The geology of central Isla Hoste, southern Chile: sedimentation, magmatism and tectonics in part of a Mesozoic back-arc basin

Abstract

SummaryCentral Isla Hoste lies towards the Pacific side of a Mesozoic back-arc basin in southern Chile, behind a magmatic arc represented by the Patagonian batholith. The volcaniclastic sediments on Isla Hoste were derived from the magmatic arc and deposited in the back-arc basin by turbidity currents. These sediments may, in part, overlie mafic volcanic and intrusive rocks. Geochemical and lithologic data are used to suggest an ocean-floor origin for these mafic igneous rocks on central Isla Hoste. The sedimentary and mafic igneous rocks were deformed and uplifted during the middle Cretaceous Andean orogeny. However, the nature of the crust underlying most of the sedimentary rocks in the back-arc basin and the style of deformation in most of this basement are unknown. Therefore the role, if any, of subduction within the back-arc basin during the middle Cretaceous ‘closure’ of this basin is not certain. Post-kinematic intrusions within the back-arc basin are common. These intrusions will confuse attempts to determine by geophysical means the nature of the pre-kinematic basement of the back-arc basin and attempts to outline the present extent of the basin in offshore regions.