First Boron systematic approach in the Cenozoic extra-Andean basaltic volcanism in Patagonia

MASSAFERRO GI; GMÉLING K; NÉMETH K; HALLER MJ

San Salvador de Jujuy

Congreso; XVII Congreso Geológico Argentino; 2008

Asociación Geológica Argentina

Four representative samples of Cenozoic extra-Andean alkaline basalts have been analyzed by prompt gamma activation method to determine Boron and other elements concentration including mayor and incompatible elements.                 Two of these samples belong to the Crater Basalt Volcanic Field, located near Gastre, province of Chubut. This field has been dated between 1 and 0.23 Ma (Pékskay et al. 2007). The B contents are of 2.19 and 3.43 µg/g respectively, that is in accordance with the OIB contents determined by Chaussidon & Jambon (1994). This concentration is relatively low comparing to arc rocks, pointing out low interaction with slab derived fluids, which is consistent with the long distance to the arc and the relatively depleted source region of the alkaline basalts.                 Another sample belongs to Pali Aike Volcanic Field, located in the southern edge of Patagonia region. The B content is 2.22 µg/g, also relatively low. In this case the explanation is the geotectonic frame: the age of this volcanic field is Pliocene-Quaternary and is located over an asthenospheric window, so there is no interaction with slab derived fluids.                 The last sample comes from Cerro Chivato, a diatreme of presumably Eocene age, located near Paso de Indios, in Northern-central Patagonia. These rocks have the higher content of B (7.61 µg/g), just like some other alkaline samples from maar volcanoes measured in central Europe (Gméling et al. 2007). It is probably that the elevated content in B obeys to interaction with groundwater during eruption, as no other geochemical evidences indicate contamination with slab derived fluids.