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1.
Olivine and augite minette powders have been equilibrated from one bar to nearly 2.0 kbar (water-saturated), and from 900
to 1300° C, and then quenched rapidly, at oxygen fugacities controlled between the nickel-nickel oxide (NNO) and hematite-magnetite
(HM) oxygen buffers. The liquidus of both samples is suppressed ∼100° C at water-saturated conditions and 1500 bar. Both lavas
contained between 3 and 4 wt% water at the stage of phenocryst precipitation. The partitioning of ferric and ferrous iron
between phlogopite and liquid has been determined on eight samples across 3 log f O2 units; when these determinations are combined with previous studies, Fe2O3/(Σ FeO total) of Mg-rich biotite can be calculated knowing log f
O2, T, and X
Fe. Thermodynamic modelling of biotite-liquid equilibria results in two expressions for calculating activity coefficients (γ)
for annite and phlogopite in natural biotites. Based on the partitioning of BaO and TiO2 between biotite and liquid, we have formulated a thermometer and barometer. Over the range of 400° C, TiO2 partitioning between phlogopite and liquid is a function of temperature (±50° C), and is insensitive to pressure and H2O and O2 activities. BaO partitioning between phlogopite and liquid is a function of both temperature and pressure (±4 kbar), the
latter being most important. Applying the TiO2 and BaO partitioning expressions to lamprophyre and lamproite suites shows that Mexican minettes equilibrated at low pressures
(5 to 15 kbar;±4 kbar) and temperatures (1090 to 1160° C; ±50° C), while Australian lamproites equilibrated at higher P (up to 30 kbar; ±4 kbar) and T (1125 to 1400° C; ±50° C). Experimental glass compositions and phenocryst fractionation calculations, together with the BaO-
and TiO2- based pressure calculations indicate that felsic minettes from the Mexican suite of lavas can be generated by simple fractionation
of a more mafic parent minette at mid to lower crustal pressures.
Received: 1 August 1994/Accepted: 30 June 1995 相似文献
2.
Anna Pietranik Francois Holtz Jürgen Koepke Jacek Puziewicz 《Mineralogy and Petrology》2009,97(1-2):1-21
Crystallization experiments were performed on quartz diorite (~55 wt.% SiO2, 3.1–8.4 wt.% MgO) from the G?siniec Intrusion (Bohemian Massif, SW Poland) at 1?2 kbar, 750–850°C, various mole fractions of water and with fO2 buffered by the NNO buffer. The two natural quartz diorites (leucocratic poikilitic quartz diorite - ‘LPD’ and melanocratic quartz diorite - ‘MD’) differ in whole rock and mineral composition with MD being richer in MgO and poorer in CaO than LPD, probably due to accumulation of mafic minerals or melt removal in MD. LPD represents melt composition and is used to reconstruct crystallization conditions in the G?siniec Intrusion. The crystallization history of LPD magma, deduced from experimental and natural mineral compositions, includes a higher pressure stage probably followed by emplacement at ~2 kbar of partly crystallized magma at temperatures ~850?800°C and quick cooling. The mineral assemblage present in LPD requires water contents in the magma of at least 5 wt% and oxygen fugacity below that controlled by the NNO buffer. The compositions of mafic minerals in the MD composition were equilibrated at temperatures below 775°C and at subsolidus conditions. The equilibration was probably due to the reaction between water-rich, oxidizing residual melt and the cumulatic-restitic mineral assemblage. MD is characterized by occurrence of the euhedral cummingtonite and increasing anorthite content in the rims of plagioclase. A similar reaction was reproduced experimentally in both LPD and MD compositions indicating that cummingtonite may be a late magmatic phase in quartz dioritic systems, crystallizing very close to solidus and only from water saturated magma. 相似文献
3.
Jürgen Konzett 《Contributions to Mineralogy and Petrology》1997,128(4):385-404
Experiments have been conducted in a peralkaline Ti-KNCMASH system representative of MARID-type bulk compositions to delimit
the stability field of K-richterite in a Ti-rich hydrous mantle assemblage, to assess the compositional variation of amphibole
and coexisting phases as a function of P and T, and to characterise the composition of partial melts derived from the hydrous assemblage. K-richterite is stable in experiments
from 0.5 to 8.0 GPa coexisting with phlogopite, clinopyroxene and a Ti-phase (titanite, rutile or rutile + perovskite). At
8.0 GPa, garnet appears as an additional phase. The upper T stability limit of K-richterite is 1200–1250 °C at 4.0 GPa and 1300–1400 °C at 8.0 GPa. In the presence of phlogopite, K-richterite
shows a systematic increase in K with increasing P to 1.03 pfu (per formula unit) at 8.0 GPa/1100 °C. In the absence of phlogopite, K-richterite attains a maximum of 1.14 K
pfu at 8.0 GPa/1200 °C. Titanium in both amphibole and mica decreases continuously towards high P with a nearly constant partitioning while Ti in clinopyroxene remains more or less constant. In all experiments below 6.0 GPa
ΣSi + Al in K-richterite is less than 8.0 when normalised to 23 oxygens+stoichiometric OH. Rutiles in the Ti-KNCMASH system
are characterised by minor Al and Mg contents that show a systematic variation in concentration with P(T) and the coexisting assemblage. Partial melts produced in the Ti-KNCMASH system are extremely peralkaline [(K2O+Na2O)/Al2O3 = 1.7–3.7], Si-poor (40–45 wt% SiO2), and Ti-rich (5.6–9.2 wt% TiO2) and are very similar to certain Ti-rich lamproite glasses. At 4.0 GPa, the solidus is thought to coincide with the K-richterite-out
reaction, the first melt is saturated in a phlogopite-rutile-lherzolite assemblage. Both phlogopite and rutile disappear ca.
