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Modern analogues of Archaean charnockite are important because they facilitate investigations into processes of early crustal formation and tectonic transition. Herein, we present the results of the petrography, geochemistry, and isotope geochronology of Late Neoarchean charnockites in the Daqingshan terrane at the northern margin of the North China Craton. The sources, petrogenesis, and tectonic implications of the samples obtained are determined based on their geochemical characteristics. Charnockites mainly exhibit magnesian and calc–alkaline characteristics; furthermore, they contain high amounts of light rare-earth elements, with slightly positive Eu anomalies. Analysis of zircon U–Pb dating using a sensitive high-resolution ion microprobe reveals that Hademengou–Xiwulanbulang (HDMG–XWLBL) charnockites were emplaced during the (i) Late Neoarchean (ca. 2500 Ma), with zircon εHf(t) values ranging from 1.57 to 7.81; (ii) single-stage model ages (TDM1) from 2529 to 2637 Ma; and (iii) two-stage model ages (TDM2) from 2710 to 2820 Ma. A comparative study has performed on the petrography, geochemistry, and geochronology of charnockite and granulite shown that the parent magma of the charnockites is the product of the partial melting of granulite. Combining our results with geological data pertaining to the Archaean structural evolution of the Daqingshan terrane, we speculate that the Late Neoarchean HDMG–XWLBL charnockite was formed during a subduction-related thermo-tectonic event in the northern margin of the North China Craton. [ABSTRACT FROM AUTHOR]

The strength of rock under uniaxial compression, commonly known as Uniaxial Compressive Strength (UCS), plays a crucial role in various geomechanical applications such as designing foundations, mining projects, slopes in rocks, tunnel construction, and rock characterization. However, sampling and preparation can become challenging in some rocks, making it difficult to determine the UCS of the rocks directly. Therefore, indirect approaches are widely used for estimating UCS. This study presents two Machine Learning Models, Simple Linear Regression and Step-wise Regression, implemented in Python to calculate the UCS of Charnockite rocks. The models consider Ultrasonic Pulse Velocity (UPV), Schmidt Hammer Rebound Number (N), Brazilian Tensile Strength (BTS), and Point Load Index (PLI) as factors for forecasting the UCS of Charnockite samples. Three regression metrics, including Coefficient of Regression (R2), Root Mean Square Error (RMSE), and Mean Absolute Error (MAE), were used to evaluate and compare the performance of the models. The results indicate a high predictive capability of both models. Notably, the Step-wise model achieved a testing R2 of 0.99 and a training R2 of 0.988 for predicting Charnockite strength, making it the most accurate model. The analysis of the influential factors indicates that UPV plays a significant role in predicting the UCS of Charnockite. [ABSTRACT FROM AUTHOR]

Madurai Block (MB) and Trivandrum Block (TB), composed of similar high-grade gneisses separated by the Achankovil shear zone (AKSZ), represent two different crustal domains with distinct crustal evolutionary history. Geochemistry of garnet-biotite gneisses and charnockites from both the blocks shows that the studied rocks are magnesian and calcic to calc-alkaline in nature, indicating magmatic-arc settings. Both the litholunits from the TB and MB displayed an enrichment of light rare earth elements, depletion of high field strength elements and flat heavy rare earth elements pattern. In addition to these, the garnet-biotite gneisses of the TB shows a strong negative Eu anomaly, suggesting the crustal contamination of the source and post-Archean granitoid origin. In the Nb vs. Y diagram, most of the charnockites and garnet-biotite gneisses from the MB and TB fall within the syn-collisional granite and volcanic-arc field. Rb vs. (Y+Nb) and Ta vs. Yb diagrams show a volcanic-arc granite trend for all the lithounits. In the modified La/Yb vs. Th/Yb plot, most of the MB rocks fall within the island-arc field and the TB rocks fall within the continental margin-arc field. Such chemical signatures, characteristic of arc magmatism in active continental margins, suggest subduction-related geodynamic settings along the AKSZ. [ABSTRACT FROM AUTHOR]

The role of S during high-grade metamorphism is a topic that has not garnered much interest in the literature until recently. In this review, the role of S as an active component in high grade hypersaline fluids is reviewed per a series of regional studies involving orthopyroxene-bearing granulite-facies granitoids. These include the Shevaroy Block and Nilgiri Block, southern India; the Bamble Sector, southwest Norway; the Val Strona traverse of the Ivrea-Verbano Zone, northern Italy; and the Lewisian Complex, northwest Scotland. In each these terranes, S-bearing, high-grade, low H2O activity fluids are conjectured to have been present during granulite-facies metamorphism and to have contributed to the dehydration of the rock, the oxidation state of the rock, and trace element mobility, leaving behind pyrite and/or pyrrhotite as traces of its presence. The various mineral equilibria reactions between the various oxidation states of S in these fluids and the oxide and silicate minerals encountered by the fluid are explored and a coherent framework of interdependent chemical reactions are developed, which describe both oxidation of the rock and the formation of pyrite and pyrrhotite during both peak- and post-peak metamorphism. [ABSTRACT FROM AUTHOR]

Orthopyroxene granitoids (designated as charnockites or granitoids of the charnockite series) are characterized by varying silica and felsic mineral content, with the orthopyroxene (hypersthene) phase as the main characteristic mafic mineral component. These rocks are abyssal and represent parts of intrusions or form their own igneous complexes at the depth of the lower crust under CO2-undersaturated and dry conditions, which can be achieved within any tectonic setting. Therefore, petrogenetic models for orthopyroxene granitoids as well as for all types of granitoids from different locations are sufficiently applicable for a reconstruction of paleogeodynamic conditions in a certain region. The East Antarctic shield is characterized by Archean blocks embedded within orogens of Mesoproterozoic, Late Mesoproterozoic‒Early Neoproterosoic and Late Neoproterosoic‒Early Paleozoic age, and syn- and post-orogenic intrusions composed of orthopyroxene granitoids and related rocks are widely spread and form a prominent volume of the East Antarctic orogens. According to paleogeodynamic reconstructions of Rodinia, Pannotia and Gondwana supercontinents the East Antarctic shield represents a significant volume of supercontinents' crust. Petrogenetic models for East Antarctic orthopyroxene granitoids became fundamental for any paleogeodynamic reconstractions of supercontinents. We collected structural geology, tectonics, and geochronology data for orthopyroxene granitoid intrusions belonging to orogens of certain age and combined with the plotting of geochemical data in major and rare element tectonic discrimination diagrams, also analyzed the Sm‒Nd isotope system data. The East Antarctic orthopyroxene granitoids tightly related to orogens are characterized by magmatic sources determined as combination of mafic lower crust, upper crust and juvenile mantle materials mixing up in different proportions depending on type of orogeny. It was established that orthopyroxene granitoids related to Mesoproterozoic and Late Mesoproterozoic‒Early Neoproterosoic orogens formed at different stages of long-lived collision transforming from ocean‒continent to continent‒continent types whereas Late Neoproterosoic‒Early Paleozoic orthopyroxene granitoids arose in post-collision tectonic setting. [ABSTRACT FROM AUTHOR]

The Granulite Terrane of Southern India is a collage of Mesoarchean–Neoproterozoic crustal blocks that underwent high‐grade metamorphism associated with the final assembly of the Gondwana supercontinent during late Neoproterozoic–Cambrian. Here, we investigate the charnockites and associated sapphirine‐bearing semipelitic granulites from the eastern part of the Madurai Block (MB). We present new petrographic, mineral chemistry, and geochronological data to constrain the P–T–t evolution of the block and unravel the timescale and source of heat for the ultrahigh‐temperature metamorphism. Both the rock types contain coarse‐grained porphyroblastic garnet and orthopyroxene, yielding peak P–T conditions of 950 ± 30°C at 10.5 ± 0.8 kbar and 970 ± 40°C at 10 ± 0.5 kbar for semipelite and charnockite, respectively, using conventional thermobarometry. Peak ultrahigh temperatures are further supported by high Al content in the orthopyroxene (8.78 wt% Al2O3) coexisting with garnet (XMg: up to 0.57) and feldspar thermometry of the mesoperthites and antiperthites in the semipelite, yielding 950–980°C at 10 kbar. Subsequent decompression has led to the formation of coronal orthopyroxene3 + plagioclase3 in the charnockite and symplectic orthopyroxene3 + cordierite ± sapphirine ± plagioclase3 in the semipelite, yielding P–T range of 950–850°C and 9.5–6.8 kbar for semipelites and 950–820°C and 8–6.5 kbar for charnockite. Based on the obtained P–T estimates, preserved reaction textures, and phase equilibria modelling in the MnNCKFMASHTO system, a clockwise P–T evolution with isothermal decompression followed by cooling is inferred for both the rock types. Texturally constrained in situ monazite dating and rare earth element (REE) patterns show that the core of matrix monazite having low‐Th, Y, and extreme heavy rare earth element (HREE) depletion, yielding weighted mean ages of 582 ± 12 and 590 ± 22 Ma for semipelite and charnockite, respectively, dates the prograde evolution. The mantle of the matrix monazite in semipelite and comparable rim in charnockite, having relative Th‐enrichment compared to the core, yielding weighted mean ages of 552 ± 9 and 557 ± 13 Ma, respectively, dates extensive dissolution–reprecipitation from the melt at the peak stage. The relatively Th‐ and Y‐rich and moderately HREE‐depleted rim of matrix monazite in the semipelite, yielding weighted age of 516 ± 6 Ma, date initial garnet breakdown during post‐peak melt crystallization. By contrast, compositionally homogenous HREE + Y‐enriched monazite in the symplectite and retrograde monazites yielding weighted mean ages of 487 ± 47 Ma for semipelites and 508 ± 19 Ma for charnockites dates extensive garnet breakdown during final stages of melt crystallization and subsequent cooling. Our findings point to collision initiation at ~590 Ma, with the peak conditions attained at ~550 Ma followed by extensional collapse at ~510–490 Ma, resulting in rapid exhumation of lower crustal rocks to mid‐crustal levels under sustained ultrahigh‐temperature (UHT) conditions, followed by cooling to reach a stable geotherm. Our results suggest a long‐lived hot orogeny in the MB, where the UHT conditions were sustained for at least 40 MYr. The UHT conditions were most likely attained in the core of a long‐lived hot orogen by the combined effect of conductive heating through radioactive decay and mantle heat supply, with the former being the primary driver. [ABSTRACT FROM AUTHOR]

