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The Southern Granulite terrane, southern India, comprises a vast exposure of deep crust and forms a key region in the reconstruction of the Gondwana supercontinent. An E-W-trending crustal-scale shear zone, the Palghat-Cauvery suture zone system, which formed during the late Neoproterozoic- Cambrian (0.75-0.50 Ga), marks a prominent terrane boundary separating terranes with a predominantly late Neoarchean (ca. 2.5 Ga) regional granulite metamorphism to the north from those with an Ediacaran- Cambrian (0.63-0.50 Ga) regional granulite metamorphism to the south. Focusing on the younger granulite metamorphic domains, we present here new zircon U-Pb ages and Hf isotopic compositions for 11 charnockite orthogneisses from the Madurai, Trivandrum, and Nagercoil blocks and contribute to the resolution of the age of their magmatic protoliths. This study shows that the charnockite orthogneisses south of the Palghat-Cauvery suture zone relate to a minimum of four distinct episodes of felsic magmatism centered at: ca. 2.62-2.46 Ga, ca. 2.05-1.84 Ga, ca. 1.0- 0.9 Ga, and ca. 0.80-0.76 Ga, pertaining to the Siderian, Orosirian, and Tonian Periods. Hafnium isotope analyses of zircon grains from the charnockite gneisses suggest that the protoliths of the ca. 2.05-1.98 Ga gneisses from the Trivandrum and Nagercoil blocks and the ca. 1.0-0.9 Ga gneisses along the southeastern Madurai block involved a significant juvenile magma component, while the protoliths of charnockite gneisses elsewhere in the Madurai block formed mainly through recycling of older crust up to ca. 3.2 Ga. A regional granulite-facies metamorphic imprint during the Ediacaran-Cambrian marked an advanced stage in the amalgamation of the Madurai, Trivandrum, and Nagercoil blocks into the East African orogen and its collision with the Dharwar craton. [ABSTRACT FROM AUTHOR]

The fluoride contamination in drinking water is already gone to the alarming level and it needs the immediate involvement and attention of all people to solve this problem. Fluoride problem is higher in hard rock terrains in worldwide and Madurai is such type of hard rock region. Totally 54 samples were collected from the Madurai district of Tamilnadu with respect to lithology. The samples collected were analysed for major cations and anions using standard procedures. The higher concentration of fluoride is noted in the Charnockite rock types of northern part of the study area. 20 % of samples are below 0.5 ppm and 6 % of samples are above 1.5 ppm exceeding the permissible limit. The affinity between the pH and fluoride ions in groundwater suggests that dissolution of fluoride bearing minerals in groundwater. The higher concentration of fluoride ions are observed in the lower EC concentration. The isotopic study suggests that fluoride is geogenic in nature. In factor scores, fluoride is noted in association with pH which indicates the dissolution process. [ABSTRACT FROM AUTHOR]

Most igneous charnockites are interpreted to have crystallized at hot and dry conditions, i.e. at >800 °C and <3 wt.% HO and with an important CO component in the system. These charnockites are metaluminous to weakly peraluminous and their formation involves a significant mantle-derived component. This study, in contrast, investigates the crystallization conditions of strongly peraluminous, metasediment-sourced charnockites from the Qinzhou Bay Granitic Complex, South China. To constrain the temperature-melt HO crystallization paths for the studied peraluminous charnockites, petrographic characterization was combined with fluid inclusion compositional data, mineral thermometry, and thermodynamic modelling. The uncertainties of the thermodynamic modelling in reconstructing the crystallization conditions of the granitic magmas have been evaluated by comparison between modelled and experimental phase relations for a moderately evolved, peraluminous granite (~70 wt.% SiO). The comparison suggests that the modelling reproduces the experimentally derived phase saturation boundaries with uncertainties of 20-60 °C and 0.5-1 wt.% HO for systems with ≤1-2 wt.% initial melt HO at ~0.2 GPa. For the investigated natural systems, the thermometric estimates and modelling indicate that orthopyroxene crystallized at relatively low temperature (750-790 ± 30 °C) and moderately high to high melt HO content (3.5-5.6 ± 0.5 wt.%). The charnockites finally solidified at relatively 'cold' and 'wet' conditions. This suggests that thermodynamic modelling affords a possible approach to constrain charnockite crystallization as tested here for peraluminous, moderately low pressure (≤0.3 GPa), and overall HO-poor systems (≤1-2 wt.% HO total), but yields results with increasing uncertainty for high-pressure or HO-rich granitic systems. [ABSTRACT FROM AUTHOR]

Hydrogeophysical study of parts of Charnockite terrain of Akure, southwestern Nigeria was carried out using the electrical resistivity method. The study involved one hundred and fifty two (152) Schlumberger geoelectric soundings (with seven (7) of them parametric)) alongside static water level measurements in 102 hand-dug wells. The Precambrian Crystalline Basement Complex rocks underlying the area consist largely of Charnockite with some granite and migmatite-gneiss bodies. The interpreted results enabled the determination of overburden thickness, longitudinal unit conductance (S) and coefficient of anisotropy (λ). The static water level measurements were used to determine the vadose zone thickness and groundwater flow direction. The overburden thickness in the study area ranges between 2.0 and 66.9 m; bedrock resistivity range between 748 and ∞ Ω-m while the vadose zone thickness ranges between 0.5 and 11.3 m. The groundwater potential of the area was classified based on the overburden thickness (h) and resistivity values (ρ). Thus, areas characterized by 100 ≤ ρ ≤ 800 Ω-m with h ≥ 45 m are classified as high, while areas presenting 15 ≤ h ≤ 45 m are classified as medium and areas of h ≤ 15 m are classified as low. A modified geologic classification of the study area using λ values was undertaken with λ ≤ 1.2 areas classified as Charnockite while areas with λ > 1.2 classified as granite and migmatite-gneiss complex. A correlation of the field geological map with the λ map presents a good correlation especially within areas underlain by Charnockite. [ABSTRACT FROM AUTHOR]

[Display omitted] • Charnockite magma intruded the lower crust of the Eastern Ghats Province in two pulses (∼980–940 Ma and ∼ 1020–1000 Ma). • The magma had variable chemistry and shows subduction-collision signatures. • This charnockite later suffered granulite facies metamorphism. • This charnockite is a of the Mawson charnockite of the Rayner Province. • Charnockites of the India-Antarctica sector formed by successive arc-continent collisions. Massif type charnockite was emplaced in the lower crust of the Eastern Ghats Province and is now exposed over a large geographic area. The rock shows clear evidence of magmatic emplacement in lower crustal metasedimentary rocks, which occur as enclaves within the charnockite. Textural data suggest the magma underwent subsolidus cooling and subsequently metamorphosed to granulite facies (up to ∼ 910 °C, 9 kbar). Geochemical data show that the charnockite magma had variable chemistry which was acquired by differentiation and possible crustal contamination. The rock shows both high- and low-SiO 2 types, with weakly peraluminous to metaluminous characters. Trace and REE fractionation trends suggest the magma had calcic to calc-alkaline affinities and was emplaced in a continental arc type collisional setting. Theoretical modelling suggests that such a magma could be generated by melting of a hydrated basaltic slab under CO 2 -rich fluid. U-Pb analysis on oscillatory zoned zircon domains from eight samples yields crystallization ages for the magma. While the majority of the samples show crystallization ages within ca. 980–940 Ma (978 ± 16 Ma, 968 ± 22 Ma, 951 ± 9 Ma, 954 ± 8 Ma, 951 ± 13 Ma and 939 ± 27 Ma), two samples yield crystallization ages of 1002 ± 13 Ma and 1020 ± 16 Ma. This implies two-phase emplacement of the charnockite magma which can be correlated with the tectonometamorphic evolution of the province. While the earlier pulse of charnockite magmatism is broadly synchronous with the first cycle (M 1) of metamorphism, the later pulse followed when the lower crust was still hot. The two pulses of charnockite magmatism are broadly synchronous with those of the Mawson charnockite of the Rayner Province, East Antarctica. It is argued that the charnockite magmatism in the combined Rayner-Eastern Ghats Province was extensive and resulted from arc-continent accretion and collision between the India and East Antarctica during ca. 1030–900 Ma. [ABSTRACT FROM AUTHOR]

The Late Archean Tectonic Events in the Jining Area of North China Craton: New Evidence from Zircon SHRIMP U-Pb Geochronology of Charnockite. [Extracted from the article]

