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1.
AbstractWe compared the disintegration processes and mineralogic and chemical evolution pathways of two Quaternary basalts at Bakrit and Ifrane, weathered in the same physiographic and hydrologic conditions, but differing in texture according to the quantity of glass present. At Bakrit, quite abundant glass favoured the formation of a microfissure network throughout the rock and its disintegration without any distinct weathering front. As a result, basaltic sand with polymineral grains and a clayey-silty matrix were produced. At Ifrane, weathering of a glass-poor basalt produced only a clayey-silty saprolite. In glass-rich basalts, secondary minerals formed in microfissures and were 2/1 clay-mineral rich. In glass-poor basalts, secondary minerals formed mainly within primary minerals and were 1/1 clay-mineral rich. Because glass could be easily dissolved, it protected the minerals of close chemical composition, especially the plagioclases. The order of basalt-mineral weathering (olivine, labrador, augite, Fe-Ti oxides) was modified when glass was abundant (glass, olivine, augite, labrador, Fe-Ti oxides). © Elsevier, Paris 相似文献
2.
本文对天池火山玄武岩盾,粗面质-碱流质层状锥体以及顶部的粗面质-碱流质碎屑岩类及熔岩的岩石矿物成分做了系统分析,发现在玄武岩类中的主要矿物组合为斜长石、富钙辉石以及富镁橄榄石,而粗面岩-碱流岩类的主要矿物组合为碱性长石、富铁的辉石及橄榄石,并开始出现石英、独居石以及大量的铁钛氧化物,符合结晶分异的演化趋势。同时在玄武岩类及粗面-碱流岩类中均存在不平衡矿物,再结合矿物环带的成分变化、矿物的熔蚀现象及不同特征的岩石条带等,认为天池火山在黑石沟玄武岩、第一、三造锥阶段粗面岩以及千年大喷发的浮岩中均存在岩浆混合作用。根据岩石学及年代学等特征,认为不同时期的玄武质岩浆来自同一地幔源区,经不同程度的结晶分异作用形成,前造锥阶段及造锥阶段的岩石由不同阶段的玄武岩演化而来,全新世的碱流岩类则由造锥阶段粗面岩类演化而来。 相似文献
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Quaternary alkaline basalts of Middle Atlas, are weathered into spheroidal volumes organized into weathering cover. In the profile studied, the study of transformations from a fresh core basalt to the most weathered rinds, has been analysed using BESI images (backscattred electron image analysis). A part from the microscopic analysis of each weatherted basalt, proportions of primary minerals, clays and pore space has been quantified in different stages of weathering. Indeed, in fresh core basalt, weathering is characterized by a first dissolution of the glass, followed by feldspar transformations in twinning plans, cleavages and in micropores inherited from the magmatic and cristallographic history of the rock.
In most basaltic weathered rinds, pore spaces given by the dissolution of the glass, were filled by a mixture of clays and iron products. In these samples, feldspars are completely dissolved giving important porosity occupied by small quantity of halloysite and kaolinite. The olivine and pyroxene transformations are accompanied by weak pore space formation. At the bottom of the soil, this porosity decreases in response to filling by later secondary products which come from the upper part of the soil by weathering solutions. 相似文献
5.
