The Cerro Bitiche Andesitic Field: Petrological diversity and implications for magmatic evolution of mafic volcanic centers from the northern Puna.

MARO, GUADALUPE; CAFFE, PABLO J.

BULLETIN OF VOLCANOLOGY

SPRINGER

Lugar: Berlin; Año: 2016 vol. 78 p. 1 - 18

0258-8900

 TheCerro Bitiche Andesitic Field (CBAF) is one of the two largest mafic volcanicfields in northern Puna (22-24ºS) and is spatially and temporally associatedwith ignimbrites erupted from some central Andean Altiplano Puna VolcanicComplex calderas. The CBAF comprises seven scoria cones and widespread high-Kcalcalkaline lava flows that cover an area of 200 km2. Although allerupted rocks have a relatively narrow chemical range (56-62% SiO2,3-6% MgO), there is a broad diversity of mineral compositions and textures. Theleast evolved lavas (~58-61% SiO2) are high-Mg andesites with scarce(<10%) microphenocrysts of either olivine or orthopyroxene. The smallcompositional range and low phenocryst content indicate evolution controlled bylow percentages (<10%) of fractional crystallization of olivine andclinopyroxene of magmas similar to the least evolved rocks from the field,accompanied by assimilation during rapid ascent through the crust. Evolvedandesites (~62 wt.% SiO2), on the other hand, are porphyritic rockswith plagioclase + orthopyroxene + biotite and ubiquitous phenocrystdisequilibrium textures. These magmas were likely stored in crustal reservoirs,where they experienced convection caused by mafic magma underplating, magmamixing and/or assimilation. Trace element and mineral compositions of CBAFlavas provide evidence for complex evolution of distinct magma batches.