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

Abstract

Reconnaissance field studies on the Patagonian Batholith exposed S of Tierra del Fuego, together with 49 new K-Ar and Rb-Sr mineral dates, render new insights into two main aspects of the late Mesozoic geology: the geochronology and composition of the batholith, and time relations between the emplacement of the plutons and deformation. The envelope of the batholith in this area is mainly composed of late Jurassic-early Cretaceous sedimentary and volcanic rocks formed in an island arc-marginal basin system. Three main plutonic groups have been recognized which have yielded mineral dates, interpreted as crystallization ages, ranging from 141 to 34 Ma. The earliest is a gabbroic assemblage, including gabbros, diorites and hornblendites exposed as relicts within later granitoids and with dates ranging from 141 to 103 Ma. The Canal Beagle Plutonic Group is composed of granitoids characterized by a penetrative syn-magmatic foliation and with dates of 113 to 81 Ma. The Seno Ano Nuevo Plutonic Group is formed of granitoids with dates of 60 to 34 Ma 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 intrusion of the gabbroic assemblage, and, in part at least, of the Canal Beagle Plutonic Group. Folding of the marginal basin infill, which has been related to the closure of the marginal basin, occurred from about 100 to 93 Ma ago. The gabbroic assemblage was apparently mainly pre-tectonic, whereas the Seno Ano Nuevo Plutonic Group was clearly intruded after this deformational event. A post-tectonic or possibly late-tectonic emplacement for the youngest plutons of the Canal Beagle Plutonic Group and a pre- or syn-tectonic intrusion for the oldest is inferred.

Continental underthrusting and obduction during the Cretaceous closure of the Rocas Verdes rift basin, Cordillera Darwin, Patagonian Andes

“…This result reflects a refinement of previously reported ages from Beagle Suite plutons, which typically yielded large errors (see Hervé et al [1984] and compilation by Kohn et al [1995]). It also is compatible with stratigraphic evidence and detrital zircon data from the northern part of the Magallanes foreland basin, which suggest that foreland sedimentation is no older than 92 ± 1 Ma [Fildani et al, 2003], although thrusting most likely initiated earlier [see also Kohn et al, 1995;Calderón et al, 2007].…”

Shallow architecture of Fuegian Andes lineaments based on Electrical Resistivity Tomography (ERT). Evidences of transverse extensional faulting in the central Beagle Channel area

“…The Late Jurassic-Neogene Fuegian Batholith crops out in the southwestern archipelago of Tierra del Fuego Hervé et al, 1984), related to the subduction of Pacific Ocean f loor beneath the South American Plate which took place at least since the Late Jurassic.…”

Constraints on deformation of the Southern Andes since the Cretaceous from anisotropy of magnetic susceptibility

“…2), from SW to NE: (i) a coastal magmatic arc, including the calc-alkaline igneous suite from the Patagonian Batholith emplaced between the Late Jurassic and Neogene (Hervé et al, 1984Pankhurst et al, 2000;González-Guillot et al, 2011);(ii) the Rocas Verdes marginal basin units, including weakly metamorphosed relics of its ocean floor (Sarmiento and Tortuga ophiolite complexes; Stern and De Witt, 2004;Cunningham, 1994) and its sedimentary cover Olivero and Malumián, 2008); (iii) Cordillera Darwin exposing late Paleozoic basement schists affected by thick-skinned tectonics (Kohn et al, 1995;Klepeis, 1994;Hervé et al, 2008;Klepeis et al, 2010;Maloney et al, 2011Maloney et al, , 2013; and (iv) the thin-skinned…”