胶南王台变质基性熔岩：元古宙洋壳残片   总被引：4，自引：0，他引：4  

宋明春  倪志耀  王仁民 《矿物岩石地球化学通报》2001,20(2):84-87

胶南王台变质基性熔岩的地球化学特征表现为拉班玄武岩系列 ,具平坦型稀土配分模式 ,高强场相容元素含量与N MORB相近 ,εNd(t) =1.82～ 6 .35 ,△2 0 7Pb 2 0 4Pb为 - 6 .748～ - 8.0 0 0 ,形成于洋中脊环境。它的存在表明鲁东地区发育有元古宙古洋壳残片 ,华北古陆块南缘在早 中元古宙似应处于大洋环境  相似文献   

安徽岳西脉状英安质角砾熔岩的发现、特征及意义   总被引：2，自引：0，他引：2  

路玉林  钱存超  周存亭 《安徽地质》1996,(4)

作者通过１：５万区调工作，于大别山腹地发现了脉状英安质角砾熔岩。通过对其岩石学、岩石化学、地球化学等的研究，认为它可与北淮阳地区毛坦厂火山岩旋回作对比，从而对认识大别造山带热隆－侵蚀史等具有重要意义。  相似文献   

内蒙白旗地区火山碎斑熔岩斜长石成分及其有序度   总被引：1，自引：0，他引：1  

赖绍聪  隆平 《西北地质》1997,18(3):8-12

白旗碎斑熔岩中斜长石以更长石为主，其有序度低，指示了岩石高温火山成因的特征，从岩体边缘相到中心相至根部相，长石类型，化学成分和有序度具有一定的变化规律，反映了岩体不同岩相带成岩条件的差异性。  相似文献   

青岛地区玄武岩蓄水条件探讨   总被引：1，自引：0，他引：1  

郑继民  曹钦臣  赵广涛  邱汉学 《中国海洋大学学报(自然科学版)》1992,(2)

提出在青岛开发利用玄武岩地下水资源。探讨白垩纪与第三纪玄武岩孔洞裂隙水分布、赋存特征、蓄水条件、富集规律、水量与水质评价、利用现状,开发利用存在的问题以及合理开发玄武岩地下水资源的主要措施。  相似文献   

Silicic lava dome growth in the 1934–1935 Showa Iwo-jima eruption, Kikai caldera, south of Kyushu, Japan     

Fukashi Maeno  Hiromitsu Taniguchi 《Bulletin of Volcanology》2006,68(7-8):673-688

The 1934–1935 Showa Iwo-jima eruption started with a silicic lava extrusion onto the floor of the submarine Kikai caldera and ceased with the emergence of a lava dome. The central part of the emergent dome consists of lower microcrystalline rhyolite, grading upward into finely vesicular lava, overlain by coarsely vesicular lava with pumice breccia at the top. The lava surface is folded, and folds become tighter toward the marginal part of the dome. The dome margin is characterized by two zones: a fracture zone and a breccia zone. The fracture zone is composed of alternating layers of massive lava and welded oxidized breccia. The breccia zone is the outermost part of the dome, and consists of glassy breccia interpreted to be hyaloclastite. The lava dome contains lava with two slightly different chemical compositions; the marginal part being more dacitic and the central part more rhyolitic. The fold geometry and chemical compositions indicate that the marginal dacite had a slightly higher temperature, lower viscosity, and lower yield stress than the central rhyolite. The high-temperature dacite lava began to effuse in the earlier stage from the central crater. The front of the dome came in contact with seawater and formed hyaloclastite. During the later stage, low-temperature rhyolite lava effused subaerially. As lava was injected into the growing dome, the fracture zone was produced by successive fracturing, ramping, and brecciation of the moving dome front. In the marginal part, hyaloclastite was ramped above the sea surface by progressive increments of the new lava. The central part was folded, forming pumice breccia and wrinkles. Subaerial emplacement of lava was the dominant process during the growth of the Showa Iwo-jima dome.Editorial Responsibility J. McPhie  相似文献   

