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1.
The Mantle Source for Olivine Nephelinite, Basanite, and Alkaline Olivine Basalt at Fort Selkirk, Yukon, Canada 总被引：2，自引：1，他引：1
Olivine nephelinite, basanite, and transitional alkaline basaltlavas of the Quaternary Fort Selkirk volcanic complex in thecentral Yukon represent three distinct alkaline magma serieswhich have evolved along diverging paths. They cannot be relatedby low-pressure crystal-liquid fractionation, and systematicisotopic differences make it difficult to derive them by variabledegrees of melting of a common mantle source. Field evidencerequires, however, that these three magma series are intimatelyrelated in time and space, and they share a number of anomalouschemical characteristics including low Ca/Na ratios with respectto the majority of terrestrial equivalents. When the effectsof differential olivine fractionation are ignored, the compositionalspectrum of the Fort Selkirk lavas approximates a binary mixingline between transitional alkaline basalt and olivine nephelinite.A population gap along this mixing line, located between thecompositions of the nephelinite and basanite lavas, coincideswith the compositions of amphibole and/or amphibole–garnet–clinopyroxeneassemblages observed in mantle xenoliths. This compositionalgap may represent a thermal divide separating two minimum-meltcompositions in a mantle source consisting of a lherzolite hostcut by amphibole–garnet–clinopyroxenite veins. Theolivine nephelinite endmember may have been derived by earlymelting in the amphibole–garnet–clinopyroxeniteveins, whereas the transitional alkaline basalt would representmore extensive melting of the host lherzolite. 相似文献
2.
Four volcanoes form Terceira, one of the islands of the Azores group; three contain both basaltic and peralkaline and one only peralkaline rocks. A recently active basaltic fissure zone trends NW-SE across the island.The rocks fall into the alkaline olivine basalt suite although some young basalts are of transitional affinity. The geochemistry shows two general basaltic series: 1) undersaturated, found in lavas of the oldest volcano and in some recent fissure zone basalts and hawaiites; 2) saturated, found in the younger basaltic lavas.Since the emergence of Terceira there has been a contemporaneity of basalt and salic peralkaline lavas. The younger rocks show a bimodal composition distribution, the most voluminous compositions being alkali olivine basalt and comendite with negligible volume in the benmoreite-trachyte range. Two processes appear viable for the derivation of voluminous oversaturated peralkaline rocks: 1) partial melting of upper mantle material giving small magma batches of contrasting composition or 2) fractionation from a transitional basaltic parental magma.Now at Department of Geology, Victoria University of Wellington, New Zealand. 相似文献
3.
The alkaline igneous centres of eastern Uganda comprise a youngerTertiary group represented by dissected volcanoes and an olderCretaceous (?) group composed entirely of equivalent intrusiveformations. Both the extrusive and the intrusive suites are characterizedby extreme silica undersaturation and richness in alkalis, especiallysoda; they largely conform to a nephelinite series and an ijolite-carbonatiteseries, respectively. From field, petrographic, and chemical data it is argued thatthe immediately parental magma was of nephelinite/melteigitecomposition. The courses of evolution of the volcanic and plutonicrocks followed odivergent trends, owing to differences in theirphysico-chemical environments. The volcanic series evolved towardsa phonolitic or trachytic residium, whereas the ijolite seriesmaintained silica undersaturation and tended towards final enrichmentin lime, alkalis, and volatiles, including carbon dioxide. Thefinal residuum from this course of evolution was a carbonatiteor alkali carbonatite. The evidence suggests that the felspar-bearing rocks (trachytes,phonolites, syenites, and nepheline syenites) have had a numberof different modes of origin. Apart from evolution in the volcanicseries of crystallization differentiation, they appear to haveformed by fenitization of Basement rocks and by felspathizationof felspathoidal rocks, such as ijolites. Extrusive equivalentsmay then have arisen by mobilization. 相似文献
4.
