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1.
Summary
Melting of a spinel lherzolite with a spinel clinopyroxenite layer was investigated experimentally from 3.5 to 20 kbar and
from 1200 to 1450 °C. The melt fraction in the spinel pyroxenite layer increases rapidly, and clinopyroxene disappears leaving
olivine-spinel residua according to the reaction Cpx + Sp = Ol + Liq. The melt in the pyroxenite layer reacts with the surrounding
lherzolite resulting in the formation of an essentially monomineral (olivine) zone with interstitial melt near the former
pyroxenite. Melt compositions in the central melt pool are similar to those produced by other authors in melting experiments
with peridotites similar to the bulk compositions of our samples. It is suggested that similar small-scale mantle heterogeneities
(i.e. thin pyroxenite layers in lherzolite) may exert significant influence on mantle rheology and melt segregation, whereas
melt compositions are not strongly affected and controlled by the dominating lherzolite lithology.
Received October 10, 2000; revised version accepted August 31, 2001 相似文献
2.
Elisabetta Rampone Giovanni B. Piccardo Albrecht W. Hofmann 《Contributions to Mineralogy and Petrology》2008,156(4):453-475
Spinel and plagioclase peridotites from the Mt.Maggiore (Corsica, France) ophiolitic massif record a composite asthenosphere–lithosphere
history of partial melting and subsequent multi-stage melt–rock interaction. Cpx-poor spinel lherzolites are consistent with
mantle residues after low-degree fractional melting (F = 5–10%). Opx + spinel symplectites at the rims of orthopyroxene porphyroclasts indicate post-melting lithospheric cooling
(T = 970–1,100°C); this was followed by formation of olivine embayments within pyroxene porphyroclasts by melt–rock interaction.
Enrichment in modal olivine (up to 85 wt%) at constant bulk Mg values, and variable absolute REE contents (at constant LREE/HREE)
indicate olivine precipitation and pyroxene dissolution during reactive porous melt flow. This stage occurred at spinel-facies
depths, after incorporation of the peridotites in the thermal lithosphere. Plagioclase-enriched peridotites show melt impregnation
microtextures, like opx + plag intergrowths replacing exsolved cpx porphyroclasts and interstitial gabbronoritic veinlets.
This second melt–rock interaction stage caused systematic chemical changes in clinopyroxene (e.g. Ti, REE, Zr, Y increase),
related to the concomitant effects of local melt–rock interaction at decreasing melt mass, and crystallization of small (<3%)
trapped melt fractions. LREE depletion in minerals of the gabbronoritic veinlets indicates that the impregnating melts were
more depleted than normal MORB. Preserved microtextural evidence of previous melt–rock interaction in the impregnated peridotites
suggests that they were progressively uplifted in response to lithosphere extension and thinning. Migrating melts were likely
produced by mantle upwelling and melting related to extension; they were modified from olivine-saturated to opx-saturated
compositions, and caused different styles of melt–rock interaction (reactive spinel harzburgites, vs. impregnated plagioclase
peridotites) depending on the lithospheric depths at which interaction occurred.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
3.
Jonas Mota e Silva Cesar Fonseca Ferreira Filho Bernhard Bühn Elton Luiz Dantas 《Mineralium Deposita》2011,46(1):57-90
The “Americano do Brasil” Complex (ABC) is part of a cluster of coeval synorogenic mafic–ultramafic intrusions emplaced during
the Brasiliano/Pan-African Orogenic Cycle in Brazil. The medium-sized ABC consists of interlayered dunite, peridotite, websterite,
and gabbronorite. High Fo values of olivine (up to Fo88) and the crystallization sequence of the ABC (Ol + Chr ≥ Ol + Opx + Chr ≥ Cpx + Opx ≥ Opx + Pl + Cpx ≥ Opx + Pl + Cpx + Ilm + Mag)
suggest crystallization from tholeiitic high-MgO parental magmas. Light rare earth element (REE)-enriched mantle-normalized
REE profiles and εNd(T) values of +2.4 for cumulate rocks from the ABC suggest a depleted mantle source for the parental magma.
The ABC Ni–Cu sulfide deposit (3.1 Mt at 1.12 wt.% Ni and 1.02 wt.% Cu) consists of three distinctively different orebodies
(S1, S2, and G2). The S2 orebody, an unusual occurrence of stratiform massive sulfide hosted by dunite and peridotite in the
interior of a layered intrusion, results from sulfides accumulated at the transient base of the magma chamber following a
new influx of parental magma. The G2 orebody has an irregular and roughly cylindrical shape, consisting mainly of net-textured
sulfides. The G2 orebody is hosted by peridotite and pyroxenite and located stratigraphically below the S1 orebody. S2 and
G2 orebodies are characterized by low Cu/Cu + Ni ratios (mainly below 0.4). The S1 orebody, hosted by websterite and gabbronorite
in the more fractionated sequence of the ABC, is a cluster of several irregular discontinuous orebodies of Ni–Cu disseminated
sulfides. The sulfides of the S1 orebody have high Cu/Cu + Ni ratios (mainly between 0.5 and 0.8) and are highly depleted
in PGE. The S1 orebody is interpreted to result from a later event of sulfide segregation in the magma chamber, possibly following
the event that originated the G2 orebody. The bulk of δ34S values for sulfides of the ABC orebodies and their host rocks fall in the range of 0 ± 2‰. Higher δ34S values (between 3‰ and 5‰) are restricted to pyrite from xenoliths of gneiss located close to the S1 orebody and sulfides
from the S1 orebody. Crustal xenoliths and chemical data (lithogeochemistry and sulfur isotope composition) provide evidence
of crustal contamination of the igneous rocks hosting the S1 orebody, suggesting that sulfur saturation was induced by contamination
with sulfide-bearing crustal rocks. The ABC deposit is an example of Ni–Cu sulfide mineralization hosted by synorogenic mafic–ultramafic
intrusions. The S2 orebody is the first documented example of an economic stratiform massive sulfide orebody located within
layered intrusions, expanding the opportunities for exploration of Ni–Cu sulfides in orogenic regions worldwide. 相似文献
4.
