AS ABOVE, SO BELOW: THE COMPLEMENTARY RECORD OF ARCHEAN LATE TECTONIC SEDIMENTATION, IMBRICATION AND EXTENSIONAL COLLAPSE IN JUXTAPOSED MID- AND UPPER-CRUST OF THE WESTERN SLAVE PROVINCE, CANADA

Studies of greenstone belts and adjacent high grade domains often emphasize the different elements they record of an orogen’s tectonic history. Recent study of juxtaposed mid- and upper-crust of the western Neoarchean Slave Province demonstrates a remarkable similarity in their tectonic evolution. The Indin-Snare Lakes area is underlain by the Indin Lake supracrustal belt (ILSB) and Snare granulite domain. The ILSB records establishment of ca. 2690-2660 Ga marginal basin-arc sequence on thinned Mesoarchean crust and subsequent < 2630 Ma deep marine, syn-tectonic, foredeep sedimentation. Shortly thereafter, ca.2609 Ma, a southwest-vergent, fold-thrust belt imbricated the lithostratigraphic succession. Subsequent, 2609-2588 Ma, oblique shortening was associated with calc-alkaline magmatism and low-pressure, *4kbar, regional metamorphism. Decompression and refolding are localized in the metamorphic aureoles of 2590-2585 Ma S-type granitoid plutons. A similar record has been recognised in the adjacent Snare granulite domain. Two paragneisses yield detrital zircon ages of 2624 and 2600 Ma, coeval with and younger than the foredeep turbidites, respectively. The domain's regional structure, comprising intercalated 3100-2600 Ma ortho- and paragneisses and 2600-2585 Ma granitoid rocks, was established slightly later than that of the ILSB, with ca. 2590 Ma isoclinal folding and thickening culminating in ca. 2588 Ma, 7-8 kbar granulite-facies metamorphism. At ca. 2580 Ma, 2-4 kbar of exhumation occurred, with pervasive decompression textures formed adjacent to a major late, oblique-normal detachment fault forming the boundary with the ILSB. The ILSB and granulite domain clearly represent parts of a vertical crustal section now juxtaposed by detachment faulting that is attributed to tectonic exhumation of a thickened crustal welt. Burial of the paragneisses, some of youngest supracrustal rocks identified in the Slave Province, to mid-crustal depths by ca. 2600 is the most direct evidence available that thrust imbrication played a major role in crustal thickening.