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1.
Yongjun Gao Jochen Hoefs Eric Hellebrand Anette von der Handt Jonathan E. Snow 《Contributions to Mineralogy and Petrology》2007,153(4):429-442
Major and trace element profiles of clinopyroxene grains in oceanic gabbros from ODP Hole 735B have been investigated by a
combined in situ analytical study with ion probe, and electron microprobe. In contrast to the homogeneous major element compositions,
trace elements (REE, Y, Cr, Sr, and Zr) show continuous core to rim zoning profiles. The observed trace element systematics
in clinopyroxene cannot be explained by a simple diffusive exchange between melts and gabbros along grain boundaries. A simultaneous
modification of the melt composition is required to generate the zoning, although Rayleigh fractional crystallization modelling
could mimic the general shape of the profiles. Simultaneous metasomatism between the cumulate crystal and the porous melt
during crystal accumulation is the most likely process to explain the zoning. Deformation during solidification of the crystal
mush could have caused squeezing out of the incompatible element enriched residual melts (interstitial liquid). Migration
of the melt along grain boundaries might carry these melt out of the system. This process named as synkinematic differentiation
or differentiation by deformation (Natland and Dick in J Volcanol Geotherm Res 110(3–4):191–233, 2001) may act as an important magma evolution mechanism in the oceanic crust, at least at slow-spreading ridges. 相似文献
2.
Mauro Lo Cascio Yan Liang Nobumichi Shimizu Paul C. Hess 《Contributions to Mineralogy and Petrology》2008,156(1):87-102
The grain-scale processes of peridotite melting were examined at 1,340°C and 1.5 GPa using reaction couples formed by juxtaposing
pre-synthesized clinopyroxenite against pre-synthesized orthopyroxenite or harzburgite in graphite and platinum-lined molybdenum
capsules. Reaction between the clinopyroxene and orthopyroxene-rich aggregates produces a melt-enriched, orthopyroxene-free,
olivine + clinopyroxene reactive boundary layer. Major and trace element abundance in clinopyroxene vary systematically across
the reactive boundary layer with compositional trends similar to the published clinopyroxene core-to-rim compositional variations
in the bulk lherzolite partial melting studies conducted at similar P–T conditions. The growth of the reactive boundary layer takes place at the expense of the orthopyroxenite or harzburgite and
is consistent with grain-scale processes that involve dissolution, precipitation, reprecipitation, and diffusive exchange
between the interstitial melt and surrounding crystals. An important consequence of dissolution–reprecipitation during crystal-melt
interaction is the dramatic decrease in diffusive reequilibration time between coexisting minerals and melt. This effect is
especially important for high charged, slow diffusing cations during peridotite melting and melt-rock reaction. Apparent clinopyroxene-melt
partition coefficients for REE, Sr, Y, Ti, and Zr, measured from reprecipitated clinopyroxene and coexisting melt in the reactive
boundary layer, approach their equilibrium values reported in the literature. Disequilibrium melting models based on volume
diffusion in solid limited mechanism are likely to significantly underestimate the rates at which major and trace elements
in residual minerals reequilibrate with their surrounding melt.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
3.
U. Wiechert Dmitri A. Ionov Karl Hans Wedepohl 《Contributions to Mineralogy and Petrology》1997,126(4):345-364
Spinel peridotite xenoliths from the Atsagin-Dush volcanic centre, SE Mongolia range from fertile lherzolites to clinopyroxene(cpx)-bearing
harzburgites. The cpx-poor peridotites typically contain interstitial fine-grained material and silicate glass and abundant
fluid inclusions in minerals, some have large vesicular melt pockets that apparently formed after primary clinopyroxene and
spinel. No volatile-bearing minerals (amphibole, phlogopite, apatite, carbonate) have been found in any of the xenoliths.
