首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
Conclusion In summary, there are no existing clinopyroxene-liquid REE distribution data obtained under appropriate conditions to permit numerical modeling of trace elements to constitute a critical test of the pyroxene fractionation process. There are, however, numerous clinopyroxeneliquid partitioning data in the literature that give qualitatively similar patterns to those observed in grospydites. Further, the high pressure fractionation model accounts for the major-element and exsolution phenomena in a manner directly consistent with experimental petrologic studies, and can qualitatively account for the trace element and isotopic characteristics of the rocks in a manner consistent with the crystal chemistry of the phases. We therefore continue to prefer the high-pressure clinopyroxene fractionation model over a low-pressure plagioclase fractionation model for the origin of the grospydites.  相似文献   

2.
Trace element distribution in Central Dabie eclogites   总被引:16,自引:0,他引:16  
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   

3.
Eclogite xenoliths from the mantle have experienced a wide variety of processes and P-T conditions, many of which are recorded in the mineral compositions and textures. Exsolution of garnet from clinopyroxene is one such texture, occurring in a minority of mantle eclogites. New analyses of clinopyroxene and garnet of eclogite xenoliths from kimberlites at Bellsbank (South Africa) and Obnazhënnaya (Yakutia, Russia) are presented here, and these are combined with data from the literature. Exsolution of garnet from clinopyroxene is generally lamellar, although lens-shaped garnets are also present. Major- and trace-element characteristics show a wide range of compositions and include eclogite Groups A, B, and C. Rare-earth element (REE) concentrations of garnet and pyroxene were determined by SIMS, and the REE patterns are subtly different from those in ordinary eclogites. Differences include the absence of prominent Eu anomalies in samples of this study and differences in the slopes of chondrite-normalized REE patterns. It is possible that these signatures are unique to exsolved eclogites, a result of subsolidus elemental partitioning during exsolution. Some reconstructed whole-rock compositions are aluminuous; comparison with ordinary eclogites shows only minor differences, implying a similar origin. If the immediate precursor to the exsolved eclogites was a monomineralic pyroxenite, the excess aluminium was tied up in Tschermak's molecule, although the occasional presence of kyanite exsolution lamellae is indicative of a Ca-Eskola component. Reconstructed pyroxenes from kyanite- and corundum-rich samples contain unrealistic amounts of aluminium for mantle pyroxenes. A protolith (or parental pyroxene) threshold of 24% Al2O3 may exist, above which (as in a plagioclase cumulate) the final assemblage is kyanite- and/or corundum-bearing.  相似文献   

4.
5.
Trace element characteristics of seven coesite-bearing eclogitic xenoliths from the Roberts Victor kimberlite demonstrate that this suite of eclogites originated as gabbroic cumulates in oceanic crust that was subsequently subducted. All but one of the garnets show positive Eu anomalies, accompanied by a flat heavy rare earth pattern, which is atypical of garnet, but characteristic of plagioclase, arguing for a considerable amount of plagioclase in the protoliths. Forward modelling of the accumulation of liquidus minerals from primitive komatiitic, picritic, and basaltic liquids suggests that at least some of the eclogite protoliths were not derived from basaltic parental liquids, whereas derivation from either komatiitic or picritic liquids is possible. The reconstructed eclogite bulk rocks compare favourably with oceanic gabbros from ODP hole 735B (SW Indian Ridge), even to the extent that oxygen isotopic systematics show signs of low-temperature seawater alteration. However, the oxygen isotope trends are the reverse of what is expected for cumulates in the lower section of the oceanic crust. These new findings show that δ18O values in eclogitic xenoliths, despite being sound indicators for their interaction with hydrothermal fluids at low pressure, do not necessarily bear a simple relationship with the inferred oceanic crustal stratigraphy of the protoliths.  相似文献   

