Tectono-metamorphic events in the Paleozoic coastal metamorphic complexes of south-central Chile: the Hualpén–Laraquete segment (36.5–37.5° S)

Metamorphic complexes along the coast of south-central Chile are interpreted as a Late Paleozoic paired metamorphic belt constructed during ocean–continent subduction in the SW Gondwana margin. Low pressure–temperature units are referred to as the Eastern Series, while high pressure–temperature units are referred to as the Western Series. A detailed field and structural analysis (36.7–37.15° S) depicted three deformation events: (1) S 1 foliation interpreted as the onset of frontal accretion, followed by the intrusion of the Coastal Batholith ( c. 320–300 Ma) that generated a thermal overprint on the Eastern Series, with north–south-trending isograds; (2) S 2 foliation wrapping relict S 1 in albite porphyroblasts interpreted as basal accretion in the Western Series; and (3) a D 3 event controlled by WNW–ESE-trending post-accretionary sinistral faults that offset the Eastern–Western Series contact and generated NE–SW- to north–south-trending folds. This event was influenced by the rigid backstop of the Coastal Batholith, disrupting the isograds from the previous thermal overprint and also affecting Upper Triassic units. A 40 Ar/ 39 Ar age of 275 ± 6 Ma on syn-S 2 white mica records the retrograde metamorphic event of the Western Series. Although passive uplift by basal accretion and oceanic relief arrival is suggested in a recurrent model to explain the exhumation, our data suggest that strain partitioning along strike-slip systems took place during the Late Paleozoic in the SW Gondwana margin.