科研之友
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摘要
In the Mesoproterozoic Kunene Intrusive Complex (Angola-Namibia) one of the largest massif-type anorthosite complexes in the world, two successively emplaced anorthosite varieties can be recognized. The older white anorthosite suite consists of pyroxene-bearing anorthosite and leucogabbronorite, whereas the younger dark anorthosite suite is dominated by olivine-bearing anorthosite and leucotroctolite. The oxygen isotope and trace element characteristics of plagioclase and minor phases of the two distinct anorthosite varieties are consistent with their derivation from a mantle-derived parental melt that was subject to crustal contamination during the early stages of evolution. The trace element zoning patterns of plagioclase demonstrate that the older white anorthosite was derived by simultaneous fractional crystallization of plagioclase, pyroxene and Fe-Ti oxides during and after crustal contamination. In contrast, the subsequently emplaced dark anorthosite evolved after replenishment with mantle-derived parental melts by fractional crystallization of plagioclase, olivine and Fe-Ti oxides at magmatic temperatures above 1150 degrees C and experienced less crustal contamination.