The paper presents authors' original detailed data on rocks of the Archean Pon'goma-Navolok charnockite−enderbite complex in northern Karelia. The rocks practically have not been modified and are preserved within a rigid block among Paleoproterozoic zones of ductile deformations and metamorphism. The geochemistry of the rocks and their isotope−geochemical features indicate that the protolith from which the enderbite melts of the main phase of the massif were derived may have been amphibolites. The enderbite melts were derived from these amphibolites under the effect of K2O-, Na2O-, and SiO2-bearing fluids; and the enderbites were subsequently charnockitized with the involvement of fluids enriched in K2O and SiO2. Physicochemical modeling indicates that the enderbite melt was derived from the amphibolite protolith at a depth of about 45 km (P = 14.8 kbar, T = 1030−1080°C) under the effect of saline H2O−CO2 fluid. Comparison of the P−T parameters of the granulite-facies metamorphism of the metabasites and the parameters under which the enderbite melts were derived indicates that Archean granulite-facies metamorphism in the Belomorian belt in northern Karelia was of contact but not regional nature and was induced by the high-temperature field of an emplaced enderbite massif. The orthogneisses hosting the Pan'goma-Navolok massif inherit geochemical features of the unsheared, ungneissose, and unmetamorphosed enderbites. This means that enderbites analogous to those of the Pan'goma-Navolok massif may have served as the protolith of some of the orthogneisses, and that enderbites may have been spread more widely in the Archean than the currently preserved single enderbite massifs. [ABSTRACT FROM AUTHOR]

The South Indian Granulite Terrane is traversed by several crustal scale shear zones, however the tectonic significance of the shear zones are poorly understood. The tectonic relevance of the Bavali Shear Zone (BSZ) ‒ in the WNW extremity of the Moyar Shear Zone ‒ at the interface between the Paleoarchean to Neoarchean Western Dharwar Craton (WDC) in the north and the late Neoarchean Nilgiri block in the south is poorly constrained. The most conspicuous feature in the WDC is a set of N-striking gently-plunging upright folds and N-striking dextral shear zones (deformation D4). These D4 structures are superposed on a shallowly-dipping D3 recumbent folds and gently-dipping mylonite fabrics in a suite of anatectic gneisses, lower-grade supracrustal rocks and foliated granitoids. In regional scale, the D3 fold axes curve into the WNW-striking BSZ (D5 deformation), a steep-dipping transpressional shear zone with dextral kinematics. The BSZ is characterized by steeply-plunging stretching lineations sub-parallel to the hinges of reclined folds on the pre-shearing fabrics in the lithologies of the adjacent cratons. Syn-D5 charnockite veins suggest the BSZ formed at T > 850 °C. Existing U–Pb (zircon) dates and monazite chemical dates (this study), indicate that the deformation-metamorphism-magmatism in the WDC and the Nilgiri block occurred between 3400 and 2500 Ma; by contrast the high-T D5 oblique crustal shortening in the BSZ contemporaneous with multiple felsic emplacements was active between 830 and 720 Ma. The BSZ collision orogeny possibly preceded the eventual integration of the Greater India landmass with the Gondwanaland during the early-Palaeozoic. [ABSTRACT FROM AUTHOR]

Due to the influence of various factors such as mineral composition and crystal size, the failure and fracture evolution of granite under three-point bending tests have not been fully determined. In this study, active/passive AE tests are conducted on a cuboid granite specimen at a constant loading rate under a three-point bending test. Acoustic emission monitoring and DIC (Digital Image Correlation) technology are used to investigate the fracture mode and evolution during the fracture process of the specimen. Through analyzing the moment tensor inversion, RA (rise time/amplitude), AF (average frequency) and surface strain field variation characteristics, the fracture characteristics of the specimen is determined. The results show that the fracture of the specimen failure occurs instantaneously. In the early loading stage of the specimen, the main frequency and amplitude of the AE signals are low. However, a large number of high, medium and low frequency AE signals are observed when there is a fracture, which can serve as a precursor to determine the specimen fracture. The fracture type of the specimen is primarily linear tension fracture, with a small proportion of shear fracture, double force couple fracture, and mixed fracture sources. The strain on the surface of the granite specimen is mainly in the X-direction, with a significant increase of proportion in the early stage of fracture. Prior to fracture, the main fracture rapidly propagates from the bottom to the middle of the specimen, leading to the final specimen failure, where it breaks into two distinct blocks along the observable main fracture. [ABSTRACT FROM AUTHOR]

Charnockites (orthopyroxene-bearing granitoids) constitute one of the major components in many Precambrian high-grade metamorphic terranes of the world. They are broadly classified into two types based on the nature of occurrence as massive charnockite that forms large (magmatic) batholiths, and incipient charnockite which occurs as patches, veins and lenses of mesoscopic scale developed through local dehydration reactions within felsic (both igneous and sedimentary) protoliths. Here we present petrological data on representative charnockites of different ages and tectonic settings from various parts of the world and evaluate their formation conditions based on phase equilibrium modeling in the system NCKFMASHTO. Massive charnockites ranging from Neoarchean to Paleoproterozoic age from the Salem and Nagercoil Blocks (southern India), Napier Complex (Antarctica), and the Limpopo Complex (Zimbabwe) record P-T conditions that are broadly equivalent to the regional P-T conditions of high-grade metamorphism recorded in these terranes, ranging from normal granultes to ultrahigh-temperature metamorphic rocks. Typical unmetamorphosed magmatic charnockite in a late Paleoproterozoic post-collisional extensional setting and carrying K-feldspar phenocrysts from the North China Craton yield a wide P-T stability range. Incipient charnockite from southern India records P-T conditions that are slightly lower than the peak P-T regimes estimated for the region. Regardless of the discrepancies in P-T conditions estimated from the phase equilibria approach, the data confirm that these rocks, in all the cases considered in this study, were generated under low aH2O conditions. The available fluid inclusion data from both massive and incipient charnockites confirm that the water activity was buffered to low levels, possibly through the presence of CO2-rich fluids, to stabilize the index mineral orthopyroxene in these rocks. Charnockites formed in different plate tectonic settings; in most cases as arc magmas within subduction-collision settings and some cases, post-collisional extension during different periods in Earth history, and serve as potential archives of melt and fluid processes in the continental crust.

