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As one of the oldest crustal blocks in Southern Peninsular India, the Coorg Block has been the focus of investigations related to crustal evolution in the early history of the Earth with implications on Mesoarchean plate tectonic processes. The Coorg Block is dominantly composed of arc magmatic rocks and bordered on the north by the Mercara Suture Zone, a Mesoproterozoic subduction-collision zone hosting extruded high-pressure and ultra-high temperature metapelitic and meta-mafic rocks. Here, we report the occurrence of a dismembered gabbro-anorthosite complex corresponding to a layered intrusion from the northern margin of the Coorg Block. We present results from an integrated study on the petrology, mineral chemistry, P-T phase equilibria, whole-rock geochemistry, and zircon and monazite U–Pb geochronology to understand the magmatic and metamorphic evolution of the layered intrusion and associated rocks. The geochemical data suggest that the parental magma was generated within a suprasubduction zone setting. Phase equilibrium modelling of garnet-bearing metagabbro from the Coorg Block suggests metamorphic P–T range of 10.5-11 kbar at 1000-1100°C corresponding to ultra-high temperature conditions. The zircon U-Pb data from the various rock types of the mafic-ultramafic suite yield weighted mean ages at 3176 Ma, 3174 Ma, 3143 Ma, and 3124 Ma whereas the associated charnockite shows a slightly older age of 3319±12 Ma. Metamorphic zircon from charnockite yield an age of 3101 Ma, close to the monazite age of 3110±24 Ma from the same rock, constraining the timing of metamorphism as Mesoarchean, and marking the collisional event between the Coorg Block and the Dharwar Craton along the Mercara Suture Zone. We propose a tectonic model involving southward subduction of the Western Dharwar Block beneath the northern margin of the Coorg Block that can explain the extensive arc magmatism and suprasubduction zone rock suites, followed by ocean closure and collision along the Mercara Suture Zone, accompanied by high P-T metamorphism.

Akure area in southwestern Nigeria falls within the basement complex underlain by migmatite, quartzite granite and charnockite. Geochemical features of these crystalline rocks and their overlying in-situ weathering profiles are investigated and reported. Analytical result from ICP-MS facility at the University of Malaya reveals average SiO2 content in quartzite (91.1%), granite (73.8%), migmatite (67.4%) and charnockite (58.6%) categorize the rocks as siliceous. SiO2 contents in the weathering profiles above these rocks are 61.9%, 60.2%, 52.2% and 54.6% respectively. Alumina contents in the weathering profiles overlying quartzite (23.8%), granite (19.9%), migmatite (26.3%) and charnockite (24.3%) are substantially higher than the precursor rocks. In the same order, average alkali (Na2O+K2O) contents in the profiles are 3.38%, 3.42%, 3.48% and 2.68%. Chemical features of the profiles reflect that there exists some correlation between the chemistry of crystalline basement and their in-situ weathering profiles. The residual soils contain low plastic clays with kaolinitic characteristics and compare well with other clays reported from other parts of Nigeria basement complex.

Our study of a banded charnockite complex of the Muhlig-Hofmannfjella in Dronning Maud Land, Antarctica, illustrates how the combination of high-temperature (re-)crystallization processes, ...

The global ‘type area’ charnockites and those in the surrounding localities within Madras block of the Southern Granulite Terrane in India dominantly comprise felsic to intermediate, coarse to medium grained, orthopyroxene-bearing anhydrous granulite facies rocks with sporadic garnet. In several localities, the charnockitic suite contains mafic magmatic enclaves of gabbroic to dioritic composition showing calcic and peraluminous composition. The charnockite suite shows compositional range from monzonite through granodiorite to granite, and are calcic and calc-alkalic, peraluminous, including both magnesian and ferroan types. Their major and trace element variations are consistent with progressive magmatic differentiation. The charnockites show high Ba-Sr content with a trend from normal arc-related rocks to adakites. The geochemical features of the charnockites and mafic enclaves are consistent with subduction-related arc setting, and slab-derived magmas interacting with mantle wedge peridotite. The P-T conditions as estimated through mineral phase equilibria modelling and pseudosection computations of representative charnockite and mafic enclave samples show a range of ca. 7 to 9 kbar and 870 to 960 °C, suggesting high- to ultra-high temperature granulite facies conditions during the peak metamorphism. The zircon grains from the charnockites show magmatic features with oscillatory or banded zoning, and in many cases display core-rim structure indicating dissolution and metamorphic overgrowth. The magmatic grains/domains show typical steep LREE to HREE pattern, whereas the metamorphic domains show relatively flat HREE. Magmatic zircon U-Pb data indicate crystallization ages of ca. 2.53 Ga to 2.57 Ga. The identical age from magmatic zircon grains in the mafic enclaves suggests bimodal magmatism with underplated mafic magmas intruding into the felsic magma chamber. The U-Pb data from metamorphic zircon and monazite indicate that all the rocks were metamorphosed coevally at ca. 2.47 Ga to 2.49 Ga, soon after their emplacement. The close timing between magmatism and metamorphism of ca. 40 Myr also suggests the formation of the magmatic suite along an active convergent margin, followed by collisional metamorphism during the termination of subduction and ocean closure. The Lu-Hf analyses of magmatic domains in zircon show mostly positive ɛHf(t) values up to +8.7, with only a few spots showing slightly negative values up to −0.8. Zircon grains in the mafic enclaves also show mostly positive ɛHf(t) values up to +4.3. The U-Pb-Hf data are consistent with juvenile arc building during late Neoarchean, with no significant older components. Together with the Hf model ages, the data indicate that the magmas were derived from depleted mantle components of Meso- to Neoarchean age, which would suggest an active subduction regime that continued until the ocean closure during end Neoarchean-earliest Paleoproterozoic. The granulite blocks surrounding the southern margin of the Dharwar craton including the Madras block are interpreted as multiple arcs that coalesced and accreted onto the craton during the Neoarchean-Paleoproterozoic transition. These blocks, which are dominated by charnockites and ranging in age from Mesoarchean to late Neoarchean, and their equivalents in other cratonic fragments over the globe, can be correlated to the ‘expanded Ur’, in building the oldest supercontinent on Earth.

In the geochemical analysis of charnockite matrix, PIXE results do not show either the minor or traces of thorium and uranium even though they are present in that charnockite composition. Because of a continuous range of elements in charnockite composition and characteristic X-rays of some elements present at similar to characteristic X-rays of thorium and uranium. Therefore, Th and U traces quantification are limited due to the interferences in the PIXE spectrum at similar characteristic X-ray energies of the elements. Otherwise, it is possible for quantification, if the composition does not contain the elements at similar characteristic X-rays of Th and U or using complementary techniques.

Since granitic rocks in high-grade terranes commonly undergo amphibolite-granulite facies meta-morphic overprint, recovering magmatic records from the metamorphic modification remains a major challenge. Here, we report an early Paleozoic, garnet-bearing Yunlu charnockite that outcropped in the Yunkai terrane of the Cathaysia block from South China and underwent amphibole-grade metamorphic overprint in the late Devonian. Field observation, micro-texture, and mineral geochemistry combined with diffusion modeling constrain that the metamorphic overprint with an extremely short duration of ~0.2–0.5 Ma only influences a narrow rim of 900 °C, and an initial H2O content of ~4.0 wt% with rare CO2 components. The orthopyroxene-garnet, biotite-garnet, and biotite-orthopyroxene thermometers yield a consistent temperature range of 770–820 ± 60 °C, which is significantly higher than the H2O-saturated solidus temperature of ~630 °C estimated from experimental results and two-feldspar thermometry. These results indicate that the early crystallized minerals (e.g., garnet, orthopyroxene, and some euhedral biotite) of the Yunlu charnockite equilibrate at higher temperatures with crystallinities of ~30–45%, rather than the H2O-saturated solidus conditions. We thus propose a hypothesis of melt extraction at 780–820 °C in a deep-seated, slowly cooling, partially crystalline magma reservoir. The melt extraction physically segregates the early crystallized minerals from residual interstitial melts, which inhibits element diffusion equilibration between these minerals and interstitial melts. Granite thermometry commonly yields a large range of temperature estimations, which may be related to melt extraction events. Our study shows that melt extraction recorded in granites can be identified by combining micro-texture, mineral thermometry and rhyolite-MELTS modeling, which further provides quantitative insights into the fractionation process of silicic magmas.

