T. V. Kaulina

Mesoarchean subduction processes: 2.87 Ga eclogites from the Kola Peninsula, Russia

The nature of tectonic processes on the early Earth is still controversial. The scarcity of high-pressure metamorphic rocks such as eclogite (the high-pressure equivalent of basalt) in Archean cratons has been used to argue that plate tectonics did not operate until Earth had cooled to a critical point, perhaps around the 2.5 Ga Archean-Proterozoic transition. However, eclogites occur as meter- to kilometer-sized lenses enclosed in Archean gneisses of the Belomorian Province of the Fennoscandian shield. Geochemistry and internal features suggest that the protoliths of the eclogites were interlayered olivine gabbros, troctolites, and Fe-Ti oxide gabbros. Greenschist facies mineral parageneses are enclosed in prograde-zoned eclogite garnets, and peak metamorphic conditions define an apparent thermal gradient (12–15 °C/km), consistent with metamorphism in a warm Archean subduction zone. We show here that these eclogites represent the oldest known high-pressure metamorphic rocks. U-Pb dating and Hf isotope analyses of zircons from the eclogites and a crosscutting felsic vein define a minimum age of 2.87 Ga for the Uzkaya Salma eclogite; a 2.70 Ga age for the Shirokaya Salma eclogite is interpreted as the age of a granulite facies overprint. Thermal overprinting and growth of new zircon also occurred during the Svecofennian (1.9–1.8 Ga) orogeny. These new data imply that plate tectonic processes operated at least locally in late Mesoarchean time. The adakitic nature of the felsic vein suggests that partial melting of hydrated eclogites could produce Archean tonalite-trondhjemite-granodiorite–type magmas.

The Belomorian eclogite province: Unique evidence of Meso-Neoarchaean subduction and collision

The Belomorian eclogite province (BEP) recently revealed in the eastern part of the Fennoscandian shield is a unique Archaean object. The age of the crust eclogites known in the world outside the BEP does not exceed two billion years [1], which corresponds to the middle of the Paleoproterozoic. Eclogites with an age not less than 2.72 Ga [2] were found for the first time within the Belomorian province. The studies of the BEP open principally new opportunities, first, for the reconstruction of the geodynamic processes in the his� tory of the Early Precambrian crust of the region, and second, for a more correct concept about the geody� namics of the Early Precambrian as a whole, because the lack of reliable findings of Archaean eclogites is one of the arguments against the reality of subduction and application of plate tectonics to the modeling of the Archaean geodynamics.

Dating of key events in the Precambrian polystage complexes: An example from Archaen Belomorian Eclogite Province, Russia

The identification of discrete tectono-thermal events, their sequence, and absolute age is a difficult problem in the highly deformed polymetamorphic Precambrian complexes. The Archean and Paleoproterozoic eclogites are distinguished in the Gridino eclogitebearing melange [1]. Archean eclogites are small equant and elongated boudins and lenses in the granite gneiss matrix and have a U–Pb age of ~2.7 Ga [2]. They are considered a metamorphic product of the Archean oceanic protolith [1]. The Paleoproterozoic eclogites are represented by undeformed and deformed (folded, boudined) eclogitized dikes of different age complexes. They are compositionally similar to the Archean eclogites and, in addition to the Archean zircons, contain Paleoproterozoic zircons with an age ~2.45–2.42 Ga. All mafic bodies (dikes of different generations and boudins) were subsequently overprinted by eclogites, high-grade granulite, and amphibolite-facies events (Fig. 1).

New geochronological data on metamorphic and igneous rocks from the Gridino Village area (Belomorian eclogitic province)

In the Belomorian eclogitic province, eclogites aretraceable in the meridional direction from SalmaStrait (Imandra Lake) via the islands and coast of theKrasnaya Estuary of the White Sea [1] and the GridinoVillage area [2] to the Onezhskaya Estuary coast. Thestudy area is located in the wellexposed coastal zoneand adjacent islands of the White Sea near the villageof Gridino. An eclogitebearing complex approximately 50 km long (from the northwest southeastward) and 10 km wide was described in [2] as anArchean eclogitebearing melange and thoroughlyillustrated in [3] using rocks from Stolbikha Island asan example. The complex includes eclogites andeclogitized mafic dikes [2, 4]. The mafic rocks demonstrate distinct successive stages of metamorphic transformations under eclogite (maximal pressure 15–16 kbar),elevatedpressure granulite (

