Episodic magmatism and segmentation of the Gondwanan arc in Chile (21–38°S): Insights into Carboniferous to early Permian subduction processes and deformation

Abstract

The Gondwanan cycle unfolds along the southwestern margin of Gondwana during the late Paleozoic, driven by the subduction of the proto-Pacific plate beneath the continental margin. Its geological record in Chile comprises accretionary complexes that emerge discontinuously along the coast, together with belts of igneous rocks, predominantly intermediate in composition, which constitute the coeval Gondwanan magmatic arc.

Based on extensive geochemical data, geochronology and field observations, the magmatic belt can be divided into three segments: Northern (21°–27° S), North-Central (27°–31° S), and Southern-Central (33°–38° S), according to varying percentages of exposed plutonic and volcanic rocks, the ages of magmatic pulses, and proximity to coeval accretionary complexes. The northern and north-central segments exhibit continuous activity for over 50 million years, from 330 to 280 Ma, with arc-trench distances of about 100–150 km. In contrast, the Southern-Central segment is located close to the accretionary complex (0–30 km) and concentrates its magmatic activity during the Pennsylvanian (322-300 Ma).

The marked episodic behavior of the Gondwanan arc in the northern and north-central segments is characterized by a High Magma Addition Rates (HMAR) event at 300-279 Ma that coincides with a peak in basal accretion within the coastal prism and localized orogeny in the foreland (San Rafael orogenic stage). Despite these events, various petrogenetic indicators suggest that both crustal and mantle magma sources remained stable throughout most of the Gondwanan cycle, with no evident arc thickening during the HMAR event. These deformation processes correlated in time with the diachronous arrival of oceanic reliefs to the margin, previous to onset of the Choiyoi Province.