In the chemical characterization of charnokite is well investigated by using PIXE and other analytical techniques, but PIXE not given information about some of elements completely, because every technique including PIXE has proper limitations. To obtain the complete geochemical explanation of matrix charnockite composition, the experimental factors behind missing elements in PIXE at 3 MeV techniques with comparison must known and hence are used for the analysis of matrix compositions related to the earth materials like charnockite. In this study, the results obtained from PIXE compared with other analytical techniques and experimental factors of PIXE are discussed. By investigating the geochemical nature of complex charnockite material, the experimental factors which are related to the missing elements in this study of wide range of elements obtained from PIXE spectrum through the previous analytical techniques have been discussed.

Orthopyroxene-bearing felsic gneiss occurs as foliation-parallel layers and bands together with aluminous granulite, mafic granulite, and quartzofeldspathic granulite in the Chilka Lake migmatite complex of the Proterozoic Eastern Ghats Belt, India. The rock was classified previously as charnockite which underwent granulite-facies metamorphism. Field and textural features of this rock show evidence of the partial melting of a biotite-bearing greywacke protolith. Orthopyroxene with/without garnet and cordierite were produced with K-feldspar as peritectic phases of incongruent melting of presumed metaluminous sediments. Fluid-inclusion data suggest the presence of high-density CO2-rich fluids during peak metamorphism, which are similar to those found in associated aluminous granulite. Whole-rock major and trace element data show wide variability of the source materials whereas REE distributions show enriched LREE and flat HREE patterns. Zircon grains from representative samples show the presence of inherited cores having spot dates (SHRIMP) in the range c. 1790–3270 Ma. The overgrowth on zircon was formed predominantly during c. 780–730 Ma and sporadically during c. 550–520 Ma. Some neoblastic zircons with c. 780–730 Ma ages are also present. U-rich dark zones surrounding cores appear partially metamictised, but spot ages from this zone vary within c. 1000–900 Ma. The

Massif-type anorthosites are voluminous, plagioclase-dominated batholiths that occur worldwide, but only during the Proterozoic Eon. Granitoids are closely associated with the anorthosites, and they collectively may form an AMCG suite (i.e., anorthosite, mangerite, charnockite, granite). Many fundamental questions regarding the origin of the AMCG complexes remain unresolved, including their tectonic setting and mode of emplacement. Here, we present new data from reconnaissance structural mapping, U–Pb LA-ICP-MS zircon dating, and 40Ar/39Ar amphibole and mica dating from a 500 km2 area straddling the western margin of one of the world’s largest (≥ 15,000 km2), but also least studied AMCG suites, the Kunene Complex (KC) in Angola. The oldest recognized (pre-Kunene) deformation event D1 produced a steep WNW–ESE-striking S1 fabric in supracrustal rocks, migmatite and Paleoproterozoic (1800–1780 Ma) granodiorite before ~ 1680 Ma. This was folded by the D2 event, resulting in steep, N–S-striking S2 leucosomes and gneissosity in the rocks surrounding the KC. Concordant magmatic layering and lamination, and high- to low-temperature gneissic foliation in the marginal Kunene anorthosite and coeval megacrystic granite are parallel with S2 fabrics in the Paleoproterozoic country rocks. Mineral stretching lineations L2 in all rock types across intrusive contacts are steep and associated with west-side-up (thrust) shearing. Overlapping U–Pb zircon/baddeleyite ages from the Kunene megacrystic granite and Kunene anorthosite, with 40Ar/39Ar mica ages from the mantling Paleoproterozoic country rocks, attest to progressive contraction, thrusting and exhumation of the Paleoproterozoic country rocks onto the Kunene anorthosite in the interval 1410–1380 Ma. We suggest that thermal softening of the country rocks caused by heat dissipation from the earliest phase (1500–1410 Ma) of ponding of hot anorthositic magma in the deep crust localized D2 deformation at the margin of the KC. Our data point to a tectonic model whereby anorthosite sheets were emplaced at a high angle to the shortening direction and along host-rock S2 anisotropy deep in the crust and cooled during progressive ductile thrusting and exhumation of the country rocks. These results question the current view that Proterozoic AMCG suites are emplaced in extensional environments as large diapiric bodies and favor formation in a continental arc setting.

Chemical weathering in a groundwater basin is a key to understanding global climate change for a long-term scale due to its association with carbon sequestration. The present study aims to characterize and to quantify silicate weathering rate (SWR), carbon dioxide consumption rate and carbonate weathering rate (CWR) in hard rock terrain aided by major ion chemistry. The proposed study area Shanmuganadhi is marked with superior rainfall, oscillating temperature and runoff with litho-units encompassing charnockite and hornblende–biotite gneiss. Groundwater samples (n = 60) were collected from diverse locations and analysed for major chemical constituents. Groundwater geochemistry seems to be influenced by geochemical reactions combining dissolution and precipitation of solids, cation exchange and adsorption along with minor contribution from anthropogenic activities. The SWR calculated for charnockite and hornblende–biotite gneiss was 3.07 tons km−2 year−1 and 5.12 tons km−2 year−1, respectively. The calculated CWR of charnockite and hornblende–biotite gneiss was 0.079 tons km−2 year−1 and 0.74 tons km−2 year−1, respectively. The calculated CO2 consumption rates via silicate weathering were 1.4 × 103 mol km−2 year−1 for charnockite and 5.8 × 103 mol km−2 year−1 for hornblende–biotite gneiss. Lithology, climate and relief were the key factors isolated to control weathering and CO2 consumption rates.

Orthopyroxene-bearing tonalites/trondhjemites with scarce quartz diorites comprise the Café enderbite that crops out in three Neoarchean plutons in the central portion of the Canaã dos Carajás domain, Carajás Province, northern Brazil. Intrinsic parameters based on the mineral chemistry of plagioclase, biotite, amphibole, and pyroxene constrain crystallization conditions to 1150–850°C and 750–600 MPa, moderate water content in the melt (4.8–5.6 wt.%) and relatively oxidizing conditions, between the fayalite–magnetite–quartz (FMQ) and nickel– nickel oxide (NNO) + 1.7 buffers. Geochemical modeling indicates that the Café enderbite evolved via at least two fractional crystallization stages – quartz diorite to orthopyroxene tonalite and orthopyroxene tonalite to orthopyroxene trondhjemite – with high crystal content (45–60%, or even higher). This high crystal content during fractional crystallization was the key factor to the preservation of orthopyroxene in the magmatic system as it left only a relatively small proportion of melt to react with early-formed orthopyroxene.

The Precambrian Eastern Ghats Group of rocks consisting of a series of regionally metamorphosed rocks such as khondalite, charnockite, calc-granulite and quartzite hosts several pockets to lensoidal Mn-ores in Odisha, Eastern India. The Mn-minerals identified in these deposits are Mn-silicates and lower Mn-oxides with Mn-oxyhydroxides. Lithiophorite, an aluminous Mn-oxyhydroxide mineral, is conspicuous with other secondary Mn-phases. It generally occurs in two habits, such as cryptocrystalline/crystalline aggregates either as vug fillings or as replacement of other minerals like cryptomelane/romanechite/goethite/graphite. Two morphological types of lithiophorite viz. globular and platy were examined in detail by optical and electron microscopy. The electron probe micro-analyses (EPMA) of these two morpho-types reveal the cryptocrystalline (globular) type to be rich in both CoO and NiO, while the platy crystalline type is preferentially enriched in NiO and depleted in CoO. Compositional map for both the types also supports such selective entrapment. Binary plots of electron probe data for MnO2 and Al2O3 versus CoO and NiO in the globular type show strong positive relation confirming to their presence in adsorbed state. In contrast, the NiO in platy type show strong positive relation with Al2O3 only indicating desorption of Co and a part of Mn from the structure during crystallisation and its subsequent diadochic substitution in the alumina lattice.