Kīlauea is the youngest of five basaltic shield volcanoes on the island of Hawai’i. It is located to the south‐east of the much larger Mauna Loa volcano, and rose above sea level about 100 ka ago. Kīlauea is one of the most monitored, and arguably the best understood volcanoes on Earth, providing scientists with a good understanding of its current eruption, in which magma rises from depth and is stored beneath its 4 × 3.2 km summit caldera in an underground reservoir. The reservoir is connected to a lava lake within a crater called Halema’uma’u, which is situated on the floor of the caldera. When magma drains from the summit area it travels in underground conduits and emerges on the flanks of the volcano at a rift zone, where it erupts through fissures. The magma is sometimes stored in other reservoirs along the way. This link between summit magma storage and fissure eruptions on the flanks has occurred thousands of times at many Hawai’ian volcanoes. The current eruptive episode is, however, a ‘once‐in‐a‐century’ show, because it is the first time since 1924 that fissure‐fed lava flow eruptions have been accompanied by significant explosive eruptions within Halema’uma’u Crater. This gives scientists a unique opportunity to use modern methods to understand exactly how such hazardous explosions happen at Kīlauea, a volcano that receives about 2 million visitors a year. 相似文献
5.
火山喷发是严重的地质灾害之一。全球各地都有火山分布 ,我国也有近千座火山。其中长白山火山、五大莲池火山和腾冲火山是我国最具潜在灾难性喷发危险的活火山。以长白山火山为例 ,阐述用建立火山信息系统的方法监测、预测、评估火山灾害 ,达到减灾、防灾的目的 相似文献
6.
7.
Zhifeng Wan Xianqing Wang Ye Lu Yuefeng Sun Bin Xia 《International Geology Review》2017,59(13):1723-1735
Mud volcanoes can provide important information about the underlying strata, hydrocarbon accumulation, and recent neotectonic movements in an area. The fluids erupting from mud volcanoes provide important information about their formation and evolution. The ion concentration and the hydrogen and oxygen isotopes of the fluids that were erupted from the three mud volcano groups, Baiyanggou, Aiqigou, and Dushanzi, and nearby rivers in the southern margin of the Junggar basin, northwestern China, are studied. The concentrations of Na and Cl in mud volcano fluids are clearly elevated, displayed as the Na-Cl type. The δD and δ18O values of the fluids are similar between the Baiyanggou and Dushanzi mud volcanoes, which are mainly from ancient sedimentary pore water. However, the Aiqigou mud volcano is depleted in dissolved Cl and shows lower δ18O values with mixed sources, including deep pore and local meteoric water. Two types of mud volcanoes are proposed in this study. One type is low-energy mud volcanoes with a low volume of fluid of deep origin on the hillcrest, which display as mud pool/pie/hole. The other type is high-energy mud volcanoes having mixed fluid origin in the valley and formed in the shape of a mud cone (dome). 相似文献
8.
Jeff Standish Dennis Geist Karen Harpp Mark D. Kurz 《Contributions to Mineralogy and Petrology》1998,133(1-2):136-148
Roca Redonda volcano is a mostly submarine shield volcano that rises nearly 3 km from the adjacent seafloor. Over twenty
lava flows and palagonite tuff are exposed in a 60 meter high oblong outcrop above sea level, and several other flows are
exposed in the shallow water surrounding the islet. Thick, slightly alkaline picritic flows form the base of the section.
Thinner picrites interbedded with sparsely porphyritic alkali-olivine basaltic pahoehoe toes characterize the upper section.
The subaerial section probably records the filling of a palagonite tuff cone with younger lavas. Numerous fumaroles that may
have a magmatic component are present in the shallow (<30 m) submarine zone and indicate that the volcano is probably still
active. Three lava types are exposed: the basal picrites with 19% > MgO > 14%, high-Mg basalts with MgO of about 9%, and low-Mg
basalts with MgO of about 6%. The Sr and Nd isotopic ratios of the three lava types are within analytical uncertainty. Olivine
compositions indicate that the picrites are basaltic liquids that have accumulated olivine whose composition is in equilibrium
with the host basaltic liquid. Apparently, basaltic magmas percolated through dunite and troctolite that had crystallized
from slightly older Roca Redonda basaltic magma. Lavas from Roca Redonda have enriched trace element contents and isotopic
ratios relative to nearby Wolf volcano, but they are quite similar to lavas from Cerro Azul and Ecuador volcanoes. The common
characteristic of these volcanoes is that they lie on the periphery of the archipelago and are in a stage of subaerial growth.