R. G. Berman L. Ya Aranovich D. R. M. Pattison 《Contributions to Mineralogy and Petrology》1995,119(1):30-42
The garnet (Grt)-clinopyroxene (Cpx) Fe-Mg exchange thermometer has been re-evaluated through analysis of phase equilibrium
experiments defining the Fe-Mg exchange between Grt and Cpx, Grt and Ol (Ol=Olivine), and Cpx and Ol, together with thermophysical
and other phase equilibrium constraints on solid solution and individual end-member properties. Results show that all data
are mutually compatible if the heterogeneity range of Grt and Cpx in run products previously obtained by Pattison and Newton
(PN) are accounted for in assessing equilibrium Grt-Cpx compositions. Derived mixing properties are in good agreement with
results from numerous recent phase equilibrium studies. Application of the newly calibrated thermometer to a number of amphibolite
to granulite facies terrains indicates temperatures between 70 and 200 ° C above PN’s thermometer, and general compatibility
with independent temperature estimates.
Received: 3 September 1993 / Accepted: 16 June 1994 相似文献
5.
The influence of water on melting of mantle peridotite 总被引：47，自引：8，他引：39
This experimental study examines the effects of variable concentrations of dissolved H2O on the compositions of silicate melts and their coexisting mineral assemblage of olivine + orthopyroxene ± clinopyroxene ± spinel ± garnet.
Experiments were performed at pressures of 1.2 to 2.0 GPa and temperatures of 1100 to 1345 °C, with up to ∼12 wt% H2O dissolved in the liquid. The effects of increasing the concentration of dissolved H2O on the major element compositions of melts in equilibrium with a spinel lherzolite mineral assemblage are to decrease the
concentrations of SiO2, FeO, MgO, and CaO. The concentration of Al2O3 is unaffected. The lower SiO2 contents of the hydrous melts result from an increase in the activity coefficient for SiO2 with increasing dissolved H2O. The lower concentrations of FeO and MgO result from the lower temperatures at which H2O-bearing melts coexist with mantle minerals as compared to anhydrous melts. These compositional changes produce an elevated
SiO2/(MgO + FeO) ratio in hydrous peridotite partial melts, making them relatively SiO2 rich when compared to anhydrous melts on a volatile-free basis. Hydrous peridotite melting reactions are affected primarily
by the lowered mantle solidus. Temperature-induced compositional variations in coexisting pyroxenes lower the proportion of
clinopyroxene entering the melt relative to orthopyroxene. Isobaric batch melting calculations indicate that fluid-undersaturated
peridotite melting is characterized by significantly lower melt productivity than anhydrous peridotite melting, and that the
peridotite melting process in subduction zones is strongly influenced by the composition of the H2O-rich component introduced into the mantle wedge from the subducted slab.
Received: 7 April 1997 / Accepted: 9 January 1998 相似文献
6.
Alfons M. van den Kerkhof Geoffrey H. Grantham 《Contributions to Mineralogy and Petrology》1999,137(1-2):115-132
In the Port Edward area of southern Kwa-Zulu Natal, South Africa, charnockitic aureoles up to 10 m in width in the normally
garnetiferous Nicholson's Point Granite, are developed adjacent to intrusive contacts with the Port Edward Enderbite and anhydrous
pegmatitic veins. Mineralogical differences between the country rock and charnockitic aureole suggest that the dehydration
reaction Bt + Qtz → Opx + Kfs + H2O and the reaction of Grt + Qtz → Opx + Pl were responsible for the charnockitization. The compositions of fluid inclusions
show systematic variation with: (1) the Port Edward Enderbite being dominated by CO2 and N2 fluid inclusions; (2) the non-charnockitized granite by saline aqueous inclusions with 18–23 EqWt% NaCl; (3) the charnockitic
aureoles by low-salinity and pure water inclusions (<7 EqWt% NaCl); (4) the pegmatites by aqueous inclusions of various salinity
with minor CO2. As a result of the thermal event the homogenization temperatures of the inclusions in charnockite show a much larger range
(up to 390 °C) compared to the fluid inclusions in granite (mostly <250 °C). Contrary to fluid-controlled charnockitization
(brines, CO2) which may have taken place along shear zones away from the intrusive body, the present “proximal” charnockitized granite
formed directly at the contact with enderbite. The inclusions indicate contact metamorphism induced by the intrusion of “dry”
enderbitic magma into “wet” granite resulting in local dehydration. This was confirmed by cathodoluminescence microscopy showing
textures indicative for the local reduction of structural water in the charnockite quartz. Two-pyroxene thermometry on the
Port Edward Enderbite suggests intrusion at temperatures of ∼1000–1050 °C into country rock with temperature of <700 °C. The
temperature of aureole formation must have been between ∼700 °C (breakdown of pyrite to form pyrrhotite) and ∼1000 °C. Charnockitization
was probably controlled largely by heat related to anhydrous intrusions causing dehydration reactions and resulting in the
release and subsequent trapping of dehydration fluids. The salinity of the metamorphic fluid in the contact zones is supposed
to have been higher at an early stage of contact metamorphism, but it has lost its salt content by K-metasomatic reactions
and/or the preferential migration of the saline fluids out of the contact zones towards the enderbite. The low water activity
inhibited the localized melting of the granite. Mineral thermobarometry suggests that after charnockite aureole genesis, an
isobaric cooling path was followed during which reequilibration of most of the aqueous inclusions occurred.