6.
Summary Granitic pegmatites characterized by advanced accumulation and fractionation of incompatible rare lithophile elements (Li, Rb, Cs, Be, Ta Nb, B, P and F), often contain mineral assemblages which host lithium-rich micas. Lepidolite and lithian muscovite occur in high-pressure spodumene, low-pressure petalite, phosphorus-enriched amblygonite and fluorine-rich lepidolite subtypes of orogenic affiliated complex type granitic pegmatites and rarely in anorogenic affiliated amazonite-bearingTrace element data determined by X-ray fluorescence for lepidolite of various pegmatite subtypes, morphology (book, scaly, fine-grained), position within the pegmatite (primary zones, replacement units, pockets), mineral assemblages and tectonic affinity (orogenic vs anorogenic) show extreme fractionation of Rb and Cs; modest levels of T1, Ga, Nb, Ta, Sn and Zn; and typically low abundances of Ba, Sr, Ni, Pb, Y, V, W and Zr. Extreme fractionation is indicated by low values of K/Rb, K/Cs and Nb/Ta which are lowest in lepidolite from petalite subtype pegmatites.No systematic differences in trace element content is evident among the different lepidolite morphologies or paragenetic position. Lepidolite from spodumene subtype pegmatites are generally slightly less fractionated than those from petalite or lepidolite subtype pegmatites.
Spurenelement-Chemie von Lithium-reichen Glimmern aus granitischen Pegmatiten
Zusammenfassung Granitische Pegmatite, die durch fortgeschrittene Anreicherung und Fraktionierung von inkompatiblen, seltenen, lithophilen Elementen (Li, Rb, Cs, Be, Ta Nb, B, P und F) charakterisiert sind, enthalten häufig Mineralparagenesen mit Lithium-reichen Glimmern. Lepidolith und Li-Muskowit treten in Hochdruck-Spodumen, in Niedrigdruck-Petalit, in mit Phosphor angereichertem Amblygonit und in Fluor-reichen Lepidolith-Unterarten aus komplexen orogenen granitischen Pegmatiten und selten auch aus anorogenen, Amazonit-führenden Pegmatiten, auf.Spurenelement-Daten aus der Röntgenfluoreszenzanalyse von Lepidolith aus verschiedenen Pegmatit-Untertypen, die Morphologie (tafelig, schuppig, feinkörnig), die Position innerhalb des Pegmatits (primäre Zonen, verdrängte Einheiten, Taschen), Mineralbestände und tektonische Affinität (orogen gegen anorogen) zeigen eine extreme Fraktionierung von Rb und Cs, bescheidene Gehalte an TI, Ga, Nb, Ta, Sn und Zn; und typischerweise geringe Häufigkeiten von Ba, Sr, Ni, Pb, Y, V, W und Zr. Die extreme Fraktionierung wird durch niedrige Werte von K/Rb, K/Cs und Nb/Ta angezeigt, die in Lepidolith von Pegmatiten des Petalit-Subtyps am niedrigsten sind.Aus den verschiedenen Morphologien oder paragenetischen Positionen von Lepidolith sind keine systematischen Unterschiede im Spurenelementgehalt ersichtlich. Lepidolith aus Pegmatiten des Spodumen-Subtyps sind generell etwas weniger fraktioniert als jene von Pegmatiten des Petalit- oder Lepidolith-Subtyps.


With 4 Figures  相似文献   

7.
Analytical data are presented for Apollo 14 fines ( < 1 mm) sample 14163,136 for 31 trace elements. The heavy REE are enriched monotonically by factors of 105 ± 10 over chondrites. Eu shows a large depletion (30 × chondrites) and the light REE show a smooth progressive enrichment with a slight fall at La. Ba, Cs, Th, U, Nb, Zr and Hf are strongly enriched, relative to chondritic abundances. Thus the outer portions of the moon sampled by the Imbrium event, and now represented by the Fra Mauro Formation, possessed high concentrations (100–200 × chondrites) for many elements, prior to the excavation of the mare basins. A correlation may exist between Gd/Eu and Zr/Hf ratios in lunar materials.  相似文献   