This suggests that Galápagos volcanoes may go through a juvenile alkaline stage before a mature tholeiitic stage, analogous
to the Loihi stage of Hawaiian volcanism. A low 3He/4He ratio in olivine from one of the picrites indicates a small contribution by the Galápagos mantle plume.
Received: 15 December 1997 / Accepted: 6 May 1998 相似文献
9.
In late Cretaceous time, subsilicic, alkalic magmas formed sills,laccoliths, plug-like bodies, small volcanoes, and a few dikesin Cretaceous sedimentary rocks of the Texas coastal plain alongan arcuate trend approximately coinciding with the buried Ouachitastructural belt. Transverse structural features apparently localizedthe igneous activity in two centers. In the larger center nearUvalde, Texas about half of the bodies are melilite-olivinenephelinite, a third olivine nephelinite and the remainder analcitephonolite, olivine basalt, and nepheline basanite, in orderof decreasing abundance. Basaltic and nephelinitic magmas were the primary magmas fromwhich all igneous rocks of the province were derived. Removalof olivine gave rise to a small range in chemical compositionof the basaltic rocks, but not gradation toward silica undersaturation.Nephelinitic magmas with compositions near that at which normativecalcium orthosilicate appears differentiated along two trendsto form melilite-olivine nephelinite as one end product andthrough nepheline basanite to analcite phonolite as the other.These two trends arose independently, their courses being determinedby the composition of the primary nephelinitic magma and theplane Fo-Di-Ne which has no piercing point at low pressure. 相似文献
10.
T. F. D. Nielsen I. P. Solovova I. V. Veksler 《Contributions to Mineralogy and Petrology》1997,126(4):331-344
Perovskite and melilite crystals from melilitolites of the ultramafic alkaline Gardiner complex (East Greenland) contain
crystallised melt inclusions derived from: (1) melilitite; (2) low-alkali carbonatite; (3) natrocarbonatite. The melilitite
inclusion (1) homogenisation temperature of 1060 °C is similar to liquidus temperatures of experimentally investigated natural
melilitites. The compositions are peralkaline, low in MgO (ca.␣5 wt%), Ni and Cr, and they are low-pressure fractionates of
more magnesian larnite-normative ultramafic lamprophyre-type melts of primary mantle origin. Low-alkali carbonatite compositions
(2) homogenise at 1060–1030 °C and are compositionally similar to immiscible calcite carbonatite dykes derived from the melilitolite
magma. Natrocarbonatite inclusions (3) homogenise between 1030 and 900 °C and are compositionally similar to natrocarbonatite
lava from Oldoinyo Lengai. Nephelinitic to phonolitic dykes which are related to the calcite carbonatite dykes, are very Zr-rich
and agpaitic (molecular Na2O + K2O/Al2O3 > 1.2) and resemble nephelinites of Oldoinyo Lengai. The petrographic, geochemical and temporal relationships indicate unmixing
of carbonatite compositions (ca. 10% alkalies) from evolving melilitite melt and continued fractionation of melilitite to
nephelinite. It is suggested that the natrocarbonatite compositions represent degassed supercritical high temperature fluid
formed in a cooling body of strongly larnite-normative nephelinite or evolved melilitite. The Gardiner complex and similar
melilitolite and carbonatite-bearing ultramafic alkaline complexes are believed to represent subvolcanic complexes formed
beneath volcanoes comparable to Oldoinyo Lengai and that the suggested origin of natrocarbonatite may be applied to natrocarbonatites
of Oldoinyo Lengai.
Received: 18 January 1996 / Accepted: 2 September 1996 相似文献
11.
