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1.
Xenoliths of lower crustal and upper mantle rocks from the Cima volcanic field (CVF) commonly contain glass pockets, veins,
and planar trains of glass and/or fluid inclusions in primary minerals. Glass pockets occupy spaces formerly occupied by primary
minerals of the host rocks, but there is a general lack of correspondence between the composition of the glass and that of
the replaced primary minerals. The melting is considered to have been induced by infiltration of basaltic magma and differentiates
of basaltic magma from complex conduits formed by hydraulic fracturing of the mantle and crustal rocks, and to have occurred
during the episode of CVF magmatism between ∼7.5 Ma and present. Variable compositions of quenched melts resulted from mixing
of introduced melts and products of melting of primary minerals, reaction with primary minerals, partial crystallization,
and fractionation resulting from melt and volatile expulsion upon entrainment of the xenoliths. High silica melts ( >∼60%
SiO2) may result by mixing introduced melts with siliceous melts produced by reaction of orthopyroxene. Other quenched melt compositions
range from those comparable to the host basalts to those with intermediate Si compositions and elevated Al, alkalis, Ti, P,
and S; groundmass compositions of CVF basalts are consistent with infiltration of fractionates of those basalts, but near-solidus
melting may also contribute to formation of glass with intermediate silica contents with infiltration only of volatile constituents.
Received: 15 June 1995 / Accepted: 13 December 1995 相似文献
2.
Archaean volcanic rocks and volcanogenic sediments exposed in a regional syncline south of Meekatharra, Western Australia are described. Initial volcanic activity produced a suite of high-Mg basalts containing 10–19% MgO. Pillowed tholeiitic basalts overlie the high-Mg basalts. These lower units are thought to have been derived from a central fracture zone. The uppermost units consist of volcanogenic sediments interlayered with andesite and dacite flows which appear to have been derived from a marginal andesite pile to the east. The Archaean sequence has been tightly folded, cross-faulted and intruded by post-Archaean dykes.The central succession is predominantly submarine, although the marginal andesite pile may be in part subaerial. Whilst there are some similarities with the Marda complex to the southeast (Hallberg et al., 1976), the rocks near Meekatharra are more analogous to those associated with modern island arcs. 相似文献
3.
The geodynamic setting of the Xigaze ophiolite has long been debated. Structural and geochemical evidence suggest the Xigaze ophiolite was formed at a slow‐spreading ridge (Nicolas et al., 1981; Liu et al., 2016). Based on incompatible element concentrations, the Xigaze ophiolite volcanics are consistent with the ubiquitous subduction signature in suprasubduction zone (Bedard et al., 2009; Hebert et al., 2012; Dai et al., 2013). It is noteworthy that the Xigaze ophiolite is different from the Geotimes and Lasail and Velly units from Oman ophiolite, respectively. The mafic rocks of the Xigaze ophiolite generally resemble typical N‐MORB and Geotimes volcanics in composition except for slight depletions of Th and Nb (Fig.1a). Although the Xigaze rocks have similar Th and Nb concentrations to Lasail and Velly rocks, most incompatible elements in the Xigaze rocks are comparable to N‐MORB. Petrography in gabbro of Xigaze ophiolite shows that euhedral plagioclases are enclosed by clinopyroxenes suggesting that these minerals have crystallized from an anhydrous magma (Sisson and Grove, 1993). Although the Xigaze volcanic rocks are slightly depleted in Th and Nb, they have MORB‐like trace element characteristics implying that they are derived from an anhydrous MORB magma at spreading centre. Godard et al. (2006) suggested that the mantle source of the Oman ophiolite have element and isotopic characteristics similar to Indian Ocean MORB, where the mantle preserved some older slab materials. A negative Nb anomaly of Oman Geotimes volcanic rocks may be resulted from contamination of the slab materials via decompression melting of the convecting mantle. Moreover, the Xigaze rocks have 1.27–3.18 of (Th/Nb)N ratios similar with those of Geotimes volcanics ((Th/Nb)N =0.51–2.77) and lower than those of Lasail and Velly units ((Th/Nb)N =2.12–6.35). These features suggest that the Xigaze ophiolite may have formed at the spreading centre. 相似文献
4.
