Gneiss Complex Research Articles

Field Investigation with their Textural Relationship of the Metapelites around Gopinathpur, East Singhbhum, India

ABSTRACT Proterozoic mobile belts are considered as fringing region of the Archaean-Proterozoic cratons and preserve the best evidence of sedimentation, magmatism, deformation, and metamorphism depending on the type of tectonic settings. The North Singhbhum Mobile Belt (NSMB) is a north-dipping ductile shear zone of Proterozoic age distinguished by multiple folded, low to mediumgrade metapelites and meta-igneous rocks sandwiched between the Archaean Singhbhum Craton in the South, and the Palaeo-Neo Proterozoic Chotanagpur Gneissic Complex (CGC) in the north. Since NSMB consists of a thick sequence of sediments that were deposited from Paleoproterozoic to Mesoproterozoic, it is therefore important for determining the syn- and post-orogenic processes to decode the time-space tectono-metamorphic history of this mobile belt. Field observations indicate the presence of an anticlinorium with an east-west trending fold axis, where rocks from greenschist facies (chlorite-biotite-garnet-schist) are commonly found at the limb, transitioning to amphibolite facies towards (garnet-staurolite-sillimanite gneiss) the hinge zone. Textural studies demonstrate the alignment of micaceous minerals that create the S1 schistosity plane overprinted by S2 crenulation cleavage in the chlorite-schist and mica-schist. The garnet and staurolite porphyroblast exhibit syn- to posttectonic growth, suggesting static growth conditions during the waning phase of metamorphism. Studies pertaining to mineral assemblages further imply that fibrolite formation is more favorable during the primary stages of metamorphism (M1) associated with D1 deformation.

Petrochronology and geochemistry of migmatites from the Assam-Meghalaya gneissic complex (NE India): Implications for the crustal anatexis and reworking during Gondwana assembly

Petrochronology and geochemistry of migmatites from the Assam-Meghalaya gneissic complex (NE India): Implications for the crustal anatexis and reworking during Gondwana assembly

Mineral Chemistry and Petrochronology of Zircon from Dudhi Group, Northwestern Chhotanagpur Granite Gneiss Complex, India

ABSTRACT The study analyzes zircons in granites and uraniferous pegmatoid leucosome mobilizates in the Dudhi Group in the northwestern part of the Chhotanagpur Granite Gneiss Complex (CGGC) of Sonbhadra District. The results show that the granites are strongly evolved with low Zr/Hf values and high Hf contents. The Dubha granite and all pegmatoid leucosomes are moderately evolved, with Zr/Hf values between 55 and 25. The Riebeckite granite of Jaurahi exhibits theoretical fractionation, while the Dubha granite doesn’t show fractionation. The study also finds that the Riebeckite granite, Barhaur granite, Dubha granites, and uraniferous pegmatoid leucosomes have inherited zircons with high and fluctuating M values and highly anomalous Zr. The granites and uraniferous pegmatoid leucosomes have formed at high temperature and high-pressure conditions. The study also shows that the chemical ages of the granites and uraniferous pegmatoid leucosomes of the Dudhi Group show chemical age peaks at 3485 Ma, 2974 Ma, 2680 Ma, 2634 Ma, 2509 Ma, 2365Ma, 2250Ma, 2147 Ma, ~1850 Ma, ~1650 Ma, 1000-800 Ma, 200-600 Ma, corresponding to magmatic cores, orogenies, metamorphism, and deformation and supercontinents building and breakups i.e. Sclavia, Ur, Nuna-Columbia to Rodinia, and Pangea-Amasia.

