Recent publications suggest that most of the fluid flo
w in the upper oceanic crust is channelized through small volumes of rock and vented into the ocean. This implies that at flanks of generally thinly sedimented mid-ocean ridges, focused discharge at the seafloor should be concentrated most likely at outcrops, high-angle normal faults or seamounts. These vents should be associated
with a significant heat flo
w signature. Ho
wever, only fe
w observations
world
wide support this assumption up to no
w. On our quest for focused fluid exchange bet
ween young oceanic crust and the ocean
we surveyed a 720 km long and 40–90 km
wide off-axis portion of seafloor intersecting the East Pacific Rise near 14°14′S. A
wealth of geophysical methods including high-resolution s
wath mapping bathymetry, single channel seismics, sediment echo sounding, magnetics and heat flo
w determinations
were used. Heat flo
w data in the tectonic corridor cover crustal ages of 0.3–9.3 Ma. With respect to the conductive plate cooling model the data sho
w the
well-kno
wn pattern of lo
w values close to the ridge, associated
with vigorous hydrothermal circulation of cold sea
water through the young upper crust, and a fast recovery to almost lithospheric conductive cooling values at a surprisingly young crustal age of 9.3 Ma. Although the sediment cover is fairly thin, measurements
with a 3.6 m violin bo
w type heat probe
were possible almost every
where
within the investigated area. A detailed survey bet
ween t
wo large seamounts at 4.5 Ma revealed localized extremely high values of up to 618 mW/m
2 (275 % of the expected heat flo
w) at the foot of the seamount. This is interpreted as a clear indication of focused discharge of hydrothermal fluid. If
we, ho
wever, relate heat flo
w normalized by the expected conductive heat loss to the character of igneous basement, heat flo
w is highest in areas
with an almost flat and sedimented basement, and lo
west
within
![](/images/glyphs/BQ1.GIF)
10–20 km of seamounts and other rough basement relief. We therefore hypothesize that the large number of seamounts covering the ocean floors governs a major amount of convective heat loss of aging oceanic lithosphere.