Allan H. Treiman 《Chemie der Erde / Geochemistry》2005,65(3):203-270
The seven nakhlite meteorites are augite-rich igneous rocks that formed in flows or shallow intrusions of basaltic magma on Mars. They consist of euhedral to subhedral crystals of augite and olivine (to 1 cm long) in fine-grained mesostases. The augite crystals have homogeneous cores of Mg′=63% and rims that are normally zoned to iron enrichment. The core-rim zoning is cut by iron-enriched zones along fractures and is replaced locally by ferroan low-Ca pyroxene. The core compositions of the olivines vary inversely with the steepness of their rim zoning - sharp rim zoning goes with the most magnesian cores (Mg′=42%), homogeneous olivines are the most ferroan. The olivine and augite crystals contain multiphase inclusions representing trapped magma. Among the olivine and augite crystals is mesostasis, composed principally of plagioclase and/or glass, with euhedra of titanomagnetite and many minor minerals. Olivine and mesostasis glass are partially replaced by veinlets and patches of iddingsite, a mixture of smectite clays, iron oxy-hydroxides and carbonate minerals. In the mesostasis are rare patches of a salt alteration assemblage: halite, siderite, and anhydrite/gypsum. The nakhlites are little shocked, but have been affected chemically and biologically by their residence on Earth.Differences among the chemical compositions of the nakhlites can be ascribed mostly to different proportions of augite, olivine, and mesostasis. Compared to common basalts, they are rich in Ca, strongly depleted in Al, and enriched in magmaphile (incompatible) elements, including the LREE. Nakhlites contain little pre-terrestrial organic matter. Oxygen isotope ratios are not terrestrial, and are different in anhydrous silicates and in iddingsite. The alteration assemblages all have heavy oxygen and heavy carbon, while D/H values are extreme and scattered. Igneous sulfur had a solar-system isotopic ratio, but in most minerals was altered to higher and lower values. High precision analyses show mass-independent fractionations of S isotopes. Nitrogen and noble gases are complex and represent three components: two mantle sources (Chas-E and Chas-S), and fractionated Martian atmosphere.The nakhlites are igneous cumulate rocks, formed from basaltic magma at ∼1.3 Ga, containing excess crystals over what would form from pure magma. After accumulation of their augite and olivine crystals, they were affected (to various degrees) by crystallization of the magma, element diffusion among minerals and magma, chemical reactions among minerals and magma, magma movement among the crystals, and post-igneous chemical equilibration. The extent of these modifications varies, from least to greatest, in the order: MIL03346, NWA817, Y000593, Nakhla=Governador Valadares, Lafayette, and NWA998.Chemical, isotopic, and chronologic data confirm that the nakhlites formed on Mars, most likely in thick lava flows or shallow intrusions. Their crystallization ages, referenced to crater count chronologies for Mars, suggest that the nakhlites formed on the large volcanic constructs of Tharsis, Elysium, or Syrtis Major. The nakhlites were suffused with liquid water, probably at ∼620 ma. This water dissolved olivine and mesostasis glass, and deposited iddingsite and salt minerals in their places. The nakhlites were ejected from Mars at ∼10.75 Ma by an asteroid impact and fell to Earth within the last 10,000 years.Although the nakhlites are enriched in incompatible elements, their source mantle was strongly depleted. This depletion event was ancient, as the nakhlites’ source mantle was fractionated while short-lived radionuclides (e.g., ) were still active. This differentiation event may have been core formation coupled with a magma ocean, as is inferred for the moon. 相似文献
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One-atmosphere, melting experiments, controlled at the fayalite-magnetite-quartz oxygen buffer, on mildly alkalic and transitional basalts from Iceland show that these begin to crystallize Fe-Ti oxide minerals (magnetite and/or ilmenite) at 1105±5°C, apparently independently of bulk composition and the order of silicate and oxide mineral crystallization. Most samples crystalline plagioclase and olivine as the first two crystalline phases, augite as the third phase, and an Fe-Ti oxide mineral as the fourth phase. The main effects of Fe-Ti oxide crystallization are a marked decrease in FeO and TiO2 in the liquid, and a notable increase in SiO2 and Al2O3, and the minor oxides K2O and P2O5, with decreasing temperature. The most silicic glasses are compositionally mugearitic and shoshonitic basaltic andesites. Because the smallest amount of glass that could be analyzed with the microprobe represents 20–55 percent liquid remaining, it can be expected that more silicic liquids will occur at lower temperatures. On normative, pseudoternary projections, the general effect of Fe-Ti oxide crystallization for mildly alkalic and transitional basalts is a marked increase in normative quartz. This is caused by a strong systematic convergence, with the appearance of Fe-Ti oxides, of the bulk solid precipitates toward the liquid compositions, as projected on the triangle plagioclase-diopside-olivine. For alkalic basalts, the bulk solid precipitate shows an increase in normative diopside with falling temperature and Fe-Ti oxide crystallization. This causes the liquids to move toward decreasing normative diopside and relatively little variation in nepheline. The experimental observations imply that mildly alkalic and transitional magmas, without stabilizing a Fe-Ti oxide mineral, will not evolve toward early silica saturation. 相似文献
8.
