During the “Azores Tephra” cruise M141 on the German research vessel RV Meteor in September 2017 we carried
out pore fluid analyses of 28 gravity cores recovered from the Azores Plateau. The pore fluids were analysed for
total alkalinity, ammonium, methane and other major elements such as Na, Ca, Cl, B, Mg and Sr and allow, for
the first time, to perform a thorough analysis of sub-seafloor fluid origin and secondary alteration processes in this
area of intense tectonic and volcanic activity.
Pore fluids in sediments of the Azores Plateau are generally affected by the alteration of marine volcanic deposits.
Moreover, due to local heating of the plateau, shallow hydrothermal fluid venting occurs e.g. known at the D.
Joao de Castro seamount in the Terceira Rift (Cardigos et al., 2005). Here, for the first time, we present fluid
geochemistry data from deep-water hydrothermal seepage areas of the Azores Plateau. The present status of
geochemical analyses, suggests that there are two different types of hydrothermal seepage systems: In many
places on the plateau a slightly acidic (CO2-rich) hydrothermal fluid percolates through the sediments; Along the
Terceira Rift, which marks the northern border of the plateau, also methane-rich fluid seeps are suspected.
We will present a comprehensive interpretation of the available data set, with respect to geochemical processes
occurring at the hydrothermally-driven seepage systems, fluid and gas sources, the activity of the seeps, and the
role of ash alteration.
Cardigos, F., Colaço, A., Dando, P. R., Ávila, S. P., Sarradin, P. M., Tempera, F., Conceição, P., Pascoal,
A., and Serrão Santos, R., 2005, Shallow water hydrothermal vent field fluids and communities of the D. João de
Castro Seamount (Azores): Chemical Geology, v. 224, no. 1-3, p. 153-168.
Conference or Workshop Item