The present work is focussed on a suite of high-grade rocks including mafic granulite, aluminous granulite, khondalite, charnockite, and augen gneiss along with medium-grade rocks like olivine-bearing metanorite, gabbro, and porphyritic granite of the Angul domain at the northern margin of the Proterozoic Eastern Ghats Province (EGP). Based on the petrological and geothermobarometric data, two distinct metamorphic events have been identified. The imprints of the earlier event (MA1) are preserved in the mafic granulite, aluminous granulite, khondalite, augen gneiss, and fine-grained charnockite, but those are best preserved in mafic granulite and aluminous granulite. In mafic granulite, orthopyroxene + clinopyroxene + plagioclase ± garnet+ ilmenite ± quartz assemblage was stabilised at the peak MA1 conditions, whereas the peak MA1 assemblage is represented by Fe3+-garnet + hematite + magnetite + cordierite + K-feldspar + plagioclase + sillimanite + quartz + melt in aluminous granulite. Phase equilibria modelling and thermobarometric data suggest the P–T conditions of >850°C, 7 to 8 kbar for this event. The retrograde metamorphism (MA1R) involved minor decompression (down to ~5 kbar) and subsequent cooling to form biotite- and hornblende-bearing mineral assemblages in aluminous granulite and mafic granulite, respectively. Texturally constrained monazite (U–Th–total Pb) and zircon (U–Pb) data from the former rock suggest ca. 1200 Ma age of the MA1 metamorphism, which was associated with granitic and charnockitic magmatism as constrained from oscillatory-zoned zircon domains in the augen gneiss and fine-grained charnockite. The rock ensemble was affected by a younger metamorphic event (MA2), which is texturally characterised by partial replacement of hornblende (developed during MA1R) to orthopyroxene ± clinopyroxene + plagioclase ± ilmenite + melt assemblage in mafic granulite. Moreover, biotite of aluminous granulite has undergone dehydration melting to produce garnet + cordierite-bearing assemblage. Garnet in the above assemblage did not form as porphyroblastic phase and overgrew the MA1 garnet. The MA2 event followed a counterclockwise P–T trajectory, causing heating (up to 800°C) with associated loading (from 4.0 to 5.8 kbar) along the prograde path. Monazite U–Th–total Pb data from aluminous granulite and khondalite suggest MA2 ages of 987 ± 12 and 975 ± 16 Ma, respectively. Fine-grained charnockite and augen gneiss also recorded the imprints of MA2 event by developing thin to thick sector-zoned overgrowth yielding group ages of 979 ± 12 and 982 ± 29 Ma, respectively. Zircon overgrowth in mafic granulite formed at 962 ± 13 Ma. The MA2 event coincides with the crystallisation of coarse-grained charnockite at 983 ± 22 Ma and porphyritic granite at 960 ± 10 Ma. Geochronological data, thus, indicate that the Angul domain underwent the MA2 metamorphism and associated magmatism at ca. 990 to 960 Ma. The apparent absence of MA1 event (~1200 Ma) in the greater part of the EGP and its dominance in the Angul domain suggest that the latter was possibly an exotic block at ca. 1200 Ma and joined with the rest of the EGP only after ca. 960 Ma. We further suggest that the metamorphic history of the Angul domain is strikingly different from the rest of the EGP, but matches well with that of the Prydz Bay region of the East Antarctica. [ABSTRACT FROM AUTHOR]

Phosphorus, P deficiency by adsorption and fixation of applied P is a critical problem in the tropical soils coupled with wastage of agricultural land and potential nutrients from crop residues’ decomposition necessitates conservancy and sustainable management. Maize stover biochar (mB) and sawmill waste biochar (sB) pyrolysed for 60-minute at 460 °C using Top-Lit Up Draft (TLUD) carbonizer were characterized by morphological, elemental and proximate properties analysed by Scanning Electron Microscope (SEM), CHNS Elemental Analyser and appropriate methods, respectively. Phosphorus (P) adsorption potential of the biochars in charnockite-originated soils were evaluated using adsorption isotherms after adding biochars at 0, 5, 10 and 20% (w/w) with concentrations of 0, 15, 30, 60, 90, 120, 150 mg P/L. SEM showed macropores (>50 nm) embedded biochars, with higher elemental C and H in sB while mB contained higher N, S, O, available P and pH. P-adsorption decreased inconsistently with increasing biochar rates resulting in P-desorption. Low Langmuir adsorption maximum (Qm) were recorded (−0.0350 to 0.1250 mg kg−1) mostly with negative separation factors (RL) and the adsorption process were favourable for mB amended soils having Freundlich heterogeneity factor (nF) of 4.476–9.634 but not for sB amended soils (nF = 0.638–2.812). Biochar production conserved nutrient loss and potentially reduced soil P fixation.

Results of a geochemical and geochronological study of the Paleoproterozoic rock assemblage in the Haisyn block of the Ros-Tikych Domain of the Ukrainian Shield are reported. Within the block, the Haisyn Complex comprises granitoids, including pyroxene-bearing diorites, quartz diorites, granodiorites, amphibole-biotite and biotite granites, and aplite and pegmatite granites. Monazite U-Pb isotope age of charnockitic syenite belonging to the Haisyn Complex was defined at 2027 ± 6 Ma. This age coeval with the time of granulite facies metamorphism and emplacement of numerous granitic intrusions in the area. The Sm–Nd apatite isochron yielded an age of 2100 ± 150 Ma. The εNd isochron value of − 5 indicates a long crustal residence time of the crustal protolith. Geochemical data do not indicate any enrichment of the studied rocks in relation to the Eoarchean and Neoarchean charnockites developed in the same area. So, if the model of partial melting of the older crustal protolith is involved then the degree of melting must be quite high. However, deep negative anomalies of Sr, Eu, Zr, and Ti indicate that plagioclase, zircon, and Fe–Ti oxides probably remained unmelted in the source. The Haisyn block was buried in the lower crust at high temperature and pressure conditions in the Paleoproterozoic time. Such a situation resulted in partial melting of the existing crust and formation of melts, containing undigested zircon and bearing ancient Nd isotope signature. [ABSTRACT FROM AUTHOR]

Manufactured sand (MS) has been started utilizing as an alternative in constructions due to the escalated demand for river sand (RS). The microfine aggregate (MFA) is a salient constituent in manufactured sand, which is a crushed reactive form of parent rocks having particles less than 0.075 mm. This paper presents the effects of varying microfine aggregate levels on bleeding, plastic shrinkage cracking (PSC) and compressive strength of MS made concrete. Two types of MS were utilized: MS from Hornblende‐Gneiss rock (MH) and MS from Charnockite rock (MC) and the MFA level was ranged from 0% to 12% at 3% increments and the reference concrete was prepared with RS alone. With the MFA levels, the bleeding of MS concretes was reduced where, at 0% MFA level the maximum bleeding rates were observed for MC (1.63 kg/m2) and MH (0.84 kg/m2) concretes. PSC results were analyzed from an image processing technique, which revealed an increasing trend of mean and maximum crack widths, crack length and crack area with the MFA levels. At 0% MFA, the mean crack width of MC (0.19 mm) and MH (0.17 mm) concretes manifested marginally similar to RS concrete (0.17 mm). The decreasing bleeding with the MFA levels can be attributed to the increasing severity to PSC. Moreover, the optimum 28 days compressive strength of MC (57.5 MPa) and MH (56.1 MPa) concretes was achieved at 3% MFA level which are higher than RS concrete (51.5 MPa). Consequently, the MFA level should be limited to 3% for better plastic and hardened performance of MS made concrete. [ABSTRACT FROM AUTHOR]

Charnockites form an important component of the lower continental crust. Quantitative investigation on the properties of magmas that can stabilize orthopyroxene at solidi is crucial to understanding the petrogenesis of igneous charnockites. This study has performed detailed petrologic analyses and thermodynamic constraints on the Paleoproterozoic high-maficity (FeOT + MgO = 5–14 wt%) and peraluminous charnockites from the Jining Complex in the North China Craton. These charnockites occur as intrusions in granulite facies terranes and contain the mineral assemblages including prevalent perthitic/antiperthitic feldspars and garnet with minor biotite (usually less than ~5 vol%) beside orthopyroxene. The Jining charnockitic magmas were ascertained to have ultrahigh temperatures up to 1050–1100°C, poor H2O contents around 0.14–0.42 wt% and limited aluminum saturation indexes (ASIs) of 1.0–1.3. The stabilization of orthopyroxene at the solidus is attributed to low magmatic H2O contents and ASIs, which have maxima of 1.2 wt% and 1.5, respectively, and are positively correlated to bulk-rock maficity. Such charnockitic magmas could not release H2O-rich fluids near solidi, as the H2O is buffered by the orthopyroxene–biotite pair. Moreover, combined geochemical discrimination and progressive melting modelling reveal that the Jining charnockites were generated by partial melting of a greywackic granulite source, with about 15%–40% entrainment of solid phases in mushy magmas. The melting occurs at temperatures as high as 1050–1100°C, obviously beyond biotite stabilities, and involves quartz, feldspars and garnet as melting reactants, which differs from the previous proposition that peraluminous charnockites are related to biotite dehydration melting. The resultant magmas are substantially enriched in maficity and depleted in H2O due to both the melt compositions per se and the high entraining capability. Such peraluminous charnockite plutons massively emplaced in granulite facies terranes indicate post-orogenic ultrahigh-temperature anatexis of metasedimentary rocks in conditions close to the crustal dry solidus. [ABSTRACT FROM AUTHOR]

The petrochemistry of charnockitic rocks from the Awo-Osuntedo area of southwestern Nigeria were investigated with the objectives of presenting their petrogenesis and geotectonic setting at the time of their emplacement. The rocks were mainly found within the migmatitic gneiss country rock and associated pegmatites. They occurred as small intrusive bodies and are composed mainly of orthopyroxene, clinopyroxene, quartz, biotite, secondary amphibole, plagioclase and alkaline feldspars with a small compositional range between basic and intermediate respectively for Awo and Osuntedo rocks. The small Eu* anomalies (0.9-1.47) with an average of 1.2 combined with elemental signatures indicate that the rocks were derived from an enriched mantle with some crustal contamination and emplaced in an environment similar to the arc region of tectonic setting. Though, the rocks have dry mineral assemblages, there is no geochemical evidence to suggest they were derived from melting that was associated with granulite facies metamorphism rather the small sizes of the plutons and the geochemical signatures particularly high magnesian and calc-alkaline nature are typical of the Caledonian type charnockite formed during delamination of thickened continental crust after collisional orogeny. [ABSTRACT FROM AUTHOR]