The behaviour of Li and Mg isotopes during primary phase dissolution and secondary mineral formation in basalt 总被引:1,自引:0,他引:1
Josh Wimpenny Sigurður R. Gíslason Abdelmouhcine Gannoun Philip A.E. Pogge Von Strandmann 《Geochimica et cosmochimica acta》2010,74(18):5259-6026
This study presents lithium (Li) and magnesium (Mg) isotope data from experiments designed to assess the effects of dissolution of primary phases and the formation of secondary minerals during the weathering of basalt. Basalt glass and olivine dissolution experiments were performed in mixed through-flow reactors under controlled equilibrium conditions, at low pH (2-4) in order to keep solutions undersaturated (i.e. far-from equilibrium) and inhibit the formation of secondary minerals. Combined dissolution-precipitation experiments were performed at high pH (10 and 11) increasing the saturation state of the solutions (moving the system closer to equilibrium) and thereby promoting the formation of secondary minerals.At conditions far from equilibrium saturation state modelling and solution stoichiometry suggest that little secondary mineral formation has occurred. This is supported by the similarity of the dissolution rates of basalt glass and olivine obtained here compared to those of previous experiments. The δ7Li isotope composition of the experimental solution is indistinguishable from that of the initial basalt glass or olivine indicating that little fractionation has occurred. In contrast, the same experimental solutions have light Mg isotope compositions relative to the primary phases, and the solution becomes progressively lighter with time. In the absence of any evidence for secondary mineral formation the most likely explanation for these light Mg isotope compositions is that there has been preferential loss of light Mg during primary phase dissolution.For the experiments undertaken at close to equilibrium conditions the results of saturation state modelling and changes in solution chemistry suggest that secondary mineral formation has occurred. X-ray diffraction (XRD) measurements of the reacted mineral products from these experiments confirm that the principal secondary phase that has formed is chrysotile. Lithium isotope ratios of the experimental fluid become increasingly heavy with time, consistent with previous experimental work and natural data indicating that 6Li is preferentially incorporated into secondary minerals, leaving the solution enriched in 7Li. The behaviour of Mg isotopes is different from that anticipated or observed in natural systems. Similar to the far from equilibrium experiments initially light Mg is lost during olivine dissolution, but with time the δ26Mg value of the solution becomes increasingly heavy. This suggests either preferential loss of light, and then heavy Mg from olivine, or that the secondary phase preferentially incorporates light Mg from solution. Assuming that the secondary phase is chrysotile, a Mg-silicate, the sense of Mg fractionation is opposite to that previously associated with silicate soils and implies that the fractionation of Mg isotopes during silicate precipitation may be mineral specific. If secondary silicates do preferentially remove light Mg from solution then this could be a possible mechanism for the relatively heavy δ26Mg value of seawater. This study highlights the utility of experimental studies to quantify the effects of natural weathering reactions on the Li and Mg geochemical cycles. 相似文献
9.
The ocellar lamprophyre dyke (ENE-WSW) is recorded at Wadi Nugrus, Eastern Desert, Egypt. It cuts porphyritic biotite granites
and varies in thickness from 0.5 to 1.5 m and up to 3 km in length. The lamprophyre dyke has been altered, and it is characterized
by porphyritic and panidiomorphic textures with plagioclase, olivine, and augite constituting the porphyritic phase in a fine
groundmass of the same composition. Rutile, titanite, apatite, fluorite, graphite, calcite, allanite, autunite and Fe-Ti oxides
are accessory minerals. Kaolinite, chlorite and epidote are secondary minerals. Carbonitization and hematitization are common.