Ultrahigh-temperature granulites from the Shillong-Meghalaya Gneissic Complex, NE India: Implications for the Indo-Antarctic Correlation

Ultrahigh-temperature granulites from the Shillong-Meghalaya Gneissic Complex, NE India: Implications for the Indo-Antarctic Correlation

Compositional and Numerical Geomorphology Along a Basement–Foreland Transition, SE Germany, with Special Reference to Landscape-Forming Indices and Parameters in Genetic and Applied Terrain Analyses

The Münchberg Gneiss Complex (Central European Variscides, Germany) is separated by a deep-seated lineamentary fault zone, the Franconian Lineamentary Fault Zone, from its Mesozoic foreland. The study area offers insight into a great variety of landforms created by fluvial and mass wasting processes together with their bedrocks, covering the full range from unmetamorphosed sediments to high-grade regionally metamorphic rocks. It renders the region an ideal place to conduct a study of compositional and numerical geomorphology and their landscape-forming indices and parameters. The landforms under consideration are sculpted out of the bedrocks (erosional landforms) and overlain by depositional landforms which are discussed by means of numerical landform indices (LFIs), all of which are coined for the first time in the current paper. They are designed to be suitable for applied geosciences such as extractive/economic geology as well as environmental geology. The erosional landform series are subdivided into three categories: (1) The landscape roughness indices, e.g., VeSival (vertical sinuosity—valley of landform series) and the VaSlAnalti (variation in slope angle altitude), which are used for a first order classification of landscapes into relief generations. The second order classification LFIs are devoted to the material properties of the landforms’ bedrocks, such as the rock strength (VeSilith) and the bedrock anisotropy (VaSlAnnorm). The third order scheme describes the hydrography as to its vertical changes by the inclination of the talweg and the different types of knickpoints (IncTallith/grad) and horizontal sinuosity (HoSilith/grad). The study area is subjected to a tripartite zonation into the headwater zone, synonymous with the paleoplain which undergoes some dissection at its edge, the step-fault plain representative of the track zone which undergoes widespread fluvial piracy, and the foreland plains which act as an intermediate sedimentary trap named the deposition zone. The area can be described in space and time with these landform indices reflecting fluvial and mass wasting processes operative in four different stages (around 17 Ma, 6 to 4 Ma, <1.7 Ma, and <0.4 Ma). The various groups of LFIs are a function of landscape maturity (pre-mature, mature, and super-mature). The depositional landforms are numerically defined in the same way and only differ from each other by their subscripts. Their set of LFIs is a mirror image of the composition of depositional landforms in relation to their grain size. The leading part of the acronym, such as QuantSanheav and QuantGravlith, refers to the process of quantification, the second part to the grain size, such as sand and gravel, and the subscript to the material, such as heavy minerals or lithological fragments. The three numerical indices applicable to depositional landforms are a direct measurement of the hydrodynamic and gravity-driven conditions of the fluvial and mass wasting processes using granulometry, grain morphology, and situmetry (clast orientation). Together with the previous compositional indices, the latter directly translate into the provenance analysis which can be used for environmental analyses and as a tool for mineral exploration. It creates a network between numerical geomorphology, geomorphometry, and the E&E issue disciplines (economic/extractive geology vs. environmental geology). The linguistics of the LFIs adopted in this publication are designed so as to be open for individual amendments by the reader. An easy adaptation to different landform suites worldwide, irrespective of their climatic conditions, geodynamic setting, and age of formation, is feasible due to the use of a software and a database available on a global basis.

Geochemistry and petrogenesis of Mesoproterozoic mafic granulite and amphibolite dykes from Saltora, Bankura district, Chhotanagpur Gneissic Complex, eastern India: Implications for their emplacement in within-plate setting

Geochemistry and petrogenesis of Mesoproterozoic mafic granulite and amphibolite dykes from Saltora, Bankura district, Chhotanagpur Gneissic Complex, eastern India: Implications for their emplacement in within-plate setting

Petrogenesis of the Jaisamand sanukitoids and associated TTGs: Constraints on the Neoarchean tectonic evolution of the southern Aravalli-Banded Gneissic Complex, northwest India

Petrogenesis of the Jaisamand sanukitoids and associated TTGs: Constraints on the Neoarchean tectonic evolution of the southern Aravalli-Banded Gneissic Complex, northwest India

Geochemistry of serpentinites from the central portion of the Rio Piranhas-Seridó Domain, Borborema Province, Northeastern Brazil: Implications for genesis and geotectonic environment