The Walker Top Granite (here formally named) is a peraluminous megacrystic granite that occurs in the Cat Square terrane, Inner Piedmont, part of the southern Appalachian Acadian- Neoacadian deformational and metamorphic core. The granite occurs as disconnected concordant to semi- concordant plutons in migmatitic, sillimanite zone rocks of the Brindle Creek thrust sheet. Locally garnet- bearing, the Walker Top Granite contains blocky alkali feldspar megacrysts 1– 10 cm long in a groundmass of muscovite- biotite-quartz- plagioclase- alkali feldspar and accessory to trace zircon, titanite, epidote, sillimanite (xenocrysts), and apatite. It varies from granite to granodiorite and contains several xenoliths of biotite gneiss, amphibolite, quartzite, and in one location encloses charnockite (here formally named Vale Charnockite). New sensitive high-resolution ion microprobe U-Pb zircon magmatic crystallization ages obtained from the plutons of the Walker Top Granite are: 407 ± 1 Ma in the Brushy Mountains; 366 ± 2 Ma in the South Mountains; and 358 ± 5 Ma in the Vale– Cat Square area. An age of 366 ± 3 Ma was obtained from the Vale Charnockite at its type locality. Major-, trace- element, and isotopic chemistry indicates that Walker Top is a high- K, peraluminous granite, plotting as volcanic arc or syn-collisional on tectonic discrimination diagrams and suggests that it represents deep- seated anatectic magma with S- to I- type affinity. The alkali calcic, ferroan Vale Charnockite likely formed by deep crustal melting, and similar geochemical and trace- element compositions suggest a similar tectonic origin as Walker Top Granite. The discontinuous nature of the Walker Top Granite plutons precludes it intruded as a volcanic arc. Instead, the peraluminous nature, common xenoliths of surrounding country rock, and geochemical and isotopic signatures suggest it formed by partial melting of Cat Square and Tugaloo terrane rocks. Following emplacement and crystallization, Walker Top plutons were deformed into elliptical to linear shapes—SW- directed sheath folds—enveloped by partially melted, pelitic and quart-zofeldspathic rocks. Collectively, Walker Top and other plutons helped weaken the crust and facilitate lateral crustal flow in a SW-directed, tectonically driven orogenic channel during the Acadian- Neoacadian event. A comparison with the northern Appalachians recognizes a similar temporal magmatic and deformational history during the Acadian and Neoacadian orogenies, although while the Walker Top Granite intruded the lower plate during eastward subduction beneath the peri- Gondwanan Carolina superterrane, the northern Appalachian plutons intruded the upper plate during subduction of the Avalon superterrane westward beneath Laurentia. We hypothesize that a transform fault, located near the southern end of the New York promontory, accommodated oppositely directed lateral plate motion and different subduction polarity between the Carolina and Avalon superterranes during the Acadian and Neoacadian orogenies. [ABSTRACT FROM AUTHOR]

Lateritic bauxite are the products of intense sub-aerial weathering of rocks. It is characterized by a particular enrichment of aluminium-hydroxide minerals such as gibbsite, boehmite and diaspore. Bauxite ore is the result of weathering of various parent rocks such as khondalite, Deccan trap basalt, granite gneiss, charnockite, etc. The two types of lateritic bauxite deposits are located in India viz high level and low level (coastal), situated in the regions namely Eastern ghat, Western ghat, central India, Gujarat, and in union territory Jammu. There are distinct geological variations in the mode of occurrence and ore body configuration. The geological, chemico-mineralogical and petrological characteristics are varying in deposits from region to region. The Eastern ghat and west coast bauxite is dominant in gibbsite minerals however, the central Indian bauxite is mixed gibbsitic boehmite and at places diasporic in nature. For the present study, representative samples of bauxite have been collected from Indian deposits. The samples were characterized for chemical composition, mineralogy and petrography. The bond work index tests have been performed on bauxite samples by standard procedure. The bond work index of ore indicates how much energy is required to grind the ore and it is a very significant property from a plant point of view. The laboratory results show that the eastern ghat bauxite is soft (BWI-10 kwh/mt) as compared to Central Indian bauxite (16 kwh/mt). The studies indicate that the base rock/parent rock, geological formation, mineralogy, etc. play an important role in the hardness of bauxite. In the present paper, details of the Bond work index of various bauxite are specified and factors responsible for the hardness of the ore is being highlighted. [ABSTRACT FROM AUTHOR]

Phosphorus, P deficiency by adsorption and fixation of applied P is a critical problem in the tropical soils coupled with wastage of agricultural land and potential nutrients from crop residues' decomposition necessitates conservancy and sustainable management. Maize stover biochar (mB) and sawmill waste biochar (sB) pyrolysed for 60-minute at 460 °C using Top-Lit Up Draft (TLUD) carbonizer were characterized by morphological, elemental and proximate properties analysed by Scanning Electron Microscope (SEM), CHNS Elemental Analyser and appropriate methods, respectively. Phosphorus (P) adsorption potential of the biochars in charnockite-originated soils were evaluated using adsorption isotherms after adding biochars at 0, 5, 10 and 20% (w/w) with concentrations of 0, 15, 30, 60, 90, 120, 150 mg P/L. SEM showed macropores (>50 nm) embedded biochars, with higher elemental C and H in sB while mB contained higher N, S, O, available P and pH. P-adsorption decreased inconsistently with increasing biochar rates resulting in P-desorption. Low Langmuir adsorption maximum (Qm) were recorded (−0.0350 to 0.1250 mg kg−1) mostly with negative separation factors (R L) and the adsorption process were favourable for mB amended soils having Freundlich heterogeneity factor (n F) of 4.476–9.634 but not for sB amended soils (n F = 0.638–2.812). Biochar production conserved nutrient loss and potentially reduced soil P fixation. [ABSTRACT FROM AUTHOR]

In the Indian peninsula, the Singhbhum, Bastar, and Dharwar cratons in the South India Block (SIB) constitute a contiguous mass of >2.5 Ga crystalline rocks. Did the cratons develop as a coherently evolved mass since their origin, or do these cratons constitute an assembly of disparately evolved cratons? Variably-deformed charnockites in the Karimnagar granulite belt and associated blastoporphyritic granitoids at the NE fringe of the Eastern Dharwar Craton (EDC) contain enclaves of mafic granulites, high-Al metapelites and anatectic quartzofeldspathic gneisses. The charnockites are demonstrably intrusive into the enclave suite. The enclave suite exhibits steeply-plunging reclined folds; the axial planes of the folds coincide with the N-striking tectonic fabrics in the Karimnagar charnockite/granitoids. The foliated charnockites display magmatic flow texture defined by trains of euhedral alkali feldspar, contain euhedral-subhedral pyroxene phenocrysts, and the quartz grains exhibit abundant chessboard microstructure. The weakly-strained euhedral laths of feldspars and pyroxenes phenocrysts share high-energy boundaries between themselves, and with quartz. Emplacement temperatures of the magmatic charnockites at ∼900 °C are obtained from Al-in-Opx thermometry. Whole rock chemistry is consistent with an arc-related origin for most charnockites. In zircons within charnockites, variably zoned cores yield ages of 2680 ± 15 Ma and 2504 ± 12 Ma in the U Pb Concordia plot. Recrystallized domains in zircon grains yielded upper intercept ages constrained between 2510 ± 4 Ma and 2509 ± 3 Ma, identical with the U-Th-Pb chemical ages (2502–2508 Ma) retrieved from monazites. The zircon εHf(t) values (− 4.85 to 1.31) suggest the ∼2.5 Ga magmatic charnockites were derived from <3.0 Ga crustal sources. The late Neoarchean magmatic charnockites in the EDC margin were emplaced in a 2.7–2.5 Ga convergent tectonic setting, and the high- T magmatic charnockites formed due to delamination of a subducting (E -W shortening) oceanic crust. The subduction possibly relates to the late Neoarchean growth of the Dharwar craton involving the assembly of disparately-evolved crustal blocks, now parts of the Dharwar craton. The findings suggest that the emplacement of Karimnagar magmatic charnockites in a contractional setting is unrelated to an accretion between the Eastern Dharwar and the Bastar cratons, as suggested by earlier workers. • Karimnagar charnockite intrude 2.7 Ga UHT granulite in NE margin, East Dharwar craton. • The 2.5 Ga high-T charnockites emplaced synchronous with E -W crustal shortening. • The peraluminous magmatic charnockites have arc-related to within-plate intrusive. • Zircon Lu Hf systematics proves charnockites derived from ∼3.0–2.7 Ga recycled crust. • Charnockites formed by subduction-related mantle delamination within Dharwar craton. [ABSTRACT FROM AUTHOR]

