Crustal structure of the Ordovician Macquarie Arc,Eastern Lachlan Orogen,based on seismic‐reflection profiling     

R. A. Glen  R. J. Korsch  N. G. Direen  L. E. A. Jones  D. W. Johnstone  K. C. Lawrie 《Australian Journal of Earth Sciences》2013,60(2):323-348

In the Eastern Lachlan Orogen, the mineralised Molong and Junee‐Narromine Volcanic Belts are two structural belts that once formed part of the Ordovician Macquarie Arc, but are now separated by younger Silurian‐Devonian strata as well as by Ordovician quartz‐rich turbidites. Interpretation of deep seismic reflection and refraction data across and along these belts provides answers to some of the key questions in understanding the evolution of the Eastern Lachlan Orogen—the relationship between coeval Ordovician volcanics and quartz‐rich turbidites, and the relationship between separate belts of Ordovician volcanics and the intervening strata. In particular, the data provide evidence for major thrust juxtaposition of the arc rocks and Ordovician quartz‐rich turbidites, with Wagga Belt rocks thrust eastward over the arc rocks of the Junee‐Narromine Volcanic Belt, and the Adaminaby Group thrust north over arc rocks in the southern part of the Molong Volcanic Belt. The seismic data also provide evidence for regional contraction, especially for crustal‐scale deformation in the western part of the Junee‐Narromine Volcanic Belt. The data further suggest that this belt and the Ordovician quartz‐rich turbidites to the east (Kirribilli Formation) were together thrust over ?Cambrian‐Ordovician rocks of the Jindalee Group and associated rocks along west‐dipping inferred faults that belong to a set that characterises the middle crust of the Eastern Lachlan Orogen. The Macquarie Arc was subsequently rifted apart in the Silurian‐Devonian, with Ordovician volcanics preserved under the younger troughs and shelves (e.g. Hill End Trough). The Molong Volcanic Belt, in particular, was reworked by major down‐to‐the‐east normal faults that were thrust‐reactivated with younger‐on‐older geometries in the late Early ‐ Middle Devonian and again in the Carboniferous.  相似文献   

论五大连池火山岩浆演化   总被引：14，自引：3，他引：14  

夏林圻 《岩石学报》1990,6(1):13-29,T001

五大连池第四纪火山事件为同源多期喷发。据矿物中岩浆包裹体温压地球化学研究,五大连池火山岩浆为一种含水2～4％(wt.％)的富钾玄武质岩浆,浅部结晶(压力<100MPa)。火山演化历史中,从中更新世早期至近代(1719～1721年)喷发,岩浆的MgO、CaO,FeO含量、CO_2浓度,首晶相橄榄石的结晶温度和压力不断增高;SiO_2、TiO_2、K_2O含量、氧逸度和H_2O、CH_4、H_2S的浓度趋于下降,Cl、P、F的浓度也呈现有规律变化。这些特点是岩浆房内岩浆分层作用的反映,火山岩浆的喷发序次与岩浆房内的分层次序相反。火山岩浆的低S含量(<600ppm)及Sr、O、Nd、Pb等同位素研究数据表明,它们源自上地慢,且基本未受地壳物质混染。  相似文献   

海南岛石碌群中双峰火山岩Sm—Nd同位素特征兼论石碌铁矿成矿背景   总被引：9，自引：1，他引：9  

方中  赵建新 《地球化学》1993,(4):326-336

对海南岛石碌群第６层及其相当层位中海相双峰火山岩Ｓｍ－Ｎｄ同位素，微量和稀土元素的研究表明，位于火山岩带西段军营和石碌的细碧岩具有Ｎ－ＭＯＲＢ特征，在中段和东段芙蓉田和兰洋的变拉斑玄武岩具有Ｅ－ＭＯＲＢ和ＩＲＴ（初始裂谷拉斑玄武岩）特征。石碌群的玄武岩和石碌Ｆｅ－Ｃｏ－Ｃｕ矿床分别与红海裂谷中南段的新生代玄武岩和Ａｔｈａｎｔｉｓ Ⅱ ＤｅｅＰ多金属矿床有许多相同之处。双峰火山岩的另一端元为壳源型石  相似文献   

华北板块北缘中段含铁变质岩系的时代和构造环境初探   总被引：15，自引：1，他引：15  

徐备  陈斌 《地质论评》1994,40(4):307-311

内蒙北部苏尼特右旗以北二道井、哈拉干和红格尔地区的含铁变质岩系中变质基性火山岩Ｓｍ－Ｎｄ全岩等时线年龄为１５１１±７６Ｍａ，这表明该岩系属中元古代而不是以往推测的早古生代，等时线的εＮｄ（ｔ）值为＋６．３±１．７，属亏损型地幔源区岩相学分析表明它形成于规模不大，具中等水深和较弱水动力条件的较封闭海域。据上述特征推测，华北板块北缘中曾存在中元古代初动型火山陆缘。  相似文献   

福建省东部火山岩地区银矿成矿地质条件及找矿方向     

朱熙道  叶允钧 《福建地质》1994,13(2):83-98

通过对该区银矿床地质特征、成矿地质条件和成矿规律的研究，将区内银矿按成因、成矿作用、矿床地质特征等划分为三类六型。指出了火山－次火山热液型银矿是本区银矿的重要类型。总结了银矿的找矿标志，提出了本区银矿的主攻类型和主攻地区。  相似文献   