150 °C above the solidus. At 8.0 GPa, the solidus must be located at T≤1400 °C. At this temperature, a melt is in equilibrium with a garnet- rutile-lherzolite assemblage. As opposed to 4.0 GPa, phlogopite
does not buffer the melt composition at 8.0 GPa. The experimental results suggest that partial melting of MARID-type assemblages
at pressures ≥4.0 GPa can generate Si-poor and partly ultrapotassic melts similar in composition to that of olivine lamproites.
Received: 23 December 1996 / Accepted: 20 March 1997 相似文献
4.
A precise olivine-augite Mg-Fe-exchange geothermometer 总被引:4,自引:1,他引:4
Robert R. Loucks 《Contributions to Mineralogy and Petrology》1996,125(2-3):140-150
Olivine and augite that were experimentally equilibrated in the temperature interval 1175–1080°C at 1 bar in natural basaltic
and andesitic bulk compositions are used to calibrate an Mg-Fe2+ cation-exchange geothermometer. Within its temperature interval of experimental calibration, and over a broad range in olivine
Mg/Fe ratio, the geothermometer has a standard error of ±6°C. In compositionally simpler synthetic systems, the same calibration
retrieves appropriate experimental temperatures up to at least 1250°C. In application to intermediate and felsic volcanic
rocks erupted at ∼1080 –800°C (below the range of experimental calibration), calculated olivine-augite temperatures are in
good agreement with Fe-Ti oxide thermometry in the same samples. These results encourage confidence in the olivine-augite
geothermometer over at least the 800–1250°C interval at low pressures. Sparse experimental data up to 1250°C at higher pressures
for olivine + augite in the assemblage olivine + plagioclase + augite ± pigeonite or orthopyroxene suggest that the low-pressure
calibration recovers experimental temperatures without systematic bias to pressures of 10 kbar. Examples illustrate applications
to determining igneous equilibration temperatures in holocrystalline extrusive and intrusive rocks, and to estimating intratelluric
H2O content dissolved in magmas.
Received: 24 February 1995 / Accepted: 1 March 1996 相似文献
5.
Phase relations of phlogopite with magnesite from 4 to 8 GPa 总被引:2,自引:2,他引:0
To evaluate the stability of phlogopite in the presence of carbonate in the Earth’s mantle, we conducted a series of experiments
in the KMAS–H2O–CO2 system. A mixture consisting of synthetic phlogopite (phl) and natural magnesite (mag) was prepared (phl90-mag10; wt%) and run at pressures from 4 to 8 GPa at temperatures ranging from 1,150 to 1,550°C. We bracketed the solidus between
1,200 and 1,250°C at pressures of 4, 5 and 6 GPa and between 1,150 and 1,200°C at a pressure of 7 GPa. Below the solidus,
phlogopite coexists with magnesite, pyrope and a fluid. At the solidus, magnesite is the first phase to react out, and enstatite
and olivine appear. Phlogopite melts over a temperature range of ~150°C. The amount of garnet increases above solidus from
~10 to ~30 modal% to higher pressures and temperatures. A dramatic change in the composition of quench phlogopite is observed
with increasing pressure from similar to primary phlogopite at 4 GPa to hypersilicic at pressures ≥5 GPa. Relative to CO2-free systems, the solidus is lowered such, that, if carbonation reactions and phlogopite metasomatism take place above a
subducting slab in a very hot (Cascadia-type) subduction environment, phlogopite will melt at a pressure of ~7.5 GPa. In a
cold (40 mWm−2) subcontinental lithospheric mantle, phlogopite is stable to a depth of 200 km in the presence of carbonate and can coexist
with a fluid that becomes Si-rich with increasing pressure. Ascending kimberlitic melts that are produced at greater depths
could react with peridotite at the base of the subcontinental lithospheric mantle, crystallizing phlogopite and carbonate
at a depth of 180–200 km. 相似文献
6.
Mineral chemistry of submarine lavas from Hilo Ridge, Hawaii: implications for magmatic processes within Hawaiian rift zones 总被引:10,自引:0,他引:10
Huai-Jen Yang Frederick A. Frey David A. Clague Michael O. Garcia 《Contributions to Mineralogy and Petrology》1999,135(4):355-372
The crustal history of volcanic rocks can be inferred from the mineralogy and compositions of their phenocrysts which record
episodes of magma mixing as well as the pressures and temperatures when magmas cooled. Submarine lavas erupted on the Hilo
Ridge, a rift zone directly east of Mauna Kea volcano, contain olivine, plagioclase, augite ±orthopyroxene phenocrysts. The
compositions of these phenocryst phases provide constraints on the magmatic processes beneath Hawaiian rift zones. In these
samples, olivine phenocrysts are normally zoned with homogeneous cores ranging from ∼ Fo81 to Fo91. In contrast, plagioclase, augite and orthopyroxene phenocrysts display more than one episode of reverse zoning. Within each
sample, plagioclase, augite and orthopyroxene phenocrysts have similar zoning profiles. However, there are significant differences
between samples. In three samples these phases exhibit large compositional contrasts, e.g., Mg# [100 × Mg/(Mg+Fe+2)] of augite varies from 71 in cores to 82 in rims. Some submarine lavas from the Puna Ridge (Kilauea volcano) contain phenocrysts
with similar reverse zonation.