Rounded to sub-rounded porphyritic and zoned ocelli with radiate or brush-like shapes are generally common and represent physical
traps for mineralization. The ocellar features are interpreted to represent the late stage of magmatic segregation or magmatic
crystallization involving two immiscible magmatic liquids. 相似文献
10.
Dimitrios Xirouchakis David S. DraperCraig S. Schwandt Antonio Lanzirotti 《Geochimica et cosmochimica acta》2002,66(10):1867-1880
The texture of Los Angeles (stone 1) is dominated by relatively large (0.5−2.0 mm) anhedral to subhedral grains of pyroxene, and generally subhedral to euhedral shocked plagioclase feldspar (maskelynite). Minor phases include subhedral titanomagnetite and ilmenite, Fe-rich olivine, olivine+augite-dominated symplectites [some of which include a Si-rich phase and some which do not], pyrrhotite, phosphate(s), and an impact shock-related alkali- and silica-rich glass closely associated with anhedral to euhedral silica grains. Observations and model calculations indicate that the initial crystallization of Mg-rich pigeonitic pyroxenes at ≤1150 °C, probably concomitantly with plagioclase, was followed by pigeonitic and augitic compositions between 1100 and 1050 °C whereas between 1050 and 920 to 905 °C pyroxene of single composition crystallized. Below 920 to 905 °C, single composition Fe-rich clinopyroxene exsolved to augite and pigeonite. Initial appearance of titanomagnetite probably occurred near 990 °C and FMQ-1.5 whereas at and below 990 °C and ≥FMQ-1.5 titanomagnetite and single composition Fe-rich clinopyroxene may have started to react, producing ilmenite and olivine. However, judging from the most common titanomagnetite compositions, we infer that most of this reaction likely occurred between 950 and 900 °C at FMQ-1.0±0.2 and nearly simultaneously with pyroxene exsolution, thus producing assemblages of pigeonite, titanomagnetite, olivine, ilmenite, and augite. We deem this reaction as the most plausible explanation for the formation of the olivine+augite-dominated symplectites in Los Angeles. But we cannot preclude possible contributions to the symplectites from the shock-related alkali- and silica-rich glass or shocked plagioclase, and the breakdown of Fe-rich pigeonite compositions to olivine+augite+silica below 900 °C. Reactions between Fe-Ti oxides and silicate minerals in Los Angeles and other similar basaltic Martian meteorites can control the T-fO2 equilibration path during cooling, which may better explain the relative differences in fO2 among the basaltic Martian meteorites. 相似文献
11.
四川省峨边县玄武岩矿资源丰富,但尚无开发利用纤维用玄武岩的矿山。从玄武岩的矿石组构、化学成分和玄武岩拉丝性能判别指标3个方面开展纤维用玄武岩评价工作。研究结果显示:研究区致密块状玄武岩和杏仁状玄武岩多属拉斑系列与碱性系列的过渡型岩石,玻基玄武岩均为碱性系列;拉斑玄武岩系列矿石的化学成分具有SiO2含量较高、(K2O+Na2O)和TiO2含量较低、FeO/MgO值较大的特征;区内致密块状玄武岩适合连续玄武岩纤维生产,而杏仁状玄武岩的杏仁中含有石英和方解石等次矿物,玻基玄武岩具有火山玻璃成分含量高、杏仁状构造及酸度系数过高等特征,均不宜作为生产玄武岩纤维的原料。研究区玄武岩矿具备纤维用玄武岩资源储备地的潜力,建议采用综合开发的方式利用玄武岩矿资源。 相似文献
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13.
