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1.
Adélie Delacour Marie-Christine Gerbe Jean-Claude Thouret Gerhard Wörner Perrine Paquereau-Lebti 《Bulletin of Volcanology》2007,69(6):581-608
Minor centres in the Central Volcanic Zone (CVZ) of the Andes occur in different places and are essential indicators of magmatic
processes leading to formation of composite volcano. The Andahua–Orcopampa and Huambo monogenetic fields are located in a
unique tectonic setting, in and along the margins of a deep valley. This valley, oblique to the NW–SE-trend of the CVZ, is
located between two composite volcanoes (Nevado Coropuna to the east and Nevado Sabancaya to the west). Structural analysis
of these volcanic fields, based on SPOT satellite images, indicates four main groups of faults. These faults may have controlled
magma ascent and the distribution of most centres in this deep valley shaped by en-echelon faulting. Morphometric criteria
and 14C age dating attest to four main periods of activity: Late Pleistocene, Early to Middle Holocene, Late Holocene and Historic.
The two most interesting features of the cones are the wide compositional range of their lavas (52.1 to 68.1 wt.% SiO2) and the unusual occurrence of mafic lavas (olivine-rich basaltic andesites and basaltic andesites). Occurrence of such minor
volcanic centres and mafic magmas in the CVZ may provide clues about the magma source in southern Peru. Such information is
otherwise difficult to obtain because lavas produced by composite volcanoes are affected by shallow processes that strongly
mask source signatures. Major, trace, and rare earth elements, as well as Sr-, Nd-, Pb- and O-isotope data obtained on high-K
calc-alkaline lavas of the Andahua–Orcopampa and Huambo volcanic province characterise their source and their evolution. These
lavas display a range comparable to those of the CVZ composite volcanoes for radiogenic and stable isotopes (87Sr/86Sr: 0.70591–0.70694, 143Nd/144Nd: 0.512317–0.512509, 206Pb/204Pb: 18.30–18.63, 207Pb/204Pb: 15.57–15.60, 208Pb/204Pb: 38.49–38.64, and δ
18O: 7.1–10.0‰ SMOW), attesting to involvement of a crustal component. Sediment is absent from the Peru–Chile trench, and hence
cannot be the source of such enrichment. Partial melts of the lowermost part of the thick Andean continental crust with a
granulitic garnet-bearing residue added to mantle-derived arc magmas in a high-pressure MASH [melting, assimilation, storage
and homogenisation] zone may play a major role in magma genesis. This may also explain the chemical characteristics of the
Andahua–Orcopampa and Huambo magmas. Fractional crystallisation processes are the main governors of magma evolution for the
Andahua–Orcopampa and Huambo volcanic province. An open-system evolution is, however, required to explain some O-isotopes
and some major and trace elements values. Modelling of AFC processes suggests the Charcani gneisses and the local Andahua–Orcopampa
and Huambo basement may be plausible contaminants. 相似文献
2.
Lava drainback has been observed during many eruptions at Kilauea Volcano: magma erupts, degasses in lava fountains, collects
in surface ponds, and then drains back beneath the surface. Time series data for melt inclusions from the 1959 Kilauea Iki
picrite provide important evidence concerning the effects of drainback on the H2O contents of basaltic magmas at Kilauea. Melt inclusions in olivine from the first eruptive episode, before any drainback
occurred, have an average H2O content of 0.7±0.2 wt.%. In contrast, many inclusions from the later episodes, erupted after substantial amounts of surface
degassed lava had drained back down the vent, have H2O contents that are much lower (≥0.24 wt.% H2O). Water contents in melt inclusions from magmas erupted at Pu'u 'O'o on the east rift zone vary from 0.39–0.51 wt.% H2O in tephra from high fountains to 0.10–0.28 wt.% H2O in spatter from low fountains. The low H2O contents of many melt inclusions from Pu'u 'O'o and post-drainback episodes of Kilauea Iki reveal that prior to crystallization
of the enclosing olivine host, the melts must have exsolved H2O at pressures substantially less than those in Kilauea's summit magma reservoir. Such low-pressure H2O exsolution probably occurred as surface degassed magma was recycled by drainback and mixing with less degassed magma at
depth. Recognition of the effects of low-pressure degassing and drainback leads to an estimate of 0.7 wt.% H2O for differentiated tholeiitic magma in Kilauea's summit magma storage reservoir. Data for MgO-rich submarine glasses (Clague
et al. 1995) and melt inclusions from Kilauea Iki demonstrate that primary Kilauean tholeiitic magma has an H2O/K2O mass ratio of ∼1.3. At transition zone and upper mantle depths in the Hawaiian plume source, H2O probably resides partly in a small amount of hydrous silicate melt.
Received: 31 March 1997 / Accepted: 17 November 1997 相似文献
3.