The compositional variations of these phenocrysts can be explained by mixing of a multiphase (plagioclase, augite and orthopyroxene)
saturated, evolved magma with more mafic magma saturated only with olivine. The differences in the compositional ranges of
plagioclase, augite and orthopyroxene crystals between samples indicate that these samples were derived from isolated magma
chambers which had undergone distinct fractionation and mixing histories. The samples containing plagioclase and pyroxene
with small compositional variations reflect magmas that were buffered near the olivine + melt ⇒Low-Ca pyroxene + augite +
plagioclase reaction point by frequent intrusions of mafic olivine-bearing magmas. Samples containing plagioclase and pyroxene
phenocrysts with large compositional ranges reflect magmas that evolved beyond this reaction point when there was no replenishment
with olivine-saturated magma. Two of these samples contain augite cores with Mg# of ∼71, corresponding to Mg# of 36–40 in
equilibrium melts, and augite in another sample has Mg# of 63–65 which is in equilibrium with a very evolved melt with a Mg#
of ∼30. Such highly evolved magmas also exist beneath the Puna Ridge of Kilauea volcano. They are rarely erupted during the
shield building stage, but may commonly form in ephemeral magma pockets in the rift zones.
The compositions of clinopyroxene phenocryst rims and associated glass rinds indicate that most of the samples were last equilibrated
at 2–3 kbar and 1130–1160 °C. However, in one sample, augite and glass rind compositions reflect crystallization at higher
pressures (4–5 kbar). This sample provides evidence for magma mixing at relatively high pressures and perhaps transport of
magma from the summit conduits to the rift zone along the oceanic crust-mantle boundary.
Received: 8 July 1998 / Accepted: 2 January 1999 相似文献
7.
Dehydration melting of tonalitic compositions (phlogopite or biotite-plagioclase-quartz assemblages) is investigated within
a temperature range of 700–1000°C and pressure range of 2–15 kbar. The solid reaction products in the case of the phlogopite-plagioclase(An45)-quartz starting material are enstatite, clinopyroxene and potassium feldspar, with amphiboles occurring occasionally. At
12 kbar, zoisite is observed below 800°C, and garnet at 900°C. The reaction products of dehydration melting of the biotite
(Ann50)-plagioclase (An45)-quartz assemblage are melt, orthopyroxene, clinopyroxene, amphibole and potassium feldspar. At pressures > 8 kbar and temperatures
below 800°C, epidote is also formed. Almandine-rich garnet appears above 10 kbar at temperatures ≥ 750°C. The composition
of melts is granitic to granodioritic, hence showing the importance of dehydration melting of tonalites for the formation
of granitic melts and granulitic restites at pressure-temperature conditions within the continental crust. The melt compositions
plot close to the cotectic line dividing the liquidus surfaces between quartz and potassium feldspar in the haplogranite system
at 5 kbar and a
H
2O = 1. The composition of the melts changes with the composition of the starting material, temperature and pressure. With increasing
temperature, the melt becomes enriched in Al2O3 and FeO+MgO. Potash in the melt is highest just when biotite disappears. The amount of CaO decreases up to 900°C at 5 kbar
whereas at higher temperatures it increases as amphibole, clinopyroxene and more An-component dissolve in the melt. The Na2O content of the melt increases slightly with increase in temperature. The composition of the melt at temperatures > 900°C
approaches that of the starting assemblage. The melt fraction varies with composition and proportion of hydrous phases in
the starting composition as well as temperature and pressure. With increasing modal biotite from 20 to 30 wt%, the melt proportion
increases from 19.8 to 22.3 vol.% (850°C and 5 kbar). With increasing temperature from 800 to 950°C (at 5 kbar), the increase
in melt fraction is from 11 to 25.8 vol.%. The effect of pressure on the melt fraction is observed to be relatively small
and the melt proportion in the same assemblage decreases at 850°C from 19.8 vol.% at 5 kbar to 15.3 vol.% at 15 kbar. Selected
experiments were reversed at 2 and 5 kbar to demonstrate that near equilibrium compositions were obtained in runs of longer
duration.
Received: 27 December 1995 / Accepted: 7 May 1996 相似文献
8.
