The Cordilheira Intrusive Suite: Late Proterozoic peraluminous granitoids from southern Brazil

The Cordilheira Intrusive Suite is made up of peraluminous two-mica leucogranites related to the Brasiliano Cycle. Located in the east region of the Sul-rio-grandense Shield, in southernmost Brazil, the granitic bodies were emplaced mainly inside mylonitic zones belonging to a transcurrent system with NE orientation. The structural relationship of this intrusion with shear zones indicates a syn- to late-kinematic emplacement. The Cordilheira Intrusive Suite rocks are mainly syenogranites and monzogranites, with inequigranular texture, sometimes modified by mylonitic deformational effects. Mineralogically they are composed of alkali feldspar, plagioclase, quartz, muscovite and biotite, with minor amounts of gamet, tourmaline, apatite, zircon, sphene and fluorite. The analyzed samples show a SiO2 range of 71.55 to 77.68%, and a reduction in the K2O/Na2O ratio with increasing differentiation. Trace-element contents, including REE, are similar to that of granites produced by partial melting of quartz-feldspathic rocks. Field relationships and geochemical data are suggestive of partial crustal melting along transcurrent shear zones developed during the late orogenic stages of the Brasiliano Cycle. The evidence considered in this paper shows the remarkable similarity of the Cordilheira Intrusive Suite to Hercynian granitoids of Portugal and France.