Paleoproterozoic eclogites in the salma area, Northwestern Belomorian Mobile Belt: Composition and isotopic geochronologic characteristics of minerals and metamorphic age

Скублов, С. Г.; Березин, А. В.; Мельник, А. Е.

doi:10.1134/s0869591111050055

Cited by 47 publications

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“…In this study we applied the LuHf garnet clinopyroxene geochronology, which are rock forming minerals of apo gabbro eclogites of the BMB. Consequently, the Lu-Hf datings of garnet provide unambiguous evidence for the age of meta morphism of the eclogite facies, provided that the blocking temperature was not exceeded (see discus sion below).We studied four eclogite samples from the Salma area (Samples 46 and 21) and Gridino (Samples 102 and 108), which were preliminarily dated using the U-Pb method by zircons providing evidence for the Svekofennian (~1.9 Ga) age of eclogites [3,4]. According to the specific geochemical characteristics, the studied grains or rims of zircons correspond to zir cons precisely of the eclogite facies [3,4].…”

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confidence: 98%

“…We studied four eclogite samples from the Salma area (Samples 46 and 21) and Gridino (Samples 102 and 108), which were preliminarily dated using the U-Pb method by zircons providing evidence for the Svekofennian (~1.9 Ga) age of eclogites [3,4]. According to the specific geochemical characteristics, the studied grains or rims of zircons correspond to zir cons precisely of the eclogite facies [3,4].…”

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confidence: 99%

“…According to the specific geochemical characteristics, the studied grains or rims of zircons correspond to zir cons precisely of the eclogite facies [3,4]. Eclogitized gabbro (Samples 46 and 102) are the most abundant eclogite type in the BMB.…”

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First Lu-Hf garnet ages of eclogites from the Belomorian Mobile Belt (Baltic Shield, Russia)

et al. 2012

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Eclogites from the north eastern border of the Bel morian Mobile Belt (BMB) have not only been used for regional geodynamic reconstructions [1], but also as first direct evidence for plate tectonic processes in the Mesoarchean [2]. M.V. Mints and coworkers (2010) dated zircons from eclogites of the Salma area related to the so called Belomorian Meso-Neoar chean eclogite province and interpreted the age of 2.87 Ga obtained for some zircons as the age of meta morphism of the eclogite facies [2]. However, rocks of the Salma area undoubtedly underwent eclogite meta morphism with an age of ~1.9 Ga in the Paleoprotero zoic [2][3][4]; for this reason, there is a question of whether or not zircon datings of 2.87 Ga correspond to the age of Mesoarchean eclogite metamorphism [1, 2], or whether this is the age of the magmatic protolith (gabbro) of eclogites [3,4], or if it represents a low P metamorphic event. In this study we applied the LuHf garnet clinopyroxene geochronology, which are rock forming minerals of apo gabbro eclogites of the BMB. Consequently, the Lu-Hf datings of garnet provide unambiguous evidence for the age of meta morphism of the eclogite facies, provided that the blocking temperature was not exceeded (see discus sion below).We studied four eclogite samples from the Salma area (Samples 46 and 21) and Gridino (Samples 102 and 108), which were preliminarily dated using the U-Pb method by zircons providing evidence for the Svekofennian (~1.9 Ga) age of eclogites [3,4]. According to the specific geochemical characteristics, the studied grains or rims of zircons correspond to zir cons precisely of the eclogite facies [3,4]. Eclogitized gabbro (Samples 46 and 102) are the most abundant eclogite type in the BMB. These are homogeneous fine granular bimineral rocks mainly composed of omphacite partially replaced by decompression sym plectites of plagioclase and clinopyroxene with a very low portion of the jadeitic end member and numerous garnet porphyroblasts. Eclogitized ultrabasic rocks (Samples 21 and 108) form coarse granular garnetclinopyroxene bodies (with a thickness up to 20 cm) and aggregates in the central parts of metaultrabasite bodies transformed mainly into secondary tremo lite-actinolite schist (Sample 21) or amphibolite (Sample 108) along the perimeter.Mineral monofractions were sorted according to standard methods using heavy liquids at the Institute of Precambrian Geology and Geochronology, Russian Academy of Sciences, and finally manually separated under a binocular microscope. For each sample three garnet monofractions were independently analyzed (Table 1). Both whole rock powders and mineral sepa rates were dissolved using a selective digestion proce dure, aiming to dissolve the major silicate phases, while leaving behind refractory phases, such as rutile and zircon [5]. This approach circumvents a potential age bias due to zircon and other mineral inclusions [6] and frequently results in high precision Lu-Hf ages (e.g., [5,7,8]). These authors also provide detailed methodological sections, ...

