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

• Published in: Journal of Metamorphic Geology
• Main Authors: Yu, H. L., Zhang, L. F., Wei, C. J., Li, X. L., Guo, J. H.
• Other Authors: Zhang, LF (reprint author), Peking Univ, MOE Key Lab Orogen Belt & Crustal Evolut, Sch Earth & Space Sci, Beijing, Peoples R China., Peking Univ, MOE Key Lab Orogen Belt & Crustal Evolut, Sch Earth & Space Sci, Beijing, Peoples R China., Inst Geol & Geophys CAS, State Key Lab Lithospher Evolut, Beijing, Peoples R China.
• Format: Journal/Newspaper
• Language: English
• Published: JOURNAL OF METAMORPHIC GEOLOGY 2017
• Subjects: Gridino-type eclogite; Paleoproterozoic; phase equilibria modelling; P-T path; zircon U-Pb age; STYLE PLATE-TECTONICS; LAPLAND-KOLA OROGEN; MOBILE BELT; PALEOPROTEROZOIC ECLOGITES; BALTIC SHIELD; FENNOSCANDIAN SHIELD; UHP METAMORPHISM; THERMAL REGIMES; ZIRCON; EVOLUTION; Gridino; Fennoscandian; Lapland
• Online Access: https://hdl.handle.net/20.500.11897/470696; https://doi.org/10.1111/jmg.12258

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. 2.70Ga; they are interpreted to be magmatic in origin. Zircon cores have O-18 of 5.64-6.07 parts per thousand 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. 1.90Ga; they are interpreted to be metamorphic in origin. Zircon rims have elevated O-18 of 6.23-6.80 parts per thousand, 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 degrees C at >18kbar for the Gridino-type eclogites suggest an apparent thermal gradient of <39-42 degrees C/kbar for the Lapland-Kola collisional orogeny. National Nature Science Foundation of China [41121062, 41172196, 41311120071] SCI(E) ARTICLE 8 855-869 35