北祁连山奥陶纪弧后盆地火山岩浆成因   总被引：27，自引：6，他引：27       下载免费PDF全文

夏林圻夏祖春  徐学义 《中国地质》2003,30(1):48-60

本文对北祁连山早古生代弧后盆地熔岩的岩石地球化学研究结果加以报道。样品的分布将南部弧后盆地拉伸最早阶段发育的岛弧裂谷化区和北部的弧后海底扩张区联系起来。熔岩的岩相学和地球化学特点反映了拉伸方式的改变,北部是典型的弧后盆地基性熔岩,向南则逐渐向岛弧熔岩过渡。海底扩张区以玻质(现已脱玻化)、少斑基性熔岩为特征,长英质熔岩和斑状基性熔岩产于南部岛弧裂谷化区。成熟岛弧部分(Y<20×10-6,TiO2<0.60%,Th/Yb>0.60)和弧后扩张区(Y>20×10-6,TiO2>1.0%,Th/Yb<0.60)在地球化学上相互有别。从由海底扩张形成的弧后盆地基性熔岩,向南经过逐渐与岛弧岩石相似的熔岩,直至裂谷区最南部的岛弧熔岩,它们的地球化学成分显示逐渐的变化。这种变化反映了弧后盆地形成过程中弧后盆地之下地幔对流方式和熔体产生作用的改变:从初始岛弧裂谷之下由消减板片俯冲引起的地幔下沉,转变为弧后海底扩张带之下的地幔上隆。早期岛弧裂谷阶段,裂谷轴捕获了岛弧岩浆流,从而使得喷出的熔岩在成分上与岛弧熔岩无法区分;随着弧后拉张继续,弧后盆地变宽,岛弧岩浆流逐渐离开裂谷轴,最终产生一个似洋中脊的减压熔融系统———弧后盆地岩浆系统。  相似文献   

Petrology of the prehistoric lavas and dyke of the Barren Island,Andaman Sea,Indian Ocean     

M. A. Alam  D. Chandrasekharam  O. Vaselli  B. Capaccioni  P. Manetti  P. B. Santo 《Journal of Earth System Science》2004,113(4):715-721

Although Barren Island (Andaman Sea, Indian Ocean) witnessed several volcanic eruptions during historic times, the eruptions that led to the formation of this volcanic island occurred mainly during prehistoric times. It is still active and currently in the fumarolic stage. Its volcanic evolution appears to be characterized by a constructive phase with the piling up of lava flows and scoria deposits and Strombolian activities, followed by a sudden collapse of the main cone. Deposits of a possible caldera-forming eruption were not recognized earlier. After a period of peri-calderic hydromagmatic activity, whose deposits presently mantle inner and outer caldera walls, a new phase of intracalderic Vulcanian activities took place. A prominent dyke in the SE inner side of the caldera wall was recognized. Petrographically the lava flows and dyke are similar but they differ in their chemical composition (viz., SiO₂, MgO, Ni, Cr) significantly. Similarity in major, minor and trace element composition (viz., K/La, K/Nb, K/Rb, K/Ti ratios) of these rocks together with Chondrite normalized trace element (Rb, Ba, Sr, P, Zr, Ti and Nb) and REE (La, Ce, Nd and Y) patterns of the Barren Island prehistoric lava flows and dyke and low-K lavas of Sunda Arc indicates that Barren Island must have evolved from a source similar to that of Sunda Arc lavas during the Quaternary Period.  相似文献   

Formation of clastogenic lava flows during fissure eruption and scoria cone collapse: the 1986 eruption of Izu-Oshima Volcano, eastern Japan     