Claude Robin Jean-Philippe Eissen Pablo Samaniego Hervé Martin Minard Hall Joseph Cotten 《Bulletin of Volcanology》2009,71(3):233-258
The Mojanda–Fuya Fuya Volcanic Complex consists of two nearby volcanoes, Mojanda and Fuya Fuya. The older one, Mojanda volcano
(0.6 to 0.2 Ma), was first constructed by andesites and high-silica andesites forming a large stratovolcano (Lower Mojanda).
This edifice was capped by a basaltic andesite and andesitic cone (Upper Mojanda), which collapsed later to form a 3-km-wide
summit caldera, after large phreatomagmatic eruptions. The Lower Fuya Fuya edifice was constructed by the extrusion of viscous
Si-rich andesitic lavas and dacitic domes, and the emission of a thick sequence of pyroclastic-flow and fallout deposits which
include two voluminous rhyolitic layers. An intermediate construction phase at Fuya Fuya is represented by a mainly effusive
cone, andesitic in composition (San Bartolo edifice), the construction of which was interrupted by a major sector collapse
in the Late Pleistocene. Finally, a complex of thick siliceous lavas and domes was emplaced within the avalanche amphitheatre,
forming the Upper Fuya Fuya volcanic centre. This paper shows that the general evolution from an effusive to an explosive
eruptive style is related to a progressive adakitic contribution to the magma source. Although all the rocks of the complex
are included in the medium-K field of continental arcs, the Fuya Fuya suite (61–75 wt.% SiO2) shows depletion in Y and HREE and high Sr/Y and La/Yb values, compared to the less silicic Mojanda suite (55–66.5 wt.% SiO2). The Mojanda calc-alkaline suite was generated by partial melting of an adakite-metasomatised mantle source that left a
residue with 2% garnet, followed by fractional crystallization of dominant plagioclase + pyroxene + olivine at shallow, intra-crustal
depths. For Fuya Fuya, geochemical and mineralogical data suggest either (1) partial melting of a similar metasomatised mantle
with more garnet in the residue (4%), followed by fractional crystallization involving plagioclase, amphibole and pyroxene,
or (2) mixing of mafic mantle-derived magma from the Mojanda suite and slab melts, followed by the same fractional crystallization
process. 相似文献
4.
Ian S. E. Carmichael Holli M. Frey Rebecca A. Lange Chris M. Hall 《Bulletin of Volcanology》2006,68(5):407-419
Located at the volcanic front in the western Mexican arc, in the Colima Rift, is the active Volcán Colima, which lies on the southern end of the massive (∼450 km3) Colima-Nevado volcanic complex. Along the margins of this andesitic volcanic complex, is a group of 11 scoria cones and associated lavas, which have been dated by the 40Ar/39Ar method. Nine scoria cones erupted ∼1.3 km3 of alkaline magma (basanite, leucite-basanite, minette) between 450 and 60 ka, with >99% between 240 and 60 ka. Two additional cones (both the oldest and calc-alkaline) erupted <0.003 km3 of basalt (0.5 Ma) and <0.003 km3 of basaltic andesite (1.2 Ma), respectively. Cone and lava volumes were estimated with the aid of digital elevation models (DEMs). The eruption rate for these scoria cones and their associated lavas over the last 1.2 Myr is ∼1.2 km3/Myr, which is more than 400 times smaller than that from the andesitic Colima-Nevado edifice. In addition to these alkaline Colima cones, two other potassic basalts erupted at the volcanic front, but ∼200 km to the ESE (near the historically active Volcán Jorullo), and were dated at 1.06 and 0.10 Ma. These potassic suites reflect the tendency in the west-central Mexican arc for magmas close to the volcanic front to be enriched in K2O relative to those farther from the trench.Ferric-ferrous analyses on pristine samples from the alkaline cones adjacent to V. Colima and V. Jorullo indicate that their oxygen fugacities relative to the nickel-nickel oxide buffer are significantly higher (ΔNN0=2–4) than those for the calc-alkaline magma types (0–1.5). These ΔNNO values correlate positively with Ba concentrations and likely reflect the influence of a slab-derived fluid. As a result of the high oxidation states, the solubility of sulfur in these potassic magmas is enhanced. Indeed the sulfur content of both the whole rock and the apatite phenocrysts (and in olivine melt inclusions reported in the literature) suggest that part of their pre-eruptive sulfur gas (SO2) concentrations could have been discharged to the atmosphere in amounts comparable to the 1982 eruption of El Chichón, although over a prolonged period spanning thousands of years (not per eruption).Electronic Supplementary Material Supplementary material is available for this article at
Editorial responsibility: J. Donnelly-Nolan 相似文献
5.