Fifteen peridotite xenoliths have been analysed for major and trace elements; whole-rock Sr isotope compositions and O isotope
composition of all minerals were determined for 13 xenoliths. Trace element composition and Sr-Nd isotope compositions were
also determined in 11 clinopyroxene and melt pocket separates. Regular variations of major and moderately incompatible trace
elements (e.g. heavy-rare-earth elements) in the peridotite series are consistent with its formation as a result of variable
degrees of melt extraction from a fertile lherzolite protolith. The Nd isotope compositions of LREE (light-rare-earth elements)-depleted
clinopyroxenes indicate an old (≥ 1 billion years) depletion event. Clinopyroxene-rich lherzolites are commonly depleted in
LREE and other incompatible trace elements whereas cpx-poor peridotites show metasomatic enrichment that can be related to
the abundance of fine-grained interstitial material, glass and fluid inclusions in minerals. The absence of hydrous minerals,
ubiquitous CO2-rich microinclusions in the enriched samples and negative anomalies of Nb, Hf, Zr, and Ti in primitive mantle-normalized
trace element patterns of whole rocks and clinopyroxenes indicate that carbonate melts may have been responsible for the metasomatic
enrichment. Low Cu and S contents and high δ34S values in whole-rock peridotites could be explained by interaction with oxidized fluids that may have been derived from
subducted oceanic crust. The Sr-Nd isotope compositions of LREE-depleted clinopyroxenes plot either in the MORB (mid-ocean-ridge
basalt) field or to the right of the mantle array, the latter may be due to enrichment in radiogenic Sr. The LREE-enriched
clinopyroxenes and melt pockets plot in the ocean island-basalt field and have Sr-Nd isotope signatures consistent with derivation
from a mixture of the DMM (depleted MORB mantle) and EM (enriched mantle) II sources.
Received: 18 January 1996 / Accepted: 23 August 1996 相似文献
4.
Riccardo Tribuzio Massimo Tiepolo Riccardo Vannucci Piero Bottazzi 《Contributions to Mineralogy and Petrology》1999,134(2-3):123-133
The trace element distribution in three selected olivine-bearing gabbros from the Northern Apennine ophiolites has been determined.
These rocks consist of euhedral plagioclase and olivine, and subhedral to poikilitic clinopyroxene. Fe-Ti-oxides, titanian
pargasite, orthopyroxene and apatite occur as interstitial accessory minerals. Plagioclase, clinopyroxene and accessory minerals
were analysed for rare earth (REE) and selected trace elements by secondary ion mass spectrometry. Both plagioclase and clinopyroxene
are compositionally zoned. The plagioclase rims have slightly lower anorthite component and higher light REE (LREE), Ba and
K than the cores. Likewise, the clinopyroxene rims show a slight Mg and Cr decrease, and a marked increase in Zr, REE and
Y relative to the core. The rims of plagioclase and clinopyroxene, Fe-Ti-oxides, apatite and titanian pargasite most likely
formed through post-cumulus fractional crystallization of interstitial liquid. It is argued that such interstitial liquid
had an exotic component, probably related to the infiltration of highly evolved, slightly LREE enriched liquid in the cumulate
pile. On the basis of mass balance calculations, we show that Fe-Ti-oxides play an important role in the Ti budget of the
whole rock, as does apatite for LREE.
Received: 15 January 1998 / Accepted: 22 September 1998 相似文献
5.
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
6.
Millennial timescale resolution of rhyolite magma recharge at Tarawera volcano: insights from quartz chemistry and melt inclusions 总被引:4,自引:4,他引:0
Phil Shane Victoria C. Smith Ian Nairn 《Contributions to Mineralogy and Petrology》2008,156(3):397-411
Most rhyolite eruption episodes of Tarawera volcano have emitted several physiochemically distinct magma batches (∼1–10 km3). These episodes were separated on a millennial timescale. The magma batches were relatively homogeneous in temperature and
composition at pumice scale (>4 cm), but experienced isolated crystallisation histories. At the sub-cm scale, matrix glasses
have trace element compositions (Sr, Ba, Rb) that vary by factors up to 2.5, indicating incomplete mixing of separate melts.
Some quartz-hosted melt inclusions are depleted in compatible trace elements (Sr, Ti, Ba) compared to enclosing matrix glasses.
This could reflect re-melting of felsic crystals deeper in the crystal pile. Individual quartz crystals display a variety
of cathodoluminescence brightness and Ti zoning patterns including rapid changes in melt chemistry and/or temperature (∼50–100°C),
and point to multi-cycle crystallisation histories. The Tarawera magma system consisted of a crystal-rich mass containing
waxing and waning melt pockets that were periodically recharged by silicic melts driven by basaltic intrusion.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
7.
