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1.
A.V.Kargin L.V.Sazonova A.A.Nosova N.M.Lebedeva Yu.A.Kostitsyn E.V.Kovalchuk V.V.Tretyachenko Ya.S.Tikhomirova 《地学前缘(英文版)》2019,10(5):1941-1959
We present petrography and mineral chemistry for both phlogopite,from mantle-derived xenoliths(garnet peridotite,eclogite and clinopyroxene-phlogopite rocks)and for megacryst,macrocryst and groundmass flakes from the Grib kimberlite in the Arkhangelsk diamond province of Russia to provide new insights into multi-stage metasomatism in the subcratonic lithospheric mantle(SCLM)and the origin of phlogopite in kimberlite.Based on the analysed xenoliths,phlogopite is characterized by several generations.The first generation(Phil)occurs as coarse,discrete grains within garnet peridotite and eclogite xenoliths and as a rock-forming mineral within clinopyroxene-phlogopite xenoliths.The second phlogopite generation(Phl2)occurs as rims and outer zones that surround the Phil grains and as fine flakes within kimberlite-related veinlets filled with carbonate,serpentine,chlorite and spinel.In garnet peridotite xenoliths,phlogopite occurs as overgrowths surrounding garnet porphyroblasts,within which phlogopite is associated with Cr-spinel and minor carbonate.In eclogite xenoliths,phlogopite occasionally associates with carbonate bearing veinlet networks.Phlogopite,from the kimberlite,occurs as megacrysts,macrocrysts,microcrysts and fine flakes in the groundmass and matrix of kimberlitic pyroclasts.Most phlogopite grains within the kimberlite are characterised by signs of deformation and form partly fragmented grains,which indicates that they are the disintegrated fragments of previously larger grains.Phil,within the garnet peridotite and clinopyroxene-phlogopite xenoliths,is characterised by low Ti and Cr contents(TiO_21 wt.%,Cr_2 O_31 wt.% and Mg# = 100 × Mg/(Mg+ Fe)92)typical of primary peridotite phlogopite in mantle peridotite xenoliths from global kimberlite occurrences.They formed during SCLM metasomatism that led to a transformation from garnet peridotite to clinopyroxene-phlogopite rocks and the crystallisation of phlogopite and high-Cr clinopyroxene megacrysts before the generation of host-kimberlite magmas.One of the possible processes to generate low-Ti-Cr phlogopite is via the replacement of garnet during its interaction with a metasomatic agent enriched in K and H_2O.Rb-Sr isotopic data indicates that the metasomatic agent had a contribution of more radiogenic source than the host-kimberlite magma.Compared with peridotite xenoliths,eclogite xenoliths feature low-Ti phlogopites that are depleted in Cr_2O_3 despite a wider range of TiO_2 concentrations.The presence of phlogopite in eclogite xenoliths indicates that metasomatic processes affected peridotite as well as eclogite within the SCLM beneath the Grib kimberlite.Phl2 has high Ti and Cr concentrations(TiO_22 wt.%,Cr_2O_31 wt.% and Mg# = 100× Mg/(Mg + Fe)92)and compositionally overlaps with phlogopite from polymict brecc:ia xenoliths that occur in global kimberlite formations.These phlogopites are the product of kimberlitic magma and mantle rock interaction at mantle depths where Phl2 overgrew Phil grains or crystallized directly from stalled batches of kimberlitic magmas.Megacrysts,most macrocrysts and microcrysts are disintegrated phlogopite fragments from metasomatised peridotite and eclogite xenoliths.Fine phlogopite flakes within kimberlite groundmass represent mixing of high-Ti-Cr phlogopite antecrysts and high-Ti and low-Cr kimberlitic phlogopite with high Al and Ba contents that may have formed individual grains or overgrown antecrysts.Based on the results of this study,we propose a schematic model of SCLM metasomatism involving phlogopite crystallization,megacryst formation,and genesis of kimberlite magmas as recorded by the Grib pipe. 相似文献
2.
Mark Brearley Christopher M. Scarfe Toshitsugu Fujii 《Contributions to Mineralogy and Petrology》1984,88(1-2):53-63
Approximately 200 upper mantle xenoliths from Summit Lake, near Prince George, British Columbia, were collected from a basanitoid flow of Late Cenozoic (possibly post-glacial) age. The most abundant xenolith is spinel lherzolite (55%), with subordinate wehrlite (22%), clinopyroxenite (10%), olivine websterite (10%), websterite (2%) and dunite (1%). Xenoliths have granular textures and both green chrome diopside-bearing and black aluminous augitebearing xenoliths are present. About 5% of the xenoliths are banded on a cm scale, suggesting that the upper mantle beneath north-central British Columbia is heterogeneous on a scale of cm to meters.Microprobe data on the mineral phases indicate that the xenoliths are generally well equilibrated. Typically in spinel lherzolite, olivines are Fo89, orthopyroxenes are En90 and chrome diopside is Wo45En50Fs5. Spinels vary in composition from xenolith to xenolith. The evidence for partial melting observed in five xenoliths, may be due to heating during incorporation of the xenoliths within the host magma or to instability caused by decompression as the xenoliths are transported to the surface.Using element partition geothermometers, equilibration temperatures are calculated to be between 1080–1100° C. Pressures, estimated from a Cordilleran geotherm, are between 18–20 kbar. These temperatures are somewhat higher than estimates from xenoliths from other localities in Late Cenozoic alkali basalts in south and central British Columbia. It is concluded, therefore, that either the Summit Lake suite represents samples from a deeper source region in the upper mantle or the Late Cenozoic geotherm varied in time and space.On leave from the Geological Institute, University of Tokyo 相似文献
3.
