Magmatic Differentiation in the Uwekahuna Laccolith, Kilauea Caldera, Hawaii

Petrographic and chemicoal studies of a suite of rocks fromthe Uwekahuna laccolith of Kilauea Volcano show that the originalmafic tholeiitic magma differentiated into tholeiitic picrite,tholeiitic olivine gabbro, and an aphanitic rock approachingquartz-basalt in composition. Mechanisms involved were an initialgravity settling of olivine and a final filter pressing of theresidual liquid. The range of composition represented by therocks of the laccolith is as great as that found among all hithertoanalysed lavas of the volcano. ²Present address: U.S. Geological Survey, Menlo Park, California