Recycled crustal melt injection into lithospheric mantle: implication from cumulative composite and pyroxenite xenoliths 总被引:3,自引:0,他引:3
Hong-Fu Zhang Eizo Nakamura Katsura Kobayashi Ji-Feng Ying Yan-Jie Tang 《International Journal of Earth Sciences》2010,99(6):1167-1186
A rare composite xenolith and abundant cumulative pyroxenites obtained from the Mesozoic Fangcheng basalts on the eastern
North China Craton record a complex history of melt percolation and circulation in the subcontinental lithospheric mantle.
The composite xenolith has a dunite core and an olivine clinopyroxenite rim. The dunite is of cumulative origin and has a
granular recrystallized texture and extremely low Mg# [100 Mg/(Mg + Fe) = 81–82] contents in olivines. The olivine clinopyroxenite
contains larger clinopyroxene and/or orthopyroxene with a few fine-grained olivine and tiny phlogopite, feldspar, and/or carbonate
minerals interstitial to clinopyroxene. The clinopyroxene has low Mg# (83–85). Compositional similarity between dunitic olivine
and pyroxenitic one indicates a sequential crystallization of dunite and pyroxenite from a precursor melt. Pyroxenite xenoliths
include olivine websterites and clinopyroxenites, both are of cumulative origin. Estimation of the melt from major oxides
in olivines and REE concentrations in clinopyroxenes in these composite and pyroxenite xenoliths suggests a derivation from
subducted crustal materials, consistent with the highly enriched EMII-like Sr and Nd isotopic ratios observed in the pyroxenites.
Occurrence of phlogopite, feldspar and carbonate minerals in some xenoliths requires the melt rich in alkalis (K, Na), silica
and volatiles (water and CO2) at the latest stage as well, similar to highly silicic and potassic melts. Thus, the occurrence of these composite and pyroxenite
xenoliths provides an evidence for voluminous injection of recycled crustal melts into the lithosphere beneath the southeastern
North China Craton at the Late Mesozoic, a reason for the rapid lithospheric enrichment in both elemental and isotopic compositions. 相似文献
8.
Ben-Xun Su Hong-Fu Zhang Yue-Heng Yang Patrick Asamoah Sakyi Ji-Feng Ying Yan-Jie Tang 《Mineralogy and Petrology》2012,104(3-4):225-247
Major and trace element compositions of constituent minerals, partly decomposed rims of orthopyroxenes (DRO), ‘closed’ melt pockets (CMP) and open melt pockets (OMP) in some Western Qinling peridotite xenoliths were obtained by LA-ICP-MS. Systematic core-to-rim compositional variations of garnet, clinopyroxene and orthopyroxene demonstrate that these minerals underwent variable degrees of subsolidus breakdown or partial melting. Both DROs and CMPs consist of similar mineral assemblages and are characterized by high TiO2, CaO + Na2O and low MgO contents; they are enriched in LREE and LILE compositions, have positive anomalies in Pb, Sr and particularly Ti, negative Th and U, and variable Zr and Hf anomalies. These chemical features are distinct and reflect reactions involving the orthopyroxenes. Compared to the CMPs, the OMPs, which are composed of a complex assemblage of minerals, display lower FeO and MgO contents, larger ranges in SiO2 and Na2O, higher TiO2, Al2O3, CaO and trace element concentrations, slightly negative Zr and Hf anomalies, and apparently negative Ti anomalies. Modeling calculations of partial fusion of orthopyroxenes and clinopyroxenes suggest that the CMPs most likely originated from the breakdown of orthopyroxenes with variably minor contribution of external melts from the melting of clinopyroxenes, whereas the OMPs were probably formed from the modification of the CMPs through the interaction with large amount of external melts. 相似文献
9.
