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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]

Rock magnetism and anisotropy of magnetic susceptibility (AMS) results are reported for the first time from the southernmost (Nagercoil) charnockites of the Southern Granulite Terrane (SGT), south India. Forty-eight oriented block samples from nine sites have been collected and analysed. The integrated results of isothermal remanent magnetization (IRM), hysteresis loops, day plot, and thermomagnetic curves indicate the presence of magnetite with pseudo-single domain (PSD) and multidomain (MD) magnetite particles dominating the studied samples. Rock magnetic investigations reveal that the ratio of remanence (Mrs/Ms) range from 0.04 to 0.53 and the coercivity ratio (Hcr/Hc) between 1.19 and 5.17. The magnetization saturation was at 250–300 mT, and the coercive force ranged from 24 to 41 mT in all the samples. The results of the thermomagnetic study reveal the Curie temperatures between 560 °C and 580 °C, indicating the presence of magnetite. The observed principal AMS axes show mainly two types of magnetic fabrics. The first one shows the maximum susceptibility axes (K1) horizontal to sub-horizontal, and the minimum susceptibility axes (K3) plot near the pole. The second fabric describes that the minimum susceptibility axes (K3) show intermediate to vertical and the maximum susceptibility axes (K1) plot near the horizontal to sub-horizontal. AMS studies reveal that Nagercoil charnockites formed during the late-stage metamorphic event, magma flow (magnetic grains aligned) was sub-horizontal to horizontal, and the magnetic fabric grains are from prolate to oblate in shape. [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]

The geological position, U-Pb monazite age, and composition of charnockites from the central part of the Anabar shield are presented. The charnockites are localized in a block of the Paleoproterozoic metasedimentary granulite-facies rocks, which include aluminous schists, sapphirine-bearing schists, and hypersthene plagiogneisses typical of the Archean Daldyn granulite complex. Moderate-K charnockites form small pockets and lenses in the hypersthene plagiogneisses, inherit their gneissic appearance, and are related with them by gradual transitions. High-K charnockites compose large vein bodies with cutting contacts. The charnockites differ in the structural position, but have similar age (1982 Ma) and are separated in time from metasedimentary rocks, whose age is estimated at 2.4–2.5 Ga. Hypersthene plagiogneisses correspond to igneous rocks of predominantly intermediate composition, while charnockites are granodiorites and granites. Compared to the plagiogneisses, charnockites are enriched in Th, light REE, Zr, Nb, Rb, and Ba. Hypersthene plagiogneisses and charnockites are characterized by a highly fractionated REE distribution pattern with an increase in (La/Yb)n and Eu minimum in charnockites. According to geochemical data and close Nd isotopic composition, high-K charnockites could have been generated during the high-temperature melting of hypersthene plagiogneisses. Charnockites (~2.0 Ga) are almost coeval to the Paleoproterozoic granulite metamorphism and emplacement of granite intrusion in collision zones. All these processes are caused by the accretion of Early Precambrian terranes into the structure of the Siberian craton. Charnockitization was superimposed on the hypersthene plagiogneisses, which have been already deformed in folds and migmatized, and on the metasedimentary sequence. This process completes the formation of the granulite complex of the Anabar Shield. [ABSTRACT FROM AUTHOR]

Abstract Analytical data of groundwater samples collected from weathered and deep fractured zones in the Precambrian charnockite aquifers in Kerala, India, have been studied to understand their hydrochemical variations and reasons thereof. Concentrations of the majority of the constituents analyzed were found to increase with increasing depth of aquifers, with the exception of nitrate. Studies indicate that various processes such as ion exchange reactions, carbonate weathering and silicate weathering are active in both the aquifers which influence the hydrochemical composition of groundwater in them. The prevailing groundwater quality in the aquifers is dependent on the dominance of each process in relation to others. Principal component analysis of the data suggests that contamination from anthropogenic sources has a major role in determining the hydrochemical characteristics of groundwater in the weathered zone unlike in the case of fractured aquifers where water–rock interaction is the major factor responsible. The study also indicates limited hydraulic connection between the weathered and fractured aquifers at the local scale.

