T132 Assembling Laurentia: Mesoproterozoic to Early Neoproterozoic Tectonic Evolution of Laurentia and Its Role within the Supercontinent Rodinia I

Wednesday, 28 October 2020
1:30 PM - 5:30 PM
Meeting Rooms

OBLIQUE EXTENSION DURING COLLISIONAL OROGENESIS AND THE ARCHITECTURE OF THE ADIRONDACK MOUNTAINS, SOUTHERN GRENVILLE PROVINCE

Paper number: T132-12
Program: Technical Sessions
Time: 4:05 PM – 4:20 PM

Authors

Abstract

Collisional orogenesis generates significant gravitational instabilities that can result in the collapse of an orogenic system. The Mesoproterozoic Grenville Province of eastern North America exposes the roots of an orogenic belt that formed during episodic accretion, back-arc spreading and collapse (1.19-1.14 Ga Shawinigan orogeny), and continental collision (1.09-1.0 Ga Ottawan Orogeny), and is thus an ideal location to study the lower to mid-crustal response of orogenesis involving overthickened crust. The Adirondack uplift, New York (USA) exposes the southern extension of the contiguous Grenville Province and is divided into the amphibolite-facies Lowlands and granulite-facies Highlands. The highlands are bound by localized structures interpreted to have exhumed granulite-facies rocks during orogenic collapse immediately after the Ottawan Orogeny. Despite significant inquiry, distinguishing structures and metamorphic assemblages formed during the Shawinigan vs Ottawan phases of regional tectonism within the Adirondack Highlands remains difficult.

The Adirondack Highlands are segmented into E-W trending belts of high-grade tectonite and intervening domains with oblique and shallower tectonic elements. Multi-chronometer petrochronology adjacent to the 3000 km2 Marcy anorthosite massif (Mm) suggests that deformation around and over the Mm occurred from 1070-1050 Ma, interpreted as a thick-ductile detachment (the Mm detachment zone). Metamorphic assemblages record evidence of cooling and decompression during top-to-the southeast shear interpreted to be a consequence of orogenic collapse of the lower to middle crust during uplift of the massif. Syn-to post kinematic corona-growth, 1060-1035 Ma leucogranitic plutonism, and mineralization from 1045-980 Ma was all focused within the detachment zone(s). Recent monazite petrochronology focused on the formation of E-W isoclinal folding and an axial planar gneissosity continuous across the Highlands formed from 1060-1045 Ma. These data support a structural model invoking strain partitioning during oblique extension. Strike-slip and horizontal-shortening deformation was partitioned into E-W trending belts and intervening domes formed from top-to-the southeast collapse of a Himalayan-scaled orogenic plateau.

Geological Society of America Abstracts with Programs. Vol. 52, No. 6

doi: 10.1130/abs/2020AM-359267

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