Thierry Calmus Carlos Pallares Ren�� C. Maury Alfredo Aguill��n-Robles Herv�� Bellon Mathieu Benoit Fran?ois Michaud 《Pure and Applied Geophysics》2011,168(8-9):1303-1330
The study of the geochemical compositions and K-Ar or Ar-Ar ages of ca. 350 Neogene and Quaternary lavas from Baja California, the Gulf of California and Sonora allows us to discuss the nature of their mantle or crustal sources, the conditions of their melting and the tectonic regime prevailing during their genesis and emplacement. Nine petrographic/geochemical groups are distinguished: ??regular?? calc-alkaline lavas; adakites; magnesian andesites and related basalts and basaltic andesites; niobium-enriched basalts; alkali basalts and trachybasalts; oceanic (MORB-type) basalts; tholeiitic/transitional basalts and basaltic andesites; peralkaline rhyolites (comendites); and icelandites. We show that the spatial and temporal distribution of these lava types provides constraints on their sources and the geodynamic setting controlling their partial melting. Three successive stages are distinguished. Between 23 and 13 Ma, calc-alkaline lavas linked to the subduction of the Pacific-Farallon plate formed the Comondú and central coast of the Sonora volcanic arc. In the extensional domain of western Sonora, lithospheric mantle-derived tholeiitic to transitional basalts and basaltic andesites were emplaced within the southern extension of the Basin and Range province. The end of the Farallon subduction was marked by the emplacement of much more complex Middle to Late Miocene volcanic associations, between 13 and 7 Ma. Calc-alkaline activity became sporadic and was replaced by unusual post-subduction magma types including adakites, niobium-enriched basalts, magnesian andesites, comendites and icelandites. The spatial and temporal distribution of these lavas is consistent with the development of a slab tear, evolving into a 200-km-wide slab window sub-parallel to the trench, and extending from the Pacific coast of Baja California to coastal Sonora. Tholeiitic, transitional and alkali basalts of subslab origin ascended through this window, and adakites derived from the partial melting of its upper lip, relatively close to the trench. Calc-alkaline lavas, magnesian andesites and niobium-enriched basalts formed from hydrous melting of the supraslab mantle triggered by the uprise of hot Pacific asthenosphere through the window. During the Plio-Quaternary, the ??no-slab?? regime following the sinking of the old part of the Farallon plate within the deep mantle allowed the emplacement of alkali and tholeiitic/transitional basalts of deep asthenospheric origin in Baja California and Sonora. The lithospheric rupture connected with the opening of the Gulf of California generated a high thermal regime associated to asthenospheric uprise and emplaced Quaternary depleted MORB-type tholeiites. This thermal regime also induced partial melting of the thinned lithospheric mantle of the Gulf area, generating calc-alkaline lavas as well as adakites derived from slivers of oceanic crust incorporated within this mantle. 相似文献
6.
Contrasting origins of Cenozoic silicic volcanic rocks from the western Cordillera of the United States 总被引:2,自引:0,他引:2
Two fundamentally different types of silicic volcanic rocks formed during the Cenozoic of the western Cordillera of the United
States. Large volumes of dacite and rhyolite, mostly ignimbrites, erupted in the Oligocene in what is now the Great Basin
and contrast with rhyolites erupted along the Snake River Plain during the Late Cenozoic. The Great Basin dacites and rhyolites
are generally calc-alkaline, magnesian, oxidized, wet, cool (<850°C), Sr-and Al-rich, and Fe-poor. These silicic rocks are
interpreted to have been derived from mafic parent magmas generated by dehydration of oceanic lithosphere and melting in the
mantle wedge above a subduction zone. Plagioclase fractionation was minimized by the high water fugacity and oxide precipitation
was enhanced by high oxygen fugacity. This resulted in the formation of Si-, Al-, and Sr-rich differentiates with low Fe/Mg
ratios, relatively low temperatures, and declining densities. Magma mixing, large proportions of crustal assimilation, and
polybaric crystal fractionation were all important processes in generating this Oligocene suite. In contrast, most of the
rhyolites of the Snake River Plain are alkaline to calc-alkaline, ferroan, reduced, dry, hot (830–1,050°C), Sr-and Al-poor,
and Nb-and Fe-rich. They are part of a distinctly bimodal sequence with tholeiitic basalt. These characteristics were largely
imposed by their derivation from parental basalt (with low fH2O and low fO2) which formed by partial melting in or above a mantle plume. The differences in intensive parameters caused early precipitation
of plagioclase and retarded crystallization of Fe–Ti oxides. Fractionation led to higher density magmas and mid-crustal entrapment.
Renewed intrusion of mafic magma caused partial melting of the intrusive complex. Varying degrees of partial melting, fractionation,
and minor assimilation of older crust led to the array of rhyolite compositions. Only very small volumes of distinctive rhyolite
were derived by fractional crystallization of Fe-rich intermediate magmas like those of the Craters of the Moon-Cedar Butte
trend.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
7.
Analyses of the latest Jurassic Santiago Peak volcanic rocks from the western zone of the Peninsular Ranges batholith reveal the existence of two independent groups; one comprising basalts and andesites of the island arc tholeiitic series, and the second made up of the dacites and rhyolites of the subalkaline (calc-alkaline?) series or silicic series. The basalts and andesites have V, Co and Ni contents similar to those estimated for the residual melts in equilibrium with the Peninsular Ranges gabbros. This fact together with the tholeiitic nature of the gabbros and the intimate spatial and temporal relationship between the SPV and the gabbros suggests that the basalts and andesites had a common origin with the gabbros. The mafic volcanism and plutonism seems to have occurred in a youthful island arc and the silicic volcanism in a mature island arc or a continental margin. 相似文献
8.
