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Research in Geochemistry - The Incipient
Rift
at 2°40'N, east of the East Pacific Rise
Emily
Klein and co-PI Deborah
Smith (Woods Hole) have recently been funded to explore
the geochemical and geologic variations along the "Incipient
Rift" at 2o 40 N, east of the East Pacific Rise.
The cruise took place in the summer of 2002.
The primary goal of the study was to use magmatism of the
Incipient Rift, the northern boundary of the Galapagos Microplate,
to explore the chemical systematics produced within the steady-state
melting regime of the EPR as a function of distance from the
axis. To date, no studies have been able to address how melt
compositions change with increasing distance from the ridge,
and thus identify true variations in melts produced in the
distal portions of the melting regime. The potential of doing
this exists at the Incipient Rift, located immediately east
of the East Pacific Rise (EPR) at 2°40'N. This rift is a magmatically
active, slowly diverging spreading center separating the Cocos
and Galapagos plates. Recently, we performed limited basalt
glass sampling of the Incipient Rift, over ~17 km of its length,
beginning ~10 km east of the EPR. Our spatially systematic
chemical results offer the tantalizing prospect that the Incipient
Rift, because it is adjacent and orthogonal to the EPR and
has undergone very little extension, is tapping off-axis magmas
produced within the steady-state melting regime of the EPR.
In order to accomplish our goal we conducted a 23-day cruise
during which we systematically sampled lavas and collect multi-beam
bathymetry data over the entire Incipient Rift from its initiation
to its eastern termination at crust with typical EPR north-south
abyssal hill lineations. With a spatially extensive, off-axis,
high-quality chemical data set, we were able to address a
range of fundamental questions concerning processes occurring
in the EPR melting regime. For example, we modeled our chemical
data in light of existing theoretical models of the "shape"
of the melting regime beneath fast-spreading ridges to shed
light on the style of upwelling, melting, and melt focusing.
We also ran several camera tows within the Rift and along
the bounding scarps. The camera work within the Rift guided
the sampling efforts by helping to define the distribution
of magmatism within the Incipient Rift and its linking ridge
to the adjacent EPR. Reconnaissance camera work on the slopes
bounding the Incipient Rift was used to address a secondary
goal of our proposed study: to determine whether the scarps
expose deeper crustal lithologies, as at the Hess
Deep.
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