Zircon‐bearing, crystallized melt inclusions in peritectic garnet from the western Adirondack Mountains, New York State, USA

Abstract

Crystallized melt inclusions (MI) occur in garnet from metapelitic gneiss extracted from a hydroelectric plant on the Black River at Port Leyden, NY (western Adirondack Highlands). The garnet host grains are small (0.5–1.0 mm), euhedral neoblasts that formed peritectically during biotite melting accompanying the Ottawan phase of the Grenville Orogeny. The crystallized MI are typically 10–25 μm in diameter and occur randomly in garnet. Nearly all of the crystallized MI observed contain a relatively large (3–15 μm), often euhedral, zircon grain surrounded by finer‐grained (some <1 μm) phases with energy dispersive X‐ray spectra consistent with biotite, K‐feldspar, quartz, and albite. The inclusions are similar in size and composition to those described in garnet from other migmatites and are similarly interpreted as crystallized anatectic melt. Low Zr solubility in silicate melt indicates that the large zircon grain in each inclusion must be a trapped solid. It is inferred that micrometer‐scale droplets of anatectic melt chemically adhered to occluded zircon grains in biotite while peritectic garnet grew around them.

Microstructures and petrology of melt inclusions in the anatectic sequence of Jubrique (Betic Cordillera, S Spain): Implications for crustal anatexis

“…These MI represent primary anatectic melts generated during partial melting of the enclaves at depth, because: (i) they are trapped within minerals crystallized during anatexis at pressures of ≈5-7 kbar; (ii) they are primary inclusions based on their distribution in the host (following criteria from Roedder (1984); (iii) they have leucogranitic compositions similar to glasses generated in experimental studies of crustal anatexis, and close to the haplogranitic eutectics (Cesare et al, 1997(Cesare et al, , 2003(Cesare et al, , 2007Acosta-Vigil et al, 2007. Melt inclusions were also described in crustal crystalline rocks, such as UHP gneisses and eclogites associated with subduction of continental crust (Hwang et al, 2001;Stöckhert et al, 2001Stöckhert et al, , 2009Ferrando et al, 2005;Korsakov and Hermann, 2006;Lang and Gilotti, 2007;Zeng et al, 2009;Gao et al, 2012Gao et al, , 2013Liu et al, 2013), and LP-to-MP anatectic terranes associated with crustal thickening (Cesare et al, 2009(Cesare et al, , 2011Bartoli, 2012;Ferrero et al, 2012;Bartoli et al, 2013a;Darling, 2013). In the case of UHP rocks, inclusions have been named as melt inclusions, multiphase inclusions, or polyphase inclusions, and have been interpreted as former melts or dense supercritial fluids.…”

“…The number of MI occurrences in anatectic terranes reported in the literature is quite modest and, among those cases, only a few provide bulk compositional data from the MI (Cesare et al, 2011;Ferrero et al, 2012;Bartoli et al, 2013b). This is due to the relatively recent discovery of MI in crustal anatectic rocks (Cesare et al, 1997(Cesare et al, , 2009(Cesare et al, , 2011Hwang et al, 2001;Stöckhert et al, 2001Stöckhert et al, , 2009Korsakov and Hermann, 2006;Gao et al, 2012;Darling, 2013;Liu et al, 2013) and, more importantly, the very recent development of appropriate methodologies to recover the information encrypted within these former droplets of melt (Malaspina et al, 2006;Perchuck et al, 2008;Bartoli et al, 2013aBartoli et al, , 2013b.…”

Microscopic Blue Sapphire in Nelsonite from the Western Adirondack Mountains of New York State, USA

“…In the western Adirondack Highlands, this event was characterized by deep burial, granulite-facies metamorphism, intense shearing, and local intrusion of granitic igneous rocks [10]. In the immediate study area, estimates of metamorphic temperature and pressure were provided by [11] and revised slightly by [12], who determined conditions of at least 780 • C and 6.0 ± 0.5 kilobars. These estimates are based on hercynite-silicate equilibria and biotite melting reactions.…”

Significance of “stretched” mineral inclusions for reconstructing P–T exhumation history

“…1). Quartz inclusions were trapped in peritectic garnets at temperatures <800 °C and pressures of ~0.6 GPa (Florence et al 1995;Darling 2013;Fig. 2a, b).…”

“…3). Owing Darling 2013) to slow cooling rates inferred for the Adirondack highlands, temperatures remained above 600 °C for 50-100 million years (Mezger et al 1991;Bonamici et al 2011). If P-T conditions during metamorphism at the Hooper Mine were based on cristobalite inclusions in garnet, one would interpret the garnets to have formed at T > 1470 °C and P < ~0.5 GPa, resulting in an error in inferred formation conditions of ~0.7 GPa and >600 °C and well outside the stability field of the host garnet.…”