8.
Trace element chemistry of major rivers in Orissa State, India   总被引:1,自引:1,他引:1  
 Geochemical analyses of surface waters from rivers flowing through Orissa State, India, indicated that trace element concentrations were extremely variable and consistently higher than world river average. The Brahmani River was the most solute-rich river studied, followed by the Baitarani and Mahanadi Rivers. Although all three rivers drain similar geology, the Brahmani River catchment is heavily industrialized, and water samples collected upstream and downstream from industries indicated that anthropogenic activity directly influenced its chemical composition. Samples collected from several towns, in all three river systems, did not invariably show similar patterns, with various elements having higher dissolved concentrations upstream. Because the concentration of total solids increased downstream, this implied that some components of the sewage had effectively sequestered available elements from solution and converted them to particulate material. Although the impact of pollution is clearly recognizable in water samples collected in proximity to the anthropogenic source, there are only slight elemental accumulations in the lower reaches of the Mahanadi River, with no accumulation in the Brahmani River. Apparently for these large rivers, discharged effluent becomes rapidly diluted, while complexation and sedimentation further removes trace elements from the water column. However, in the less voluminous Baitarani River, elementar enrichment near the river's mouth suggests that in this secondary river, where dilution effects are less, the concerns over regional water quality may be more prevalent. Received: 1 April 1995 · Accepted: 30 August 1995  相似文献   

9.
Ion microprobe data for minerals from the eclogites of the Atbashi Range (South Tianshan) constrain the distribution of trace (Rb, Sr, Ba, Cr, V, Zr, Hf, Nb, Ta, U, Th, and Y) and rare-earth elements (REE) in zoned garnets and mineral inclusions in them. This study showed that garnets from the Atbashi eclogites are the main hosts for heavy REE; epidotes are important hosts for REE, Y, Sr, Th, and U; and omphacites are depleted in almost all trace elements compared with the bulk-rock compositions. Garnet, as well as epidote and omphacite inclusions exhibit systematic rimward depletion in a number of trace elements, which is related to the depletion of the rock matrix in these elements during crystallization. Deviations from this trend, including the enrichment of garnet rims in HREE and strong variations in the REE contents of garnets and mineral inclusions, can be explained by metamorphic reactions involving the destabilization of REE-bearing minerals. Our data suggest that the mobility of trace elements under eclogites-facies conditions is mainly controlled by the stability of certain minerals.  相似文献   

10.
Summary Experiments at 25 kbar and 1000°C, on a model trace element-enriched carbonatite-eridotite mix, produced augite + pargasite ± garnet ± dolomite coexisting with a carbonatite melt. Proton microprobe analysis of the phases showed that key trace elements (Rb, Ba, Sr, Nb, Ta, Zr, Y and REE) all partitioned strongly into the melt (with the exception of Y, Ho and Lu in garnet), verifying that carbonatite is potentially a highly effective metasomatizing agent. The data also indicate that carbonatitic metasomatism will impart higher Ba/Rb, Ba/Nb, Nb/Ta, Sr/Ta, La/Ta, and lower Zr/Y, with little change to Sr/Nb, in affected mantle.
Spurenelementverteilung zwischen Silikatmineralen und Karbonatit bei 25 kbar: Anwendung für die Mantel-Metasomatose
Zusammenfassung Experimente mit einer Modell-mischung von Karbonatit-Peridotit, angereichert mit Spurenelementen, produzierten bei 25 kbar und 1000°C Augit + Pargasit ± Granat ±Dolomit coexistierend mit einer Karbonatitschmelze. Protonmikrosonden-Analyse der Phasen zeigte, dass alle Schlüsselspurenelemente (Rb, Ba, Sr, Nb, Ta, Zr, Y and REE) stark in der Schmelze angereichert werden (mit der Ausnahme von Y, Ho und Lu in Granat), was beweist, dass Karbonatit potentiell ein sehr effektives Agens für Metasomatose ist. Die Daten zeigen weiterhin, dass karbonatitische Metasomatose in betroffenen Mantel höhere Ba/Rb, Ba/Nb, Nb/Ta, Sr/Ta, La/Ta und niedrigere Zr/Y produziert, mit geringen Äderungen für Sr/Nb.