D. H. Richter E. J. Moll-Stalcup T. P. Miller M. A. Lanphere G. B. Dalrymple R. L. Smith 《Bulletin of Volcanology》1994,56(1):29-46
Mount Drum is one of the youngest volcanoes in the subduction-related Wrangell volcanic field (80×200 km) of southcentral
Alaska. It lies at the northwest end of a series of large, andesite-dominated shield volcanoes that show a northwesterly progression
of age from 26 Ma near the Alaska-Yukon border to about 0.2 Ma at Mount Drum. The volcano was constructed between 750 and
250 ka during at least two cycles of cone building and ring-dome emplacement and was partially destroyed by violent explosive
activity probably after 250 ka. Cone lavas range from basaltic andesite to dacite in composition; ring-domes are dacite to
rhyolite. The last constructional activity occurred in the vicinity of Snider Peak, on the south flank of the volcano, where
extensive dacite flows and a dacite dome erupted at about 250 ka. The climactic explosive eruption, that destroyed the top
and a part of the south flank of the volcano, produced more than 7 km3 of proximal hot and cold avalanche deposits and distal mudflows. The Mount Drum rocks have medium-K, calc-alkaline affinities
and are generally plagioclase phyric. Silica contents range from 55.8 to 74.0 wt%, with a compositional gap between 66.8 and
72.8 wt%. All the rocks are enriched in alkali elements and depleted in Ta relative to the LREE, typical of volcanic arc rocks,
but have higher MgO contents at a given SiO2, than typical orogenic medium-K andesites. Strontium-isotope ratios vary from 0.70292 to 0.70353. The compositional range
of Mount Drum lavas is best explained by a combination of diverse parental magmas, magma mixing, and fractionation. The small,
but significant, range in 87Sr/86Sr ratios in the basaltic andesites and the wide range of incompatible-element ratios exhibited by the basaltic andesites
and andesites suggests the presence of compositionally diverse parent magmas. The lavas show abundant petrographic evidence
of magma mixing, such as bimodal phenocryst size, resorbed phenocrysts, reaction rims, and disequilibrium mineral assemblages.
In addition, some dacites and andesites contain Mg and Ni-rich olivines and/or have high MgO, Cr, Ni, Co, and Sc contents
that are not in equilibrium with the host rock and indicate mixing between basalt or cumulate material and more evolved magmas.
Incompatible element variations suggest that fractionation is responsible for some of the compositional range between basaltic
andesite and dacite, but the rhyolites have K, Ba, Th, and Rb contents that are too low for the magmas to be generated by
fractionation of the intermediate rocks. Limited Sr-isotope data support the possibility that the rhyolites may be partial
melts of underlying volcanic rocks.
Received March 13, 1993/Accepted September 10, 1993 相似文献
9.
The 1783–1784 Laki tholeiitic basalt fissure eruption in Iceland was one of the greatest atmospheric pollution events of
the past 250 years, with widespread effects in the northern hemisphere. The degassing history and volatile budget of this
event are determined by measurements of pre-eruption and residual contents of sulfur, chlorine, and fluorine in the products
of all phases of the eruption. In fissure eruptions such as Laki, degassing occurs in two stages: by explosive activity or
lava fountaining at the vents, and from the lava as it flows away from the vents. Using the measured sulfur concentrations
in glass inclusions in phenocrysts and in groundmass glasses of quenched eruption products, we calculate that the total accumulative
atmospheric mass loading of sulfur dioxide was 122 Mt over a period of 8 months. This volatile release is sufficient to have
generated ∼250 Mt of H2SO4 aerosols, an amount which agrees with an independent estimate of the Laki aerosol yield based on atmospheric turbidity measurements.
Most of this volatile mass (∼60 wt.%) was released during the first 1.5 months of activity. The measured chlorine and fluorine
concentrations in the samples indicate that the atmospheric loading of hydrochloric acid and hydrofluoric acid was ∼7.0 and
15.0 Mt, respectively. Furthermore, ∼75% of the volatile mass dissolved by the Laki magma was released at the vents and carried
by eruption columns to altitudes between 6 and 13 km. The high degree of degassing at the vents is attributed to development
of a separated two-phase flow in the upper magma conduit, and implies that high-discharge basaltic eruptions such as Laki
are able to loft huge quantities of gas to altitudes where the resulting aerosols can reside for months or even 1–2 years.
The atmospheric volatile contribution due to subsequent degassing of the Laki lava flow is only 18 wt.% of the total dissolved
in the magma, and these emissions were confined to the lowest regions of the troposphere and therefore important only over
Iceland. This study indicates that determination of the amount of sulfur degassed from the Laki magma batch by measurements
of sulfur in the volcanic products (the petrologic method) yields a result which is sufficient to account for the mass of
aerosols estimated by other methods.