Serpentinites from the central portion of the Rio Piranhas-Seridó Domain (RPSD), in the northeast portion of the Borborema Province (BP), occur in association with the Caicó Complex gneisses, paragnaisses/schists of the Seridó Group. Serpentinites, which were sampled in two localities near the city of São Tomé-RN, are melanocratic rocks, fine-grained, greenish in color and foliation consistent with the regional trend. The mineralogical composition is primarily composed of serpentine, which occurs as a replacement for the iron and magnesium minerals of the protolith, with chlorite, muscovite, tremolite, calcite-dolomite, quartz, and opaque minerals as accessory phases. Chemical analyzes show SiO2 values ranging from 35.72 to 43.48%, MgO> 28.88%, Fe2O3 between 7.08 and 11.29%, Al2O3 < 3.42% and very low TiO2, CaO, K2O and Na2O, suggesting an ultrabasic composition. Graphs obtained with the major elements ratios indicate olivine as the primary mineral, and despite the influence of metamorphic processes, the rock still retains the chemistry predominant in the protolith. The high magnesium content points to a komatiitic signature, implying in high temperature, high pressure and high degree of partial melting in the protolith genesis. Data acquired in this study corroborate the bibliography and suggest a compatible scenario for the studied serpentinites to be part of a greenstone belt.

Petrogenesis of Late Stenian Syn-Orogenic A-Type Granites in the Chhotanagpur Gneissic Complex and Eastern Indian Shield

We report the petrogenesis of arfvedsonite granites from the Dimra Pahar pluton in the Chhotanagpur Gneissic Complex based on petrology, whole-rock chemistry, mineral chemistry, and La-ICP-MS zircon U-Pb ages and Hf-Lu isotopic analyses. These granites are dominantly peralkaline, occasionally peraluminous, and demonstrate features of A1-type granites. The magma was emplaced at a shallow depth and had a high liquidus temperature, fO2 (>NNO), and water saturation. The zircons exhibit three distinct U-Pb isotopic ages. The oldest (1324 ± 6 Ma), large-sized inherited zircons (εHf(t) = +1.65 to +7.64), show complex zoning and signs of partial resorption. The euhedral, prismatic-bipyramidal zircons displaying oscillatory zoning (εHf(t) = −3.43 to +1.43) reveal a crystallization age of 1046 ± 7 Ma. Their thin periphery (εHf(t) = −3.23 to +0.27) grew during retrograde metamorphism (995 ± 6 Ma). The whole-rock geochemistry and the Hf-isotope values imply that the parental magma of these granites resulted from the anatexis of metasomatized lithospheric mantle sources. These granites intruded in a syn-orogenic (syn-collisional exhumation) stage of the orogeny.

The South Purulia Shear Zone, eastern India: Its anatomy and implication for timing the Rodinia-age collision in the eastern part of the Central Indian Tectonic Zone

Abstract The Proterozoic Central Indian Tectonic Zone (CITZ) is an ~1500-km-long collision zone between the North India and the South India blocks. The age of collision is debated, but constraining the age of collision is crucial for reconstructing the paleogeographic position of India in the Precambrian. In this study, mesoscale structures, metamorphic pressure-temperature path, U-Pb zircon dates, and monazite chemical dates are combined to constrain the collision age. In the eastern part of the CITZ, the North Singhbhum Mobile Belt (NSMB) comprising 1.5–1.3 Ga low-grade phyllites and schists and the 1.88 Ga Ranibandh granitoid are juxtaposed with the Chottanagpur Gneiss Complex (CGC; eastern CITZ) dominated by 1.76 Ga anatectic basement gneisses intruded by 1.67 Ga, 1.57 Ga, and pre-collisional 1.02 Ga felsic intrusives. The juxtaposition of the disparately evolved crustal domains along the South Purulia Shear Zone (SPSZ) involved top-to-the-south thrusting consistent with amphibolite facies loading. Continued oblique N-S shortening of the thickened crust led to nucleation of ESE-striking, steeply dipping left-lateral transpressional shear zones tens of kilometers wide that obliterated pre-collisional structures in the rheologically weak NSMB phyllites and schists but are weakly developed in the rheologically strong CGC rocks. The 1.02–0.91 Ga oblique collision between the North India and South India blocks along the SPSZ suggests the paleopole data pre-dating the collision are unlikely to ascertain the paleogeographic position of the Indian landmass because the landmass did not exist in its entirety before 1.02–0.91 Ga. But the paleopole data may help locate the North India and South India blocks independent of each other.