SHAW CLIFF S. J.; EYZAGUIRRE JIMENA; FRYER BRIAN; GAGNON JOEL 《Journal of Petrology》2005,46(5):945-972
Xenoliths record two distinct events in the mantle below theQuarternary West Eifel Volcanic Field, Germany. The first, duringthe Hercynian Orogeny, led to widespread formation of secondary,Ti-poor amphibole, clinopyroxene and phlogopite. The signatureof the second event, related to Quaternary volcanism, variesacross the field. At Dreiser Weiher and Meerfelder Maar, thisevent is characterized by amphibolephlogopiteclinopyroxeneveins, hosted in lherzolite and harzburgite xenoliths broughtto the surface by sodic olivine nephelinitebasanite suitelavas. These veins formed from crystallization of sodic magmathat flowed along fractures in the mantle. At Rockeskyller Kopf,Gees and Baarley, the Quaternary event is characterized by wehrlitexenoliths, many of which have phlogopiteclinopyroxeneveins, that were transported by potassic foid suite lavas. Wehrliteformed by reaction of lherzoliteharzburgite, with a largevolume of potassic magma that flowed along grain boundariesrather than in fractures. During reaction, orthopyroxene wasconsumed and secondary clinopyroxene, olivine and phlogopiteprecipitated. Veins formed in wehrlites only during periodicover-pressure events. The composition of the magmas parentalto the veins is similar to the lavas that carried the xenolithsto surface, indicating that the source of foid and olivine nephelinitebasanitesuite magma is domainal, as was the flow regime and magma flux. KEY WORDS: Eifel; mantle xenoliths; metasomatism; trace elements 相似文献
4.
Summary Ti-bearing phlogopite-biotite is dominant in Ugandan kamafugite-carbonatite effusives and their entrained alkali clinopyroxenite
xenoliths. It occurs as xeno/phenocrysts, microphenocrysts and groundmass minerals and also as a major xenolith mineral. Xenocrystic
micas in kamafugites and carbonatites are aluminous (> 12 wt% Al2O3), typically contain significant levels of Cr (up to 1.1 wt% Cr2O3), and are Ba-poor. Microphenocryst and groundmass micas in feldspathoidal rocks extend to Al-poor compositions, are depleted
in Cr, and are generally enriched in Ba. In general, xenocrystic micas occupy the Al2O3 and TiO2 compositional field of the xenolith mica, and on the basis of Mg#, and high P, T experimental evidence they probably crystallised
at mantle pressures. Mica xenocryst Cr contents range from those in Cr-poor megacryst and MARID phlogopite to higher values
found in primary and metasomatic phlogopites in kimberlite-hosted peridotite xenoliths. Such Cr contents in Ugandan mica xenocrysts
are considered consistent with derivation from carbonate-bearing phlogopite wehrlite and phlogopite-clinopyroxenite mantle.
Olivine melilitite xenocryst micas are distinguished by higher Mg# and Cr content than mica in clinopyroxenite xenoliths and
mica in Katwe-Kikorongo mixed melilitite-carbonatite tephra. Higher Al2O3 distinguishes Fort Portal carbonatite xenocrysts and some contain high Cr. It is suggested that the genesis of Katwe-Kikorongo
olivine melilitite and Fort Portal carbonatite involves a carbonate-bearing phlogopite wehrlite source while the source of
the mixed carbonatite-melilitite rocks may be carbonate-bearing phlogopite clinopyroxenite.
Received January 24, 2000; revised version accepted September 27, 2001 相似文献
5.