A rare porphyritic charnockite that is girdled by and mineralogically grades to biotite granite occurs as a part of the Chotanagpur Granite Gneissic Complex (CGGC) in and around Massanjore, Jharkhand, India. Preservation of certain textural features, including (a) euhedral to subhedral grains of orthopyroxene, (b) low dihedral angle subtended by orthopyroxene and plagioclase grains, and (c) relict intergranular and porphyritic textures, are consistent with the view that orthopyroxene in the studied rocks has a magmatic origin. Preserved magmatic features and other petrological attributes of these rocks do not support any significant mass change beyond a few tens of microns during the overprinting high-grade metamorphism. The geochemical variation of the felsic rock suite (porphyritic charnockite and biotite granite) indicates that they are cogenetic and are derived from a ferroan A-type granitoid magma by crystal fractionation. The observed geochemical trend of the studied felsic rock suites has been simulated by phase equilibria modelling in the open system using the system components Na 2 O-CaO-K 2 O-FeO-MgO-Al 2 O 3 -SiO 2 -H 2 O-TiO 2 -O 2. The observed mineralogical and geochemical attributes and the results of the modelling study are consistent with a petrogenetic process in which high magma temperature (> 900 °C), low pressure, and low water activity in the parental melt favoured the separation of an orthopyroxene bearing cumulate assemblage (orthopyroxene + plagioclase + quartz + K-feldspar + ilmenite + magnetite) in the initial part of the magmatic differentiation. Removal of this anhydrous cumulitic assemblage raised the bulk H 2 O content in the residual melt. Orthopyroxene became unstable with respect to biotite in the evolved melt that eventually crystallised minerals that formed the biotite granite. An increase in magma f O 2 also restricts the orthopyroxene stability in felsic magma. Taken together all the petrological and geochemical attributes, we demonstrate that fractionation of an orthopyroxene-bearing crystal cumulate from the melt is essential to form the charnockites, and that the biotite granite forms from the evolved melt after the fractionation. The charnockite-biotite granite association of the studied area was formed in an extensional tectonic setting, presumably during the breakdown of the Columbia Supercontinent. • Orthopyroxene stability in felsic magma is dependent on T, aH 2 O, fO 2 of the magma. • Biotite crystallisation affects orthopyroxene stability in felsic magma. • Magma differentiation played a key role in the preservation of igneous charnockite. • The igneous charnockite of CGGC relates to the Mesoproterozoic ferroan magmatism. [ABSTRACT FROM AUTHOR]

The Venda Nova and Várzea Alegre Plutons in southeastern Brazil are post-collisional complexes formed during the gravitational collapse of the Araçuaí-Ribeira orogenic system during amalgamation of SW Gondwana. This study focuses on the petrological, geochemical, geochronological and zircon Lu-Hf isotopic signatures of both plutons to constrain and complete their ages and to characterize mantle vs. crustal source components. The Venda Nova Pluton is divided into an inner, mildly alkaline, and an outer, calc-alkaline domain. One diorite, three quartz syenites and two granites from the inner domain give LA-ICP-MS zircon U-Pb ages of 492–477 ± 8 Ma. The outer domain is dominated by charnockites and norites, six measured charnockites give two zircon ages of 620–606 ± 11 Ma and 500–476 ± 14 Ma, corresponding to zircon core and rim, respectively; the only norite yielding zircons gives a nominal age of 567 ± 13 Ma, which cannot be simply interpreted as emplacement age. The various intrusives from the Várzea Alegre Pluton (gabbronorites, charnockites, monzogranites, syenogranites) straddle the alkaline to calc-alkaline affinity and yield all together a uniform age of 500 ± 8 Ma. This confirms that all lithologies from the Venda Nova inner domain and Várzea Alegre Pluton belong to the post-collisional G5 suite of this region. The Venda Nova outer domain charnockites, fit age-wise into the pre-collisional arc-related magmatism (G1 suite). The zircon rim ages obtained on these charnockites represent minor fluid-assisted partial remelting and resetting of the U-Pb system during the emplacement of the inner domain. Individual norite zircons show ages ranging from the charnockite intrusion age to the metamorphic thermal peak in this region. The Lu-Hf isotopes measured on the dated zircon crystals, yield mantle values for the charnockites from the Venda Nova outer domain (εHf: 3.4 ± 1.2 to 6.8 ± 1.5), indicating an isotopically depleted mantle source, consistent with arc magmatism. Instead, the Venda Nova inner domain and the Várzea Alegre Pluton have relatively radiogenic values (εHf: −12.3 ± 1.5 to −8.8 ± 2.9 and − 11.1 ± 1.1 to −7.4 ± 1.3, respectively) and show no significant variation between all lithologies, indicating a source dominated by a previously crustally enriched mantle with only minor crustal assimilation occurring during magma emplacement. Interestingly, the charnockite rim of Venda Nova is 100 Ma older than the inner (mildly alkaline) post-orogenic domain and belongs to the pre-orogenic calc-alkaline arc suite, while the charnockite ring at Várzea Alegre is part of the intrusion, both in time and geochemistry, and shows no increased crustal signature with respect to the rest of the pluton. • Age and magmatic source constrain of Venda Nova and Várzea Alegre Pluton. • Venda Nova inner domain + entire Várzea Alegre are post-orogenic (G5, ∼500 Ma). • G5-suite melts derive from a previously crustal enriched lithospheric mantle. • Venda Nova calc-alkaline charnockite rim (G1, ∼610 Ma) derived from depleted mantle. • Constant εHf with differentiation suggests minor crustal assimilation. [ABSTRACT FROM AUTHOR]

Charnockites constitute the major rock type in the crustal blocks of Southern Granulite Terrain (SGT) in India. Here we present petrology, mineral chemistry, and geochemistry of the oldest charnockites in the SGT from the Coorg Block. The charnockites from this block are dominantly composed of orthopyroxene, clinopyroxene, hornblende, biotite, K-feldspar, plagioclase, ilmenite, and minor garnet. Geochemical features of the charnockites indicate granitic to granodioritic protolith. In terms of aluminum saturation index, these rocks are metaluminous and represent magnesian, calc-alkaline to calcic series similar to fractionated I-type granites. They are characterized by high Mg#, enrichment of L.I.L.E. (Rb, Ba, Th, and K) and LREE (La, Ce, Nd), depletion of HFSE (Nb, Ta, Zr, Sr, P, and Ti), typical of volcanic arc granitoid. Their geochemical characteristics are consistent with crystal fractionation of the parental magma and chemically evolved magma. Mineral chemistry of orthopyroxene shows the trend of igneous pyroxene. The rocks were subjected to granulite facies metamorphism with estimated pressure-temperature conditions of 760–800 °C and 7.1–8.4 kbar. The Coorg charnockites represent vestiges of Mesoarchean arc magmatism and crust building.

The Nagercoil block situated at the southernmost tip of India occupies a key position in the East Gondwana collisional tectonic models. The Nagercoil block is dominated by Orosirian I-type charnockite massifs that host numerous gabbroic emplacements. Our present understanding about the crustal architecture of the Nagercoil block is derived mostly from these charnockites, while detailed studies on gabbros are lacking. We present new petrology, geochemistry, and zircon U-Pb/Hf isotopic data of gabbros from the Nagercoil block to understand their petrogenesis and tectonic significance. The results reveal that these are formed by the partial melting of a subduction-modified lithospheric mantle source in a continental arc setting. Zircon U-Pb geochronology results reveal that the gabbros were emplaced between 561 and 531 Ma. Hafnium isotopic studies on zircons argue for a mid-Mesoproterozoic melting source with near-juvenile magmatic signatures. The Hf-TDM ages together with the available data from the terrane point to the involvement of the adjacent Achankovil unit as a possible melting source contributor. The genetic link between the Achankovil unit and Sri Lanka together with the remarkable similarity in ages and isotopic characteristics of mafic rocks from both these terranes point to their coeval formation during the East African Orogeny associated with the final stages of the Gondwana supercontinent assembly. [ABSTRACT FROM AUTHOR]

The super-large Baerzhe Be–Nb–Zr–REE deposit in NE China is hosted in the Early Cretaceous peralkaline granites. In this work, the newly discovered granitic dikes developed around the Baerzhe deposit were studied for the first time, focusing on their genesis and genetic relationships with the Baerzhe peralkaline granites. Zircon U-Pb dating of these granitic rocks (including the granite porphyry, rhyolite and miarolitic granite) yielded Early Cretaceous ages of 125–121 Ma. Their mineral assemblages and geochemical features suggest that they share similar features with the peralkaline A-type granites. Their geochemical data and zircon Hf isotopic compositions (εHf(t) = +3.4 to +10.5) indicate that the peralkaline granitic rocks were formed by the partial melting of dehydrated charnockite with extensive plagioclase crystal fractionation, which resulted in a peralkaline affinity. There are two types of distinct zircons in the studied samples: the type I zircon with a bright rim and dark core, which may represent a cumulate mineral phase captured together with aggregates during eruption, and the type II zircon with a higher evolution degree crystallized in the residual melts. Combined with the simulation results using whole-rock trace elements, we proposed that the peralkaline granitic dikes represent more evolved interstitial melts than the Baerzhe granitic magma. In the Early Cretaceous extensional tectonic settings, mantle-derived magma upwelled, which induced the melting of the lower crust and prolonged the evolutionary process of the magma crystal mush. [ABSTRACT FROM AUTHOR]