福建上杭盆地中生代火山岩首次发现开来石     

张之Shen  杨玲雅 《福建地质》1994,13(3):188-192

在１：５万上杭幅重砂野外调查中，在上杭盆地中生代火山岩河系中首次发现开来石。经中国地质大学Ｘ光单晶粉晶分析、桂林有色金属地质研究所电子探针成分分析结果，均与国外有关文献中的开来石相一致。是我省首次发现的含砷稀土矿物。它为在该区中生代火山岩中寻找稀土资源提供新的线索。此外该矿物常与黄金、辰砂等相伴生，笔者初步认为可以根据伴生金的相关元素Ａｓ开来石组合寻找金，是本区很值得注意的一种寻找金的方法。  相似文献   

Bifurcation of volcanic plumes in a crosswind     

Gerald G. J. Ernst  John P. Davis  R. Stephen J. Sparks 《Bulletin of Volcanology》1994,56(3):159-169

Bent-over buoyant jets distorted by a crosscurrent develop a vortex pair structure and can bifurcate to produce two distinct lobes which diverge from one another downwind. The region downwind of the source between the lobes has relatively low proportions of discharged fluid. Factors invoked by previous workers to cause or enhance bifurcation include buoyancy, release of latent heat at the plume edge by evaporating water droplets, geometry and orientation of the source, and the encounter with a density interface on the rising path of the plume. We suggest that the pressure distribution around the vortex pair of a rising plume may initially trigger bifurcation. We also report new experimental observations confirming that bifurcation becomes stronger for stronger bent-over plumes, identifying that bifurcation can also occur for straight-edged plumes but gradually disappears for stronger plumes which form a gravity current at their final level and spread for a significant distance against the current. Observations from satellites and the ground are reviewed and confirm that volcanic plumes can show bifurcation and a large range of bifurcation angles. Many of the bifurcating plumes spread out at the tropopause level and suggest the tropopause may act on the plumes as a density interface enhancing bifurcation. Even for quite moderate bifurcation angles, the two plume lobes become rapidly separated downwind by distances of tens of kilometers. Such bifurcating plumes drifting apart can only result in bilobate tephra fall deposits. The tephra fall deposit from the 16 km elevation, SE spreading, bifurcating volcanic plume erupted on 15 May 1981 from Mt Pagan was sampled by previous workers and clearly displayed bilobate characteristics. Examples of bilobate tephra fall deposits are reviewed and their origin briefly discussed. Bilobate deposits are common and may result from many causes. Plume bifurcation should be considered one of the possible mechanisms which can account for come examples of bilobate tephra fall deposits.  相似文献   

Seismic activity related to the 1991 eruption of Colima Volcano,Mexico     

Francisco Núñez-Cornú  F. Alejandro Nava  Servando De la Cruz-Reyna  Zenón Jiménez  Carmen Valencia  Rosalía García-Arthur 《Bulletin of Volcanology》1994,56(3):228-237

Ten years after the last effusive eruption and at least 15 years of seismic quiescence, volcanic seismic activity started at Colima volcano on 14 February 1991, with a seismic crisis which reached counts of more than 100 per day and showed a diversity of earthquake types. Four other distinct seismic crises followed, before a mild effusive eruption in April 1991. The second crisis preceded the extrusion of an andesitic scoriaceous lava lobe, first reported on 1 March; during this crisis an interesting temporary concentration of seismic foci below the crater was observed shortly before the extrusion was detected. The third crisis was constituted by shallow seismicity, featuring possible mild degassing explosion-induced activity in the form of hiccups (episodes of simple wavelets that repeat with diminishing amplitude), and accompanied by increased fumarolic activity. The growth of the new lava dome was accompanied by changing seismicity. On 16 April during the fifth crisis which consisted of some relatively large, shallow, volcanic earthquakes and numerous avalanches of older dome material, part of the newly extruded dome, which had grown towards the edge of the old dome, collapsed, producing the largest avalanches and ash flows. Afterwards, block lava began to flow slowly along the SW flank of the volcano, generating frequent small incandescent avalanches. The seismicity associated with the stages of this eruptive activity shows some interesting features: most earthquake foci were located north of the summit, some of them relatively deep (7–11 km below the summit level), underneath the saddle between the Colima and the older Nevado volcanoes. An apparently seismic quiet region appears between 4 and 7 km below the summit level. In June, harmonic tremors were detected for the first time, but no changes in the eruptive activity could be correlated with them. After June, the seismicity decreasing trend was established, and the effusive activity stopped on September 1991.  相似文献   

Is there a correlation between larger local earthquakes and the end of eruptions at Mount Etna volcano, Sicily?     

Stefano Gresta  Warner Marzocchi  Francesco Mulargia 《Geophysical Journal International》1994,116(1):230-232

  相似文献   

闽北早古生代岛弧火山岩的岩石地球化学特征   总被引：1，自引：0，他引：1  

陈汉林  曾华生 《矿物学报》1994,14(2):186-194

作者系统地研究了福建政和早古生代岛弧火山岩的岩石地球化学特征。研究表明该火山岩是以岛弧拉斑玄武岩-钙碱性火山岩组合为特征的岛弧火山岩系列，并具有从拉斑系列向钙碱性系列演化的特征；该火山岩源于亏损地幔，并且受到一定的陆壳物质混染，基性的拉斑玄武质系列受到陆壳物质混染较少，而中性钙碱性系列则受到较大程度混染。  相似文献