Granulite Belt Research Articles

Paleozoic to Mesozoic paleotectonic reconstructions of Gondwana assembly: Insights from petrography, heavy mineral chemistry and detrital U–Th–total Pb monazite geochronology of sandstones in the Pranhita-Godavari Basin (SE India)

The provenance study of Paleo-Mesozoic sediments of the Pranhita-Godavari (P-G) Basin, located in the southeastern India is crucial for the reconstruction of the eastern Gondwanaland, including the India-Antarctica connection. This study examines petrography, heavy mineral chemistry and detrital monazite geochronology of the Permo-Carboniferous to Cretaceous, predominantly fluviatile sandstones in the P-G Basin to track the possible sediment sources in East Antarctica and Eastern India. The sandstones show a gradual shift in composition from feldspatho-quartzose to quartzose arenite from older to younger succession, accompanied by a change in source terranes in a changing setting from transitional continental to the cratonic interior. The heavy minerals of the sandstones are dominated by garnet, rutile, ilmenite, monazite and zircon in order of decreasing abundance. The mineral chemistry of garnet and rutile indicates the predominance of sources from amphibolite to granulite facies rocks with minor inputs from metapelitic sources. The increase in textural and mineralogical maturity of sandstones accompanied by a gradual increase in ilmenite alteration from the bottom to the top of the succession indicates the attainment of tectonic stability with time. U–Th–total Pb dating of detrital monazites yielded three distinct major clusters at (1) 2556–2125 Ma, (2) 969–715 Ma, and (3) 581–418 Ma. Based on the correlation of source composition and monazite geochronology and paleocurrent data, the source of sediments is traced to the orogens of the Eastern Ghats mobile belt, East Antarctica (including Rayner and Napier complex), Karimnagar granulite belt, Khammam schist belt, and Bhopalpatnam granulite belt, situated to the west, south, and southeast of the present outcrops of the P-G Gondwana succession. The younger age populations possibly represent the sediment input from Kuunga Orogen, which represents the youngest orogenic event (635–488 Ma) in the Gondwana assembly. The rocks of Kuunga orogeny, occurring to the south of the basin, was a minor contributor to the P-G Gondwana sediments of this basin. The new data supports that the Eastern Ghats Mobile Belt of India and East Antarctica were conjugate to each other till the Late Triassic Period, both of which contributed major sediments to the P-G Gondwana Basin.

Thermal and Physical Properties of Barrovian Metamorphic Sequence Rocks in the Ailao Shan‐Red River Shear Zone, and Implications for Crustal Channel Flow

AbstractThe collisional history between Greater India and the Eurasian plate has been well constrained by the study of exhumed Barrovian metamorphic sequence (BMS) rocks in the Himalayan Range. However, in the southeastern Tibetan Plateau, the collisional records have been obscured by intense, regional‐scale strike‐slip overprinting and recrystallization. Here, in BMS rocks from the Ailao Shan–Red River shear zone (ARSZ), we report the first discovery of a >250 km long, high‐pressure (high‐P) granulite belt (>1.0 GPa), identified by the presence of relict kyanite and associated decompression reaction textures. Petrological phase equilibrium modeling showed that exposed micaschists in the region represent exhumed middle crust (20–25 km, 600–670°C), while the high‐P granulite rocks are remnants of thickened lower crust (45–55 km, 800–850°C). This indicates that the northeast edge of the ARSZ experienced an additional ∼25 km of uplift and exhumation compared to the southwest side, facilitated by brittle thrusting/imbrication along the Ailao Shan fault (micaschists) and ductile extrusion along the Red River fault (granulite). Geochronological study shows that the upper portion of the BMS preserves older metamorphic ages (52–34 Ma) than the lower portion (32–29 Ma), which was attributed to spatial variation in cooling rates. Using calculated P–T–t–d paths, we also examined variation in density and seismic wave speeds for BMS in the ARSZ. Our data correlate with fieldwork conducted elsewhere within the Himalayan Range indicating that the kyanite to sillimanite transition zone may serve as a “cap” for the horizontal migration of melt within the lower crust.

Evidence of fluid-induced myrmekite formation after alkali-feldspar megacrysts: an example from a meta-porphyritic granitoid in Makrohar, Madhya Pradesh, India