NEUMANN ELSE-RAGNHILD; GRIFFIN WILLIAM LINDSEY; PEARSON NORMAN J.; O'REILLY SUZANNE YVONNE 《Journal of Petrology》2004,45(12):2573-2612
Laser ablation microprobe data are presented for olivine, orthopyroxeneand clinopyroxene in spinel harzburgite and lherzolite xenolithsfrom La Palma, Hierro, and Lanzarote, and new whole-rock trace-elementdata for xenoliths from Hierro and Lanzarote. The xenolithsshow evidence of strong major, trace element and Sr isotopedepletion (87Sr/86Sr 0·7027 in clinopyroxene in themost refractory harzburgites) overprinted by metasomatism. Thelow Sr isotope ratios are not compatible with the former suggestionof a mantle plume in the area during opening of the AtlanticOcean. Estimates suggest that the composition of the originaloceanic lithospheric mantle beneath the Canary Islands correspondsto the residues after 2530% fractional melting of primordialmantle material; it is thus significantly more refractory thannormal mid-ocean ridge basalt (MORB) mantle. Thetrace element compositions and Sr isotopic ratios of the mineralsleast affected by metasomatization indicate that the upper mantlebeneath the Canary Islands originally formed as highly refractoryoceanic lithosphere during the opening of the Atlantic Oceanin the area. During the Canarian intraplate event the uppermantle was metasomatized; the metasomatic processes includecryptic metasomatism, resetting of the SrNd isotopicratios to values within the range of Canary Islands basalts,formation of minor amounts of phlogopite, and meltwall-rockreactions. The upper mantle beneath Tenerife and La Palma isstrongly metasomatized by carbonatitic or carbonaceous meltshighly enriched in light rare earth elements (REE) relativeto heavy REE, and depleted in ZrHf and Ti relative toREE. In the lithospheric mantle beneath Hierro and Lanzarote,metasomatism has been relatively weak, and appears to be causedby high-Si melts producing concave-upwards trace element patternsin clinopyroxene with weak negative Zr and Ti anomalies. TiAlFe-richharzburgites/lherzolites, dunites, wehrlites and clinopyroxenitesformed from mildly alkaline basaltic melts (similar to thosethat dominate the exposed parts of the islands), and appearto be mainly restricted to magma conduits; the alkali basaltmelts have caused only local metasomatism in the mantle wall-rocksof such conduits. The various metasomatic fluids formed as theresults of immiscible separations, meltwall-rock reactionsand chromatographic fractionation either from a CO2-rich basalticprimary melt, or, alternatively, from a basaltic and a siliceouscarbonatite or carbonaceous silicate melt. KEY WORDS: mantle xenoliths; mantle minerals; trace elements; depletion; carbonatite metasomatism 相似文献
6.
Upper mantle xenoliths from Wikieup, AZ, provide abundant evidence for magmatic modification of the uppermost mantle beneath
the Transition Zone between the Colorado Plateau and the southern Basin and Range province. Upper mantle lithologies in this
xenolith suite are represented by spinel peridotite, wehrlite, plagioclase peridotite, and Al-augite group pyroxenites. Isotopic
data for these xenoliths yield relatively uniform values and suggest a common petrogenesis. Al-augite-bearing gabbro and pyroxenite
xenoliths from this locality are interpreted to have formed by crystal fractionation processes from parent alkali basalts
similar to the Wikieup host basalt. Mineral and whole rock compositions show consistent trends of increasing incompatible
element contents (Fe, Al, Ca, Na, K, LIL, and LREE), and decreasing compatible element contents (Mg, Cr, Ni) from spinel peridotite
to wehrlite to plagioclase peridotite to the host basalt composition. These compositional trends are interpreted as resulting
from varying degrees of magma-mantle wall rock interaction as ascending mafic magmas infiltrated upper mantle peridotite.
Small degrees of melt infiltration resulted in slightly modified spinel peridotite compositions while moderate degrees metasomatized
spinel peridotite to wehrlite, and the highest degrees metasomatized it to plagioclase peridotite. Whole rock compositions
and clinopyroxene, plagioclase, and whole rock isotopic data suggest that the infiltrating magmas were the same as those from
which the gabbros and pyroxenites crystallized, and that they were alkalic in composition, similar to the Wikieup host alkali
olivine basalts. Relatively uniform 143Nd/144Nd for the mineral separates and whole rocks in spite of the significantly wide range in their 147Sm/144Nd (0.71–0.23 in clinopyroxene) suggests that the Wikieup xenoliths including gabbro, pyroxenite, peridotite, wehrlite, and
plagioclase peridotite, are all relatively young rocks formed or metasomatized by a relatively recent magmatic episode.
Received: 21 May 1996 / Accepted: 23 December 1996 相似文献
7.
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
8.