The Salma Eclogites of the Belomorian Province, Russia: HP/UHP Metamorphism Through the Subduction of Mesoarchean Oceanic Crust

Publisher Summary Eclogite-facies mafic rocks occur within gray gneisses of TTG affinity in the northeastern part of the Belomorian Province, Kola Peninsula. These are characterized by widespread omphacite-breakdown textures and locally preserved relics of omphacite. Thermobarometry indicates a clockwise PT path. Garnet inclusions suggest a prograde path passing from surface-weathering conditions through the low-grade green schist facies (pumpellyiteactinolite facies) before reaching the eclogite facies. Peak metamorphic conditions are estimated to be about 700‑750°C and > 14‑15 kbar. Needle-shaped inclusions (rods) of quartz in omphacite suggest that the peak P-T conditions of studied eclogites could reach significantly higher pressure than estimated in the present study. The retrograde path passed through granulite facies to upper amphibolite facies by near-isothermal decompression. The results of UPb dating and Hf-isotope analysis of zircons from the eclogites and cross-cutting felsic vein can be used to infer an approximate 2.89 Ga age for the oceanic crust, which was subducted and underwent eclogite-facies metamorphism between 2.87 and 2.82 Ga. The granulite-facies overprint is likely to have occurred at 2.72 Ga. Thermal overprinting and growth of new zircon also occurred during the Svecofennian (1.9‑1.8 Ga) orogeny. These new data imply that plate tectonic processes (“hot subduction”) operated at least locally in the late Mesoarchean. The petrology and geochemistry of the Salma eclogites and related TTG rocks can be best explained by subduction of Archean oceanic crust. The adakitic nature of the felsic vein inside the Salma eclogites suggests that partial melting of hydrated eclogites could produce Archean TTG-type magmas.

Geochemical and U–Pb zircon age characterization of granites of the Bathani Volcano Sedimentary sequence, Chotanagpur Granite Gneiss Complex, eastern India: vestiges of the Nuna supercontinent in the Central Indian Tectonic Zone

Abstract The Central Indian Tectonic Zone (CITZ) marks the suture zone where the North and South Indian cratonic blocks amalgamated to form the Greater Indian Landmass (GIL). It consists of three broad domains from west to east: the central CITZ occupying the central region of mainland India juxtaposed between two mobile belts, namely the Sausar Mobile Belt (SMB) in the south and the Mahakoshal Mobile Belt (MMB) in the north; the Chotanagpur Granite Gneiss Complex (CGGC) lying east of the main CITZ; and the easternmost Shillong Plateau Gneissic Complex (SPGC). The studied granites are from the Bathani Volcano Sedimentary sequence (BVSs) from the northern margin of the CGGC. These are high-K, calc-alkaline, I-type granites related to arc magmatism and are interpreted to have formed by partial melting of an igneous source at upper-crustal depths. The granitic magma underwent extensive fractional crystallization of plagioclase, biotite, K-feldspar and ilmenite during emplacement. The U–Pb (ID-TIMS) zircon emplacement age is c. 1.7–1.6 Ga for these granites. This episode of magmatism can be correlated to the global event of the Nuna supercontinent assembly also reported from the MMB of the central CITZ. We infer that the BVSs is the eastern continuation of the MMB of the central CITZ.

The long (3.7–2.1 Ga) and multistage evolution of the Bug Granulite–Gneiss Complex, Ukrainian Shield, based on the SIMS U–Pb ages and geochemistry of zircons from a single sample

Abstract Multidisciplinary studies of zircons, rock-forming minerals and the whole-rock composition of granulite samples from the Bug Granulite–Gneiss Complex, Ukraine (including ion microprobe REE analysis, secondary ion mass spectrometry (SIMS) U–Pb and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) Lu–Hf analysis of zircons from a single sample) have revealed three major stages in the geological evolution of the complex. (i) At 3.66 Ga, a mafic intrusion contaminated with felsic rocks formed, as evidenced by 3.74 Ga zircon xenocrysts with inclusions of plagioclase, K-feldspar and quartz. (ii) At 3.59–3.55 Ga, high-temperature and high- to moderate-pressure granulite-facies metamorphism accompanied by migmatization and deformation resulted in the formation of mafic granulites. (iii) At 2.1–2.0 Ga, metamorphic overprinting occurred, and metatrachybasaltic dykes intruded at approximately 2.0 Ga. The metamorphic mineral assemblages recorded in the dykes formed at temperatures similar to those of the 3.59–3.55 Ga metamorphism but at pressures 2–3 kbar lower. This metamorphism disturbed the Sm–Nd whole-rock system, altered the Hf isotope system of the older zircons and resulted in Pb loss in small zircon grains. This complex event history recorded in zircons from a single rock corresponds to major stages of the geological evolution of both the Dniester–Bug Province and the entire Ukrainian Shield.

