Lavras granite emplacement and gold mineralization during the development of the post-collisional volcanoplutonic center, west of the Sul-riograndense Shield: Geophysical and structural data

Based on the integration of original and available geological, geophysical and structural data, we assess the construction of the Lavras granite in an evolving volcanoplutonic center. This center encompasses the Lavras do Sul intrusive complex and the Hilário trachyandesitic sequence (604 - 590 Ma), both formed in the western foreland setting during the post-collisional period of the Dom Feliciano Orogeny, Sul-riograndense Shield. Brittle structures and magnetic lineaments indicate the volcanic activity starting near the orogenic collapse, since it was initially controlled by NW-SE and WNW-ESE-striking dextral transtensive systems that inverted to sinistral during tectonic relaxation. The intrusive complex was formed from the north to the south, with emplacement of the Tapera monzonite and the Lavras granite respectively, following slip change along the N70-75°W fault zone cutting it across. The granite has moderate dimensions (325 km³) and a tabular shape (length - L: thickness - T ≈ 3:1) tapering to the south, as deduced from gravity data. AMS petrofabric (anisotropy of magnetic susceptibility) reinforces two compositional-structural domains in the center and in the border of this granite body, represented by the magnesian terms (granodiorite and monzogranite) and the ferroan ones (syenogranite and alkali feldspar granite) respectively. These data together with brittle structures point to a multistage pluton constructed in two resurgent episodes involving: (1) the central laccolith through the emplacement of granodiorite beneath the monzogranite sill; and (2) the annular intrusions of ferroan granites, induced by expansion of the high-level reservoir due to recharge with lamprophyric mafic-ultramafic magmas. Its structural control, spatial distribution and association with lamprophyric dykes attest the link of gold mineralization with the last resurgent episode in a mature volcanoplutonic center.

Resurgent Pluton; Brittle Structures; Transtensive Tectonic; Lamprophyre; Magnetic Data