Abstract A meta-porphyritic granitoid in the Makrohar Granulite Belt, Central India contains extensive myrmekite. This work evaluates the controls of fluid in relation to deformation and the formation of myrmekite all along the periphery of an alkali-feldspar megacryst. Two different myrmekite morphologies are present: (1) vermicular intergrowth of plagioclase (An38–39) and quartz (Myr1); and (2) polygonal aggregates of coarse plagioclase (An45–46) and quartz (Myr2). Petrographic features suggest that myrmekite Myr1 nucleates on alkali-feldspar and plagioclase porphyroclasts and the myrmekite front moved into the alkali feldspar by replacing it; and that myrmekite Myr2 and the secondary biotite which replaces plagioclase porphyroclasts and garnet form together. Deformation had a decisive role in forming the polygonal aggregates of Myr2, however field and microtextural features do not support any significant control of deformation during the formation of Myr1. Reaction modelling and a mass-balance calculation suggest that Ca and Na are added to, and K is removed from, the alkali feldspar during the myrmekite formation at nearly constant Si and Al. However, the secondary biotite-forming reaction, consumes K and releases Ca. Interpretation of the reaction textures in different isothermal–isobaric sections of μK2O–μCaO in the KCFASH system suggest that CaO and K2O moved in opposite directions for myrmekitisation and along their respective chemical potential gradients created between the sites of formation of myrmekite and secondary biotite. The feedback mechanism which operated between the two reaction sites was controlled by infiltration of brine-rich fluid in the meta-granitoid during a regional hydration event (550–600oC and 5–6 kbar). Volume reduction of ~10% during the formation Myr1 and Myr2 drew the brine-rich fluid towards the alkali feldspar and thus facilitated the process of myrmekite formation. Variation in the morphology of quartz in the myrmekite is attributed to the cooling of the complex.

Primary cordierite with > 2.5 wt% CO2 from the UHT Bakhuis Granulite Belt, Surinam: CO2 fluid phase saturation during ultrahigh-temperature metamorphism

The Paleoproterozoic Bakhuis Granulite Belt (BGB) in Surinam, South America, shows ultrahigh-temperature metamorphism (UHTM) at temperatures of around 1000 °C which, unusually, produced peak-to-near-peak cordierite with sillimanite and, in some cases, Al-rich orthopyroxene on a regional scale. Mg-rich cordierite (Mg/(Mg + Fe) = 0.88) in a sillimanite-bearing metapelitic granulite has a maximum birefringence of second-order blue (ca. 0.020) indicative of a considerable amount of CO2 (> 2 wt%) within its structural channels. SIMS microanalysis confirms the presence of 2.57 ± 0.19 wt% CO2, the highest CO2 concentration found in natural cordierite. This high CO2 content has enabled the stability of cordierite to extend into UHT conditions at high pressures and very low to negligible H2O activity. Based on a modified calibration of the H2O–CO2 incorporation model of Harley et al. (J Metamorph Geol 20:71–86, 2002), this cordierite occupies a stability field that extends from 8.8 ± 0.6 kbar at 750 °C to 11.3 ± 0.65 kbar at 1050 °C. Volatile-saturated cordierite with 2.57 wt% CO2 and negligible H2O (0.04 wt%) indicates fluid-present carbonic conditions with a CO2 activity near 1.0 at peak or near-peak pressures of 10.5–11.3 kbar under UHT temperatures of 950–1050 °C. The measured H2O content of the cordierite in the metapelite is far too low to be consistent with partial melting at 1000–1050 °C, implying either that nearly all of any H2O originally in this cordierite under UHT conditions was lost during post-peak cooling or that the cordierite was formed after migmatization. The high level of CO2 required to ensure fluid saturation of the c. 11 kbar UHT cordierite is proposed to have been derived from an external, possibly mantle, source.

Petrogenesis and in situ U-Pb zircon dates of a suite of granitoid in the northern part of the Central Indian tectonic Zone: Implications for prolonged arc magmatism during the formation of the Columbia supercontinent

The timing and petrogenesis of magmatic rocks in the Central Indian Tectonic zone (CITZ) have paramount importance in understanding the (a) growth of the Indian shield and (b) formation and disintegration of the Columbia and Rodinia supercontinents. In this study, the petrology, geochemistry and U-Pb in-situ zircon dating of a suite of porphyritic granitoids from the Makrohar Granulite Belt (MKGB) of the CITZ are presented. The studied rock suite develops megacrystic K-feldspar and plagioclase phenocrysts, embedded in medium to fine-grained matrix of biotite ± amphibole + quartz + K-feldspar + plagioclase + ilmenite ± garnet with widely variable phenocryst to matrix ratio. The bulk compositions of the studied rocks overlap with the compositions of the I-type granitoid, emplaced in a continental arc setting. The in-situ U-Pb zircon age fixes the timing of magmatism at 1750 Ma. Systematic geochemical trends combined with the variation in modal mineralogy suggest crystal fractionation to be the dominant process during the evolution of this arc magma. Phase equilibrium modeling in Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2-O2 system under various physicochemical conditions suggests that both post-emplacement fractionation of a felsic magma and combined fractionation-crustal assimilation of a mafic magma at shallow depths (≤5 kbar) can produce the chemical variation observed in the studied arc granites. Petrography and field evidences negate substantial granite formation from combined fractionation and crustal assimilation of arc basalt in the studied area. Plagioclase and K-feldspar occur as early crystallising phases. Variation of the modeled melt compositions simulates the variations of the major element compositions in the studied granitoid suite. The ca. 1750 Ma old arc magmatism in the MKGB is also reported from the Mahakoshal Supracrustal Belt (MSB). This feature is consistent with the view that both MKGB and MSB, now separated by the Son Narmada South Fault formed a coherent block till 1750 Ma. In combination with the published information, the present study demonstrates southward progression of the arc front in the Indian shield from ca. 1900 Ma to ca. 1600 Ma during growth of the Columbia supercontinent.

