Marañón fold and thrust belt

The Marañón fold and thrust belt (Spanish: faja corrida y plegada del Marañón) is a 1,000 kilometres (620 mi) long, northwest–southeast trending belt of deformed rocks located in the Andes of central Peru. The formation of the belt defines the Incaic Phase of the Andean orogeny.

Prior to the deformation and uplift the rocks forming the Marañón fold and thrust belt constituted the fill of a marine back-arc basin that existed in the Mesozoic and was parallel to the present-day coast. The west-dipping Chonta Fault existed as a normal fault within this basin and allowed continued basin subsidence and sediment accumulation in the Mesozoic. The onset of Andean orogeny first caused the basin to rise and dry up with red beds being deposited in its eastern part. Then the sedimentary basin was subject of a complete basin inversion. During deformation Chonta Fault acted as a barrier "damming-up" folded and thrust strata west of it. This makes the fault define the limits of two different styles of thin-skinned deformation within the belt. The fault was reactivated as an inverse fault during basin inversion in the Eocene.