Modeling episodic tremor and slip events in the ductile carbonates of the Glarus thrust

Abstract:

The exposed Glarus thrust displays mid-crustal deformation with tens of kilometers of displacement on an ultra-thin layer, the principal slip zone (PSZ) as shown in Figure 1. Geological observations indicate that this structure resulted from repeated stick-slip events in the presence of highly over-pressured fluids. Here we show that the major characteristics of the Glarus thrust movement (localization, periodicity and evidence of pressurized fluids) can be reconciled by the coupling of two processes, namely shear heating and fluid release by carbonate decomposition. During this coupling, slow ductile creep deformation raises the temperature through shear heating and ultimately activates chemical decomposition of carbonates. The subsequent release of highly over-pressurized fluids forms and lubricates the PSZ, allowing a ductile fault to move tens of kilometers on millimeter-thick bands in episodic stick-slip events. This model identifies carbonate decomposition as a key process for motion on the Glarus thrust and explains the source of over-pressured fluids accessing the PSZ.