Received: 8 November 1998 / Accepted: 21 June 1999 相似文献
7.
对来自滇东南马关木厂的尖晶石二辉橄榄岩中名义上无水矿物(NAMs)进行显微傅里叶变换红外光谱(Micro-FTIR)分析,结果显示,单斜辉石、斜方辉石和橄榄石中均含有以羟基形式存在的结构水,单斜辉石的水含量为160×10~(-6)~557×10~(-6)(质量分数,下同),斜方辉石的水含量为85×10~(-6)~207×10~(-6),橄榄石的水含量为5×10~(-6)~12×10~(-6),根据矿物百分比含量估算的全岩水含量为46×10~(-6)~137×10~(-6);元素地球化学特征表明,本次研究的橄榄岩包体是岩石圈地幔经历较低程度部分熔融的残余;低(La/Yb)N值(0.22~0.57)以及高Ti/Eu比值(4 076~6 772)暗示橄榄岩可能经历了以硅酸盐熔体为交代介质的微弱地幔交代作用;单斜辉石的微量元素组成比较单一,整体表现出高场强元素、大离子亲石元素以及轻稀土元素的同步亏损;结合中国东部地区已经发表的橄榄岩包体含水量数据来看,滇东南马关木厂岩石圈地幔具有明显富水的特征,可能与该区自中生代以来遭受的新特提斯洋壳大规模俯冲流体交代作用有关;与华北克拉通含水量的明显差异有可能反映的是两地岩石圈地幔正处于不同的演化阶段。 相似文献
8.
P -T paths from anatectic pelites 总被引：2，自引：1，他引：1
Frank S. Spear Matthew J. Kohn John T. Cheney 《Contributions to Mineralogy and Petrology》1999,134(1):17-32
A relatively simple petrogenetic grid for partial melting of pelitic rocks in the NCKFMASH system is presented based on the
assumption that the only H2O available for melting is through dehydration reactions. The grid includes both discontinuous and continuous Fe-Mg reactions;
contours of Fe/(Fe+Mg) for continuous reactions define P-T vectors along which continuous melting will occur. For biotite-bearing assemblages (garnet+biotite + sillimanite + K-feldspar + liquid
and garnet + biotite + cordierite + K-feldspar + liquid), Fe/(Fe+Mg) contours have negative slopes and melting will occur
with increasing temperature or pressure. For biotite-absent assemblages (garnet + cordierite + sillimanite + K-feldspar + liquid
or garnet + cordierite + orthopyroxene + K-feldspar + liquid) Fe/(Fe + Mg) contours have flat slopes and melting will occur
only with increasing pressure. The grid predicts that abundant matrix K-feldspar should only be observed if rocks are heated
at P < 3.8 kbar, that abundant retrograde muscovite should only be observed if rocks are cooled at P > 3.8 kbar, and that generation of late biotite + sillimanite replacing garnet, cordierite, or as selvages around leu- cosomes
should be common in rocks in which melt is not removed. There is also a predicted field for dehydration melting of staurolite
between 5 and 12 kbar. Textures in migmatites from New Hampshire, USA, suggest that prograde dehydration melting reactions
are very nearly completely reversible during cooling and crystallization in rocks in which melt is not removed. Therefore,
many reaction textures in “low grade” migmatites may represent retrograde rather than prograde reactions.
Received: 5 March 1998 / Accepted: 7 August 1998 相似文献
9.
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
10.
