“Pipe vesicles” in basalt: Trails left by dense immiscible melt droplets sinking through a viscous basal thermal boundary layer

摘要: Abstract Pipe vesicles, tubular cavities found in the basal parts of pāhoehoe lava flows worldwide, constitute one their fundamental primary structures. Like other pipe vesicles have been ascribed to gas bubbles, whether rising buoyantly through viscous or trapped an inward-moving solidification front. These models involve special and unrealistic conditions still poorly explain characteristic features vesicles. In a new model proposed here, are postulated be hollow trails left by droplets dense, immiscible iron-rich silicate sulphide melt sinking thermal boundary layer just above lower chilled margin flow unit. Driven gravity, sink vertically static lava, but obliquely mobile such as undergoing gravitational spreading. Viscous fluid dynamic forces tend deform resist motion. The inverted-Y, inverted-V lambda (λ) shapes individual reflect downward branching, with large droplet breaking up partially crystallized, highly polymerized basalt layer. do not yield directions even on local (centimeters meters) scale, indirect indicators widespread liquid immiscibility processes basalts potential commercial Fe-Cu-Ni mineralization. As (cavities escape), term is necessary, “vermiform pāhoehoe”, having good descriptive power no genetic connonations, suggested for “pipe vesicles”.