The Han-Xing region is located in the south Taihang Mountains (TM) in the central part of the North China Craton, and is an important iron producing area. The iron deposits in this region are of skarn type, related to an Early Cretaceous high-Mg diorite complex, including gabbro diorite, hornblende diorite, diorite, diorite porphyrite, and monzonite. In this study we report the detailed mineral chemistry of the high-Mg diorites and skarn rocks. The olivine in the gabbro diorite shows chemical composition similar to that in mantle peridotite xenoliths. Clinopyroxene in the gabbro diorite is dominantly augite, with only minor diopside, whereas the clinopyroxenes in the diorite and monzonite are diopside. Amphiboles in the high-Mg diorites show compositional range from magnesiohornblende to magnesiohastingsite, with minor pargasite and tschermakite. Most plagioclase in the high-Mg diorite is andesine and oligoclase. The magnesio-biotite in gabbro diorites shows chemical characteristics of re-equilibrated primary biotites and those in calc-alkaline rocks. In the diorite and diorite porphyrite, plagioclase shows complex chemical zoning. Clinopyroxene and garnet in skarn rocks show varying FeO contents, the former containing low FeO (< 9 wt.%) and occurring as the major skarn mineral in large-scale iron deposits, and the latter within small-scale iron deposits with high FeO (mostly > 25 wt.%) content. We computed the pressure, temperature, oxygen fugacity and water contents based on the mineral chemistry of amphibole and biotite. Based on the results, the magma crystallization can be divided into two stages, one within the deep magma chamber, forming clinopyroxene, amphibole and plagioclase phenocrysts; the other after emplacement, forming the rim of phenocrysts and matrix minerals. The magma during the early stage shows high temperature (~ 900 °C–950 °C), pressure (~ 300 MPa–500 MPa), relatively high logfO2 (NNO–NNO + 2), and H2O content in melt (4%–8%). During the late stage, the magma temperature dropped to about 750 °C, and pressure came down to less than 100 MPa, with the logfO2 rising to NNO + 1–NNO + 2.The zoning of amphibole and plagioclase records the process of magma mixing and crystallization, with injection of mafic magma into the felsic magma chamber. The relatively high logfO2 and H2O content inhibited partitioning of iron into mafic minerals and favored concentration of Fe in the melt. Iron ore precipitation occurred when the magma was emplaced at shallow level, and was principally controlled by the chemical composition of carbonate wall rocks. The high logfO2, Fe3 + rich ore-forming fluid generated andradite and clinopyroxene when it reacted with limestone and dolomitic limestone respectively. 相似文献
9.
A. A. Gurenko Thor H. Hansteen Hans-Ulrich Schmincke 《Contributions to Mineralogy and Petrology》1996,124(3-4):422-435
Picritic units of the Miocene shield volcanics on Gran Canaria, Canary Islands, contain olivine and clinopyroxene phenocrysts
with abundant primary melt, crystal and fluid inclusions. Composition and crystallization conditions of primary magmas in
equilibrium with olivine Fo90-92 were inferred from high-temperature microthermometric quench experiments, low-temperature microthermometry of fluid inclusions
and simulation of the reverse path of olivine fractional crystallization based on major element composition of melt inclusions.
Primary magmas parental for the Miocene shield basalts range from transitional to alkaline picrites (14.7–19.3 wt% MgO, 43.2–45.7
wt% SiO2). Crystallization of these primary magmas is believed to have occurred over the temperature range 1490–1150° C at pressures
≈5 kbar producing olivine of Fo80.6-90.2, high-Ti chrome spinel [Mg/ (Mg+Fe2+)=0.32–0.56, Cr/(Cr+Al)=0.50–0.78, 2.52–8.58 wt% TiO2], and clinopyroxene [Mg/(Mg+Fe)=0.79–0.88, Wo44.1-45.3, En43.9-48.0, Fs6.8-11.0] which appeared on the liquidus together with olivine≈Fo86. Redox conditions evolved from intermediate between the QFM and WM buffers to late-stage conditions of NNO+1 to NNO+2. The
primary magmas crystallized in the presence of an essentially pure CO2 fluid. The primary magmas originated at pressures >30 kbar and temperatures of 1500–1600° C, assuming equilibrium with mantle
peridotite. This implies melting of the mantle source at a depth of ≈100 km within the garnet stability field followed by
migration of melts into magma reservoirs located at the boundary between the upper mantle and lower crust. The temperatures
and pressures of primary magma generation suggest that the Canarian plume originated in the lower mantle at depth ≈900 km
that supports the plume concept of origin of the Canary Islands.
Received: 23 October 1995/Accepted: 21 February 1996 相似文献
10.
In this paper we describe the mineralogy and geochemistry of basanites and melt inclusions in minerals from the Tergesh pipe,
northern Minusinsk Depression. The rocks are composed of olivine and clinopyroxene phenocrysts and a groundmass of olivine,
clinopyroxene, titanomagnetite, plagioclase, apatite, ilmenite, and glass. Melt inclusions were found only in the olivine
and clinopyroxene phenocrysts. Primary melt inclusions in olivine contain glass, rh?nite, clinopyroxene, a sulfide globule,
and low-density fluid. The phase composition of melt inclusions in clinopyroxene is glass + low-density fluid ± xenogenous
magnetite. According to thermometric investigations, the olivine phenocrysts began crystallizing at T = 1280–1320°C and P > 3.5 kbar, whereas groundmass minerals were formed under near-surface conditions at T ≤ 1200°C. The oxygen fugacity gradually changed during basanite crystallization from oxidizing (NNO) to more reducing conditions
(QFM). The investigation of glass compositions (heated and unheated inclusions in phenocrysts and groundmass) showed that
the evolution of a basanite melt during its crystallization included mainly an increase in SiO2, Al2O3, and alkalis, while a decrease in femic components, and the melt composition moved gradually toward tephriphonolite and trachyandesite.
Geochemical evidence suggests that the primary basanite melt was derived from a mantle source affected by differentiation.
Original Russian Text ? T.Yu. Timina, V.V. Sharygin, A.V. Golovin, 2006, published in Geokhimiya, 2006, No. 8, pp. 814–833. 相似文献
11.