《矿物学报》2013,(Z2)
<正>There are many skarn deposits that occur in volcanic rocks as stratiform and lentoid bodies,for example the Lower Yangtze River Valley,Western Tianshan Mountains and Lhasa Terrane in China,the Nuuk in West Greeland and the Austroalpine Alps(e.g.Xv et al.,1984;Appel,1994;Raith and Stein,2000;Wang et al.,2001;Gu et al.,2007;Hou et al.,2011;Zhou et al.,2011;Jiang et al.,2012;Xu et al.,2010;Wang et al.,2012;Yu et al.,2011).Despite 相似文献
5.
《Geodinamica Acta》1998,11(5):205-215
We 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). 相似文献
6.
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
7.
天然沸石是岩石圈上部分布最广的硅酸盐矿物之一,它普遍地见于各种火山岩和火山-沉积岩中。沸石不仅在岩浆期后热液阶段生成,而且在沉积-成岩作用阶段、表生作用(风化)阶段、低级变质阶段都可以生成。由于沸石对周围的物理化学条件和热、动力变质作用反应灵敏,因此,它是了解地质体形成时的地质环境及其变化的良好的指示矿物。本文概述了我国东部中生代火山岩中沸石岩的分布、时代、产出的地层岩性剖面、原岩类型、矿物组合及其生成顺序,并探讨了它的形成条件和成因类型,其中主要涉及具有工业意义的斜发沸石岩和丝光沸石岩。 相似文献
8.
Trace element concentrations of altered basaltic glass shards (layer silicates) and zeolites in volcaniclastic sediments drilled in the volcanic apron northeast of Gran Canaria during Ocean Drilling Program (ODP) leg 157 document variable element mobilities during low-temperature alteration processes in a marine environment. Clay minerals (saponite, montmorillonite, smectite) replacing volcanic glass particles are enriched in transition metals and rare earth elements (REE). The degree of retention of REE within the alteration products of the basaltic glass is correlated with the field strength of the cations. The high field-strength elements are preferentially retained or enriched in the alteration products by sorption through clay minerals. Most trace elements are enriched in a boundary layer close to the interface mineral-altered glass. This boundary layer has a key function for the physico-chemical conditions of the subsequent alteration process by providing a large reactive surface and by lowering the fluid permeability. The release of most elements is buffered by incorporation into secondary precipitates (sodium-rich zeolites, phillipsite, Fe- and Mn-oxides) as shown by calculated distribution coefficients between altered glasses and authigenic minerals. Chemical fluxes change from an open to a closed system behavior during prograde low-temperature alteration of volcaniclastic sediments with no significant trace metal flux from the sediment to the water column. 相似文献
9.
西南三江造山带火山岩—构造组合及其意义 总被引：67，自引：0，他引：67
岩石构造组合是指表示板块边界或特定的板块内部环境特征的岩石结合。中国西南“三江”造山带的火山岩可划分为五种火山岩－构造组合：洋脊型／准洋脊型组合，岛弧及陆缘弧组合，碰撞型组合，碰撞后组合及陆内拉张型组合。阐述了各种火山岩－构造组合的特点及构造含义。对在造山带火山岩岩石－构造组合分析中经常遇到的一些问题，如“构造岩片”研究方法、地球化学判别图解的使用条件、准洋脊型火山型组合的构造含义、蛇绿岩带－火山弧的成对性、岩浆作用的同步性和滞后性、以及火山岩的深部“探针”作用等问题进行了讨论。 相似文献
10.
