Segregation vesicles in basaltic lava

Abstract

The dark fine-grained igneous material lining vesicles in amygdaloidal basaltic lavas from Walli, New South Wales, Australia, represents solidified residual melt which moved into early-formed vesicles before consolidation of the lava. In this manner segregation vesicles were produced. The effect probably represents an increase in the confining pressure applied to the fluid within the vesicles. Partial crystallization of a vesicular lava followed by completion of crystallization at a higher confining pressure (for example, at a deeper marine environment) could produce the observed features. The pervasive low-grade regional metamorphism was in no way involved in the production of the segregation vesicles.