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

Author:

Baird Graham B.1

Affiliation:

1. Department of Earth and Atmospheric Sciences, University of Northern Colorado, Campus Box 100, Greeley, Colorado 80639, USA

Abstract

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.

Publisher

Geological Society of America

Subject

Stratigraphy,Geology

Reference101 articles.

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2. Fabric analysis of the Diana Syenite within the Carthage-Colton Mylonite Zone, Northwest Adirondacks, based on the comparison of its magnetofabrics and petrofabrics [M.A. thesis];Baird,2001

3. The strain and geometry of meso-scale ductile shear zones and the associated fluid flow [Ph.D. thesis];Baird,2006

4. Tectonic significance of mylonite kinematic indicators within the Carthage-Colton Mylonite Zone, Northwest Adirondacks, New York;Baird;Geological Society of America Abstracts with Programs,2008

5. Modeling the influence of tectonic extrusion and volume loss on the geometry, displacement, vorticity, and strain compatibility of ductile shear zones;Baird;Journal of Structural Geology,2007

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