Evidence of frictional melting in the form of pseudotachylite is innumerably found along the Gangavalli fault zone (GFZ), southern India. Such catastrophic deformation influences the strength of rock masses across the fault zone. In this paper, we have investigated the strength variation in fault zone rocks during post-seismic deformation. The experimental study suggests that the average uniaxial compressive strength (UCS) for pseudotachylite hosting charnockite (i.e., Pt-charnockite) is almost double (45.58 MPa) as compared to the pseudotachylite devoid charnockite (i.e., D-charnockite) of 24 MPa. The melt associate seismic deformation shows high stress drop due to melt lubrication at the fault interface and simultaneously produced numerous fractures in the rock. We have determined the stability and denseness of both rock types using acoustic emission (AE) technique that remarks a distinct difference in AE signatures. The analysis indicates a more stable and dense Mogi type-III signature for post-seismic deformed rocks that are assisted by pseudotachylite melt. However, negligible AE energy is observed in the D-charnockite. We proposed that the melt-assisted seismic deformations are more inhibitable to reactivate the slip surfaces than the conventional earthquake-deformed rock having no melting phenomenon and therefore, pseudotachylites enhance the strength of fault zone rocks during post-seismic deformation. [ABSTRACT FROM AUTHOR]

The Southern Granulite Terrane (SGT) in India is composed of Archaean to Proterozoic crustal blocks and intervening shear/suture zones. The Nallamalai shear zone lies along the eastern flank of the Shevaroy Block. This study is focused on the eastern part of this shear zone where the basement rocks are dominantly composed of charnockite, quartzo-feldspathic gneiss and metagabbro, all of which preserve original magmatic texture. Zircon U-Pb LA-ICPMS analysis on the charnockite samples yielded an age of 2680 to 2500 Ma for the protolith emplacement followed by metamorphism at 2520 to 2450 Ma. Magmatic zircon grains in the quartzo-feldspathic gneiss and metagabbro yielded weighted mean ages of ca. 2557 Ma and ca. 2583 Ma with metamorphism at ca. 2518 Ma. Zircon Lu-Hf data suggest that the protolith of metagabbro was sourced mainly from the recycled Mesoarchaean crustal component. The ƐHf(t) of charnockite (−0.4 to 4.1) and quartzo-feldspathic gneiss (0.5 to 6.0) represent a combined source of the mantle as well as recycling crust. All the rocks underwent amphibolite to granulite facies metamorphism and petrological studies and pseudosection modelling shows a similar P-T range of 7–8 kbar and 650–830°C. Results from the present study suggest that crustal evolution along the eastern flank of the Nallamalai Shear Zone involved melting of older crustal components (Mesoarchaean age) with significant juvenile input (ƐHf(t) = ~+6.0) within a continental arc setting. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract 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.

Fractionation of felsic magma has been critical for the formation of high-silica rhyolites, chemical differentiation of the continental crust, and enrichment of economically valuable ores. Intermediate-to-intermediate–felsic cumulate rocks have recently received considerable attention, because they contain much information on the fractionation process of felsic parental magma. Nevertheless, the petrogenesis of strongly peraluminous, mafic cumulate rocks associated with felsic rocks remains controversial due to poor outcropping. Here, an early Paleozoic garnet-bearing norite–quartz jotunite–charnockite suite (NJC suite) is identified in the Yunkai terrane, South China Block. All rock types have peraluminous mineral assemblages consisting of garnet, orthopyroxene, biotite, plagioclase, K-feldspar, quartz, and accessory minerals (ilmenite, zircon, and monazite/apatite). These minerals have different volume fractions in various rock types but share comparable geochemical compositions, which result in linear correlations on major- and trace-element diagrams. Similar and crust-derived whole-rock Sr–Nd–Hf [(87Sr/86Sr)i = 0.71778–0.72389, εNd(t) = − 7.4 to − 9.3, εHf(t) = − 7.5 to − 8.5], and zircon Hf–O [εHf(t) = − 5.0 to − 13.4, δ18O = 7.85–10.09‰] isotope compositions and the presence of inherited zircons suggest a metasedimentary source for this suite. Detailed mineralogical studies of garnet, orthopyroxene, plagioclase, ilmenite, and zircon suggest a possible magmatic origin for these minerals, although the peritectic origin cannot be excluded. The compositional variation in various rock types is likely induced by crystal accumulation instead of selective restite entrainment. The cumulate origin of the NJC suite is further supported by the following features: (1) the garnet-bearing norites, quartz jotunites, and charnockites show cumulate-related microtextures defined by plagioclase, orthopyroxene, and garnet aggregation; (2) crystal size distributions (CSDs) of plagioclase and orthopyroxene in these rocks exhibit upward-deflected patterns caused by crystal accumulation; (3) the compositional disequilibrium of Mg# between orthopyroxene and whole rocks suggests that orthopyroxenes were in equilibrium with cumulates characterized by orthopyroxene accumulation; (4) temperatures recorded by ferromagnesian minerals (garnet–orthopyroxene, garnet–biotite, and orthopyroxene–biotite Fe–Mg thermometers) that are higher than the solidus temperature yielded by a two-feldspar thermometer suggests melt extraction for the Yunlu charnockite; (5) the whole-rock compositions of the NJC suite deviate from metasediment-sourced experimental melts; and (6) magmatic orthopyroxene preservation in charnockites suggests that the magma experienced melt loss and crystal accumulation before solidification. Mass balance calculations and rhyolite-MELTS modeling show that the norite, quartz jotunite, and charnockite cumulates could have formed by hindered settling coupled with gravitational compaction at crystallinities of ~ 0.2–0.25, ~ 0.30–0.35, and ≥ 0.5 respectively, from a felsic parental magma. Incomplete crystal-melt separation (controlled by different settling velocities) combined with successive crystal accumulation is responsible for the formation of cumulate rocks with various mineral proportions and comparable mineral compositions in different rock types. This study proposes a novel petrogenetic model for norites, i.e., norites could have formed by crystal accumulation of crust-derived felsic magmas without the involvement of mantle-derived mafic magma. In contrast to the mafic highly peraluminous granitoids generated by selected restite entrainment, the Yunlu NJC suite exhibits distinctive compositional characteristics governed by crystal accumulation. In this case, the crystal accumulation role must be considered for constraining the petrogenesis of the high-maficity strongly peraluminous granitoids. [ABSTRACT FROM AUTHOR]

Major element compositional spectrum, formation in diverse magmatic and metamorphic rocks, and relative stability during sediment transport, burial, and diagenesis make garnet an important indicator of sedimentary provenances. However, a fundamental question yet to be answered is whether the low-grossular–high-pyrope detrital garnets reflect source characteristics or record sedimentary processes. To address this problem, we have analysed garnets from the beach sands of the East Coast of India and in the source lithologies of the catchment area within the Eastern Ghats Mobile Belt. Investigated garnets show a broad compositional spectrum; most garnets are dominated by almandine 49 – 86% with variable contents of pyrope 9 – 47% , minor grossular 0.8 – 15% , and low spessartine 0.5 – 4%. Using multiple proxies, including a state-of-the-art machine-learning-based garnet discrimination scheme, we found that 96 % of analysed beach sand garnets are of metamorphic origin and 4 % igneous. Amongst the metamorphic garnets, 85 % were derived from granulite facies, 5 % from eclogite/ultrahigh-pressure facies, 5 % from amphibolite facies, and 1 % from blueschist/greenschist facies rocks. Concerning host-rock bulk composition, 93 % of garnets belong to intermediate–felsic/meta-sedimentary class and 7 % belong to the mafic category. The chemistries of the beach sand detrital garnets of the East Coast of India are readily coupled with the compositions of the garnets from source rock lithologies of the Eastern Ghats Mobile Belt. Very low-grossular garnets are derived from meta-pelitic rocks (khondalites) and mafic granulites, whereas slightly grossular-rich garnets are derived from charnockites. The present study indicates that the low-grossular–high-pyrope detrital garnets are vital signposts of sedimentary provenances. We advocate that the high P-T granulite facies mobile belts are distinctive sources for the low-grossular–high-pyrope detrital garnets. • High P-T granulite facies mobile belts are distinctive sources for the low-grossular–high-pyrope detrital garnets. • Alm-Prp garnets are derived from meta-pelites, migmatites, and mafic granulites; Alm-Prp-Grs garnets are from charnockites. • The source for the Bengal Fan low-grossular–high-pyrope garnets possibly lies in the Eastern Ghats Belt. • Sedimentary basins with high proportions of low-grossular–high-pyrope garnets can be linked to (palaeo-) orogenic belts. [ABSTRACT FROM AUTHOR]

