Left: Figure from Masson  showing a subduction zone region. Right:
Sketch showing expected heat flow variations near subduction zones after
Uyeda . Heat flow is expected to decrease on the incoming plate approaching
due to flexure (starting about 300 km from the trench) and faulting
in the outer trench region (starting
about 50-75 km from the trench). FB=Forearc Basin. SC=Subduction Complex.
It has been commonly assumed that heat flow in the incoming plate at subduction
zones is lower than expected for crust of that age due to increased
hydrothermal circulation from flexure and faulting.
I tested this suggestion by examining heat flow measurements made near
all trenches and compared these values
to the average measured heat flow for the same age crust.
I found that there is no change in heat flow
approaching the trench near subduction zones due to flexing and faulting of
the crust as previously commonly assumed.
However, on average, heat flow in the overriding plate is ~60% of that
in the incoming plate [Stein, 2003].
Heat flow fraction (measured/observed global average heat flow for that age) with
distance from the trench axis. Within the faulted outer trench slope,
heat flow fraction does not decrease compared to the average values.
Hence this analysis suggests that the incoming crust at subduction zones has
the same thermal structure as expected for its age compared to
lithosphere far from plate boundaries. Sparse measurements on
incoming crust with relatively thin sedimentary cover have slightly lower
heat flow, suggesting more water circulation.
Masson, D. G., Fault patterns at
outer trench walls,
Mar. Geophys. Res., 13,
Stein, C. A., Heat flow and flexure at subduction zones,
Geophys. Res. Lett., 30,
No. 23, 2197 doi 10.1029/2003GL018478,
(05 December) 2003.
For pdf click here
Some basic problems in the trench-arc-back arc system, in
Island Arcs, Deep-sea Trenches and Back-arc Basins, Maurice Ewing
eds., Talwani, M and
Pitman, W. C. III, 1-14,
Am. Geophys. Un.,
This material is based upon work supported by the National Science Foundation under Grant No. 0001941.
Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.