The Aimorés Complex is an inversely zoned multistage ring-like structure which crops out over about 150 km2 and wasintruded approximately 500 Ma years ago, during the post-collision event related to Araçuai-Ribeira Fold Belt. This complexconsists of a monzodioritic core with hypersthene, and a charnockitic intermediary ring encircled by granodiorites. Thecontact between core and rim is marked by a mingled/mixed zone, where small occurrences of garnet-granite were also found.Abundant enclaves of different shapes and sizes occur showing circular, diffuse and sharp contacts with the groundmass. Thecontact with the country rocks is sharp and sub-vertical, varying from concordant to discordant and presenting dips toward theintrusion. The enclosing rocks are orthogneiss, which have experienced high-amphibolite to granulite-facies metamorphism.Most of the facies of the complex are metaluminous, except for the large enclaves embedded in the inner portion, which areperaluminous. The aluminium saturation index is approximately 1 and the agpaitic index ((Na+K)/Al) ranges from 0.45 to0.77. The negative correlation of CaO, MgO, Fe2O3, TiO2 e P2O5 in the Harker diagram can be explained by pyroxene andfeldspar fractionation. The MgO/TiO2 ratio close to 1 and the tectonic discrimination diagrams are compatible with postcollisionalgranitoids, as well as the sum of Zr, Nb, Ce and Y (500 - 1.000 ppm). The Ba/Sr, Sr/Rb, Ba/Rb and Zn/MgO ratiosindicate that there was initially fractionation by pyroxene and plagioclase, followed later by fractionation by amphibole, biotiteand K-feldspar. Geochemical data probably reflects the combination of crystal fractionation and/or crustal contamination andmagma mingling/mixing processes.

The Central Zone (CZ) of the Limpopo Belt in southern Africa is a complex high-grade metamorphic zone that experienced a, in part, poorly understood poly-metamorphic history. To address this, we present petrological and SHRIMP U Pb zircon age data for samples of a garnet- and orthopyroxene-bearing cordierite-orthoamphibole (Grt-Opx-Crd-Oam) paragneiss and a charnockite from the Baines Drift and the Phikwe Complexes, respectively. The two complexes are the north-western segments of the CZ in which the metamorphic history is poorly constrained. High-pressure (HP) granulite facies metamorphism and a clockwise P-T evolution for the feldspar-free Grt-Opx-Crd-Oam gneiss of the Baines Drift Complex are constrained by the application of pseudosection modelling, Grt-Opx thermometry, and quartz in-garnet (QinG) elastic barometry. Our results show that the peak-metamorphic garnet-orthopyroxene-rutile-ilmenite-quartz assemblage formed at HP granulite facies conditions of >900 °C and 14 kbar, followed by significant decompression at granulite facies conditions, as recorded by conspicuous orthopyroxene-cordierite coronas around garnet. The widespread formation of orthoamphibole documents subsequent near-isobaric cooling into the amphibolite facies. Based on the formation of metamorphic zircon in the Grt-Opx-Crd-Oam gneiss we precisely determined an age of 2014 ± 8 Ma for HP granulite facies metamorphism in the Baines Drift Complex. Rare detrital zircons document a possible deposition of the sedimentary protolith later than ca. 2.55 Ga, as part of a poorly documented Paleoproterozoic sediment sequence of the Central Zone. The clockwise P-T path and the age of HP granulite facies metamorphism in the Baines Drift Complex as constrained here, are consistent with constraints from 2.02 Ga metamorphism in the Beit Bridge Complex, the major segment of the CZ. The HP metamorphism is interpreted to reflect intracontinental Paleoproterozoic transpressional orogeny within the consolidated Kaapvaal-Zimbabwe Craton. The association of lower-crustal HP granulite facies rocks of the Baines Drift Complex next to mid-crustal upper-amphibolite facies rocks of the Phikwe Complex may reflect progress of nappe tectonics during the Paleoproterozoic orogeny. SHRIMP U Pb zircon data indicate that the granite protolith of the charnockite from the Phikwe Complex intruded at 2586 ± 27 Ma, broadly synchronously with major granitoid emplacement in the Beit Bridge Complex. The similar P-T evolution of ca. 2.02 Ga metamorphism and comparable voluminous granite emplacement at ca. 2.6 Ga indicate a common evolution of the Baines Drift, the Phikwe and the Beit Bridge Complexes in the CZ of the Limpopo Belt. • HP granulite facies metamorphism is detected in the Central Zone of the Limpopo Belt. • HP granulite facies metamorphism is dated at 2014 ± 8 Ma (mid Paleoproterozoic). • Paleoproterozoic metamorphism followed a clockwise P-T path with strong uplift. • Protoliths of metasediments in the Central Zone were deposited later than 2.55 Ga. • Paleoproterozoic HP metamorphism reflects intracratonic transpressional orogeny. [ABSTRACT FROM AUTHOR]

Igneous charnockites are high-temperature orthopyroxene-bearing granitoids, which constitute an important part of many high-grade terranes. High temperature (typically >750–800 °C) is considered to be a key factor regarding the formation of igneous charnockites, because orthopyroxene reacts with hydrous melts to form biotite and/or amphibole at low temperatures as predicted by equilibrium phase relations. Microstructural records of igneous charnockites suggest that the hydrous crystallization reaction occurs at near equilibrium conditions. Thus, it remains a puzzling question how orthopyroxene is preserved in granitoids that generally solidify at H 2 O-saturated solidus temperatures (<700 °C). Here, we synthesize mineralogical, petrological, and geochemical data for 32 charnockite plutons worldwide to evaluate the possible preservation mechanisms of orthopyroxene in granitoids. These igneous charnockites are classified as I-A-S types based on their mineral assemblages and whole-rock compositions. The orthopyroxene crystals in the igneous charnockites systematically have lower Al 2 O 3 contents than those in metamorphic rocks, suggesting a magmatic origin of the former. Magmatic orthopyroxene is possibly preserved by two mechanisms, preventing back-reactions with hydrous melts: one mechanism deduced from fluid-inclusion studies highlights the importance of CO 2 , which can reduce the H 2 O activity and elevate the solidus temperature to the stability field of orthopyroxene. Physical constraints on fluid transport suggest that this mechanism is feasible when an orthopyroxene-bearing mushy reservoir is flushed by large amounts (>10–20 vol%) of CO 2 -rich fluids, which could form a permeable flow through bubble channels in the pore medium and significantly elevate the CO 2 content (>1000 ppm at pressures of >0.2 GPa) dissolved in the interstitial melts. Available fluid-inclusion studies suggest that such a mechanism may have played an important role in the formation of some I- and A-type charnockites. Nonetheless, deducing the fluid composition solely from fluid-inclusion studies is ambiguous, since the trapping of fluid inclusions may leave a potentially non-representative record due to the different wetting characteristics of CO 2 and H 2 O, as well as post-trapping grain-boundary migration recrystallisation, favoring the entrapment of CO 2 -rich inclusions. A further alternative mechanism is to extract hydrous melts from an orthopyroxene-bearing mush, thereby restricting the back-reaction of orthopyroxene during progressive crystallization. Igneous charnockites have maximum P 2 O 5 contents of up to 1.0–1.2 wt% at 55–60 wt% SiO 2 and Zr contents of up to >400–600 ppm at 60–65 wt% SiO 2. The nonsynchronous variations in P 2 O 5 and Zr contents can best be explained by melt extraction from a mush that saturates apatite earlier than zircon during magma evolution. This process produces apatite- and zircon-rich cumulate charnockites that have significantly higher P 2 O 5 and Zr contents than global orthopyroxene-free granitoids. Many I-A-S type charnockites are believed to have formed through this mechanism and represent cumulate granitoids that had lost a significant amount (>20–40%) of hydrous interstitial melt. Our study reveals that the formation of igneous charnockite depends on extreme magmatic processes such as flushing of large amounts of CO 2 or high degree of crystal-melt segregation, and not merely on the high temperature of crystallization. Further studies on igneous charnockite should shed new light on quantifying the carbon flux and understanding the differentiation of the continental crust. [ABSTRACT FROM AUTHOR]