Janet M. Sumner 《Bulletin of Volcanology》1998,60(3):195-212

The 1986 eruption of B fissure at Izu-Oshima Volcano, Japan, produced, among other products, one andesite and two basaltic andesite lava flows. Locally the three flows resemble vent-effused holocrystalline blocky or aa lava; however, remnant clast outlines can be identified at most localities, indicating that the flows were spatter fed or clastogenic. The basaltic andesite flows are interpreted to have formed by two main processes: (a) reconstitution of fountain-generated spatter around vent areas by syn-depositional agglutination and coalescence, followed by extensional non-particulate flow, and (b) syn-eruptive collapse of a rapidly built spatter and scoria cone by rotational slip and extensional sliding. These processes produced two morphologically distinct lobes in both flows by: (a) earlier non-particulate flow of agglutinate and coalesced spatter, which formed a thin lobe of rubbly aa lava (ca. 5 m thick) with characteristic open extension cracks revealing a homogeneous, holocrystalline interior, and (b) later scoria-cone collapse, which created a larger lobe of irregular thickness (<20 m) made of large detached blocks of scoria cone interpreted to have been rafted along on a flow of coalesced spatter. The source regions of these lava flows are characterized by horseshoe-shaped scarps (<30 m high), with meso-blocks (ca. 30 m in diameter) of bedded scoria at the base. One lava flow has a secondary lateral collapse zone with lower (ca. 7 m) scarps. Backward-tilted meso-blocks are interpreted to be the product of rotational slip, and forward-tilted blocks the result of simple toppling. Squeeze-ups of coalesced spatter along the leading edge of the meso-blocks indicate that coalescence occurred in the basal part of the scoria cone. This low-viscosity, coalesced spatter acted as a lubricating layer along which basal failure of the scoria cone occurred. Rotational sliding gave way to extensional translational sliding as the slide mass spread out onto the present caldera floor. Squeeze-ups concentrated at the distal margin indicate that the extensional regime changed to one of compression, probably as a result of cooling of the flow front. Sliding material piled up behind the slowing flow front, and coalesced spatter was squeezed up from the interior of the flow through fractures and between rafted blocks. The andesite flow, although morphologically similar to the other two flows, has a slightly different chemical composition which corresponds to the earliest stage of the eruption. It is a much smaller lava flow emitted from the base of the scoria cone 2 days after the eruption had ceased. This lava is interpreted to have been formed by post-depositional coalescence of spatter under the influence of the in-situ cooling rate and load pressure of the deposit. Extrusion occurred through the lower part of the scoria cone, and subsequent non-particulate flow of coalesced material produced a blocky and aa lava flow. The mechanisms of formation of the lava flows described may be more common during explosive eruptions of mafic magma than previously envisaged. Received: 30 May 1997 / Accepted: 19 May 1998  相似文献   

Thick lava flows of Karisimbi Volcano, Rwanda: insights from SIR-C interferometric topography     

Mary E. MacKay  Scott K. Rowland  Peter J. Mouginis-Mark  Harold Garbeil 《Bulletin of Volcanology》1998,60(4):239-251

 We use a digital elevation model (DEM) derived from interferometrically processed SIR-C radar data to estimate the thickness of massive trachyte lava flows on the east flank of Karisimbi Volcano, Rwanda. The flows are as long as 12 km and average 40–60 m (up to >140 m) in thickness. By calculating and subtracting a reference surface from the DEM, we derived a map of flow thickness, which we used to calculate the volume (up to 1 km³ for an individual flow, and 1.8 km³ for all the identified flows) and yield strength of several flows (23–124 kPa). Using the DEM we estimated apparent viscosity based on the spacing of large folds (1.2×10¹² to 5.5×10¹² Pa s for surface viscosity, and 7.5×10¹⁰ to 5.2×10¹¹ Pa s for interior viscosity, for a strain interval of 24 h). We use shaded-relief images of the DEM to map basic flow structures such as channels, shear zones, and surface folds, as well as flow boundaries. The flow thickness map also proves invaluable in mapping flows where flow boundaries are indistinct and poorly expressed in the radar backscatter and shaded-relief images. Received: 6 September 1997 / Accepted: 15 May 1998  相似文献   

Comparison of the response of the Landsat 7 Enhanced Thematic Mapper Plus and the Earth Observing-1 Advanced Land Imager over active lava flows     

Stephen J. Donegan  Luke P. Flynn   《Journal of Volcanology and Geothermal Research》2004,135(1-2):105

Using near simultaneously acquired Landsat 7 Enhanced Thematic Mapper Plus (ETM+) and Earth Observing-1 Advanced Land Imager (ALI) data we assess the relative radiant responses over active lava flows from the Mt. Etna July/August 2001 flank eruption. By assessing the extent of saturation between the two instruments and using the dual-band method of extracting sub pixel thermal information, we show that the ALI represents an improvement over the ETM+ in the present ability to assess temperatures of hot active lava flows for a number of reasons. (1) The extra spectral channels provided by ALI compliment the current SWIR channels on ETM+ by providing a greater number of paired channel combinations for input into the dual-band method. Thus, dual-band temperature solutions can be determined for a greater range of lava flow types than previously possible using the two paired channel combinations available with the ETM+. (2) The ALI instrument is less susceptible than ETM+ to saturation within the SWIR, especially when using channels 5, 5p and 4p at wavelengths of 1.65, 1.25 and 0.87 μm respectively. (3) The greater radiometric sensitivity of the ALI 12 bit electronics coupled with a significantly higher signal to noise ratio aid in obtaining successful dual-band solutions.  相似文献