Discovery of ultrahigh-temperature metamorphism in the Acadian orogen, Connecticut, USA

Abstract

Connecticut, USA Discovery of ultrahigh-temperature metamorphism in the Acadian orogen, Email alerting services articles cite this article to receive free e-mail alerts when new www.gsapubs.org/cgi/alerts click Subscribe to subscribe to Geology www.gsapubs.org/subscriptions/ click Permission request to contact GSA http://www.geosociety.org/pubs/copyrt.htm#gsa click official positions of the Society. citizenship, gender, religion, or political viewpoint. Opinions presented in this publication do not reflect presentation of diverse opinions and positions by scientists worldwide, regardless of their race, includes a reference to the article's full citation. GSA provides this and other forums for the the abstracts only of their articles on their own or their organization's Web site providing the posting to further education and science. This file may not be posted to any Web site, but authors may post works and to make unlimited copies of items in GSA's journals for noncommercial use in classrooms requests to GSA, to use a single figure, a single table, and/or a brief paragraph of text in subsequent their employment. Individual scientists are hereby granted permission, without fees or further Copyright not claimed on content prepared wholly by U.S. government employees within scope of Notes articles must include the digital object identifier (DOIs) and date of initial publication.

Exsolution of rutile or apatite precipitates surrounding ruptured inclusions in garnet from UHT and UHP rocks

“…This study investigates halos of rutile needles (or plates) with or without apatite inclusions surrounding ruptured fluid inclusions or inferred former coesite inclusions in garnet. We focus on two localities: (i) UHT metapelitic gneisses within the southern end of the CMT in northeastern CT, USA (Ague & Eckert, ; Ague et al ., ) and (ii) diamondiferous saidenbachite from the Saxonian Erzgebirge (Massonne, ). Halos from both localities have rutile needles and/or plates; apatite coexists with rutile in the Erzgebirge rocks (Table ).…”

Quartz, mica, and amphibole exsolution from majoritic garnet reveals ultra-deep sediment subduction, Appalachian orogen

“…S7 and Materials and Methods). These minerals are well known from UHT and/or HPG rocks at the locality (24)(25)(26), so their absence in the rocks of this study suggests matrix equilibration at UHP conditions in excess of about 3 GPa. This pressure result holds for a wide range of H 2 O activities and even at minimum is still ~2.6 GPa ( fig.…”

“…We study ~1050°C garnet-sillimanite-K-feldspar-biotite-quartz gneiss from the Brimfield Schist HPG-UHT field area (24,25), located within one of several westward-dipping thrust fault-bound slices in the southern CMT. The rocks are highly aluminous (up to ~40 vol% garnet and ~30 vol% Al 2 SiO 5 ) and are inferred to have metasedimentary, likely metapelitic, protoliths.…”

“…S2). The field area has a complex history involving granulite (~750°C) and amphibolite facies (~575°C) overprints that produced a number of post-peak phases including cordierite and spinel (25). The rocks of this study were almost certainly affected by these events, but the macroscopic mineralogical changes appear to have been relatively minor, primarily the pseudomorphic conversion of kyanite to sillimanite, alteration of matrix rutile to ilmenite, and alteration of garnet to biotite (or other hydrous phases) and rutile to ilmenite along cracks in garnet.…”

Ultrahigh‐temperature metamorphism in the Helanshan complex of the Khondalite Belt, North China Craton: Petrology and phase equilibria of spinel‐bearing pelitic granulites

“…to 500 Ma) systems (Brown, 2006(Brown, , 2007(Brown, , 2014 and, therefore, are important for understanding the geodynamic process in the early Earth, such as the rheological behaviour of the crust (Lund, Piazolo, & Harley, 2006), crustal growth and differentiation (Sawyer, Cesare, & Brown, 2011), and the heat source or tectonic settings for such extreme temperatures (Ague, Eckert, Chu, Baxter, & Chamberlain, 2013;Brown, 2007Brown, , 2014Clark, Fitzsimons, Healy, & Harley, 2011;Harley, 2008;Kelsey & Hand, 2015;Lund et al, 2006;Sawyer et al, 2011). Recent studies have confirmed that metamorphic temperatures >1,000°C are indeed obtainable, based on multiple thermobarometric methods (Korhonen, Clark, Brown, & Taylor, 2014;Mitchell & Harley, 2017), and have demonstrated that some pelitic granulites without the diagnostic mineral assemblages of UHT metamorphism also experienced these conditions based on ternary feldspar, Zr-in-rutile, Ti-in-zircon thermometry, and phase equilibria modelling (Ague et al, 2013;Gou, Zhang, Zhang, & Wang, 2014;Jiao, Guo, Mao, & Zhao, 2011;Li & Wei, 2016;Liu et al, 2012). These recent studies lead us to reevaluate some high-grade metamorphic complexes in the Khondalite Belt in the North China Craton (NCC) to confirm whether the metamorphism reached UHT conditions and to clarify the geodynamic implications.…”