Monique Seyler J. -P. Lorand H. J. B. Dick M. Drouin 《Contributions to Mineralogy and Petrology》2007,153(3):303-319
ODP Leg 209 Site 1274 mantle peridotites are highly refractory in terms of lack of residual clinopyroxene, olivine Mg# (up
to 0.92) and spinel Cr# (∼0.5), suggesting high degree of partial melting (>20%). Detailed studies of their microstructures
show that they have extensively reacted with a pervading intergranular melt prior to cooling in the lithosphere, leading to
crystallization of olivine, clinopyroxene and spinel at the expense of orthopyroxene. The least reacted harzburgites are too
rich in orthopyroxene to be simple residues of low-pressure (spinel field) partial melting. Cu-rich sulfides that precipitated
with the clinopyroxenes indicate that the intergranular melt was generated by no more than 12% melting of a MORB mantle or
by more extensive melting of a clinopyroxene-rich lithology. Rare olivine-rich lherzolitic domains, characterized by relics
of coarse clinopyroxenes intergrown with magmatic sulfides, support the second interpretation. Further, coarse and intergranular
clinopyroxenes are highly depleted in REE, Zr and Ti. A two-stage partial melting/melt–rock reaction history is proposed,
in which initial mantle underwent depletion and refertilization after an earlier high pressure (garnet field) melting event
before upwelling and remelting beneath the present-day ridge. The ultra-depleted compositions were acquired through melt re-equilibration
with residual harzburgites.
Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users. 相似文献
10.
Experimental comparison of trace element partitioning between clinopyroxene and melt in carbonate and silicate systems, and implications for mantle metasomatism 总被引:13,自引:2,他引:11
Experiments in the systems diopside-albite (Di-Ab) and diopside-albite-dolomite (Di-Ab-Dmt), doped with a wide range of trace
elements, have been used to characterise the difference between clinopyroxene-silicate melt and clinopyroxene-carbonate melt
partitioning. Experiments in Di-Ab-Dmt yielded clinopyroxene and olivine in equilibrium with CO2-saturated dolomitic carbonate melt at 3 GPa, 1375 °C. The experiments in Di-Ab were designed to bracket those conditions
(3 GPa, 1640 °C and 0.8 GPa, 1375 °C), and so minimise the contribution of differential temperature and pressure to partitioning.
Partition coefficients, determined by SIMS analysis of run products, differ markedly for some elements between Di-Ab and Di-Ab-Dmt
systems. Notably, in the carbonate system clinopyroxene-melt partition coefficients for Si, Al, Ga, heavy REE, Ti and Zr are
higher by factors of 5 to 200 than in the silicate system. Conversely, partition coefficients for Nb, light REE, alkali metals
and alkaline earths show much less fractionation (<3). The observed differences compare quantitatively with experimental data
on partitioning between immiscible carbonate and silicate melts, indicating that changes in melt chemistry provide the dominant
control on variation in partition coefficients in this case. The importance of melt chemistry in controlling several aspects
of element partitioning is discussed in light of the energetics of the partitioning process. The compositions of clinopyroxene
and carbonate melt in our experiments closely match those of near-solidus melts and crystals in CMAS-CO2 at 3 GPa, suggesting that our partition coefficients have direct relevance to melting of carbonated mantle lherzolite. Melts
so produced will be characterised by elevated incompatible trace element concentrations, due to the low degrees of melting
involved, but marked depletions of Ti and Zr, and fractionated REE patterns. These are common features of natural carbonatites.
The different behaviour of trace elements in carbonate and silicate systems will lead to contrasted styles of trace element
metasomatism in the mantle.
Received: 15 July 1999 / Accepted: 18 February 2000 相似文献
11.
The Finero phlogopite-peridotite massif: an example of subduction-related metasomatism 总被引:13,自引:0,他引:13
Alberto Zanetti Maurizio Mazzucchelli Giorgio Rivalenti Riccardo Vannucci 《Contributions to Mineralogy and Petrology》1999,134(2-3):107-122
The Finero peridotite massif is a harzburgite that suffered a dramatic metasomatic enrichment resulting in the pervasive
presence of amphibole and phlogopite and in the sporadic occurrence of apatite and carbonate (dolomite)-bearing domains. Pyroxenite
(websterite) dykes also contain phlogopite and amphibole, but are rare. Peridotite bulk-rock composition retained highly depleted
major element characteristics, but was enriched in K, Rb, Ba, Sr, LREE (light rare earth elements) (LaN/YbN = 8–17) and depleted in Nb. It has high radiogenic Sr (87Sr/86Sr(270) = 0.7055–0.7093), low radiogenic Nd (ɛNd(270) = −1 to −3) and EMII-like Pb isotopes. Two pyroxenite – peridotite sections examined in detail show the virtual absence of
major and trace element gradients in the mineral phases. In both rock types, pyroxenes and olivines have the most unfertile
major element composition observed in Ivrea peridotites, spinels are the richest in Cr, and amphibole is pargasite. Clinopyroxenes
exhibit LREE-enriched patterns (LaN/YbN ∼16), negative Ti and Zr and generally positive Sr anomaly. Amphibole has similar characteristics, except a weak negative
Sr anomaly, but incompatible element concentration ∼1.9 (Sr) to ∼7.9 (Ti) times higher than that of coexisting clinopyroxene.
