Matt Miller @(n
f―ΘwκU)
Imaging of a subducted mid-ocean ridge:
P- and S-wave teleseismic
tomography of the upper mantle beneath southern Chile at latitude 47
degrees south and the implications for the thermal effects of ridge
subduction.
2007N530ϊ
The Chile Triple Junction in South America is situated at ~47 degrees
south; a place where the diverging oceanic Nazca and Antarctic plates
subduct underneath the South American continent.
Subduction of the spreading ridge can transmit excess heat to the overlying
plate, which could potentially cause forearc magmatism, including formation
of granitic batholiths, and regional metamorphism. The Chile Triple
Junction is the unique site on the present-day Earth, where we can
investigate such potential interactions contributing to the growth of the
continental crust.
The Seismic Experiment in the Aisen Region of Chile (SEARCH) project
operated a network of up to 60 broadband seismometers on-shore to the east
of this triple junction between 2004 and 2006, over a 6 Ma old segment of
subducted mid-ocean ridge. Here the P-wave velocity structure is examined
beneath this region between ~40 and ~400 km depth using 2534 P-wave
residuals from 173 teleseismic earthquakes. The data shows a region of
relatively fast velocity to the north of the triple junction, dipping at
around 40 degrees eastwards, proposed to be the subducting Nazca plate.
Further to the south a relative low velocity zone lies at depths < 100 km
associated with elevated temperature due to the subducted ridge segment.
The lower-resolution S-wave tomography will also be presented and the
possibility of combining the datasets discussed. This data provides greater
constraints on the thermal modelling of this subduction process, and agrees
with the hypothesis that the subduction of an active spreading ridge can
cause a drastic thermal impact along the subducting slab.