Experimental determination of aluminous clinopyroxene-melt partition coefficients for potassic liquids, with application to the evolution of the Roman Province potassic magmas

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doi: 10.1016/S0009-2541(00)00259-X
Authors:Wood, Bernard J.; Trigila, Raffaello
Author Affiliations:Primary:
University of Bristol, Department of Earth Sciences, Bristol, United Kingdom
Universita di Roma "La Sapienza", Italy
Volume Title:Chemical Geology
Source:Chemical Geology, 172(3-4), p.213-223. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0009-2541
Publication Date:2001
Note:In English. 35 refs.; illus., incl. 4 tables
Summary:We have experimentally determined the partition coefficients of rare earth elements (REE), HFSE (Ti, Zr, Hf, Nb, Ta) and other trace elements between clinopyroxene and potassic silicate melts at 0.1-200 MPa and 1042-1140°C. The major and trace element contents of clinopyroxene and liquid were determined by electron probe and ion microprobe, respectively. The liquidus clinopyroxenes are extremely rich in Al2O3 (up to 12%) and Fe2O3, which enables us to test suggestions that partition coefficients of HFSE and REE depend on the Al content of the clinopyroxene (e.g., Lundstrom, C. C., Shaw, H. F., Ryerson, F. J., Williams, Q., Gill, J., 1998. Crystal chemical control of clinopyroxene-melt partitioning in the Di-Ab-An system: implications for elemental fractionations in the depleted mantle. Geochim. Cosmochim. Acta 62, 2849-2862.). When compared with previous data for low-alumina clinopyroxene crystallised under similar P-T conditions, the increase in weight partition coefficient Di (=[I]xtl/[I]liq) for all the HFSE and REE is dramatic. For Ti and the REE, partition coefficients increase by about one order of magnitude as Aliv concentration of clinopyroxene increases from 0.02 to 0.5. For Nb, Ta and Zr, the effect is even more pronounced, a two order of magnitude increase being found to correspond to this increase in Aliv. We applied the data to model the fractionation of historic lavas from Vesuvius. Previous work using the major elements (Belkin, H. E., Kilburn, C. R. J., DeVivo, B., 1993. Sampling and major element chemistry of the recent (AD 1631-1944) Vesuvius activity. J. Volcanol. Geotherm. Res. 58, 273-290.) indicates a liquid line of descent from trachybasalt to leucite tephrite dominated by clinopyroxene crystallisation. The REE and HFSE concentrations in the lavas are consistent with 40-50% fractional crystallisation of clinopyroxene (accompanied by minor leucite) between the two magmatic endmembers, with partition coefficients for the REE appropriate for clinopyroxenes containing ≤7.5 wt.% Al2O3. Pyroxenes of the latter composition are frequent phenocrysts in the lavas and previous experimental work (Dolfi, D., Trigila, R., 1988. Chemical relations between clinopyroxenes and coexisting glasses obtained from melting experiments on alkaline basic lavas. Rend. Soc. Ital. Mineral. Petrol. 43, 1101-1110; Trigila, R., De Benedetti, A. A., 1993. Petrogenesis of Vesuvius historical lavas constrained by Pearce element ratio analysis and experimental phase equilibria. J. Volcanol. Geotherm. Res. 58, 315-343.) implies that they precipitate under very low pressure low water activity conditions, i.e. within the magma chamber at <200 MPa. Abstract Copyright (2001) Elsevier, B.V.
Sections:Experimental mineralogy
Subjects:Aluminum; Applications; Chain silicates; Chemical fractionation; Clinopyroxene; Crystal chemistry; Electron probe data; Experimental studies; Fractional crystallization; Geochemistry; High pressure; High temperature; Igneous rocks; Ion probe data; Laboratory studies; Liquid phase; Magmas; Major elements; Mass spectra; Melts; Metals; P-T conditions; Partition coefficients; Potassic composition; Pressure; Pyroxene group; Rare earths; Silicates; Spectra; Temperature; Trace elements; Volcanic rocks; Volcanoes; Campania Italy; Europe; Italy; Latium Italy; Mount Etna; Rome Italy; Sicily Italy; Southern Europe; Vesuvius
Coordinates:N374500 N374500 E0150100 E0150100
N404900 N404900 E0142600 E0142600
N411400 N425000 E0140000 E0113000
Abstract Numbers:02M/378
Record ID:2001020002
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
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