《Gondwana Research》2001,4(3):427-436
The ‘Three Phenocryst Basalts’ (TPB) from Pavagadh hill constitute one of the most primitive basalts in Deccan traps. Electron microprobe analyses of phenocryst minerals from the TPB reveal that the Fo % of olivine varies from 89 to 68, the clinopyroxene grains are diopside/salite or augite and the Cr# [Cr/(Cr+Al)] in spinel is about 0.65. The An content of feldspar varies from 63 to 67. The mineral chemical data allow us to infer that olivine and spinel crystallized early, and when olivine attained Fo76–73%, the crystallization of clinopyroxene was initiated. Plagioclase crystallization occurred at the late stage. It is indicated that the source region of the TPB may possibly be undepleted mantle (lherzolite zone) at about 85 km depth and 27 kbar pressure, where Cr# of spinel is about 0.47. 相似文献
14.
The Late-Proterozoic Bjerkreim-Sokndal Layered Intrusion (BKSK) consists of andesine anorthosite, leuconorite, troctolite, norite, gabbronorite, jotunite, mangerite, quartz mangerite and charnockite. The sequence of appearance of cumulus minerals and their compositions suggest a parent magma that was evolved, had plagioclase (±olivine) on the liquidus, was sufficiently TiO2-rich for hemo-ilmenite to crystallise early, and low in CaO and CaO/Al2O3compared to basalts as reflected by the sodic plagioclases and the delayed appearance of cumulus augite. Fine- to medium-grained jotunites found along the northern contact of the BKSK consist of plagioclase (An45–53), inverted pigeonite (Mg# = 55-50), sparse augite (Mg# = 69-59), Fe-Ti oxides, K-feldspar, quartz and apatite. They are basic to intermediate rocks with relatively high FeOtotal, high TiO2, low MgO/MgO + FeO, moderate Al2O3 and low CaO and normative diopside. The jotunites have compositions that are consistent with the parental magma for the lower part of the BKSK Layered Series, and are interpreted as being marginal chills. Similar, but slightly more differentiated, jotunite magmas were subsequently emplaced into the BKSK and the surrounding region as broad dykes and small plutons. Jotunite is a minor rock type in most massif-type anorthosite provinces but may have an important petrological significance. 相似文献
15.
东天山香山铜镍-钛铁成矿与两类岩浆演化关系探讨 总被引:1,自引:0,他引:1
香山矿床是东天山唯一一个铜镍矿体与钛铁矿体共存的复合型矿床,目前普遍被认为是同源岩浆高度演化的产物。但为何区内众多同时代镁铁-超镁铁质岩体中只有香山岩体产出有大型钛铁矿床?这一问题仍有待进一步探讨。本文通过系统对比香山与其相邻的黄山东、黄山和黄山南等典型铜镍矿的地球化学特征、母岩浆性质及岩浆演化过程,认为香山岩体母岩浆相对其相邻典型铜镍矿床并不富集Fe和Ti,且其母岩浆早期演化过程及分异演化程度相似。模拟计算表明:岩浆体系早期都处于较还原的环境(f_(O_2)QFM+1),而且都发生了大量橄榄石、斜方辉石和单斜辉石的分离结晶和硫化物的熔离,由此消耗了岩浆体系中大量的Fe,导致残余岩浆中Fe含量降低;另外在岩浆演化的各阶段,尤其到岩浆演化后期,大量角闪石的结晶进一步降低了残余岩浆中的Fe和Ti的含量,不能造成Fe和Ti的逐渐富集,据此我们认为同源岩浆演化不具备形成钛铁矿床的物质基础。通过初步对比东天山地区典型铜镍矿床和钛铁矿床与该地区早二叠世两类玄武岩的地球化学特征及演化趋势,我们初步推测东天山地区铜镍成矿与钛铁成矿是两类不同性质岩浆独立演化的产物,铜镍成矿可能与拉斑玄武质岩浆演化密切相关,而钛铁矿则可能与碱性玄武岩演化密切相关。 相似文献
16.