Experimental melting relationships for a mafic minette (mica-lamprophyre) from Buell Park, Arizona were determined under fO2 conditions equivalent to the ironwüstite-graphite and quartz-fayalite-magnetite buffers, at pressures of 10–20 kbar. A comparison between experimental products and phenocrysts in the most primitive minettes indicates that those lavas preserve a near-liquidus assemblage of olivine, diopside and Ti-rich phlogopite crystallized in the upper mantle under fO2QFM and in the presence of an H2O-bearing fluid phase. It is suggested that micalamprophyric (minette) magmas may originate from a metasomatized, garnet-bearing peridotitic source at deeper levels in the mantle (P20 kbar) but can also be in equilibrium with a phlogopite-bearing wehrlite (±opx) source at pressures of 17–20 kbar, under reducing or oxidizing mantle conditions. Owing to their rapid crystallization rate and high liquidus temperatures, a series of potassic daughter melts (potassic latites and felsic minettes) can be formed by segregation from mafic minette parents during their ascent through the cooler continental crust. The preservation of olivine in equilibrium with phlogopite phenocrysts in primitive minettes precludes a petrogenetic process dominated by assimilation/fractional crystallization in a shallow magma chamber and supports a model by which some lamprophyric magmas are brought to near surface conditions at temperatures in the range of 1,000–1,200° C and chilled rapidly. 相似文献
12.
High pressure phase relations of primitive high-alumina basalts from Medicine Lake volcano,northern California 总被引:8,自引:1,他引:8
Karen S. Bartels Rosamond J. Kinzler Timothy L. Grove 《Contributions to Mineralogy and Petrology》1991,108(3):253-270
Anhydrous phase relations were determined at 1 atm and 10 to 15 kbar for primitive high-alumina basalts (79–35g and 82–72f)
from Giant Crater at Medicine Lake volcano. These compositions are multiply saturated with olivine+augite+plagioclase+spinel+/-orthopyroxene
near the liquidus at about 11 kbar. Experiments on mixtures of sample 79–35g with orthopyroxene and olivine determined the
location of the multiple saturation boundaries where liquid coexists with the assemblage olivine+augite+orthopyroxene+plagioclase
at 10 kbar and olivine+augite+orthopyroxene+spinel at 15 kbar. The mix experiments showed that primitive Medicine Lake high
alumina basalts (HABs) are close in composition to liquids in equilibrium with a mantle lherzolite source containing olivine+augite+
orthopyroxene+spinel+plagioclase at 11 kbar. Orthopyroxene observed as a near liquidus phase in an 11 kbar experiment on sample
82–72f supports this conclusion. The most primitive HABs from Medicine Lake are low in K2O (0.07 wt.%), high in MgO (>10 wt.%) and Ni (231 ppm), and have light-rare earth element depletions and large ion lithophile
element enrichments. A model for the origin of these near-primary high-alumina basalts is that they are partial melts of a
MORB-like mantle lherzolite source that has been enriched by a fluid component derived from the subducted slab. The HAB magma
segregated from its mantle residue just below the base of the crust near the crust-mantle boundary. 相似文献
13.
Summary Mantle-derived xenoliths from Baarley in the Quaternary West Eifel volcanic field contain six distinct varieties of glass
in veins, selvages and pools. 1) Silica-undersaturated glass rich in zoned clinopyroxene microlites that forms jackets around
and veins within the xenoliths. This glass is compositionally similar to groundmass glass in the host basanite. 2) Silica-undersaturated
alkaline glass that contains microlites of Cr-diopside, olivine and spinel associated with amphibole in peridotites. This
glass locally contains corroded primary spinel and phlogopite. 3) Silica-undersaturated glass associated with diopside, spinel ± olivine
and rh?nite microlites in partly to completely broken down amphibole grains in clinopyroxenites. 4) Silica-undersaturated
to silica-saturated, potassic glass in microlite-rich fringes around phlogopite grains in peridotite. 5) Silica-undersaturated
potassic glass in glimmerite xenoliths. 6) Silica-rich glass around partly dissolved orthopyroxene crystals in peridotites.
Geothermometry of orthopyroxene–clinopyroxene pairs (P = 1.5 GPa) gives temperatures of ∼ 850 °C for unveined xenoliths to
950–1020 °C for veined xenoliths. Clinopyroxene – melt thermobarometry shows that Cr-diopside – type 2 glass pairs in harzburgite
formed at 1.4 to 1.1 GPa and ∼ 1250 °C whereas Cr-diopside – type 2 glass pairs in wehrlite formed at 0.9 to 0.7 GPa and 1120–1200 °C.
This bimodal distribution in pressure and temperature suggests that harzburgite xenoliths may have been entrained at greater
depth than wehrlite xenoliths.
Glass in the Baarley xenoliths has three different origins: infiltration of an early host melt different in composition from
the erupted host basanite; partial melting of amphibole; reaction of either of these melts with xenolith minerals. The composition
of type 1 glass suggests that jackets are accumulations of relatively evolved host magma. Mass balance modelling of the type
2 glass and its microlites indicates that it results from breakdown of disseminated amphibole and reaction of the melt with
the surrounding xenolith minerals. Type 3 glass in clinopyroxenite xenoliths is the result of breakdown of amphibole at low
pressure. Type 4 and 5 glass formed by reaction between phlogopite and type 2 melt or jacket melt. Type 6 glass associated
with orthopyroxene is due to the incongruent dissolution of orthopyroxene by any of the above mentioned melts.
Compositional gradients in xenolith olivine adjacent to type 2 glass pools and jacket glass can be modelled as Fe–Mg interdiffusion
profiles that indicate melt – olivine contact times between 0.5 and 58 days. Together with the clinopyroxene – melt thermobarometry
calculations these data suggest that the glass (melt) formed over a short time due to decompression melting of amphibole and
infiltration of evolved host melt. None of the glass in these xenoliths can be directly related to metasomatism or any other
process that occurred insitu in the mantle.
