Fluid inclusions in gabbroic xenoliths from Lanzarote and La Palma, Canary Islands

Abstract

To learn more about the fluids that were present in the Canary Islands oceanic crust during the magmatism, fluid inclusions in gabbroic xenoliths from Lanzarote and La Palma have been studied. The fluids were originally incorporated in the ascending Canary Island melts and their compositions are pure CO2 or CO2 + H2S, where the proportion of H2S is about 1%. CO2 + H2S fluids are more common in the crust beneath La Palma than Lanzarote. CO2-bearing sulphide and silicate melts were also present in the crust. Calculated fluid pressures show that infiltration-areas of Canary Island melts in the crust beneath Lanzarote have a minimum depth of 11,4 km. Equivalent areas in the crust beneath La Palma have a minimum depth of 10,8 km. Magma chambers where Canary Island cumulates formed, have a minimum depth of 11,2 km beneath La Palma. CO2 + H2S fluid dominate in fluids associated with magma chambers where Canary Island melts formed cumulates. Lanzarote s location close to the African continental margin has affected the fluid inclusions as well as the gabbroic xenolith; more fault and fracture zones in the crust have resulted in more damaged xenoliths and fluid inclusions. Consequently, xenoliths from Lanzarote are dominated by fluids trapped relatively late. The xenoliths made temporary residence in one or several magma chambers before reaching the surface. Together with some decrepitation during the transport, this resulted in trapping of fluids with many different Th in the same xenolith.