Received: 30 May 1995 / Accepted: 19 April 1996 相似文献
10.
Luca Caricchi Anne Pommier Mattia Pistone Jonathan Castro Alain Burgisser Diego Perugini 《Bulletin of Volcanology》2011,73(9):1245-1257
Experiments have been performed to determine the effect of deformation on degassing of bubble-bearing melts. Cylindrical specimens
of phonolitic composition, initial water content of 1.5 wt.% and 2 vol.% bubbles, have been deformed in simple-shear (torsional
configuration) in an internally heated Paterson-type pressure vessel at temperatures of 798–848 K, 100–180 MPa confining pressure
and different final strains. Micro-structural analyses of the samples before and after deformation have been performed in
two and three dimensions using optical microscopy, a nanotomography machine and synchrotron tomography. The water content
of the glasses before and after deformation has been measured using Fourier Transform Infrared Spectroscopy (FTIR). In samples
strained up to a total of γ ∼ 2 the bubbles record accurately the total strain, whereas at higher strains (γ ∼ 10) the bubbles
become very flattened and elongate in the direction of shear. The residual water content of the glasses remains constant up
to a strain of γ ∼ 2 and then decreases to about 0.2 wt.% at γ ∼ 10. Results show that strain enhances bubble coalescence
and degassing even at low bubble volume-fractions. Noticeably, deformation produced a strongly water under-saturated melt.
This suggests that degassing may occur at great depths in the volcanic conduit and may force the magma to become super-cooled
early during ascent to the Earth’s surface potentially contributing to the genesis of obsidian. 相似文献
11.
R. N. Brothers 《Bulletin of Volcanology》1970,34(1):308-329
Eruptive suites from Tonga (tholeiitic), Raoul Island (tholeiitic) and Macauley Island (high-alumina) are characterised by low alkalis, an absence of andesites in the range 56–65% silica, and restricted acidity for minor glassy differentiates (SiO2=65–68 %). These volcanics form a chain of islands overlying a seismic zone which extends from Tonga to the central volcanic region of North Island, New Zealand where a calc-alkaline series contains basaltic, andesitic and rhyolitic members in that order of increasing abundance. Within this continental suite, tholeiitic and high-alumina phases are recognised as closely similar to the intra-oceanic Tonga-Kermadec magma types and show petrochemical gradation into the medium-silica andesites, apparently by sialic assimilation. 相似文献
12.
WANG Xiaorui GAO Shan LIU Xiaoming YUAN Honglin HU Zhaochu ZHANG Hong WANG Xuance 《中国科学D辑(英文版)》2006,49(9):904-914
The Yixian Formation at Sihetun in western Liao- ning Province has attracted considerable attention over the last two decades due to discovery of a wide range of well-preserved ‘feathered’ dinosaurs and primitive bird fossils[1―4]. This formation is dominated by vol- canic rocks, with fossil-bearing lacustrine sedimentary rocks at the upper part of the section[4]. The sedimen- tary rocks contain thin layers of tuff. According to previous studies[4], the total thickness of the Yixian Form… 相似文献
13.
The Mascota volcanic field is located in the Jalisco Block of western Mexico, where the Rivera Plate subducts beneath the North American Plate. It spans an area of ∼ 2000 km2 and contains ∼ 87 small cones and lava flows of minette, absarokite, basic hornblende lamprophyre, basaltic andesite, and andesite. There are no contemporary dacite or rhyolite lavas. New 40Ar/39Ar ages are presented for 35 samples, which are combined with nine dates from the literature to document the eruptive history of this volcanic field. The oldest lavas (2.4 to 0.5 Ma) are found in the southern part of the field area, whereas the youngest lavas (predominantly < 0.5 Ma) are found in the northern portion. On the basis of these ages, field mapping, and the use of ortho aerial photographs and digital elevation models, it is estimated that a combined volume of 6.8 ± 3.1 km3 erupted in the last 2.4 Myr, which leads to an average eruption rate of ∼ 0.003 km3/kyr, and an average volume per eruptive unit of < 0.1 km3. The dominant lava type is andesite (2.1 ± 0.9 km3), followed by absarokite (1.6 ± 0.8 km3), basaltic andesite (1.2 ± 0.5 km3), basic hornblende lamprophyre (1.0 ± 0.4 km3), and minette (0.9 ± 0.5 km3). Thus, the medium-K andesite and basaltic andesite comprise approximately half (49%) of the erupted magma, with twice as much andesite as basaltic andesite, and they occur in close spatial and temporal association with the highly potassic, lamprophyric lavas. There is no time progression to the type of magma erupted. A wide variety of evidence indicate that the high-MgO (8–9 wt.% ) basaltic andesites (52–53% wt.% SiO2) were formed by H2O flux melting of the asthenopheric arc mantle wedge, whereas the mafic minettes and absarokites were formed by partial melting (induced by thermal erosion) of depleted lithospheric mantle containing phlogopite-bearing veins. There is only limited differentiation of the potassic magmas, with none more evolved than 55.4 wt.% SiO2 and 4.4 wt.% MgO. This may be attributable to rapid crystallization of the mantle-derived melts in the deep crust, owing to their low volumes. Thus, the andesites (58–63 wt.% SiO2) are notable for being both the most voluminous and the most evolved of all lava types in the Mascota volcanic field, which is not consistent with their extraction from extensively crystallized (60–70%), low-volume intrusions. Instead, the evidence supports the origin of the andesites by partial melting of amphibolitized, mafic lower crust, driven by the emplacement of the minettes, absarokites, and the high-Mg basaltic andesites. 相似文献
14.
