Abstract:

The Cenozoic volcanic rocks in the Fildes Peninsula are composed of High Al-basalt, basaltic andesite, andesite, and dacite belonging to a calc-alkaline volcanic series with low characterized and high Al concentrations, This has been confirmed with the major element composition, the trace element and the rare earth element concentrations of studied rocks. The volcanism in this area can be divided into two stages. Stratigraphically the Great Wall Formation was formed in the Paleocene and the Fossil Formation occurred on the boundary between Eocene and Oligocene. Using a new indicator, the Sr/Ca - Ba/Ca systematics proposed by Onuma (1980, 1981) and Sr, Ba, Ca concentrations in volcanic lavas and subvolcanic rocks analysed with NAA, the authors find that the Cenozoic volcanic rocks, high -Al basaltic volcanic rocks, whether from volcanic strata or from subvolcanic intrusions formed in different stages, could be considered as a primary member, and the fractional crystallization of clinopyroxene and plagioclase controlled the evolution of the primary magma and resulted in formation of the basaltic-andesitic, andesitic and dacitic magmas. This result strongly supports the petro-genesis model proposed from petrographical, mineralogical and petrochemical evidences. The evolution of the volcanic rocks on the Filldes Peninsula is estimated to be compatible with that in the southern Chile.