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Csaba Szabó Károly Hidas Enik&#; Bali Zoltán Zajacz István Kovács Kyounghee Yang Tibor Guzmics Kálmán Török 《Island Arc》2009,18(2):375-400
In this paper we present a detailed textural and geochemical study of two equigranular textured amphibole-bearing spinel lherzolite xenoliths from Szigliget, Bakony–Balaton Highland Volcanic Field (BBHVF, western Hungary) containing abundant primary silicate melt inclusions (SMIs) in clinopyroxene rims and secondary SMIs in orthopyroxene (and rarely spinel) along healed fractures. The SMIs are dominantly composed of silicate glass and CO2 -rich bubbles. Clinopyroxene and orthopyroxene are zoned in both studied xenoliths, especially with respect to Fe, Mg, Na, and Al contents. Cores of clinopyroxenes in both xenoliths show trace element distribution close to primitive mantle. Rims of clinopyroxenes are enriched in Th, U, light rare earth elements (LREEs) and medium REEs (MREEs). Amphiboles in the Szg08 xenolith exhibit elevated Rb, Ba, Nb, Ta, LREE, and MREE contents. The composition of silicate glass in the SMIs covers a wide range from the basaltic trachyandesite and andesite to phonolitic compositions. The glasses are particularly rich in P2 O5 . Both primary and secondary SMIs are strongly enriched in incompatible trace elements (mostly U, Th, La, Zr) and display a slight negative Hf anomaly. The development of zoned pyroxenes, as well as the entrapment of primary SMIs in the clinopyroxene rims, happened after partial melting and subsequent crystallization of clinopyroxenes, most probably due to an interaction between hot volatile-bearing evolved melt and mantle wall-rocks. This silicate melt filled microfractures in orthopyroxenes (and rarely spinels) resulting in secondary SMIs. 相似文献
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Tibor Guzmics Roger H. Mitchell Csaba Szabó Márta Berkesi Ralf Milke Rainer Abart 《Contributions to Mineralogy and Petrology》2011,161(2):177-196
Kerimasi calciocarbonatite consists principally of calcite together with lesser apatite, magnetite, and monticellite. Calcite
hosts fluid and S-bearing Na–K–Ca-carbonate inclusions. Carbonatite melt and fluid inclusions occur in apatite and magnetite,
and silicate melt inclusions in magnetite. This study presents statistically significant compositional data for quenched S-
and P-bearing, Ca-alkali-rich carbonatite melt inclusions in magnetite and apatite. Magnetite-hosted silicate melts are peralkaline
with normative sodium-metasilicate. On the basis of our microthermometric results on apatite-hosted melt inclusions and forsterite–monticellite
phase relationships, temperatures of the early stage of magma evolution are estimated to be 900–1,000°C. At this time three
immiscible liquid phases coexisted: (1) a Ca-rich, P-, S- and alkali-bearing carbonatite melt, (2) a Mg- and Fe-rich, peralkaline
silicate melt, and (3) a C–O–H–S-alkali fluid. During the development of coexisting carbonatite and silicate melts, the Si/Al
and Mg/Fe ratio of the silicate melt decreased with contemporaneous increase in alkalis due to olivine fractionation, whereas
the alkali content of the carbonatite melt increased with concomitant decrease in CaO resulting from calcite fractionation.
Overall the peralkalinity of the bulk composition of the immiscible melts increased, resulting in a decrease in the size of
the miscibility gap in the pseudoquaternary system studied. Inclusion data indicate the formation of a carbonatite magma that
is extremely enriched in alkalis with a composition similar to that of Oldoinyo Lengai natrocarbonatite. In contrast to the
bulk compositions of calciocarbonatite rocks, the melt inclusions investigated contain significant amount of alkalis (Na2O + K2O) that is at least 5–10 wt%. The compositions of carbonatite melt inclusions are considered as being better representatives
of parental magma composition than those of any bulk rock. 相似文献
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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
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