The 1800 Kaupulehu flow on Hualalai Volcano, Hawaii, containsabundant xcnoliths of dunitc, wehrlite, and olivine clinopyroxenitewith minor gabbro, troctolite, anorthosite, and wcbstcrite.The petrography and mineral compositions of 41 dunite, wehrlite,and olivine clinopyroxenite xenoliths have been studied, andclinopyroxene separates from eight of these have been analyzedfor Ba, K, Rb, Sr, rare earth elements, 87Sr/86Sr, and 143Nd/144Nd.Temperatures of equilibration obtained by olivine-spinel andpyroxene geothermometry range from 1000 to 1200 C. Mineralogicaldata combined with published fluid inclusion data indicate depthsof origin in the range of 830 km. The rarity of orthopyroxene, the presence of Fe-rich olivine(Fo8189) and clinopyroxene (Fs512), and the occurrenceof high TiO2 in spinel (0.92.8 wt.%) and clinopyroxene(0351.33 wt%) all indicate that the xenoliths are cumulates,not residues from partial fusion. The separated clinopyrox-eneshave 87Sr/86Sr (0-70348.0-70367) and 143Nd/144Nd (0.512930.51299)values that are different from Sr and Nd isotope ratios of Pacificabyssal basalts (>0.7032 and >0-5130, respectively). Also,clinopyroxenes and spinels in the xenoliths have generally higherTiO2 contents (>O.35 and >0.91 wt.%, respectively) thantheir counterparts in abyssal cumulates (<0.40 and <0.70wt%,respectively). These differences indicate that the xenolithsare not a normal component of oceanic crust. Because the xenoliths and alkalic to transitional Hualalai lavashave similar values for Cr/(Cr + Al) and Cr/(Cr + Al + Fe3+)of spinels, 87Sr/86Sr of clinopyroxenes, and whole-rock 3He/4He,we conclude that the xenoliths are cumulates from such magmas.Multiple parental magmas for the xenoliths are indicated byslightly heterogeneous 87Sr/86Sr of clinopyroxene separates.Depths of formation of the xenoliths are estimated to be {smalltilde}830 km. Extensive crystallization of olivine in the absence of pyroxenesand plagioclase is a characteristic and prominent feature ofHawaiian tholeiitic magmatism. Dunite xenoliths crystallizedfrom alkalic magmas have previously been reported from MaunaKea Volcano (Atwill & Garcia, 1985) and Loihi Seamount (Clague,1988). Our finding of an alkalic signature for dunite xenolithsfrom a third Hawaiian volcano, Hualalai, shows that early olivinecrystallization should be considered a characteristic not justof Hawaiian tholeiitic magmatism but also of Hawaiian alkalicmagmatism. 相似文献
9.
Origin of Fe-rich lherzolites and wehrlites from Tok,SE Siberia by reactive melt percolation in refractory mantle peridotites 总被引:2,自引:2,他引:0
Lherzolite–wehrlite (LW) series xenoliths from the quaternary Tok volcanic field in the southeastern Siberian craton are distinguished
from the more common lherzolite–harzburgite (LH) series by (a) low Mg numbers (0.84–0.89) at high modal olivine (66–84%) and
(b) widespread replacement of orthopyroxene (0–12%) and spinel by clinopyroxene (7–22%). The LW series peridotites are typically
enriched in Ca, Fe, Mn and Ti, and depleted in Si, Ni and Cr relative to refractory LH series rocks (Mg number ≥0.89), which
are metasomatised partial melting residues. Numerical modelling of Fe–Mg solid/liquid exchange during melt percolation demonstrates
that LW series rocks can form by reaction of host refractory peridotites with evolved (Mg numbers 0.6–0.7), silica-undersaturated
silicate melts at high melt/rock ratios, which replace orthopyroxene with clinopyroxene and decrease Mg numbers. This process
is most likely related to underplating and fractionation of basaltic magma in the shallow mantle, which also produced olivine–clinopyroxene
cumulates found among the Tok xenoliths. 相似文献
10.
Chromite-bearing peridotites of the Ordovician Miyamori ophiolitecomplex exhibit spatial mineralogical variations on scales rangingfrom several centimeters to a few kilometers. The largest variationscorrespond to the entire structure of the complex, which featuresa layered zone of interstratified harzburgite, wehrlite, andvarious pyroxenites sandwiched between zones of unlayered harzburgiteand dunite containing only minor pyroxenite bands. All zonesexhibit the same deformation microstructures, tabular equigranularto porphyroclastic textures, and strong mineral aggregate lineation.Harzburgite from the unlayered zones is characterized by olivinevalues of 100Mg/(Mg+Fe)=9193.5 and chromite values of100Cr/(Cr+Al+Fe3+)=4075. These variables exhibit a positivecorrelation, which is typical of harzburgites and lherzolitesfrom the basal units of ophiolites and from xenoliths in alkalibasalts and kimberlites. The harzburgite is therefore interpretedas a residue from partial melting in the mantle. By contrast,harzburgite in the interlayered zone features olivine valuesof 100Mg/(Mg+Fe)=8892 and chromite values of 100Cr/(Cr+Al+Fe3+)=4060,and in this case the variables tend to show a negative correlationin any given locality and they partly overlap data from theintercalated wehrlite and dunite. The harzburgite of the layeredzone is interpreted as residual mantle that reacted with evolvedmelts that then crystallized as wehrlite and dunite. The harzburgitein the unlayered zones is more refractory than that in the layeredzone, even after removing effects of reaction. This differencecan be explained either by enhanced partial melting and meltextraction in the unlayered zones, possibly owing to the preferentialintroduction of a waterrich fluid, or by melt segregation fromthe unlayered zones and transfer to the layered zone in responseto a piezometric pressure gradient and compaction of a solidresidual matrix. Mineralogical evidence suggests that evolvedmelts migrated through conduits formed in the layered zone byfracturing or diapirism. 相似文献
11.
