Development of interconnected talc networks and weakening of continental low-angle normal faults

Fault zones that slip when oriented at large angles to the maximum compressive stress, i.e.,
weak faults, represent a signifi cant mechanical problem. Here we document fault weakening
induced by dissolution of dolomite and subsequent precipitation of calcite + abundant
talc along a low-angle normal fault. Within the fault core, talc forms an interconnected foliated
network that deforms by frictional sliding along 50–200-nm-thick talc lamellae. The low
frictional strength of talc, combined with dissolution-precipitation creep, can explain slip on
low-angle normal faults. In addition, the stable sliding behavior of talc is consistent with the
absence of strong earthquakes along such structures. The development of phyllosilicates such
as talc by fl uid-assisted processes within fault zones cutting Mg-rich carbonate sequences may
be widespread, leading to profound and long-term fault weakness.

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