Diamonds have been discovered in mantle peridotites and chromitites of six ophiolitic massifs along the 1300 km‐long Yarlung‐Zangbo suture (Bai et al., 1993; Yang et al., 2014; Xu et al., 2015), and in the Dongqiao and Dingqing mantle peridotites of the Bangong‐Nujiang suture in the eastern Tethyan zone (Robinson et al., 2004; Xiong et al., 2018). Recently, in‐situ diamond, coesite and other UHP mineral have also been reported in the Nidar ophiolite of the western Yarlung‐Zangbo suture (Das et al., 2015, 2017). The above‐mentioned diamond‐bearing ophiolites represent remnants of the eastern Mesozoic Tethyan oceanic lithosphere. New publications show that diamonds also occur in chromitites in the Pozanti‐Karsanti ophiolite of Turkey, and in the Mirdita ophiolite of Albania in the western Tethyan zone (Lian et al., 2017; Xiong et al., 2017; Wu et al., 2018). Similar diamonds and associated minerals have also reported from Paleozoic ophiolitic chromitites of Central Asian Orogenic Belt of China and the Ray‐Iz ophiolite in the Polar Urals, Russia (Yang et al., 2015a, b; Tian et al., 2015; Huang et al, 2015). Importantly, in‐situ diamonds have been recovered in chromitites of both the Luobusa ophiolite in Tbet and the Ray‐Iz ophiolite in Russia (Yang et al., 2014, 2015a). The extensive occurrences of such ultra‐high pressure (UHP) minerals in many ophiolites suggest formation by similar geological events in different oceans and orogenic belts of different ages. Compared to diamonds from kimberlites and UHP metamorphic belts, micro‐diamonds from ophiolites present a new occurrence of diamond that requires significantly different physical and chemical conditions of formation in Earth's mantle. The forms of chromite and qingsongites (BN) indicate that ophiolitic chromitite may form at depths of >150‐380 km or even deeper in the mantle (Yang et al., 2007; Dobrthinetskaya et al., 2009). The very light C isotope composition (δ13C ‐18 to ‐28‰) of these ophiolitic diamonds and their Mn‐bearing mineral inclusions, as well as coesite and clinopyroxene lamallae in chromite grains all indicate recycling of ancient continental or oceanic crustal materials into the deep mantle (>300 km) or down to the mantle transition zone via subduction (Yang et al., 2014, 2015a; Robinson et al., 2015; Moe et al., 2018). These new observations and new data strongly suggest that micro‐diamonds and their host podiform chromitite may have formed near the transition zone in the deep mantle, and that they were then transported upward into shallow mantle depths by convection processes. The in‐situ occurrence of micro‐diamonds has been well‐demonstrated by different groups of international researchers, along with other UHP minerals in podiform chromitites and ophiolitic peridotites clearly indicate their deep mantle origin and effectively address questions of possible contamination during sample processing and analytical work. The widespread occurrence of ophiolite‐hosted diamonds and associated UHP mineral groups suggests that they may be a common feature of in‐situ oceanic mantle. The fundamental scientific question to address here is how and where these micro‐diamonds and UHP minerals first crystallized, how they were incorporated into ophiolitic chromitites and peridotites and how they were preserved during transport to the surface. Thus, diamonds and UHP minerals in ophiolites have raised new scientific problems and opened a new window for geologists to study recycling from crust to deep mantle and back to the surface. 相似文献
11.
The composition and evolution of an Oligocene regolith on top of the Sesia–Lanzo Zone (Western Alps)
Notburga Kapferer Ivan Mercolli Alfons Berger 《International Journal of Earth Sciences》2011,100(5):1115-1127
An Oligocene paleosurface (regolith) lies on top of the high-pressure metamorphic rocks of the Sesia–Lanzo Zone near Biella,
NW Italy. Only the saprock, the lowermost part in a regolith profile, is preserved. No evidence for any paleosoil can be observed.
