New Al-40/Ar-39 dates from the Las Tazas complex, northern Chile: Tectonicsignificance

The Atacama Fault Zone is a major Mesozoic structure that trends along the Coastal Batholith of northern Chile. Part of the fault zone underwent a kin ematic change from dip-slip to strike-slip displacement during the Early Cr etaceous. The Las Tazas complex intruded the fault zone during this change. New analyses of country rock protomylonites from the edge of the complex f irmly constrain the age of the change to 130 Ma and confirm that the comple x was emplaced during active displacement along the fault zone. The intrusi on heated its immediate country rocks and allowed localised ductile shearin g during emplacement, Upper crustal intrusions like the Las Tazas complex a re ideal targets for geochronological studies of major shear zones. (C) 200 0 Elsevier Science Ltd. All rights reserved.