INSTITUTO SUPERIOR DE CORRELACION GEOLOGICA
Unidad Ejecutora - UE
Petrographical and geochemical features of the granite-pegmatite transition in the Velasco Pegmatitic District, NW Argentina
SARDI, F., MURATA, M., GROSSE, P.
NEUES JAHRBUCH FUR GEOLOGIE UND PALAONTOLOGIE-ABHANDLUNGEN
Lugar: Stuttgart, Alemania; Año: 2009
The Carboniferous post-orogenic Huaco and Sanagasta granites are located in the central sector of the Velasco range, northwestern Argentina, and they host rare-element (Be) pegmatites. They are highly fractionated peraluminous granites with porphyritic textures, with variable sizes and abundances of K-feldspar megacrysts. Two different types of parental granites are recognized: a Regional Porphyritic Granite (RPG), located away from the Be-pegmatite, and an Adjacent Porphyritic Granite (APG), located around them. At the pegmatite margins, aplites (MA), or more rarely equigranular leucogranites, are in contact with the APG. The granite-to-pegmatite transition is characterized by decreasing biotite/muscovite ratios and TiO2-Fe2O3t-MgO contents, which is consistent with fractional crystallization of biotite, and also by decreasing megacryst and grain size. A continuous magmatic crystallization trend from the RPG to the APG is observed, whereas the MA constitutes the earliest stage of pegmatite formation, characterized by depletion in ferromagnesian elements, calcium and some trace elements (Ba, Sr, Y, Nb, Ce, Zr, Th). However, the granite-pegmatite evolution occurred by differentiation from a common magma source.