A new A-type granitoid occurrence in southernmost Fennoscandia: geochemistry, age and origin of rapakivi-type quartz monzonite from the Pietkowo IG1 borehole, NE Poland

Rapakivi-type quartz monzonite and the underlying dark-grey granodiorite from the Pietkowo IG1 borehole, in the Polish part of southernmost Fennoscandia have been investigated using whole-rock geochemistry, Sm–Nd isotope geochemistry and U–Pb zircon dating. The quartz monzonite was emplaced at 1495–1491 Ma, although slightly older zircon cores (antecrysts) of 1513 Ma imply a two-stage crystallization. The geochemical similarities with Mazury Complex granitoids, their metaluminous and alkali-calcic nature, elevated contents of F, Ga and high-field-strength-elements (HFSE), indicate that the Pietkowo IG1 rapakivi-type quartz monzonite is an ‘A-type’ granitoid. The presence of magnetite and titanite indicates crystallization under oxidizing conditions. The rock is classified as A2 sub-type, and the Nb/Y ratio implies a within-plate setting. The dark-grey granodiorite, dated to 1813 Ma, has a calc-alkaline character, typical of a volcanic-arc environment. Initial whole rock εNd values range between -2.9 and -3.3 for the rapakivi-type quartz monzonite and from -1.0 to + 1.1 for the dark-grey granodiorite. We suggest that the A-type Pietkowo IG1 rapakivi-type quartz monzonite was generated from the dark-grey granodiorite via partial melting at middle to lower crustal levels. The most plausible ascent route for the quartz monzonite was via lithospheric-scale weakness zones, between the eastern margin of the Mazowsze Domain and Belarus-Podlasie Granulite Belt, i.e., the Białystok fault. Therefore, the Pietkowo IG1 rapakivi-type quartz monzonite is a representative of the Mesoproterozoic A-type granitoid occurrence in southernmost Fennoscandia.

The Nature of Enderbites From Bug Area According to the Data of Sm-Nd, U-Pb and Lu-Hf Methods

As a result of the mineralogical and isotopic-geochemical study of U-Pb, Lu-Hf, isotopic systems of zircons from Pobug enderbites, the existence of crustal and juvenile enderbites was established. Negative values of (εNd) and negative values of εHf in zircons from enderbito-gneisses of the Middle Bouh area, Lityn enderbite, and Sabariv enderbite indicate their crustal nature, origin by account of older (Eoarchean?) rocks series, the protolith for which was probably mafic protocrust. The transformation of these rocks occurred pulsatingly 3.6-3.4, 3.0-2.8 and 2.1-1.9 billion years ago. The presence of "typomorphic" zircons in enderbites is also evidence of their crustal nature. Juvenile enderbites 117/79, from the quarry in Tyvriv and 127/79 from the quarry in the village of Holoskove have positive εNd and positive εHf values in zircons, indicating their formation from a juvenile source. They are 2080 and 2070 million years old, respectively. It is believed that it is the juvenile rocks that give increase to the continental crust, which is consistent with the idea that the growth of continents was accompanied by the addition of new sialic material from the mantle. At the same time, rocks that are an addition to the сгust may not differ in composition from older rocks. The available isotopic-geochemical and geological data indicate at least three stages of formation of enderbites (TTG association) within the Pobug granulite belt. The oldest of them is represented by enderbites (enderbito-gneisses) of the Haivoron complex. The next TTG association (Lityn complex, ~2.8 billion years ago) is more widespread, and in general forms a wide "shell" around the protocontinental core, formed by the rocks of the Haivoron complex. The youngest TTG association in the borders of the Pobug granulite belt (Berdychiv complex) is often represented by numerous intrusive bodies of juvenile enderbites, with xenoliths of more ancient rocks.

Metamorphic evolution of mafic granulites from Tiyara area, Makrohar granulite belt, Singrauli district, Madhya Pradesh, India

Metamorphic evolution of mafic granulites from Tiyara area, Makrohar granulite belt, Singrauli district, Madhya Pradesh, India

Rhyacian evolution of high-grade metamorphic rocks of the Porto Nacional Granulite Complex, based on geocronological data U-Pb-Hf in zircon and U- Pb in monazite