Francesco Princivalle Gabriella Salviulo Andrea Marzoli Enzo M. Piccirillo 《Contributions to Mineralogy and Petrology》2000,139(5):503-508
The crystal chemistry of six clinopyroxenes enclosed in protogranular spinel-peridotite mantle xenoliths from Lake Nji (Cameroon,
W Africa) was studied by means of single-crystal X-ray diffraction and electron microprobe. These spinel-peridotite xenoliths
are characterised by clinopyroxene contents distinctly higher than those reported by Lee et al. (1996) for spinel-peridotite
xenoliths of the same region (19–11% and 15–8% respectively) and by high clinopyroxene/orthopyroxene ratios: 0.7–2.7 (present
study) and about 0.4 (Lee et al. 1996). The clinopyroxene crystal chemistry indicates that the xenoliths show the compositional
features of a mantle source contaminated by small-volume melts, responsible for the high clinopyroxene content. The protogranular
texture of the Cameroon xenoliths (upper portion of lithospheric mantle) testifies that the spinel peridotite and the associated
small-volume melts completely re-equilibrated at the spinel-peridotite facies. This is also supported by the petrological
and geochemical data of Lee et al. (1996) on the Etinde–Biu Plateau spinel-peridotite xenoliths, which underwent Late Proterozoic–Early
Paleozoic enrichment in incompatible trace elements.
Received: 6 October 1999 / Accepted: 27 March 2000 相似文献
12.
Harzburgite and lherzolite tectonites from the Horoman peridotite complex, Hokkaido, northern Japan, contain variable amounts
of secondary phlogopite and amphibole. Phlogopite-rich veinlets parallel to the foliation planes usually cut olivine-rich
parts of the rocks; single-grained interstitial phlogopites are usually associated with orthopyroxene grains. Amphiboles are
disseminated in rocks or sometimes occur in the phlogopite-rich veinlets. Within individual veinlets, phlogopites show extensive
inter-grain variations in K/(K + Na) ratio (0.96–0.75), generally decreasing from the central (usually the thickest) part
towards the marginal parts of veinlets. In contrast, Ti contents are nearly constant in Ti-poor veins or decrease slightly
with decreasing K/(K + Na) in T-rich veins. Variation of Ti in phlogopites is very large (0.1–6.8 wt%) and is inversely correlated
with Mg/(Mg + Fe*) (Fe*, total iron) atomic ratios, which vary from 0.96 to 0.88. Intra-vein variation of phlogopite chemistry (especially K/(K +
Na) ratio) could be achieved by in situ fractional crystallization of trapped fluids; variation of Ti, however, cannot be
explained by in situ fractionation of the fluids, indicating various Ti contents of the parent fluids. It is suggested that
fluids responsible for the formation of the Horoman phlogopites and amphiboles were magmatic volatiles successively released
from evolving alkali basaltic magmas. Individual fluids trapped within peridotites were fractionated, precipitating phlogopites
successively poorer in K. When the fluids became rich enough in Na, amphiboles co-precipitated with phlogopites. Similar fractional
crystallization of phlogopites and amphiboles is expected in the upper mantle on a larger scale if fluids move upwards. This
process may control, at least partly, a lateral K/Na distribution in the upper mantle; K and Na may be concentrated in deeper
and shallower parts, respectively. 相似文献
13.
Origin of spongy textures in clinopyroxene and spinel from mantle xenoliths, Hessian Depression, Germany 总被引:1,自引:0,他引:1
Summary Spongy textures are observed in anhydrous Group 1 mantle xenoliths (harzburgite, lherzolite and wehrlite) hosted in Tertiary
alkali basaltic lavas from the Hessian Depression, Germany. These textures are developed only on clinopyroxene and spinel,
and occur as rims or cross-cutting veinlets and patches showing optical continuity with the host grain. They are often associated
with pools of amorphous glassy material. There is no preferential development of spongy domains against the xenolith-lava
contact suggesting that the host magma did not play any significant role in their formation. Spongy clinopyroxene and spinel
occur in all rock types, but, are more pervasive in wehrlite.
Chemically, spongy domains of clinopyroxene and spinel are more refractory than unaffected areas, which is consistent with
their formation through a partial melting event. The associated glassy material shows chemical characteristics which suggest
that the melt pools are genetically related to the development of the spongy textures. The partial melting event was probably
triggered by the infiltration of a low-density fluid. The fluid may have evolved from a silicate melt responsible for the
metasomatic Fe-enrichment recorded in wehrlite. In this context, the more pervasive development of spongy clinopyroxene in
wehrlite may be explained by a higher concentration of the evolved fluid phase at proximity to its silicate melt source.
Received March 15, 2000; revised version accepted September 6, 2001 相似文献
14.
