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Origin of carbonatites by liquid immiscibility (1979)

HAMILTON, D. L. ; FREESTONE, IAN C. ; DAWSON, J. BARRY ; [et al.]

[s.l.] : Nature Publishing Group

Nature 279 (1979), S. 52-54

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ISSN: 1476-4687

Source: Nature Archives 1869 - 2009

Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics

Notes: [Auszug] While previous experimental work suggests that high concentrations of Na2O are required for immiscibility7'14'15, the great majority of analysed carbonatites are rich in CaO with Na2O as only a minor constituent, seemingly ruling out a role for immiscibility in their genesis (for example, mean of ...

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1038/279052a0

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Manganese thermometer for mantle peridotites (1979)

Delaney, J. S. ; Smith, J. V. ; Dawson, J. B. ; [et al.]

Springer

Contributions to mineralogy and petrology 71 (1979), S. 157-169

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ISSN: 1432-0967

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences

Notes: Abstract The temperature dependence of the Mn-Mg distribution between garnet and clinopyroxene, originally proposed by Carswell, was confirmed by Shimizu and Allègre (1978) using ion microprobe and electron microprobe data. High precision electron microprobe analyses of a larger set of 52 Iherzolites from S. Africa and Malaita, Solomon Islands show considerable scatter in the temperature dependence of this distribution, and correlation with the CaO content of the garnet is indicated. A new distribution coefficient is based on the reaction: $$\begin{gathered} \operatorname{Mn} _{\text{2}} \operatorname{Si} _2 \operatorname{O} _6 {\text{ + }}\operatorname{CaAl} _{2/3} \operatorname{SiO} _4 {\text{ + }}\operatorname{MgAl} _{2/3} \operatorname{SiO} _4 \hfill \\ {\text{Mn - pyroxene grossular pyrope}} \hfill \\ {\text{ }} \rightleftharpoons \operatorname{CaMgSi} _2 \operatorname{O} _6 {\text{ + }}2\operatorname{MnAl} _{2/3} \operatorname{SiO} _4 \hfill \\ {\text{ diopside spessartine}} \hfill \\ \end{gathered} $$ It was calibrated against temperature determined from two independent thermometers (Wells pyroxene and O'Neill-Wood garnet-olivine) for Iherzolitic assemblages, and shown to to be sensitive to within + 50 °C for most specimens in the range 900 °– 1,300 ° C. This distribution coefficient appears independent of pressure within the uncertainty of the available data, and has the potential to be a third independent thermometer for use in garnet Iherzolites and possibly eclogites.