Remote sensing and magnetic characterization of the Au mineralization and its structural implications: Meatiq dome, Eastern Desert, Egypt

Remote sensing and magnetic characterization of the Au mineralization and its structural implications: Meatiq dome, Eastern Desert, Egypt

The Relationships between the Internal Nappe Zone and the Regional Mylonitic Complex in the NE Variscan Sardinia (Italy): Insight from a New Possible Regional Interpretation?

This study presents an updated interpretation of geological data collected between 1984 and 2022. The area under consideration holds significant regional importance as it is located between the Internal Nappe Zone (INZ) and the Regional Mylonitic Complex (RMC). Re-evaluation of the geological data has highlighted a more intricate structural framework than what is currently documented in the existing literature. This paper aims to illustrate, through structural analysis, that the Posada Valley Shear Zone (PVSZ) does not serve as the transitional boundary between the Inner Nappe Zone and the Regional Mylonitic Complex or High-Grade Metamorphic Complex (HGMC) as traditionally thought. Instead, the authors’ findings indicate that the transition boundary is confined to a shear band with a variable thickness ranging from 10 to 70 m at its widest points. The development of the Posada Valley Shear Zone is characterized by a series of transitions from mylonite I S-C to mylonite II S-C, extending over approximately 5 km. The formation of the Posada Valley Shear Zone is chronologically confined between the development of the East Variscan Shear Zone (EVSZ) and the emplacement of the Late Variscan granites. The differing orientations of Sm and S3 observed in the mylonitic events of the Posada Valley Shear Zone and the Regional Mylonitic Complex, respectively, are likely attributable to an anticlockwise rotation of the shortening directions during the upper Carboniferous period. Furthermore, this study proposes that the Condensed Isogrades Zone (CIZ), despite its unclear formation mechanism, should be recognized as the true transition zone between the Inner Nappe Zone and the Regional Mylonitic Complex or High-Grade Metamorphic Complex. This new interpretation challenges the previously accepted notion of increasing Variscan metamorphic zonation toward the northeast. This conclusion is supported by the identification of the same NE–SW orientation of the D2 tectonic event in both the Old Gneiss Complex (OGC in the Regional Mylonitic Complex) and the lithologies of the Inner Nappe Zone and the Condensed Isogrades Zone. The comprehensive analysis and new insights provided in this paper contribute to a refined understanding of the geological relationships and processes within this region, offering significant implications for future geological studies and interpretations.

Zircon geochemistry from early evolved terranes records coeval stagnant- and mobile-lid tectonic regimes

Determining the mechanisms by which the earliest continental crust was generated and reworked is important for constraining the evolution of Earth's geodynamic, surface, and atmospheric conditions. However, the details of early plate tectonic settings often remain obscured by the intervening ~4 Ga of crustal recycling. Covariations of U, Nb, Sc, and Yb in zircon have been shown to faithfully reflect Phanerozoic whole-rock-based plate-tectonic discriminators and are therefore useful in distinguishing zircons crystallized in ridge, plume, and arc-like environments, both in the present and in deep time. However, application of these proxies to deciphering tectonic settings on the early Earth has thus far been limited to select portions of the detrital zircon record. Here, we present in situ trace-element and oxygen isotope compositions for magmatic zircons from crystalline crustal rocks of the Acasta Gneiss Complex and the Saglek-Hebron Complex, Canada. Integrated with information from whole-rock geochemistry and zircon U-Pb, Hf, and O isotopes, our zircon U-Nb-Sc-Yb results reveal that melting of hydrated basalt was not restricted to a single tectonomagmatic process during the Archean but was operative during the reworking of Hadean protocrust and the generation of juvenile crust within two cratons, as early as 3.9 Ga. We observe zircon trace-element compositions indicative of hydrous melting in settings that otherwise host seemingly differing whole-rock geochemistry, zircon Hf, and zircon O isotopes, suggesting contemporaneous operation of stagnant-lid (oceanic plateau) and mobile-lid (arc-like) regimes in the early Archean.

