Computer Science
Scientific paper
Nov 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996gecoa..60.4497m&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 60, Issue 22, pp.4497-4508
Computer Science
Scientific paper
Oxygen isotope data are presented for silicate minerals separated from a variety of rock types from the 130 Ma Okenyenya igneous complex of northwestern Namibia. These rock types include a tholeiitic suite ranging from olivine gabbro to quartz monzodiorite and syenite, and an alkaline suite including gabbro, syenite, nepheline syenite, and essexite. In general, the difference in 18 O values between coexisting feldspar, pyroxene, and biotite are consistent with equilibrium at high temperatures and preclude significant interaction with magmatic or external fluids. The 18 O values of pyroxene can be used to model magmatic processes and show a systematic increase from 7.1-9.0 along a transect through a tholeiitic olivine gabbro-quartz monzodioritic body, corresponding to a systematic decrease in Mg#. Pyroxene 18 O values also show a strong correlation with initial strontium and neodymium isotope ratios, with the alkaline suite having lower 18 O values, lower initial strontium-isotope ratios, and higher initial neodymium isotope ratios than the tholeiitic suite. Simple oxygen mass balance calculations suggest that the extremes of isotope composition resulted from at least 60% contamination by material of similar isotope composition to the nearby southern Etendeka quartz latites. Assimilation/crystal fractionation models of oxygen, strontium, and neodymium isotope data suggest that the rate of assimilation was high and may have approached simple mixing. The contaminated tholeiitic olivine gabbro-quartz monzodioritic body was the earliest to crystallize in the complex and this was followed by relatively uncontaminated silica-undersaturated magmas.
Harris Chris
Le Roex Anton P.
Martinez Iúma A.
Milner Simon C.
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