The article reports on the geological, mineralogical, geochemical and isotope-geochemical studies of granitoids (charnockites) from the Tatarnikovsky massif located in the northern part of the Baikal uplift of the Siberian craton basement. The age of the studied granitoids is 1.85 Ga. Like other unmetamorphosed granitoids and associated volcanic, the granitoids dated 1.88–1.84 Ga are abundant in the southern area of the Siberian craton. These rocks are a part of the South Siberian post-collisional magmatic belt. The Tatarnikovsky granitoids form a series of small massifs confined to the Davan tectonic zone. However, unlike the rocks of the Davan zone, these granitoids have not been subjected to dynamometamorphism, mylonitization and metasomatism, and seem younger than the geologic structure of this zone. The formation of granitoids coincides in time with the youngest formations in the North Baikal volcanoplutonic belt (1.85–1.84 Ga). The Tatarnikovsky granitoids have two facies varieties – coarse-grained and medium-fine-grained porphyric, the transition being gradual. Considering the mineral composition of the granitoids, specifically the presence of orthopyroxene, these rocks can be classified as charnockites. The research results presented in this article are based on the study of charnockites in the Tatarnikovsky massif, the largest in the Tatarnikovsky complex. The chemical composition of the Tatarnikovsky coarse-grained granitoids corresponds to monzonite and syenite, and fine-grained porphyry granitoids are granosyenite. All the studied granitoids are close to alkaline and calc-alkaline, metaluminous (ASI=0.83–0.97), ferrous (FeO*/(FeO*+MgO)=0.86–0.89) granite, with high concentrations of Nb, Y, Zr, and Ba, and low concentrations of Sr. According to their geochemical characteristics, the Tatarnikovsky granitoids correspond to A-type granite. These rocks show negative values εNd(t)=–1.4…–3.5 and model age ТNdDM=2.4–2.5 Ga. The temperature estimated for the initial stages of crystallization of granitoid melts suggests that granitoids formed at high temperatures, 890–960°С (i.e. the zircon saturation temperature). The granitoid melts crystallized in hypabyssal conditions at the pressure of 2.2–2.9 kbar, as well as in conditions of low or moderate oxygen fugacity. According to the mineralogical, geochemical and isotope-geochemical data, the Tatarnikovsky charnockite could have resulted from melting of mafic rocks from the lower crust (gabbroid, and ferrodiorite) which are products of differentiation of the tholeiitic mantle magmas that had intruded into the base of the continental crust. Taking into account the high concentrations of Ba and the positive anomalies of Eu in the distribution spectra of rare-earth elements (REE) of the coarse-grained granitoids, it can be suggested that these granitoids are the products of partial melting of the crustalmafic source. The fine-grained porphyry granitoids with higher silica contents and lower Ba and Zr contents than those in the coarse-grained granitoids, as well as the negative anomalies of Eu in the REE distribution spectra, are the products of fractional crystallization of the granitoid melt. With regard to formation of the unified structure of the Siberian craton, the geodynamic setting for formation of the Tatarnikovsky charnockite is considered as postcollisional extension due to the fact that these rocks belong to the South Siberian post-collisional magmatic belt. However, on a more local scale of the Baikal uplift of the Siberian craton basement, we suggest that the intercontinental rifting setting was in place during the intrusion of the Tatarnikovsky granitoids, the rocks of the North Baikal volcanoplutonic belt, the granitoids of the Primorsky and Achadsky complexes that cross the rocks of the Akitkan fold belt, collision events in which ceased 1.98–1.97 Ga ago.

Analytical data of groundwater samples collected from weathered and deep fractured zones in the Precambrian charnockite aquifers in Kerala, India, have been studied to understand their hydrochemical variations and reasons thereof. Concentrations of the majority of the constituents analyzed were found to increase with increasing depth of aquifers, with the exception of nitrate. Studies indicate that various processes such as ion exchange reactions, carbonate weathering and silicate weathering are active in both the aquifers which influence the hydrochemical composition of groundwater in them. The prevailing groundwater quality in the aquifers is dependent on the dominance of each process in relation to others. Principal component analysis of the data suggests that contamination from anthropogenic sources has a major role in determining the hydrochemical characteristics of groundwater in the weathered zone unlike in the case of fractured aquifers where water–rock interaction is the major factor responsible. The study also indicates limited hydraulic connection between the weathered and fractured aquifers at the local scale. [ABSTRACT FROM AUTHOR]