With 1 Figure  相似文献   

11.
Summary The Nemby mantle xenoliths are represented by spinel peridotites variably affected by “metasomatic processes” in Proterozoic times (1.2–0.5 Ga). Clinopyroxene compositional variations mainly reflect variably degrees of basalt extraction and mantle “metasomatic processes”. Clinopyroxene crystal chemistry allows to estimate the equilibration pressure by V(Cell) and V(M1) relationship. The investigated clinopyroxenes yielded a pressure range of 12–18 kb. Therefore, the Nemby xenoliths are representative of about 20 km thickness of subcontinental lithospheric mantle of the South America platform at Tertiary times (ca. 46 Ma).
Zusammenfassung Klinopyroxene aus metasomatischen Spinell-Peridotit-Mantel Xenolithen aus Nemby (Paraguay): Kristallchemie und petrologische Bedeutung Die Mantelxenolithe aus Nemby sind Spinellperidodite, die in verschiedenem Ausma? im Proterozoikum (1.2 bis 0.5 Ga) durch “metasomatische Prozesse” beeinflusst wurden. Variationen in der Zusammensetzung der Klinopyroxene lassen variable Ausma?e von Basaltextraktion und Mantelmetasomatose erkennen. Die Kristallchemie der Pyroxene erm?glicht es, den Gleichgewichtsdruck durch V(Cell) und V(M1) Beziehungen zu bestimmen. Die untersuchten Klinopyroxene zeigten Drucke im Bereich von 12 bis 18 kb. Die Nemby Xenolithe sind deshalb repr?sentativ für einen ungef?hr 20 km dicken subkontinentalen lithosph?rischen Mantel der südamerikanischen Plattform im Terti?r (ca. 46 Ma).


Received February 1, 1999; revised version accepted November 26, 1999  相似文献   

12.
The occurrence of CO2-rich lavas (carbonatites, kimberlites) and carbonate-rich xenoliths provide evidence for the existence of carbonatitic melts in the mantle. To model the chemical composition of such melts in the deep mantle, we experimentally determined partition coefficients for 23 trace elements (including REE, U-Th, HFSE, LILE) between deep mantle minerals and carbonatite liquids at 20 and 25 GPa and 1600 °C. Under these conditions, majoritic garnet and CaSiO3 perovskite are the main reservoirs for trace elements. This study used both femtosecond LA-ICP-MS and SIMS techniques to measure reliable trace element concentrations. Comparison of the two techniques shows a general agreement, except for Sc and Ba. Our experimentally determined partition coefficients are consistent with the lattice strain model. The data suggest an effect of melt structure on partition coefficients in this pressure range. For instance, strain-free partition coefficient (D0) for majorite-carbonatite melts do not follow the order of cation valence, , observed for majorite-CO2-free silicate melts. The newly determined partition coefficients were combined with trace element composition of majoritic garnets found as inclusions in diamond to model trace element patterns of deep-seated carbonatites. The result compares favorably with natural carbonatites. This suggests that carbonatites can originate from the mantle transition zone.  相似文献   

13.
Cenozoic lavas from Hainan Island,South China,comprise quartz tholeiite,olivine tholeiite,alkali basalt,and basanite and form a continuous,tholeiite-dominated,compositional spectrum.Highly incompatible elements and their relationships with isotopes in these lavas are shown to be useful in evaluating mantle-source composition,whereas modeling suggests that ratios of elements with bulk partition coefficients significantly larger than those of Nb and Ta may be sensitive to partial melting.Th/Ta and La/Nb ratios of alkali basalts are lower than those of tholeiites,and they are all lower than those of the primitive mantle,These ratios correlate positively with ^207Pb/^204Pb and ^87Sr/^86Sr ratios.Such relationships can be explained by mixing of depleted and enriched source components.A depleted component is indicated by alkali basalt compositions and is similar to some depleted OIB (PREMA).The enriched component,similar to sediment compositions,is indicated by tholeiites with high LILE/HFSE,^207Pb/^204Pb,and ^87Sr/^86Sr ratios.In general,basalts from Hainan and the South China Basin(SCB)share common geochemical characters.e.g.high Rb/Sr,Th/Ta,^207Pb/^206Pb,and low Ba/Th ratios.Such a geochemical trend is comparable to that of EMII-type OIB and best explained as the result of subduction.Occurrence of these characteristics in both continental Hainan basalts and SCB seamout basalts indicates the presence of a South China geochemical domain that exists in the mantle region below the lithosphere.  相似文献   