Late Pleistocene or Recent lavas from San Quintin, Baja California are basanitoids and alkali basalts. The surface quench temperatures of the lavas average 1 005° C with log
=–11.4, as deduced from the groundmass Fe-Ti oxides. Spinel lherzolite xenoliths and megacrysts of augite and andesine have been found in lava flows and cinder deposits. Using analytical data on the rocks and minerals and simple thermodynamic expressions, the pressures and temperatures of equilibration of lavas and xenoliths, megacrysts and phenocrysts have been calculated. The lavas could have been in equilibrium with lherzolite at 1 330–1 410° C and 27.5–31.6 kb, the more silica-poor liquid having the higher values. The basanitoid could have equilibrated with the megacrysts at about 10.5 kb and with phenocrysts at about 1.4 kb and 1130° C. The variation in composition of the lavas may be explained by a rising zone of melting within the mantle, the most silica-poor liquid having the deepest source. The source of the San Quintin basalts is probably related to spreading of the ocean floor in the Gulf of California. 相似文献
17.
A transmission electron microscope study of the microstructuresof olivine, augite and ortho-pyroxene in the Artfj?llet gabbroshows that the gabbro has been affected by two phases of deformation,exsolution and alteration. During the first phase, deformationand annealing of olivine led to the formation of elongated subgrains,with (100) subgrain boundaries consisting of regularly spacededge dislocations with [100] Burgers vectors. Localized strongerdeformation resulted in the development of mosaic subgrainswith (100) and (001) boundaries. Exsolution produced blebs and(100) lamellae of orthopyroxene in augite. Two types of blebsoccur, referred to as symplectitic augite and blebby augite.Symplectitic augite formed through discontinuous precipitation.The blebs in blebby augite are considered to have nucleatedat subgrain boundaries or dislocations in the augite. Blebs,melon pips and (100) lamellae of augite formed in orthopyroxene.These blebs and melon pips are thought to be due to nucleationat dislocations or to thickening of (100) lamellae at dislocations.Brown hornblende formed as blebs in augite and to a lesser extentorthopyroxene. This first event took place while the gabbrowas at a temperature of c. 900-1000 ?C and is thought to berelated to D2b, a regional flattening and thrusting event. Renewed exsolution in the pyroxenes occurred later, probablybefore the second subsolidus phase, -but its timing is poorlyconstrained. "100" lamellae of low-Ca clinopyroxene formed inaugite at an estimated temperature of c. 600 ?C. Thin (100)lamellae and Guinier-Preston zones were developed in orthopyroxene. During the second phase, deformation resulted mainly in cracks,along which hydrous fluids entered the gabbro, causing a variabledegree of metamorphism at a temperature of c. 500-550 ?C. Inolivine irregular dislocations of mixed edge-screw characterformed. Cr-spinel with an unknown phase, or magnetite with diopsideprecipitated in the olivine. Oxide minerals formed in the pyroxenesand brown hornblende: Cr-spinel in Cr-rich augite; rutile andilmenite in other augite, orthopyroxene and brown hornblende.The formation of these oxide minerals is thought to be due toexsolution of cations such as Ti and Cr, which these mineralsdo not tolerate in their structures at low temperatures, combinedwith oxidation in the case of magnetite in olivine. Alterationresulted in thin amphibole lamellae parallel to (010) in augite.This second subsolidus phase is correlated with the D3 regionaldeformation phase and the concomitant retrograde metamorphism. 相似文献
18.
《Lithos》1987,20(2):135-151
DSDP Hole 504B, located on the south flank of the Costa Rica Rift, shows the most complete reference section through the upper oceanic crust; 274.5 m into the sediment and 1075.5 m into the basement have been penetrated.Very unusual secondary parageneses occur in some basaltic massive flows recovered at DSDP Hole 504 B. Replacement of magmatic augite by secondary Ti- and/or Na-rich augite and aegirine-augite was observed in five veins between the 298 and 685 m sub-basement depth; one of these veins also contains melanite (Ti-rich andradite) and another one contains fassaite. These minerals seem independent of, and prior to, other alteration stages.The conditions of formation and origin of the fluids responsible for the crystallization of these unusual minerals are discussed. Several arguments suggest that their origin is not hydrothermal, but possibly deuteric: (1) these minerals probably formed at higher temperatures than hydrothermal minerals from DSDP Hole 504 B (300–400°C for melanite, 800–1000°C (?) for fassaite, >400°C for aegirine-augite); (2) the chemical composition of the studied minerals are not compatible with the chemical composition of hydrothermal fluids responsible for the alteration at DSDP Hole 504 B; (3) the distribution and chemical composition of these minerals seem to be independent of the alteration zonation and thus of depth; and (4) these minerals are anhydrous, in contrast to mostly hydrated minerals from DSDP Hole 504 B known to be hydrothermal in origin. Moreover, since these minerals occur in subophitic or coarse-grained basalts, their crystallization may have been enhanced by the long standing stability of the physico-chemical conditions existing in the veins. 相似文献
19.
