DEFORMATION OF THE SOUTHERN CARTHAGE-COLTON MYLONITE ZONE AND ITS POTENTIAL ROLES IN COMPRESSIONAL AND EXTENSIONAL TECTONICS IN THE ADIRONDACK SEGMENT OF THE GRENVILLE PROVINCE, NORTHERN NEW YORK STATE

The c. 1.4-1.0 Ga rocks of the Adirondacks in northern New York State are a southern portion of the Grenville Province, which was built through accretionary and collisional tectonics during the amalgamation of the supercontinent Rodinia. Like many large orogens, the Grenville Province underwent tectonic collapse. The Carthage-Colton Mylonite zone (CCMZ) is a major structure in the Adirondacks and is believed to have formed during tectonic collapse and core complex formation. In order to better understand how the CCMZ deformation history connects to such models, the meta-igneous Diana Complex, which spans the southern CCMZ, was investigated via petrologic, geochronologic, and structural means.

Bulk rock chemistry and U-Pb zircon dating establish that the Diana Complex is likely much thicker than 6 km, therefore, crustal-scale offsets did not produce a lithological discontinuity. Major ductile structures include a NW dipping penetrative mylonitic fabric and variably oriented meso-scale ductile shear zones. Detailed structural analysis, paired with hornblende-plagioclase thermometry and other published datasets, reveal that these structures predominately formed from a major c. 1050 Ma top to the SSE shearing event at ~700^oC.

The top to the SSE shearing event, given the NW dip of the CCMZ, may have resulted from compressional tectonics, which would be consistent with rapid cooling and possible rotation of the hanging wall while the foot wall received protracted metamorphism and deformation. Later extension along the CCMZ, accompanied by foot wall exhumation and proposed core complex formation, maybe accommodated by structures poorly exposed in the study area. An alternative model proposes the CCMZ initially formed as a sub-horizontal mid-crustal mylonite zone as part of a developing core complex. The top to the SSE shearing occurred during the initial stages of collapse. With continued collapse, the foot wall is exhumed which rotates the CCMZ into the dipping structure it is today. This preferred model too is consistent with the thermal patterns of the hanging wall and can be connected to structures found across the foot wall and beyond.