Mantle Xenoliths from the Southeastern Slave Craton: Evidence for Chemical Zonation in a Thick, Cold Lithosphere 总被引:7,自引:3,他引:7
We present the first data on the petrology of the mantle lithosphereof the Southeastern (SE) Slave craton, Canada. These are basedon petrographic, mineralogical and geochemical studies of mantlexenoliths in Pipe 5034 of the Cambrian Gahcho Kué kimberlitecluster. Major types of mantle xenoliths include altered eclogite,coarse garnet or spinel peridotite, and deformed garnet peridotite.The peridotites belong to the low-temperature suite and formedat T=6001300°C and P= 2580 kbar in a thick(at least 220250 km), cool lithosphere. The SE Slavemantle is cooler than the mantle of other Archaean cratons andthat below other terranes of the Slave craton. The thick lithosphereand the relatively cool thermal regime provide favourable conditionsfor formation and preservation of diamonds beneath the SE Slaveterrane. Similar to average Archaean mantle worldwide, the SESlave peridotite is depleted in magmaphile major elements andcontains olivine with forsterite content of 9193·5.With respect to olivine composition and mode, all terranes ofthe Slave mantle show broadly similar compositions and are relativelyorthopyroxene-poor compared with those of the Kaapvaal and Siberiancratons. The SE Slave spinel peridotite is poorer in Al, Caand Fe, and richer in Mg than deeper garnet peridotite. Thegreater chemical depletion of the shallow upper mantle is typicalof all terranes of the Slave craton and may be common for thesubcontinental lithospheric peridotitic mantle in general. Peridotiticxenoliths of the SE Slave craton were impregnated by kimberliticfluids that caused late-stage recrystallization of primary clinopyroxene,spinel, olivine and spinel-facies orthopyroxene, and formationof interstitial clinopyroxene. This kimberlite-related recrystallizationdepleted primary pyroxenes and spinel in Al. The kimberliticfluid was oxidizing, Ti-, Fe- and K-rich, and Na-poor, and introducedserpentine, chlorite, phlogopite and spinel into peridotitesat P < 35 kbar. KEY WORDS: kimberlite xenolith; lithosphere; mantle terrane; chemical zoning; thermobarometry; Slave craton 相似文献
15.
Garnetite Xenoliths and Mantle-Water Interactions Below the Colorado Plateau, Southwestern United States 总被引:1,自引:0,他引:1
Garnetite xenoliths from ultramafic diatremes in northeasternArizona provide insights into hydration and metasomatism inthe mantle. The garnetites contain more than 95% garnet, someof which has complex compositional zonation related to growthin fractures within grains. Accessory minerals include rutile,ilmenite, chlorite, clinopyroxene, and zircon. Zircon grainsin one rock were analyzed in situ to determine UPb agesand Hf isotopic compositions. Most UPb analyses ploton or near concordia in the range 6085 Ma but a few arediscordant. The range in 176Hf/177Hf is about 0·28180·2828,with grains zoned to more radiogenic Hf from interiors to rims.The garnetite protolith contained zircons at least 1·8Ga in age, and garnet and additional zircon crystallized episodicallyduring the interval 8560 Ma. The garnetites are interpretedas mantle analogues of rodingites, formed in metasomatic reactionzones caused by waterrock interactions in Proterozoicmantle during late Cretaceous and Cenozoic subduction of theFarallon plate. Associated eclogite xenoliths may have beenparts of these same reaction zones. The rodingite hypothesisrequires serpentinization in the mantle wedge 700 km from thetrench, beginning 510 Myr before tectonism related tolow-angle subduction. KEY WORDS: garnetite; LuHf, mantle; rodingite; metasomatism 相似文献
16.
Geochemistry and Sr–Nd isotopic compositions of mantle xenoliths from the Monte Vulture carbonatite–melilitite volcano, central southern Italy 总被引:2,自引:0,他引:2
H. Downes T. Kostoula A. Jones A. Beard M. Thirlwall J.-L. Bodinier 《Contributions to Mineralogy and Petrology》2002,144(1):78-92
Spinel peridotite xenoliths found in the Monte Vulture carbonatite-melilitite volcano have been derived from the subcontinental lithospheric mantle beneath central southern Italy. Clinopyroxene-poor lherzolites and harzburgites are the most common rock types, with subordinate wehrlites and dunites. Small quantities of phlogopite and carbonate are present in a few samples. The peridotites record a large degree of partial melting and have experienced subsequent enrichment which has increased their LILE and LREE contents, but in most cases their HFSE contents are low. Despite being carried to the surface by a carbonatite-melilitite host, the whole-rock and clinopyroxene compositions of the xenoliths have a trace-element signature more closely resembling that of silicate-melt metasomatised mantle rather than carbonatite-metasomatised peridotites. 87Sr/86Sr and 143Nd/144Nd isotopic ratios for clinopyroxene from the Vulture peridotites are 0.7042-0.7058 and 0.51260-0.5131 respectively. They form a trend away from the depleted mantle to the composition of the host magmas, and show a significant enrichment in 87Sr/86Sr compared with most European mantle samples. The mantle beneath Monte Vulture has had a complex evolution - we propose that the lithosphere had already undergone extensive partial melting before being affected by metasomatism from a silicate melt which may have been subduction-related. 相似文献
17.
