MODELING METAMORPHIC MINERAL FORMATION IN ADIRONDACK ANORTHOSITE

The Marcy massif is a large (3000 sq km) composite anorthosite body with associated rocks that dominates the Adirondacks High Peaks. The Adirondack Highlands, part of the Mesoproterozoic Grenville Province, experienced a series of igneous and metamorphic events between 1.3 and 1.0 Ga during the assembly of Rodinia. Anorthosite in the Adirondacks has an emplacement age of 1.15 Ga, and commonly shows metamorphic Cpx, Opx, garnet, and other minerals as coronas where relict igneous minerals are preserved, and also in granoblastic textures in more completely recrystallized lithologies.

The first goal of this study is to constrain metamorphic conditions of a suite of coronitic anorthosites and granitoids at several key localities: the area east of North Hudson, along Rt. 3 between Lake Placid and Tupper Lake, and the Tahawas Fe-Ti mining district. The thermodynamic software package Theriak-Domino was used to calculate pseudosections using bulk major element compositions determined by XRF in order to plot each sample in pressure-temperature space at the time of metamorphism. Reasonable approximations of water content and oxidation states during metamorphism were made in order to account for presence of metamorphic Fe-Ti oxides and hydrous phases. Preliminary analysis is consistent with observed granulite facies assemblages at temperatures >600°C and pressures of 5–13 kbar, which matches conventional P–T estimates. The second goal of this study is to characterize zircon crystals that are spatially associated with garnet coronas. These zircon are found either as inclusions in ilmenite or at the border of metamorphic Cpx and primary plagioclase, and were targeted for U-Pb geochronology. Grain mounts from rocks with similar textures have been shown in previous studies to have zircon with Ottawan (ca. 1.07) or Rigolet (ca. 1.0 Ga) ages. Our LA-ICPMS analysis of zircon in thin section has so-far found similar results.

Session No. 10--Booth# 32

T27. Precambrian Assembly of a Continent from the Northeast to the Mid-Continent to the Southwest: Modern Approaches to Study Ancient Crust (Posters)

Sunday, 19 March 2017: 8:00 AM-12:00 PM

Grand Ballroom, 17th Floor (Omni William Penn Hotel)

Geological Society of America Abstracts with Programs. Vol. 49, No. 2
doi: 10.1130/abs/2017NE-291524

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