REE distribution in zircon from reference rocks of the Arctic region: Evidence from study by the LA-ICP-MS method

The results of the LA-ICP-MS analysis of the concentrations of REEs, U, Th, and Hf in zircon from Paleo- and Neoarchean reference rocks of the Kola region (garnet–amphibole gneiss, basic and acid granulites, and granite pegmatite) are reported. A new methodology of the study of accessory zircons has been validated and modified. The accuracy of the results is confirmed by analysis of standard zircons Temora 1 and 91 500 and by comparison with the data obtained in other laboratories.

Mineral Chemistry, Sr–Nd Isotope Geochemistry and Petrogenesis of the Granites of Bathani Volcano-Sedimentary Sequence from the Northern Fringe of Chotanagpur Granite Gneiss Complex of Eastern India

New geochemical, mineral chemical, Sr–Nd isotope data of the granites from Bathani Volcano Sedimentary sequence (BVSs) from northern margin of Chotanagpur Granite Gneiss Complex of Central Indian Tectonic Zone has been presented in this paper to understand its petrogenesis and implications for crustal growth in the eastern Indian shield. Petrographically, they are coarse-grained granites with biotite, plagioclase feldspar and K-feldspar as major constituent phases with minor presence of muscovite. Granites are silica rich (62.42–71.08 wt%), high-K, calc-alkaline and peraluminous in nature. Trace element wise they show an overall enriched large ion lithophile elements (LILE) pattern with negative anomalies for Ba, Nb, Sr, P, Eu, Ti and Zr. They are characterized by fractionated REE patterns with enrichments in LREE relative to HREE and display pronounced negative Eu anomalies. The granites presents a lower (143Nd/144Nd)i values varying from 0.51130 to 0.51164 with eNd(t) values varying from 2.21 to −4.96 and low (87Sr/86Sr)i (0.705–0.711) and relatively old depleted mantle model age of TDM1 1886–2517 Ma. The emplacement age of the BVSs granites took place at ~1600 Ma as revealed by whole rock Rb–Sr isochron age. Interpretation of the observed data indicates that they are I-type granite related to arc magmatism and is the product of partial melting of a pre-existing metabasic crust due to heat generated by an underplating basaltic magma pool coupled with extensive fractional crystallization of plagioclase, biotite and K-feldspar during emplacement.

Stages in the formation of uranium mineralization in the Salla-Koulajarvinskaya zone (Northern Karelia): Geological and isotope geochronological data

On the basis of U–Pb, Rb–Sr and Sm–Nd isotopic data, it is shown that formation of uranium mineralization in the Paleoproterozoic Salla-Koulajarvinsky belt (Northern Karelia) was a long-lasting mult-stage process that developed over more than 1 Ga: from the Paleoproterozoic to the Paleozoic. The first stage, 1.75 Ga ago, corresponds to the Svekofennian metamorphic event—regional albitization. The process was dated by the Rb–Sr (isochronic age of albitites is 1754 ± 39 Ma) and U–Pb methods (the age of rutile is 1756 ± 8 Ma). At this stage, with a lower temperature limit of 400–450°C, conditions were favorable for the mobilization and migration of uranium, but not for its deposition in minerals. The second stage, 1.62 Ga ago, was a time of alteration of rocks at the regressive stage of the Svekofennian metamorphic event, when carbonate and chlorite rocks formed after albitites. The age of this stage was estimated as 1627 ± 42 Ma according to ThO2, UO2, and PbO contents in uraninite. Probably, the deposition of uraninite took place at this stage at temperature not higher than 300–350°C. The final, third stage, 385 Ma ago, corresponds to the Paleozoic tectonic activation and formation of Caledonian alkaline intrusions. Uranium minerals were probably redeposited at this stage; the U–Pb age of brannerite is 385 ± 2 Ma.