Petrogenesis of magmatic charnockite-biotite granite suite from parts of the Chotanagpur Granite Gneissic Complex (CGGC), eastern Indian shield: Implication for the break down of the Columbia Supercontinent

Petrogenesis of magmatic charnockite-biotite granite suite from parts of the Chotanagpur Granite Gneissic Complex (CGGC), eastern Indian shield: Implication for the break down of the Columbia Supercontinent

Evidence of back-folding in the Beas Valley puts Himalayan tectonic models on trial

Evidence of back-folding in the Beas Valley puts Himalayan tectonic models on trial

Abiotic synthesis of graphitic carbons in the Eoarchean Saglek-Hebron metasedimentary rocks

Graphite in metasedimentary rocks of the Eoarchean Saglek-Hebron Gneiss Complex (Canada) is depleted in 13C and has been interpreted as one of the oldest traces of life on Earth. The variation in crystallinity of this oldest graphitic carbon could possibly confirm the effect of metamorphism on original biomass, but this is still unexplored. Here, we report specific mineral associations with graphitic carbons that also have a range of crystallinity in the Saglek-Hebron metasedimentary rocks. Petrographic, geochemical and spectroscopic analyses in the Saglek-Hebron banded iron formations suggest that poorly crystalline graphite is likely deposited from C-H-O fluids derived from thermal decomposition of syngenetic organic matter, which is preserved as crystalline graphite during prograde metamorphism. In comparison, in the Saglek-Hebron marble, disseminations of graphite co-occur with carbonate and magnetite disseminations, pointing to abiotic synthesis of graphitic carbons via decarbonation. Our results thus highlight that variably crystalline graphitic carbons in the Saglek-Hebron metasedimentary rocks are potential abiotic products on early Earth, which lay the groundwork for identifying the preservation of prebiotic organic matter through metamorphism on Earth and beyond.

The significance of Paleoarchean granitoids from the Saglek Block, Labrador, Canada

The Saglek Block in the Nain Province of northeast Canada is part of the North Atlantic Craton. It comprises Archean gneisses that record magmatic and metamorphic ages between ca. 3.9 and 2.5 Ga. In this study, a grey banded gneiss from Maidmonts Island records an age of 3.72 Ga, which is equated with Uivak I gneisses reported from across the Saglek Block, and contains 3.8 Ga xenocrysts. These rocks were deformed and metamorphosed prior to the intrusion of augen gneiss protoliths on both Maidmonts and Mentzel islands that record U-Pb zircon ages of 3.33 Ga. These rocks are composed of ferroan calc-alkaline granite and granodiorite and were likely generated by partial melting of pre-existing quartzo-feldspathic crust, as attested by the presence of ca. 3.8 Ga xenocrysts. Such augen gneiss was previously classified as ca. 3.6 Ga ‘Uivak II gneiss’, a term we argue should now be abandoned. The final magmatic events recorded on Maidmonts and Mentzel islands took place in the Neoproterozoic with the emplacement of granitic stocks at ca. 2.72 Ga, and sills and dykes at ca. 2.57 Ga. This sequence of magmatic events from the Eoarchean to Neoarchean is very similar to that recorded in the Itsaq Gneiss Complex of southwest Greenland, where, based on the Hf signature, it has been suggested that a change in tectonic environment resulted from the initiation of subduction at ca. 3.2 Ga. Although Lu-Hf and Sm-Nd isotopic signatures from the ca. 3.33 Ga gneisses have been interpreted in the literature as due to partial melting of Hadean mafic crust, alternatively, they can be generated by partial melting of Eoarchean continental crust in a continental arc setting. We argue this is more consistent with the non-TTG geochemistry of the augen gneisses.

