Published in the journal Science, “Rocks from the Mantle Transition Zone: Majorite-Bearing Xenoliths from Malaita, Southwest Pacific” investigates the terrestrial origins of majorite garnet and other minerals. These specimens are believed to have formed very deep within the mantle (approximately 470-670 km) at intense pressures (approximately 22-27 GPa). Majorite usually forms anywhere between 12-26 GPa and is considered analogous with these hypothesized limits of formation pressures. These extremely rare, Majoritic Garnets were found in xenoliths and macrocrysts along with other ultrahigh pressure minerals; including magnesium-perovskite, calcium-perovskite, micro-diamond, and other aluminum silicates. Interestingly, these mantle xenoliths and garnet macrocryst samples were discovered from small stream-gravel located in drainage systems in the eastern and north central part of the island of Malaita. These 19 samples were subjected to over 600 types of analysis to determine variations in composition.
The authors purpose that these xenoliths formed in the lower mantle and were transported to the Earth’s surface in ultra-mafic magma either during an alnoites eruption approximately 34 million years ago during the Ontong Java Plateau Basalt eruption; which is one of the largest igneous regions created via plume materials on Earth. This publication was significant because majorite was originally discovered in the Coorara meteorite that was found in 1970 near Coorara in western Australia . As a side note, this paper also gives interesting insight into temperature gradients, dynamic composition of the transition zone, and the mantle.
The authors purpose that these xenoliths formed in the lower mantle and were transported to the Earth’s surface in ultra-mafic magma either during an alnoites eruption approximately 34 million years ago during the Ontong Java Plateau Basalt eruption; which is one of the largest igneous regions created via plume materials on Earth. This publication was significant because majorite was originally discovered in the Coorara meteorite that was found in 1970 near Coorara in western Australia . As a side note, this paper also gives interesting insight into temperature gradients, dynamic composition of the transition zone, and the mantle.