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Fig. 13 | Progress in Earth and Planetary Science

Fig. 13

From: The Atlantis Bank Gabbro Massif, Southwest Indian Ridge

Fig. 13

Thin section microphotograph 4 cm across under cross polars. Augite oikocrysts in olivine gabbro JR31-12-6, with a curved irregular contact shown by the yellow line. The augite encloses partially resorbed plagioclase chadocrysts but no olivine, which is found elsewhere in the sample. Analytical spots are shown by white points. White boxes next to points give the Mg#, weight percent TiO2, Cr2O3, and Al2O3 in the pyroxene analyses as indicated by the small inset box in the upper left corner. Large inset shows the Cpx data in TiO2 and Cr2O3 versus Mg# binary plots. Also shown is an inset plot of core to rim plagioclase compositions oriented parallel to the actual line of analytical points for one elongate chadocryst (gray line) and for a shorter crossing traverse (black line). Field of view is 4 mm across. With the exception of the long, reversely zoned traverse (An65 to An61), the compositions of the remaining six plagioclase crystals are very uniform (An61.6±1.7). By contrast augite is strongly zoned with Mg# varying from 74.9 to 86.1 and Al2O3 from 1.86 to 3.4 wt.%, whereas TiO2 and Cr2O3 vary inversely by factors of 3- and 7-fold with Mg#

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