STRUCTURAL EVOLUTION AND EARLY ACCRETION OF THE ARCHEAN MALARTIC COMPOSITE BLOCK, SOUTHERN ABITIBI GREENSTONE-BELT, QUEBEC, CANADA

The Malartic Composite Block of the southern Abitibi belt underwent at least two phases of ductile deformation over a period of 25 Ma during the late Archean. It is divided into seven tectono-stratigraphic doma ins on the basis of their lithological content, structural styles, and geochemical affinities of the volcanic and plutonic rocks. The Malart ic Composite Block is bounded to the south by the sedimentary rocks of the Kewagama Group that have been also affected by deformation. The c rosscutting relationships between the structural elements, along with precise geochronological data, provide a basis for evaluation of the e volution of the deformation in this part of the southern Abitibi. The D-1 tectonic event produced ductile thrust faults and folds in the maf ic and ultramafic domains of the Malartic Composite Block. The calc-al kalic rocks of the Val-d'Or Domain (2705 Ma) were erupted on top of th ese deformed domains, thus establishing the minimum age for D-1. The D -2 event is divided into three increments that are linked to the same progressive deformation. D-2.1 produced northwest-trending folds in th e rocks of the Kewagama Group, but did not affect the rocks of the Mal artic Composite Block. The age of the youngest detrital zircon in the Kewagama indicates that D-2.1 was active after 2687 Ma. D-2.2 develope d a consistent east-west regional foliation that overprints all the ro cks of the area. Radiometric data on related metamorphic minerals indi cate an age of 2680 Ma for this event. Locally, S-2.2 is modified by F o(2.3) folds of asymmetric Z shape associated with a late dextral tran scurrent shearing. A minor D-3 event produced small, local conjugate k ink folds recording an east-west shortening.