[Display omitted] • This study reports the first identification of ca. 2.5 Ga and ca. 2.1 Ga charnockites in Zhuozi. • The ca. 2.5 Ga and ca. 2.1 Ga charnockites are homologous (Mesoarchean to Neoarchean TTGs and related intermediate-mafic rocks). • The ca. 2.5 Ga and ca. 2.1 Ga charnockites were formed at relatively high-pressure (subduction-collision) and low-pressure (intracontinental rifting) conditions, respectively. • The precursor of the Khondalite Belt may experience a subduction-collision process at ca. 2.6–2.45 Ga, followed by a long-term intracontinental rifting at ca. 2.45–2.0 Ga before the final subduction-collision at ca. 2.0–1.9 Ga. The Khondalite Belt (KB), a Paleoproterozoic collisional orogen in the North China Craton (NCC), lacks a well-established pre-collisional tectonic evolution due to the paucity of late Neoarchean to middle Paleoproterozoic magmatic rocks. This study focuses on the poorly dated charnockites in the Zhuozi area, the eastern segment of the KB. Through an integrated field investigation, petrography, SHRIMP and LA-ICP-MS zircon U-Pb dating, zircon Lu-Hf isotopic analysis, and whole-rock geochemistry, this study determines the formation ages, petrogenesis, and tectonic settings of the targeted charnockites, and further constrains the Neoarchean to Paleoproterozoic tectonic evolution of the KB. The charnockites crystallized at ca. 2.5 Ga and ca. 2.1 Ga and were metamorphosed at ca. 1.9 Ga. The ca. 2.5 Ga charnockites are magnesian and exhibit high Ba-Sr affinity, with SiO 2 , MgO contents and Mg# values of 66.20–71.43 wt%, 1.10–2.34 wt% and 34–49, respectively. Most samples are enriched in light rare earth elements (LREEs), Ba, Sr (Sr/Y = 11.79–34.94), and Eu (Eu/Eu* = 0.56–1.67), but depleted in heavy rare earth elements (HREEs, La N /Yb N = 10.14–42.81), Th, Nb, Ta, P, and Ti. The magmatic zircons have ε Hf (t) ranging from + 2.8 to + 5.8 and Hf model ages (T DM2) of 2711–2822 Ma. In comparison, the ca. 2.1 Ga charnockites are ferroan and exhibit A-type granite affinity, with higher SiO 2 (73.23–77.73 wt%) but lower MgO (0.03–0.27 wt%) contents and Mg# values (2–13). Most samples are enriched in LREEs, Rb, Zr, and Hf, but depleted in HREEs (La N /Yb N = 12.72–23.41), Nb, Ta, Sr (Sr/Y = 1.51–5.58), P, Ti, and Eu (Eu/Eu* = 0.24–1.11). The magmatic zircons have ε Hf (t) ranging from −4.0 to +0.8 and T DM2 of 2749–2916 Ma. The available data suggest that the two episodes of charnockites are homologous (Mesoarchean-Neoarchean TTGs and related intermediate-mafic rocks), with ca. 2.5 Ga and ca. 2.1 Ga charnockites formed at relatively high-pressure (subduction-collision) and low-pressure (intracontinental rifting) conditions, respectively. Combined with previous studies, the precursor of the KB may experience a subduction-collision process at ca. 2.6–2.45 Ga, followed by long-term intracontinental rifting events at ca. 2.45–2.0 Ga prior to the final subduction-collision at ca. 2.0–1.9 Ga. [ABSTRACT FROM AUTHOR]

The Yinshan Block, part of the Neoarchaean basement of the Western Block of the North China Craton, is composed of granite–greenstone and granulite–charnockite complexes. We report research on a suite of charnockites from the granulite–charnockite complex and characterize their geochemistry, zircon U–Pb geochronology, and Hf isotopic composition. The charnockites can be divided into intermediate (SiO2 = 59–63 wt.%) and silicic (SiO2 = 69–71 wt.%) groups. U–Pb zircon data yield protolith formation ages of 2524 ± 4 Ma, 2533 ± 15 Ma, followed by metamorphism at 2498 ± 3 Ma, 2490 ± 11 Ma, respectively, for these groups. Although the intermediate charnockites are characterized by higher Al2O3, TiO2, Fe2O3T, MnO, MgO, CaO, P2O5, K2O, Sr, and ΣREE content than the silicic charnockites, the ages and Hf isotopic composition of zircons and REE patterns of both intermediate and silicic charnockites are remarkably consistent, which indicates that they are genetically related. These charnockites are predominantly metaluminous to slightly peraluminous, calc-alkalic to calcic, and magnesian – characteristics generally related to a subduction setting. High-Sr + Ba granites with low K2O/Na2O characteristics, shown by these charnockites, imply a mixture of mafic and felsic magmas generated from an enriched mantle + lower crust. High MgO, Ni, Cr and Mg#, low K2O/Na2O, and metaluminous to slightly peraluminous natures imply that the source rocks most likely were amphibolites. Coeval calc-alkaline magmatism and high-T granulite-facies metamorphism under low-H2O activity in the area lead us to propose a model involving mid-ocean ridge subduction within a Neoarchaean convergent margin. The arc-related rocks accreted along the continent margin, and became a barrier when the lithospheric mantle ascended through the slab window. Melt derived from the decompressing mantle mixed with melt derived from the overlying, juvenile lower crust melt, which was warmed and metamorphosed by the ascending lithospheric mantle. [ABSTRACT FROM AUTHOR]

