1.9 Ga eclogite from the Archean-Paleoproterozoic Belomorian Province, Russia

Quartz and orthopyroxene exsolution lamellae in clinopyroxene and the metamorphic P–T path of Belomorian eclogites

“…Although the actual onset time of the eclogite facies metamorphism is another subject of debate, at this moment, we are inclined to consider the Salma eclogites are of late‐Palaeoproterozoic age ( c . 1.9 Ga; Li et al., ; Liu et al., ) with corresponding similar metamorphic P–T path(s) (Figure , path 1 and path 2). Comparison with other Precambrian high‐grade belts, such as the Palaeoproterozoic Usagaran belt (Tanzania; Figure , path 6, after Collins et al., ) and the Hengshan Complex (NCC, China; Figure , path 7, after Zhao et al., ), reveals consistence with respect to the high‐ P/T geothermal gradient and the general type of medium‐temperature eclogite‐high‐ P granulite metamorphism (E‐HPGM; Brown, , ).…”

“…Altogether, a clockwise P‐T trajectory is proposed for the Shirokaya Salma eclogites with an inferred (warm) geothermal gradient of 40–50°C/kbar (~12–13°C/km; Figure , path 1, this work). Surprisingly, this evolution resembles the one in the adjacent 1.9 Ga Uzkaya Salma eclogite (Figure , path 2, after Li et al., ), but it clearly differs from the earlier estimated peak and retrograde conditions of ≥13–14 kbar, ~700°C and 8–13 kbar, 700–750°C, respectively (Figure , path 3, after Kaulina et al., ; Konilov et al., ; Yapaskurt et al., ). Compared to the Gridino eclogites of the Belomorian Province, they may have similar pressure peak conditions though (Figure , path 4, eclogitized dyke, after Perchuk & Morgunova, ; path 5, boudin eclogites, after Li, Zhang, Wei, & Slabunov, ).…”

“…Dokukina & Konilov, ; Mints et al., ). However, our recent studies have only revealed late‐Palaeoproterozoic eclogite facies metamorphism in adjacent areas (Kuru‐Vaara and Uzkaya Salma, see Li et al., ; Liu et al., ), raising the question as to the actual age of the Belomorian eclogites. Furthermore, the reconstruction of a reliable metamorphic P–T trajectory for the Belomorian eclogites is a vital task in gaining a better understanding of the Precambrian tectonometamorphic regime in the Belomorian Province as well as elsewhere on Earth.…”

“…Altogether, a zigzag P–T path has been concluded (Dokukina et al., , ; Kaulina et al., ; Konilov et al., ; Mints, Belousova, et al., ; Mints, Konilov, et al., ; Mints et al., , ). However, recent geochronological data of the Salma eclogites argue for an eclogite facies event at 1.9 Ga (Li et al., ; Liu et al., ). The Shirokaya and Uzkaya Salma eclogite occurrences are situated rather close to each other geographically (several kilometres apart) near the Salma Strait of Lake Imandra at the 1,192–1,198th km road mark of the St. Petersburg–Murmansk federal highway.…”

“…We believe a more sophisticated examination should be undertaken, with focus on the petrology of pristine eclogite (sensu stricto), to derive more reliable P–T paths of their metamorphic evolution. For this work, we selected representative rock samples, a pristine eclogite, two moderately retrograded eclogites that contain omphacite relicts, and an intensely retrograded eclogitic rock (the apoeclogite of the Russian literature) from Shirokaya Salma (a subcomplex of the Salma Complex), which is less studied than the adjacent Uzkaya Salma and Kuru‐Vaara localities (see Konilov et al., ; Li, Yu, Zhang, Wei, & Bader, ; Liu et al., ; Mints, Belousova, et al., ; Mints, Konilov, et al., ; Mints et al., ; Shchipansky, Khodorevskaya, Konilov, & Slabunov, ; Shchipansky, Khodorevskaya, & Slabunov, ; Shchipansky & Slabunov, ).…”