Breccia-cored columnar rosettes in a rubbly pahoehoe lava flow, Elephanta Island, Deccan Traps, and a model for their origin

摘要: Abstract Rubbly pahoehoe lava flows are abundant in many continental flood basalts including the Deccan Traps. However, structures with radial joint columns surrounding cores of flow-top breccia (FTB), reported from some rubbly flows, yet unknown other basaltic provinces. A previous study these “breccia-cored columnar rosettes” ruled out explanations such as volcanic vents and tubes, showed that had grown outwards cold FTB inclusions incorporated into hot molten interiors. How highly vesicular (thus low-density) blocks might have sunk flow interiors has remained a puzzle. Here we describe new example FTB-cored rosettes, Elephanta Island Mumbai harbor. Noting (1) thick probably form by rapid inflation (involving injections largely advancing flow), (2) transitional to ‘a’ā (which continuously shed their top clinker front them they advance), propose model for rosettes. We suggest under were shedding advanced and, high-eruption rate injection inflation, frontal breakouts would incorporate this rubble, thickening carrying rubble interior. This implies that, far sinking interior, may been rising, until supply stopped, began solidifying, developed outward each inclusion already inferred, forming Those which recycling most became Deccan.