The Friersdale Charnockite is a late-Mesoproterozoic (1078 ± 10 Ma), fine- to medium-grained to porphyritic orthopyroxene-bearing monzogranite intrusion with characteristic opalescent quartz that outcrops in the Keimoes-Upington region of the Northern Cape, South Africa. The weakly to undeformed, northwest-southeast trending granitoid body represents the most extensive member of the Keimoes Suite and intruded across the tectonicboundary between the granulite facies Kakamas and Areachap Terranes of the Namaqua-Natal Metamorphic Province during the final stages of the main Namaqua orogeny. The Friersdale Charnockite is a metaluminous, ferrous and potassic monzogranite with major, trace, REE and isotope chemistries suggesting a mixed crustal source with significant input from both Paleoproterozoic- and Mesoproterozoic-aged source regions. [ABSTRACT FROM AUTHOR]

Several generations of Paleozoic granitic rocks are studied with Sm-Nd isotopic methods in the northwestern part of the Aktau-Dzhungar microcontinent of Central Kazakhstan (Atasu-Mointy divide). The initial Nd isotopic composition of the granitic rocks varies in a relatively narrow range from-0.1 to-3.5ε; the Nd model ages are also similar (1.11-1.46 Ga). These results indicate that the crustal source of all the Paleozoic granitic rocks of the region had similar composition and, probably, age. It is shown that the t (DM) values of the Paleozoic granites reflect different proportions between ancient and juvenile material in the crustal source. [ABSTRACT FROM AUTHOR]

The geochemical and Sm-Nd isotope characteristics of Late Precambrian and Early Cambrian sandstones previously related to the sedimentary cover of the Dzabkhan continental block are reported. It is established that the Riphean and Vendian sedimentary rocks of the Ul'zitgol'skaya and Tsaganolomskaya Formations were accumulated within the Dzabkhan continental block as a result of recycling of the terrigenous deposits formed at the expense of destruction of basement rocks and younger granite. The formation of terrigenous rocks of the Bayangol'skaya Formation after a gap in sedimentation occurred in the sedimentary basin, where only the Late Riphean formations of the juvenile crust, probably of the Dzabkhan-Mandal block were the sources, without the contribution of the ancient crustal material. The Tsaganolomskaya and Bayangol'skaya Formations were formed in different sedimentary basins and cannot be related to the same complex. [ABSTRACT FROM AUTHOR]

The geochemical evolution of biotite (Bt) from garnet-bearing associations in the granite-forming series of the Nimnyr Block (Aldan Shield) is considered. The series includes the primary rock (gneiss or basic rock), autochthonous enderbite- or charnockite-gneiss (Lc1), migmatitic leucosome (Lc2, Lc4), and paraautochthonous charnockite (Lc3-ch1) and (Lc5-ch2 → grn). Bt in each series is characterized by an individual, significant difference in the concentrations of Ti, V, Cr; rarely Al, Fe, Mg, and Rb; and very rarely La, Ce, Nd, and Gd. The uniform trend of evolution of Bt compositions in the series was established for Al, K, (K + Na)/Al, rarely for Mg, Ti, and К. In contrast to the series with ch2, Bt becomes enriched in LREEs from autochthonous Lc1 to allochthonous Lc2 and Lc3. The different compositional variations of Bt in relation some minor elements is explained by the different composition of the material, which underwent melting, temperature variations (from 820 to 750°C), and changes in pH of the mineral-forming medium. [ABSTRACT FROM AUTHOR]

The Kerala Khondalite Belt (KKB) of the southern India encompasses volumetrically significant magmatic components. Among these, orthopyroxene-bearing, felsic ortho-granulites, popularly known as charnockites in Indian context, constitute an important lithology. In contrast to the well-known phenomena of arrested charnockitization, the geochemical characteristics and petrogenesis of these ortho-granulite suites remain poorly studied, leaving geodynamic models envisaged for the KKB highly conjectural. In this paper, we try to bridge this gap with detailed results on orthopyroxene-bearing, felsic ortho-granulites spread over the entire KKB and propose a new petrogenetic and crustal evolution model. Based on geochemical characteristics, the orthopyroxene-bearing, felsic ortho-granulites (charnockites sensu lato ) of KKB are classified into (1) tonalitic (TC), (2) granitic (GC), and (3) augen (AC) suites. Members of the TC follow sodic (characterized by decreasing CaO/Na 2 O), whereas those of the GC and AC follow calc-alkaline trends of differentiation. Geochemical patterns of the TC resemble those of the Archaean tonalite–trondhjemite–granodiorite (TTG) suites, with slightly magnesian character (average Mg# = 33), moderate LREE (average La N = 154), low HREE (average Yb N = 6) and Y (1–53 ppm; average 11 ppm). The TC is also characterized by positive to slightly negative europium anomalies (Eu/Eu* = 0.7 to 1.67). The GC and AC suites, on the other hand, resemble post-Archaean arc-related granites. The GC displays ferroan nature (average Mg# = 22), low to moderate degrees of REE fractionation (average [La/Yb] N = 34.84), high contents of Y (5–128 ppm; average 68), and low Sr/Y (1–98) ratios. Significant negative Eu anomalies (Eu/Eu* = 0.18–0.91; average 0.50) and low Sr (65–690 ppm) are also noted in the GC. Similar chemical characteristics are shown by the AC, with ferroan nature (average Mg# = 21), low to moderate degrees of REE fractionation (average [La/Yb] N = 26), high contents of Y (71–99 ppm; average 87), and low Sr/Y (average 2) ratios with significant negative Eu anomalies (Eu/Eu* = 0.03–0.31; average 0.23) and low Sr (average 160 ppm) contents. The protoliths of the TC are interpreted as being derived from partial melting of thickened oceanic-arc crust composed of Archaean mafic composite source rocks ( i.e., eclogite and/or garnet amphibolite) with a garnet amphibolite residue. Geochemical features of the GC, such as high Rb/Sr (average 1.80) and Ba/Sr ratios (average values > 6), are considered as evidence for crustal reworking in their genesis, suggesting remelting of a quartzo-feldspathic (TTG) source, within the plagioclase stability fields. The geochemical features of the felsic ortho-granulite suite, substantiated with published geochronological data on members of the TC, GC, and AC suites, suggest a four-stage crustal evolution of the KKB. The first stage is marked by the formation of an over-thickened oceanic-arc. Zircon Hf c model ages of the TC and GC suites constrain the time of this juvenile magmatic crust-forming event as Meso- to Neoarchaean (2.8 to 2.6 Ga). The second stage corresponds to the production of TTG magmas by melting of the over-thickened oceanic-arc crust, subsequent to basaltic underplating during Palaeoproterozoic ( ca. 2.1 Ga). The third stage was initiated by a transition in subduction style from shallow to steep due to continent-arc accretion. This stage is marked by the formation of granitic magmas through partial melting of the TTG crust and their differentiation into GC and TC. The zircon crystallization ages (1.89 and 1.85 Ga) of the GC indicate arc accretion occurred during the Palaeoproterozoic. The fourth stage of crustal evolution is correlated with the Mesoproterozoic (~ 1.5 Ga) emplacement of megacrystic K-feldspar granites (protoliths to the AC and augen gneisses). The distinct petrography, geochemistry and crystallization ages of the AC suggests recurrence of megacrystic, high-K calc-alkaline granitoids as the product of final phases of crustal-remelting marking subduction cessation. All these magmatic events are fairly well correlated with the major episodes of crustal growth observed in the once contiguous continental fragments (Sri Lanka and Madagascar) and worldwide events (2.7, 1.9, and 1.2 Ga) implying similar episodic nature in the lower crustal evolution of the KKB. [ABSTRACT FROM AUTHOR]

Mineral weathering of bedrock in the context of landscape evolution provides useful insights in understanding the physico-chemical and climate processes. In this paper, we report mineral and petrographical features supported by geochemical results on the weathering of charnockite rocks exposed along the east coast, Chennai. The exposed rocks consist of medium to fine grained charnockite and are intensely weathered, fractured with weathering rind. Micromorphology of the unweathered charnockite core rock, weathering rind and soil show that the weathering processes are characterised by progressive physical and chemical attack on the labile minerals with the formation of neoformed clay minerals substituting the original rock fabric. The alteration of minerals has produced Fe oxides and clay minerals such as halloysite and kaolinite. Ferruginous oxides etch and impregnate into the plagioclase and othropyroxene microcracks and fractures during the advanced weathering stage. Microfabric alterations in microfractures and its variations occur in the weathering rind thereby, affect the chanrnockite weathering landscape. Geochemical data and chemical weathering indices (CIA, CIW, PIA and CWI) indicate insitu weathering due to stronger physical weathering compared to chemical alteration. UCC and chondrite normalized trace and REE data of the core rock, weathering and soil show similar spider spectra again pointing to insitu weathering with minor recycling. Negative Eu anomaly is due to the alteration of the alkali feldspars. Weathering of the core rock to soil grades towards the increase of quartz grains and Fe oxides in the weathering rind and soils. Weathering rind exhibits formation of clays such as kaolinite, halloysite and gibbsite formed under the humid, alternate dry and wet conditions. [ABSTRACT FROM AUTHOR]