Marked geochemical gradients occur toward apatite and carbonate-bearing domains which are randomly distributed in both the
sections examined. In these regions, pyroxenes and amphibole (edenite) are lower in mg## and higher in Na2O, and spinels and phlogopite are richer in Cr2O3. Both the mineral assemblage and the incompatible trace element characteristics of the mineral phases recall the typical
signatures of “carbonatite” metasomatism (HFSE depletion, Sr, LILE and LREE enrichment). Clinopyroxene has higher REE and
Sr concentrations than amphibole (amph/cpxDREE,Sr = 0.7–0.9) and lower Ti and Zr concentrations. It is proposed that the petrographic and geochemical features observed at
Finero are consistent with a subduction environment. The lack of chemical gradients between pyroxenite and peridotite is explained
by a model where melts derived from an eclogite-facies slab infiltrate the overhanging harzburgitic mantle wedge and, because
of the special thermal structure of subduction zones, become heated to the temperature of the peridotite. If the resulting
temperature is above that of the incipient melting of the hydrous peridotite system, the slab-derived melt equilibrates with
the harzburgite and a crystal mush consisting of harzburgite and a silica saturated, hydrous melt is formed. During cooling,
the crystal mush crystallizes producing the observed sequence of mineral phases and their observed chemical characteristics.
In this context pyroxenites are regions of higher concentration of the melt in equilibrium with the harzburgite and not passage-ways
through which exotic melts percolated. Only negligible chemical gradients can appear as an effect of the crystallization process,
which also accounts for the high amphibole/clinopyroxene incompatible trace element ratios. The major element refractory composition
is explained by an initially high peridotite/melt ratio. The apatite, carbonate-bearing domains are the result of the presence
of some CO2 in the slab-derived melt. The CO2/H2O ratio in the peridotite mush increased by crystallization of hydrous phases (amphibole and phlogopite) locally resulting
in the unmixing of a late carbonate fluid. The proposed scenario is consistent with subduction of probably Variscan age and
with the occurrence of modal metasomatism before peridotite incorporation in the crust.
Received: 20 July 1998 / Accepted: 28 October 1998 相似文献
12.
In situ trace element analyses of constituent minerals in mantle xenoliths occurring in an alnöite diatreme and in nephelinite plugs emplaced within the central zone of the Damara Belt have been determined by laser ablation ICP-MS. Primitive mantle-normalized trace element patterns of clinopyroxene and amphibole indicate the presence of both depleted MORB-like mantle and variably enriched mantle beneath this region. Clinopyroxenes showing geochemical depletion have low La/Smn ratios (0.02–0.2), whereas those showing variable enrichment have La/Smn ranging up to 3.8 and La/Ybn to 9.1. The most enriched clinopyroxenes coexist with amphibole showing similar REE patterns (La/Smn = 1.3–4.1; La/Ybn = 4.5–9). Primitive mantle-normalized trace element patterns allow further groups to be distinguished amongst the variably enriched clinopyroxenes: one having strong relative depletion in Rb–Ba, Ta–Nb and relative enrichment in Th–U; another with similar characteristics but with additional strong relative depletion in Zr–Hf; and one showing no significant anomalies. Amphiboles show similar normalized trace element patterns to co-existing clinopyroxene. Clinopyroxene and amphiboles showing LREEN enrichment have high Sr and low Nd isotope ratios compared to clinopyroxene with LREE-depleted patterns. Numerical simulation of melt percolation through the mantle via reactive porous flow is used to show that the chromatographic affect associated with such a melt migration process is able to account for the fractionation seen in La–Ce–Nd in cryptically metasomatized clinopyroxenes in Type 1 xenoliths, where melt–matrix interactions occur near the percolation front, whereas REE patterns in clinopyroxenes proximal to the source of metasomatic melt/fluid match those found in modally metasomatized Type 2 xenoliths. The strong fractionation between Rb–Ba, Th–U and Ta–Nb shown by some cryptically metasomatized xenoliths can be also accounted for by reactive porous flow, provided amphibole crystallizes from the percolating melt/fluid close to its source. The presence of amphibole in vein-like structures in some xenoliths is consistent with this interpretation. The strong depletion in Zr–Hf in clinopyroxene and amphibole in some xenoliths cannot be accounted for by melt migration processes and requires metasomatism by a separate carbonate-rich melt/fluid. When taken together with published isotope data on these same xenoliths, the source of metasomatic enrichment of the previously depleted (MORB-like) sub-Damaran lithospheric mantle is attributed to the upwelling Tristan plume head at the time of continental breakup. 相似文献
13.