In western part of the CEIM (Central-East Iranian Microcontinent) (Bayazeh area, Isfahan province, Iran), a series of Paleozoic
basaltic rocks, occur. Major minerals of these basalts are olivine, clinopyroxene (diopside, augite), plagioclase (albite),
sanidine, amphibole (kaersutite), phlogopite, ilmenite and magnetite. Secondary minerals include epidote, pumpellyite, albite,
calcite and chlorite. Olivine and clinopyroxene are as phenocryst, while feldspars are restricted to groundmass. Chemical
composition of clinopyroxenes indicates crystallization during ascending of magma. Geochemical analysis of whole rock samples
shows that these rocks are characterized by low SiO2 (43.21–48.45 wt %), high TiO2 (1.81–3.00 wt %) and P2O5 (0.18–0.34 wt %). Petrography, chemistry of clinopyroxenes and whole rock analyses reveal an alkaline nature of these basalts.
They are enriched in alkalis (Na2O + K2O = 4.1–7.7 wt %), LILE, HFSE and LREE. The Bayazeh alkali-basalts present strong enrichment in LREE relative to HREE (La/Lu
ratio = 77.6–119.6) and were dominantly derived from partial melting of a metasomatized asthenospheric garnet-amphibole lherzolite.
Field relationships reveal that junction of faults in west of the Bayazeh prepared a suitable path for ascending of magma
from deep regions to surface and intra-plate continental magmatism. The Paleo-Tethys subduction from lower to upper Paleozoic
is too enough for mantle enrichment in volatiles and basaltic alkaline magmatisrn in upper Paleozoic of Bayazeh area. 相似文献
20.
David M. Harris Alfred T. Anderson Jr. 《Contributions to Mineralogy and Petrology》1984,87(2):120-128
The products of the 1974 eruption of Fuego, a subduction zone volcano in Guatemala, have been investigated through study of
silicate melt inclusions in olivine. The melt inclusions sampled liquids in regions where olivine, plagioclase, magnetite,
and augite were precipitating. Comparisons of the erupted ash, groundmass, and melt inclusion compositions suggest that the
inclusions represent samples of liquids present in a thermal boundary layer of the magma body. The concentrations of H2O and CO2 in glass inclusions were determined by a vacuum fusion manometric technique using individual olivine crystals (Fo77 to Fo71)
with glass inclusion compositions that ranged from high-alumina basalt to basaltic andesite. Water, Cl, and K2O concentrations increased by a factor of two as the olivine crystals became more iron-rich (Fo77 to Fo71) and as the glass
inclusions increased in SiO2 from 51 to 54 wt.% SiO2. The concentration of H2O in the melt increased from 1.6 wt.% in the least differentiated liquid to about 3.5% in a more differentiated liquid. Carbon
dioxide is about an order of magnitude less abundant than H2O in these inclusions. The gas saturation pressures for pure H2O in equilibrium with the melt inclusions, which were calculated from the glass inclusion compositions using the solubility
model of Burnham (1979), are given approximately by P(H2O)(Pa)=(SiO2−48.5 wt.%) × 1.45 × 107. The concentrations of water in the melt and the gas saturation pressures increased from about 1.5% to 3.5% and from 300
to 850 bars, respectively, during pre-eruption crystallization. 相似文献