Geology of part of a long-lived dynamic plate margin: the coastal cordillera of north-central Chile, latitude 30°51′–31°S

Abstract

A complex composed of ultrabasic and basaltic lavas, chert, arkose, and conglomerate was assembled in the coast of north-central Chile (lat. 30°30′–31°S) prior to 200 Ma. The character of, and relationships between, the rock formations exposed here are consistent with an autochthonous evolution of this part of Chile in the last 200 Ma. Three major episodes of deformation and metamorphism have been observed in this area. The first episode (F1) produced a compositional layering (S1) and amphibolite-facies metamorphism coeval with the intrusion of an extensive igneous complex between 220 and 200 Ma. A second episode of deformation (F2) locally formed reverse faults and tight, recumbent folds in S1. Units in which F2 folds are well developed yield K–Ar and Rb–Sr ages between 163 and 140 Ma. At between 140 and 126 Ma, upright, open to tight folds (F3) formed with sharp hinges and axial planes that strike north and dip steeply east. Structures of similar age, style, and orientation have been reported as far south as Tierra del Fuego. The timing of the F3 deformation appears to correspond to the opening of the South Atlantic Ocean and accelerated westward motion of South America.

Structural overprint of a late Paleozoic accretionary system in north-central Chile (34°-35°S) during post-accretional deformation

“…Hence, the cataclastic deformation episode is largely confi ned to Jurassic times. Similar semi-brittle strike-slip zones of considerable size cross-cut by Jurassic dykes are widely observed further north along the coast of north-central Chile (Rebolledo and Charrier, 1997;Irvine et al, 1988). Summarizing the cataclastic structures may be best explained as related to a left-lateral strike-slip system (Fig.…”

“…On the other hand, the local semi-brittle shear zones are cut by undeformed basalt and rhyolite dykes. A rhyolite dyke in the study area was dated at 138 Ma consistent with Jurassic to Lower Cretaceous ages of the widespread bimodal magmatism in the forearc further north (Irvine et al, 1988). Hence, the cataclastic deformation episode is largely confi ned to Jurassic times.…”

“…A-E. Deformation features in the Western Series: A. subhorizontal isoclinal rootless intrafolial F 2 -folds at Punta Lobos (34°26'S); B. subhorizontal S 1 -and S 2 -foliation transposed subparallel to relic bedding s 0 ; C. garnet σ clasts south of Punta Sirena (34°32'S) in deeply subducted garnet micaschist; D. s 2 -crenulation foliation deformed by F 3 -folds and s 3 -foliation planes; E. quartz-fi lled tension gashes cross-cutting s 2 -foliation as latest deformation during exhumation; also note the fi rst generation of quartz veins transposed parallel to the penetrative foliation; F. post-accretional cataclastic sinistral shear zone at Infi ernillo cliffs in Pichilemu (34°24'S). Glodny et al (2005), Vásquez and Franz (2008) and Irvine et al (1988) in other parts of central Chile. According to Vásquez and Franz (2008) To estimate fi nite strain variation in rocks of the Western and Eastern Series, R f /Φ analyses in metagreywackes and X-ray texture goniometry (XTG) on phyllosilicate-rich rocks were carried out.…”

Structure of the Andean Palaeozoic basement in the Chilean coast at 31º 30’ S: Geodynamic evolution of a subduction margin

“…In the Chilean coast, the existence of rock suites that formed part of a Palaeozoic accretionary prism during subduction of the palaeo-Pacific plate is accepted since the works of Hervé (1988), Hervé et al (1988) and Irwin et al (1988). These rocks are exposed in several discontinuous outcrops from the Península de Mejillones (23º S latitude, see Fig.…”

International Lateinamerika-Kolloquium 2009

“…This complex is also composed of bimodal association with leucogranites, gabbros and mingling structures (Gana, 1991, Parada et al, 1999. Whole rock Rb/Sr ages range between 200 and 220 Ma (Irwin et al, 1988). The isotopic signature in the Limarí complex as well as in the late Triassic intrusive suites in south central Chile is mantle-related with variable degree of assimilation of crustal melts.…”