Charnockites in the Datian region of the northeastern Cathaysia Block, South China have an assemblage of garnet, clinopyroxene, orthopyroxene, plagioclase, anti-perthite, K-feldspar, biotite, quartz and ilmenite. Phase equilibrium modeling indicates that the Datian charnockite was formed at T = 845–855 °C and P = 8.2–8.4 kbar with corresponding water activity lower than 0.50. Fluid inclusions in the Datian charnockite are dominated by N 2 and CO 2 with minor CH 4 . The fluids homogenized to liquid at −153.0 to −138.8 °C and 18.3–21.6 °C, respectively, showing a low-density nature. The low-density fluids could be attributed to selective leakage of water due to the affinity of water to melt and decompression-dominated retrograde process. Combined with previous studies, a two-stage formation model is proposed to interpret the petrogenesis of the Datian charnockite, viz emplaced at the Paleoproterozoic and underwent the granulite-facies metamorphism during the Phanerozoic tectonic event. [ABSTRACT FROM AUTHOR]

Incipient charnockites have been widely used as evidence for the infiltration of CO2-rich fluids driving dehydration of the lower crust. Rocks exposed at Kakkod quarry in the Trivandrum Block of southern India allow for a thorough investigation of the metamorphic evolution by preserving not only orthopyroxene-bearing charnockite patches in a host garnet-biotite felsic gneiss, but also layers of garnet-sillimanite metapelite gneiss. Thermodynamic phase equilibria modelling of all three bulk compositions indicates consistent peak-metamorphic conditions of 830-925 °C and 6-9 kbar with retrograde evolution involving suprasolidus decompression at high temperature. These models suggest that orthopyroxene was most likely stabilized close to the metamorphic peak as a result of small compositional heterogeneities in the host garnet-biotite gneiss. There is insufficient evidence to determine whether the heterogeneities were inherited from the protolith or introduced during syn-metamorphic fluid flow. U-Pb geochronology of monazite and zircon from all three rock types constrains the peak of metamorphism and orthopyroxene growth to have occurred between the onset of high-grade metamorphism at c. 590 Ma and the onset of melt crystallization at c. 540 Ma. The majority of metamorphic zircon growth occurred during protracted melt crystallization between c. 540 and 510 Ma. Melt crystallization was followed by the influx of aqueous, alkali-rich fluids likely derived from melts crystallizing at depth. This late fluid flow led to retrogression of orthopyroxene, the observed outcrop pattern and to the textural and isotopic modification of monazite grains at c. 525-490 Ma. [ABSTRACT FROM AUTHOR]

Integrated in-situ analyses of zircon U–Pb ages and Hf–O isotopes are reported for charnockite, trondhjemite and associated amphibolite in the Archean Ntem Complex of the NW Congo Craton, southern Cameroon. The charnockite crystallized at ∼2.92 Ga, coincident with the timing of extensive occurrence of high-temperature magmatism possibly related to mantle plume activity worldwide. They are characterized by zircon δ 18 O values of ∼5.9‰ and ɛHf( t ) values of ∼0.0, with Hf model ages of ∼3.5–3.3 Ga. On the basis of the new isotopic and literature data we suggest that the charnockites were generated by partial melting of a Paleoarchean mafic crustal source possibly triggered by 2.92 Ga mantle plume activity. The trondhjemite and associated amphibolite protolith crystallized synchronously at ∼2.87–2.86 Ga. The trondhjemite exhibits zircon δ 18 O values of ∼6.0‰ and negative ɛHf( t ) values of ca. −3.7, with Hf model ages of ∼3.8–3.5 Ga, whereas the amphibolite has positive zircon ɛHf( t ) values of ∼2.3 and δ 18 O values of ∼4.6‰, lower than that (∼5.3‰) of zircons from juvenile mantle-derived magmas. The trondhjemite was most likely generated by high-pressure partial melting of an Eoarchean crustal protolith possibly triggered by the synchronous mafic magmatism. An ancient ∼3.8 Ga-old proto-crust may have existed in the NW Congo Craton. [ABSTRACT FROM AUTHOR]

The Irumide Belt sensu lato of eastern Zambia situated between the Bangweulu Block and the Zimbabwe Craton is one of the Mesoproterozoic belts in southern Africa, which developed during the formation of the supercontinent Rodinia. Though in several of these belts the orogenic evolution seems to be connected to a long lasting high temperature history (∼200 Ma), the duration and geodynamic causes of the metamorphism in this particular belt have not been studied. Here we report the results of an integrated petrological study and texturally controlled in situ monazite dating of spinel–quartz and orthopyroxene–cordierite granulites and associated charnockites and mafic rocks from the Chipata Terrane of the Southern Irumide Belt (SIB), which revealed a single stage high to ultra-high temperature (HT, UHT) metamorphism during the Mesoproterozoic Irumide orogeny. The earliest textural relicts of the prograde evolution are patchy sillimanite aggregates interpreted to represent pseudomorphs after andalusite. Sillimanite inclusions in garnet indicate garnet growth in the sillimanite stability field. During peak metamorphism garnet + sillimanite reacted to form spinel + quartz. In associated garnet–orthopyroxene–cordierite granulites, peak orthopyroxene has high Al 2 O 3 contents of up to 7.9 wt%. These peak metamorphic features point to UHT conditions of 900–1000 °C (UHT) at ∼5–6 kbar, in agreement with the occurrence of inverted pigeonite in associated charnockites. Orthopyroxene + cordierite coronas around prograde garnet in the second assemblage indicates decompression at UHT conditions after peak metamorphism. Subsequent isobaric cooling (IBC) led to reversal of mineral reactions and thus to replacement of spinel + quartz by garnet 2 + sillimanite 2 + cordierite. The IBC at still high pressures is also indicated by the formation of garnet and clinopyroxene coronas between orthopyroxene and plagioclase in associated mafic rocks. During late-stage retrogression the formation of kyanite + chlorite + quartz ± staurolite ± magnesite at the expense of cordierite and garnet in garnet–cordierite–sillimanite gneiss indicates prevailing high pressures (>4–5 kbar) during cooling below temperatures of ∼550 °C. Monazite grains occurring in different textural settings (inclusions in garnet, and in matrix) revealed ages between 1031 ± 4 and 1013 ± 4 Ma for the peak HT to UHT metamorphism of the Chipata terrane of the SIB. The metamorphism is almost synchronous with the age of intracrustal melting in the northern Irumide Belt (IB; 1020–950 Ma) and slightly younger than the age of continental margin arc magmatism in the SIB (∼1090–1040 Ma). The metamorphism therefore most likely occurred as a consequence of subduction related magmatism and the collision between the IB (margin of the Bangweulu block) and the SIB (margin of an unknown southern craton) during the Mesoproterozoic Irumide orogeny. [ABSTRACT FROM AUTHOR]

Pudukkottai region in the northeastern part of the Madurai Block exposes the garnetiferous pink granite that intruded the biotite gneiss. Charnockite patches are associated with both the rock types. Rb-Sr biotite and Sm-Nd whole-rock isochron ages indicate a regional uplift and cooling at ∼550 Ma. The initial Nd isotope ratios ( $\varepsilon _{\text {Nd}}^{\mathrm {t}}=-20$ to −22) and Nd depleted-mantle model ages (T = 2.25 to 2.79 Ga) indicate a common crustal source for the pink-granite and associated charnockite, while the biotite gneiss and the charnockite within it represent an older crustal source ( $\varepsilon _{\text {Nd}}^{\mathrm {t}}= -29$ and T = > 3.2 Ga). The Rb-Sr whole-rock data and initial Sr-Nd isotope ratios also help demonstrate the partial but systematic equilibration of Sr isotope and Rb/Sr ratios during metamorphic mineral-reactions resulting in an 'apparent whole-rock isochron'. The available geochronological results from the Madurai Block indicate four major periods of magmatism and metamorphism: Neoarchaean-Paleoproterozoic, Mesoproterozoic, mid-Neoproterozoic and late-Neoproterozoic. We suggest that the high-grade and ultrahigh-temperature metamorphism was preceded by magmatism which 'prepared' the residual crust to sustain the high P- T conditions. There also appears to be cyclicity in the tectono-magmatic events and an evolutionary model for the Madurai Block should account for the cyclicity in the preserved records. [ABSTRACT FROM AUTHOR]

