Evidence for Neoarchean hydrous arc magmatism, the anorthosite-bearing Mayville Intrusion, western Superior Province, Canada

Comparisons Between Tethyan Anorthosite‐Bearing Ophiolites and Archean Anorthosite‐Bearing Layered Intrusions: Implications for Archean Geodynamic Processes

“…There is a paucity of dome and basin structures, which are thought to be suggestive of vertical tectonics, associated with Archean anorthosite-bearing layered intrusions (Table S2; Bédard, 2006Bédard, , 2018Bédard et al, 2013;Polat et al, 2015). This observation, coupled with the occurrence of low-angle thrust faults, indicates that these layered intrusions formed through modern-style plate tectonics rather than vertical, sagduction tectonics (Polat et al, 2015;Sotiriou et al, 2020).…”

“…The identification of magmatic amphibole in gabbroic cumulates has been interpreted to reflect their crystallization from hydrous magmas in a subduction zone geodynamic setting (Claeson & Meurer, 2004). Magmatic amphibole has been identified in anorthosites and leucogabbros in the Archean megacrystic anorthosite-bearing Fiskenaesset, Naajat Kuuat, Bird River, Mayville, Sittampundi, Konkanhundi, and São José do Jacuipe layered intrusions, which have all been interpreted to have formed in a subduction zone setting (Hoffmann et al, 2012;Mohan et al, 2013;Piaia et al, 2017;Polat et al, 2011Polat et al, , 2012Rollinson et al, 2010;Santosh & Li, 2018;Sotiriou, Polat, Frei, Yang, et al, 2019;Sotiriou et al, 2020). The Neoarchean Mayville Intrusion in the western Superior Province of Canada contains abundant well-preserved magmatic amphibole that occurs interstitially to cumulus calcic plagioclase megacrysts (Sotiriou et al, 2020).…”

“…Based on textural and chemical evidence, amphibole in some Archean anorthosite‐bearing layered intrusions has been interpreted to be of magmatic origin and be indicative of hydrous magmatism (Hoffmann et al, 2012; Mohan et al, 2013; Piaia et al, 2017; Polat et al, 2011; Rollinson et al, 2010; Santosh & Li, 2018; Sotiriou, Polat, Frei, Yang, & et al, 2019; Sotiriou et al, 2020). The textural evidence for magmatic amphibole includes serrated igneous boundaries with calcic plagioclase, whole‐grain optical continuity and extinction, its occurrence as interstitial oikocrysts, and its anhedral form (Hoffmann et al, 2012; Mohan et al, 2013; Piaia et al, 2017; Polat et al, 2011; Rollinson et al, 2010; Santosh & Li, 2018; Sotiriou, Polat, Frei, Yang, et al, 2019; Sotiriou et al, 2020). This textural evidence distinguishes magmatic amphibole from metamorphic amphibole, which does not have serrated grain boundaries, does not occur as interstitial oikocrysts, and is euhedral (Sotiriou et al, 2020).…”

“…The textural evidence for magmatic amphibole includes serrated igneous boundaries with calcic plagioclase, whole‐grain optical continuity and extinction, its occurrence as interstitial oikocrysts, and its anhedral form (Hoffmann et al, 2012; Mohan et al, 2013; Piaia et al, 2017; Polat et al, 2011; Rollinson et al, 2010; Santosh & Li, 2018; Sotiriou, Polat, Frei, Yang, et al, 2019; Sotiriou et al, 2020). This textural evidence distinguishes magmatic amphibole from metamorphic amphibole, which does not have serrated grain boundaries, does not occur as interstitial oikocrysts, and is euhedral (Sotiriou et al, 2020). Primary magnesiohornblende can also be distinguished from metamorphic actinolite in these layered intrusions based on its higher Si apfu values (Leake et al, 1997; Sotiriou et al, 2020).…”

“…This textural evidence distinguishes magmatic amphibole from metamorphic amphibole, which does not have serrated grain boundaries, does not occur as interstitial oikocrysts, and is euhedral (Sotiriou et al, 2020). Primary magnesiohornblende can also be distinguished from metamorphic actinolite in these layered intrusions based on its higher Si apfu values (Leake et al, 1997; Sotiriou et al, 2020). The 2,743 Ma Mayville Intrusion in the Superior Province of Canada has well‐preserved magmatic amphibole; however, some recrystallization to secondary actinolite has occurred (Sotiriou et al, 2020).…”