PROVENANCE AND TECTONIC EVOLUTION RECORDED BY SUCCESSOR BASINS IN THE SOUTHERN ABITIBI SUBPROVINCE: INSIGHTS FROM NEW U-PB LA-ICP-MS ANALYSES OF DETRITAL ZIRCON

Understanding the detrital zircon provenance of syntectonic successor basins provides insight into the geodynamic and paleogeographic evolution of the associated orogen. We utilized laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) to obtain a statistically robust number of U-Pb detrital zircon ages for successor basin samples from the southern Abitibi subprovince (SAS). Orogenesis in the SAS relates to Neoarchean tectonic amalgamation of the Superior Province. The SAS displays a characteristic lithotectonic evolution defined by a period of primary volcanic construction at ~2750-2695 Ma followed by regional orogenesis, denudation, and the development of successor basin successions at <2690-2669 Ma. In the SAS, two distinct types of successor basins are recognized based on sedimentological, structural, and geochronological constraints: the <2690-2685 Ma, turbidite-dominated Porcupine assemblage and the <2679-2669 Ma, coarse clastic-dominated Timiskaming assemblage. To establish the provenance of these rocks we analyzed 14 graywacke samples from both assemblages across the SAS. To relate the provenance observed in these samples to regional tectonism they were compared to compiled zircon data from throughout the Superior Province.

Statistical analysis of the U-Pb LA-ICP-MS results reveals that Porcupine and Timiskaming samples contain 75-95% Neoarchean and 5-25% Mesoarchean zircon grains. Neoarchean supracrustal sources are ubiquitous in the SAS and their predominance likely reflects local derivation. However, no Mesoarchean sources occur in the SAS, necessitating input from an adjacent hinterland. Overall, the older Porcupine samples contain ~5% Mesoarchean zircon, while the younger Timiskaming samples contain ~13% Mesoarchean zircon. This suggests that detritus from the hinterland was more prevalent in the SAS during the later stages of orogenesis. Compilation data for the Superior Province indicates that the hinterland was to the north and is, in part, comprised of the Winnipeg River, Marmion, and Opatica terranes/subprovinces. Transterrane detrital transport, progressive hinterland emergence, and foreland-directed propagation of the orogenic front recorded by SAS successor basins is similar to that observed in modern style collisional orogens.