Archaean Kuru-Vaara eclogites in the northern Belomorian Province, Fennoscandian Shield: crustal architecture, timing, and tectonic implications

Self Cite

The Shirokaya Salma eclogite-bearing complex is located in the Archean-Palaeoproterozoic Belomorian Province (Russia). Its eclogites and eclogitic rocks show multiple clinopyroxene breakdown textures, characterized by quartz-amphibole, orthopyroxene and plagioclase lamellae. Representative samples, a fresh eclogite, two partly retrograded eclogites, and a strongly retrograded eclogitic rock, were collected for this study. Two distinct mineral assemblages-(1) omphacite+gar-net+quartz+rutileAEamphibole and (2) clinopyroxene+garnet+amphibole+plagio-clase+quartz+rutile+ilmeniteAEorthopyroxene-are described. Based on phase equilibria modelling, these assemblages correspond to the eclogite and granulite facies metamorphism that occurred at 16-18 kbar, 750-800°C and 11-15 kbar, 820-850°C, respectively. The quartz-amphibole lamellae in clinopyroxene formed during retrogression with water ingress, but do not imply UHP metamorphism.The superfine orthopyroxene lamellae developed due to breakdown of an antecedent clinopyroxene (omphacite) during retrogression that was triggered by decompression from the peak of metamorphism, while the coarser orthopyroxene grains and rods formed afterwards. The P-T path reconstructed for the Shirokaya Salma eclogites is comparable to that of the adjacent 1.9 Ga Uzkaya Salma eclogite (Belomorian Province), and those of several other Palaeoproterozoic high-grade metamorphic terranes worldwide, facts allowing us to debate the exact timing of eclogite facies metamorphism in the Belomorian Province. K E Y W O R D SBelomorian eclogite, clinopyroxene breakdown, pseudosection, PT path | INTRODUCTIONClinopyroxene breakdown textures have been recognized in many Phanerozoic high-grade metamorphic rocks worldwide. Quartz lamellae commonly found in them occur, for instance, in the ultrahigh-pressure (UHP) terranes of DabieSulu (Tsai & Liou, 2000), the Kokchetav Massif (Katayama, Parkinson, Okamoto, Nakajima, & Maruyama, 2000) and the Western Tianshan (Zhang, Ellis, & Jiang, 2002;Zhang, Song, Liou, Ai, & Li, 2005). The oriented precipitation of quartz in clinopyroxene is interpreted as resulting from breakdown of non-stoichiometric Ca-Escolabearing (CaEs, Ca 0.5 [ ] 0.5 AlSi 2 O 6 ) clinopyroxene due to the reaction CaEs=CaTs+Qz (Smith, 1984;Smyth, 1980). Quartz lamellae associated with amphibole have been widely observed in the high-pressure, high-temperature (HP-HT) terranes of the Bohemian Massif (Faryad & Fisera, 2015), the Kontum Massif Nakano, Osanai, Owada, Nam, et al., 2007) Page, Essene, & Mukasa, 2003 and Greek Rhodope (Proyer, Krenn, & Hoinkes, 2009), where they are indicative of fluid-driven retrogression. Furthermore, slow cooling with decompression is usually considered as being responsible for the exsolution of orthopyroxene ((Mg,Fe) 2 Si 2 O 6 ) in clinopyroxene, a process that commonly proceeds in (ultra)high-T granulites (e.g. Fonarev, Pilugin, Savko, & Novikova, 2006;Harley, 1987;Liu, Zhao, Zhao, Chen, & Liu, 2003;Sandiford & Powell, 1986) and ultrahigh-pressure metamorphic roc...

Section: Geological Settingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Zhang

Wei

et al. 2017

Self Cite

“…Since an Archean age (2.87–2.72 Ga) was ascribed to eclogites of the Belomorian Province (Mints et al., ; Volodichev, Slabunov, Bibikova, Konilov, & Kuzenko, ), the so‐called “oldest eclogite” has attracted much attention. Recently, two major eclogite types have been recognized in the Belomorian Province in the southwestern foreland of the Paleoproterozoic Lapland–Kola collisional orogeny (Figure a,b), the Salma and Gridino types (Balagansky et al, ; Dokukina et al., ; Li, Zhang, Wei & Slabunov, ; Liu et al., ; Mints, Dokukina, & Konilov, ; Mints et al., ; Perchuk & Morgunova, ). Compared with the Salma‐type eclogites, those in the Gridino area are more abundant and less retrogressed (Mints et al., ).…”