Phase relations of diamond and syngenetic minerals were experimentally investigated in the multicomponent system natural carbonatite-diamond
at a pressure of 8.5 GPa and temperatures of 1300–1800°C (within the thermodynamic stability field of diamond). Under such
conditions, the natural carbonatite of the Chagatai complex (Uzbekistan) acquires the mineralogy of Ca-rich eclogites (grospydites).
The melting phase diagram of this system (syngenesis diagram) was constructed; an important element of this diagram is the
diamond solubility curve in completely miscible carbonate-silicate melts (solubility values are 15–18 wt % C). The diamond
solubility curve divides the phase diagram into two fields corresponding to (1) phase relations involving diamond-undersaturated
melts-solutions of carbon with garnet as a liquidus phase (region of diamond dissolution) and (2) phase relations with diamond-saturated
melts-solutions with diamond as a liquidus phase (region of diamond crystallization). During a temperature decrease in the
region of diamond crystallization from carbonate-silicate melts, the crystallization of diamond is accompanied by the sequential
formation of the following phase assemblages: diamond + garnet + melt, diamond + garnet + clinopyroxene + melt, and diamond
+ garnet + clinopyroxene + carbonate + melt, and the subsolidus assemblage diamond + garnet + clinopyroxene + carbonate is
eventually formed. This is indicative of the paragenetic nature of silicate and carbonate minerals co-crystallizing with diamond
and corresponding primary inclusions trapped by the growing diamond. A physicochemical mechanism was proposed for the formation
of diamond in carbonate-silicate melts. The obtained results were used to analyze the physicochemical behavior of a natural
diamond-forming magma chamber. 相似文献
14.
We report the results of LA-ICP-MS analyses of rock forming minerals in clinopyroxene-apatite-K feldspar-phlogopite (CAKP) metasomatic xenoliths and primary carbonatite melt inclusions (CMI) hosted in apatite (Ap) and K feldspar (Kfs). The xenoliths are from the Cretaceous lamprophyre dikes of the Transdanubian Central Range, Hungary. The CMI in Ap have phosphorus dolomitic composition as opposed to CMI in Kfs, which display dolomitic alkali-aluminosiliceous character. The melts found in CMI in Ap and in Kfs likely formed by liquid-liquid separation from an originally carbonate- and phosphorous-rich melt. Primitive mantle (PM) normalized trace element distributions of both Ap- and Kfs-hosted CMI (n = 60 and 20, respectively) reveal a strong negative Ti-anomaly, and an extreme enrichment in incompatible elements (U, Th, LILE and LREE) relative to HREE, Sc, V, Ni and Cr. Rarely, apatites contain unique CMI, which show major- and trace-element signature transitional to K feldspar-hosted CMI. This is due to heterogeneous entrapment of an immiscible phosphorous-bearing carbonatite melt and a carbonate-bearing alkali aluminosiliceous melt, which is a further evidence for their co-existence. CMI reveal that U, Th, Pb, Nb, Ta, P, Sr, Y and REE partitioned into the phosphorous-bearing carbonatite melt, whereas Cs, Rb, Na, K, B, Al, Zr and Hf preferred the silicate-bearing liquid.PM normalized REE pattern (high LREE/HREE), elevated Zr and Hf contents and negative Ti anomaly of clinopyroxene (Cpx) indicate that its formation is genetically linked to carbonatite metasomatism attested by CMI. Trace element partitioning between the studied Cpx and CMI is in accordance with experimentally determined trace element distributions between Cpx and carbonatite melt. Cpx, which occur in samples with high modal proportion of apatite represent mantle section, which interacted with a higher amount of “initial” carbonatite melt than Cpx from apatite-poor xenoliths. This is confirmed by higher Cr, Ni, V, Sc, Ti and lower Zr, as well as Hf concentration in Cpx from xenoliths with low modal abundance of Ap. CMI reveal that Ti, V, Ni and Cr were in lower concentration in the “initial” carbonatite melt than in PM. Contrarily, Zr and Hf were more abundant in this melt than in PM. Consequently, a continuously migrating “initial” carbonatite melt, increased Zr and Hf concentration, and decreased Ti, Sc, V, Ni and especially Cr in the clinopyroxenes. Our findings suggest that the studied CAKP rocks were formed by carbonatite melt metasomatism, which occurred in an open system in the upper mantle. 相似文献
15.
