HR: 14:55h
AN: V12G-06    [PDF]
TI: A Comparison of two Northeastern Atlantic Rift Systems With Hawaiian Rift Systems
AU: * Galipp, K
EM: kgalipp@uni-bremen.de
AF: Universit\"{„}t Bremen Fachbereich Geowissenschaften, Klagenfurter Str, Bremen, 28359 Germany
AU: Schwarz, S
EM: sschwarz@uni-bremen.de
AF: Universit\"{„}t Bremen Fachbereich Geowissenschaften, Klagenfurter Str, Bremen, 28359 Germany
AU: Kl\"{u}gel, A
EM: akluegel@uni-bremen.de
AF: Universit\"{„}t Bremen Fachbereich Geowissenschaften, Klagenfurter Str, Bremen, 28359 Germany
AB: Models on magma transport within and beneath rift zones are largely based on Hawaiian volcanoes and are not necessarily transferable to other oceanic islands. We carried out comparative studies on the active Cumbre Vieja rift zone of La Palma (Canary Islands) and on the fossile Madeira and Desertas rift systems (Madeira Archipelago) representing shield stage volcanoes at hotspots less productive than the Hawaiian. Different barometers were used to constrain magma pathways beneath the Madeira and La Palma rift systems and to compare the results with models for Hawaiian rift zones. Pressures obtained by cpx-melt barometry are interpreted to reflect major fractionation levels and generally indicate depth ranges within the uppermost mantle: 16-27 km for Cumbre Vieja, 15-32 km for Madeira and 16-28 km for Desertas. In contrast, microthermometry of CO2-rich fluid inclusions yields pressures within the lowermost crust to uppermost mantle (Cumbre Vieja: 7-14 km, Madeira: 8-10 km, Desertas: 9-17 km) that are interpreted as temporary stagnation levels. Further stagnation within the upper crust that may reflect shallow rift pathways was only found for the Desertas rift at 2-4 km depth. Our models of the magma plumbing systems beneath La Palma, Madeira and Desertas are thus characterized by (i) major fractionation levels in the upper mantle, (ii) temporary stagnation levels in the lower crust to the Moho, and (iii) local rift pathways. In none of the investigated volcanoes there are any indicators of a high-level magma reservoir feeding the rift zones. This is an important difference to models for Hawaiian rift zones characterized by shallow subcaldera magma chambers from where rift zones emanate. For Hawaii there is also evidence for prior magma storage and fractionation near the mantle/crust boundary and within the upper mantle, similar to the situation at the at the Atlantic rift systems studied. The lack of long-lived shallow magma chambers at La Palma and Madeira is best explained by their lower eruption rates as compared to Hawaii and the lower buoyancy fluxes of the respective mantle plumes.
DE: 8145 Physics of magma and magma bodies
DE: 8439 Physics and chemistry of magma bodies
DE: 9325 Atlantic Ocean
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting