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Origin of Geochemical Variability by Arc-Continent Collision in the Biru Area, Southern Sulawesi (Indonesia) 总被引:1,自引:0,他引:1
Analyses of igneous rocks from the Eocene calc-alkaline andMiocene potassic volcanic arc in southwest Sulawesi indicatethat magmas became more heterogeneous in their trace elementand PbSrNd isotopic signature following the collisionof the Buton microcontinent with the arc at 相似文献
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ELBURG MARLINA; KAMENETSKY VADIM S.; NIKOGOSIAN IGOR; FODEN JOHN; SOBOLEV ALEXANDER V. 《Journal of Petrology》2006,47(12):2433-2462
Mineral and melt inclusions in olivines from the most Mg-richmagma from the southern West Sulawesi Volcanic Province indicatethat two distinct melts contributed to its petrogenesis. Thecontribution that dominates the whole-rock composition comesfrom a liquid with high CaO (up to 16 wt %) and low Al2O3 contents(CaO/Al2O3 up to 1), in equilibrium with spinel, olivine (Fo8591;CaO 0·350·5 wt %; NiO 0·20·30wt %) and clinopyroxene. The other component is richer in SiO2(>50 wt %) and Al2O3 (1921 wt %), but contains significantlyless CaO (<4 wt %); it is in equilibrium with Cr-rich spinelwith a low TiO2 content, olivine with low CaO and high NiO content(Fo9094; CaO 0·050·20 wt %; NiO0·350·5 wt %), and orthopyroxene. Boththe high- and low-CaO melts are potassium-rich (>3 wt % K2O).The high-CaO melt has a normalized trace element pattern thatis typical for subduction-related volcanic rocks, with negativeTaNb and Ti anomalies, positive K, Pb and Sr anomalies,and a relatively flat heavy rare earth element (HREE) pattern.The low-CaO melt shows Y and HREE depletion (Gdn/Ybn 41), butits trace element pattern resembles that of the whole-rock andhigh-CaO melt in other respects, suggesting only small distinctionsin source areas between the two components. We propose thatthe depth of melting and the dominance of H2O- or CO2-bearingfluids were the main controls on generating these contrastingmagmas in a syn-collisional environment. The composition ofthe low-CaO magma does not have any obvious rock equivalent,and it is possible that this type of magma does not easily reachthe Earth's surface without the assistance of a water-poor carriermagma. KEY WORDS: melt inclusions; mineral chemistry; olivine; syn-collisional magmatism; ankaramites; low-Ca magma 相似文献
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Genetic Significance of Multiple Enclave Types in a Peraluminous Ignimbrite Suite, Lachlan Fold Belt, Australia 总被引:4,自引:1,他引:3
The Violet Town Volcanics (Lachlan Fold Belt, Australia) arean S-type ignimbrite suite containing microgranitoid enclaves,basaltic andesite enclaves and enclaves of high-silica rhyolite.The microgranitoid enclaves are similar to those in peraluminousgranites. They typically have lower initial 87Sr/86Sr and higherNd than the host, and represent globules of a mafic, mantle-derivedmagma, which was hybridized by mixing and diffusional exchangewith the host magma. The basaltic andesite enclaves were incorporatedinto the ignimbrite as xenoliths, but their parental magma mayhave been similar to that of the microgranitoid enclaves. Theyare isotopically less depleted than other mantle-derived rocksfrom the Lachlan Fold Belt, reflecting contamination by crustalmaterial, or derivation from less depleted mantle sources. Thehigh-silica rhyolite enclaves, previously interpreted to berelated to the ignimbrite by crystal fractionation, have Ndvalues up to 3 units higher than their host, and cannot be relatedto their host by crystal fractionation or assimilation-fractionalcrystallization (AFC) processes. The coexistence of S-type magmasand mantle-derived magmas suggests that the latter may haveplayed a role in the Palaeozoic magmatism of the Lachlan FoldBelt, acting as a heat source for melting and perhaps also contributingchemical components to the crustally derived magmas. KEY WORDS: enclaves; magma mingling; magma mixing; S-type
*Present address: Department of Geology and Geophysics, University of Adelaide, Adelaide, S.A. 5005, Australia. Telephone: +-61-8-3035973. Fax: +-61-8-3034347. e-mail: melburg{at}geology.adelaide.edu.au 相似文献
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Rates and Processes of Potassic Magma Evolution beneath Sangeang Api Volcano, East Sunda Arc, Indonesia 总被引:11,自引:3,他引:11
TURNER SIMON; FODEN JOHN; GEORGE RHIANNON; EVANS PETER; VARNE RICK; ELBURG MARLINA; JENNER GEORGE 《Journal of Petrology》2003,44(3):491-515
U-series isotopes can provide unique insights into the physicalprocesses of magma evolution by constraining the time scalesover which they operate. This, however, requires rock suitesthat provide a clear and complete record of the liquid lineof descent. Sangeang Api volcano, in the east Sunda arc, providessuch an opportunity because it erupts potassic lavas (SiO2 相似文献
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