The intraplate Baegdusan (Changbai) and Ulleung volcanoes located on the border of China, North Korea, and East/Japan Sea, respectively, have been explained by appeals to both hotspots and asthenospheric mantle upwelling (wet plume) caused by the stagnant Pacific plate. To understand the origin of the Baegdusan and Ulleung volcanism, we performed geochemical analyses on the tephra deposits in the East/Japan Sea basins originating from the Baegdusan and Ulleung volcanoes. The volcanic glass in the tephra from the Baegdusan and Ulleung volcanoes ranged from alkaline trachyte to peralkaline rhyolite and from phonolite to trachyte, respectively. The tephra from the two intraplate volcanoes showed highly enriched incompatible elements, such as Tb, Nb, Hf, and Ta, distinct from those of the ordinary arc volcanoes of the Japanese islands. The straddle distribution of the Th/Yb and Ta/Yb ratios of the tephra deposits from the Baegdusan volcano may originate from the alkali basaltic magma resulting from mixing between the wet plume from the stagnant Pacific plate in the transition zone and the overlying shallow asthenospheric mantle. In contrast, the deposits from the Ulleung volcano show a minor contribution of the stagnant slab to the basaltic magma, implying either partial melting of a more enriched mantle, smaller degrees of partial melting of a garnet-bearing mantle source, or a combination of both processes as the magma genesis. Our study indicated that the Baegdusan and Ulleung volcanoes have different magma sources and evolutionary histories. 相似文献
12.
Principe is one of the volcanic centres comprising the Cameroun line in West Africa. The volcanic rocks can be divided into two stratigraphic units:
- Younger lava series — basanite and nephelinite overlying.
- Older lava series — transitional to mildly alkaline basalt and hawaiite.
- Phonolites which evolved by low pressure crystal fractionation of the younger lava series basanitic magma, and
- Tristanite — trachyte — trachyphonolite suite which may have evolved by high pressure crystal fractionation of the older lava series magma.
13.
活火山是指1万年来有过喷发历史的全新世火山。火山的高分辨年代学对火山灾害评估和火山分类具有重要意义。对于缺乏历史记载的全新世火山,直接对火山岩进行同位素定年很困难。本文利用具有高时间分辨率的镭-钍-铀非平衡确定中国东部年轻火山的年龄。根据镭-钍-铀同位素,海南岛的马鞍岭和雷虎岭是全新世火山(马鞍岭:4.3ka;雷虎岭:4.7ka);镜泊湖火山(4.9ka)也是全新世火山;龙岗火山存在晚更新世和全新世活动(7.0ka,15.0ka);大兴安岭阿尔山和诺敏河Ra/Th非平衡消失但~(230)Th/~(238)U非平衡显著,属于晚更新世喷发(阿尔山:63ka;诺敏河:71ka)。海南岛的马鞍岭火山、雷虎岭火山和东北地区的龙岗火山、镜泊湖火山,是4座活火山。至于东北地区的阿尔山和诺敏河火山是否是活火山,有待测试更多样品的Ra/Th同位素。五大连池老黑山和火烧山有历史喷发记录,这与它们都存在显著Ra/Th非平衡一致。五大连池老黑山和火烧山的岩浆滞留年龄分别小于4.2ka和3.2ka,岩浆上升速率 18～23m/y。 相似文献
14.
《International Geology Review》2012,54(11):1642-1646
As the composition of volcanic rocks changes from intermediate to acidic, their concentrations of radioactive elements increase, in two out of the three volcanoes examined here. The reverse is true of the third volcano. Significant enrichment of uranium develops only in the latest portions of the melt, but thorium is enriched gradually and smoothly. U-Th and SiO2-K correlations are found to be regionally obscure. 相似文献
15.