The Porto Nacional Complex in the northern portion of the Goiás Massif, in north-central Brazil, represents a Paleoproterozoic/Archean microcontinent reworked in the Neoproterozoic during the Brasiliano Cycle. This NE-SW-trending belt of high-grade metamorphic rocks consists, predominantly, of orthogranulites in addition to aluminous paragneisses that reached high-grade metamorphic conditions in the granulite facies (∼860 °C and 9 kbar). The zircon U–Pb geochronological results obtained on orthogranulite (enderbite) crystal cores yielded an age of 2.16 Ga, however, the crystal borders present lower values (2.09 Ga). These results represent, respectively, the age of igneous crystals of tonalitic protoliths, and high-grade metamorphism. The zircon crystals of another enderbite sample yielded lower values of about 2.09 Ga, reinforcing the interpretation of metamorphic zircons. The U–Pb geochronological results between 2.09 Ga and 2.10 Ga obtained on monazite from the aluminous paragneisses, coincide with the values obtained for enderbite metamorphic zircon crystals, allowing us to define the high-grade metamorphism age and the formation of igneous protoliths in the Rhyacian. This small age difference demonstrates the metamorphism role contemporary to the magmatism of the tonalitic protoliths of the Porto Nacional Complex, related to the Late-Transamazonian orogeny. The Hf-TDMC model ages suggest two crust formation episodes that gave rise to the following rocks: one from the Siderian (2.40–2.48 Ga) and another from the Neo-Mesoarchean (2.52–3.01 Ga). The positive petrogenetic parameters ƐHf(t) (+3.9 to +5.2) evidence a mantle source derivation for the Siderian material, while the negative and positive petrogenetic parameters ƐHf(t) (−4.6 to +3.3) indicate a mixture between crustal and juvenile material for the Neo-Mesoarchean material. These results allow us to disregard the proposed correlation between this high-grade metamorphic terrain with the Porangatu-Talismã Granulitic Belt, which occurs to the south of this region, whose thermo-tectonic evolution is related to the late Neoproterozoic. On the other hand, there are records of several other Rhyacian similar granulitic terrains, such as the granulites of the Bacajá and Tartarugal Grande in the Amazonian Craton, the Itabuna-Salvador-Curaçá Granulitic Belt in the São Francisco Craton, as well as in the Bakhuis Belt, in Suriname, and Limpopo Belt in the West African Craton.

Geochronological and geochemical constraints on the petrogenesis of alkali granites from the Makrohar Granulite Belt: Evidence for Mesoproterozoic extensional regime in the eastern Central Indian Shield

The Chotanagpur Gneissic Complex (CGC) is characterized by the Makrohar Granulite Belt (MGB) at its north‐western margin parallel to Son‐Narmada lineaments. The MGB exhibits a typical association of mantle‐derived mafic tholeiitic and alkaline rocks along with the felsic units. The zircon U–Pb data on the intrusive granite gneiss from this association define a crystallization age of 1,498 ± 38 Ma, representing a widespread Mesoproterozoic within‐plate magmatic event in CGC synchronous with the breakup of the Columbia Supercontinent. These granite gneisses have an alkaline affinity and are metaluminous in character. They exhibit many of the geochemical characteristics of anorogenic (A‐type) magmas, including enrichment of incompatible trace elements, like Zr, Hf, Nb, Y, Ga, and rare earth elements (REE), but low in Ba and Sr as well as high FeOt/(FeOt + MgO) (~0.98) values and Ga/Al (~3.92) ratios. They show less fractionated REE patterns, characterized by relatively enriched LREE and flat HREE with negative Eu anomaly, and have high Zr‐saturation temperatures (~955°C). Considering their field characteristics and all the geochemical and isotopic features, we conclude that they were derived from melting the lower crust metasomatized by mantle‐derived alkali‐rich fluids due to asthenospheric upwelling.

Geoheritage of the Kandalaksha region (Kola Peninsula, White Sea, Arctic Russia), Evaluation, and Geotourism Opportunities

The subarctic Kandalaksha region abounds in many tourist values and is notably characterized by a richness of geology, nature, history, and landscape. Its mountains are located directly on the coast of the White Sea. The skerry-fiord coast is the habitat of many seabirds that nest on its many islands. There is also large mammals such as seals and bears. The coastal area and islands are a reserve within the National Park that was established to protect the breeding areas of the seabirds. Despite its location near the Arctic Circle, the area has a relatively mild climate. Many of the villages and towns in the area have a centuries-old history inextricably linked to the indigenous peoples (Karelians, Sami) who inhabited the area, as well as to the “Pomors,” the first Russian colonizers of the area. On top of this, this is a location with an environment that contains numerous examples of flora and fauna, as well as a geologically and geomorphologically interesting landscape connected with glaciation, abrasion, and isostatic movements. Here, the geological substrate, made up of Paleoproterozoic collisional structures of the Lapland Granulite Belt, was repeatedly tectonically rejuvenated within the forming aulacogen of the White Sea and the Kola-Lapland Mobile Belt, along with numerous Paleozoic intrusions of kimberlite and alkaline rocks. The youngest processes are associated with Pleistocene glaciation and isostatic relaxation in the Holocene. All these features contribute to the high tourist potential of the area. At present, it is being developed in a more or less organized way with the participation of private capital. This article presents a proposal for the systematic development of the area in question and the formalization of tourist routes in the area. This article aims to meet this need by proposing a tourist trail in the Kandalaksha area so as to enable tourists to explore this remarkable area.

