Characteristics and origin of the glass spherules from the Paleocene flood basalt province of western Greenland

Details Characteristics and origin of the glass spherules from the Paleocene flood basalt province of western Greenland Characteristics and origin of the glass spherules from the Paleocene flood basalt province of western Greenland

Mar 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996gecoa..60..815r&link_type=abstract

Geochimica et Cosmochimica Acta, Volume 60, Issue 5, p. 815-830.

Computer Science

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Scientific paper

Glass spherules have been found in several Paleocene sandstone beds in central Nuussuaq, western Greenland. These beds are a mixture of glass, smectite, and calcite with rare occurrence of graphite and metal. The glass varies from a basaltic to a basic-andesitic composition and displays, on a micrometer scale, Mg, Al, Ca, Fe, Ni, and Cu enrichments relative to the bulk composition. These enrichments are associated with resorbed silicate crystals (plagioclase, pyroxene, and olivine) and partly oxidized metal-sulphide inclusions. The spherules have high Co, Ni, Cu, and Ir concentrations positively correlated with Fe. The high Cu content of the glass and the nonmeteoritic Ir/Cu and Ir/Ni (or Ir/Co) ratios of the spherules exclude a meteoritic origin for these elements. These compositional characteristics indicate a purely terrestrial origin, and likely result from the contamination of a basaltic-andesitic melt by sulphide liquid formed through reduction of a magma by C-rich sediments. This mechanism has already been proposed to account for the occurrence of Fe-bearing basalts and andesites in the Nuussuaq and Disko area. This origin is further supported by the high Cr content of the glasses, consistent with a highly magnesian tholeiitic picrite basalt for the parent magma, and the presence of metal, sulphide, and graphite in the spherule layers. The occurrence in the glass of rounded magnetite resulting from the oxidation of sulphide, and of dendritic spinel crystals characteristic of a rapid growth from a high temperature melt, show that the spherules were quenched in an oxidizing environment. We conclude that Nuussuaq glass spherules result from rapid and incomplete oxidation of liquid droplets generated by one or several episods of lava fountains.

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