[Display omitted] • Protoliths of mafic granulites and associated rocks derived from sub-alkaline tholeiitic magma. • Magmatism peaked at 3.1 Ga and occurred in a subduction-related arc setting. • High grade metamorphism at ca. 3.0 associated with collision. • Charnockites and mafic granulites represent the roots of this microblock. The Coorg Block in southern India is an archive of Paleo-Mesoarchean arc magmatism and continental building in the early Earth. Here we investigate a suite of mafic and ultramafic rocks and associated lithologies to characterize the roots of this microcontinent. We present petrologic, geochemical, as well as U-Pb and Lu-Hf data on zircon and U-Pb data on monazite from these rocks which provide insights into the petrogenesis of the rocks as well as the timings of magmatism and subsequent metamorphism. The geochemical features of the mafic granulites indicate that the rock suite was derived from the fractionation of a sub-alkaline tholeiite magma. Most of the rocks correspond to arc setting in a subduction-related tectonic regime. The rocks exhibit relative enrichment in LILE, Pb, and LREE with depletion in HFSE such as Nb and Ta suggesting partial melting of a metasomatized mantle wedge. Their high LILE/HFSE and LREE/HFSE ratios indicate slab dehydration and mantle wedge melting in typical island arc settings. The overall trace element and REE patterns of the rocks indicate that the source magma of the ultramafic and mafic rocks might have been derived from a refractory mantle source followed by the metasomatic enrichment of lithospheric mantle wedge by incompatible elements through the influx of subduction-derived fluids/melts. We present comprehensive zircon U-Pb data and Lu-Hf data on a suite of mafic granulite, garnet-bearing granulite, tremolite actinolite schist, charnockite, and anorthositic gabbro as well as monazite U-Pb data from a charnockite sample. Most zircon grains show cores with magmatic crystallization features and many grains are mantled by metamorphic rims. The age data show a prominent peak at 3.1 Ga for most of the rocks suggesting that the major crustal building in the Coorg Block occurred during the Mesoarchean. Rocks on the margins of the block were affected by the younger (Neoarchean) tectonothermal event in the surrounding blocks. The Lu-Hf isotopic data on zircon grains with ca. 3.1 Ga ages show εHf(t) values ranging from −4.4 to + 3.7 (average + 0.3). In the εHf(t) versus 207Pb/206Pb age diagram, the plots are distributed close to the CHUR line suggesting Paleo-Eoarchean juvenile magma sources. The voluminous mafic lower crust at the root of the Coorg Block is consistent with addition of mafic magmas through slab melting induced by high mantle potential temperatures in the Archean, as well as the interaction of fluids/melts with the mantle wedge. [ABSTRACT FROM AUTHOR]

Smaller diameter detectors yield better energy resolution of elements at low X-ray energies, whereas thicker detectors have higher detection efficiency when X-ray energies are around 20 keV. In PIXE systems, M X-rays are typically low energy (1-3 keV), L X-rays are of intermediate energy (1-20 keV), and K X-rays are high energy (> 20 keV). This difficulty will develop in the presence of X rays created by significant elements that have a somewhat higher energy than X rays generated by trace elements in this energy area of the spectrum. K X-ray energy from Ti, V, Cr, Mn, and Fe conceals the L X-ray energies from the REE in charnockite, which were analysed using earlier approaches such as titanite in this case. [Extracted from the article]

The Cr-rich Jacurici Complex is located at the limit between the Serrinha Block and the Salvador-Curaçá Belt, Northeastern São Francisco Craton. In order to better understand the age span of magmatism and tectonism, we have studied a basement high-grade charnockite orthogneiss, a metanorite of the Complex and a crosscuting undeformed quartz-feldspar pegmatite. For the orthogneiss, SHRIMP U-Pb ages of zircon cores and overgrowth rims yielded, 2966 ± 9 Ma for crystallization and 2091 ± 10 Ma for metamorphism, respectively. Zircons from the metanorite show internal textures consistent with high grade metamorphism. The U-Pb LA-ICP-MS age determination provided a 2099 ± 6 Ma metamorphic age for the Jacurici Complex, indicating it was already emplaced during amalgamation around 2.1 Ga. Zircons from the undeformed quartz-feldspar pegmatite provided a LA-ICP-MS U-Pb age of 2083 ± 11Ma, marking the end of the N-S transcurrence. The magmatic Jacurici Complex age remains undefined, but is equal to, or older than, 2.1 Ga. Therefore, possible correlations with other mafic-ultramafic intrusions, such as the Cu-rich Caraíba Complex, should be reassessed. Our results indicate that the N-S transcurrence ended earlier in the Jacurici Complex region than in the northwestern area of the Salvador-Curaçá belt. [ABSTRACT FROM AUTHOR]

Deformation and magnetic fabrics across the Salem and Namakkal Granulite Blocks (southern India) have been integrated to understand the poly-phase (D1–D3 ductile and D4 brittle) tectonic reworking in the study area. D1 gneissic fabric (S1) is the dominant regional-scale mesoscopic fabric in the charnockite host. Localized ductile shearing at low temperature and development of shear bands, mylonite and phyllonite zone with respectively transposed-S1, mylonite (SM) and phyllonite (SP) fabric characterize D3 phase. Presence of true shear zone rocks with distinct deformation and magnetic fabrics helps in demarcating a new Belur–Sarkar Nattar Mangalam–Udayapatti shear zone (BNUSZ). Magnetic fabrics are deformation-controlled and result in vorticity variation from simple shear (Wn = 0.85) to general shear (Wn = 0.64) to pure shear (Wn = 0.1) across the BNUSZ. Magnetic fabrics document a progressive transition from early ductile shear zone to late-stage thrust and flip of the σ1 stress axis from WNW–ESE to NNE–SSW. Down-dip magnetic lineation, north-verging WNW–ESE trending asymmetric folding on SP and pole to S1 recognize a forelimb thrust with northward transport. Stress-localization on the forelimb of D3 shear-induced asymmetric fold initiates thrust. Phyllonitization helps in partitioning of D3 strain and concomitant structural complexity in hangingwall, south of the BNUSZ. Research highlights: A new Belur–Sarkar Nattar Mangalam–Udayapatti Shear zone (BNUSZ) is identified in the Salem Granulite Block (SGB). The BNUSZ represents the sole tectonic marker for last D3 ductile shearing in the SGB. Deformation and magnetic fabric development suggest a forelimb thrust origin for the BNUSZ. A fold-first tectonic model best explains the initiation of the BNUSZ thrust. [ABSTRACT FROM AUTHOR]

The presence of fluoride in the groundwater in the Thirukkazhukundram Block in south India is now becoming an increasingly alarming issue. With the semi-arid climatic conditions, charnockite and gneiss rocks form the basement, contributing to the geology of the study area. The pre-monsoon (August 2016) and post-monsoon (February 2017) fluoride concentrations have an average output of 1.3 mg.L-1 and 0.72 mg.L-1 respectively. As of date, only in Neikuppi, the fluoride contamination is found to be 2 mg.L-1 in pre-monsoon which is beyond the accepted limit as per the WHO standards. Other 29 locations taken up for study have fluoride value fluctuation from 1 mg.L-1 to 2 mg.L-1 in the pre-monsoon and from 0 to 1.5 mg.L-1 in the post-monsoon. The main factor responsible for this fluoride contamination lies in the study area's hydro-geological condition which must be attended to immediately to prevent a public health problem in the future. [ABSTRACT FROM AUTHOR]

The origin of large miarolitic (also known as "chamber") pegmatites is not fully understood although they may have great economic value. The formation of cavities in magmatic bodies is related to melt degassing and gas or fluid flow through partially solidified magma. In this paper, the origin of the Volyn pegmatite field, located in the Palaeoproterozoic Korosten anorthosite-mangerite-charnockite-granite (AMCG) complex, North- western region of the Ukrainian Shield, is discussed. Pegmatites of the field host deposits of piezoelectric quartz that is accompanied by gem-quality beryl and topaz. The Volyn pegmatite field is confined to granites located in the south-western part of the Korosten complex and extends for 22 km along the contact with the anorthosite massif within the Korosten plutonic complex. Geological data indicate hybridization of basic melts and partly crystallized granites, as well as direct impact of fluids derived from basic melts on the chamber pegmatites. The new U-Pb zircon ages obtained for granites and pegmatites of the Korosten complex confirm that the rock assemblage in the northern part of the complex crystallized between 1800 and 1780 Ma, whereas rocks in the southern part intruded mainly between 1768 and 1755 Ma. U-Pb zircon ages for granites from the south-western part of the Korosten complex indicate that granites were emplaced at 1770-1765 Ma, a few million years prior to the intrusion of the gabbro-anorthosite massif (1762-1758 Ma), while chamber pegmatites in these granites crystallized at 1760 ± 3 Ma, coevally with the basic rocks. Ultimately, the formation of the chamber pegmatites was related to the reheating of the semi-crystallized granitic intrusion and to fluids migrating from the underlying gabbro-anorthosite massif. [ABSTRACT FROM AUTHOR]

The Kosavankovilpatti area consists mainly of granulite facies rocks and is part of the Madurai block in the Southern Granulite Terrane, India. The garnet-cordierite gneiss collected at this location exhibits well-preserved metamorphic reaction textures and is used to infer the metamorphic history of the study area. Garnet resorption at the expense of orthopyroxene-cordierite and spinel-cordierite symplectites characterize the retrograde stages of metamorphism. Phase relationships for bulk rock composition in the MnO-Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2 (MnNCKFMASHT) system, as well as the application of multi equilibrium calculations for the peak metamorphic assemblages, yield maximum temperature (T) and pressure (P) conditions of 900 °C and 9 kbar, respectively. These estimated results are lower compared to those reported for the sapphirine-bearing granulites from the Madurai block that characterize UHT metamorphism. The post-peak P-T path, constructed for garnet-cordierite gneiss based on observed microstructural relationships and thermobarometry results, is characterized by a decompressive P-T segment ending at 810 °C and 5.5 kbar. The geochronological results of SHRIMP U-Pb give an age of 521 ± 30 Ma for the decompression metamorphic overprint that was superimposed on the protolith formation of the garnet-cordierite gneiss at 2561 ± 72 Ma. The proposed P-T path implies that the granulites in the Kosavankovilpatti section probably resulted from denudation of the thickened continental crust. In this way, the present study allows us to understand how this part of the lower continental crust could have evolved during prolonged heating without actually attaining UHT conditions. [ABSTRACT FROM AUTHOR]

