Abstract

An example of thermal gradient inversion below a major thrust is described from the carbonates of the Olympos autochthon in northeast Greece. On the basis of several hundred probe analyses, temperatures have been determined across 3 km of structural height using calcite-dolomite geothermometry. The inversion is interpreted in terms of shear heating accompanying the Tertiary emplacement of the overlying metamorphic sheet.

Significant heating is restricted to the uppermost 1 km of the Olympos platform, where the carbonates have been deformed partly by steady-state flow. A simple heat-conduction calculation gives an estimate of about 0.6 m.y. for the duration of the shear heating, and geological constraints suggest that the minimum Tertiary movement on the thrust is 15 km, equivalent to a strain rate of 10−12 s−1 during overthrusting.

More detailed numerical modeling shows that the high rates of movement implied by this strain rate are essential to the generation of the inferred thermal profile. An additional requirement of a shear stress of several hundred bars at the thrust suggests that a horizontal compressive stress was necessary to maintain the movement. The shear strength behavior deduced for the Olympos carbonates is in good agreement with the extrapolation to geological strain rates of Heard's and Heard and Raleigh's experimental data for the Yule marble.

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