REGIONAL-SCALE STRUCTURAL ARCHITECTURE OF A NEOARCHEAN FAULT USING COMBINATION OF FIELD OBSERVATIONS AND SEISMIC REFLECTION IMAGERY: EXAMPLE OF THE BARLOW FAULT ZONE, ABITIBI SUBPROVINCE, CANADA

Crustal-scale fault zones exert first-order control on gold mineralization in Archean greenstone belts. Understanding 3D geometry of faults is essential for gold exploration, but linking observations from fieldworks and geophysical studies remains challenging. A seismic reflection survey performed by the Metal Earth project in the NE part of the Abitibi Subprovince imaged a prominent south-verging reflector correlated at surface to the Barlow Fault, hence providing the opportunity to better link field characteristics with seismic imagery. The structural and kinematic evolution of the fault is interpreted using mapping and P-T determination on Al-in-amphibole geobarometry. The Barlow Fault consists of several E-trending segments that dip shallowly (30°) to steeply (85°) to the south. The fault delimits fluvial sedimentary sequences to the south from mafic volcanic rocks to the north, and the shallowest dipping segment includes slivers of mafic sills. The fault zone is up to 1,500 m wide at surface and is expressed by a well-developed E-trending penetrative foliation with steeply plunging stretching lineations. The geometric characteristics of the fault match those of the associated seismic reflector. The strong signature on the seismic survey is induced by mafic sills within the shallow dip fault zone. Mineral assemblages south and north of the fault indicate amphibolite metamorphic facies. Al-in-amphibole geothermobarometer yielded maximum P-T conditions of 550±50 °C and 6±1.2 kbars both in sedimentary and igneous rocks. Kinematic indicators indicate south over north reverse movement. The fault is interpreted as an antithetic thrust fault associated to the collision between the Abitibi and Opatica subprovinces. Limited vertical extent of the fault (6 km) from seismic imagery, high-grade regional metamorphism and lack of significant hydrothermal alterations in the fault can account for the weak gold endowment in comparison to large gold-bearing structures in the Abitibi Subprovince.