The timing of tectonomagmatic events and petrogenesis of ortho- and paragneisses within the high-grade southern Bushmanland Domain (SBD) of the Namaqua Metamorphic Province is, largely, poorly constrained. U-Pb age dating and whole rock lithogeochemistry of the rocks of the upper granulite facies Kliprand dome provide constraints with regards to the evolution of the SBD during the 1.2–1.0 Ga Namaquan Orogeny. The SBD has a greater juvenile component, particularly added between ∼1.1 and 1.02 Ga, compared to the northern Bushmanland Domain (NBD). This is reflected in marginally younger TDM model ages (1.60–1.95 Ga) than for the NBD (∼1.9–2.4 Ga), and higher eNd(t) values for magmatic rocks, particularly for the late- to post-tectonic Spektakel Suite (SS), concentrated in the SBD. The ∼1.06 Ga Klein Lieslap Charnockite of the SS was derived from reworking of radiogenic Paleoproterozoic arc crust, but has a large juvenile depleted component compared to that of the ∼1.19 Ga Grootberg Gneiss of the syn-tectonic Little Namaqualand Suite. SBD mafic magmas were derived from low degrees of partial melting of subduction-influenced enriched subcontinental lithospheric mantle. The pre-tectonic ∼1.17 Ga Oorkraal Suite shows limited crustal contamination of mantle-derived melts. The post-tectonic ∼1.05 Ga Koperberg Suite was derived from deeper mantle melting than that in the NBD, but shows less crustal contamination. The supracrustal Kamiesberg Group was derived from mixed, reworked Meso- to Paleoproterozoic crust that showed a more dominant depleted component compared to that in the NBD. Incongruent anatexis of the paragneisses gave rise to crosscutting garnetiferous quartzofeldspathic segregations, notably the strongly peraluminous ∼1.07 Ga Ibequas Leucogranite. D2 deformation, at ∼1.11–1.09 Ga, resulted in penetrative foliation. D3 deformation, related to the development of a sub-vertical foliation in the limbs of F2 folds, is constrained to ∼1.07–1.06 Ga, between emplacement of the Ibequas Leucogranite and the Koperberg Suite. Peak granulite facies M3 metamorphism occurred at ∼1.05–1.02 Ga. These age constraints are similar to those of the NBD reflecting a synchronous tectonomagmatic and kinematic history. The SBD represents a deeper crustal level with a greater mantle influence than the NBD.

The Nilgiri Block, southern India represents an exhumed section of lower, late Archean (2500 Ma) crust. The northern highlands of the Nilgiri Block are characterized by metagabbros with pyroxenite inlayers. A two-pyroxene granulite zone acts as a transition between the metagabbros and charnockites, which are exposed in the central and southern part of the Nilgiri highlands. Thermobarometry results indicate a SW–NE regional trend both in temperature (∼650–800°C) and in pressure (700–1100 MPa) over the Nilgiri highlands. In the charnockites, composite rutile–ilmenite grains are the dominant oxide assemblage. In the two-pyroxene granulites, hemo-ilmenite–magnetite is dominant with coexisting rutile–ilmenite composite grains in a few samples in the vicinity of the boundary with the charnockites. In the metagabbros, hemo-ilmenite–magnetite is the dominant oxide assemblage. The principal sulphide mineral in the charnockite is pyrrhotite with minor pyrite–chalcopyrite exsolution lamellae or blebs. In the two-pyroxene granulites and the metagabbros, the principal sulphide assemblage consists of discrete pyrite grains with magnetite rims and pyrite–pyrrhotite–chalcocopyrite associations. From these observations, a specific oxidation trend is seen. The northern granulite-facies metagabbros and two-pyroxene granulites of the Nilgiri highlands are highly oxidized compared with the charnockites from the central and southern regions. This higher oxidation state is proposed to be the result of highly oxidizing agents (probably as SO3) in low H2O activity grain boundary NaCl saline fluids with a dissolved CaSO4 component present during granulite-facies metamorphism of the metagabbros and two-pyroxene granulites. Eventually these agents became more reducing, owing to the inherent buffering of the original tonalite–granodiorite granitoids at the graphite–CO2 buffer, such that S took the form of H2S during the granulite-facies metamorphism of the charnockites. At the same time, these saline fluids were also responsible the solid-state conversion of biotite and amphibole to orthopyroxene and clinopyroxene in the metagabbro, two-pyroxene granulite, and charnockite.

Thermal conductivity of individual rock types plays a noteworthy role in melting of the ice mass at the contact with the rocks. These are heavily influenced by their mineral constituents and the structural fabrics within the rocks. In the decreasing order of influence on melting of the nearby ice mass, the exposed rock units of Schirmacher Oasis are demarcated as metapelites (6.1 ± 0.37 Wm−1K−1), quartzofeldspathic augen gneiss (6.08 ± 0.04 Wm−1K−1), garnet rich biotite quartzofeldspathic gneiss with rare layers of amphibolites (4.34 ± 0.68 Wm−1K−1), charnockite-enderbite interlayered with pyroxene granulite (3.99 ± 0.44 Wm− 1K−1), quartzofeldspathic gneiss ± garnet with few enclaves of charnockite and pyroxene granulites (3.53 ± 0.22 Wm−1K−1), norite (3.38 ± 0.26 Wm−1K−1), dolerite dykes (3.32 ± 0.15 Wm−1K−1). Metamafic and metaultramafic rocks occurring as enclaves in charnockitic zones (3.07 ± 0.11 Wm−1K−1), nodular basaltic dykes (2.98 ± 0.16 Wm−1K−1) and lamprophyre dykes (2.77 ± 0.18 Wm− 1K−1). The detail investigation around Dakshin Gangotri Glacier snout at the margin of the Schirmacher Oasis and the Polar ice sheet indicates that the rocks with higher thermal conductivity values show a higher average annual recession than that of the lower thermal conductivity values. The spatial distribution and the variations in the thermal conductivity of the rocks in different places within the Schirmacher Oasis are one of the factors contributing to the differential rate of Polar ice sheet recession at its margin.

A comparative study was performed on the petrography, geochemistry and geochronology of charnockite and granulite in the Xiwulanbulang (XWLBL) area, northern margin of the North China Craton, NW Ch...

The majority of PIXE analytical study on geosciences has used 3 MeV proton beams for excitation and these studies generally uses the K-X-rays for low Z elements and L-X-rays for high Z elements. The present study of resulting spectra of metamorphic high grade rocks like charnockite can require striping techniques to resolve interference problems between low and high Z elements on the applications of light energy-PIXE using Si (Li) detector. In all forms of X-ray analysis, including thick-target light energy-PIXE, the X-ray signal is a dependent of the ionization cross section and for low-energy protons, the cross section is high for the K shells of light elements and the L shells of heavy elements in charnockite rock providing sufficient fluorescent yield for analytical purposes. For Z > 55, 3 MeV protons cannot ionize K-shell electrons and analysis depends on the use of L-X-ray lines in charnockite rock. Such L-X-ray spectra are complicated and can be affected by interferences K-X-rays from low Z elements. The low Z elements present in the charnockite were identified by previous complementary analytical techniques, but not identified in this study due to the above PIXE experiment limitations, and also particularly due to the dimensions of Si (Li) detector because of low energy K-X-rays of the elements absorbed by the detector window. Both interferences complexity and detector efficiency can lead to difficulties and ambiguity in the interpretation of spectra of low Z charnockite composition, a problem that is exacerbated by uncertainty in relative K-X-ray line intensities of low Z elements. From this investigation, the light energy-PIXE is ideal for the analysis of low Z&thinsp

The Kanyakumari coastal area in the southernmost part of Tamil Nadu, India is a well-known natural high background radiation area due to the abundance of monazite in beach placer deposits. In the present study, the concentrations of major oxides, rare earth elements (REEs), Th and U were measured to understand geochemical characteristics of these monazite sands. Based on the ambient dose rate, 23 locations covering an area of about 60 km along the coast were selected for sample collection. The concentrations of U and Th ranged from 1.1 to 737.8 μg g−1 and 25.2–12250.6 μg g−1, respectively. The Th/U ratio ranged from 2.2 to 61.6, which clearly indicated that Th was the dominant contributing radionuclide to the enhanced natural radioactivity in this coastal region. The chondrite-normalized REEs pattern of the placer deposits showed enrichment in light REEs and depletion in heavy REEs with a negative Eu anomaly that indicated the monazite sands were derived from granite, charnockite, and granitoid rocks from the Nagercoil and the Trivandrum Blocks of the Southern Granulite Terrain.

This research uses geophysical techniques such as magnetic and electrical resistivity tomography to image the lateritic bauxite bearing zones in Orin Ekiti, Southwestern Nigeria. The high-resolution aeromagnetic data were utilized for generating the total magnetic intensity (TMI) map. Different filtering techniques such as Euler deconvolution and total horizontal derivative were also carried out to enhance better understanding of bauxite deposit, with the generation of different maps therein. Low magnetic intensities were observed over charnockitic rock which is a host material for bauxite occurrence. Magnetic low trending NE–SW was observed in the study area. The (EUD and THDR) maps were then superimposed on the geologic map to geo-reference areas that have dominant charnockite. The depth extent and structural signature interpreted from magnetic interpretations show that significant deposit in the study area is at shallow depth which tallies with the geology of bauxite as being a supergene enrichment (surficial deposit). 2D ERT results obtained from five traverses with inter-traverse separation of 45 m and traverse length of 100 m each, established in the NW–SE direction to image the lateritic bauxite deposit based on the prospect shown from the aeromagnetic analysis. The images display the constant resistivity regimes beneath the traverses with different colour bands. The 2D ERT profiles and 3D inversion results show bauxitic zones to be of high resistivity which ranges from 154 to 3814 Ω m, the migmatite gneiss and granitic rocks (unaltered parent rocks) are of considerably lower resistivity than the weathered charnockitic rock and by extension bauxitic zones. These different techniques used in this study have however shown that the area of interest for bauxitic deposit in Orin Ekiti trends in the NE–SW direction with a dominant concentration in the north-eastern (NE) part. By the same token, this research has been able to substantiate the fact that bauxite deposits occur as supergene enrichment.