XU Wang ZHENG Guodong MA Xiangxian Danielle FORTIN David R. HILTON LIANG Shouyun CHEN Zhi HU Guoyi 《《地质学报》英文版》2018,92(6):2201-2213
Organic-inorganic interactions occurring in petroleum-related mud volcanoes can help predict the chemical processes that are responsible for methane emissions to the atmosphere. Seven samples of mud breccia directly ejected from one crater were collected in the Dushanzi mud volcano, along with one argillite sample of the original reddish host rocks distal from the crater, for comparison purposes. The mineral and chemical compositions as well as iron species of all samples were determined using XRD, XRF and M?ssbauer spectroscopy, respectively. The results indicate that a series of marked reactions occurred in the mud volcano systems, more specifically in the mud breccia when compared to the original rocks. Changes mainly included: (1) some conversion of clay minerals from smectite into chlorite and illite, and the precipitation of secondary carbonate minerals such as calcite and siderite; (2) silicon depletion and significant elemental enrichment of iron, manganese, magnesium, calcium and phosphorus; and (3) transformation of iron from ferric species in hematite and smectite into ferrous species in siderite, chlorite and illite. These geochemical reactions likely induced the color changes of the original reddish Neogene argillite to the gray or black mud breccia, as a result of reduction of elements and/or alteration of minerals associated with the oxidation of hydrocarbons. Our results also suggest that greenhouse gases emitted from the mud volcanoes are lowered through a series of methane oxidation reactions and carbon fixation (i.e., through carbonate precipitation). 相似文献
16.
中国上地幔角闪石及其成因意义 总被引：12，自引：2，他引：12
我国土地幔成因角闪石以高铝(一般>2.0)为特征,以TiO_2、Cr_2O_3含量差异相区别,划分为韭闪石和钛角闪石两大类。韭闪石又有四种不同的成因类型:贫铬、钛型(Cr_2O_3=0.15％,TiO_2=0.07％),富铬型(Cr_2O_3=2.18％),富钛型(TiO_2=3.14％)和富铬、钛型(Cr_2O_3=2.59％,TiO_2=3.16％)。除贫铬、钛型韭闪石发现于苏北-胶南高压变质岩石中外,其它三种韭闪石(产于大陆区)和钛角闪石(产于台湾西部)均来自各种地幔橄榄岩、辉石岩及新生代玄武岩中。不管它们的产出方式如何(填隙、嵌晶、巨晶和包裹体子矿物),都直接或间接与地幔流体的交代作用有关,但各具成因之特点。 相似文献
17.
云南腾冲黑空山、马鞍山和打莺山火山粗安岩显微结构特征及其火山学意义 总被引：1，自引：1，他引：0
火山喷发物记录了岩浆的整个活动历史,对火山喷发物的研究可以了解大量的岩浆活动特征信息。本文对腾冲火山区的三座全新世火山——黑空山、马鞍山和打莺山火山熔岩进行了详细的研究,包括熔岩和斑晶的成分、显微结构特征和斑晶的晶体大小分布(CSD)分析。研究发现,黑空山、马鞍山和打莺山火山熔岩以粗安岩为主,三座火山粗安岩中的斑晶成分范围接近,但它们的显微结构特征具有一定的差异,反映了不同的岩浆环境,推测来自不同的岩浆囊。黑空山粗安岩中斜长石斑晶的CSD曲线呈微上凹形,反映了小规模的岩浆混合作用。马鞍山和打莺山粗安岩的微斑晶CSD曲线呈很好的线性关系,说明微斑晶形成时的环境相对稳定,推测这些微斑晶是在岩浆上升过程中,停留在地壳的某处并形成一个小型的岩浆囊后受围岩的冷却作用形成。根据以上的分析,认为腾冲火山区下在横向和纵向上均至少存在两个岩浆囊。 相似文献
18.
Rodriguez Fabian Toulkeridis Theofilos Sandoval Washington Padilla Oswaldo Mato Fernando 《Natural Hazards》2017,85(1):605-618
Natural Hazards - The Cotopaxi volcano in north-central Ecuador is one of the most dangerous volcanoes of the world due to its ability to generate far-reaching lahars, which are able to destroy... 相似文献
19.
近年来的最新调研成果表明，叶家山破火山群由７个破火山和１个层状火山（喷发中心）所组成，各火山机构相互叠置，与卫星ＴＭ遥感影象解译成果相吻合。火山作用经历了６个阶段的火山喷发，周围发育有环状、放射状断裂和岩脉、岩墙，是省内较为典型的破火山群机构，是寻找火山岩非金属矿的有利部位。火山活动的构造环境为拉张环境，物质来源于地壳。 相似文献