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The geochemistry and isotopic age of eclogites from the Belomorian Belt (Kola Peninsula); evidence for subducted Archean oceanic crust

A. A. Shchipansky, L. I. Khodorevskaya and A. I. Slabunov
The geochemistry and isotopic age of eclogites from the Belomorian Belt (Kola Peninsula); evidence for subducted Archean oceanic crust
Russian Geology and Geophysics (March 2012) 53 (3): 262-280

Abstract

We present results of geochemical studies and isotope dating of eclogites and associated rocks from the Kuru-Vaara quarry, Belomorian Belt, Northeastern Baltic Shield. The southern and northern eclogites are similar in geochemical features. Their protoliths were primitive, mainly high-Mg basalts of oceanic affinity derived from a primitive mantle source rather than from a depleted mantle source characteristic of modern MORB. The post-eclogitic intrusive rocks show obvious evidence for crustal contamination. The eclogite-hosting tonalitetrondhjemite-granodiorite (TTG) gneisses form a coherent series including high-Al and low-Al varieties. The trace element data show that the TTG series formed through the hydrous partial melting of the southern eclogites in the presence of garnet and amphibole in the field of the rutile stability (>15 kbar). Zircons from the southern eclogites exhibit features of their strong re-equilibration by coupled dissolution-reprecipitation processes but have locally preserved patches with a primary magmatic zoning. The geochemistry of the patches points to the oceanic provenance of protolithic zircons; their isotope dating (SHRIMP-II) yielded a concordant age of 2821 + or - 21 Ma. Zircons from the trondhjemite gneiss with geochemical features of Archean adakite were dated at 2805 + or - 11 Ma, which suggests the syneclogitic facies origin of the TTG melts. The concordant age of high-pressure zircons from the northern eclogites is 2722 + or - 21 Ma, close to the age of the earlier described Gridino eclogites. The overview of the isotopically dated eclogite bodies show the presence of at least three temporally distinct groups of eclogites in the Belomorian Belt, approximately 2.86-2.87, approximately 2.82-2.80, and approximately 2.72 Ga, which is in a good accordance with the known isotopic ages for major crust-forming events in the belt. This, in turn, implies a close genetic relationship between the eclogites and the TTG origin, which might be consistent with the model of the short intermitted events of subduction of the thickened Archean oceanic crust. The presence of HP/UHP eclogites of different ages and the structural style of the Belomorian Belt permit it to be assigned to megamelange belts.


ISSN: 1068-7971
Serial Title: Russian Geology and Geophysics
Serial Volume: 53
Serial Issue: 3
Title: The geochemistry and isotopic age of eclogites from the Belomorian Belt (Kola Peninsula); evidence for subducted Archean oceanic crust
Affiliation: Russian Academy of Sciences, Geological Institute, Moscow, Russian Federation
Pages: 262-280
Published: 201203
Text Language: English
Publisher: Allerton Press, New York, NY, United States
References: 67
Accession Number: 2021-044943
Categories: GeochronologyGeochemistry of rocks, soils, and sedimentsIgneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables
N66°00'00" - N70°00'00", E32°00'00" - E42°00'00"
Secondary Affiliation: Russian Academy of Sciences, Institute of Experimental Mineralogy, RUS, Russian FederationRussian Academy of Sciences, Karelian Research Center, RUS, Russian Federation
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2021, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 2021
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