To understand the sub-surface lithology variation and identify possible groundwater potential zones, multi-electrode resistivity scanning was carried out at 7 locations in the part of Chittar sub-basin, Tirunelveli District, South India. Physiographically, the selected study area is a plain and falls under the semi-arid climatic type. Archaean crystalline of hornblende biotite gneiss and charnockite are the major rock types, pediments and buried pediments are the major geomorphological units. A length of 100 m was scanned using 50 electrodes with interspacing of 2 m by SSR-MP-AT-ME model resistivity meter and analysed in IPI 2WIN software. The data obtained from resistivity showed huge resistivity variations in areas where Narikudi, Rastha, Therkkupatti and Vagaikulam locations represented ≤ 1000 Ohm m and Alagiyapandiapuram, Muthamalpuram and Nilethanallur locations represented 9000 Ohm m. To validate the scanning interpretation, constructed geoelectric layers were correlated to existing lithology of the region and it showed an appreciable match. Considering the resistivity range of 50 to 120 Ohm m and bore well lithology, Narikudi and Muthamalpuram locations have been identified as potential groundwater zones while Nilethanallur, Rastha, Therkkupatti, Alagiyapandiapuram and Vagaikulam locations were also identified as low to moderate groundwater zones.

Ala River is the main river that drains Akure metropolis in southwestern Nigeria. The river takes its sources from deep-seated fractures in granite and charnockite rock bodies at the North and North-western regions of Akure town, flowing through quartzite and granite gneiss exposures. This study was carried out to assess the geochemical processes influencing the quality of Ala river water. The dendritic river system, covering an area of about 427 km2, was studied and water was sampled at thirty-seven (37) points for in-situ determination of some physicochemical parameters and dissolved concentrations of the major ions. pH values obtained varied between 7.16 and 7.75, electrical conductivity ranged from 123 to 520 µs/cm, total dissolved solids varied between 62 and 260 mg/l-CaCO3 while average temperature value was 26.65 °C. Relative concentration of cations and anions were in the order of Ca2+ > Mg2+ > Na+ > K+ and HCO3− > SO42− > Cl− > NO3−. Mean values of dissolved Na+, K+, Ca2+, Mg2+, Fe2+, Cl−, HCO3−, SO42−, NO3−, and PO42− were 34.028, 8.872, 34.175, 18.289, 0.428, 16.543, 56.41, 12.503, 0.495 and 2.029 mg/l, respectively. Two hydochemical facies namely Calcium-Bicarbonate facies and mixed calcium–magnesium–chloride facies dominated the chemistry of the water. CaHCO3 facies revealed the contribution of geogenic processes while the mixed Ca(Mg)-Cl type reflected domestically induced anthropogenic activities influencing chemistry of the water. Gibbs diagrams identified rock–water interaction as an important geochemical process in the study area. Silicate weathering of rocks and carbonate weathering were identified as the important geochemical processes which influence the water chemistry of the study area.

This study presents major element, radioactive element and rare earth element (REE) concentrations of the Garampeta to Markandi beach along the southern coast of Odisha, India to delineate the source signature and resource potential of the beach placer deposits. Average ∑REE concentration of the beach sand samples is about four times higher than the average crustal concentration. The LREE concentration is higher than HREE, with a pronounced negative europium anomaly. The study also discusses about the radioelement 238U, 232Th and 40K concentrations in the study area, and their relationship with REE. Weathering condition of the source rock, based on the major elements and Th/U ratio indicated a reasonably high degree of weathering. Major element and the REE composition along with the europium anomaly, relate the beach placers to mainly charnockite and khondalite source. An elevated level of thorium (> 60 times than the average UCC values) as exhibited by the samples could be attributed due to the presence of monazites. The high concentration of REEs like Nd and Dy along with La and Ce indicates significant REE resource potential in the beach placers which is important for the resource potential in terms of the strategic mineral reserves of the country.

We document kinematics and rheological behaviour of brittle shears (~50 cm wide) postdating solid-state tectonic fabric in the Salem–Attur (SASZ) and Bhavani (BSZ) shear zone that constitute a Paleoproterozoic (~2500 Ma) suture juxtaposing disparate granulite blocks in south India. We constrain brittle deformation mechanisms from established relationship between changing orientation of deflected strain marker (quartz vein) and foliation within the shear band with respect to their orientation outside the shear band. Quartz c-axis orientation in charnockite (host lithology) and phyllonite (reworked charnockite) from the SASZ show presence of mixed basal 〈a〉 (low-T) and prism 〈a〉 (high-T) slip, and single basal 〈a〉 slip mechanism, respectively. This suggests considerable cooling of the granulite block prior to the onset of brittle shearing. Distribution of strain parameters – effective shear strain (Γ), shear strain (γ), stretch K2 along intermediate strain axis Y – from margin to the centre of the shear band, show peaked distribution with a single maximum at the shear zone centre. This implies rheological-weakening/strain-softening induced localizing shear zone character. Kinematically heterogeneous strain distribution during brittle shearing varies from transpression dominated for the BSZ to transpression-to-transtension switchover for the SASZ. Demonstrably, contrasting cooling-exhumation, hitherto unexplored, characterizes post-accretionary tectonics along the paleo-suture zone.

International audience; The Leonian (3400–3100 Ma) and Liberian (2850–2700 Ma) events are important magmatic and tectono-metamorphic events in the Archean domain of the Man-Leo Shield in the southern West Africa Craton. The older Leonian event was associated with crust formation, which was variably reworked during the younger Liberian event. In the Man domain of western Côte d’Ivoire, zircon in-situ dating by LA-ICPMS of Granulitic Grey Gneisses (GGGs), the Mangouin charnockite and the Lagoulalé augen orthogneiss allows for the re-evaluation of magmatic and metamorphic activity related to the Leonian and Liberian events. We report here our findings that the GGGs represent the oldest rocks in the study area and formed during the Leonian event. The ages recorded in the GGGs in the Man area are 3156±24, 3098±19, 3093±49 and 3019±53 Ma. The ages of 3156±24 and 3098±19 Ma represent Leonian juvenile magmatism while those of 3093±49 and 3019±53 Ma represent Leonian metamorphism. The ages of the Mangouin charnockite and the Lagoulalé augen orthogneiss are 2798±8 Ma and 2795±9 Ma, respectively, and are interpreted to record peak metamorphic conditions during the Liberian event. Zircon from the augen orthogneiss includes an inherited core with an age of 3121±37 Ma, which corresponds to Leonian GGG ages. This inheritance indicates that the Mangouin charnockite and the Lagoulalé augen orthogneiss were derived either partially or completely from Leonian formations. A previously constrained Sm–Nd model age of 3250 Ma for the charnockite and augen orthogneiss agrees with such a process. The majority of Th/U is higher, indicating a magmatic origin for most zircons. The Leonian and Liberian events are proposed as two distinct events in Man-Leo Shield.

Voluminous pseudotachylites occur along NE-SW trending Gangavalli sinistral strike-slip fault in the Southern Granulite Terrane of South India. We made a field, microscope and geochemistry study of the pseudotachylites, and determined the parent rock composition, frictional shear resistance (τf) and melt pressure (Pm). Based on the result, we made a preliminary interpretation of source property of the earthquake. The pseudotachylite veins belong to two types, (i) the fault veins were produced by in-situ melting, these were used to compute the τf during coseismic slip, and (ii) the injected veins formed due to dilation of the pre-existing weak planes, these have been used to calculate the Pm. The pseudotachylites bear chemical similarity with charnockites in that they show andesite to granite composition in TAS diagram, calc-alkaline trend in AFM plot, possess REE fractionation with LREE enrichment and lack Eu anomaly. Hence, pseudotachylites were derived from melting of the charnockite. Further, the pseudotachylites are dominated by hexagonal β-quartz clasts that suggest the maximum temperature of melting was at 1550 ℃. The fault veins exhibit thickness/displacement ratio varying between 0.03 and 0.1. Assuming that there is no loss of melt from fault veins, maximum shear resistance is estimated at 48.95 MPa, characteristic of large magnitude-earthquake. The injected veins are thicker, show varied geometry and dominantly are aligned in NE-SW direction. The melt pressure Pm > σ2, stress ratio Φ = 0.87 and driving pressure R′ = 0.9 were calculated from stereoplot and 3D Mohr circle. Higher stress ratio indicates σ2 ≈ σ1 that leads to flip-flop of σ1 from horizontal to vertical. This was probably the result of stress drop during stick-slip mechanism.