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First Lu-Hf garnet ages of eclogites from the Belomorian Mobile Belt (Baltic Shield, Russia)

et al. 2012

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“…Archaean rocks predominate in the northeast, and include tonalitetrondhjemite-granodiorite (TTG) suites, subordinate greenstone belts and paragneisses, yielding ages mainly between 2.9 and 2.7 Ga (Hölta et al, 2008 and references therein). High-grade metamorphic events recorded in these rocks include 2.9-2.7 Ga, eclogite-or granulitefacies metamorphism, as well as younger, c. 1.9 Ga, highgrade metamorphic overprinting Mints et al, 2010;Skublov et al, 2011), related to Fennoscandian reamalgamation.…”

Section: Figure 1 Fennoscandia and Its Location Within The East Euromentioning

confidence: 97%

Geology and metallogenic potential of the northwesternmost Norrbotten Province around Altevatn in Troms, northern Norway

Slagstad¹,

Willemoes-Wissing²,

Coint³

et al. 2016

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“…The oldest crustal eclogite occurrences are latest Early Proterozoic, associated with high-P granulites in the Usagaran-Ubendian mobile belts of Tanzania (Sklyarov et al 1998;Möller 1995;Boniface et al 2012). Archean eclogite was reported from the Kola Peninsula, Russia (Volodichev et al 2004;Mints et al 2010), but U-Pb zircon geochronology identified Early Proterozoic metamorphic rims around Archean magmatic zircon cores (Skublov et al 2011). Eclogites, particularly those formed in a transitional eclogite-granulite facies P-T range, thus are not necessarily indicators of subduction-zone metamorphism.…”

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Plate-tectonic evolution of the Earth: bottom-up and top-down mantle circulation

2016

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Abstract:Intense devolatilization and chemical-density differentiation attended accretion of planetesimals on the primordial Earth. These processes gradually abated after cooling and solidification of an early magma ocean. By 4.3 or 4.2 Ga, water oceans were present, so surface temperatures had fallen far below low-pressure solidi of dry peridotite, basalt, and granite, ϳ1300, ϳ1120, and ϳ950°C, respectively. At less than half their T solidi, rocky materials existed as thin lithospheric slabs in the near-surface Hadean Earth. Stagnant-lid convection may have occurred initially but was at least episodically overwhelmed by subduction because effective, massive heat transfer necessitated vigorous mantle overturn in the early, hot planet. Bottom-up mantle convection, including voluminous plume ascent, efficiently rid the Earth of deep-seated heat. It declined over time as cooling and top-down lithospheric sinking increased. Thickening and both lateral extensional + contractional deformation typified the post-Hadean lithosphere. Stages of geologic evolution included (i) 4.5-4.4 Ga, magma ocean overturn involved ephemeral, surficial rocky platelets; (ii) 4.4-2.7 Ga, formation of oceanic and small continental plates were obliterated by return mantle flow prior to ϳ4.0 Ga; continental material gradually accumulated as largely sub-sea, sialic crust-capped lithospheric collages; (iii) 2.7-1.0 Ga, progressive suturing of old shields + younger orogenic belts led to cratonal plates typified by emerging continental freeboard, increasing sedimentary differentiation, and episodic glaciation during transpolar drift; onset of temporally limited stagnant-lid mantle convection occurred beneath enlarging supercontinents; (iv) 1.0 Ga-present, laminar-flowing asthenospheric cells are now capped by giant, stately moving plates. Near-restriction of komatiitic lavas to the Archean, and appearance of multicycle sediments, ophiolite complexes ± alkaline igneous rocks, and high-pressure-ultrahigh-pressure (HP-UHP) metamorphic belts in progressively younger Proterozoic and Phanerozoic orogens reflect increasing negative buoyancy of cool oceanic lithosphere, but decreasing subductability of enlarging, more buoyant continental plates. Attending supercontinental assembly, density instabilities of thickening oceanic plates began to control overturn of suboceanic mantle as cold, top-down convection. Over time, the scales and dynamics of hot asthenospheric upwelling versus lithospheric foundering + mantle return flow (bottom-up plume-driven ascent versus top-down plate subduction) evolved gradually, reflecting planetary cooling. These evolving plate-tectonic processes have accompanied the Earth's thermal history since ϳ4.4 Ga.Résumé : Un intense dégagement de matières volatiles et une différentiation selon la densité chimique faisait partie de l'accrétion de planétésimaux à la Terre primordiale. Ces processus ont grandement diminué après le refroidissement et la solidification d'un océan primitif de magma. Vers 4,3 ou 4,2 Ga, il existait des océan...

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Paleoproterozoic eclogites in the salma area, Northwestern Belomorian Mobile Belt: Composition and isotopic geochronologic characteristics of minerals and metamorphic age

Cited by 47 publications

References 25 publications

First Lu-Hf garnet ages of eclogites from the Belomorian Mobile Belt (Baltic Shield, Russia)

First Lu-Hf garnet ages of eclogites from the Belomorian Mobile Belt (Baltic Shield, Russia)

Geology and metallogenic potential of the northwesternmost Norrbotten Province around Altevatn in Troms, northern Norway

Plate-tectonic evolution of the Earth: bottom-up and top-down mantle circulation

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