%0 Journal Article %J Geological Society of America Bulletin %D 2017 %T Lyon Mountain ferroan leucogranite suite: Magmatic response to extensional thinning of overthickened crust in the core of the Grenville orogen %A J. R. Chiarenzelli %A Selleck, B. %A M. V. Lupulescu %A Bickford, M. E. %A Valley, P. %A McLelland, L. %X

Evidence is presented for the crystallization age (ca. 1066−1033 Ma) and origin of the Lyon Mountain Granite (formerly Lyon Mountain Gneiss), a widespread magnetite-bearing leucogranitic igneous suite in the Adirondack Highlands. Recent reinterpretations of U-Pb zircon results have led some to propose that the Lyon Mountain Granite was intruded synchronously with the Shawinigan anorthosite-mangerite-charnockite-granite (AMCG) suite at ca. 1165−1145 Ma. However, this interpretation conflicts with the recognized chronology of the region based on field and analytical studies, which have established a late to postkinematic Ottawan crystallization age (ca. 1050 Ma). Herein, we show that the older ages reported are a consequence of zircon inheritance; we summarize existing and provide new U-Pb zircon data expanding the recognized extent of the Lyon Mountain Granite; and we review long-recognized field relationships and temporal associations among structures within the region and southern Grenville Province. Field relations include a spatial, and likely temporal, link with iron oxide−apatite deposits, gabbroic and amphibolite bodies, and association with late extensional faults and hydrothermal alteration. The variable fabric of the Lyon Mountain Granite is a consequence of magmatic/intrusive processes, proximity to synintrusive structures, and timing of intrusion relative to deformation during an ∼30 m.y. period. The Lyon Mountain Granite formed during late Ottawan anatexis related to gravitational collapse of overthickened crust. Its anhydrous ferroan nature, zircon xenocryst population, and association with magnetite-apatite deposits can be explained by partial melting of Shawinigan-aged, AMCG-dominated lower crust.

%B Geological Society of America Bulletin %V 129 %P 1472-1488 %G eng %U https://pubs.geoscienceworld.org/gsabulletin/article/doi/10.1130/B31697.1/208117/lyon-mountain-ferroan-leucogranite-suite-magmatic %N 11-12 %R 10.1130/B31697.1