Syn-collisional exhumation of hot middle crust in the Adirondack Mountains (New York, USA): Implications for extensional orogenesis in the southern Grenville province

Abstract

Extensional deformation in the lower to middle continental crust is increasingly recognized and shown to have significant impact on crustal architecture, magma emplacement, fluid flow, and ore deposits. Application of the concept of extensional strain to ancient orogenic systems, like the Grenville province of eastern North America, has helped decipher the structural evolution of these regions. The Marcy massif is a ∼3000 km2 Mesoproterozoic anorthosite batholith in the Adirondack Mountains (New York, USA) of the southern Grenville province. Bedrock geology mapping at 1:24,000 scale paired with characterization of bedrock exposed by recent landslides provides a glimpse into the structural architecture of the massif and its margin. New data demonstrate granulite- to amphibolite-facies deformational fabrics parallel the margin of the batholith, and that the Marcy massif is draped by a southeast-directed detachment zone. Within the massif, strain is localized into mutually offsetting conjugate shear zones with antithetic kinematic indicators. These relationships indicate that strain was coaxial within the Marcy massif, and that subsimple shear components of strain were partitioned along its margin. In situ U–Th–total Pb monazite analysis shows that deformation around and over the Marcy massif occurred from 1070 to 1060 Ma during granulite-facies metamorphism, and monazite from all samples record evidence for fluid-mediated dissolution reprecipitation from 1050 to 980 Ma. We interpret that rocks cooled isobarically after accretionary orogenesis and emplacement of the anorthosite-mangerite-charnockite-granite plutonic suite at ca. 1160–1140 Ma. Gravitational collapse during the Ottawan phase of the Grenville orogeny initiated along a southeast-directed detachment zone (Marcy massif detachment zone), which accommodated intrusion of the Lyon Mountain Granite Gneiss, and facilitated substantial fluid flow that catalyzed the formation of major ore deposits in the Adirondack Highlands.

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

“…The overall top-to-the-SSE kinematics is consistent with the warped ca. 1070-1060 Ma Marcy Massif detachment zone described by Regan et al (2019) and suggests that this deformation style may be pervasive throughout the Highlands.…”

“…Current mapping depicts the Highlands possessing an arcing northeast-southwest to east-west to northwest-southeast structural grain from west to east (Fig 1B;McLelland and Isachsen, 1980). With more detailed mapping in the Highlands, structures consistent with the asymmetric metamorphic core complex model (model 2) may be identified (see Regan et al, 2019). However, perhaps the extent of partial melting was not significant enough in the Highlands to allow such dome or sub-dome structures to develop.…”

“…0.98 Ga (Rivers, 2008;McLelland et al, 2010). However, recent work within the Grenville province also emphasizes the importance of tectonic collapse late in its history, as exemplified by work in the Adirondacks, the Morin terrane, the east side of the Mékinac-Taureau domain, and the Ottawa River Gneiss Complex Wong et al, 2011;Rivers and Schwerdtner, 2015;Soucy La Roche et al, 2015;Schwerdtner et al, 2016;Dufréchou, 2017;Regan et al, 2019).…”

Age and Origin of Silicocarbonate Pegmatites of the Adirondack Region

“…The occurrence in Stone Valley, near Colton, NY, unequivocally ties the emplacement of some silicocarbonate melts to brittle faulting, late in the movement history of the CCsz. The timing is synchronous with uplift, exhumation, leucogranite intrusion, and widespread fluid infiltration of the Adirondack Region [35,36,[40][41][42][43][44][45][46].…”

“…Silicocarbonate intrusion (circa 1050 Ma) corresponds with the intrusion of the Lyon Mountain granite suite and associated granitic pegmatites [33][34][35]45]. It also occurred during the intrusion of the iron oxide-apatite deposits of the eastern Adirondacks and associated albitization and/or alkali-metasomatism of the Lyon Mountain granite host (35,42,45,46).…”