Temperature evolution of an oceanic fracture zone Xiaopeng Tong & Janine Bühler

Outline Background Lithosphere flexure at Fracture zone Mathematical derivation Temperature & bathymetry Comparison between the model and the data Conclusion

Background An oceanic fracture zone is the boundary between lithosphere of different ages. A fracture zone is a linear oceanic feature--often hundreds, even thousands of kilometers long--resulting from the action of offset mid-ocean ridge axis segments. They are a consequence of plate tectonics. Lithospheric plates on either side of an active transform fault move in opposite directions; here, strike-slip activity is possible. Fracture zones extend past the transform faults, away from the ridge axis; seismically inactive (because both plate segments are moving in the same direction), they display evidence of past transform fault activity.

Lithosphere flexure at FZ Phenomenon Flexure near the FZ in the oceanic litho Reason Permanence of the initial bathymetric step across the FZ Difference subsidence rate on either side of the FZ

Modeling Calculate the flexure Consistent with the observed data! Elastic plate model Thickness He(T) Consistent with the observed data!

But… They ignore the thermal conduction completely !

Problem Ridge Transform fault FZ t t0 x Ridge

Mathematical derivation 1 T -- temperature Tm -- temperature of the mantle x -- distance vertical to FZ z -- depth t0 -- the age offset t -- age of the older seafloor t-t0 -- age of the younger one The solution to this problem for an arbitrary initial temperature distribution can be expressed as a two-dimensional Convolution of the initial temperature with a line source Green’s function Green function method (Carslaw and Jaeger , 1959)

Mathematical derivation 2

Mathematical derivation 3 substitution First part of the integration

Mathematical derivation 4 Second part of the integration By Magic math

Final solution of temperature

Temperature evolution

Numerical approach...

Topography of the FZ 1 Ridge Local isostatic balance Transform fault x Ridge

Topography of the FZ 2

Topography of the FZ 3 Final solution of the topography

Comparison

Conclusions Topography calculations solely based on local isostatic compensation can not explain the observed data We need to consider elastic flexure of the lithosphere (ie coupled fracture zones, fixed topographic step) New studies use dynamic models that allow the fault zones to freely slip