Near-Ultrahigh Pressure Processing of Continental Crust: Miocene Crustal Xenoliths from the Pamir 总被引:8,自引:0,他引:8
HACKER BRADLEY; LUFFI PETER; LUTKOV VALERY; MINAEV VLADISLAV; RATSCHBACHER LOTHAR; PLANK TERRY; DUCEA MIHAI; PATINO-DOUCE ALBERTO; McWILLIAMS MICHAEL; METCALF JIM 《Journal of Petrology》2005,46(8):1661-1687
Xenoliths of subducted crustal origin hosted by Miocene ultrapotassicigneous rocks in the southern Pamir provide important new informationregarding the geological processes accompanying tectonism duringthe Indo-Eurasian collision. Four types have been studied: sanidineeclogites (omphacite, garnet, sanidine, quartz, biotite, kyanite),felsic granulites (garnet, quartz, sanidine and kyanite), basalticeclogites (omphacite and garnet), and a glimmerite (biotite,clinopyroxene and sanidine). Apatite, rutile and carbonate arethe most abundant minor phases. Hydrous phases (biotite andphengite in felsic granulites and basaltic eclogites, amphibolesin mafic and sanidine eclogites) and plagioclase form minorinclusions in garnet or kyanite. Solid-phase thermobarometryreveals recrystallization at mainly ultrahigh temperatures of10001100°C and near-ultrahigh pressures of 2·52·8GPa. Textures, parageneses and mineral compositions suggestderivation of the xenoliths from subducted basaltic, tonaliticand pelitic crust that experienced high-pressure dehydrationmelting, K-rich metasomatism, and solid-state re-equilibration.The timing of these processes is constrained by zircon agesfrom the xenoliths and 40Ar/39Ar ages of the host volcanic rocksto 5711 Ma. These xenoliths reveal that deeply subductedcrust may undergo extensive dehydration-driven partial melting,density-driven differentiation and disaggregation, and sequestrationwithin the mantle. These processes may also contribute to thealkaline volcanism observed in continent-collision zones. KEY WORDS: xenolith; high-pressure; subduction; Pamir; Tibet 相似文献
18.
Mineral Chemistry of Peridotites from Paleozoic, Mesozoic and Cenozoic Lithosphere: Constraints on Mantle Evolution beneath Eastern China 总被引:24,自引:0,他引:24
ZHENG JIANPING; GRIFFIN WILLIAM L.; O'REILLY SUZANNE Y.; YANG JINSUI; LI TIANFU; ZHANG MING; ZHANG RUTH Y.; LIOU JOHN G. 《Journal of Petrology》2006,47(11):2233-2256
Major- and trace-element data on the constituent minerals ofgarnet peridotite xenoliths hosted in early Paleozoic (457500Ma) kimberlites and Neogene (1618 Ma) volcanic rockswithin the North China Craton are compared with those from thepre-pilot hole of the Chinese Continental Scientific DrillingProject (CCSD-PP1) in the tectonically exhumed Triassic (220Ma) Sulu ultrahigh-pressure (UHP) terrane along its southernmargin. PT estimates for the Paleozoic and Neogene peridotitexenoliths reflect different model geotherms corresponding tosurface heat flows of 40 mW/m2 (Paleozoic) and 80 mW/m2 (Neogene).Garnet peridotite xenoliths or xenocrysts from the Paleozoickimberlites are strongly depleted, similar to peridotites fromother areas of cratonic mantle, with magnesium olivine (meanFo92.7), Cr-rich garnet and clinopyroxene with high La/Yb. Garnet(and spinel) peridotite xenoliths hosted in Neogene basaltsare derived from fertile mantle; they have high Al2O3 and TiO2contents, low-Mg-number olivine (mean Fo89.5), low-Cr garnetand diopside with flat rare earth element (REE) patterns. Thedifferences between the Paleozoic and Neogene xenoliths suggestthat a buoyant refractory lithospheric keel present beneaththe eastern North China Craton in Paleozoic times was at leastpartly replaced by younger, hotter and more fertile lithosphericmantle during MesozoicCenozoic times. Garnet peridotitesfrom the Sulu UHP terrane have less magnesian olivine (Fo91.5),and lower-Cr garnet than the Paleozoic xenoliths. The diopsideshave low heavy REE (HREE) contents and sinusoidal to light REE(LREE)-enriched REE patterns. These features, and their highMg/Si and low CaO and Al2O3 contents, indicate that the CCSD-PP1peridotites represent a moderately refractory mantle protolith.Details of mineral chemistry indicate that this protolith experiencedcomplex metasomatism by asthenosphere-derived melts or fluidsin Mesoproterozoic, and subsolidus re-equilibration involvingfluids/melts derived from the subducted Yangtze continentalcrust during UHP metamorphism in the early Mesozoic. Tectonicextension of the subcontinental lithospheric mantle of the NorthChina Craton and exhumation of the Sulu UHP rocks in the earlyMesozoic induced upwelling of the asthenosphere. Peridotitessampled by the Neogene basalts represent newly formed lithospherederived by cooling of the upwelling asthenospheric mantle inJurassicCretaceous and Paleogene time. KEY WORDS: garnet peridotite xenoliths; North China Craton; lithospheric thinning; Sulu UHP terrane; UHP lithosphere evolution; mantle replacement 相似文献
19.
