The Shoshonitic suite of Hewhoepen pluton. Tierra del Fuego.

CERREDO, M. E.; REMESAL, M.; TASSONE, A.; LIPPAI, H.

La Plata, Buenos Aires. Argentina.

Congreso; XVI Congreso Geológico Argentino; 2005

AGA

The Hewhoepen pluton (HP) is a small (<10 km2) intrusive body located at the southeastern edge of the Lago Fagnano (Figure 1). It is discordantly emplaced in Lower Cretaceous (Olivero and Medina 2001) mudstones. The host black mudstones (either massive or laminated), often display pencil cleavage and multilayer sets of thin quartz veins. Tiny biotite flakes and sericite/muscovite rims around detritic feldspar cores characterize contact mudstones. Rare, cm-scale xenoliths of biotite-plagioclase schists are found locally within the pluton (Cerredo et al. 2000). K/Ar whole rock dating yielded a Late Cretaceous age of 93 ± 4 Ma (Acevedo et al. 2000). Magnetic and gravimetric modelling of the area has revealed the presence of a geometrically complex body partly exposed at Cerro Hewhoepen which, at the shallower depths, can be viewed as a composite plug, with roots located at subsurface depths of about 8 Km (Cerredo et al. 2000; Tassone et al., 2005) Analysis of chemical data along with the recognized petrographic facies allow to present a preliminary petrologic characterization of this pluton.