International audience; Understanding fractionation of silicic magma is crucial to advance our knowledge of differentiation of continental crust, enrichment of elements of economic interest, and plutonic–volcanic connection. Microstructural records afford critical appraisals for silicic magma fractionation, yet are rarely reported in granite plutons. Here we combine detailed microstructural observations and thermodynamic modeling to quantify the components and the conditions of silicic magma fractionation using the peraluminous Jiuzhou pluton (South China) as an example. The pluton shows compositional gradients from primitive orthopyroxene-bearing granite (charnockite) at stratigraphically low levels to relatively evolved orthopyroxene-free granite at stratigraphically high levels. Deviation of whole-rock compositions from metasediment-sourced experimental melts, and step-zoned plagioclase and alkali feldspar crystals in the exposed rocks suggest open-system fractionation by melt extraction, partial dissolution, and subsequent crystallization from trapped minimum melt. Crystal cluster and chain fabrics and viscous deformation are more abundant in the charnockites than in the overlying orthopyroxene-free granites, suggesting that gravitational, compaction-driven fractionation increased towards the bottom of the pluton. Field observations, thermodynamic modeling and petrographic studies further demonstrate that gravitational compaction reduces the trapped melt fraction of a crystal mush with thickness of ≥100 m from ∼30 wt% at the upper level to ∼10 wt% at the lower level of the pluton. Significant melt extraction restricted back-reaction with high-temperature phases during progressive crystallization, which preserved orthopyroxene during the solidification of granitic magma. The compositional, mineralogical and textural zoning of the Jiuzhou pluton suggests that incremental fractionation of granite systems may be an important process that produces compositionally zoned cumulate. Incremental fractionation may occur in many zoned granite plutons worldwide, causing their whole-rock composition to deviate from their primary melt composition. Detailed microstructural examination for these granite plutons may provide insights into the mechanism(s) for melt extraction and crystal accumulation of silicic magma, providing key insights towards quantifying fractionation of magma systems.

We present zircon U-Pb (SHRIMP) and monazite U-Th-total Pb (EPMA) ages from a suite of high-grade rocks of the Phulbani domain of the Eastern Ghats Belt, India. These ages are integrated with the metamorphic and magmatic histories of the Phulbani domain to put precise time constraints on the tectonothermal evolution of the northern part of the Eastern Ghats Belt. Zircon from the coarse-grained charnockite rock shows crystallization age of ca. 970 Ma. Aluminous granulite contains spinel and quartz-bearing mineral assemblage indicating ultrahigh temperature metamorphism (>900 °C at 8–10 kbar) which possibly occurred during ca. 987 Ma as revealed from monazite included in porphyroblastic garnet. Monazite in the aluminous granulite and the migmatitic felsic gneiss grew dominantly at 966 ± 4 Ma and 968 ± 4 Ma ages respectively, which are interpreted as the cooling ages subsequent to peak metamorphism. Oscillatory-zoned zircon grains of the felsic augen gneiss yield ca. 1173 Ma age which is interpreted as the crystallization age of the granitic protolith. This ca. 1173 Ma age granite possibly composed a part of the Proterozoic basement of the Eastern Ghats Province. A monazite age of 781 ± 15 Ma from the aluminous granulite may indicate the timing of a localized shear-induced thermal process in the Phulbani domain. The presently studied rock suite thus recorded three distinct events (ca. 1173 Ma, ca. 1000–900 Ma and ca. 781 Ma) of magmatism, metamorphism and deformation of Eastern Ghats Belt. Metamorphic and magmatic histories of the Phulbani domain are similar to those of the adjacent Visakhapatnam domain and the Rayner Province of East Antarctica during the time frame ca. 1000–900 Ma.

The Spektakel Suite comprises voluminous late- to post-tectonic granitoids that intruded the pre-tectonic gneisses of the Bushmanland Subprovince (BSP) of the Mesoproterozoic Namaqua-Natal Metamorphic Province (NNMP). Based on new U-Pb zircon geochronology and geochemical data, we redefine the suite as consisting of 22 plutons of porphyritic monzogranite, granodiorite and charnockite that intruded the granulitic core of the BSP between 1097 and 1033 Ma. The new data show that some granites previously incorporated into the Spektakel Suite should be excluded: a) garnetiferous leucogranites (Concordia, Hangsfontein and Ibequas Granites) are excluded on petrological grounds and genetic considerations and b) the porphyritic Nuwefontein Granite (∼783 Ma) is younger and is now placed within the Richtersveld Suite. The Spektakel Suite has geochemical and isotopic compositions suggesting that it was derived from recycled Palaeoproterozoic crust with Mesoproterozoic mantle input. The main Namaqua Orogeny (D2) in the BSP comprises at least two phases of compressional tectonics at ∼1200 Ma and ∼1110 Ma separated by a period of extension. The new ages for the Spektakel Suite tightly constrain the end of D2 to between 1109 Ma, the age of the youngest pre-tectonic gneiss and 1097 Ma, the age of the oldest Spektakel Suite granite. Peak low-P, high-T metamorphism (∼1050–1020 Ma) occurred well after D2 and its close spatial and temporal relationship to the Spektakel Suite suggests this prolonged period of granite magmatism was responsible for the transfer of the heat into the BSP. Several other late- to post-tectonic megacrystic granitic suites intruded into other tectonic domains across the NNMP coevally with the Spektakel Suite, indicating widespread granite magmatism at this time, probably due to mafic under- and intra-plating in a back-arc setting as previously suggested.

Southern peninsular India preserves records of Late Neoarchean Early Paleoproterozoic continental building and cratonization. A transect from the Paleoarchean Dharwar Craton to the Neoarchean arc magmatic complex in the Nilgiri Block across the intervening Moyar Suture Zone reveals an arc-accretionary complex composed of banded iron formation (BIF), amphibolite, metatuff, garnet-kyanite schist, metagabbro, pyroxenite and charnockite. Here we investigate the petrology, geochronology and petrogenesis of the pyroxenite and garnet-clinopyroxenite. The pyroxenite is mainly composed of orthopyroxene and clinopyroxene with local domains/pockets enriched in a clinopyroxene-gamet assemblage. Thermobarometric calculations and phase equilibria modeling suggest that the orthopyroxene-and clinopyroxene-rich domains formed at 900-1000 degrees C, 1-1.2 GPa whereas the garnet-and clinopyroxene-rich domains record higher pressure of about 1.8-2 GPa at similar temperature conditions (900-1000 degrees C). Zircon U-Pb SHRIMP dating show weighted mean Pb-207-Pb-206 age of 2532 +/- 22 Ma, with metamorphic overgrowth at 2520 +/- 27 Ma and 2478 +/- 27 Ma. We propose a tectonic model involving decoupling and break-off of the oceanic plate along the southern flanks of the Dharwar Craton, which initiated oceanic plate subduction. Slab melting eventually built the Nilgiri volcanic arc on top of the overriding plate along the flanks of the Dharwar Craton. Our study supports an active plate tectonic regime at the end of the Archean Era, aiding in the growth of paleo-continents and their assembly into stable cratons. (C) 2018 Elsevier B.V. All rights reserved.

Geotechnical tests were carried out on twenty subsoil samples obtained from ten locations at the depth of 1 and 2 m within Federal University of Technology, Akure, Nigeria. The area is typical of basement complex. The test include; Natural Moisture Content, Grain Size Analyses, Specific Gravity, Atterberg Limits, Compaction, California Bearing Ratio (CBR), and Unconfined Compression Tests. The ten locations where the soil samples were collected were selected across the geological classification of the area. ArcGIS 10.1 software was used to generate maps showing the geotechnical parameters distribution across four geological formations within the area at 1 and 2 m depth. It was observed that the distribution of each geotechnical parameter correlates with the composition of the weathering end-product of the geology. The rocks underlain the area includes; Migimatite Gneiss, Quartzite, Charnockite and Biotite Granite. The poorest geotechnical parameters were obtained within subsoil underlain by Charnockite, hence are most unsuitable soil to host the foundation of civil engineering structures, while the area underlie by weathering end-product of quartzite rock is of good geotechnical parameters and most suitable soil to host the foundation of civil engineering structures. The weathering end-products of Charnockite, Migimatite and Granite rocks give relatively high shear strength than that of quartzite, indicating low cohesive nature of the weathering end-product of quartzite. Key words: Geological classification, geotechnical parameter, weathering, road base.