Received November 23, 1999; revised version accepted September 5, 2001 相似文献
14.
The paper presents data on naturally quenched melt inclusions in olivine (Fo 69–84) from Late Pleistocene pyroclastic rocks
of Zhupanovsky volcano in the frontal zone of the Eastern Volcanic Belt of Kamchatka. The composition of the melt inclusions
provides insight into the latest crystallization stages (∼70% crystallization) of the parental melt (∼46.4 wt % SiO2, ∼2.5 wt % H2O, ∼0.3 wt % S), which proceeded at decompression and started at a depth of approximately 10 km from the surface. The crystallization
temperature was estimated at 1100 ± 20°C at an oxygen fugacity of ΔFMQ = 0.9–1.7. The melts evolved due to the simultaneous
crystallization of olivine, plagioclase, pyroxene, chromite, and magnetite (Ol: Pl: Cpx: (Crt-Mt) ∼ 13: 54: 24: 4) along the tholeiite evolutionary trend and became progressively enriched in FeO, SiO2, Na2O, and K2O and depleted in MgO, CaO, and Al2O3. Melt crystallization was associated with the segregation of fluid rich in S-bearing compounds and, to a lesser extent, in
H2O and Cl. The primary melt of Zhupanovsky volcano (whose composition was estimated from data on the most primitive melt inclusions)
had a composition of low-Si (∼45 wt % SiO2) picrobasalt (∼14 wt % MgO), as is typical of parental melts in Kamchatka and other island arcs, and was different from MORB.
This primary melt could be derived by ∼8% melting of mantle peridotite of composition close to the MORB source, under pressures
of 1.5 ± 0.2 GPa and temperatures 20–30°C lower than the solidus temperature of “dry” peridotite (1230–1240°C). Melting was
induced by the interaction of the hot peridotite with a hydrous component that was brought to the mantle from the subducted
slab and was also responsible for the enrichment of the Zhupanovsky magmas in LREE, LILE, B, Cl, Th, U, and Pb. The hydrous
component in the magma source of Zhupanovsky volcano was produced by the partial slab melting under water-saturated conditions
at temperatures of 760–810°C and pressures of ∼3.5 GPa. As the depth of the subducted slab beneath Kamchatkan volcanoes varies
from 100 to 125 km, the composition of the hydrous component drastically changes from relatively low-temperature H2O-rich fluid to higher temperature H2O-bearing melt. The geothermal gradient at the surface of the slab within the depth range of 100–125 km beneath Kamchatka
was estimated at 4°C/km. 相似文献
15.
Quaternary minettes and associated volcanic rocks of Mascota,western Mexico: a consequence of plate extension above a subduction modified mantle wedge 总被引:12,自引:0,他引:12
I. S. E. Carmichael R. A. Lange James F. Luhr 《Contributions to Mineralogy and Petrology》1996,124(3-4):302-333
Pleistocene-Holocene volcanism in the Jalisco block of western Mexico is confined to two conspicuous grabens, where potassic
eruptives range from absarokites (48–52% SiO2) and minettes (49–54% SiO2) through basaltic andesites (53–57% SiO2), the most voluminous type, to andesites and their lamprophyric equivalent spessartite (58–62% SiO2); there are no contemporary rhyolitic rocks. This suite has high concentrations of Mg, Cr (<550 ppm) and Ni (<450 ppm) accompanied
by large concentrations of K, P, Ba (<4000 ppm) and Sr (<5000 ppm) and elements such as LREE and Zr (<600 ppm). No combination
of crystal fractionation and/or crustal contamination can reproduce the compositional range of these magmas, which nevertheless
are believed to be genetically related because of their proximity in time and space. Hydrous minerals in the lamprophyres
and the typical absence of plagioclase phenocrysts in both basaltic andesites and andesites reflect the relatively high concentrations
of water in the magmas, which suppressed the crystallisation of feldspar. Experimental verification of the minimal amounts
of water required to reproduce the phenocryst assemblages in selected rocks range from 3.5 to 6%. During ascent in a volcanic
conduit, andesitic magma may lose water and consequently precipitate plagioclase, or it may ascend more rapidly, retaining
more of its initial water, which stabilises phenocrysts of hornblende at the expense of plagioclase. Our estimates of water
concentrations, which are consistent with the various low pressure phenocryst assemblages, will be minimal for the magmas
in their source regions, and the process of magmatic dewatering on ascent may be typical in well established volcanic conduits.
In accord with the compositions of phenocrystic olivine in the basaltic andesites and the minettes, the values of FeO and
Fe2O3 of the bulk lavas and scoriae are demonstrably pristine. As a consequence, there are two characteristic features of the Mascota
suite: the high range of relative oxygen fugacities (ΔNNO=1–5) and the high Mg# (MgO/MgO+FeO) that ranges from 0.70 to 0.91
(with only one andesite as low as 0.66). From the evidence of phlogopite phenocrysts, a partial melt involving phlogopite
would have a higher Mg# than one from olivine (Fo90) and pyroxene alone. As the Mascota series shows a correlation between K2O and Mg#, we conclude that it was generated by partial fusion of the mantle wedge, with a variable contribution of phlogopite
and apatite from veins throughout the lherzolitic assemblage. In conformity with an origin by varying increments of partial
fusion of a phlogopite-bearing mantle, all incompatible elements vary linearly with Ti (or K) as if phlogopite (+apatite)
in the source dominated their contribution to the partial melts. Fluids from dehydration of the subducting slab presumably
deposit hydrous and other minerals in veins in the mantle wedge and also increase its redox state. As the Mascota volcanism
occurs in grabens closer to the trench than the main andesite arc, it is concluded that the eruption of these small volumes
of hydrous magmas require the tectonically favored ascent paths offered by the extensional grabens to reach the surface from
their mantle sources.