A gravity survey was conducted on the Windmill Islands, East Antarctica, during the 2004–05 summer season. The aim of the study was to investigate the subsurface geology of the Windmill Islands area. Ninety-seven gravity stations were established. Additionally, 49 observations from a survey in 1993–94 were re-reduced and merged with the 2004–05 data. A three-dimensional subsurface model was constructed from the merged gravity dataset to determine the subsurface geology of the Windmill Islands. The main country rock in the Windmill Islands is a Garnet-bearing Granite Gneiss. A relatively dense intrusive charnockite unit, the Ardery Charnockite, generates the dominant gravity high of the study area and has been modelled to extend to depths of 7–13 km. It has moderate to steep contacts against the surrounding Garnet-bearing Granite Gneiss. The Ardery Charnockite surrounds a less dense granite pluton, the Ford Granite, which is modelled to a depth of 6–12 km and creates a localized gravity low. This granitic pluton extends at depth towards the east. The modelling process has also shown that Mitchell Peninsula is linked to the adjacent Law Dome ice cap by an ‘ice ramp’ of approximately 100 m thickness. [ABSTRACT FROM PUBLISHER]

The Bakhuis Granulite Belt (BGB) is a metamorphic terrain within the Guiana Shield that experienced ultrahigh-temperature (UHT) metamorphism at 2.07–2.05 Ga. In the southwest of the BGB, the Kabalebo charnockites were emplaced at ca. 1.99 Ga and thus postdate UHT metamorphism by at least 60 Myr. Two generations of gabbroic intrusions have been recognized within the BGB, which could act as a heat source for the two UHT events. A younger generation of tholeiitic “Charlie” gabbros yields a baddeleyite U/Pb age of 1971 ± 15 Ma. The presence of a metamorphic overprint indicates that the hornblende-bearing “Moi–Moi” metagabbros predate the Charlie gabbros. Large zircons with complex zoning patterns are found in a Moi–Moi metagabbro sample. The main growth domains of these zircons give an age of 1984 ± 4 Ma, which is indistinguishable from the surrounding charnockites. Matching trace element and Hf isotope characteristics indicate that the complex zircons are derived from the charnockites. We argue that the emplacement of the metagabbros and charnockite magmatism were contemporaneous and that zircon grains from the charnockitic melt were mechanically transferred to the gabbroic bodies during magma mingling. The new ages for the gabbroic bodies in the BGB confirm that they are contemporaneous with, and the likely heat source for, charnockite magmatism, but that they are not associated with the 2.07–2.05 Ga UHT event. Furthermore, the new ages and recognition of the Moi–Moi metagabbros as an Alaskan-type complex provide the first direct evidence for late Transamazonian subduction zone magmatism in the Guiana Shield. [ABSTRACT FROM PUBLISHER]

The tectonic setting of the late Paleoproterozoic suite of anorthosite, mangerite, charnockite and alkali-feldspar granite (AMCG) on the northern margin of the North China Craton (NCC) is controversial. This paper reports on the petrology, geochronology and geochemistry of the Beibaiqi, Beipuzi and Shibalitai mangerites in the Longhua area and the Shinao mangerite in the Jianping area. Zircon U–Pb dating reveals that these mangerites formed 1768–1725 Ma, similar to the other lithologies (1753–1673 Ma) of the AMCG suite on the northern margin of the NCC. The mangerites have intermediate SiO 2 contents (57.2–66.8 wt.%) and high K 2 O (4.04–7.05 wt.%) and Na 2 O (3.75–5.50 wt.%) contents, which belong to alkaline series rocks. They are enriched in light rare-earth elements (REEs) and large-ion lithophile elements (LILEs) of Rb, Ba and K, and they are depleted in heavy REEs and the high field-strength elements (HFSEs) of Th, U, Nb, Ta, Ti and P. The zircon ɛ Hf ( t ) values of these mangerites are negative (−8.3 to −1.7), with depleted mantle model ages ( T DM ) and average crustal two-stage modal ages ( T 2DM ) from 2250 Ma to 2533 Ma and 2573 Ma to 2959 Ma, respectively. These geochemical characteristics suggest that these mangerites originated from the early Precambrian lower crust of the NCC. Compared with the mangerites, the other lithologies of the AMCG suite display different evolutionary trends of their major elements and different distribution patterns of their REEs and trace elements, indicating that those lithologies were not formed through fractional crystallization by the same primary magma. The anorthosites share similar distribution patterns of REEs and trace elements and zircon Hf isotopic composition with associated norites. The data suggest that the anorthosites were formed by noritic magmas through fractional crystallization at the base of the lower crust. The alkali-granites and rapakivi granites display the geochemical features of A-type granites, and might have originated from partial melting of the mid-upper crust. Combined with regional geological data, these findings suggest that the AMCG suite occurred in a post-collisional/post-orogenic extensional setting rather than an anorogenic continental rift setting. [ABSTRACT FROM AUTHOR]

Comment on "Limitation of uranium and thorium traces in charnockite matrix-PIXE analyses at 3 MeV with Si (Li) detector" These elements Br, Rb, Sr, and Mo are traced out in the charnockite composition in the above Table 3." They have mentioned, "from the above results Table 3, L-X-ray's energies of Th and U are similar K X-ray energies of Br 13.292 keV, Rb 13.396 keV, Sr 15.835 keV, Mo 17.480 keV. [Extracted from the article]

Post-collisional reversely zoned plutons occurring in the Araçuaí belt frequently show basic cores enveloped by felsic rocks, with intense magma mingling/mixing features. The Venda Nova (VN) pluton presents, in addition to its mafic core composed of gabbronorites surrounded by syenomonzonites, a narrow ring of charnockite and norite. The VN is considered as a marker of the last magmatic phases of the Araçuaí orogenic collapse and bears one of the few high-quality Cambrian paleomagnetic data for the West Gondwana, but no geochronological data is yet available for it. In this paper, we report new in-situ U-Pb geochronological data (SHRIMP II) for the syenomonzonite, gabbro and charnockite of the Venda Nova pluton. These data are discussed and compared to the geochemical and geochronological data available for the post-collisional magmatic rocks of the Araçuaí orogen. The concordant ages of the syenomonzonite (496.9 ± 4.2 Ma, MSWD = 0.0019, n = 14) and gabbro (500.6 ± 3.7 Ma, MSWD = 0.0290, n = 14) are likely the crystallization age of the main plutonic body and corroborate the previous interpretation of paleomagnetic data. In contrast, two age groups were identified for the charnockite: Group I (n = 14, 624.0 ± 3.1 Ma, MSWD = 0.116), which includes zircon borders and rims without evidence of border reaction, and Group II (n = 6, 483.7 ± 7.4 Ma, MSWD = 0.0003) from zircon grains with luminous rims and older cores. Since the Venda Nova charnockite has (i) a distinct geochemical signature compared to other post-collisional charnockite bodies found in the same region, (ii) higher magnetic anisotropy degrees compared to other border units of the same intrusion, and (iii) marked sub-solidus deformation features, the Group I ages are suggested as the crystallization age of these rocks, while Group II ages would be better interpreted as a resetting due to the thermal influence of the syenomonzonite and gabbro intrusions. This implies that the VN is a composite magmatic complex with contributions of magmas from the pre-collisional magmatic arc and from the post-collisional melts originated in the crust and mantle across the Araçuaí lithosphere during orogen collapse. • The Venda Nova (VN) is a reversely zoned pluton in the Araçuaí orogen (AO, Brazil). • U-Pb data from syenomonzonites, gabbros and charnockites is provided. • Syenomonzonites (496.9 ± 4.2 Ma) and gabbros (500.6 ± 3.7 Ma) date the post-collisional event of the AO. • Charnockites are suggested to be far older (624.0 ± 3.1 Ma) and part of a pre-collisional setting. [ABSTRACT FROM AUTHOR]