The Serra da Providência suite (SPS) is constituted of quartz mangerite-charnockite-rapakivi granite and coeval mafic rocks, intruded during the 1.60–1.53 Ga interval into Paleoproterozoic metamorphic basement (Jamari Complex) in the Juruena-Rondônia geochronologic province, SW Amazonian Craton. In this region the Serra da Providência suite consists of two batholiths and several small plutons represented by syeno-monzogranites and igneous quartz mangerite and charnockites. The Serra da Providência granites are ferroan, calc-alkalic to alkali-calcic and characterized by high Na2O + K2O, Rb, Zr, Y, Nb, Ta, Ce, Zn, Ga, and REE (except for Eu), moderate Ba, and low Sr, MgO, and CaO. Ga/Al, Y/Nb, FeOT/(FeOT + MgO) and K2O/Na2O ratios are high and Sr/Ba and Rb/Ba are low and are geochemically similar to typical A2-subtype granites. The SPS charnockites and quartz mangerites display values of FeOT, MgO, CaO, Ba, Rb, Sr, Nb/Ta and Zr/Hf similar to the SPS A-type granites. The occurrence of magnetite as an accessory phase and the high FeOT/(FeOT + MgO) in granites, charnockites and quartz mangerites suggest crystallization from a relatively oxidized magma and also explain the occurrence of titanite as a primary phase in these granites, similar to those reported in several localities of the Amazonian Craton. The parental magma of the mafic rocks of the SPS probably had mainly enriched sources and resulted from melting of heterogeneous mantle reservoirs with coherent chemical characteristics. Trace elements data indicate subduction-modified mantle sources for the mafic rocks that are in agreement with the post-collisional character of this magmatism. A large set of whole-rock Sm–Nd isotope data (Bettencourt et al., 1999; Scandolara, 2006; Santos et al., 2008 and this work) demonstrate that granites, charnockites and quartz mangerites of the study area are the product of magmas derived from interaction between enriched mantle derived magmas (in very subordinate proportions) and recycled crust in larger proportion. The source region is dominated by Paleoproterozoic material, but several samples yield Archaean model ages that are the first evidence for such ancient source materials in the SW Amazonian Craton. The Serra da Providência suite was emplaced during the post-collisional stage of the Juruena-Jamari arc and Madeirinha orogeny (Scandolara et al., 2011), and post-dates the collision between the Tapajós (Tapajós-Parima geochronological province, Pará, Brazil) and Bolívia (palaeocontinent which precedes Sunsás geochronological province) blocks. Its geochemical and structural features are coincident with those recognized in post-collisional granitoids. Geochemical data suggest that complex processes which involved crustal melting, fractional crystallization, magma mixing and, in some extent, crustal assimilation were responsible for the magmatism of the Serra da Providência suite. The magmas that constitute the Serra da Providência suite resulted from varying degrees of partial melting of a compositionally heterogeneous source. The nature of the source and the degree of melting exerted a significant control over compositional variation in some of the parental magmas which were also affected by subsequent fractional crystallization and mingling processes. Internal variations in composition observed in several bodies can be the result of incremental amalgamation of different magma pulses that varied mainly in the degree of partial melting. [ABSTRACT FROM AUTHOR]

Abstract: The Venda Nova Pluton (VNP) is a zoned ring structure emplaced in the southern portion of the Neoproterozoic Araçuai Belt, in Espírito Santo, Brazil. It is a slightly westward tilted cylinder-like intrusion, with an almost circular horizontal section. In the center of this structure, an off-centered gabbro-noritic core, surrounded by syeno-monzonitic rocks, intrudes an outer ring of charnockites and norite. These envelop the syeno-monzonitic and gabbro-noritic center, as a narrow discontinuous belt. While, in the core intrusion, mingling and mixing processes are widespread and well documented in the literature, in the outer ring, the norite and charnockite layers show predominantly homogeneous and isotropic internal structures. Nevertheless, smaller interaction zones between charnockites and norite denote a comparatively more restricted mingling process. The norite is a fine-grained rock with hypidiomorphic granular to intergranular texture. The charnockites are medium-grained and made up of: (a) orthopyroxene-tonalite, (b) orthopyroxene-quartz-diorite, and (c) orthopyroxene-granodiorite with hypidiomorphic granular to porphyritic textures. In all lithotypes both ortho- and clinopyroxene are replaced by hornblende and biotite. Two contrasting compositional sequences have been recognized, based on whole rock geochemistry: (1) a basic, with tholeiitic affinities (norite) and, (2) an intermediate, medium-K calc-alkaline, comprising the charnockites. Estimated crystallization temperatures, which have been calculated from micro-probe analysis of pyroxenes, range from 915 ± 25 °C to 960 ± 50 °C. Re-equilibration temperature (ilmenite-magnetite calibration) is around 600 ± 50 °C. This indicates oxygen fugacities four order of magnitude below the FMQ-buffer and a reduced environment. Coeval pressure conditions estimated from the Al-content in hornblende range from 5.5 ± 0.6kbar. Data obtained for the norite point toward an evolution from the partial melting of an anhydrous tholeiitic mantle magma. The charnockites may correspond to the differentiation of a calc-alkaline parental magma. The later could be the hybrid product from the contamination and mixing between the anhydrous tholeiitic magma with other deeper crustal sources. Further the magmatic system evolved through fractionation of orthopyroxene, clinopyroxene, plagioclase and ilmenite. Our results support the hypothesis for the evolution of the Venda Nova Pluton through a mantle-crust delamination process probably related to the collapse of the Araçuai orogeny. [Copyright &y& Elsevier]

