Magma evolution revealed by anorthite-rich plagioclase cumulate xenoliths from the Ontong Java Plateau: Insights into LIP magma dynamics and melt evolution

摘要

Petrologic studies of igneous rocks often rely on whole-rock analyses alone to deduce source and melting histories. Whole-rock compositions represent a mixture of the processes responsible for the final texture and composition of the rock, but do not emphasize the evolutionary processes that the rock may have experienced. We examine the major, minor, and trace element compositions of plagioclase phenocrysts and plagioclase-rich cumulate xenoliths from a sequence of Kwaimbaita pillow basalt and massive flows recovered from Ocean Drilling Program (ODP) Site 1183 on the expansive ～ 122 Ma Ontong Java Plateau (OJP) and from subaerial outcrops on the island of Malaita, Solomon Islands. These data are used to reconstruct equilibrium liquid compositions to understand magma dynamics, magma evolution, and the distribution basalt types across the OJP. Results reveal that crystals frequently are out of equilibrium with their host basalt. Two distinct compositional zones are present in plagioclase phenocrysts and xenolith crystals — An_(80-86) and An_(65-79).