A Crustal-Scale Fold Nappe from the Trans-Hudson Orogen, Northern Baffin Island, Arctic Canada
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Abstract
The recognition of crystalline basement nappes in deeply eroded orogens, which is critical to elucidating the tectonic and geodynamic histories of cratonic terranes, relies on the identification of key geometric and kinematic structural elements. These include (i) synformal anticlines and/or antiformal synclines along the nappe’s overturned lower limb; (ii) parasitic folds with thinned long limbs elongated parallel to transport direction; and (iii) a stretching lineation that records the nappe transport direction and which is coeval with and perpendicular to a fold axis-parallel lineation. The structure, stratigraphy and geophysics of the Isortoq Fault Zone (IFZ) and nearby supracrustal Isortoq and Eqe Bay belts (Rae craton, northern Baffin Island) suggest the occurrence of a regional synformal anticline interpreted as part of the lower limb of a Paleoproterozoic southeast-verging nappe. The northern northeast-striking, moderately southeast-dipping Isortoq belt is structurally thinned, metamorphosed to upper amphibolite to granulite facies, sheared (by the top-to-the-southeast IFZ) and overturned, with strata younging down-section to the northwest. In contrast, the southern east-northeast-striking, steeply southeast-dipping Eqe Bay belt is structurally thickened, comparatively less metamorphosed and less deformed, and stratigraphically youngs to the southeast. The geometry and orientation of the belts mirror those of mesoscale parasitic S- and Z-folds exhibiting thinned elongated limbs and thickened short limbs. The IFZ and associated faults represent a brittle-ductile shear zone formed at the base of the nappe during propagation; offsets along these faults are responsible for the distribution of isograds. The Isortoq nappe occurs along strike (and may be genetically associated) with southwest-verging Rinkian nappes exposed >200 km to the northeast. South-verging fold nappes developed along the southern margin of the Rae craton contrast with north-verging, thin-skinned thrust sheets of the Foxe fold belt to the south, emphasizing the complex kinematics of the assembly of the Nuna supercontinent.
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