Section: Introductionmentioning

confidence: 99%

“…Modified after H€ oltt€ as et al (2008). (c) Geological map of the Stolbikha Island and sample locations (modified after Li, Zhang, Wei, & Slabunov 2015) foreland of the Paleoproterozoic Lapland-Kola collisional orogeny (Figure 1a,b), the Salma and Gridino types (Balagansky et al, 2014;Dokukina et al, 2014;Li, Zhang, Wei & Slabunov, 2015;Liu et al, 2017;Mints et al, 2010;Perchuk & Morgunova, 2014). Compared with the Salma-type eclogites, those in the Gridino area are more abundant and less retrogressed .…”

Section: Introductionmentioning

confidence: 99%

Age and P–T conditions of the Gridino‐type eclogite in the Belomorian Province, Russia

Zhang

Wei

et al. 2017

Although eclogites in the Belomorian Province have been regarded as Archean in age and among the oldest in the world, there are also multiple studies that have proposed a Paleoproterozoic age. Here, we present new data for the Gridino‐type eclogites, which occur as boudins and metamorphosed dykes within tonalite–trondhjemite–granodiorite gneisses. Zircon from these eclogites has core and rim structures. The cores display high Th/U ratios (0.18–0.45), negative Eu anomalies and strong enrichment in HREE, and have Neoarchean U–Pb ages of c. 2.70 Ga; they are interpreted to be magmatic in origin. Zircon cores have δ18O of 5.64–6.07‰ suggesting the possibility of crystallization from evolved mantle‐derived magmas. In contrast, the rims, which include the eclogite facies minerals omphacite and garnet, are characterized by low Th/U ratios (<0.035) and flat HREE patterns, and yield U–Pb ages of c. 1.90 Ga; they are interpreted to be metamorphic in origin. Zircon rims have elevated δ18O of 6.23–6.80‰, which was acquired during eclogite facies metamorphism. Based on petrography and phase equilibria modelling, we recognize a prograde epidote amphibolite facies mineral assemblage, the peak eclogite facies mineral assemblage and a retrograde high‐P amphibolite facies mineral assemblage. The peak metamorphic conditions of 695–755°C at >18 kbar for the Gridino‐type eclogites suggest an apparent thermal gradient of <39–42°C/kbar for the Lapland–Kola collisional orogeny.

“…The vein-like or lenticular garnet-phengite-quartz bodies in blocks of subduction-related eclogites were studied in the Kuru-Vaara quarry (Figs 2 & 3). The occurrence of these veins had been noted by Dokukina et al (2012bDokukina et al ( , 2014a, Shchipansky et al (2012b) and Balagansky et al (2015).…”

mentioning

confidence: 54%

Melting of eclogite facies sedimentary rocks in the Belomorian Eclogite Province, Russia

Dokukina

Mints

Konilov

2016

The eclogites exposed along northeastern boundary of the Belomorian orogen in the eastern Fennoscandian Shield were formed as a result of Mesoarchean–Neoarchean subduction and collision. As has been shown previously, the common protolith of the Salma‐type subduction‐related eclogite was oceanic layered gabbro. In this paper, we characterize eclogites formed from volcanic–sedimentary rocks of the upper oceanic crust, which comprised pillow lavas and associated aluminous sediments that filled the interpillow space intercalated with lava flows. As a result of eclogite facies metamorphism, the aluminous sediments have been transformed into coarse‐grained garnet–phengite–quartz rocks under pressure no lower than 21 kbar at a temperature of ~650 °C. Alternatively, we cannot rule out the possibility that the garnet–phengite–quartz veins represent solidified felsic melts that were produced by melting of boron‐bearing hydrothermally altered oceanic crust in the subduction zone. During transfer to the upper crust under high‐P granulite facies conditions, phengite underwent incongruent melting with formation of complex polymineralic pseudomorphs consisting of feldspar, biotite, muscovite and kyanite with corundum and dumortierite. The peak of high‐T metamorphism during exhumation of the eclogites is estimated at 850–900 °C, i.e. at least 50–100 °C higher than previous estimates.