14.
Type I and Type II eclogite xenoliths from the Roberts Victor kimberlite (South Africa) show marked differences in terms of microstructures, mineralogy, major- and trace-element compositions and oxygen-isotope compositions. The unequilibrated microstructures of Type I eclogites, their typical accessory assemblages (phologopite, diamond, sulphides, fluid inclusions) and the ubiquitous presence of “melt pockets” in garnets provide strong evidence of metasomatism. Type II eclogites systematically lack such features and are microstructurally more equilibrated. Type I eclogites are more magnesium-rich than most Type II (mean Mg# = 0.56 vs. 0.46), while Type II eclogites are generally more Ca-rich (mean CaO = 9 vs. 12 wt%) and Fe-rich (mean FeO = 10 vs. 12 wt%). Type I eclogites are systematically enriched in LREE, Sr, Ba, alkali elements, HFSE, Th and U compared to the more depleted Type II eclogites. Calculated trace-element patterns of fluids in equilibrium with Type I eclogites are closely similar to those of volatile-rich small-volume mantle melts in the carbonatite-kimberlite spectrum commonly inferred to be responsible for mantle metasomatism. Although oxygen isotopes are often used to argue for a subduction origin of mantle eclogites, correlations between δ18O of garnet and typical metasomatic tracers suggest that the metasomatic process also has shifted the oxygen-isotope compositions of the Type I eclogites toward heavier values. Roberts Victor Type I eclogites thus carry the imprint of a metasomatic process that strongly modified their major-element, trace-element and isotopic compositions, while the more pristine Type II eclogites escaped this modification. Therefore, attempts to constrain the origin of Roberts Victor eclogites should not be based on the much more abundant Type I eclogites, which retain little geochemical memory of their protoliths. The most suitable materials for such investigations may be the less metasomatised, but more rare, Type II eclogites.  相似文献   

15.
16.
Mordenite is a zeolite whose approximate composition is (Na2, K2,Ca)4[Al8Si40O96] 28 H2O. Unit cell dimensions, determined by X-ray powder diffractometry for 35 natural samples, fell within the following ranges: a=18.052–18.168, b=20.404–20.527, c=7.501–7.537 Å. The indexed powder pattern of a typical sample is reported. Complete wet chemical analyses of 12 samples, partial analyses of three others, and 6 analyses from the literature reveal that mordenites vary only slightly in chemical composition. Si occupies 80 to 85% of the tetrahedra, and the exchangeable cations are mainly Na and Ca, with minor K. The lattice constant b is negatively correlated to the ratio Si/(Si+Al+Fe?).  相似文献   

17.
Trace element contents for pyrite from a range of sulfide mineral occurrences in the Kangiara region, eastern Australia, illustrate two main groups of pyrite. The first group, with higher Ag, Cu, Pb and Mo contents, corresponds to samples from sulfide base metal deposits and the second group, with higher Mn, Ti and Ni contents, contains samples from skarn mineralization, volcanic rocks and quartz veins. The model proposed for the development of pyrite in the Kangiara region is that the first group was formed from base metal-bearing solutions, while the second group reflects diagenetic pyrite and metamorphic pyrite. Thus, the pyrite trace element chemistry may provide a means of distinguishing types of mineral occurrences, in particular, those containing significant base metal mineralization.  相似文献   