Received: 24 January 1995 / Accepted: 21 February 1996 相似文献
16.
An absarokite from a phlogopite lherzolite source 总被引:1,自引:0,他引:1
An absarokite (SiO2 47.72 wt %, K2O 3.41 wt %) occurs in the Katamata volcano, SW Japan. The rock carries phenocrysts of olivine, phlogopite, clinopyroxene, and hornblende. Chemical compositions of bulk rock (FeO*/ MgO 0.73) and minerals (Mg-rich olivine and phlogopite, Cr-rich chromite) suggest that the absarokite is not differentiated. Melting experiments at high pressures on the Katamata absarokite have been conducted. The completely anhydrous absarokite melt coexists with olivine, orthopyroxene, and clinopyroxene at 1310° C and 1.0 GPa. The melt with 3.29 wt % of H2O also coexists with the above three phases at 1230° C and 1.4 GPa; phlogopite appears at temperatures more than 80° C below the liquidus. On the other hand, the melt is not saturated with lherzolite minerals in the presence of 5.13 wt % of H2O and crystallizes olivine and phlogopite as liquidus phases; the stability limit of phlogopite is little affected at least by the present variation of H2O content in the absarokite melt. It is suggested that the absarokite magma was segregated from the upper mantle at 1170° C and 1.7 GPa leaving a phlogopite lherzolite as a residual material on the basis of the above experimental results and the petrographical observation that olivine and phlogopite crystallize at an earlier stage of crystallization sequence than clinopyroxene. The contribution of phlogopite at the stage of melting processes is also suggested by the geochemical characteristics that the absarokite is more enriched in Rb, K, and Ba and depleted in Ca and Na than a typical alkali olivine basalt from the same volcanic field. 相似文献
17.
Liquidus phase relations in the system diopside–kalsilite–forsterite–quartz with 3 wt% F were examined at 1 bar and the locations
of important invariant points were determined at 18 kbar. At all pressures within this range a large liquidus field for fluorphlogopite
(Phl) exists, and has a large influence on both melting and fractionation processes. One eutectic point was found to the silica-rich
side of the plane Lc–Fo–Di at Di1Ks30Fo2Qz67, where a melt coexists with San, Qz, Phl and Di at 840 °C and 1 bar. Another eutectic point must exist in the silica-poor
part of the system because the phase topology determines that thermal barriers must exist. At this point a feldspathoid, either
Lc or Ks, must coexist with Fo, Phl and a Ca-bearing phase such as Di. The exact location and phase assemblage were not determined,
but the equilibrium melt must have a composition rich in Di (>29 wt%) and extremely poor in Qz (<8 wt%). The composition of
the first eutectic moves towards lower SiO2 contents with increasing pressure (Di3Ks40Fo1Qz56 at 18 kbar), whereas the second does not exist at 18 kbar due to the disappearance of Lc as a stable liquidus phase. Liquids
which coexist with mafic minerals such as En, Fo, Phl and Di are important for the genesis of potassium-rich mafic rocks by
partial melting in the mantle and for the early stages of fractional crystallisation. The equilibrium melt at the invariant
point Fo + En + Phl + Di + L at 1125 °C is very poor in Fo and Di components at atmospheric pressure (Di5Ks37Fo5Qz53), whereas at 18 kbar the melt contains large amounts of Fo and Di (Di19Ks31- Fo28Qz21), and has a composition close to that of natural lamproites. Kamafugites do not correspond to melts in this system under
any of the studied conditions, and appear to require CO2 in the source. Fractionation processes from primitive potassic basanite melts are controlled principally by the size (and
not the mere presence) of the liquidus phase field for phlogopite: at high pressures where the Phl field is large, olivine
is eliminated early from the fractionating assemblage and Cpx + Phl fractionation may lead to relatively silica-rich rock
differentiates such as trachytes. At low pressures, extensive olivine and restricted Phl crystallisation prevents silica enrichment
in the melt, resulting in phonolitic differentiates. Later crystallisation of alkali feldspar accentuates the trends laid
down in the early stages of fractionation.
Received: 2 February 1999 / Accepted: 14 October 1999 相似文献
18.
