2:45 PM - 3:00 PM
[SCG63-17] Paleo temperatures, depths and stresses evaluated using calcite twinning paleopiezometry
Keywords:geothermics, stress, vertical movements, exhumation
On the other hand, the mechanical twinning results in the simple shear, the amount of which can be evaluated from twin density (e.g., Groshong, 1972). Deformation experiments have demonstrated that the incremental strain increases effective τc value. Lacombe (2010) compiled the results of such experiments to show the relationship among temperature, strain and τc.
Once the τc value is obtained, the depth where the twinning occurred can be estimated from the differential stress determined from the twin data, because the critical differential stress is proportional to depth in the brittle upper crust. Assuming an appropriate geothermal gradient, the depth can be converted to temperature. Based on the relationship by Lacombe (2010) and the deviatoric stress tensors obtained from the data, it is possible to define and solve the simultaneous equations of temperature, depth, deviatoric stress tensor and τc.
This method was applied to a calcite vein in a Miocene graben, which was formed during the Japan Sea backarc opening. The preliminary results are introduced in the presentation.