Charnockites are Opx-bearing igneous rocks commonly found in high-grade metamorphic terranes. Despite being volumetrically minor, they show a wide range in both bulk geochemistry and intensive parameters. They form a characteristic component of the AMCG (anorthosite–mangerite–charnockite–granite) suite, but their association with typical S-type granites is less well-known. The Darongshan S-type granitic complex (DSGC) in Guangxi Province, southern China, contains granites varying in mafic silicate mineral assemblages from Bt + Crd (Darongshan suite) to Opx + Grt + Bt + Crd (Jiuzhou suite) and Opx + Crd ± Bt (Taima suite), corresponding to a geochemical transition from magnesian calc-alkalic to ferroan calc-alkalic. However, its genesis, even the accurate age of intrusion, remains highly contentious despite intensive research. In order to understand the genesis of charnockite and its genetic relationship with S-type granite; here, we first determined zircon U-Pb ages of each suite using a SIMS on the basis of a detailed petrological study. Zircon U-Pb ages show that all suites of the complex were emplaced contemporaneously at ca. 249 Ma. Monazite apparent U-Pb ages are indistinguishable from zircon U-Pb ages within analytical error. Further in situ zircon Hf-O isotope analyses reveal that the granitic complex was dominantly derived from reduced melting metasedimentary rocks (δ 18 O zircon = ca. 11‰; ε Hf ( t ) zircon = ca. − 10; Δlog FMQ ≤ 0; Mn in apatite oxybarometer) with rare material input from the mantle. The variation in δ 18 O (7.8‰–12.9‰) is more likely a result of hybridization, whereas that in ε Hf ( t ) (− 31.9 to − 1.8) is a result of both hybridization and disequilibrium melting. The variation in mineralogy and geochemistry may be interpreted as a result of entrainment of peritectic garnets from biotite-dehydration melting. Nevertheless, heat input from mantle through basaltic intrusion/underplating is considered to play a major role in high-temperature (> 850 °C) melting at mid-crustal levels (i.e. the cordierite stable field) for generation of the granitic complex. We interpret that the granites were intruded in a back-arc setting and basaltic magmatism was directly associated with slab roll-back and tearing during the latest Permian and early Triassic times. [ABSTRACT FROM AUTHOR]

The Menderes Massif is a major polymetamorphic complex in Western Turkey. The late Neoproterozoic basement consists of partially migmatized paragneisses and metapelites in association with orthogneiss intrusions. Pelitic granulite, paragneiss and orthopyroxene-bearing orthogneiss (charnockite) of the basement series form the main granulite-facies lithologies. Charnockitic metagranodiorite and metatonalite are magnesian in composition and show calc-alkalic to alkali-calcic affinities. Nd and Sr isotope systematics indicate homogeneous crustal contamination. The zircons in charnockites contain featureless overgrowth and rim textures representing metamorphic growth on magmatic cores and inherited grains. Charnockites yield crytallization age of ~590 Ma for protoliths and they record granulite-facies overprint at ~ 580 Ma. These data indicate that the Menderes Massif records late Neoproterozoic magmatic and granulite-facies metamorphic events. Furthermore, the basement rocks have been overprinted by Eocene Barrovian-type Alpine metamorphism at ~42 Ma. The geochronological data and inferred latest Neoproterozoic–early Cambrian palaeogeographic setting for the Menderes Massif to the north of present-day Arabia indicate that the granulite-facies metamorphism in the Menderes Massif can be attributed to the Kuunga Orogen (600–500 Ma) causing the final amalgamation processes for northern part of the Gondwana. [ABSTRACT FROM PUBLISHER]

Sandmata Granulite complex (SGC) of Rajasthan of Western India is a multiply deformed, metamorphosed and migmatised granulite units representing a Mesoproterozoic collisional orogen. It consists of migmatised metapelites, calcsilicate granulites, pyroxene granulites and charnockitic intrusives at 1.7 Ga. The granulites mostly occur as dismembered, isolated enclaves in garnet bearing migmatites and quartzofeldspathic gneiss. Intrusion of small scale post-tectonic granite in granulite documents the last thermal activity in the area. At the eastern part of SGC, greenschist to lower amphibolite facies rocks of Manglawar Complex (MC) are exposed. The P-T conditions of garnet formation during metamorphism in migmatite, leptynite and quartzo-feldspathic gneiss are 780-850°C and 7-8 kbar. Retrograded biotite forming reactions occur at much lower temperature of 500 to 600°C and pressure of 3.5-4.5 kbar. The intrusive granite is weakly deformed, calc-alkaline to sub-alkaline, peraluminous in nature, having trace element signature of volcanic-arc to syn-collisional granite. The chondrite-normalised REE patterns indicate a garnet-free source. The whole-rock Rb-Sr age of 1715 ± 24 Ma deduced for the granite mark its emplacement age. Intrusive nature of granite suggests that the age of granulite metamorphism and migmatization should be >1715 Ma, which is much closer to the whole-rock Rb-Sr age of migmatite and quartzofeldspathic gneiss. The whole-rock Rb-Sr analysis of migmatite gives an age of 1735±150 Ma with an initial Sr/Sr ratio of 0.704 which is interpreted as an age when the temperature of migmatization passed below the blocking temperature of Rb and Sr for biotite and plagioclase; an upper age limit of migmatization. SGC represents a major 1.9-1.7 Ga Palaeoproterozoic, tectonothermal event. The granulite facies metamorphism is succeeded by 1.7 Ga migmatisation, intrusion of calc-alkaline granite and emplacement of charnockite protolith. The whole granulite complex is subsequently cooled and later exhumed, and became juxtaposed with MC during a late major orogeny. [ABSTRACT FROM AUTHOR]

The Zunhua–Qinglong microblock in Eastern Hebei, North China Craton, exposes two contrasting charnockitic rock series in the Yuhuzhai–Taipingzhai and Cuizhangzi areas: charnockitic plagioclase gneiss series with chemical compositions of dioritic and tonalitic rocks, and charnockite series showing tonalitic and granodioritic components. Petrographic observation reveals that two types of orthopyroxenes are preserved in these rocks. Medium-fine grained anhedral orthopyroxenes are preserved in both series, and coarse grained subhedral orthopyroxenes are preserved only in the charnockite series. In situ trace element analyses reveal that the coarse grained subhedral orthopyroxenes exhibit typical chemical features of magmatic orthopyroxene, whereas the medium-fine grained anhedral orthopyroxenes display lower medium to heavy rare earth elements (REE) and no obvious Eu anomalies, resulting in left-inclined REE patterns. Combined with petrographic features, these new data indicate that the medium-fine grained anhedral orthopyroxenes were formed by granulite–facies metamorphism caused by dehydration reactions, whereas the coarse grained subhedral orthopyroxenes were directly crystallized from their magmatic precursors. Laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) zircon U–Pb isotopic dating reveals that the magmatic precursors of the charnockitic plagioclase gneiss series were emplaced between 2530 ± 17 and 2523 ± 12 Ma, and those of the charnockite series were emplaced between 2527 ± 28 and 2515 ± 22 Ma. We conclude that these magmatic precursors are contemporaneous emplacements of two Neoarchean granitoid magmatic events, which were followed by regional granulite–facies metamorphism at ∼2.45 Ga. The charnockitic plagioclase gneiss series and charnockite series exhibit similar ɛ Hf ( t ) values of −2.4 to +5.3 and −3.2 to +5.5, indicating either depleted mantle or juvenile crust affinity, and involvement of ancient crustal components. The charnockitic plagioclase gneiss series exhibit relatively low SiO 2 contents (54.1–65.2%), with various MgO contents (1.93–5.36%), Mg# (0.36–0.55), and (La/Yb) N values (3.49–56.00); the charnockite series exhibit higher SiO 2 contents (60.1–69.2%), with similar (La/Yb) N values (14.61–42.69), MgO contents (2.10–3.99%), and Mg# (0.29–0.52). These geochemical and zircon Lu–Hf isotopic features, together with chemical modeling, suggest that the magmatic precursors of the charnockitic plagioclase gneiss series may have been primarily derived from the partial melting of a depleted mantle that was metasomatized by slab-derived melts/fluids, and experienced fractional crystallization processes with hornblende and plagioclase as primary fractionated phases. The aforementioned features further suggest that the charnockite series originated from a partial melting of the subducted slab, and it was strongly contaminated by mantle peridotites. These new data, combined with the previous studies of Neoarchean basement rocks in the Zunhua–Qinglong microblock in Eastern Hebei, suggest that the magmatic precursors of these two contrasting charnockitic rock series were formed in a back-arc-related tectonic environment at a convergent plate margin. [ABSTRACT FROM AUTHOR]

