2003 Seattle Annual Meeting (November 2–5, 2003)

Paper No. 4
Presentation Time: 2:15 PM

INVERSION TECTONICS AT CORDILLERA DE DOMEYKO (NORTH CHILE) AND ITS CONTROL ON GIANT PORPHYRY COPPER EMPLACEMENT: NEW INSIGHTS ON FLAT-SLAB SUBDUCTION KINEMATICS DURING THE TERTIARY


AMILIBIA, Alejandro1, MCCLAY, Ken1, SKARMETA, Jorge2 and BOURDON, Erwan3, (1)Geology Department (Fault Dynamics Research Group), Royal Holloway Univ of London, Egham (Surrey), TW20 0EX, (2)Gerencia Corporativa de Exploraciones, Codelco-Chile, Huerfanos 1270, Santiago, Chile, (3)Geology Department, Royal Holloway Univ of London, Egham (Surrey), TW20 0EX, United Kingdom, a.amilibia@gl.rhul.ac.uk

The Cordillera de Domeyko, a complex Mesozoic-Tertiary structural belt inboard of the present-day subduction margin, is part of the north Chilean Pre-Cordillera morpho-tectonic unit. Giant porphyry copper deposits, with ages similar to the host intrusions (40-30 Ma), are aligned N-S within this structural belt. N-S alignment of deposits has lead to the widespread hypothesis that emplacement of this Eocene-Oligocene plutonic complex was controlled by regional strike-slip faults developed in a transtensional regime related to oblique subduction.

Landsat TM analysis and field observations indicate that the structure of the Precordillera is dominated by several elongate, N-S trending, basement ridges that are exhumed along steep reverse faults deforming the Triassic-Cenozoic cover. The vergence of the system changes from west to east along the trend giving a doubly-vergent “pop-up” geometry to the axial zone. Many of these geometries and structures result from reactivation of basement extensional faults related to Triassic-Jurassic extensional events. Basement short-cut faults such as the Sierra Castillo basement block are also typical, uplifting Palaeozoic rocks and shortening the footwall Mesozoic cover; showing a strong genetic relationship between thin and thick-skinned structures. Fieldwork shows no evidence of strike-slip motion on these basement faults.

Tertiary porphyry intrusions are aligned N-S, and are strongly controlled by basement-involved reverse faults that facilitated ascension of the magma and intrusion into the Mesozoic sedimentary cover as sills, mainly located at the anticlines hanging-walls.

Late Eocene-Early Oligocene giant porphyry copper bodies (Chuqicicamata & La Escondida) emplaced within Cordillera de Domeyko show adakitic affinities. This affinity combined with the structural evidence of emplacement at the end of the basement-involved deformational stage, suggest the existence of a subducting flat-slab under the Central Andes (22º-26ºS latitude), during the Tertiary. Shallowing slab would result in an easterly-migrating compressional regime in the over-riding plate characterized by thick-skinned tectonics. The resulting flat-slab would be the likely source of adakitic rocks by oceanic crust partial melting.