The high-grade metamorphic rocks of Sri Lanka place valuable constraints on the assembly of central parts of the Gondwana supercontinent. They are subdivided into the Wanni Complex (WC), Highland Complex (HC) and Vijayan Complex (VC), but their correlation with neighbouring Gondwana terranes is hindered by a poor understanding of the contact between the HC and WC. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U–Pb dating of remnant zircon cores from 45 high-grade metamorphic rocks in Sri Lanka reveals two domains with different age characteristics that correlate with the HC and WC and which help constrain the location of the boundary between them. The HC is dominated by detrital zircon ages of ca. 3500–1500 Ma from garnet–biotite gneiss, garnet–cordierite–biotite gneiss, some samples of garnet–orthopyroxene–biotite gneiss and siliceous gneiss (interpreted as paragneisses) and igneous protolith ages of ca. 2000–1800 Ma from garnet–hornblende–biotite gneiss, other samples of garnet–orthopyroxene–biotite gneiss, garnet–two-pyroxene granulite, two-pyroxene granulite and charnockite (interpreted as orthogneisses). In contrast, the WC is dominated by detrital zircon ages of ca. 1100–700 Ma from paragneisses and igneous protolith ages of ca. 1100–800 Ma from orthogneisses. This clearly suggests the HC and WC have different origins, but some of our results and previous data indicate their spatial distribution does not correspond exactly to the unit boundary proposed in earlier studies using Nd model ages. Detrital zircon and igneous protolith ages in the HC suggest that sedimentary protoliths were eroded from local 2000–1800 Ma igneous rocks and an older Paleoproterozoic to Archean craton. In contrast, the WC sedimentary protoliths were mainly eroded from local late Mesoproterozoic to Neoproterozoic igneous rocks with very minor components from an older 2500–1500 Ma craton, and in the case of the WC precursor sediments there was possibly additional detritus derived from early to middle Neoproterozoic metamorphic rocks. The relic zircon core ages in the HC are comparable with those of the Trivandrum Block and Nagercoil Block of southern India. In contrast, those ages in the WC match the Achankovil Shear Zone and Southern Madurai Block of southern India. These comparisons are also supported by Th/U ratios of detrital zircon cores from paragneisses (Th/U ratios of >0.10 for the former and not only >0.10 but also ≤0.10 for the latter). Comparisons with the Lutzow-Holm Complex of East Antarctica indicate that the geochronological characteristics of the HC and WC broadly match those of the Skallen Group, and the Ongul and Okuiwa Groups, respectively.

An attempt has been made in the present work to study the effect of type of coarse aggregate on the strength properties and fracture energy of M30, M50 and M80 grade of concretes. The aggregate used in this study includes Grey Granite (GG), Anorthosite (AS) Charnockite (CK) Limestone, (LS) and Gneiss (GS). The result shows that the strength of concrete is greatly influenced by the aggregate types in high strength concrete. However, the aggregate has not impacted the Normal Strength Concrete as the strength is governed by the characteristics of interfacial transition zone, rather than aggregate. Among all aggregates, the Grey Granite aggregate has produced concrete with highest compressive strength followed by Anorthosite, Charnockite, Limestone and Gneiss indicating that the surface texture, structure and mineralogical composition played a dominant role. The similar trend was noticed even in fracture energy and modulus of elasticity of high strength concrete.

International audience; The Permian history of the Central Asian Orogenic belt is marked by large-scale strike-slip faults that reactivate former Paleozoic structures, delineated by widespread alkaline magmatism. The genetic link between the syn-kinematic granitoids emplaced in the Tien Shan range and magmas emplaced within the Tarim Large Igneous Province, and the interaction between this plume and transcurrent tectonics, are still unsolved issues. We investigated the Pobeda massif, in the eastern Kyrgyz Tien Shan, located at the boundary between the Tien Shan range and the Tarim Craton, which exhibits a high-temperature unit. In this unit, Permian magmatism resulted in the emplacement of alkaline charnockites at mid-crustal levels. The primary mineralogical assemblage is nominally anhydrous and made of ortho- and clino-pyroxenes, fayalite, K-feldspar, plagioclase and quartz. These charnockites are associated with partially-molten paragneisses and marbles. Thermobarometry on these rocks indicates that the charnockites emplaced following the intrusion of a melt at a temperature > 1000 °C and pressure of around 6 kbar, corresponding to depth of ~20 km. The resulting thermal anomaly triggered the partial melting of paragneisses. Bulk geochemistry including Sr, Nd, Pb and Hf isotopes suggests that charnockites fit into the Tarim Large Igneous Province magmatic series, with minor crustal assimilation. U-Pb ages on zircons of charnockites and surrounding paragneisses indicate that charnockites intruded and triggered partial melting of the gneisses at c. 287, 275 and 265 Ma. 40Ar/39Ar dating on amphibole gives a similar age as the U-Pb age at 276.2 ± 2.0 Ma. 40Ar/39Ar dating on biotite from the Charnockite unit marbles gives ages at ca. 256–265 Ma, which shows that exhumation onset directly follows the HT history, and is tentatively correlated to top-to-the-North thrusting of the Charnockite unit in a transpressive context. Additional 40Ar/39Ar dating on syn-kinematic white micas from an adjacent transpressive shear-zone indicates continuation of the strike-slip tectonics at shallow crustal levels, after the exhumation of the Charnockite unit, at 248–257 Ma. These results demonstrate that Tien Shan Permian magmatism is linked to the Tarim mantle plume activity. Lithosphere-scale shear zones in the Tien Shan range, could have been responsible for lateral flow focusing of the Tarim mantle plume up to the boundary with the Tien Shan range and subsequent decompression melting resulting in the Permian magmatism observed in the Pobeda area.

In this study, we investigate the possible record of a Late Mesoproterozoic paired metamorphic belt in the Aravalli-Delhi Mobile Belt (ADMB), NW India using a suite of supracrustal and metaigneous granulites from the Pilwa-Chinwali granulite terrain at the north-western margin of the ADMB. Using metamorphic reaction textures, mineral chemistry, metamorphic reaction history, geothermobarometric computations and electron microprobe dating of monazite in 5 samples of pelitic granulite, leptynite gneiss, enderbite and charnockite, we have deduced a medium-pressure granulite facies metamorphism (P between 4.9 and 6.8 kbar, T > 760–815 °C) along a heating-cooling, counterclockwise P-T path between 1.09 and 1.01 Ga. When collated with published metamorphic and chronological constraints and geological settings of the adjoining crustal domains of the ADMB, these findings provide new insights into the developments of two tectonic domains of contrasting thermal gradients at ca. 1.0 Ga, consistent with metamorphic transformations in tectonically thickened middle-lower crustal sections during continental collision to continental subduction and in the root zones of spatially adjacent island arc, as part of the Rodinia supercontinent assembly event.

Ediacaran magmatism represents one of the most prominent features of the Borborema Province (NE Brazil), with the Umarizal intrusive suite a classical example of an anorthosite - mangerite - charnockite - granite (AMCG) association. This study presents new geochemical and petrological data, discusses its magmatic evolution, and compares the outcomes with similar rocks of Western Africa. The Umarizal suite displays mineral associations that crystallizated under high temperature (

The incipient charnockite or orthopyroxene-bearing granitic orthogneiss is a relatively common constituent in ancient granulite-facies terranes, and its formation has been often attributed to an influx of CO2-rich fluid or a removal of aqueous melt. Temporal relationship between the orthopyroxene formation and the fluid or melt migration, however, remains debatable. Here we report the first finding of incipient charnockite hosted by garnet-biotite-bearing granitic gneisses in the Sancheong–Hadong anorthosite complex, Yeongnam Massif. Both lithologies preserve a variety of field and microstructural evidence for partial melting and subsequent melt crystallization, as manifested by granitic leucosomes and biotite-rich residua. Based on the phase equilibria modeling and geothermobarometric calculation, peak metamorphic conditions of migmatities were estimated to be 5.4–6.0 kbar and 800–850 °C, which led to the biotite dehydration melting together with the orthopyroxene formation in incipient charnockite. Sensitive high-resolution ion microprobe (SHRIMP) U–Pb analyses of zircon from an incipient charnockite and a host gneiss yielded the weighted mean 207Pb/206Pb ages identical within errors; 1880 ± 5 Ma and 1872 ± 6 Ma for the cores, and 1862 ± 4 Ma and 1861 ± 4 Ma for the rims, respectively. The former is interpreted to represent the time for magmatic crystallization of granitic protoliths, whereas the latter for subsequent anatexis typified by peritectic growth of orthopyroxene. Such a timeline is consistent with two distinct thermal events previously reported from the Sancheong-Hadong anorthosite complex. By contrast, monazite grains from a biotite-bearing granitic gneiss in the charnockite zone yielded the weighted mean 207Pb/206Pb ages of 1866 ± 14 Ma and 1835 ± 11 Ma for the core and rim, respectively. The latter is consistent with 1842 ± 8 Ma, estimated from monazite neoblasts of incipient charnockite. The monazite growth during a post-peak metamorphic stage at ca. 1.84 Ga is attributed to a fluid influx event, apparently concentrated in the charnockite zone. The charnockite formation in the Yeongnam Massif further attests to the longevity (>ca. 40 m.y.) of hot orogenesis that has governed the Paleoproterozoic crustal evolution in eastern North China Craton.