A study has been carried out in crystalline hard rock aquifers of Madurai district, Tamil Nadu, to identify the spatial and temporal variations and to understand sources responsible for hydrogeochemical processes in the region. Totally, 216 samples were collected for four seasons [premonsoon (PRM), southwest monsoon (SWM), northeast monsoon (NWM), and postmonsoon (POM)]. The Na and K ions are attributed from weathering of feldspars in charnockite and fissile hornblende gneiss. The results also indicate that monsoon leaches the U ions in the groundwater and later it is reflected in the Rn levels also. The statistical relationship on the temporal data reflects the fact that Ca, Mg, Na, Cl, HCO, and SO form the spinal species, which are the chief ions playing the significant role in the geochemistry of the region. The factor loadings of the temporal data reveal the fact that the predominant factor is anthropogenic process and followed by natural weathering and U dissolution. The spatial analysis of the temporal data reveals that weathering is prominent in the NW part and that of distribution of U and Rn along the NE part of the study area. This is also reflected in the cluster analysis, and it is understood that lithology, land use pattern, lineaments, and groundwater flow direction determine the spatial variation of these ions with respect to season. [ABSTRACT FROM AUTHOR]

The Margate Granite Suite underlies much of the Margate Terrane of the Natal Metamorphic Province, SE South Africa. It consists of foliated granites grouped into four main lithotypes: garnet leucogranite, garnet-free leucogranite, charnockite and garnet-biotite augen gneiss. In this study we present new U-Pb (SHRIMP) zircon geochronological data on each of the four lithotypes to constrain the timing of emplacement of the various granite phases and of charnockite formation. Magmatic zircon ages span a period of about 125 Ma, indicating that the Margate Suite does not comprise a single coeval group of plutons. The oldest crystallisation age of 1169 ± 14 Ma, obtained from the garnet-biotite augen gneiss phase, is statistically similar to that of the Sikombe Granite which is exposed to the south of the Margate Terrane, with which a correlation is made. This implies that the magmatic history of the Margate Terrane is longer and more complex than previously thought. The original granite protolith of a sample from the charnockitised granite in the thermal aureole of the ( ca. 1040 Ma) Oribi Gorge granite yielded an age of 1135 ± 11 Ma, which is statistically similar to the published age of the gneissic Mzimilo Granite in the Mzumbe Terrane. Zircon overgrowths in this sample, dated at 1037 ± 13 Ma are coeval with the age of the Oribi Gorge granite and are interpreted to date the secondary charnockitisation of the Margate granite. A sample of a partly charnockitised garnet leucogranite provided an age of 1088 ± 9 Ma. This granite contains a pervasive foliation (S 2 ), partly obliterated in charnockitic patches, indicating that both the D 2 event and the charnockitisation are younger. This confirms previous work in which the maximum age of the main fabric-forming deformation was constrained by the 1091 ± 9 Ma age of the Glenmore Granite. A sample from the garnet leucogranite in the type area of the Margate Granite Suite yielded an age of 1043 ± 4 Ma, which is statistically similar to that of the previously dated, garnet-free leucogranite of the Portobello granite, and zircon metamorphic dates of the secondary charnockitisation event associated with emplacement of the Oribi Gorge Suite. Our new data show that the Margate Terrane was subjected to at least four magmatic/thermal events, at ∼1170 Ma, ∼1135–1140 Ma, ∼1082–1093 Ma, and 1025–1050 Ma. These events can be correlated with coeval magmatic and thermal episodes in surrounding crustal blocks within Rodinia and Gondwana. In particular the Margate Terrane appears to correlate well with the Vardeklettane Terrane of Dronning Maud Land, East Antarctica and furthermore that the Natal belt may be up to 80 Ma older than the Maud belt east of the Heimefront Shear Zone, which is made up of younger crust which was accreted westwards against the Natal belt. In this scenario, the Cape Merdith Complex, West Falkland, which shows no zircon evidence of crust older than ca. 1135 Ma, forms part of the Maud belt, not the older Natal belt. [ABSTRACT FROM AUTHOR]

A study on weathering pits called tafoni was carried out on rock surfaces that age from a few hundreds to millions of years along the east coast between Chennai and Mamallapuram. Tafoni of varying sizes and shapes such as simple circular dots to oblate to prolate, hemispherical to spherical are formed on the granite, granite gneiss, charnockites (acid and mafic) and sandstone both on exposed and inner wall surfaces. In this study, their formation is related to not only tropical weathering processes, but also to sea salt water splays causing salt mineral etching, weathering processes, besides microbial activity, algal and lichen growth accentuating their formation. [ABSTRACT FROM AUTHOR]

In the Neoarchean (~ 2.7 Ga) contact metamorphosed charnockitic footwall of the Mesoproterosoic (1.1 Ga) South Kawishiwi intrusion of the Duluth Complex, the primary metamorphic mineral assemblage and Cu–Ni–PGE sulfide mineralization is overprinted by an actinolite + chlorite + cummingtonite + prehnite + pumpellyite + quartz + calcite hydrothermal mineral assemblage along 2–3 cm thick veins. In calcite, hosted by the hydrothermal alteration zones and in a single recrystallized quartz porphyroblast, four different fluid inclusion assemblages are documented; the composition of these fluid inclusions provide p–T conditions of the fluid flow, and helps to define the origin of the fluids and evaluate their role in the remobilization and reprecipitation of the primary metamorphic sulfide assemblage. Pure CO 2 fluid inclusions were found as early inclusions in recrystallized quartz porphyroblast. These inclusions may have been trapped during the recrystallization of the quartz during the contact metamorphism of the footwall charnockite in the footwall of the SKI. The estimated trapping pressure (1.6–2.0 kbar) and temperature (810–920 °C) conditions correspond to estimates based on felsic veins in the basal zones of the South Kawishiwi intrusion. Fluid inclusion assemblages with CO 2 –H 2 O–NaCl and CH 4 –N 2 –H 2 O–NaCl compositions found in this study along healed microfractures in the recrystallized quartz porphyroblast establish the heterogeneous state of the fluids during entrapment. The estimated trapping pressure and temperature conditions (240–650 bar and 120–150 °C for CO 2 –H 2 O–NaCl inclusions and 315–360 bar and 145–165 °C for CH 4 –N 2 –H 2 O–NaCl inclusions) are significantly lower than the p–T conditions (> 700 °C and 1.6–2 kbar) during the contact metamorphism, indicating that this fluid flow might not be related to the cooling of the Duluth Complex and its contact aureole. The presence of chalcopyrite inclusions in these fluid inclusions and in the trails of these fluid inclusion assemblages confirms that at least on local scale these fluids played a role in base metal remobilization. No evidences have been observed for PGE remobilization and transport in the samples. The source of the carbonic phase in the carbonic assemblages (CO 2 ; CH 4 ) could be the graphite, present in the metasedimentary hornfelsed inclusions in the basal zones of the South Kawishiwi intrusion. The hydrothermal veins in the charnockite can be characterized by an actinolite + cummingtonite + chlorite + prehnite + pumpellyite + calcite (I–II) + quartz mineral assemblage. Chlorite thermometry yields temperatures around 276–308 °C during the earliest phase of the fluid flow. In the late calcite (II) phase, high salinity (21.6–28.8 NaCl + CaCl 2 equiv. wt.%), low temperature (90–160 °C), primary aqueous inclusions were found. Chalcopyrite (± sphalerite ± millerite), replacing and intersecting the early hydrothermal phases, are associated to the late calcite (II) phase. The composition of the formational fluids in the Canadian Shield is comparable with the composition of the studied fluid inclusions. This suggests that the composition of the fluids did not change in the past 2 Ga and base metal remobilization by formational fluids could have taken place any time after the formation of the South Kawishiwi intrusion. Sulfur isotope studies carried out on the primary metamorphic (δ 34 S = 7.4–8.9‰) and the hydrothermal sulfide mineral assemblage (δ 34 S = 5.5–5.7‰) proves, that during the hydrothermal fluid flow the primary metamorphic ores were remobilized. [ABSTRACT FROM AUTHOR]

