The Cordón de Lila Complex, central Andes, northern Chile; An Ordovician continental volcanic province

Abstract

The Precordillera of the Cordón de Lila/Sierra Almeida area south of the Salar de Atacama (25°S68°W) was the center of continuous magmatic activity from Early Ordovician to Early Permian time. Various plutonic units form a basement that is overlain by Paleozoic to Cenozoic sedimentary and volcanic sequences. A continental tholeiitic series of komatiitic and tholeiitic pillow basalts, andesitic to plagidacitic lavas, and pyroclastic flows occurs along the north-central portion of this tectonic horst and is a key example for the early Paleozoic development of the central Andes. The lavas are intercalated with hemipelatic to very shallow marine clastic sediments. The sequence is solely affected by weak deformation and burial metamorphism of its stratigraphically lowest part. Geochemical data suggest formation of parental liquids in a lherzolitic upper-mantle source, followed by low-pressure tholeiitic differentiation through combined FC and AFC processes at two distinct crustal levels. The discharge of these lavas and the accompanying flysch-type sedimentation was triggered by crustal extension during Ordovician time, which resulted in a highly segmented, horst and graben-type geodynamic environment.

Proterozoic–Paleozoic development of the basement of the Central Andes (18–26°S) — a mobile belt of the South American craton

“…Wells, 1980;Barton and Hanson, 1989). In the investigated area the widespread, long standing magmatic activity, derived from crustal melts, as indicated by the isotopic composition of pre-, syn-and post-deformational intrusions of Cambrian to Devonian age in NW Argentina (Rapela et al, 1990(Rapela et al, , 1992(Rapela et al, , 1998aGalliski et al, 1990;Damm et al, 1990Damm et al, , 1991Damm et al, , 1994 points to its important contribution to the mid-crustal heat budget. A common model to explain the mid-crustal low P/high T metamorphism, migmatization and the generation of crustal melts is magmatic underplating of mantle derived melts at the base of the lower crust (e.g.…”

“…10% higher for the given ages than ages calculated using the nonlinear model of DePaolo (1981).t DM The t DM model ages for felsic metmorphic rocks from the metamorphic basement range from 1.36 to 2.2 Ga (Table 1) without a gradient in their regional distribution. In N. Chile the average is 1.65 ^0.16 Ga 1s; n 12: Most metabasite samples have younger t DM ages than the gneiss: at Mejillones 1.45 Ga (Table 1) and 0.85±1.14 Ga (recalculated data of Damm et al, 1990), at Sierra de Limo Ân Verde 0.75 and 0.82 Ga (Table 1; Lucassen et al, 1999a) and at Cordo Ân de Lila 0.86±1.4 Ga (recalculated data of Damm et al, 1991). At Belen ages of metabasite are between 1.91± 2.05 and 0.67±1.14 Ga (recalculated data of Damm et al, 1990; additional ages of 1.54 and 1.75 Ga are reported by Basei et al, 1996, from the Belen schists at 188S, but the method of calculation is not quoted).…”

The Sierra de Macon, Plutonic expression of the Ordovician magmatic arc, Salta Province Argentina

“…Recently, a set of absolute ages was obtained that confirms an Ordovician age for most of these rocks (Palma et al, 1986;Llambías and Caminos, 1986;Blasco and Zappettini, 1996;Koukharsky et al, 2002). This confirmation for the Macon granites (Koukharsky et al, 2002) enables us to outline the paleogeography of the magmatic series and reinforces the concept of a western Puna eruptive belt (Faja Eruptiva de la Puna Occidental; Mpodozis et al, 1983;Palma et al, 1986;Damm et al, 1986Damm et al, , 1990Damm et al, , 1991Page et al, 1999;Rapela et al, 1999;Koukharsky et al, 2002). The igneous belt consists of a series of granitic bodies between 248 and 26830 0 S; among those, the Cordon de Lila complex and Sierra de Almeida in Chile and the Sierra de Taca Taca and Sierra de Macon in Argentina are the most important.…”