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7481656 
Journal Article 
Spinel-garnet relationships in mantle xenoliths from the Malaita alnoites, Solomon Islands, south-western Pacific 
Neal, CR; Nixon, PH 
1985 
88 
2 
347-354 
English 
Xenolithic alnoites (approx 34 m.y.) intruded an unusually thickened portion of the Pacific plate, known as the Ontong Java plateau. Lherzolite xenoliths from the Kwaikwai intrusion on Malaita Island contain spinels with garnet rims; primary and secondary clinopyroxenes and amphiboles are present. On the evidence of mineral composition and textures, several events are postulated to have affected the mantle below Malaita. Cooling (during separation and formation of the thickened plate) resulted in spinel reacting with clinopyroxene and amphibole to form garnet. During reaction Cr increases (along with Fe) in the spinel, thus enlarging its stability field to greater pressures, coexisting with garnet at 959-1039oC and 89-95 km. A late reheating mantle event possibly associated with alnoite eruption, produced a limited reversal of the reaction to form slivers of secondary clinopyroxene and amphibole, and Al- and Mg-rich rims in the spinels. (Authors' abstract)-C.N. 
DIAMOND DEPOSITS; DIAMONDS - Exploration; GEOLOGICAL SURVEYS - Pacific Ocean; GEOLOGY - Tectonics; ALNOITES; MALAITA ISLAND; MANTLE XENOLITHS; GARNETS