We consider the origin of rhyolites associated with tholeiitic basalt in bimodal provinces, as exemplified by the Rattlesnake
Tuff of the High Lava Plains of eastern Oregon, in comparison to rhyolites associated with calcalkaline suites in light of
recent models of extraction of rhyolite from crystal mush (Hildreth, J Volcanol Geotherm Res, 136:169–198, 2004; Bachmann and Bergantz, J Petrol, 45:1565–1582, 2004). The High Lava Plains encompass a strongly bimodal, tholeiite-rhyolite suite, spatially and compositionally
related to the Snake River Plain and Yellowstone Plateau. In our assessment we draw the distinction between fractionation
dominated processes to make rhyolites from rhyolites and processes required to make the parental rhyolite melt. New isotopic
data and compositional zoning profiles in phenocrysts confirm that crystal fractionation dominated the generation of progressively
more evolved, discrete rhyolites in the zoned Rattlesnake Tuff and are consistent with an origin of the least evolved high-silica
rhyolites by partial melting of a mafic crust. While the most evolved rhyolites are compositionally virtually indistinguishable
from those of calcalkaline suites, the parental rhyolites from bimodal suites are more Fe-rich than their calcalkaline counterparts.
Oxygen isotope thermometry yields pre-eruptive temperatures of 860°C, in keeping with 800–880°C zircon saturation temperatures.
High magmatic temperatures are common among rhyolites of bimodal suites, distinguishing them from cooler rhyolites of calcalkaline
suites. Extraction of interstitial melt from a granodioritic mush cannot produce compositions of the Rattlesnake Tuff on the
basis of major and trace element arguments (especially Fe, Ba, Sr, and Eu) and on the basis of temperature considerations.
Chemically viable parental crystal mushes are syenite and alkali (A-type) granites for the production of all more evolved
Rattlesnake Tuff rhyolites; ferro-dacitic mush is required for production of the least-evolved, parental Rattlesnake Tuff
rhyolite. Paucity of such ferro-dacitic compositions in tholeiitic bimodal suites, especially compared to the abundance of
dacitic (granodioritic) compositions in calcalkaline suites, argues against the mush extraction model for the parental rhyolite.
Furthermore, rhyolites of bimodal suites lack associated voluminous eruptions of crystal-rich ignimbrite that might represent
a parental mush, as exemplified by the “monotonous intermediate” Fish Canyon Tuff in calcalkaline suites. We conclude that
extensive fractionation is common among rhyolites and may obscure their ancestry. Fe-rich parental rhyolites common in bimodal
tholeiitic suites, as represented by Rattlesnake Tuff, may often be the result of partial melting of mafic to intermediate
crust, in contrast to calcalkaline high-silica rhyolites that are related to voluminous suites of intermediate intrusive rocks
where the pre-plutonic mush-extraction model works better.
This paper constitutes part of a special issue dedicated to Bill Bonnichsen on the petrogenesis and volcanology of anorogenic
rhyolites. 相似文献
15.
R. J. Stevenson N. S. Bagdassarov D. B. Dingwell C. Romano 《Bulletin of Volcanology》1998,60(2):89-97
As a major volatile in volcanic systems, water has a significant influence on the rheological properties of silicic magmas.
This is especially so at minor water contents relevant to the emplacement of silicic lavas. To investigate the influence of
water on the viscosity of natural rhyolitic obsidians, a novel strategy has been adopted employing parallel-plate and micropenetration
techniques. Viscosities have been determined on three types of material: (a) raw water-bearing obsidians; (b) remelted (1650 °C,
1 atm) degassed glasses of the obsidians; and (c) hydrothermally hydrated (1300 °C, 3 kbar) obsidians. Ten natural rhyolitic
obsidians (peraluminous, calc-alkaline and peralkaline) were employed: seven originated from lava flows and contained <0.2 wt.%
H2O, two samples were F-rich from pyroclastic successions, and one was an obsidian cobble with 1.5 wt.% water also associated
with pyroclastic units. Melt compositions and water contents were stable during viscometry. The measured decreases in activation
energies of viscous flow and viscosity with small amounts of water are much greater than the Shaw calculation scheme predicts.
