Belén Metamorphic Complex

The Belén Metamorphic Complex (Spanish: Complejo metamórfico Belén) is a group of metamorphic and igneous rocks that crops out in the western edge of the Altiplano plateau in the interior of northernmost Chile. [1] The rocks of the complex metamorphosed during the Early Paleozoic era but the original protoliths formed in the Proterozoic eon.[1][2] This make rocks of the Belén Metamorphic Complex the oldest rocks known in Chile.[1] To the west the rocks of the Belén Metamorphic Complex thrust along Chapiquiña-Belén fault over sediments of Cenozoic age including ignimbrites of the Oxaya Formation and rocks of Lupica Formation.[1][3] At their peak conditions of metamorphism rocks reached temperatures and pressures of 700 C and 7 kbar.[3] The timing of the metamorphism matches the age of the Famatinian orogeny in the Argentine Northwest.[3] Rocks of the Belén Metamorphic Complex were involved in one or more orogenies in the Early Paleozoic.[3]

Rocks of the complex include foliatied amphibolite, orthogneiss, serpentinite and lesser amounts of quartz-rich mica schist.[1][3]

The rocks of complex have experienced continuous exhuming during the last 15 million years as part of the ongoing Andean orogeny, with an apparent exhumation spurt 11 to 7 million years ago.[2]