Abstract: We present a detailed field and petrological study of charnockites and ultra-high temperature (UHT) granulites from the Gruf Complex, eastern Central Alps. Charnockites occur as up to 0.5km wide and 8km long, internally boudinaged, opx-bearing sheet-like bodies within the regionally dominant migmatitic biotite-orthogneisses. Granulites occur as garnet–orthopyroxene–biotite–alkali feldspar-bearing schlieren (±sapphirine, sillimanite, cordierite, corundum, spinel, plagioclase, and quartz) within charnockites and as residual enclaves both in the charnockites and the migmatitic orthogneisses. Thermobarometric calculations, P–T pseudosections and orthopyroxene Al content, show that both charnockites and granulites equilibrated at metamorphic peak conditions of T =920–940°C and P =8.5–9.5kbar. Peak assemblages were subsequently overprinted by intergrowth, symplectite and corona textures involving orthopyroxene, sapphirine, cordierite and spinel at T =720–740°C and P =7–7.5kbar. We suggest that granulites and charnockites are lower crustal relicts preserved in the migmatitic orthogneisses. Garnet diffusion modelling shows that metamorphic garnet–opx±sapphirine±sillimanite peak assemblages and post-peak reaction textures always involving cordierite developed during two separate metamorphic cycles. Peak assemblages reflect UHT metamorphism related to post-Varican Permian extension, but post-peak coronae and symplectites formed during the mid-Tertiary, upper amphibolite facies, Alpine regional metamorphism. Fluid-absent partial melting of pelitic and psammitic sediments during the Permian UHT event lead to the formation of charnockitic magmas and granulitic residues. Intense melt loss and thorough dehydration of the granulites (although retaining biotite) favoured the partial preservation of peak mineral assemblages during Alpine metamorphism. [Copyright &y& Elsevier]

Rapakivi granites characteristic practically of all old platforms are greatly variable in age and irregularly distributed over the globe. Four types of magmatic associations, which include rapakivi granites, are represented by anorthosite-mangerite-charnockite-rapakivi granite, anorthosite-mangerite-rapakivi-peralkaline granite, gabbro-rapakivi granite-foidite, and rapakivi granite-shoshonite rock series. Granitoids of these associations used to be divided into the following three groups: (1) classical rapakivi granites from magmatic associations of the first three types, which correspond to subalkaline high-K and high-Fe reduced A2-type granites exemplifying the plumasitic trend of evolution; (2) peralkaline granites of the second magmatic association representing the highly differentiated A1-type reduced granites of Na-series, which are extremely enriched in incompatible elements and show the agpaitic trend of evolution; and (3) subalkaline oxidized granites of the fourth magmatic association ranging in composition from potassic A2-type granites to S-granites. Magmatic complexes including rapakivi granites originated during the geochronological interval that spanned three supercontinental cycles 2.7−1.8, 1.8−1.0 and 1.0−0.55 Ga ago. The onset and end of each cycle constrained the assembly periods of supercontinents and the formation epochs of predominantly anorthosite-charnockite complexes of the anorthosite-mangerite-charnockite-rapakivi granite magmatic association. Peak of the respective magmatism at the time of Grenvillian Orogeny signified the transition from the tectonics of small lithospheric plates to the subsequent plate tectonics of the current type. The outburst of rapakivi granite magmatism was typical of the second cycle exclusively. The anorthosite-mangerite-charnockite-rapakivi granite magmatic series associated with this magmatism originated in back-arc settings, if we consider the latter in a broad sense as corresponding to the rear parts of peripheral orogens whose evolution lasted from ∼1.9 to 1.0 Ga. Magmatism of this kind was most active 1.8−1.3 Ga ago and represented the distal effect of subduction or collisional events along the convergent boundaries of lithospheric plates. An important factor that favored the emplacement of rapakivi granites and anorthosites in a huge volume was the thermal and rheologic state of the lithosphere inherited from antedating orogenic events, first of all from the event ∼1.9 Ga ago, which was unique in terms of heat capacity transferred into the lithosphere. Anorthosite-mangerite-rapakivi granite-peralkaline granite magmatism is connected with activity of the mantle plums only. Degradation of the rapakivi granite magmatism toward the terminal Proterozoic was controlled by the general cooling of the Earth in the course of the steady dissipation of its endogenic energy, as these processes became accelerated since the Late Riphean [ABSTRACT FROM AUTHOR]

