The morphology and origin of wide craters at Al Haruj al Abyad, Libya: maars and phreatomagmatism in a large intracontinental flood lava field?

摘要

Al Haruj al Abyad is a Miocene to Holocene intracontinental alkaline basaltic volcanic field in Libya. A NNW-SSE trending vent alignment up to 70 km in length and 7 km in width consist of at least 120 vents. Present pyroclastic rocks indicate hot emplacement from Strombolian eruptions and Hawaiian lava fountains. Craters are up to 800 in in diameter and 100 in in depth surrounded by low rims of strongly welded scoriaceous tephra. Craters often undercut the syn-volcanic paleosurface closely resembling maar-structures. It is inferred that magmatic fragmentation of the uprising melt has changed to fragmentation driven by magma-water interaction leading to an enigmatic explosive eruption that has removed the top of the scoria cones or even producing maar-like depressions. Water may have gained access to the melt during decreasing magmatic discharge in the final stage of the eruptions and produced energetic phreatomagmatic explosive eruption that ripped of the top of the volcanic edifices.