The Central Slave Basement Complex, Part II: age and tectonic significanceof high-strain zones along the basement-cover contact

The basement-cover high-strain zone enveloping parts of the Sleepy Dragon C omplex, northeast of Yellowknife, Slave Province, Canada, has been reinvest igated. Integrated stratigraphic, structural, and geochronological data sho w that the high-strain zone is of regional extent and is best interpreted a s a decollement between crystalline, ca. 2.9-3.3 Ga rocks of the Central Sl ave Basement Complex and pre-2687 Ma cover rocks. Three temporally distinct mafic dyke swarms occur within the high-strain zone. The two oldest of the se constrain the timing of the high-strain event to between 2734 +/- 2 and 2687 +/- 1 Ma. At the time of decollement development, the cover stratigrap hy consisted of (i) the Central Slave Cover Group, a thin, pre-2734 Ma succ ession of mafic and ultramafic volcanic rocks, conglomerates, fuchsitic qua rtzites, minor rhyolites, and banded iron formation; and (ii) an overlying sequence of tholeiitic pillow basalts. The Central Slave Cover Group is con sidered to be autochthonous, whereas a variety of evidence suggests that th e pillow basalts are parautochthonous to possibly allochthonous. The transp ort direction in the decollement was from northeast to southwest, and maxim um displacement was probably on the order of 10 to several tens of kilometr es. Presently, the decollement appears discontinuous due to younger intrusi ve and erosional events. Around most of the southern flanks of the Sleepy D ragon Complex, the crystalline core of the complex consists of post-decolle ment intrusive rocks and (or) is unconformably overlain by parts of the Yel lowknife Supergroup that are younger than 2687 Ma. Lineation patterns in th ese younger rocks reflect regional deformation events that postdate and are unrelated to the decollement. The new data allow two tectonic models for d evelopment of the decollement: (i) a contractional thrusting model, involvi ng collision of an eastern Slave Province arc terrane; or (ii) a syn-greens tone belt extensional model.