阻异常体,该异常体可能表明壳内岩浆囊的存在.  相似文献   

云南腾冲火山区上部地壳三维地震速度层析成像   总被引：22，自引：3，他引：22  

楼海  王椿镛  皇甫岗  秦嘉政 《地震学报》2002,24(3):243-251

根据1999年腾冲火山区人工地震探测资料，用层析成像方法反演了腾冲火山区上地壳三维P波速度结构．层析成像结果显示出，在腾冲火山区下方的上地壳内存在明显的P波低速区，该低速区在地下7～8km深度，可能与上地壳内的岩浆囊或部分熔融体有关．层析结果还显示出低速区主体在热海地区的东北侧．地表附近的低速区可能是构造破裂发育地区形成了有利于深部热流体上升的通道，因此，在热海形成最活跃的地热显示．   相似文献   

Discovery of Enclaves from Cenozoic Pulu Volcanic Rocks in West Kunlun Mountains and Its Geological Implications     

ZhangZhaochong  XiaoXuchang 《中国地质大学学报(英文版)》2002,13(1):30-34

In this paper,we present the occurrence and mineral components of the enclaves firstly dis-covered in the Cenozoic Pulu volcanic rocks in west Kunlun Mountains,and propose that the enclave is accumulated by fractional crystallization within high-level magma chamber.In addition,the chemical compostions of its primary magma are calculated.The calculated compositions are similar to those of the Kangxiwa volcanic rocks that belong to the same volcanic belt in the Pulu volcanic region,suggesting their origin from the same source region.However,the temperatures and oxygen fugacity of magmas at high-level magma chamber decreased along with fractional crystallization.  相似文献   

草滩沟群、丹凤岩群火山岩对比及其构造环境分析   总被引：2，自引：0，他引：2  

王德耀 《西北地质》2002,35(3):59-66

通过北泰岭造山带西段凤县地区1：5万辛家庄、红花铺幅区调填图及前人成果，对位于秦岭岩群南北两侧的丹凤岩群和草滩沟群火山岩的岩石类型、岩石化学及地球化学特征进行对比，认为二者均属亚碱性岩系之钙性－钙碱性系列；前者为中－基性岩组合，显示了岛弧外侧－边缘海型的构造背景特征；后者为中－酸性岩组合，具弧后盆地拉张裂谷活动背景特征。为探讨北秦岭造山带的地质发展史提供了新的资料。  相似文献   

The role of roadcuts, quarries, and other artificial exposures in geomorphology education     

James F. Petersen 《Geomorphology》2002,47(2-4)

Quarries and roadcuts are time-honored stopping points on geoscience field trips. Artificial exposures are good field sites for learning because of their accessibility, and the potential range of features they present for first-hand examination. On undergraduate-level field excursions, site discussions typically center on stratigraphic unit identification, correlation, depositional environments, paleontology, facies relationships, lithology, mineralogy, and/or structural features. It is rare (in my experience) for geomorphologic features and relationships to be the focus of attention, or even to receive more than passing mention. Yet, roadcuts and quarries offer much potential for learning about basic landform features, forms, and processes. This paper, with illustrated examples, discusses five general characteristics, present in artificial exposures, that offer opportunities for learning about geomorphology. (1) Roadcuts and quarries expose cross sections, not only of structure, but also of landforms, illustrating relationships between subsurface geology and the surface landscape. (2) The faces of roadcuts and quarries are anthropomorphic landforms of relatively well-known age and original form, two qualities that provide opportunities for discussing erosional modification over time. (3) These sites are generally nodes of intense geomorphic activity, useful for directly observing landform processes and their effects. The intensity of degradational and depositional processes at artificial exposures often produces (4) landform miniatures, and (5) landform analogs, both providing instructional examples or illustrations of geomorphic features. In addition to their utility to other geoscience sub-disciplines, roadcuts and quarries also offer important opportunities for students to learn about basic geomorphologic concepts, processes, and forms.  相似文献