Nickel-rich magnesiowiistite in Cretaceous/Tertiary boundary spherules crystallized from ultramafic, refractory silicate liquids

Details Nickel-rich magnesiowiistite in Cretaceous/Tertiary boundary spherules crystallized from ultramafic, refractory silicate liquids Nickel-rich magnesiowiistite in Cretaceous/Tertiary boundary spherules crystallized from ultramafic, refractory silicate liquids

Dec 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995gecoa..59.4967k&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 59, Issue 23, pp.4967-4974

Computer Science

7

Scientific paper

We have found trace inclusions of Ni-rich magnesiowastite within grains of magnesioferrite spinel recovered from Cretaceous /Tertiary boundary sediments from DSDP Site 596, South Pacific (23°51.20'S, 169°39.27'W) and DSDP Site 577, North Pacific (3°6.51'N, 157°43.40'E). Measured compositions of these inclusions range from (Mg. 85 Ni .74 Fe ,17 ) O to (Mg. 74 Ni .09 Fe. 1.7 ) O. Coexisting magnesioferrite and magnesiowastite can only crystallize from ultramafic, refractory, Mg-rich liquids with Mg/Si > 2 (atom ratio). Such liquid compositions cannot form as a result of fractional crystallization and are unknown to occur as a result of terrestrial igneous processes or meteoroid ablation. We infer that these minerals crystallized from liquid droplets that equilibrated with silicate vapor at high temperatures (probably >2300°C), resulting in fractionation of volatile SiO 2 from more refractory MgO. The most plausible source of this high-temperature vapor is in the fireball of the major impact event that terminated the Cretaceous.

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