Nature and Provenance of Heavy Mineral Distribution at Krishna River Delta, East Coast of India

The present study deals with four sedimentary cores viz. Turumella (120m), Inturu (160m), Ponnapalli (110m) and Nizampatnam (150m) which were recovered from the Krishna delta. Total heavy minerals wt% varies from 0.32 to 7.00 (av. 2.44%) in the study area. The major heavy minerals were noticed in four studied cores i.e. opaques (Ilmenite + magnetite), pyriboles (pyroxenes + amphiboles), garnet, zircon, monazite, rutile and other heavy minerals (epidote, kyanite, tourmaline, etc.). Heavy mineral substance in Krishna river sediments forced by basement rocks, drainage basin and weathering conditions of the river environment. The occurrence of different lithological units in the drainage basins is contributing sediments, mainly opaques (Ilmenite + magnetite) and pyriboles (Amphibole + pyroxenes) from Deccan traps as well as Archean provenance which covered more than 55% of drainage basin. The red garnets (almandine), prismatic sillimanites and rounded zircons are derived from khondalites (metapeletic rocks) and pink garnets, elongated zircons and ortho- pyroxenes are derived from charnockites of Eastern Ghat Granulite Belt (EGGB). The fresh appearance of heavy minerals indicates short residence time in depositional environment without any chemical dissolution effect. The rounded and sub rounded grains of magnetite and ilmenite indicate long distance of transportation and/or reworked nature. The sub angular grains of magnetite and ilmenite indicate that they might have been derived from nearby sources, i.e. mainly an Eastern Ghat Group of rocks. The prismatic characteristic of the sillimanite mineral grains also suggests that their derivation is from khondalitic rocks. Opaques are from Deccan traps as well as Archean provenance. Garnets, sillimanites and zircons are derived from khondalites (metapeletic rocks) and charnockites of Eastern Ghat Granulite Belt.

Neoproterozoic reworking of a Mesoproterozoic magmatic arc from the north-eastern part of the Central Indian Tectonic Zone: Implication for the growth and disintegration of the Indian shield in the Proterozoic supercontinental cycles

Thermotectonic evolution of the rocks of the Central Indian Tectonic Zone (CITZ) is crucial to understand the growth of the Indian shield and its response to the supercontinental cycles of the Earth. In this study we present field, petrology, geochemistry, in-situ U-Pb zircon and Th-U-total Pb monazite dates from a suite of felsic orthogneisses from the least studied Makrohar Granulite Belt (MKGB) of the CITZ. Petrology and geochemical data identify two rock groups: charnockitic orthogneiss (COG) and garnet orthogneiss (GOG). Geochemical fingerprints suggest that the magmatic protoliths of the gneisses are S-type granitoids, formed in a continental arc setting. In situ U-Pb zircon dates yield the time of arc magmatism at ca. 1400–1350 Ma. This is the first report of mid-Mesoproterozoic arc magmatism in the CITZ. These arc granites were subsequently metamorphosed at granulite facies condition that culminated at ∼800–850 °C, 7–7.5 kbar. A prominent gneissic (migmatitic) fabric was formed with garnet ± orthopyroxene + plagioclase + K-feldspar + quartz as peak metamorphic assemblages. After reaching the recorded P-T maxima, the studied rocks followed a decompression and cooling path to 4 kbar and 500 °C. The inferred clockwise P-T path is consistent with reworking of the Mesoproterozoic arc granites in a continent–continent collisional setting. In-situ Th-U-total Pb monazite and in-situ U-Pb ages of zircon overgrowth constrain the age of deformation and metamorphism in the span of ca. 974–913 Ma. In combination with the published information, the results of this study are consistent with the views that (a) the Indian shield participated as a coherent block in the Columbia supercontinent since ca. 1450 Ma (or before), (b) the ca. 1400–1350 Ma arc magmatism is presumably linked to collapse or closure of a basin (either north or south of the MKGB) in the CITZ in response to the prolonged accretionary phase of the Columbia supercontinent and (c) during the assembly of the Rodinia supercontinent, localized dismembered fragments of the Columbia got re-amalgamated during late Mesoproterozoic to early Neoproterozoic. Archean cratons got fused along the Proterozoic mobile belts (such as Central Indian Tectonic Zone, Eastern Ghats Mobile Belt). Different units within these mobile belts also experienced local compression during this time frame of the Grenvillian orogeny in the Indian subcontinent.