The spinel lherzolite massif at Balmuccia, northwest Italy,forms an elongate north-south trending lens (4.5 x 0.5 x 1.1km) within the pre-Alpine granulite basement complex of theIvrea zone. The western contact is a mylonite fault zone formedduring late emplacement cataclastic flow near the Insubric line;to the east the lherzolite massif is separated from the granulitesby a magmatic sheath of layered pyroxenites, pyroxene pegmatitesand meta-gabbros. Pyroxene reaction zones on gabbro dikes indunite pods which lie east of the main lherzolite massif showthat emplacement occurred at pressures >9 kb, based on peridotiteequilibria studies. Phase chemistry calculations on pyroxenitesand granulites show ambient P–T conditions to have been850 °C (Cpx–Opx equilibria) and 10–13 kb (Opx–Gt;Plg–Gt–Sill–Qtz) during emplacement of thelherzolite massif. Temperature calculations on 12 peridotitesfrom throughout the massif suggest an earlier high-T stage (1200°C; Ol–Px–Sp) followed by partial re-equilibrationat lower T (850–950 °C; Cpx–Opx). The areaswithin the lherzolite massif with the highest calculated Ol–Px–Sptemperatures have the lowest Cpx–Opx temperatures, suggestingthat the apparent Cpx–Opx temperatures are due to re-equilibrationduring emplacement. The spinel lherzolite probably originatedat 12 and 20 kb, based on the mineral assemblage Ol + Opx +Cpx + Sp + Hnbd. The inferred P–T ranges put both themassif and the granulites on a geotherm that is high for continentalcrust and implies a high surface heat flow at the time of emplacement(2.2 µcal/cm2 sec). The Balmuccia area later became thelocus of early Mesozoic rifting between the North and SouthAlpine plates. These relationships at Balmuccia are similarto the Great Basin of the western United States, where mantlexenoliths in young basalts that show P–T conditions of1100–1300 °C at 17–20 kb, occur in an area ofhigh heat flow (2.0 µCal/cm2 sec average) and extension.This suggests an association between up-welling of mantle peridotitesbelow continents and ensialic tensional tectonics. 相似文献
11.
Trace element distribution in Central Dabie eclogites 总被引：16，自引：0，他引：16
R. Sassi B. Harte D. A. Carswell H. Yujing 《Contributions to Mineralogy and Petrology》2000,139(3):298-315
Coesite-bearing eclogites from Dabieshan (central China) have been studied by ion microprobe to provide information on trace
element distributions in meta-basaltic mineral assemblages during high-pressure metamorphism. The primary mineralogy (eclogite
facies) appears to have been garnet and omphacite, usually with coesite, phengite and dolomite, together with high-alumina
titanite or rutile, or both titanite and rutile; kyanite also occurs occasionally as an apparently primary phase. It is probable
that there was some development of quartz, epidote and apatite whilst the rock remained in the eclogite facies. A later amphibolite
facies overprint led to partial replacement of some minerals and particularly symplectitic development after omphacite. They
vary from very fine-grained dusty-looking to coarser grained Am + Di + Pl symplectites. The eclogite facies minerals show
consistent trace element compositions and partition coefficients indicative of mutual equilibrium. Titanite, epidote and apatite
all show high concentrations of REE relative to clinopyroxene. The compositions of secondary (amphibolite facies) minerals
are clearly controlled by local rather than whole-rock equilibrium, with the composition of amphibole in particular depending
on whether it is replacing clinopyroxene or garnet. REE partition coefficients for Cpx/Grt show a dependence on the Ca content
of the host phases, with D
REE
Cpx/Grt
decreasing with decreasing D
Ca
. This behaviour is very similar to that seen in mantle eclogites, despite differences in estimated temperatures of formation
of 650–850 °C (Dabieshan) and 1000–1200 °C (mantle eclogites). With the exception of HREE in garnet, trace elements in the
eclogites are strongly distributed in favour of minor or accessory phases. In particular, titanite and rutile strongly concentrate
Nb and Zr, whilst LREE–MREE go largely into epidote, titanite and apatite. If these minor/accessory minerals behave in a refractory
manner during melting or fluid mobilisation events and do not contribute to the melt/fluid, then the resultant melts and fluids
will be strongly depleted in LREE–MREE.
Received: 11 February 1999 / Accepted: 31 January 2000 相似文献
12.
Experimental study of the phase and melting relations of homogeneous basalt + peridotite mixtures and implications for the petrogenesis of flood basalts 总被引：20，自引：0，他引：20
Gregory M. Yaxley 《Contributions to Mineralogy and Petrology》2000,139(3):326-338
Flood basalt provinces may constitute some of the most catastrophic volcanic events in the Earth's history. A popular model
to explain them involves adiabatic ascent of plumes of anomalously hot peridotite from a thermal boundary layer deep in the
mantle, across the peridotite solidus. However, peridotitic plumes probably require unreasonably high potential temperatures
to generate sufficient volumes of magma and high enough melting rates to produce flood volcanism. This lead to the suggestion
that low melting eclogitic or pyroxenitic heterogeneities may be present in the source regions of the flood basalts. In order
to constrain petrogenetic models for flood basalts generated in this way, an experimental investigation of the melting relations
of homogeneous peridotite + oceanic basalt mixtures has been performed. Experiments were conducted at 3.5 GPa on a fertile
peridotite (MPY90)–oceanic basalt (GA1) compositional join. The hybrid basalt + peridotite compositions crystallised garnet
lherzolite at subsolidus temperatures plus quenched ne-normative picritic liquids at temperatures just above the solidus, over the compositional range MPY90 to GA150MPY9050. The solidus temperature decreased slightly from ∼1500 °C for MPY90 to ∼1450 °C for GA150MPY9050. Compositions similar to GA130MPY9070 have 100% melting compressed into a melting interval which is approximately 50–60% smaller than that for pure MPY90, due
to a liquidus minimum. During adiabatic ascent of hybrid source material containing a few tens of percent basalt in peridotite,
the lower solidus and compressed solidus–liquidus temperature interval may conspire to substantially enhance melt productivity.