This paper provides a report of a study of a series of boudined bodies of mineralogically zoned calc-silicate bodies, some over 1 m thick, enclosed in granulite facies charnockitic gneisses on West Ongul Island, Lützow-Holm Complex, East Antarctica. Zircons extracted from the centre of one of the calc-silicate bodies indicate that they were metamorphosed around 532.3 ± 0.8 Ma and that the cores of these zircons were inherited from igneous rocks intruded 738.5 ± 1.8 Ma and possibly 605.0 ± 1.2 Ma. The meionite content of scapolite indicates that the peak metamorphic temperature reached a minimum of 790 °C. In the outermost rim of the calc-silicate scapolite is partially replaced by clinopyroxene, probably as a result of the influx of Mg bearing fluids from the surrounding charnockite gneiss during uplift and decompression. An influx of hydrous fluid resulted in the almost complete retrogressive alteration of plagioclase to sericite throughout the calc-silicates, with minor growth of amphibole after clinopyroxene and calcite after scapolite only in the innermost zone.

The Volgo-Uralia segment, which constitutes one fourth of the East European Craton, is covered by sedimentary deposits. From geophysical studies and examination of thousands of drillcores, Volgo-Uralia has been recognised as a vast high-grade terrain with a complex crustal history extending from the Palaeoarchaean to the Palaeoproterozoic. Our recent studies are focused on the search for the oldest crust formation event by extracting whole rock Sm-Nd and zircon U-Th-Pb and Lu-Hf isotope information from samples recovered by drilling in southern Volgo-Uralia. Particular attention is devoted to the Kolyvan charnockitoid rock suite, which makes up several large areas of gneisses and granitoids of enderbite, charnockite and tonalite composition. The zircon from the granitoids show complex internal structures and consists of large magmatic cores with oscillatory zoning, surrounded by CL black-and-bright bands of metamorphic rims. The crystallisation age of the cores is defined as 3140 ± 7 Ma (SHRIMP) and 3127 ± 46 Ma (LA-ICPMS), while the CL-bright rims are dated at 1950 ± 25 Ma (LA-ICPMS). The ingressive recrystallisation of primary magmatic zircon correlates with depletion in REE, which is observed in each studied core-rim pair. No differences in O-isotopic compositions have been detected between the cores and the rims. δO18 values with an average of 5.8 ± 0.3‰ (1SD) implying that no supracrustal rocks were involved in the source of the Kolyvan melts. The Hf-isotope compositions of magmatic cores (−3 to −9 eHfT) and metamorphic rims (−14 to −28 eHfT), and their similar crustal model ages from 3.42 to 3.86 Ga indicate Eo- to Palaeoarchaean crustal sources for the charnockitic magmas. Sm-Nd model ages of ca 3.46 Ga for the Kolyvan rocks are consistent with the zircon Hf-isotope data and indicate a long crustal prehistory of a source of the Mesoarchaean magmas. We conclude that the Mesoarchaean Kolyvan suite rocks was formed by reworking of Eo- to Palaeoarchaean lithosphere, which probably had been widespread throughout Volgo-Uralia. The obtained geochemical and isotope data can be reconciled in a model of deep mantle-plume activity at 3.1 Ga causing mantle underplating, extension of the Palaeoarchaean crust and high-T magmatism.

In this study,in situand erratic samples from George V Coast (East Antarctica) and southern Eyre Peninsula (Australia) have been used to characterize the microstructural, pressure–temperature and geochronological record of upper amphibolite and granulite facies polymetamorphism in the Mawson Continent to provide insight into the spatial distribution of reworking and the subice geology of the Mawson Continent. Monazite U-Pb data shows thatin situsamples from the George V Coast record exclusively 2450–2400 Ma ages, whereas most erratic samples from glacial moraines at Cape Denison and the Red Banks Charnockite record only 1720–1690 Ma ages, consistent with known ages of the Sleaford and Kimban events, respectively. Phase equilibria forward modelling reveals considerable overlap of the thermal character of these two events. Samples with unimodal 1720–1690 Ma Kimban ages reflect either formation after the Sleaford event or complete metamorphic overprinting. Rocks recording only 2450–2400 Ma ages were unaffected by the younger Kimban event, perhaps as a result of unreactive rock compositions inherited from the Sleaford event. Our results suggest the subice geology of the Mawson Continent is a pre-Sleaford-aged terrane with a cover sequence reworked during the Kimban event.

The region to the east of Palghat gap is of low elevation and nearly circular in shape. It forms a part of the Kaveri river basin. The predominantly gneissic terrain is surrounded by the charnockitic hill ranges, prominent among which are Nilgiris and Biligirirangan to the north; and Anaimalai and Kodaikanal to the south. The charnockite massifs have a steep slope facing the circular feature and a gentler slope in the opposite direction. Fractures/faults/shear zones are noticed in many parts. The Bouguer anomaly in the gneissic terrain is elliptical in shape and positive, relative to the surrounding elevated region. The magnetic contours are also elliptical and the magnetic basement is deeper by about one km compared to regions in the periphery. The shallow seismic velocity picture from Chennimalai to Palani indicates a graben structure. The velocity structure also depicts a 4–5 km Moho upwarp near Chennimalai. Junction between the gneissic and charnockitic terrain and even beyond, is marked by the presence of pseudotachylites and breccia. Field and petrographic studies indicate presence of suevite, Planar Deformation Features (PDF), Planar Fractures, diaplectic glass of quartz and plagioclase and spherical inclusion in suevite. These evidences taken together point to an extra-terrestrial impact which created a crater of approximately 120 km in diameter. Several lines of indirect evidences point to Neoproterozoic age for the impact. Kaveri Crater is the fourth largest crater on the surface of the Earth; other larger craters being Vredefort (160 km), Chicxulub (150 km) and Sudbury (130 km).

The Jagtiyal section exposes a part of the Precambrian granulite – facies terrane in the northeastern Dharwar Craton, specifically charnockite, orthogneiss, mafic granulite, garnet-cordierite gneiss and silica-deficient Mg-Al granulite. The silica-deficient Mg-Al granulites exhibit well-preserved metamorphic reaction microstructures and were used to elucidate the metamorphic history of the study area. Textural evidence exists for the prograde break-down of biotite and corundum and formation of a peak metamorphic assemblage of spinel, sapphirine, orthopyroxene, cordierite and K-feldspar. KFMASHTO system based P-T pseudosections as well as the application of multi-equilibrium calculation for mineral core compositions, gave P-T conditions of 7.5–8 kbar and 800–840 °C. The thermal peak was followed by near isothermal decompression that led to a variety of coronal textures including, successive rims on corundum, consisting of spinel + sapphirine + cordierite ± orthopyroxene, and symplectitic intergrowth of sapphirine-cordierite, orthopyroxene-cordierite, spinel-cordierite, and biotite-cordierite. Modelled P-T conditions for this stage are 4.3–4.5 kbar and 750–800 °C. Few samples show textural evidence for further retrogression leading to the break-down of sapphirine and cordierite to form chlorite, corundum, spinel and andalusite. The proposed clockwise P-T path implies that granulites from the Jagtiyal section likely resulted from thickened continental crust undergoing decompression. New U-Pb zircon geochronologic data provide evidence for a Neoarchaean (2604 ± 25 Ma) age that likely corresponds to the timing of accretion of the terrane that was subjected to high temperature metamorphism at that time. Moreover, there is evidence of a Neoproterozoic thermal overprint in the area around 638 Ma. .