Carbon and oxygen isotope analysis of CO2 trapped in silicate minerals

Knowledge of the carbon and oxygen isotope composition of CO2-rich inclusions in crust- or mantle-derived minerals is crucial for a more quantitative understanding of cycling of volatiles between Earth's deep and surficial reservoirs. In this study, we present a crushing method for analysis of combined carbon and oxygen stable isotope compositions of small (≤ nmole) amounts of CO2 in fluid and melt inclusions. During crushing, the released CO2 was cryo-trapped, and subsequently introduced into a Gas Bench II coupled to a Deltaplus Isotope Ratio Mass Spectrometry (IRMS). Reference standard CO2 introduced in the crusher chamber was analysed to a precision better than ~0.3 and ~ 0.4‰ (1σ) for carbon and oxygen, respectively. Analysis of previously analysed samples validates that the crushing technique can be applied to CO2-rich fluid inclusions in quartz samples as small as 0.2 to 5 mg. CO2 –rich quartz samples were analysed from the UHT-Bakhuis Granulite Belt (Suriname) and Val Nalps (Switzerland) as well as forsterite-rich olivine-hosted melt inclusions from Vulsini volcanic district (Italy). The carbon isotope compositions obtained from the quartz samples allow discrimination between different sources within the crust and mantle. In contrast, the oxygen isotopic signatures of the fluid inclusions containing water appear affected by isotopic exchange between CO2 and H2O in the inclusions, where for the free-water fluid inclusions can reflect the pristine δ18O value. Crushing of olivine grains with CO2 melt-inclusions displayed instantaneous adsorption of the released CO2, which leads to low CO2 yields, and considerable oxygen and carbon isotope fractionation, hampering reliable isotopic determinations. We conclude that the δ13C and δ18O values from CO2-rich inclusions can be used as an indicator of the CO2 source and to evaluate mantle CO2 outgassing and release from storages within Earth's crust. The method presented can be readily applied to determine carbon and oxygen isotopic compositions of CO2 (4.5−10 mol) in small amounts of fluid-inclusion bearing quartz.

What happened to the Early Precambrian granulite complexes of the Bug region (Ukrainian shield) and the Limpopo belt (South Africa) and how to stratify them? A tectonist’s view

The author reviews two alternative approaches (stratigenic-metamorphogenic and deformation-metamorphogenic) to the geology and mapping of the Earth’s oldest crust rocks that were metamorphized in РТ-conditions of the granulite facies, on the examples of two granulite belts — the Bug area complex (Ukrainian shield) and Limpopo belt (Southern Africa).
 There was shown a fairly good correlation of the composition and metamorphism (including the dynamometamorphism) of the rock complexes of both belts and their at least three-stage origin and transformation. The granulitic metamorphism processes within both belts happened before 3,0 b.y.a., 2,6—2,8, and c. 2,0 b.y.a. The structural-metamorphic transformations of the granulitic complexes, formation of their new structural plans with the destruction of the former (archean) by the following (proterozoan) do not allow falsifiably stratifying the archean granulitic complexes within the stratigenic-metamorphogenic approach already at the facies level. For the Bug area granulitic belt it is feasible only to isolate the Dniester-Bug and Bug series. Two of the important processes of the belt development are rock deformation in the compression and slip conditions and formation within the granulitic complexes of the sub-vertically-layered medium, slip folds with sub-vertical folds’ joints and wings. In both belts these processes began in the Neoarchean. This shows that in that time the tectonic processes were already to some significant degree propelled by plate tectonics mechanisms. Both belts had in common the formation of the linear-typeshearzonesat micro- to macroscale and their superimposition onto the deformation structures of the granulitic complexes of the preceding developmental stages. On their basis there formed the internal structure of the belts’ and their interconnections with the adjacent blocks of crust. Presumably, the archean charnokitoids and TTG-granitoids form the same structural layer of the crust, given their geochemical similarity and close age, and this layer is the base for the greenstone belts. The mineral composition, РТ-metamorphism conditions and age of granulitic belt rocks based on their U-Pb, Lu-Hf, Sm-Nd isotope systems compositions andoxygen isotope composition in Zirconium grains suggest that in the eo- and paleoarchean mantle and crust there should have already been amassed large quantities of medium-acidic matter which gave rise to the TTG complexes.

Metamorphism of the Korvatundra Structure of the Lapland–Kola Orogen (Arctic Zone of the Fennoscandian Shield)

AbstractWe study the P–T conditions and age of metamorphic evolution of the rocks that make up the Korvatundra structure in the northeast of the Fennoscandian Shield. The rocks underwent progressive metamorphism of the amphibolite facies at 625–660 ºC and 8.7–8.8 kbar 1945 ± 34 Ma (Sm–Nd data). The pegmatite cutting the metamorphic paragenesis that formed at this stage has an age of 1917 ± 6 Ma (zircon U–Pb data). Metamorphic transformations after 1917 Ma are manifested locally as discrete zones of blastomylonites in the rocks of the northern part and some inner sites of the Korvatundra structure. Both local increases and decreases in temperature and pressure are possible in these zones. The formation of light titanite with an age of 1863 ± 44 Ma marks the next stage of shear strain. Low-temperature alterations (chloritization and silicification) took place in the zones of final deformations 1722 ± 5 Ma (Rb–Sr data). Beginning from 1.94 Ga, the general deformational and metamorphic history of the Korvatundra structure, Lapland Granulite Belt, and Tana Belt confirms the assumption of the formation of a single inverted metamorphic zoning within the Korvatundra structure and the overlying Lapland–Kolvitsa Collision Belt in the Paleoproterozoic. The obtained data supplement the idea of the Paleoproterozoic geodynamic evolution of the Lapland–Kola orogen.