Field observations indicate that the regolith developed through in situ mechanical fracturing of the rocks of the Sesia–Lanzo
Zone in a continental environment. Density estimations of the regolith and the underlying rocks of the Sesia–Lanzo Zone confirm
the field observations and imply that a relatively small amount of alteration minerals was formed. The main detected alteration
phases are chlorite, various carbonates, quartz, clay minerals, Fe-oxides, and Fe-hydroxides. Chlorite differing in chemistry
and crystallographic ordering demonstrates different stages of alteration. Oxygen and carbon isotopic composition of carbonates
suggests temperatures higher than surface conditions. Illite and chlorite thermometry indicates temperatures related to the
anchizone (~250–300°C). These data are considered as a robust indication of the re-burial of the regolith together with its
substrate and its volcanic cover. The burial is closely related to the tilting of the preserved stratigraphic sequence formed
by the rocks of the Sesia–Lanzo Zone, the regolith, and the rocks of the Biella Volcanic Suite (Lanza, in Schweiz Miner Petrogr
MItt 57: 281–290, 1977; Lanza, in Geologishe Rundschau 68: 83–92, 1979). Furthermore, the burial is consistent with this sequence of subaerial rocks being very close to the intrusion depth of
the Valle del Cervo Pluton at the time of its emplacement (4–7 km; Zanoni et al., in Rend Online SGI Note Brevi 1: 199–202,
2008; Zanoni et al., in Int Geol Rev 52: 1244–1267, 2010 and references therein). 相似文献
12.
13.
腾冲地热区出露有众多热泉泉群,地热活动频繁,岩石发生强烈蚀变,形成的主要蚀变矿物包括高岭石、绢云母、蒙脱石、I/M间层矿物、石英和蛋白石。主要蚀变矿物的种类和含量受蚀变母岩性质的控制,花岗质砂砾岩和花岗岩形成高岭石,玄武岩形成伊利石和蒙托石,安山岩中发育硅化作用。泥化作用增强的趋势是安山岩→花岗岩→玄武岩→花岗质砂砾岩。由于花岗质砂砾岩在热区内广泛分布,通过蚀变作用形成了有经济价值的高岭土矿床。 相似文献
14.
M. K. G. Whateley X. Querol J. L. Fernández-Turiel E. Tuncali 《Mineralium Deposita》1996,31(6):529-538
The study focuses on the mineralogy of the upper coal seam accumulated at the top of the Çoraklar Formation (Miocene), Beypazari, Turkey. This coal seam is laterally extensive and averages 3.0 m thick, varying from 1.0 to 4.9 m. Analcime and clinoptiolite comprise up to 80% of the mineral matter (which also includes feldspars, quartz and pyrite and traces of dolomite, clay minerals and apatite) in the coal from the Cayirhan mine. Zeolites were formed when sodium-rich solutions altered aluminosilicate epiclastic material derived from contemporaneous volcanic activity. The allocthonous organic matter accumulated as a result of detrital plant and epiclastic material from an adjacent fresh-water environment being washed into a saline lake in sufficient quantities to form peat with a high mineral matter content (29.7% mean mineral matter content in raw coal). Subsequent syngenetic alteration of the volcanic glass incorporated into the peat resulted in zeolite formation. Alteration of sodium-rich epiclastic material by sodium-rich solutions resulted in the formation of analcime, whilst alteration of calcium-rich epiclastic material by sodium-rich solutions resulted in the formation of clinoptilolite. 相似文献
15.
I. P. Voinova 《Russian Journal of Pacific Geology》2016,10(3):230-238
The results of study of the volcanic rocks of the Khabarovsk accretionary complex, a fragment of the Jurassic accretionary prism of the Sikhote Alin orogenic belt (the southern part of the Russian Far East), are presented. The volcanic rocks are associated with the Lower Permian limestones in the mélange blocks and Triassic layered cherts. The petrography, petrochemistry, and geochemistry of the rocks are characterized and their geodynamic formation conditions are deduced. The volcanic rocks include oceanic plume basalts of two types: (i) OIB-like intraplate basalts formed on the oceanic islands and guyots in the Permian and Triassic and (ii) T(transitional)-MORBs (the least enriched basalts of the E-MORB type) formed on the midoceanic ridge in the Permian. In addition to basalts, the mélange hosts suprasubduction dacitic tuff lavas. 相似文献
16.