Abstract: The presence of 1.52–1.50 Ga charnockites from the anorthosite–mangerite–charnockite–granite (AMCG) Mazury complex in southern Lithuania and NE Poland, in the western East European Craton (EEC) is revealed by secondary ion mass-spectrometry (SIMS) and EPMA geochronology. Early 1.85–1.82 Ga charnockites are related to major orogeny in the region whereas the newly studied charnockites intrude the already consolidated crust. The 1.52–1.50 Ga charnockite magmatism (SIMS data on zircon) was followed by high-grade metamorphism (EPMA data on monazite), which strongly affected the surrounding rocks. The 1.85–1.81 Ga zircon cores in Lazdijai and 1.81 Ga monazite domains in the Lanowicze charnockites represent the protolith age of a volcanic island arc. The 1.52–1.50 Ga charnockite magmatism and metamorphism are likely related to the distal, Danopolonian, orogeny further to the west, at the margin of Baltica. The c.1.52–1.50 Ga AMCG magmatism and metamorphism in the western EEC as well as the paired accretionary-rapakivi suites in Amazonia, may be the inboard manifestations of the same early Mesoproterozoic orogeny associated with the juxtaposition of Amazonia and Baltica during the amalgamation of the supercontinent Columbia. [Copyright &y& Elsevier]

Laboratory data of velocity (VP and VS) and quality factor (QP and QS) of a large number of charnockites and associated granitoid gneisses of Kudankulam are reported in this article. The results show linear relationships between density and velocity, and density and Q values of both the rocks. Charnockites show higher velocities and a wide range of Poisson's ratio and Q values compared to granitoid gneisses. The laboratory velocity data when extrapolated to highpressure conditions are comparable to the published field velocity data from deep seismic sounding studies, which were carried out in the southern part of the Southern Granulite Terrain. [ABSTRACT FROM AUTHOR]

Abstract: The Nagercoil granulites form the most southerly basement rocks in peninsular India and have considerable significance in correlating the now-dispersed continents that made-up Gondwana. In this study, we date monazites and zircons in granulite-facies rocks from the Nagercoil region using the electron microprobe technique and identify a broad range of zircon ages between 2800 and 590Ma from undisputed metasedimentary gneisses. A similar range of zircon apparent ages (2500–500Ma) was obtained from massive charnockites. The majority of zircons from all analysed rocks yielded Palaeoproterozoic and early Mesoproterozoic ages between 2200 and 1530Ma. These data suggest that either: (1) the charnockite protoliths were metasedimentary; (2) were emplaced in the Neoproterozoic and contain many zircon xenocrysts; or (3) were intruded in the Palaeoproterozoic with many zircon experiencing variable Pb-loss during Neoproterozoic metamorphism. All analysed monazites yielded late Neoproterozoic/Early Palaeozoic Th–U–Pb ages between 605 and 438Ma with an age spectra maxima at 565Ma. These are interpreted to have grown during high-grade metamorphism related to the final amalgamation of Gondwana. Zircons from undisputed metasedimentary rocks preserve age profiles that share a number of similarities with the Itremo and Molo Groups in central Madagascar and may have been derived from similar-aged source rocks. [Copyright &y& Elsevier]

Abstract: The Truong Son Belt forms the eastern rim of the Indochina Block in Southeast Asia. The age of the metamorphism, mainly along NW–SE mylonitic shear zones that affects this belt, has been formerly determined at about 240–250Ma. This age corresponds to the Indosinian tectonometamorphic episode. The Kon Tum Massif, situated to the south of this belt, comprises high-temperature rocks, the Kan Nack Complex, including charnockites and granulites. The main charnockitic outcrops, restricted to the Song Ba Valley, establish the intrusive nature of these magmatic rocks within granulite facies material. Basic charnockitic rocks are mainly quartz enderbites to norites and hornblende–pyroxene granulite facies rocks. The 40Ar–39Ar age of intrusion-cooling of charnockitic magmas is determined from primary magmatic biotites at about 245Ma. In the east of the Kan Nack Complex some granulite facies rocks exhibit relicts of primary granulite facies parageneses, whereas others show evidence of overprinting by a retrogressive low-grade metamorphism. Ar–Ar dating confirm this evolution, giving ages of 400Ma for primary relict granulite facies phases and 260–270Ma from the most retrogressed samples establishing the youngest limit for the granulite facies metamorphism. Granulites intruded by charnockites in the Song Ba Valley yield ages of about 250Ma, equivalent to the ages of the charnockites, and have evidently been completely reset by these high temperature intrusions. Therefore, the Kan Nack Complex of the Kon Tum Massif is not an independent unit with respect to the Indosinian orogen, but represents the deep-crustal part of this belt. [Copyright &y& Elsevier]