Mixtures of recycled oceanic crust and peridotite in mantle plumes may therefore provide a viable source for some flood volcanics.
Evidence for this would include higher than normal Fe/Mg values in natural primary liquids, consistent with equilibration
with more Fe-rich olivine than normal pyrolitic olivine (i.e. <Fo89–92). Modelling of fractionation trends in West Greenland picrites is presented to demonstrate that melts parental to the Greenland
picrites were in equilibrium at mantle P–T conditions with olivine with Fo84–86, suggesting an Fe-enriched source compared with normal peridotite, and consistent with the presence of a basaltic component
in the source.
Received: 29 October 1999 / Accepted: 3 February 2000 相似文献
13.
The near-solidus transition from garnet lherzolite to spinel lherzolite 总被引：20，自引：1，他引：19
The position of the transition from spinel lherzolite to garnet lherzolite in the system CaO-MgO-Al2O3-SiO2 (CMAS) has been determined experimentally at near-solidus temperatures. In reversed experiments, the transition occurs between
18 and 20 kbar at 1200 °C and between 26 and 27 kbar at 1500 °C, corresponding to higher pressures than previously envisaged.
A position for the transition deeper within the Earth further complicates the explanation of the so-called garnet signatures
in the trace element and isotope patterns of mid-ocean ridge basalts. If melting during adiabatic upwelling beneath a mid-ocean
ridge begins at the depth required for the stability of garnet in peridotitic compositions, simple melting models predict
that the amount of melt produced should be much greater than the observed thickness of the oceanic crust. A partial solution
to the apparent conflict might be that (1) the rather simplistic melting models are in error, (2) that melting begins in garnet
pyroxenite veins that are believed to be stable at lower pressures than garnet lherzolite or (3) that melting does not involve
garnet at all, but it is clinopyroxene causing the trace element patterns observed in basalts erupted at mid-ocean ridges.
A second set of reversal experiments were conducted to investigate the solubility of alumina in both orthopyroxenes and clinopyroxenes
at the high temperatures near the solidus in the system CMAS. The results are compatible with most previous studies, and may
be used as a starting point to calibrate thermodynamic models for pyroxenes in chemical systems, approximating upper mantle
chemistry.
Received: 9 August 1999 / Accepted: 29 October 1999 相似文献
14.
A series of experiments on the fluid-absent melting of a quartz-rich aluminous metagreywacke has been carried out. In this
paper, we report the chemical composition of the phases present in the experimental charges as determined by electron microprobe.
This analytical work includes biotite, plagioclase, orthopyroxene, garnet, cordierite, hercynite, staurolite, gedrite, oxide,
and glass, over the range 100–1000 MPa, 780–1025 °C. Biotites are Na- and Mg-rich, with Ti contents increasing with temperature.
The compositions of plagioclase range from An17 to An35, with a significant orthoclase component, and are always different from the starting minerals. At high temperature, plagioclase
crystals correspond to ternary feldspars with Or contents in the range 11–20 mol%. Garnets are almandine pyrope grossular
spessartine solid solutions, with a regular and significant increase of the grossular content with pressure. All glasses are
silicic (SiO2 = 67.6–74.4 wt%), peraluminous, and leucocratic (FeO + MgO = 0.9–2.9 wt%), with a bulk composition close to that of peraluminous
leucogranites, even for degrees of melting as high as 60 vol.%. With increasing pressure, SiO2 contents decrease while K2O increases. At any pressure, the melt compositions are more potassic than the water-saturated granitic minima. The H2O contents estimated by mass balance are in the range 2.5–5.6 wt%. These values are higher than those predicted by thermodynamic
models. Modal compositions were estimated by mass balance calculations and by image processing of the SEM photographs. The
positions of the 20 to 70% isotects (curves of equal proportion of melt) have been located in the pressure-temperature space
between 100 MPa and 1000 MPa. With increasing pressure, the isotects shift toward lower temperature between 100 and 200 MPa,
then bend back toward higher temperature. The melting interval increases with pressure; the difference in temperature between
the 20% and the 70% isotects is 40 °C at 100 MPa, and 150 °C at 800 MPa. The position of the isotects is interpreted in terms
of both the solubility of water in the melt and the nature of the reactions involved in the melting process. A comparison
with other partial melting experiments suggests that pelites are the most fertile source rocks above 800 MPa. The difference
in fertility between pelites and greywackes decreases with decreasing pressure. A review of the glass compositions obtained
in experimental studies demonstrates that partial melting of fertile rock types in the crust (greywackes, pelites, or orthogneisses)
produces only peraluminous leucogranites. More mafic granitic compositions such as the various types of calk-alkaline rocks,
or mafic S-type rocks, have never been obtained during partial melting experiments. Thus, only peraluminous leucogranites
may correspond to liquids directly formed by partial melting of metasediments. Other types of granites involve other components
or processes, such as restite unmixing from the source region, and/or interaction with mafic mantle-derived materials.
Received: 11 July 1995 / Accepted: 27 February 1997 相似文献
15.
