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 Palaeozoic paired metamorphic belt constructed during ocean-continent subduction in the SW Gondwana margin. Low P/T units are referred as by the Eastern Series, while high P/T units to 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 (ca. 320-300 Ma) that generated a thermal overprint on the Eastern Series, with NS-trending isograds; 2) S 2 foliation wrapping relict S 1 in albite porphyroblasts interpreted as basal accretion in Western Series; 3) D 3 event controlled by WNW-ESE post-accretionary sinistral faults that offset the Eastern/Western series contact and generated NE–SW to NS trending folds. This event was influenced by the rigid backstop of the Coastal Batholith, disrupting the isograds from the previous thermal overprint, and affected also Upper Triassic units. An 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 are a recurrent model to explain exhumation, our data suggest that strain partitioning along strike-slip systems took place during the Late Palaeozoic in SW Gondwana margin.