Our study of a banded charnockite complex of the Mühlig-Hofmannfjella in Dronning Maud Land, Antarctica, illustrates how the combination of high-temperature (re-)crystallization processes, melts, and volatile fluids leads to complex intrusive, metasomatic, and structural relationships. The igneous complex consists of gently dipping sets of charnockite interlayered with dolerite and leucogranite. The banded complex formed primarily by magmatic processes, but with superimposed modifications by metasomatism. The charnockite has a ferroan composition and contains both orthopyroxene (Fs80–84) and olivine (Fa94–96). Zircon U-Pb dates the emplacement of charnockite at 515 Ma, and inherited zircon cores and negative εNd values of −3 to −5 indicate that the age of the source of the magma was about 1100 Ma. Neodymium isotopes were not homogenized during the Cambrian magmatic event, which suggests that the generation and emplacement of the magma took place in separate batches during construction of the banded complex. By contrast, the Rb-Sr system in the charnockite was extensively homogenized, likely because of the superimposed late-magmatic fluid activity, which also produced the bands and networks of leucogranites. These events occurred during the late stages of the assembly of Gondwana, with postcollisional extension and mantle upwelling maintaining a high heat flow. [ABSTRACT FROM AUTHOR]

New LA–ICP–MS U–Pb zircon ages from the Nyong Complex of southwestern Cameroon—a part of the West Central African Fold Belt—trace Late Mesoarchean (∼2,850 Ma), Middle Palaeoproterozoic (∼2,080 Ma), and Neoproterozoic (∼605 Ma) events: Two meta‐syenites and the protolith of an amphibolite are Late Mesoarchean; two meta‐granodiorites are Middle Palaeoproterozoic; the amphibolite may have recrystallized in the Middle Palaeoproterozoic; all rocks are overprinted by the Neoproterozoic event. Integration with published data shows that our amphibolite sample has one of the oldest amphibolite‐protolith ages (∼2,810 Ma) reported so far. It shares the Middle Palaeoproterozoic metamorphism/recrystallization with other, previously dated amphibolites. An earlier reported metamorphic zircon age (∼2,090 Ma) from eclogite is somewhat older than the regional Middle Palaeoproterozoic metamorphism/recrystallization ages (∼2,040 Ma) reported from amphibolites. Thus, the eclogite–amphibolite ages may date an exhumation process. A published charnockite age, interpreted as an Early Mesoarchean crystallization age, is older than the Late Mesoarchean meta‐syenite and amphibolite‐protolith dates; its Middle Palaeoproterozoic metamorphism/recrystallization age, however, is identical with the meta‐granodiorites and amphibolites. The Neoproterozoic ages demonstrate the regional overprint of the Nyong Complex during this period. Integration of the Nyong Complex ages with published ones from the entire West Central African Fold Belt, and comparison with those from West Africa and South America, support their common origin from the Palaeoproterozoic collision between the Archean Congo and São Francisco shields. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Charnockites constitute an integral component of granulite belts exposed on the northern and southern flanks of the Godavari rift, which marks the contact between the Bastar and Eastern Dharwar cratons in peninsular India. In this study, we attempt to constrain the petrogenesis of granulites from Gondpipri, Bhopalpatnam on the northern flank and Karimnagar on the southern flank of the Pranhita-Godavari valley using petrography, mineral and whole-rock geochemistry, fluid inclusion studies, and U Pb zircon geochronology. The presence of relict magmatic textures and orthopyroxene chemistry is suggestive of an igneous protolith while CO 2 -rich fluid inclusions in quartz correspond to subsequent granulite-facies overprint. Geochemically, charnockites from both granulite belts are metaluminous, magnesian, and calc-alkaline, having similar Sr and Y concentrations, Rb/Sr, Sr/Y, La N /Sm N , Gd N /Yb N , and Eu/Eu* ratios, and positive Ba Pb and negative Nb-Ta-Ti anomalies. Zircons in charnockites from both granulite belts furnish magmatic crystallization ages of ~2.5 Ga (U Pb isotope) and also record a metamorphic overprint at ca. 2473 Ma. The similarity in protolith composition and U Pb ages of zircons in charnockites on the northern and southern flanks of the Godavari rift suggest that they constitute a cogenetic and coeval suite emplaced at ~2.5 Ga in an undivided and continuous Palaeo-Mesoarchean landmass that included the Bastar and Eastern Dharwar cratons, possibly as a part of the Ur-supercontinent. This undivided landmass subsequently got split along the Pranhita-Godavari rift zone into the Bastar and Dharwar cratons. The rift valley eventually developed into a sedimentary basin hosting the Proterozoic and Gondwana Group of sediments sequentially, apparently separating the two cratons on the map. Unlabelled Image • The Neoarchean crustal accretion due to juvenile granite magmatism was related to plume activity. • The Bastar and Karimnagar granulite belts are ramifications of same 2.4 Ga tectonothermal event. • The Bastar and the Eastern Dharwar Cratons represent remnants of the erstwhile Ur Supercontinent. [ABSTRACT FROM AUTHOR]

Since granitic rocks in high-grade terranes commonly undergo amphibolite-granulite facies metamorphic 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 <100 μm for most minerals. The magmatic information can be retrieved by combining rhyolite-MELTS modeling with mineral thermobarometry using mineral core compositions to quantitatively estimate magmatic pressure, temperature, and melt H2O contents. Rhyolite-MELTS modeling results are evaluated by comparison with experimentally determined phase relations for a peraluminous granite with ~69.83 wt% SiO2 at a pressure of ~500 MPa. The comparison suggests that the modeling reproduces phase relationships of feldspars and quartz within 20–60 °C when the melt H2O contents are below 7.0 wt%, but fails to account properly for all the phases when the melt H2O contents are higher than 7.0 wt%. The modeling results using reconstructed primary magma composition of the Yunlu charnockite combined with the orthopyroxene-garnet-plagioclase-quartz thermobarometry and fluid inclusion analyses suggest that the magma was emplaced at a pressure of ~600 MPa, a temperature 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 difusion 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. [ABSTRACT FROM AUTHOR]

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<55 elements except lower K-X-rays of Z<17 elements using K-X-ray lines without high Z elements present in charnockite samples. [ABSTRACT FROM AUTHOR]

Low pressure‐high temperature (LPHT) metamorphism, with geothermal gradients in the order of 50–100°C/km, is a common feature of the late evolution of collisional orogens. These abnormal thermal conditions may be the results of complex interactions between magmatism, metamorphism and deformation. The Agly massif, in the French Pyrenees, preserves the metamorphic footprints of the late Variscan thermal structure of an almost continuous section from the upper and middle continental crust. The upper crust is characterized by a very high geothermal gradient of ~55°C/km, evolving from greenschist to amphibolite facies, while the middle crust, exposed in a gneissic core, exhibits granulite facies conditions with a near isothermal geothermal gradient (<8°C/km) between 740 and 790°C. The abnormal and discontinuous crustal geothermal gradient, dated at c. 305 Ma on syn‐granulitic monazite by LA‐ICP‐MS, is interpreted to be the result of magmatic intrusions at different structural levels in the crust: the Ansignan charnockite (c. 305 Ma) in the deepest part of the gneissic core, the Tournefort granodiorite (c. 308 Ma) at the interface between the gneissic core and the upper crust and the Saint‐Arnac granite (c. 304 Ma) in the upper section of the massif. The heat input from these magmas combined with the thermal buffering effect of the biotite dehydration‐melting reaction resulted in the near isothermal geothermal gradient in the gneissic core (melt‐enhanced geotherm). The higher geothermal gradient (>50°C/km) in the upper crust is only due to conduction between the hot middle crust and the Earth's surface. The estimated maximum finite pressure range suggests that ~10 to 12 km of crust are exposed in the Agly massif while the present‐day thickness does not exceed 5–6 km. This pressure/depth gap is consistent with the presence of several normal mylonitic shear zones that could have contributed to the subtraction of ~5 km of the rock pile. Monazite U–Th–Pb ages carried out on monazite overgrowths from a highly mylonitized sample suggest that this vertical thinning of the massif occurred at c. 296–300 Ma. This later Variscan extension might have slightly perturbed the 305 Ma geothermal gradient, resulting in an apparent higher conductive geothermal gradient in the upper crust. Although the Agly massif has been affected by Cretaceous extension and Eocene Alpine compression, we suggest that most of the present‐day thickness of the column rock was acquired by the end of the Palaeozoic. [ABSTRACT FROM AUTHOR]