Sr and Nd isotopic data from the anorthosite-mangerite-charnockite (AMC) suite of the Late-Sveconorwegian (ca. 0.93 Ga) Rogaland anorthosite province of SW Norway are discussed. The study focuses on new data obtained from three distinct rock occurrences: (1) primitive (=MgO-rich and K2O-poor) jotunites that represent the parental magmas of leuconorite and mafic plutons (87Sr/86Sr0.93 Ga=ca. 0.704–0.707, &epsiv;Nd(0.93 Ga)=+3.6 down to +1.2); (2) evolved jotunites that differentiated from the primitive jotunites and constitute the starting components of dyke-scale fractionation trends (87Sr/86Sr0.93 Ga=ca. 0.705–0.713, &epsiv;Nd(0.93 Ga)=+0.4 down to −2.0); and (3) felsic plutons (87Sr/86Sr0.93 Ga=ca. 0.707–0.723, &epsiv;Nd(0.93 Ga)=+1.4 down to −1.7). A comparison of the Sr and Nd isotopic compositions with available geochemical data (major and trace elements) is also made. Fractionation of the primitive to the evolved jotunites, below the intrusion level of the anorthosite province, is shown to have involved crustal contamination. A case of fractional crystallization and simultaneous contamination/assimilation is substantiated in the felsic cap of a layered intrusion (the Bjerkreim-Sokndal intrusion). It is further proposed that the Sr and Nd isotopic compositions of the various felsic occurrences result from fractional crystallization of primitive jotunitic melts, with or without contamination/assimilation; this strengthens the possibility for large volumes of silica-rich magmas to have been produced by fractionation, through evolved jotunites, of primitive jotunites. The entire range in Sr and Nd isotopic compositions of the Rogaland anorthosite province is interpreted as reflecting a mixing of crustal contaminants, having variable 87Sr/86Sr0.93 Ga ratios and (negative) &epsiv;Nd(0.93 Ga) values, with a more isotopically primitive source. The crustal end members of that mixing array are represented by moderately to strongly LILE-enriched high-grade gneisses from the Pre-Sveconorwegian basement of southernmost Norway, that have a crustal history extending back to 1.5–1.9 Ga in the surroundings of the anorthosite province. The primitive end member is either an unusual LREE-depleted and Rb-enriched component, possibly corresponding to an originally depleted source subsequently modified by metasomatic fluids, or a more classical depleted component; it corresponds to a gabbronoritic rock of the deep crust, as shown by recent experimental data, with a quite short crustal residence time (<0.4–0.2 Ga). If that mafic end member is the lower granulitic crust itself, this would imply the presence in the deep continental crust of southwesternmost Norway of a crustal material strongly different from the 1.7- to 1.9-Gyr-old, moderately LILE-enriched component that is supposed to constitute the largest volume of the present deep continental crust in southern Norway. [Copyright &y& Elsevier]

Detailed geochemical and petrographic analyses of a lower crustal bimodal sequence near Perdo˜es/Minas Gerais contribute to the reconstruction of the Archean–Proterozoic evolution of the southern Sa˜o Francisco craton. Trace element patterns of enderbites with tonalitic/trondhjemitic compositions (felsic members) indicate an origin by a two-phase partial melting process from a mantle source at depths, where garnet exists as a residual phase. Gabbroic rocks and mafic–ultramafic cumulates (mafic members) occur as lens-shaped elongated bodies exposed in the felsic complex. The gabbroic rocks are tholeiitic in composition, with rare earth element (REE) patterns indicating generation through relatively high percentages of partial melting from mantle material. Trace element ratios indicate a slightly depleted mantle source for the gabbroic rocks. Charnockites, which occur in the same area, are granitic/granodioritic in composition. The REE patterns indicate magma generation by intracrustal partial melting of tonalitic/trondhjemitic material, which must have occurred at depths of less than 40 km, where plagioclase is a stable residual phase.The whole-rock sequence shows a uniform PT path. The rocks were generated in granulite facies conditions. During exhumation, they underwent a strong retrograde amphibolite facies metamorphism, followed by a weak greenschist facies overprint.The granitic rocks of Perdo˜es represent a rock association that is characteristic of the transition between Archean and Proterozoic times, during which the continental crust evolved from Archean tonalitetrondhjemitegranodiorite (TTG) suites towards an increased lithologic diversity in PostArchean time, with greater amounts of more evolved and more potassium-rich granitoids (granodiorite/granite/monzogranite (GGM) suites). [Copyright &y& Elsevier]