The Kharbei Amphibolite–Gneiss Complex (Polar Urals): P–T Evolution and Results of U–Pb LA-ICP-MS Isotopic Study of Metamorphic Zircon

The Kharbei Amphibolite–Gneiss Complex (Polar Urals): P–T Evolution and Results of U–Pb LA-ICP-MS Isotopic Study of Metamorphic Zircon

The Ottawa River Gneiss Complex revisited: definition of the metamorphic core and detachment zone of a large Grenvillian metamorphic core complex

Using new and published data, we synthesize the tectonic evolution of the Ottawa River Gneiss Complex (ORGC), the metamorphic core and detachment zone of a large mid- to late-Ottawan metamorphic core complex in the western Grenville Province. Field and petrologic data indicative of retrogression and exhumation, combined with maps and schematic crustal-scale sections, are used to document spatial and temporal relationships of multi-scale structures developed during its formation, of which the largest, termed mega-cross-folds and megaboudins, occur within and define the detachment zone. Mega-cross-folds, orogen-normal structures up to 70 km in length with coaxial constrictional fabrics in their hinge-lines, formed in a single phase of deformation during retrogression and exhumation. A cluster of asymmetric megaboudins, individually from 10–50 km long with granulite-facies cores and high-strain amphibolite-facies rims, similarly formed during syntectonic retrogression and exhumation of granulite-facies precursors. We argue the mega-cross-folds developed in a regime of regional transtension, whereas the megaboudin cluster formed by extensional inversion of an anastomosing early-Ottawan thrust system, with the strain patterns of both suggesting the detachment zone was the site of intense ductile flow between the stronger metamorphic core and cover. Comparison of these results with generic numerical models of extensional collapse of overthickened continental crust suggests the first-order tectonometamorphic features of the ORGC developed during necking of the upper crust and associated large-scale extensional flow of the mid and lower crust into the domiform necked region during collapse of the early-Ottawan thrust stack.

Granitoids of the western Himalaya and Karakoram as potential geothermal reservoirs – A petrological, geochemical and petrophysical study

Hot springs in various granitoid and gneissic complexes in northern Pakistan indicate elevated geothermal gradients, which warrants their evaluation for geothermal applications. Evaluation of such prospects requires extensive knowledge of rock properties and their interaction with reservoir fluids. Our contribution provides first-order information on petrophysical, geochemical, and petrographic descriptions derived from outcrop analogs. About seventy samples of (mostly) granitoids and gneisses from the Nanga Parbat Massif (NPM), the Kohistan-Ladakh Batholith (KLB), and the Karakoram Batholith (KB) were collected. Biotite, K-feldspar, and plagioclase in the granitoid and gneiss show weak to moderate alteration, which increases in shear zones, suggesting fracture-assisted fluid interaction. Geochemical results indicate that the gneisses and granites of the NPM are mostly peraluminous S-type and show enrichment in most LREEs and depletion in HREEs. In addition, depleted Sr and Ba and enriched Rb and U in granites indicate partial melting and high fractionation. On the contrary, granitoids from the KLB are of calc-alkaline I-type and characterized by the depletion of REEs and the enrichment in Ba and Sr. The granitoids of the KB, due to their different magmatic histories, are more diverse, ranging from older I-type calc-alkaline granodiorite, and younger I-type alkaline syenite and S-type calc-alkaline granite. They show an overall enrichment in HREEs along with Ba, Th, Ta, Sr, and Lu. Allanites from syenite of the KB show significant concentrations of Th and U.Petrophysical measurements reveal low matrix porosities (0.6–3.5 %), with primarily average thermal conductivities (1.48–3.37 W m−1K −1) and thermal diffusivities (0.68–1.95 ∙10–6 m2 s−1), with minor variation in specific heat capacities (744–767 J kg−1 K−1). The NPM displays higher average thermal conductivity, thermal diffusivity, and lower porosity than the KB, while the petrophysical properties of the KLB range between these two domains.The geothermal systems in the area operate due to the thickening of a granitoid-dominant crust, which is enriched with radiogenic elements. The fault zones provide channels for meteoric water to access deeply these hot and thermally conductive rocks in the subsurface. After heat exchange, the water is discharged back to the surface as hot springs. The present data set provides a better understanding of regional geothermal regimes from petrological, geochemical, and petrophysical perspectives and assists in numerical modeling for potential geothermal assessment.