M.-A. Kaczmarek O. Müntener D. Rubatto 《Contributions to Mineralogy and Petrology》2008,155(3):295-312
The U–Pb ages and the trace element content of zircon U–Pb along with major and trace element whole rock data on gabbroic
dikes from the Lanzo lherzolitic massif, N-Italy, have been determined to constrain crustal accretion in ocean–continent transition
zones. Three Fe–Ti gabbros were dated from the central and the southern part of the massif providing middle Jurassic ages
of 161 ± 2, 158 ± 2 and 163 ± 1 Ma, which argue for magmatic activity over few millions of years. Zircon crystals are characterized
by high but variable Th/U ratios, rare earth element patterns enriched in heavy rare earths, pronounced positive Ce and negative
Eu-anomalies consistent with crystallization after substantial plagioclase fractionation. The zircon trace element composition
coupled with whole rock chemistry was used to reconstruct the crystallization history of the gabbros. A number of gabbros
crystallized in situ, and zircon precipitated from trapped, intercumulus liquid, while other gabbros represent residual liquids
that were extracted from a cumulus pile and crystallized along syn-magmatic shear zones. We propose a model in which the emplacement
mechanism of gabbroic rocks in ocean–continent transition zones evolves from in situ crystallization to stratified crystallization
with efficient extraction of residual liquid along syn-magmatic shear zones. Such an evolution of the crystallization history
is probably related to the thermal evolution of the underlying mantle lithosphere.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
16.
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
17.
We studied the chemical composition of rock-forming minerals in gabbroids from the Chirii outcrop and the evolutionary features of parental basic melt during the crystallization of these rocks. Results were compared with data for basanites from pipes of the North Minusa depression. The mineralogical composition and thermobarogeochemical data of the gabbroids were examined in detail, and chemical analyses of rock-forming minerals (clinopyroxene, plagioclase, amphibole, biotite, titanomagnetite, and apatite) were carried out. Based on the homogenization temperatures of primary melt inclusions, we established the minimum temperatures and sequence of mineral crystallization in the gabbroids: clinopyroxene (>1160 °C), plagioclase, magnetite → amphibole (>950 °C) → biotite. The rock crystallization proceeded at shallow depths. Thermometric data are confirmed by results of modeling of equilibrium gabbroid crystallization. The crystallization of parental basic melt was accompanied by the accumulation of SiO2, Al2O3, alkalies, and Cl and depletion in femic components. The melt evolved to granodiorite and alkali-syenite compositions. Compared with basanites from pipes, the parental melt had a longer evolution. The geochemical features of the gabbroids indicate that they, like basanites, crystallized from intraplate alkali-basaltoid magmas. But in petrochemistry and mineralogy the Chirii gabbroids differ considerably from the pipe basanites. 相似文献
18.
Peridotite xenoliths found in Cenozoic alkali basalts of northern Victoria Land, Antarctica, vary from fertile spinel-lherzolite
to harzburgite. They often contain glass-bearing pockets formed after primary pyroxenes and spinel. Few samples are composite
and consist of depleted spinel lherzolite crosscut by amphibole veins and/or lherzolite in contact with poikilitic wehrlite.
