DECOMPRESSION MELTING AT THE VOLCANIC FRONT OF NICARAGUA: EVIDENCE FROM CONCEPCIóN AND MADERAS VOLCANOES

We report geochemistry of Nicaraguan lavas from Maderas volcano, the first in present literature, and Concepción volcano, which compliments work done previously by Borgia & van Wyk de Vries (2003) and van Wyk de Vries (1993). These lavas from Isla de Ometepe show a minimum in slab signature due to a combination of distance from the trench and decompression melting that is not diluted by flux melting geochemistry. This is contrary to much of the Central American active volcanic front where lavas show large slab signatures and are controlled by flux melting mechanisms, which obscure the decompression signature.

Whereas lavas from Nejapa and Granada cinder cone alignments, situated in areas of localized extension in SE Nicaragua, also show affinity for decompression melting, they are peculiar in that they show limited depletion in high field strength elements (Walker, 1984). In the case of the Ometepe lavas, which exhibit depletion in high field strength elements, we show that the decompression melting is allowed by localized extensional tectonics controlled, in part, by gravity spreading of the volcanoes.