Early Palaeoproterozoic granulite-facies metamorphism and partial melting of eclogite-facies rocks in the Salma association, eastern Fennoscandian Shield, Russia

Corundum-bearing and spinel-bearing symplectites in ultrahigh-pressure eclogites record high-temperature overprint and partial melting during slab exhumation

“…Similar textures have been also reported in phengite-bearing eclogites from the Black Forest, Germany, and were interpreted as the products of phengite melting by the reaction Ph → Crn + Pl + Bt + other Al silicates + melt during the transformation from a granulite-facies to a HT-LP amphibolitefacies stage (Wimmenauer and Stenger, 1989). Moreover, based on the petrological observation and P -T estimation, Dokukina et al (2017Dokukina et al ( , 2021 revealed the polymineral assemblages consisting of Crn + Kfs + Bt + newly formed Ms + dumortierite in phengite-bearing quartz-feldspar rocks from the Belomorian eclogite province (Russia) as a dehydration melting product of phengite by the reaction Ph → Crn + Kfs + Bt + melt under HT granulite-facies conditions. Furthermore, the compositions of corundum in CPB symplectites from the studied eclogites (0.52 wt %-1.01 wt % for FeO) are similar to those of the corundum (< 2.70 wt % for FeO) produced by the experimental melting of phengite (e.g., Brearley and Rubie, 1990;Rodriguez-Navarro et al, 2003;Devineau et al, 2006;Masotta et al, 2018).…”

“…This textural feature is consistent with the presence of former silicate melts in HT metamorphic rocks (e.g., Brearley and Rubie, 1990;Holness et al, 2011;Vernon, 2011;Bartoli et al, 2013;Dokukina et al, 2021). The plagioclase moats are interpreted as textures of hydrous melt passing along the grain boundaries (Holness, 2011; Bartoli et al, 2013;Dokukina et al, 2021). (2) In the SP symplectite domain, plagioclase with clear cuspate margins extends along the symplectite boundaries (Fig.…”

Клинопироксены Из Щелочных И Силикатно-Карбонатных Пород Чикского Массива (Сангиленское Нагорье, Тыва)

“…Циркон в гранат-кианит-фенгит-кварцевых породах, датированный ID-TIMS и LA-ICPMS методом в отдельных зернах (Dokukina et al, 2021), приурочен к полиминеральным псевдоморфозам (областям формирования расплава), характеризуется высокими концентрациями Th, U, магматическими Th/U отношениями (до 1.7) и содержит включения минералов предыдущих стадий преобразований породы (фенгит, гранат, ксенотим и др.). Включения фенгита в цирконе свидетельствует о том, что эклогитовый гранат-кианит-фенгитовый парагенезис формировался до кристаллизации циркона, который рос единовременно из расплава, отделившегося в результате процессов дегидратационного плавления слюды и возможно других водосодержащих минералов.…”