18.
苏北榴辉岩中金红石的微量元素地球化学特征   总被引:5,自引:7,他引:5  
本文利用电子探针分析了苏北地区三类榴辉岩中金红石的Nb、Cr和Zr含量,在Zaek et al.(2002)的金红石Nb-Cr图解中,三类榴辉岩的原岩均为镁铁质岩,但它们具有不同的地球化学特征,即(1)小焦G类金红石榴辉岩中金红石的Nb含量最低,平均值为68ppm,而其它两类榴辉岩中金红石的Nb含量较高,平均值介于192~255ppm;(2)蓝晶石榴辉岩具有极高Cr含量,均值6106ppm,而许沟P类榴辉岩中金红石的Cr含量也较高,均值1233ppm,金红石榴辉岩中金红石Cr含量最低,均值为183ppm。利用Zaek et al.(2004)提出的金红石地质温度计,计算得出许沟P类榴辉岩的金红石形成温度介于600~751℃,平均温度689℃;演马厂M类榴辉岩的金红石温度介于507~641℃,平均温度557℃;小焦G类金红石榴辉岩金红石的形成温度介于541~673℃,平均温度613℃;新扬昌G类蓝晶石榴辉岩的金红石形成温度介于541~655℃,平均温度603℃。一种可能的解释是,榴辉岩在拆返过程中退变质作用明显,流体活动强烈,导致金红石中Zr扩散丢失,金红石中Zr含量不同程度地受到角闪岩相退变质过程中再平衡作用的影响,致使计算的温度偏低。  相似文献   

19.
Abundance data for Cs, Rb, Tl, Ba, Pb, Sr, the rare earths, Th, U, Zr, Hf, Sn, Nb, Mo, Mn, Cu, Co, Ni, Sc, V, Cr, Ag, Sb and the major elements are reported for two andesites and a dacite from Saipan, nine andesites and a dacite from Bougainville and two andesites from Fiji. The Saipan rocks are low-K varieties and contain notably low abundances of Rb, Ba, Th and U and have rare earth patterns subparallel to chondritic patterns. The Bougainville andesites include low-Si and high-K varieties which have higher concentrations of the large cations. The Fijian samples are close to the average circum-Pacific andesite and have rareearth patterns sub-parallel to those of sedimentary rocks.All the andesites contain characteristically low (< 20 ppm) values for Ni and have Ni/Co ratios < 1, and V/Ni ratios > 10.These data preclude derivation of calc-alkaline rocks by mixing of upper crustal material or by fractional crystallisation from basaltic parents. A two stage model is proposed involving sea-floor spreading and transportation of the oceanic crust down the dipping seismic plane into the mantle where it is remelted to form andesites.  相似文献   

20.
Trace element modelling of pelite-derived granites   总被引:25,自引:0,他引:25  
The presence or absence of a vapour phase during incongruent-melt reactions of muscovite and biotite together with the composition of the protolith determines the trace-element characteristics of the resulting melt, provided that equilibrium melting occurs for those phases that host the tracc elements of interest. For granitic melts, Rb, Sr and Ba provide critical constraints on the conditions that prevailed during melting, whereas REE are primarily controlled by accessory phase behaviour. Mass-balance constraints for eutectic granites that are formed by the incongruent melting of muscovite in pelites indicate that melting in the presence of a vapour phase will result in a large melt fraction, and deplete the restite in feldspar. Hence the melt will be characterized by low Rb/Sr and high Sr/Ba ratios. In contrast, vapour-absent melting will result in a smaller melt fraction, and an increase in the restitic feldspar. Consequently high Rb/Sr and low Sr/Ba ratios are predicted. Vapour-absent melting will also enhance the negative Eu anomaly in the melt. Granites that result from the incongruent melting of biotite in the source will be characterized by higher Rb concentrations than those that result from the incongruent melting of muscovite. The Himalayan leucogranites provide an example of unfractionated, crustally derived eutectic melts that are enriched in Rb but depleted in Sr and Ba relative to their metasedimentary protoliths. These compositions may be generated by the incongruent melting of muscovite as a low melt fraction (F0.1) from a pelitic source under vapour-absent conditions.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号