Origin of peraluminous granites and granodiorites, Iberian massif, Spain: an experimental test of granite petrogenesis 总被引：27，自引：0，他引：27
Antonio Castro Alberto E. Patiño Douce L. Guillermo Corretgé Jesús D. de la Rosa Mohammed El-Biad Hassan El-Hmidi 《Contributions to Mineralogy and Petrology》1999,135(2-3):255-276
The discrimination between potential source materials involved in the genesis of Iberian granites and granodiorites, as well
as the role of mantle-crust interactions, are examined using constraints imposed by melting experiments, melting-assimilation
experiments and Sr-Nd isotope systematics. The Sr-Nd isotope relationships indicate the existence of different genetic trends
in which juvenile mantle materials are involved by different mechanisms: (1) a source trend, traced by a particular evolution
of the pre-Hercynian basement and indicating mantle participation at the time of sedimentation; (2) a set of magmatic trends
traced by gabbro-tonalite-enclave-granodiorite associations, implying the incorporation of new mantle material at the time
of granite generation. These relationships strongly support a pure crustal origin for the peraluminous leucogranites, derived
from partial melting of crustal protoliths, and a hybrid origin for the peraluminous granodiorites. These granodiorites are
the most abundant granitic rocks of the Central Iberian zone (CIZ) of the Iberian massif, implying that processes of hybridisation
by assimilation and/or magma mixing played an important role in granitoid production during the Hercynian orogeny. These hypotheses
have been tested by means of melting and assimilation experiments. Melting experiments in the range 800–900 °C and at pressures
of 3, 6, 10 and 15 kbar indicate that: (1) several potential source materials such as Bt-Ms gneisses and metagreywackes are
suitable for the production of peraluminous leucogranite melts; (2) the melt compositions are always leucogranitic, regardless
of pressure; (3) pressure exerts a strong influence on the fertility of the source: experiments at 3 kbar produce more than
20 vol% of melt, compared with less than 5 vol% of melt produced at 10 and 15 kbar and at the same temperature. The melting-assimilation
experiments carried out at 1000 °C and 4, 7 and 10 kbar and using a proportion of 50% gabbro and 50% gneiss give high melt
proportions (more than 50 vol.%) and noritic residues. These melts have the composition of leucogranodiorites, and overlap
with part of the compositional range of peraluminous granodiorites of the Iberian massif. The generation of more mafic granodiorites
may be explained by the incorporation of some residual orthopyroxene to the granodiorite magmas. The low solubility of Fe + Mg
prevents the generation of granodiorite melts with more than 3 wt% of MgO + FeO at all crustal pressures. The large volumes
of peraluminous, hybrid granodiorites, produced by assimilation of crustal rocks by mantle magmas, imply that an important
episode of crustal growth took place during the Late-Palaeozoic Hercynian orogeny in the Iberian massif.
Received: 30 June 1998 / Accepted: 27 November 1998 相似文献
16.
John D. Clemens Giles T. R. Droop Gary Stevens 《Contributions to Mineralogy and Petrology》1997,129(4):308-325
The system KAlO2–MgO–SiO2–H2O–CO2 has long been used as a model for the processes of granulite-facies metamorphism and the development of orthopyroxene-bearing
mineral assemblages through the breakdown of biotite-bearing assemblages. There has been considerable controversy regarding
the role of carbon dioxide in metamorphism and partial melting. We performed new experiments in this system (at pressures
of 342 to 1500 MPa with T between 710 and 1045 °C and X
Fl
H2O between 0.05 and 1.00), accurately locating most of the dehydration and melting equilibria in P-T-X
Fl
H2O space. The most important primary result is that the univariant reaction Phl + Qtz + Fl = En + Sa + melt must be almost coincident
with the fluid-absent reaction (Phl + Qtz = En + Sa + melt) in the CO2-free subsystem. In conjunction with the results of previous measurements of CO2 solubility in silicate melts and phase equilibrium experiments, our theoretical analysis and experiments suggest that CO2 cannot act as a flux for partial melting. Crustal melting in the presence of H2O–CO2 mixed fluids will always occur at temperatures higher than with pure H2O fluid present. Magmas produced by such melting will be granitic (s.l.) in composition, with relatively high SiO2 and low MgO contents, irrespective of the H2O–CO2 ratio in any coexisting fluid phase. We find no evidence that lamprophyric magmas could be generated by partial fusion of
quartz-saturated crustal rocks. The granitic melts formed will not contain appreciable dissolved CO2. The channelled passage of hot CO2-rich fluids can cause local dehydration of the rocks through which they pass. In rock-dominated (as opposed to fluid-dominated)
systems, minor partial melting can also occur in veins initially filled with CO2-rich fluid, as dehydration and local disequilibrium drive the fluid towards H2O-rich compositions. However, CO2 is unlikely to be a significant agent in promoting regional granulite-grade metamorphism, melting, magma generation, metasomatism
or long-range silicate mass transfer in Earth's crust. The most viable model for the development of granulite-facies rocks
involves the processes of fluid-absent partial melting and withdrawal of the melt phase to higher crustal levels.
Received: 28 November 1996 / Accepted: 25 June 1997 相似文献
17.
