The Patagonian batholith S of Tierra del Fuego, Chile: timing and tectonic implications.

Reconnaissance field studies, together with 49 new K/Ar and Rb/Sr mineral dates, give new insight into the geochronology and composition of the Patagonian batholith and into the time relations between the emplacement of the plutons and deformation. The country rocks are mainly Late Jurassic-Early Cretaceous sedimentary and volcanic rocks formed in an island arc-marginal basin system. Three main plutonic groups have yielded ages ranging from 141 to 34 m.y. The earliest is a gabbroic assemblage, exposed as relics within later granitic rocks, and dated at 141-103 m.y. The Canal Beagle plutonic group of granitic rocks characterized by a penetrative syn-magmatic foliation, gave dates of 113-81 m.y., whereas the Seno Ano plutonic group consists of granitic rocks with dates of 60-34 m.y., and is mainly exposed in the outer islands, indicating a local oceanwards shift of plutonism with time. Lower Cretaceous island arc volcanism was contemporaneous with the first two plutonic groups. Folding of the marginal basin infill occurred at approx 100-93 m.y. ago (Preceding abstracts)-R.A.H.