This study focuses on the evolution of the Central Gneissic Belt of the Archean Rengali Province which evolved as a craton-margin orogenic belt. The Central Gneissic Belt is constituted of charnockite gneiss, migmatitic hornblende gneiss and granite gneiss often showing gradational contacts. While mafic granulite occurs as enclave within the charnockite gneiss, amphibolite and calc-silicate granofels enclaves are present within the granite gneiss. Mafic granulite shows peak metamorphic assemblage of garnet + clinopyroxene + plagioclase + quartz ± orthopyroxene which was stabilized at 10.6 ± 0.5 kbar and 860 ± 20 °C. Charnockite gneiss with the peak assemblage of orthopyroxene + quartz + plagioclase + K-feldspar was metamorphosed at 792 ± 48 °C and 7.6 ± 0.4 kbar. Amphibolite and migmatitic hornblende gneiss contain hornblende along with plagioclase and garnet and these rocks were metamorphosed at 800 ± 20 °C, 8.5 ± 0.2 kbar and 695 °C, 8 kbar respectively. Later meta-dolerite dikes exhibit relic igneous textures which are slightly modified by greenschist-facies metamorphism. Charnockite gneiss, migmatitic hornblende gneiss and granite gneiss show similar trace and REE characteristics (moderate fractionation in terms of La and Yb, LREE enrichment and flat HREE pattern) implying the same protolith composition for these rock groups. Based on the field, petrographic and geochemical data, we propose that the protoliths for the charnockite gneiss, the migmatitic hornblende gneiss and the granite gneiss crystallized as fractionated magma in within-plate syncollisional setting during the ca. 2860–2780 Ma orogeny at the Rengali Province.

Incipient charnockites representing granulite formation on a mesoscopic scale occur in the Ambodin Ifandana area of Ikalamavony sub-domain in south-central Madagascar. Here we report new petrological data from these rocks, and discuss the process of granulite formation on the basis of petrography, mineral equilibrium modeling, and fluid inclusion studies. The incipient charnockites occur as brownish patches, lenses, and layers characterized by an assemblage of biotite + orthopyroxene + K-feldspar + plagioclase + quartz + magnetite + ilmenite within host orthopyroxene-free biotite gneiss with an assemblage of biotite + K-feldspar + plagioclase + quartz + magnetite + ilmenite. Lenses and layers of calc-silicate rock (clinopyroxene + garnet + plagioclase + quartz + titanite + calcite) are typically associated with the charnockite. Coarse-grained charnockite occurs along the contact between the layered charnockite and calc-silicate rock. The application of mineral equilibrium modeling on the mineral assemblages in charnockite and biotite gneiss employing the NCKFMASHTO system as well as fluid inclusion study on coarse-grained charnockite defines a P–T range of 8.5–10.5 kbar and 880–900 °C, which is nearly consistent with the inferred P–T condition of the Ikalamavony sub-domain (8.0–10.5 kbar and 820–880 °C). The result of T versus H 2 O activity ( a (H 2 O)) modeling demonstrates that orthopyroxene-bearing assemblage in charnockite is stable under relatively low a (H 2 O) condition of 0.42–0.43, which is consistent with the popular models of incipient-charnockite formation related to the lowering of water activity and stabilization of orthopyroxene through dehydration of biotite. The occurrence of calc-silicate rocks adjacent to the charnockite suggests that the CO 2 -bearing fluid that caused dehydration and incipient-charnockite formation might have been derived through decarbonation of calc-silicate rocks during the initial stage of decompression slightly after the peak metamorphism. The calc-silicate rocks might have also behaved as a cap rock that trapped CO 2 infiltrated from an external source. ‘CO 2 -rich fluid ponds’ formed beneath calc-silicate layers could have enhanced dehydration of biotite to orthopyroxene, and produced layers of coarse-grained charnockite adjacent to calc-silicate layers.

The concentrations of 26 trace elements have been determined by laser ablation ICP-MS in zircons from four samples of basic rocks of the Korosten anorthosite-mangerite-charnockite-granite plutonic complex, the Ukrainian Shield. Zircons from the Fedorivka and Torchyn gabbroic intrusions and Volynsky anorthosite massif have distinctive abundances of many trace elements (REE, Sr, Y, Mn, Th). Zircons from the gabbroic massifs are unusually enriched in trace elements, while zircons from pegmatites in anorthosite are relatively depleted in trace elements. High concentrations of trace elements in zircons from gabbroic intrusions can be explained by their crystallization from residual interstitial melts enriched in incompatible elements. The zircons studied demonstrate a wide range of Ti concentrations, which reflects their temperature of crystallization: the zircons most enriched in Ti, from mafic pegmatites of the Horbuliv quarry (20–40 ppm), have the highest temperature of crystallization (845 ± 40 °C). Lower (720–770 °C) temperatures of zircon crystallization in gabbroic rocks are explained by its crystallization from the latest portions of the interstitial melt or by simultaneous crystallization of ilmenite. The Ce anomaly in zircons correlates with the degree of oxidation of the coexisting ilmenite.

Archean supracrustal granulites occur as localized slivers or rafts in granitoids, and this particular occurrence of supracrustal granulites has not been much concerned from the perspective of metamorphic evolution. The pelitic granulites in eastern Hebei occur as slivers in TTG gneisses and charnockite. Three pelitic granulite samples involving orthopyroxene–garnet gneiss (JD1334), biotite–garnet gneiss (JD1453) and sillimanite–garnet gneiss (JD15126) were collected from Taipingzhai and Laolijia areas. Based on textural observations and mineral compositions, four generations of assemblages involving final, peak, inclusion and overprinting stages are identified. The observed final assemblage yield P–T conditions of 8.0–9.5 kbar/870–890 °C. The observed peak assemblage characteristic of the absence of the matrix biotite record condition of T > 950 °C with fixed P = 9 kbar. An isobaric cooling path from peak to final assemblage is constrained by mineral isopleths. The inclusion assemblages characterized by plagioclase inclusions with high X An contents are predicted to be stable at low pressure and/or high temperature field. They form an anticlockwise P–T path. The overprinting assemblage characteristic of coronary garnet (g 2 ) coexisting with fine-grained mineral aggregates defines P–T condition of 10–12 kbar/830–880 °C. The deposition age of the sedimentary protolith of pelitic granulites was ∼2.5 Ga, coeval with the crystallization age of TTG gneisses. Both of them were later subjected to granulite facies metamorphism at ∼2.48 Ga. The Archean anticlockwise P–T paths suggest a tectonic scenario to explain the particular occurrence of the Archean supracrustal granulites. Firstly, supracrustal sediments experienced thermal event under low pressures attributed to the intrusion of high-temperature TTGs, resulting in dehydrations of hydrous phases. Then, the dried metasediments interlayered with iron-bearing formations potentially denser than the surrounding lithologies tend to drop into the TTG magma ocean, causing the pressure-increase in the metasediments. Thirdly, the dropped metasediments experienced cooling process under lower crust in coupled with the crystallization of the surrounding TTG magma to form the observed final assemblages. Finally, they uplifted as a consequence of the doming processes in Archean terranes.

Garnetiferous pelitic to psammopelitic migmatites widespread across the central and eastern part of the Aravalli–Delhi Fold Belt in NW India record two distinct orogenies, e.g. the Aravalli Orogeny (1.7–1.6 Ga) and the Delhi Orogeny (1.0 Ga). In this study, we integrate field geological studies with textural and mineral–chemical analyses,P–Tpseudosection modelling andin situmonazite dating in anatectic migmatites in the Aravalli Supergroup occurring along the Deoli–Shahpura segment. The study reveals formation of peak assemblages of garnet + sillimanite + biotite + K-feldspar + melt and garnet + muscovite + K-feldspar + melt in two anatectic migmatite samples.P–Tpseudosection modelling suggests that anatexis in the gneisses occurred at ~8 kbar and 700–800°C along a tight-loop clockwiseP–Tpath. Monazite ages from the migmatites indicate that the anatexis occurred at ~1.73–1.74 Ga. This age is similar to the Palaeoproterozoic anatexis (at 7–8 kbar) and charnockite emplacement in the Sandmata and the Mangalwar complexes, the subsolidus amphibolite-facies metamorphism in the Rajpura–Dariba and Pur–Banera supracrustal belts, and the A-type granite magmatism in the North Delhi Fold Belt. We propose that the Palaeoproterozoic migmatites in central and eastern Rajasthan are part of the one crustal unit that underwent anatexis during an accretion event along the NE–SW-trending Aravalli orogenic belt.