The compositions of multiply saturated partial melts are valuablefor the thermodynamic information that they contain, but aredifficult to determine experimentally because they exist onlyover a narrow temperature range at a given pressure. Here wetry a new approach for determining the composition of the partialmelt in equilibrium with olivine, orthopyroxene, clinopyroxeneand spinel (Ol + Opx + Cpx + Sp + Melt) in the system CaO–MgO–Al2O3–SiO2(CMAS) at 1·1 GPa: various amounts of K2O are added tothe system, and the resulting melt compositions and temperatureare extrapolated to zero K2O. The ‘sandwich’ experimentalmethod was used to minimize problems caused by quench modification,and Opx and Cpx were previously synthesized at conditions nearthose of the melting experiments to ensure they had appropriatecompositions. Results were then checked by reversal crystallizationexperiments. The results are in good agreement with previouswork, and establish the anhydrous solidus in CMAS to be at 1320± 10°C at 1·1 GPa. The effect of K2O is todepress the solidus by 5·8°C/wt %, while the meltcomposition becomes increasingly enriched in SiO2, being quartz-normativeabove 4 wt % K2O. Compared with Na2O, K2O has a stronger effectin depressing the solidus and modifying melt compositions. Theisobaric invariant point in the system CMAS–K2O at whichOl + Opx + Cpx + Sp + Melt is joined by sanidine (San) is at1240 ± 10°C. During the course of the study severalother isobaric invariant points were identified and their crystaland melt compositions determined in unreversed experiments:Opx + Cpx + Sp + An + Melt in the system CMAS at 1315 ±10°C; in CMAS–K2O, Opx + Cpx + Sp + An + San + Meltat 1230 ± 10°C and Opx + Sp + An + San + Sapph +Melt at 1230 ± 10°C, where An is anorthite and Sapphis sapphirine. Coexisting San plus An in three experiments helpdefine the An–San solvus at 1230–1250°C. KEY WORDS: feldspar solvus; igneous sapphirine; mantle solidus; partial melting; systems CMAS and CMAS–K2O 相似文献
18.
Sr isotope systematics during melt generation by intrusion of basalt into continental crust 总被引：1，自引：1，他引：0
We have studied the Sr isotopic composition of partial melts of biotite granite generated experimentally and by intrusion
of basalt into the Sierra Nevada Batholith. The experiments employed large, 3-cm cubes of granite to duplicate natural grain-boundary
textures and were performed in air over the temperature interval 1000–1250 °C, to simulate basalt-induced wall rock and xenolith
melting in the shallow crust. In both the experimental and natural analogs, fusion of plagioclase + alkali-feldspar ± quartz
and biotite + plagioclase ± quartz results in the formation of colorless and brown melt (quenched to glass) respectively.
Accordant with this melting behavior, brown glasses are enriched in radiogenic Sr and MgO, FeO, CaO, and TiO2 relative to colorless glasses. These results support recent studies indicating that the isotopic compositions of crustal
melts can reflect the relative contributions of mineral phases entering the melt, rather than the isotopic composition of
the bulk source rock. In addition, we show that at shallow-crustal conditions preferential breakdown of biotite leads to initial
high-87Sr/86Sr, low-Sr concentration melts. However, as the degree of melting increases, melts become less radiogenic yet are more enriched
in elemental Sr due to loss of biotite from the restite and increased consumption of feldspars. Our results therefore suggest,
if partial melts of granitic crust segregate rapidly during episodic magmatic underplating, successive melt batches can evolve
from high-87Sr/86Sr to low-87Sr/86Sr liquids as melting progresses.
Received: 25 August 1998 / Accepted: 10 March 1999 相似文献
19.
Entrained Macrocryst Minerals as a Key to the Source Region of Olivine Nephelinites: Humberg, Kaiserstuhl, Germany 总被引：1，自引：0，他引：1
Ulianov Alexey; Muntener Othmar; Ulmer Peter; Pettke Thomas 《Journal of Petrology》2007,48(6):1079-1118
Olivine nephelinites commonly contain macrocrysts of olivineand clinopyroxene. Some of these macrocrysts might representfragments of the source region of the host magma transportedto the Earth's surface. If this hypothesis is correct thesefragments can be used to characterize the composition of thesource region and to put constraints on the magma generationprocess. In this study, we investigate the origin of macrocrystsand mineral aggregates from an olivine nephelinite from theKaiserstuhl, Germany. We focus on clinopyroxenes (Cpx), whichcan be divided into three groups. Cpx I is relict Cpx from aggregateswith deformed olivine that is depleted in Ca and characterizedby strong light rare earth element (LREE) fractionation, lowTi/Eu and negative high field strength element (HFSE) anomalies.Its geochemical signature is consistent with formation by carbonatitemetasomatism and with equilibration in the presence of orthopyroxene.Cpx II is Ca-rich Cpx, forming both aggregates with deformedolivine and individual macrocrysts. The LREE, as for Cpx I,are strongly fractionated. Convex REE patterns may be present.The depletion in HFSE is less pronounced. Cpx III is oscillatoryzoned Cpx phenocrysts showing enrichment in Ca, convex REE patternsand no HFSE anomalies. The transition in the trace element abundancesbetween the Cpx of the three groups is gradual. However, CpxI and II did not crystallize from the host magma, as demonstratedby the presence of kink-bands and undulose extinction in theassociated olivine and by the composition of alkali aluminosilicateglass inclusions in Cpx II. Based on the Cpx relationships,we interpret the studied suite of macrocrysts and mineral aggregatesas a mixture of disintegrated fragments of the source regionof the host olivine nephelinite. The process of melt generationwas multi-stage. A primary carbonatite melt ascending from deeperlevels in the mantle, probably from the dolomite–garnetperidotite stability field, reacted with mantle peridotite alongthe solidus ledge in the system lherzolite–CO2 (< 20–22kbar) and started to crystallize carbonate minerals. Becauseof its low solidus temperature, the resulting carbonate-wehrliteassemblage melted incongruently with the formation of additionalclinopyroxene. The carbonatite melt evolved during crystallizationof carbonate minerals and concomitant incongruent melting ofthe carbonate-wehrlite, accompanied by the segregation of incipientalkali aluminosilicate melts. As a consequence of fast reactionrates in the presence of a carbonatite melt, this process probablytook place under disequilibrium conditions. Further meltingof the assemblage wehrlite + alkali aluminosilicate melt ledto the generation of the olivine nephelinite magma. It entrainedfragments of the wehrlite and brought them to the surface. KEY WORDS: carbonatite; metasomatism; source region; clinopyroxene macrocrysts; wehrlite; olivine nephelinite; Kaiserstuhl 相似文献
20.