Peridotite xenoliths are characterized by negative Al2O3–Mg# and TiO2–Mg# covariations of clino- and orthopyroxenes, low to intermediate HREE concentrations in clinopyroxene, negative Cr–Al trend
in spinel, suggesting variable degrees of partial melting. Metasomatic overprint is evidenced by trace element enrichment
in clinopyroxene and sporadic increase of Ti–Fetot. Preferential Nb, Zr, Sr enrichments in clinopyroxene associated with high Ti–Fetot contents constrain the metasomatic agent to be an alkaline basic melt. In composite xenoliths, clinopyroxene REE contents
increase next to the veins suggesting metasomatic diffusion of incompatible element. Oxygen isotope data indicate disequilibrium
conditions among clinopyroxene, olivine and orthopyroxene. The highest δ18O values are observed in minerals of the amphibole-bearing xenolith. The δ18Ocpx correlations with clinopyroxene modal abundance and geochemical parameters (e.g. Mg# and Cr#) suggest a possible influence
of partial melting on oxygen isotope composition. Thermobarometric estimates define a geotherm of 80°C/GPa for the refractory
lithosphere of NVL, in a pressure range between 1 and 2.5 GPa. Clinopyroxene microlites of melt pockets provide P–T data close
to the anhydrous peridotite solidus and confirm that they originated from heating and decompression during transport in the
host magma. All these geothermometric data constrain the mantle potential temperature to values of 1250–1350°C, consistent
with the occurrence of mantle decompressional melting in a transtensive tectonic regime for the Ross Sea region. 相似文献
19.
J. Roberge P. J. Wallace A. J. R. Kent 《Contributions to Mineralogy and Petrology》2013,165(2):237-257
To investigate the origin of compositional zonation in the Bishop Tuff magma body, we have analyzed trace elements in the matrix glass of pumice clasts and in quartz-hosted melt inclusions. Our results show contrasting patterns for quartz in different parts of the Bishop Tuff. In all samples from the early part of the eruption, trace element compositions of matrix glasses are similar to but slightly more evolved than quartz-hosted melt inclusions. This indicates a cogenetic relationship between quartz crystals and their surrounding matrix glass, consistent with in situ crystallization. The range of incompatible element concentrations in melt inclusions and matrix glass from single pumice clasts requires 16–20 wt% in situ crystallization. This is greater than the actual crystal content of the pumices (<15 % crystals). In contrast to the pattern for the early pumices, pyroclastic flow samples from the middle part of the eruption show contrasting trends: In some clasts, the matrix is more evolved than the inclusions, whereas in other clasts, the matrix is less evolved. In the late Bishop Tuff, all crystal-rich samples have matrix glasses that are less evolved than the melt inclusions. Trace element abundances indicate that the cores of quartz in the late Bishop Tuff crystallized from more differentiated rhyolitic magma that was similar in many ways, yet distinct from the early-erupted Bishop Tuff. Our results are compatible with a model of secular incremental zoning (Hildreth and Wilson in Compositional zoning of the Bishop Tuff. J Petrol 48(5):951–999, 2007), in which melt batches from underlying crystal mush rise to various levels in a growing magma body according to their buoyancy. Early- and middle-erupted quartz crystallized from highly evolved rhyolitic melt, but then some parts of the middle-erupted magma were invaded by less differentiated rhyolite such that the matrix melt at the time of eruption was less evolved than the melt inclusions. A similar process occurred but to a greater extent in magma that erupted to form the late Bishop Tuff. In addition, there was a final, major magma mixing event in the late magma that formed Ti-rich rims on quartz and Ba-rich rims on sanidine, trapped less evolved rhyolitic melt inclusions, and resulted in dark and swirly crystal-poor pumice that is a rare type throughout much of the Bishop Tuff. 相似文献
20.
Trace Element Geochemistry of Tertiary Continental Alkali Basalts from the Liuhe—Yizheng Area,Jiangsu Province,China 总被引:5,自引:0,他引:5
支霞臣 《中国地球化学学报》1991,10(3):204-216
Reported in this paper are the chemical compositions and trace element (REE,Ba,Rb,Sr,Nb,Zr,Ni,Cr,V,Ga,Y,Sc,Zn,Cu,etc)abundances of Tertiary continental alkali basalts from the Liube-yizheng area,Jiangsu Province,China.The olivine basalt,alkali olivine basalt and basanite are all derived from evolved melts which were once af-fected by different degrees of fractional crystallization of olivine and clinopyroxene(1:2)under high pres-sures.The initial melts were derived from the garnet lherzolite-type mantle source through low-degree par-tial melting.The mantle source has been affected by recent mantle-enrichment events(e.g.mantle metasomatism),resulting in incompatible trace element enrichment and long-term depletion of radiogenic isotopic compositions of Sr and Nd. 相似文献