Abstract

The Southern volcanic zone of the Archean Abitibi greenstone belt comprises several fault-bounded tectonic blocks with distinct volcanic-sedimentary sequences, pressure-temperature-time (P-T-t) histories, granite compositions, and metallogenic provinces. Pressure distributions have been mapped out from an extensive new database, derived from Al in hornblende and other geobarometers. In the composite crustal structure of the Southern volcanic zone, determined from the pressure-time data, the Lacorne block and Pontiac subprovince represent deeper crustal levels, overlain by rocks exposed at the surface in the Round Lake or Lac Abitibi-type blocks, which are in turn capped by those exposed at the surface in a Blake River-Rouyn-type block. Exposure of the deeper crustal levels and juxtaposition of these distinct tectonic blocks are interpreted to have occurred by differential block uplift caused by strike-slip faulting, which was related to oblique collisional tectonics during late-tectonic development of the Superior province in late Archean time.

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