In addition, a marked non-linear decrease in η exists with increasing water content. In contrast to the case for peralkaline
rhyolites, 0.1–0.2 wt.% water decreases activation energies significantly (up to 30%) for calc-alkaline compositions. These
results have important implications for the ease of near-surface degassing of silicic magmas during emplacement and permit
the testing of calculational models for viscosity, largely based on synthetic systems.
Received: 7 July 1997 / Accepted: 6 April 1998 相似文献
16.
Michael McCurry Karl P. Hayden Lee H. Morse Stan Mertzman 《Bulletin of Volcanology》2008,70(3):361-383
Rhyolites occur as a subordinate component of the basalt-dominated Eastern Snake River Plain volcanic field. The basalt-dominated
volcanic field spatially overlaps and post-dates voluminous late Miocene to Pliocene rhyolites of the Yellowstone–Snake River
Plain hotspot track. In some areas the basalt lavas are intruded, interlayered or overlain by ~15 km3 of cryptodomes, domes and flows of high-silica rhyolite. These post-hotspot rhyolites have distinctive A-type geochemical
signatures including high whole-rock FeOtot/(FeOtot+MgO), high Rb/Sr, low Sr (0.5–10 ppm) and are either aphyric, or contain an anhydrous phenocryst assemblage of sodic sanidine
± plagioclase + quartz > fayalite + ferroaugite > magnetite > ilmenite + accessory zircon + apatite + chevkinite. Nd- and
Sr-isotopic compositions overlap with coeval olivine tholeiites (ɛNd = −4 to −6; 87Sr/86Sri = 0.7080–0.7102) and contrast markedly with isotopically evolved Archean country rocks. In at least two cases, the rhyolite
lavas occur as cogenetic parts of compositionally zoned (~55–75% SiO2) shield volcanoes. Both consist dominantly of intermediate composition lavas and have cumulative volumes of several 10’s
of km3 each. They exhibit two distinct, systematic and continuous types of compositional trends: (1) At Cedar Butte (0.4 Ma) the
volcanic rocks are characterized by prominent curvilinear patterns of whole-rock chemical covariation. Whole-rock compositions
correlate systematically with changes in phenocryst compositions and assemblages. (2) At Unnamed Butte (1.4 Ma) the lavas
are dominated by linear patterns of whole-rock chemical covariation, disequilibrium phenocryst assemblages, and magmatic enclaves.
Intermediate compositions in this group resulted from variable amounts of mixing and hybridization of olivine tholeiite and
rhyolite parent magmas. Interestingly, models of rhyolite genesis that involve large degrees of melting of Archean crust or
previously consolidated mafic or silicic Tertiary intrusions do not produce observed ranges of Nd- and Sr-isotopes, extreme
depletions in Sr-concentration, and cogenetic spectra of intermediate rock compositions for both groups. Instead, least-squares
mass-balance, energy-constrained assimilation and fractional crystallization modeling, and mineral thermobarometry can explain
rhyolite production by 77% low-pressure fractional crystallization of a basaltic trachyandesite parent magma (~55% SiO2), accompanied by minor (0.03–7%) assimilation of Archean upper crust. We present a physical model that links the rhyolites
and parental intermediate magmas to primitive olivine tholeiite by fractional crystallization. Assimilation, recharge, mixing
and fractional melting occur to limited degrees, but are not essential parts of the rhyolite formation process.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
This paper constitutes part of a special issue dedicated to Bill Bonnichsen on the petrogenesis and volcanology of anorogenic
rhyolites. 相似文献
17.
During the 1944 eruption of Vesuvius a sudden change occurred in the dynamics of the eruptive events, linked to variations
in magma composition. K-phonotephritic magmas were erupted during the effusive phase and the first lava fountain, whereas
the emission of strongly porphyritic K-tephrites took place during the more intense fountain. Melt inclusion compositions
(major and volatile elements) highlight that the magmas feeding the eruption underwent differentiation at different pressures.
The K-tephritic volatile-rich melts (up to 3 wt.% H2O, 3000 ppm CO2, and 0.55 wt.% Cl) evolved to reach K-phonotephritic compositions by crystallization of diopside and forsteritic olivine
at total fluid pressure higher than 300 MPa. These magmas fed a very shallow reservoir. The low-pressure differentiation of
the volatile-poor K-phonotephritic magmas (H2O<1 wt.%) involved mixing, open-system degassing, and crystallization of leucite, salite, and plagioclase. The eruption was
triggered by intrusion of a volatile-rich magma batch that rose from a depth of 11–22 km into the shallow magma chamber. The
first phase of the eruption represents the partial emptying of the shallow reservoir, the top of which is within the volcanic
edifice. The newly arrived magma mixed with that resident in the shallow reservoir and forced the transition from the effusive
to the lava fountain phase of the eruption.
Received: 14 September 1998 / Accepted: 10 January 1999 相似文献
18.
