High-pressure, halogen-bearing melt preserved in ultrahigh-temperature felsic granulites of the Central Maine Terrane, Connecticut (U.S.A.)

Abstract

Inclusions of relic high pressure melts provide crucial information on the fate of crustal rocks in the deep roots of orogens during collision and crustal thickening, including at extreme temperature conditions exceeding 1000°C. However, discoveries of high pressure melt inclusions are still a relative rarity among case studies of inclusions in metamorphic minerals. Here we present the results of experimental and microchemical investigations of nanogranitoids in garnets from the felsic granulites of the Central Maine Terrane (Connecticut, US). Their successful experimental re-homogenization at ~2 GPa confirms that they originally were trapped portions of deep melts and makes them the first direct evidence of high pressure during peak metamorphism This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America. The published version is subject to change. Cite as Authors (Year) Title. American Mineralogist, in press.

The role of continental subduction in mantle metasomatism and carbon recycling revealed by melt inclusions in UHP eclogites

“…Nanogranitoids were successfully rehomogenized in the multianvil apparatus at 1000°C and 4.5 GPa, the minimum conditions expected for the formation of the garnet in the Erzgebirge UHP unit ( 24 ), and thus likely to correspond to the entrapment conditions of the melt. The attained rehomogenization confirms that garnet and melt were both stable at the metamorphic peak conditions as demonstrated in previous studies ( 19 , 27 , 29 ). Preserved and rehomogenized glassy inclusions are granitic in composition, rich in alkalis [Na 2 O + K 2 O = 9.31 weight % (wt %) and Na 2 O/K 2 O = 0.75], and slightly peraluminous [alumina saturation index: molar Al 2 O 3 /(Na 2 O + K 2 O + CaO) = 1.10] and have a low magnesium number (Mg# = 27; see table S2).…”

“…( A ) H 2 O (wt %) and CO 2 (ppm) content of glass and a rehomogenized (indicated with an asterisk) nanogranitoid from Saidenbach eclogites measured and corrected by NanoSIMS (error bar smaller than the symbol) and compared with H 2 O and CO 2 contents of lower continental crust melt inclusions in granulites [Central Maine Terrane (CMT) ( 19 ), Ivrea Zone ( 20 ), and Gruf Complex ( 61 )]. See table S5 for volatiles data, and for NanoSIMS calibration curves, see fig.…”

“…Melt in Saidenbach eclogites is more akin to anatectic melts from silicic continental crust rather than from mafic protoliths (Fig. 2), as shown by the comparison with both natural and experimental HP ( 19 ) and UHP melts from metasediments ( 45 , 46 ) and metabasites (Fig. 2 and table S3) ( 47 – 49 ).…”

Paleoproterozoic ultrahigh‐temperature metamorphism in the Alxa Block, the Khondalite Belt, North China Craton: Petrology and phase equilibria of quartz‐absent corundum‐bearing pelitic granulites

“…However, quartz-absent rocks containing mineral assemblages of garnet + spinel + corundum are not commonly discussed in the literature, although such rocks have been reported in several field areas (Asami et al, 1989(Asami et al, , 1990Dharmapriya et al, 2015;Dorfler et al, 2014Dorfler et al, , 2015Harris, 1981;Keller & Ague, 2018;Osanai et al, 2006;Ouzegane et al, 2003;Schreyer et al, 1984;Sengupta et al, 1999;Shimpo et al, 2006;Snoeyenbos et al, 1995). In a study based on phase equilibrium modelling and ternary feldspar thermometry in conjunction with textural observations, Keller and Ague (2018) obtained neareclogite-facies peak metamorphic conditions ($1040 C and $18 kbar) from quartz-absent garnet-spinel-corundum gneiss in the Central Maine Terrane, Connecticut, USA, and a recent study further confirmed these HP-UHT conditions using evidence from melt inclusions (Ferrero et al, 2021). Thus, for corundum-bearing rocks, multiple independent methods (e.g.…”

Orogenic eclogites record relative magnitude of deep crustal flow and extent of migmatite-eclogite interaction

“…There is growing recognition that lithologies with seemingly disparate records of metamorphic conditions in metamorphic terranes may have experienced the same history and differentially re-equilibrated (e.g. Arab et al, 2021;Ferrero et al, 2021). The occurrence of eclogite and HP granulite in migmatite terranes may be evidence that the exhumed material was deeply sourced despite the apparent LP-HT equilibration conditions of the migmatites.…”