High PT experiments were performed in the range 2.5–19 GPa and 800–1,500°C using a synthetic peridotite doped with trace elements
and OH-apatite or with Cl-apatite + phlogopite. The aim of the study was (1) to investigate the stability and phase relations
of apatite and its high PT breakdown products, (2) to study the compositional evolution with P and T of phosphate and coexisting
silicate phases and (3) to measure the Cl-OH partitioning between apatite and coexisting calcic amphibole, phlogopite and
K-richterite. Apatite is stable in a garnet-lherzolite assemblage in the range 2.5–8.7 GPa and 800–1,100°C. The high-P breakdown
product of apatite is tuite γ-Ca3 (PO4)2, which is stable in the range 8–15 GPa and 1,100–1,300°C. Coexisting apatite and tuite were observed at 8 GPa/1,050°C and
8.7 GPa/1,000°C. MgO in apatite increases with P from 0.8 wt% at 2.5 GPa to 3.2 wt% at 8.7 GPa. Both apatite and tuite may
contain significant Na, Sr and REE with a correlation indicating 2 Ca2+=Na+ + REE3+. Tuite has always higher Sr and REE and lower Fe and Mg than apatite. Phosphorus in the peridotite phases decreases in the
order Pmelt ≫ Pgrt ≫ PMg2SiO4 > Pcpx > Popx. The phosphate-saturated P2O5 content of garnet increases from 0.07 wt% at 2.5 GPa to 1.5 wt% at 12.8 GPa. Due to the low bulk Na content of the peridotite,
[8]Na[4]P[8]M2+
−1
[4]Si−1 only plays a minor role in controlling the phosphorus content of garnet. Instead, element correlations indicate a major contribution
of [6]M2+[4]P[6]M3+
−1
[4]Si−1. Pyroxenes contain ~200–500 ppm P and olivine has 0.14–0.23 wt% P2O5 in the P range 4–8.7 GPa without correlation with P, T or XMg. At ≥12.7 GPa, all Mg2SiO4 polymorphs have <200 ppm P. Coexisting olivine and wadsleyite show an equal preference for phosphorus. In case of coexisting
wadsleyite and ringwoodite, the latter fractionates phosphorus. Although garnet shows by far the highest phosphorus concentrations
of any peridotite silicate phase, olivine is no less important as phosphorus carrier and could store the entire bulk phosphorus
budget of primitive mantle. In the Cl-apatite + phlogopite-doped peridotite, apatite contains 0.65–1.35 wt% Cl in the PT range
2.5–8.7 GPa/800–1,000°C. Apatite coexists with calcic amphibole at 2.5 GPa, phlogopite at 2.5–5 GPa and K-richterite at 7 GPa,
and all silicates contain between 0.2 and 0.6 wt% Cl. No solid potassic phase is stable between 5 and 8.7 GPa. Cl strongly
increases the solubility of K in hydrous fluids. This may lead to the breakdown of phlogopite and give rise to the local presence
in the mantle of fluids strongly enriched in K, Cl, P and incompatible trace elements. Such fluids may get trapped as micro-inclusions
in diamonds and provide bulk compositions suitable for the formation of unusual phases such as KCl or hypersilicic Cl-rich
mica. 相似文献
19.
Shiho Hirotani Masao Ban Mitsuhiro Nakagawa 《Contributions to Mineralogy and Petrology》2009,157(6):709-734
Eruptive products of the Shirataka volcano (0.9–0.7 Ma) in NE Japan are calc-alkaline andesite–dacite, and are divisible into
six petrologic groups (G1–G6). Shirataka rocks possess mafic inclusions—basalt–basaltic andesite, except for G3 and G4. All
rocks show mixing and mingling of the mafic and silicic end-members, with trends defined by hosts and inclusions divided into
high-Cr and low-Cr types; both types coexist in G1, G2, and G5. Estimated mafic end-members are high-Cr (1120–1170°C, 48–51%
SiO2, olv ± cpx ± plg) and low-Cr type magmas (49–52% SiO2, cpx ± plg) except for the Sr isotopic composition. In contrast, the silicic end-members of both types have similar petrologic
features (790–840°C, 64–70% SiO2, hbl ± qtz ± px + plg). High-Cr type mafic and corresponding silicic end-members have lower 87Sr/86Sr ratios than the low-Cr ones in each group. The trace element model calculations suggest that the low-Cr type mafic end-member
magma is produced through ca. 20% fractional crystallization (olv ± cpx ± plg) from the high-Cr type one with assimilation
of granitoids (r = 0.02–0.05). The silicic magmas are producible through <30% partial remelting of previously emplaced basaltic magma with
assimilation of crustal components. The compositional difference between the low-K and medium-K basalts in the Shirataka volcano
is mainly attributed to the different degrees of the effect of subduction derived fluid by dehydration of phlogopite.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
20.
Near-liquidus crystallization experiments have been carried out on two basalts (12.5 and 7.8 wt% MgO) from Soufriere, St Vincent
(Lesser Antilles arc) to document the early stages of differentiation in calc-alkaline magmas. The water-undersaturated experiments
were performed mostly at 4 kbar, with 1.6 to 7.7 wt% H2O in the melt, and under oxidizing conditions (ΔNNO = −0.8 to +2.4). A few 10 kbar experiments were also performed. Early
differentiation of primitive, hydrous, high-magnesia basalts (HMB) is controlled by ol + cpx + sp fractionation. Residual
melts of typical high-alumina basalt (HAB) composition are obtained after 30–40% crystallization. The role of H2O in depressing plagioclase crystallization leads to a direct relation between the Al2O3 content of the residual melt and its H2O concentration, calibrated as a geohygrometer. The most primitive phenocryst assemblage in the Soufriere suite (Fo89.6 olivine, Mg-, Al- and Ti-rich clinopyroxene, Cr–Al spinel) crystallized from near-primary (Mg# = 73.5), hydrous (∼5 wt% H2O) and very oxidized (ΔNNO = +1.5–2.0) HMB liquids at middle crustal pressures and temperatures from ∼1,160 to ∼1,060°C. Hornblende
played no role in the early petrogenetic evolution. Derivative HAB melts may contain up to 7–8 wt% dissolved H2O. Primitive basaltic liquids at Soufriere, St Vincent, have a wide range of H2O concentrations (2–5 wt%). 相似文献