Can crystallization of olivine tholeiite give rise to potassic rhyolites?—an experimental investigation 总被引:6,自引:0,他引:6
Matthew L. Whitaker Hanna Nekvasil Donald H. Lindsley Michael McCurry 《Bulletin of Volcanology》2008,70(3):417-434
Experiments were conducted to determine whether the rhyolites and basalts of the intraplate silica-saturated potassic suites
could be genetically related through crystallization. Extreme crystallization (96–97%) of a high-MgO (10.62 wt%) olivine tholeiite
from the Snake River Plain with an initial bulk water content of 0.4 wt% at a mid-crustal pressure of 4.3 kbar generated potassic
rhyolitic liquids similar in major element chemistry to those found in the Quaternary rhyolite domes of the Snake River Plain
and their plutonic equivalents in the Proterozoic Laramie Anorthosite Complex. Residual liquids comparable in composition
to the bulk rock compositions of intermediate rocks found at the Craters of the Moon and Cedar Butte eruptive centers in the
Snake River Plain are also generated along this crystallization path.
This paper constitutes part of a special issue dedicated to Bill Bonnichsen on the petrogenesis and volcanology of anorogenic
rhyolites. 相似文献
19.
S. M. Straub 《Bulletin of Volcanology》1995,57(6):403-421
Discrete Quaternary (<400 ka) tephra fallout layers (mostly <1 cm thick) within the siliceous oozes of the central Mariana Trough at 18°N are characterized by medium-K to high-K subalkalic volcanic glasses (K2O=0.8–3.2 wt.%) with high large-ion lithophile elements (LILE)/high-field-strength elements (HFSE) ratios and Nb depletion (Ba/La35; Ba/Zr3.5; La/Nb4) typical for convergent margin volcanic rocks. Compositional zoning within layers ranges from basaltic to dacitic (SiO2=48–71 wt.%; MgO=0.7–6.5 wt.%); all layers contain basaltic andesites. The tephra layers are interpreted as single explosive eruptive events tapping chemically zoned reservoirs, the sources being the Mariana arc volcanoes (MAV) due to their proximity (100–400 km) and similar element ratios (MAV: Ba/La=36±7; Ba/Zr=3.5±0.9). The glasses investigated, however, contrast with the contemporaneous basaltic to dacitic lavas of the MAV by being more enriched in TiO2 (1.2 wt.%; MAV0.8 wt.%), FeO* (10 wt.%, MAV8–9 wt.%), K2O (1.1 wt.%; MAV0.8 wt.%) and P2O5 (0.4 wt.%; MAV0.2 wt.%). (Semi-)Incompatible trace elements (including Rare Earth Elements (REE)) of the basaltic-andesitic and dacitic glasses match those of the dacitic MAV lavas, which became enriched by fractional crystallization. Moreover, the glasses follow a tholeiitic trend of fractionation in contrast to MAV transitional trends and have a characteristic P2O5 trend that reaches a maximum of 0.6 wt.% P2O5 at 57 wt.% SiO2, whereas MAV lavas increase linearly in P2O5 from 0.1 to 0.3 wt.% with increasing silica. Both explosive and effusive series are interpreted to have evolved in common magma reservoirs by convective fractionation. Similar parental magmas are suggested to have separated into coexisting Si-andesitic to dacitic and basaltic melts by in situ crystallization. The differentiated melt is interstitial in an apatite-saturated crystalline mush of plag+px±ox±ol at the cooler chamber margins in contrast to the less differentiated basaltic to basaltic-andesitic magmas, which are not yet saturated in apatite and occupy the chamber interior. Reinjection of interstitial melt into the chamber interior and mixing with larger melt fractions of the interior liquid (mixing ratios about 1: 8–9) can explain the paradoxical behavior of apatite-controlled P and MREE variation in the basaltic andesite glasses and their MAV dacite-like fractionation patterns. The process may also account for the exclusively tholeiitic trend of fractionation of the glass shard series, but in situ crystallization alone cannot cause their absolute enrichment in (semi-)incompatible elements. The newly mixed melt is suggested to form the basaltic end member of the glass shard series. However, it must have become physically separated from the main MAV magma body (possibly by density-driven convective fractionation) in order to allow for further evolution of the contrasting geochemical paths as well as differentiation. 相似文献
20.
PENG Runmin ZHAI Yusheng WANG Zhigang & HAN Xuefeng . Key Laboratory of Lithospheric Tectonics Lithoprobing Technology Ministry of Education China University of Geosciences Beijing China . Inner Mongolia Geological Prospecting Institute Ministry of Chemical Industry Hohhot China Correspondences should be addressed to Peng Runmin 《中国科学D辑(英文版)》2005,48(6):822-833
Since the mid-1980s,Tanyaokou large Zn-Cu-Fe sulfides deposit,located at the southwest end of Langshan-Zhaertaishan-Bayan Obo Mesoproterozoic metallogenic belt in the west section of the northern margin of the North China Platform[1?9](Fig.1),has been confirmed to be submarine volcanic exhalative-sedimentary metamorphosed deposit hosted in the miogeosynclinal mud-carbonaceous formation of the Langshan Group(LG)[1],or submarine volcanic exha-lative-deposition-altered deposit[2]or stratabo… 相似文献