Neoarchean–Paleoproterozoic HP-HT metamorphism in the Bhopalpatnam granulite belt, Bastar Craton (India): Insights from phase equilibria modelling and monazite geochronology

The Bhopalpatnam Granulite Belt (BGB), located within the southwestern part of the Bastar Craton (India), is composed of granite gneisses with numerous enclaves of high-grade rocks, including quartzofeldspathic gneisses, orthopyroxene-free mafic granulite, and garnetiferous two-pyroxene granulite. In addition, the marginal parts of the belt preserve patches of garnetiferous psammo-pelitic gneisses. New petrographic, metamorphic (conventional and phase equilibria modelling) and monazite geochronological investigations of these high-grade rocks constrain the conditions and timing of granulite-facies metamorphism and enable to demonstrate the tectonometamorphic history of the BGB. The garnet-bearing psammo-pelitic gneisses underwent medium pressure-high temperature (MP-HT) and retrograde metamorphism at P-T conditions of 9.4 ± 1.0 kbar/797 ± 39 °C and 5.1 ± 1.1 kbar/697 ± 69 °C, respectively. The quartzofeldspathic gneisses experienced high pressure-high temperature metamorphism (HP-HT; 12.0 ± 0.9 kbar/785 ± 48 °C), followed by retrogressive cooling at 10.6 ± 0.8 kbar/683 ± 42 °C. The orthopyroxene-free mafic granulites and two-pyroxene granulites witnessed HP-HT metamorphism at 11.0 ± 0.8 kbar/827 ± 45 °C, followed by MP-HT metamorphism at 8.4 ± 0.9 kbar/803 ± 66 °C and retrograde cooling at 5.7 ± 1.5 kbar/555 ± 80 °C. The U–Th–total Pb dating of monazites from the quartzofeldspathic gneiss yielded peak (HP-HT) metamorphic age at 2588–2461 Ma, MP-HT metamorphism at 2499–2308 Ma, and thermal events associated with granite magmatism at 2292–2111 Ma. Based on similar clockwise P–T history and Late Archean-Early Mesoproterozoic tectonothermal events, we suggest that the Bhopalpatnam and Karimnagar granulite belts evolved coherently until the Mesoproterozoic time and eventually rifted apart during the development of the Pranhita-Godavari rift basin between ∼ 1.6–1.4 Ga. The HP-HT and MP-HT granulite-facies metamorphic episodes identified in the BGB are correlated with the continent–continent collision between Bastar and eastern Dharwar cratons.

Geochemical systematics and U–Pb zircon age of the Vulvara anorthosite massif, Lapland granulite belt, Baltic shield: magmatic sources and metamorphic alteration of the rocks

ABSTRACT The Vulvara anorthosites occur among the rocks of intermediate composition, in contrast to most Lapland granulite belt (LGB) anorthosites, associated with mafic granulites. The U-Pb, Sm-Nd and REE geochemical data were used to compare Vulvara with other LGB anorthosites. The intrusion of the Vulvara massif occurred in the interval of 2100–1965 Ma. The first metamorphic processing took place 1947 ± 11 Ma ago under granulite facies. Postgranulite transformations occurred 1900–1850 Ma ago under amphibolite facies; earlier (1896 ± 15 Ma) and later (1852 ± 17 Ma, 1846 ± 16 Ma) thermal events were established. The Vulvara anorthosites, in comparison with other LGB anorthosites, are distinguished by a more acidic composition of plagioclase, a higher F number of rocks and mafic minerals, a higher content of SiO2, Na2O, K2O, Ba, Sr, Zr, Nb, Rb, and a lower content of CaO. The Sm-Nd and REE geochemistry suggest that there are three groups of LGB anorthosites, distinguished both by age and magma source.

Petrology and crustal evolution of the Tartarugal Grande Granulitic Complex - Northeastern Amazonian Craton