The Bakhuis Granulite Belt in western Suriname is an ultrahigh-temperature (UHT) metamorphic terrain in the centre of the Paleoproterozoic (Transamazonian) Guiana Shield. Next to the UHT granulites, the belt contains a 30 by 30 km body of orthopyroxene-bearing granitoids: the Kabalebo charnockites. This setting offers an excellent opportunity to investigate the source and origin of charnockite magmatism and the common association of charnockites with (ultra)high-temperature metamorphic terrains. We present a detailed geochemical dataset and LA-ICPMS zircon U/Pb ages with the aim to investigate the geochemical and geochronological relationship between charnockite magmatism and UHT metamorphism in the Bakhuis Granulite Belt. The Kabalebo charnockites have a characteristic trace element signature with elevated K 2 O, P 2 O 5 , Zr, REE and Ba coupled with mobile element depletion, which is a consequence of high-temperature melting of anhydrous but fertile granulitic crust. Field and geochemical evidence suggests that the intermediate granulites in the Bakhuis Granulite Belt are the source of the Kabalebo charnockites. The new U/Pb zircon ages indicate that charnockite magmatism (1993–1984 Ma) postdates UHT metamorphism (2.07–2.05 Ga) by at least 60 Myr. We argue that it is not possible to maintain a thermal anomaly >200 °C in excess of a normal geothermal gradient for such a prolonged period and hence conclude that the Bakhuis Granulite Belt has experienced two distinct periods in which temperatures >950 °C were reached in the lower crust. The presence of comagmatic metadolerite enclaves in the charnockites establishes that mafic magmatism occurred contemporaneously with, and was the likely heat source for, charnockite magmatism at 1.99–1.98 Ga. In contrast, the 2.07–2.05 Ga UHT metamorphic event is not associated with felsic or mafic magmatism in the Bakhuis Granulite Belt or nearby Guiana Shield and postdates the suturing of the juvenile North Guiana TTG-greenstone belt with the West African Shield by at least 10 Myr. We postulate that the UHT metamorphism at 2.07–2.05 Ga is the result of mantle upwelling in a slab tear in the subducted West African slab that formed as the result of crustal scale shearing and boudinage. Prior to the final stabilisation of the Amazonian–West African Shield at 1.90 Ga, northward subduction at 1.99–1.98 Ga caused the emplacement of voluminous hot, mafic magma, resulting in partial melting of the Bakhuis granulite suite to form the Kabalebo charnockites. Charnockite magmatism was roughly contemporaneous with the emplacement of a large belt of shallow granites and felsic volcanic rocks in the SW Guiana Shield. Despite their similar age, the inherited zircon populations suggest that the charnockites are derived from a distinct, juvenile source while the felsic volcanic rocks include an Archaean protolith. [ABSTRACT FROM AUTHOR]

The Trans-North China Orogen (TNCO) is a major Paleoproterozoic collisional belt along which the Western and Eastern Blocks of the North China Craton were amalgamated. The Lüliang Complex occurs along the western margin of this belt and incorporates several arc magmatic suites, supracrustal sequences, granitoids and charnockites. Here we investigate the Luyashan charnockite suite, as well as the surrounding granitoids, from this complex. We present results from petrology, fluid inclusions, mineral chemistry, whole rock geochemistry and zircon U–Pb and Lu–Hf isotopic studies. The charnockites are dominantly anhydrous with the typical presence of orthopyroxene. Microthermometric and laser Raman spectroscopic data on fluid inclusions in the charnockite characterize the trapped fluids as dominantly CO 2 with traces of N 2 and CH 4 . Geochemically, the charnockite suite shows compositional variation from monzogabbro through gabbroic diorite and diorite to monzodiorite. They are dominantly calc-alkaline and ferroan type and display distinct enrichment in large ion lithophile elements with depletion in HREE. They also show prominent negative anomalies of Nb, Ta, Sr and Ti, and positive anomalies of Rb, Pb, Zr and Hf indicating crustal components in the magma source. The majority of the granitoid suite shows 207 Pb/ 206 Pb mean ages in the range of 2172–2032 Ma, correlating with similar ages reported from various groups in the Lüliang Complex, the formation of which is correlated with subduction along an active convergent margin. However, the charnockites which intrude the granitoids and their dioritic enclaves are clearly younger and show tightly constrained emplacement ages in the range of 1853–1872 Ma. The recrystallized zircons in the older granitoids also show similar ages, suggesting a prominent thermal event at this time. These ages are close to the timing of final collision between the Western and Eastern Blocks of the North China Craton and associated high-grade metamorphism at ca. 1.85 Ga. The zircon Lu–Hf isotope data reveal dominantly negative ɛ Hf( t ) values (−8.7 to −0.1) and their T DM C (2477–3042 Ma) suggest that the magma sources mainly involved Meso- to Neoarchean reworked crustal components with limited input of Paleoproterozoic juvenile components. Our study reveals that charnockite magmatism and regional metamorphism in the western margin of the TNCO broadly overlap in space and time. The geochemical features, mineral assemblages and fluid inclusion characteristics of the charnockites suggest that the rocks were derived from high temperature (900–1000 °C), CO 2 -enriched and anhydrous (less than 3%H 2 O) magmas. The magma evolved into more hydrous conditions during cooling marked by the crystallization of amphiboles at 800–850 °C. The geochemical features of the charnockite suite also suggest that these rocks were formed during a transitional phase from syn-subduction to collision. Such a scenario is compatible with a tectonic setting involving the subduction of an oceanic ridge when flushing of heat and CO 2 -rich fluids from asthenosphere into the overriding plate might have occurred through the slab window, generating hot and anhydrous magmas through melting of the basement rocks. The slab window mechanism would also account for broadly coeval high-temperature and high pressure granulites reported from the TNCO. We therefore speculate that the formation of the Luyashan charnockite suite might have been associated with ridge subduction at the terminal stage of the convergence. [ABSTRACT FROM AUTHOR]

The paper presents data on the transformations in the mineralogy and mineral assemblages of quartz- and feldspar-free magnesian orthopyroxene-clinopyroxene-biotite metaultramafic granulites converted into orthopyroxene-clinopyroxene-potassic feldspar-plagioclase-quartz charnockite. Within a 4 to 6-m aureole around the fluid conduit, the granulite has been affected by Na-K-Si-HO-CO-Cl-F brine. Thereby the magnesian metaultramafite has undergone progressive debasification and leucocratization: potassic feldspar, oligoclase, and quartz have been metasomatically formed in the interstitial space between the mafic minerals and replaced ortho- and clinopyroxene and biotite. The Fe mole fractions X of all mafic minerals increase toward the fluid conduit as follows: from 0.25 to 0.54 for Opx, from 0.15 to 0.32 for Cpx, and from 0.16 to 0.56 for Bt. The whole-rock compositions suggest that Na, K, and Si have been introduced and Mg, Fe, and Ca removed from the protolith, so that the metaultramafic rock has gradually been transformed first into a mesocratic rock and then, when partial melting started in its most significantly debasified domains, into leucocratic nebulitic migmatite with skialiths of the modified granulite, then into charnockite migma, and eventually into magma. The composition of the charnockite-forming fluid was estimated as $$X_{H_2 O} = 0.6$$, X = 0.3, and $$X_{CO_2 } = 0.1$$. The unusual F-rich composition of the fluid is reflected in that both Bt and Hbl are enriched in F and contain almost no Cl. The P- T parameters of the process, which took place at the metamorphic peak, were T ∼ 780°C, P = 8.5 kbar. Material balance plots of the rocks revealed three petrological trends of the charnockite-forming process controlled solely by the composition of the brine: (a) a trend that did not produce either Bt or Hbl during the metasomatic and anatectic stages, (b) that associated with intense amphibolization and biotitization during the metasomatic stage, and (c) a trend associated with the origin of melanocratic metasomatic Opx- Cpx- Bt- Hbl ± Pl selvages around newly formed charnockitoids, with the composition of the selvages close to the melanocratic veins produced in the peripheries of the charnockitization zone by the rapid redeposition of Mg, Fe, and Ca mobilized in the course of debasification. It follows that charnockitization proceeded according to the model of nonisochemical migmatization in an open system, a process driven first of all by the inflow of deep brines. This process differed strongly from simple closed system partial melting induced by an increase in temperature. [ABSTRACT FROM AUTHOR]