资源环境科技发展态势分析平台

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 lon-grecognized 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 similar to 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.