Bradley S. Singer James D. Myers Carol D. Frost 《Contributions to Mineralogy and Petrology》1992,110(1):87-112
In contrast to adjacent volcanic centers of the modern central Aleutian arc, Seguam Island developed on strongly extended arc crust. K-Ar dates indicate that mid-Pleistocene, late-Pleistocene, and Holocene eruptive phases constitute Seguam. This study focuses on the petrology of the mid-Pleistocene, 1.07–07 Ma, Turf Point Formation (TPF) which is dominated by an unusual suite of porphyritic basalt and basaltic andesite lavas with subordinate phenocryst-poor andesite to rhyodacite lavas. Increasing whole-rock FeO*/MgO from basalt to dacite, the anhydrous Plag+Ol+Cpx±Opx±Mt phenocryst assemblage, groundmass pigeonite, and the reaction Ol+Liq=Opx preserved in the mafic lavas indicate a tholeiitic affinity. Thermometry and comparison to published phase equilibria suggests that most TPF basalts crystallized Plag+Ol+Cpx±Mt at 1160°C between about 3–5 kb (±1–2% H2O), andesites crystallized Plag+Cpx+Opx±Mt at 1000°C between 3–4 kb with 3–5% H2O, and dacites crystallized Plag +Cpx±Opx±Mt at 1000°C between 1–2 kb with 2–3% H2O. All lavas crystallized at f
o
2 close to the NNO buffer. Mineral compositions and textures indicate equilibrium crystallization of the evolved lavas; petrographic evidence of open-system mixing or assimilation is rare. MgO, CaO, Al2O3, Cr, Ni, and Sr abundances decrease and K2O, Na2O, Rb, Ba, Zr, and Pb increase with increasing SiO2 (50–71%). LREE enrichment [(Ce/Yb)n=1.7±0.2] characterizes most TPF lavas; total REE contents increase and Eu anomalies become more negative with increasing SiO2. Relative to other Aleutian volcanic centers, TPF basalts and basaltic andesites have lower K2O, Na2O, TiO2, Rb, Ba, Sr, Zr, Y, and LREE abundances. 87Sr/86Sr ratios (0.70361–0.70375) and ratios of 206Pb/204Pb (18.88–18.97), 207Pb/204Pb (15.58–15.62), 208Pb/204Pb (38.46–38.55) are the highest measured for any suite of lavas in the oceanic portion of the Aleutian arc. Conversely, Nd values (+5.8 to+6.7) are among the lowest from the Aleutians. Sr, Nd, and Pb ratios are virtually constant from basalt through rhyodacite, whereas detectable isotopic heterogenity is observed at most other Aleutian volcanic centers. Major and trace element, REE, and Sr, Nd, and Pb isotopic compositions are consistent with the basaltic andesitic, andesitic, dacitic, and rhyodacitic liquids evolving from TPF basaltic magma via closed-system fractional crystallization alone. Fractionation models suggest that removal of 80 wt% cumulate (61% Plag, 17% Cpx, 12% Opx, 7% Ol, and 3% Mt) can produce 20 wt% rhyodacitic residual liquid per unit mass of parental basaltic liquid. Petrologic and physical constraints favor segregation of small batches of basalt from a larger mid-crustal reservoir trapped below a low-density upper crustal lid. In these small magma batches, the degree of cooling, crystallization, and fractionation are functions of the initial mass of basaltic magma segregated, the thermal state of the upper crust, and the magnitude of extension. Tholeiitic magmas erupted at Seguam evolved by substantially different mechanisms than did calc-alkaline lavas erupted at the adjacent volcanic centers of Kanaga and Adak on unextended arc crust. These variable differentiation mechanisms and liquid lines of descent reflect contrasting thermal and mechanical conditions imposed by the different tectonic environments in which these centers grew. At Seguam, intra-arc extension promoted eruption of voluminous basalt and its differentiates, unmodified by interaction with lower crustal or upper mantle wallrocks. 相似文献