HEAMAN LARRY M.; CREASER ROBERT A.; COOKENBOO HARRISON O.; CHACKO TOM 《Journal of Petrology》2006,47(4):821-858
The Jericho kimberlites are part of a small Jurassic kimberlitecluster in the northern Slave craton, Canada. A variety of datingtechniques were applied to constrain the nature and age of twoJericho kimberlites, JD-1 (170·2 ± 4·3Ma RbSr phlogopite megacrysts, 172·8 ±0·7 Ma UPb eclogite rutile, 178 ± 5 MaUPb eclogite zircon lower intercept) and JD-3 (173 ±2 Ma RbSr phlogopite megacryst; 176·6 ±3·2 Ma UPb perovskite), and all yielded identicalresults within analytical uncertainty. As there is no discernibledifference in the radiometric ages obtained for these two pipes,the composite RbSr phlogopite megacryst date of 173·1± 1·3 Ma is interpreted as the best estimate forthe emplacement age of both Jericho pipes. The initial Sr isotopecomposition of 0·7053 ± 0·0003 derivedfrom phlogopite megacrysts overlaps the range (0·70430·7084)previously reported for Jericho whole-rocks. These strontiumisotope data, combined with the radiogenic initial 206Pb/204Pbratio of 18·99 ± 0·33 obtained in thisstudy, indicate that the Jericho kimberlites are isotopicallysimilar to Group 1 kimberlites as defined in southern Africa.The Jericho kimberlites are an important new source of mantlexenoliths that hold clues to the nature of the Slave cratonsubcontinental mantle. A high proportion (30%) of the Jerichomantle xenolith population consists of various eclogite typesincluding a small number (23%) of apatite-, diamond-,kyanite- and zircon-bearing eclogites. The most striking aspectof the Jericho zircon-bearing eclogite xenoliths is their peculiargeochemistry. Reconstructed whole-rock compositions indicatethat they were derived from protoliths with high FeO, Al2O3and Na2O contents, reflected in the high-FeO (22·627·5wt %) nature of garnet and the high-Na2O (8·479·44wt %) and high-Al2O3 (13·1214·33 wt %)character of the clinopyroxene. These eclogite whole-rock compositionsare highly enriched in high field strength elements (HFSE) suchas Nb (1331134 ppm), Ta (528 ppm), Zr (17794934ppm) and Hf (2364 ppm). This HFSE enrichment is linkedto growth of large (up to 2 mm) zircon and niobian rutile crystals(up to 3 modal %) near the time of eclogite metamorphism. Thediamond-bearing eclogites on the other hand are characterizedby high-MgO (19·621·3 wt %) garnet andultralow-Na2O (0·441·50 wt %) clinopyroxene.Paleotemperature estimates indicate that both the zircon- anddiamond-bearing eclogites have similar equilibration temperaturesof 9501020°C and 9901030°C, respectively,corresponding to mantle depths of 150180 km. Integrationof petrographic, whole-rock and mineral geochemistry, geochronologyand isotope tracer techniques indicates that the Jericho zircon-bearingeclogite xenoliths have had a complex history involving Paleoproterozoicmetamorphism, thermal perturbations, and two or more episodesof Precambrian mantle metasomatism. The oldest metasomatic event(Type 1) occurred near the time of Paleoproterozoic metamorphism(1·8 Ga) and is responsible for the extreme HFSE enrichmentand growth of zircon and high-niobian rutile. A second thermalperturbation and concomitant carbonatite metasomatism (Type2) is responsible for significant apatite growth in some xenolithsand profound light rare earth element enrichment. Type 2 metasomatismoccurred in the period 1·01·3 Ga and isrecorded by relatively consistent whole-rock eclogite modelNd ages and secondary UPb zircon upper intercept dates.These eclogite xenoliths were derived from a variety of protoliths,some of which could represent metasomatized pieces of oceaniccrust, possibly linked to east-dipping subduction beneath theSlave craton during construction of the 1·881·84Ga Great Bear continental arc. Others, including the diamond-bearingeclogites, could be cumulates from mafic or ultramafic sillcomplexes that intruded the Slave lithospheric mantle at depthsof about 150180 km. KEY WORDS: zircon- and diamond-bearing eclogites; Jericho kimberlite, geochronology; Precambrian metasomatism, northern Slave Craton 相似文献
20.
我国东北小古里河-科洛-五大连池-二克山火山带钾质矿物成因及地质意义 总被引:3,自引:2,他引:1
东北黑龙江小古里河-科洛-五大连池-二克山火山岩带是我国近代保存最好的火山群之一,此带火山岩的岩石化学特点全都强碱富钾,K2O/Na2O>1.2,属于一套高钾过碱性火山岩。通过对东北钾质火山岩及金云母橄榄岩地幔捕虏体中钾质矿物金云母、白榴石的成分、结晶环境与岩浆成分及来源关系的研究,认为在岩石圈伸展构造背景下,地幔金云母橄榄岩的低度部分熔融形成钾质岩浆,钾质岩浆上升到地壳浅部经历了白榴石的结晶作用。岩浆演化晚期,因钾质矿物大量晶出导致岩浆相对富钠而出现他形霞石和方钠石等填隙矿物。火山岩及地幔捕虏体中富挥发分矿物金云母、白榴石、磷灰石、霞石和方钠石还提供了钾质岩浆富含H2O、F、Cl、P等挥发分的证据。 相似文献