Mossbauer characterization of upper mantle ferrikaersutite

Abstract

Mössbauer spectroscopy, H 2 O, and microprobe analysis techniques have been used to study upper mantle ferrikaersutite megacrysts from the scoria cones of the Ash Sham alkaline volcanic fi eld, northeastern part of the Arabian plate. Mössbauer spectra, collected at 298 K, indicate that the kaersutites are highly oxidized and all iron occurs as Fe 3+ . Two components were detected within the Fe 3+ quadrupole splitting distribution of the C-type sites and were assigned to M1 and M2-3 sites. The quadrupole splitting (QS) varies between 0.73-0.87 mm/s (Fe 3+ M1) and 1.28-1.45 mm/s (Fe 3+ M2-3). The kaersutite has a large oxy component in the amphibole OH-site (1.49-1.85 O 2-apfu) similar to the mantle-derived kaersutites. The very high ferric concentration in the kaersutites would suggest crystallization from a relatively oxidizing magma, perhaps with f O 2 close to the fayalite-magnetitequartz (FMQ), and may be a function of the high Fe 3+ /Fe tot of the metasomatic fl uid that crystallized these amphiboles.

Oxo-magnesio-hastingsite, NaCa2(Mg2Fe3+3 )(Al2Si6)O22O2, a new anhydrous amphibole from the Deeti volcanic cone, Gregory rift, northern Tanzania

“…The new mineral oxo-magnesio-hastingsite is a Ti-rich amphibole, it contains a significant amount of the NaCa 2 (Mg 3 Fe 3+ Ti)(Al 2 Si 6 )O 22 O 2 endmember and amphiboles with similar compositions are known from several other localities (e.g. Dawson and Smith, 1982;Dyar et al, 1993;Nasir and Al-Rawas, 2006). The combined evaluation of H 2 O and Fe 3+ contents, H and O isotope compositions and trace element concentrations lead to the conclusion that late-stage processes such as amphibole degassing, isotope exchange at decreasing temperatures and weathering did not affect the compositions of the minerals.…”

“…4, Table 1). Doublet 1 may be assigned to the M(1) lattice site and Doublet 2 can be assigned to Fe 3+ at the M(2,3) sites (Nasir and Al Rawas, 2006).…”

“…Dawson and Smith, 1982). They have been described as ''titaniferous pargasite and kaersutite'' (Dawson and Smith, 1982), ''oxykaersutite'' (Dyar et al, 1993) or ''ferrikaersutite'' (Nasir and Al-Rawas, 2006).…”

57Fe Mössbauer spectroscopy study of phlogopite megacrysts from an evolved carbonatitic kimberlite in the northeastern Oman Mountains

“…All parameters were allowed to vary during the final fits. Isomer shifts (IS) are referred to α-Fe at 300 K. Chemical analyses for all samples were obtained by microprobe analysis, in the same way as described elsewhere [7]. The analysis and corresponding structural formulas are given in Table 1.…”

Multiphase Mineral Inclusions in Ferrikaersutite Megacrysts : Implications for Postmagmatic Alteration of the Kaersutite Host

“…No significant chemical zoning has been detected even on the centimeter scale. Mössbauer spectroscopy indicates that all Fe in the kaersutite is Fe 3+ (Nasir and Al-Rawas, 2006). Thus, they are ferrikaersutite according to the nomenclature of Leake et al (1997).…”