The Tartarugal Grande Complex (TGC) is an association of high-grade metamorphic rocks with Archean and Paleoproterozoic protoliths, located at the border of the Archean Amapá and Rhyacian Lourenço domains, in southeastern Guiana Shield, northeast of the Amazonian Craton. It consists of felsic granulites, and aluminous leucogneisses and rare mafic granulites. Both granulites and gneisses are affected by thrust and transcurrent shear zones along NW-SE trend. Migmatization with quartz-feldspathic neosomes, with or without orthopyroxene, and garnet-rich neosomes are present in felsic granulites and leucogneisses, respectively. The gneisses have high silica contents and are peraluminous due to the presence of biotite, garnet, and cordierite, indicating the derivation from metasedimentary sequences. The felsic granulites have medium to high silica content and geochemical signature of calc-alkaline magmatic arc series. The mafic granulites are small bodies embedded in the felsic granulites and leucogneisses. They display geochemical affinities with tholeiitic series and represent ancient diabase dykes. The metamorphic paragenesis in the granulite facies is represented by Pl-antiperhtite + Qtz + Mc-mesoperthite + Opx + Cpx + Bt ± Hbl (enderbitic granulite), Pl-antiperhtite + Qtz + Mc-mesoperthite + Opx ± Bt (charnoenderbitic granulite); Mc-mesoperthite + Qtz + Pl + Opx + Bt (charnockitic granulite), Pl (An60)+Opx + Cpx ± Hbl ± Grt (mafic granulite), and Qtz + Mc + Pl ± Bt ± Grt ± Crd (leucogneiss). The presence of orthopyroxene, clinopyroxene and hornblende in equilibrium in the granulites allows estimating temperatures at 800° ± 20 °C. In addition, non-extensive anatexis under anhydrous conditions produced charnockitic neosomes in the granulites and garnet-bearing leucogranite neossomes in the paragneisses. The presence of cordierite in leucogneisses indicates low-medium pressure conditions around 6–7 kbar. The partial or total replacement of pyroxenes by hornblende and/or biotite, garnet by biotite, clinopyroxene by titanite, and myrmekite intergrowths, indicate retrometamorphism and cooling during exhumation to higher crustal levels. The U–Pb LA-ICP-MS dating on zircon from a charnoenderbitic granulite yielded an age of 2082 ± 5 Ma for the crystallization of the igneous protolith of the granulites. Metamorphic zircons from an enderbitic granulite yielded a U–Pb LA-ICP-MS age of 2045 ± 14 Ma, which corresponds to the high-grade metamorphic episode that has affected the region at the end of the Rhyacian. The age of the protoliths is not constrained but 207Pb/206Pb dates at 2.57–2.70 Ga indicated inherited crystals and/or xenocrystals from Archean source. In agreement with previous works, we conclude that the TGC consists of calcium-alkaline magmatic rocks and pelitic sedimentary sequences formed during the development of a Rhyacian magmatic arc at the edge of the Archean Amapá Block. This was followed by a thermo-tectonic event at the end of Rhyacian, around 2.05 Ga, under high-grade conditions reaching the granulite facies, with restricted anatexis. Records of the tectonic exhumation of these terranes were defined by partial disequilibrium of some mineral phases in amphibolite facies. This Late-Rhyacian thermo-tectonic event is contemporaneous to the ultra-high temperature metamorphism (2.09–2.03 Ga) of the Bakhuis Granulite Belt in Suriname. The thermal differences between these two high-grade metamorphic terrenes may be related to the different crustal levels where they settled. Late-Rhyacian asthenospheric upwelling by crustal stretching during oblique continental collision seems to be the more plausible scenario as previously proposed, even if a slab break-off scenario cannot be ruled out.

Neoarchaean and Proterozoic crustal growth and reworking in the Western Bastar Craton, Central India: Constraints from zircon, monazite geochronology and whole-rock geochemistry

The Bastar Craton is one of the oldest cratonic nuclei of the Indian shield, comprising Paleoarchean to Mesoproterozoic crust that preserves the record of protracted crustal evolution and metallogeny. This study describes whole-rock geochemistry, U-Th-Pb ages of zircon and monazite from Neoarchean TTGs, sanukitoids, and Paleo- to Mesoproterozoic granites, and Sm-Nd isotope data from mafic enclave within TTGs of the Western Bastar Craton (WBC). The TTGs and sanukitoids represent Neoarchean crust formed by collision-accretion processes. The TTGs are of two types: low-HREE and high-HREE with both groups derived from low-K mafic sources. The sanukitoids have moderate SiO2 (55.1–65.1 wt%, average = 61.7 wt%), Mg# (20–36, average = 24.7), Ni (10–40 ppm; average = 14 ppm), Sr (339–528; average = 418 ppm) and moderate to high concentrations of incompatible elements like Rb (26–112 ppm, average = 48), Ba (482–2300 ppm, average = 1542), Zr (69–593 ppm, average = 334 ppm), Nb (3.8–14.8 ppm, average = 8.7 ppm), Y (13.2–24.5 ppm, average = 19.5 ppm), and REE (91–301 ppm, average = 212)]. They post-date TTG emplacement and formed by mixing between metabasalt-derived and mantle wedge-derived melts in an arc environment. The Mul granite represents a younger Paleo- to Mesoproterozoic suite of granites that was derived by reworking of pre-existing crust. U–Pb ages of zircon constraints the TTG magmatism to 2544–2496 Ma, while Nd-model ages (3259–3142 Ma) of mafic enclaves within the TTG suggest the presence of Paleoarchean crust in the WBC.Zircon and monazite ages indicate that the emplacement of the Mul granite was synchronous with 1666–1547 Ma regional tectonothermal event. These granites were produced by reworking of older granitoid crust. The Neoarchean TTGs/sanukitoids were affected by 1666–1547 Ma tectonothermal event which constitutes a widely documented Paleo- to Mesoproterozoic orogeny in the Central Indian Tectonic Zone and Bhopalpatnam granulite belt to the south of the WBC. Copper and gold mineralization in the Thanewasna belt along the craton's western margin is linked to this tectono-magmatic event. In the global supercontinent outlook, the WBC preserves the imprints of Neoarchean events related to the Ur supercontinent as well as Paleo-Mesoproterozoic and Neoproterozoic (Grenville-age) events associated with the Columbia and Rodinia supercontinent