A stable Calcium Isotopic study on Abyssal Peridotite from the Southwest Indian Ocean Ridge
Abstract
Abyssal peridotites are the residues of partial melting beneath the Mid-oceanic ridges. These ultramafic mantle residues may undergo three possible processes including partial melting, melt-rock interaction and seawater alteration while moving from the mantle to the earth's surface. The overprinting of later processes often makes it difficult to decipher the mantle evolution of these rocks. We report Ca isotopic compositions of clinopyroxenes and orthopyroxenes mineral separates from abyssal peridotites from the Southwest Indian Ocean Ridge. These samples are well characterized for their major, trace elemental and Sr-Nd-Hf-Pb-Os isotopic compositions (1-3). Calcium isotopic measurements were performed using a 43Ca-48Ca double spike technique using a thermal ionization mass spectrometer at the Centre for Earth Sciences, IISc Bangalore with an external reproducibility of 0.08‰ (2SD) for δ44/40Ca.
The δ44/40CaSRM915a of clinopyroxenes show lower values and range from 0.15 to 0.86‰ whereas the orthopyroxene values range from 0.68 to 1.42‰. The clinopyroxenes showing the most depleted LREE signatures show the lowest δ44/40Ca values. The δ44/40CaSRM915a values of both clino- and orthopyroxenes, when considered together, correlates positively with the Mg and Fe content of the minerals and negatively with their Ti and Na contents. The δ44/40CaSRM915a values of the clinopyroxenes show a rough negative correlation with their ɛNd values, with the most depleted clinopyroxene samples showing the lowest δ44/40CaSRM915a values. Overall, preliminary δ44/40CaSRM915a values of clino- and orthopyroxenes in abyssal peridotites seem to be controlled both by the mineral composition and mantle depletion processes. References: (1) Frisby et al. (2016) Lithos 248 - 251 & 2016b Chemical Geology 440; (2) Mallick et al. (2014) G3 & (2015) EPSL; (3) Warren et al. 2009 JGR 114 & 2012 EPSL 359-360,- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.V51E0094C
- Keywords:
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- 1020 Composition of the continental crust;
- GEOCHEMISTRY;
- 1025 Composition of the mantle;
- GEOCHEMISTRY;
- 1030 Geochemical cycles;
- GEOCHEMISTRY;
- 1041 Stable isotope geochemistry;
- GEOCHEMISTRY