Hibonite-hercynite inclusion HH-1 from the Lancé (CO3) meteorite: The history of an ultrarefractory CAI

Details Hibonite-hercynite inclusion HH-1 from the Lancé (CO3) meteorite: The history of an ultrarefractory CAI Hibonite-hercynite inclusion HH-1 from the Lancé (CO3) meteorite: The history of an ultrarefractory CAI

Nov 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994gecoa..58.4779f&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 58, Issue 21, pp.4779-4793

Computer Science

6

Scientific paper

We studied the petrography, major and trace element chemistry, and magnesium, calcium, titanium and iron isotopic compositions of a hibonite-rich refractory inclusion from the Lancé CO3 meteorite. The inclusion, 290 × 230 m in size, consists of a core of hibonite crystals containing small perovskite grains, surrounded by a hercynite mantle and a thin diopside rim. The hercynite contains many small perovskite, ilmenite and sulfide grains. Trace element abundances show an ultrarefractory signature in all measured phases with an increasing depletion of the REEs heavier than Tb with increasing mass in hibonite, perovskite and ilmenite, but not hercynite. Calcium and titanium are isotopically anomalous with large deficits in 48 Ca and 50 Ti. Deficits are 60%. in 50 Ti and 11.5%. in 49 Ti in hibonite, hercynite, perovskite and ilmenite. In addition, the titanium isotopes show a mass-dependent isotopic fractionation of 8.5%./amu in favor of the heavy isotopes. Calcium isotope deficits in hibonite are 6.9%. in 42 Ca, 5.0%. in 43 Ca and 32.5%. in 48 Ca relative to 40 Ca- 44 Ca. The deficits are smaller in the rim diopside ( 48 Ca = - 21%.) and a neighboring pyroxene grain( 48 Ca = - 8%.). Magnesium shows excesses in 26 Mg, but the lack of an isochron relationship between 26 Mg / 24 Mg and 27 Al / 24 Mg indicates redistribution of radiogenic 26 Mg. Magnesium in hibonite is isotopically light ( F Mg = - 5.3%./amu). The iron isotopes in hercynite are normal. The data show that inclusion HH-1 experienced a complex metasomatic history including Fe-metasomatism, sulfurization and formation of nepheline and sodalite. The isotopic data provide not only a record of nucleosynthetic processes and nebular inhomogeneity but also a tracer of the relative movement of elements which may have occurred during alteration.

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