CRUSTAL CHANNELS AND TECTONIC ANEURISMS ACROSS THE 1090-1020 MA OTTAWAN OROGEN?

It has been well-documented that the Carthage Colton Shear Zone separates rock with differing tectonic-thermal histories, yet the nature of this zone and relationship(s) between the terranes separated across the zone remain poorly understood. To the east of the CCSZ, the Adirondack Highlands Terrane/Central Granulite Terrane (CGT) record Elzevirian-Shawinigan (1205-1170Ma), AMCG (~1155Ma) and Ottawan (1090-1020Ma) events. To the west of the CCSZ, the Adirondack Lowlands Terrane /Central Metasedimentary Belt (CMB) record Elzevirian-Shawinigan, and AMCG events with only a weak Ottawan overprint. Further to the west, the Grenville Province is subdivided into various terranes bound by shear zones in which the Ottawan Event varies widely in intensity from terrane to terrane. How could several terranes undergo granulite-upper amphibolite facies deformation and recrystallization while leaving the intervening terranes relatively untouched? Recent advances in our understanding of the tectonic development of the Himalayan Orogen may hold the answer. Along the Himalayan front, rapid erosion triggers mobilization and extrusion of the granulite core of the mountain belt. Granulite “slices” are rapidly exhumed along paired thrust/normal faults in what has been termed a tectonic aneurism. These tectonic slices (Crustal Channels) are intruded by A-type pressure release granitoids, are highly deformed, bound by shear zones that separate the granulite from surrounding rock of lower metamorphic grade, and record rapid clockwise exhumation paths. In addition, multiple “extrusions” of mobilized crust have been reported across strike of the Himalayan Front leading to a juxtiposition of small terranes with differing thermal histories. This is similar to the observed situation in the NY-Ontario section of the Grenville Province. In northern New York State, rocks in and adjacent to the CCSZ contain abundant A-Type footwall Granitoids that record clockwise P-T paths. In addition, the CCSZ separate granulite facies footwall rocks (CGT) from hanging-wall rocks CMB that remained at greenschist facies during Ottawan-time. The developing model for the CCSZ is that it represents the top of a crustal channel and the CGT represents the mobilized granulite core of the Ottawan Orogen.