DUCTILE DEFORMATION OF THE DIANA COMPLEX ALONG THE SOUTH-CENTRAL CARTHAGE-COLTON MYLONITE ZONE: RECONCILING NORTHWEST OVER SOUTHEAST OBLIQUE-SINISTRAL THRUST KINEMATICS WITH TECTONIC COLLAPSE

The Mid-Proterozoic Grenville Province of eastern North America can be described as a collage of terranes separated by complex shear zones variably active during one or more orogenic events that constructed the province. The Carthage-Colton Mylonite Zone (CCMZ) in the NW Adirondacks (northern New York State) is one complex terrane bounding shear zone in the Province and separates the Adirondack Lowlands terrane to the NW from the Adirondack Highlands terrane to the SE. The southern half of the CCMZ is dominated by the Diana Complex, a suite of predominately deformed quartz monzonite to granites with an intrusive age of c. 1160 Ma.

Detailed structural analysis of the Diana Complex reveal at least two main ductile structures: a penetrative mylonitic fabrics that dip NW with a north-trending stretching lineation, and 1-10 cm wide conjugate ultramylonite ductile shear zones geometrically bisected by the penetrative mylonitic fabric. Lineation in the ultramylonite shear zones are generally parallel to the intersection of the conjugate set and of the penetrative fabric. Field relationships suggest both structures formed during a single deformation event and nearly all kinematic indicators suggest NW over SE oblique-sinistral thrusting.

In most locations in the northern half of the CCMZ, ductile kinematic indicators formed from top to the NW normal-sensed shearing. This shearing is interpreted to result from tectonic collapse, the timing of which is constrained by the syn-kinematic intrusion of the 1045-1037 Ma Lyon Mt. Granite at the end of the Ottawan orogeny (Selleck et al., 2005). Direct dating of the NW over SE oblique-sinistral thrusting by U-Pb analysis in titanite (Bonamici et al., 2015) indicate this shearing occurred at c. 1054-1047 Ma. A variety of models might explain these combined datasets, but two models are favored: Ottawan thrusting along the CCMZ ended at c. 1047 Ma and immediately transitioned to tectonic collapse, which did not widely overprint the thrusting structures in the south-central CCMZ; or that tectonic collapse occurred via a rolling hinge during Adirondack Highlands exhumation. The latter model indicates that the apparent NW over SE oblique-sinistral thrusting kinematic indicators originated as a sub-horizontal detachment rotated during exhumation into the current orientation.