1Introduction Seamountsarethewell knownfeaturesinthe world’soceans,beingmostcommoninthePacific (Smith,1988;Pringleetal.,1991;Hasse,1991). Recentvolcanicactivityoccursinthezonesondi vergentorconvergentplatemarginsorintheintraplate regimes.Seamountsexisteitherasisolatedvolcanic edifices(Gardneretal.,1984;MertzandRenne, 1995)or,sometimes,formlinearchainstogetherwith oceanislands.Anumberofgeochronologicalinvestiga tionsonoceanislands(DuncanandMcDougall,1974; Dymond,1975;McDougall,1979… 相似文献
17.
M.El-Tokhi M.Omran A.E-Muslem 《中国地球化学学报》2005,24(1):9-17
Tholeiitic basalts in various stages of alteration were dredged from Late Cretaceous volcanic rocks (60 -67 Ma) in the Hebrides Terrace seamount area in the Atlantic Ocean. These rocks are extrusive olivine basalts, including high- and low-Al basalts. High-Al basalts are depleted in MgO, CaO, Cr,Sc, V, St, Zr and enriched in TiO2, Na2O, Nb, Rb as compared with low-A1 basalts. Petrography and bulk-rock composition (major, trace and rare-earth elements) data defined clear tholeiitic suites displaying possible liquid lines of descent related to different degrees of crystal fractionation and partial melting.Isotopic dating of dredged samples gave the guyot an age of 60 - 67 Ma, in support of the assumption that it was formed during the Late Cretaceous. 相似文献
18.
Accumulation and Post-Sedimentary Diagenesis of Tonsteins 总被引：2，自引：0，他引：2
The work is devoted to specific features of sedimentogenesis and multistage alterations of eolian volcanic ash and epiclastic clay in paleopeat bogs and their transformation into ortho- and paratonsteins, respectively. The hydrolysis of aluminosilicate minerals and volcanic glass and their alteration into monotonous submonomineral clay, which is compositionally similar to epiclastic clay, is associated with the diagenesis stage. During the catagenesis, submonomineral clay is lithified and transformed into tonsteins, which undergo recrystallization as the temperature increases. Clay minerals are replaced by illite and chlorite, while tonsteins are transformed into metatonsteins. Paragenetic relationships of clay minerals are discussed. 相似文献
19.
Microprobe analyses of glass and/or minerals from 12 selected ash-layers from the lower Tertiary mo-clay (approx. 53–54 m.y.) in northern Denmark are presented. The lower part of the ash-series provides evidence of a variety of rock types including tholeiitic basalts, rhyolite, and highly differentiated peralkaline types characterized by Ti-aegirine. The upper part of the ash-series forms a homogenous population of high Fe-high Ti-low A1 tholeiites, similar to Tertiary and recent basalts from the North Atlantic province. The presence of central volcanoes and a subvolcanic complex in the source area is indicated. This, together with variations in volcanic intensity, suggests an episode of abortive spreading in the Skagerrak-North Sea area simultaneously with the early spreading in the North Atlantic Ocean. 相似文献
20.
英峰岭剖面红土的粘土矿物和化学特征与成土环境关系 总被引：18，自引：4，他引：14
地球化学与粘土矿物学研究表明,广东雷州半岛英峰岭多期红土是拉弱武岩红土化初级阶段的产物,由剖面底层至顶层,红土成熟度依次递增。各层红土中主要粘土矿物含量和粘土的Ｆｅ２Ｏ３含量,以及工土和粘土的氧化,淋溶,富铁铝等化学特征系数与红土埋深之间呈波动起伏的关系。 相似文献