Late Ottawan orogenic collapse of the Adirondacks in the Grenville province of New York State (USA): Integrated petrologic, geochronologic, and structural analysis of the Diana Complex in the southern Carthage-Colton mylonite zone

Abstract

Crustal-scale shear zones can be highly important but complicated orogenic structures, therefore they must be studied in detail along their entire length. The Carthage-Colton mylonite zone (CCMZ) is one such shear zone in the northwestern Adirondacks of northern New York State (USA), part of the Mesoproterozoic Grenville province. The southern CCMZ is contained within the Diana Complex, and geochemistry and U-Pb zircon geochronology demonstrate that the Diana Complex is expansive and collectively crystallized at 1164.3 ± 6.2 Ma. Major ductile structures within the CCMZ and Diana Complex include a northwest-dipping penetrative regional mylonitic foliation with north-trending lineation that bisects a conjugate set of mesoscale ductile shear zones. These ductile structures formed from the same 1060–1050 Ma pure shear transitioning to a top-to-the-SSE shearing event at ∼700 °C. Other important structures include a ductile fault and breccia zones. The ductile fault formed immediately following the major ductile structures, while the breccia zones may have formed at ca. 945 Ma in greenschist facies conditions. Two models can explain the studied structures and other regional observations. Model 1 postulates that the CCMZ is an Ottawan orogeny (1090–1035 Ma) thrust, which was later reactivated locally as a tectonic collapse structure. Model 2, the preferred model, postulates that the CCMZ initially formed as a subhorizontal mid-crustal mylonite zone during collapse of the Ottawan orogen. With continued collapse, a metamorphic core complex formed and the CCMZ was rotated into is current orientation and overprinted with other structures.

The late Mesoproterozoic to early Neoproterozoic Grenvillian orogeny and the assembly of Rodinia: Turning point in the tectonic evolution of Laurentia

“…Segments of the orogenic lid are juxtaposed against mid-crustal, granulite-facies domains along post-peak, normal-sense ductile shear zones in the hanging wall of the Allochthon Boundary thrust, providing a signal of the profound post-peak extensional collapse of the orogen (e.g., Streepey et al, 2004;Rivers, 2008Rivers, , 2012. In particular, three large metamorphic core complexes, in which the granulite-facies metamorphic cores have diameters of 150 to >400 km, have been identified in the western Grenville Province, collectively supporting the inference of regional extensional collapse of double thickness crust under an orogenic plateau (Rivers, 2012;Schneider et al, 2013;Rivers and Schwerdtner, 2015;Soucy La Roche et al, 2015;Schwerdtner et al, 2016;Dufréchou, 2017;Regan et al, 2019;Baird, 2020). Collapse is interpreted to have taken place by extensional flow of the rheologically weak middle and lower crust late in the Ottawan Phase of the orogeny (ca.…”

Ultrahigh-temperature granulite-facies metamorphism and exhumation of deep crust in a migmatite dome during late- to post-orogenic collapse and extension in the central Adirondack Highlands (New York, USA)

“…In orogenic belts around the world, gravitational collapse and extension have led to formation of metamorphic core complexes or granite-cored gneiss domes and the exhumation of deep, partially molten lower-crustal rocks (e.g., Whitney et al, 2004;Rey et al, 2009). In the Grenville province, late orogenic extensional deformation is being increasingly recognized as a mechanism for magma emplacement, exhumation, and the juxtaposition of different crustal levels to produce large metamorphic discontinuities (e.g., Rivers, 2008Rivers, , 2012Regan et al, 2019;Baird, 2020).…”

Zircon U-Pb Geochronology from Ledge Mountain, Adirondack Highlands, New York

“…Lyon Mountain granite was emplaced from 1045 to 1037 Ma (Selleck et al, 2005). The Diana Complex unit is a mafic syenite gneiss located along the southern CCSZ (Selleck et al, 2005;Hamilton et al, 2004;and Baird, 2020). Zircon rims interpreted as a metamorphic event are 1122 ± 29 Ma and zircon cores indicating the timing of emplacement are 1164 ± 11 Ma .…”