The present study evaluates the enrichment and distribution of radioelements along the eastern coast of India. India possesses the second largest reserve of thorium bearing monazite in the world, in terms of heavy minerals present primarily along its long coastline. Radioelement estimation of about 30 km long beach area along the eastern coast of India is reported and implications discussed. A total number of 822 data points were studied using a portable Geiger Muller counter, to estimate the variation of dose rates, due to the ambient radionuclides along two different trends. One was parallel (northeast-southwest) and the second one perpendicular to the coastline. Pre-selected samples from in-situ radiometric surveys on the heavy mineral placers were studied further, for quantitative estimation of the abundance of radioactive elements primarily uranium and thorium, using a High Purity Germanium detector. Radioelement concentration assessment of core samples (depth ~2 m), were studied from two different beaches. Radiological parameters like radium equivalent, annual effective doserate and absorbed dose rate has been calculated based on the 238U, 232Th and 40K concentrations. Heavy mineral placers along the shoreline indicate a very high thorium (avg - 2990.22 Bq kg−1) which is due to the extensive distribution indicative of monazite. The coastal area also exhibits relatively low uranium (avg - 319.1 Bq kg−1). Based on its high thorium concentration, the area can be considered as a high natural background radiation area. Based on the concentrations of uranium and thorium, the weathering conditions and depositional environment prevalent along the beach areas have been discussed. [Display omitted] • Dose rate variation along a 30 km stretch of eastern coastal beach areas of India is reported and presented in Isorad map. • Activity concentration of 238U, 232Th and 40K measured by gamma spectrometry is estimated and presented in Isorad map. • Radiation parameters are calculated and discussions based on their possible relation with the radio-elements are provided. • Radioelement concentration of charnockite, khondalite and granite from EGMB is estimated and possible provenance discussed. • Variation of the activity concentration of 238U, 232Th and 40K of the subsurface has been estimated from two shallow cores. • Depositional environment based on the 238U, 232Th and 40K concentration of the beach sands have been investigated. [ABSTRACT FROM AUTHOR]

• Early Archean lithospheric block survived in the Volgo-Uralia, East European Craton. • In the southeastern part of the Volga-Uralia segment granitoids of the Kolyvan complex carry information on the Meso- and Palaeoarchaean history of this segment of the continental crust. • The age of the granitoid protoliths based on U-Pb isotope dating of magmatic zircon cores is ca 3150 Ma. • Isotope data (ТNd DM = 3.46 Ga, ТHf DM = 3.32–3.53 Ga) indicate that the Mesoarchaean granitoids of the Kolyvan complex were formed during melting of the Palaeoarchaean metasomatised lithospheric mantle and continental crust sources. • Structural and metamorphic modification of the granitoids occurred 1.95 Ga ago under conditions of T = 700–750 °C and P = 4–5 kbar. The Volgo-Uralia segment, which constitutes one fourth of the East European Craton, is covered by sedimentary deposits. From geophysical studies and examination of thousands of drillcores, Volgo-Uralia has been recognised as a vast high-grade terrain with a complex crustal history extending from the Palaeoarchaean to the Palaeoproterozoic. Our recent studies are focused on the search for the oldest crust formation event by extracting whole rock Sm-Nd and zircon U-Th-Pb and Lu-Hf isotope information from samples recovered by drilling in southern Volgo-Uralia. Particular attention is devoted to the Kolyvan charnockitoid rock suite, which makes up several large areas of gneisses and granitoids of enderbite, charnockite and tonalite composition. The zircon from the granitoids show complex internal structures and consists of large magmatic cores with oscillatory zoning, surrounded by CL black-and-bright bands of metamorphic rims. The crystallisation age of the cores is defined as 3140 ± 7 Ma (SHRIMP) and 3127 ± 46 Ma (LA-ICPMS), while the CL-bright rims are dated at 1950 ± 25 Ma (LA-ICPMS). The ingressive recrystallisation of primary magmatic zircon correlates with depletion in REE, which is observed in each studied core-rim pair. No differences in O-isotopic compositions have been detected between the cores and the rims. δO18 values with an average of 5.8 ± 0.3‰ (1SD) implying that no supracrustal rocks were involved in the source of the Kolyvan melts. The Hf-isotope compositions of magmatic cores (−3 to −9 ε Hf T) and metamorphic rims (−14 to −28 ε Hf T), and their similar crustal model ages from 3.42 to 3.86 Ga indicate Eo- to Palaeoarchaean crustal sources for the charnockitic magmas. Sm-Nd model ages of ca 3.46 Ga for the Kolyvan rocks are consistent with the zircon Hf-isotope data and indicate a long crustal prehistory of a source of the Mesoarchaean magmas. We conclude that the Mesoarchaean Kolyvan suite rocks was formed by reworking of Eo- to Palaeoarchaean lithosphere, which probably had been widespread throughout Volgo-Uralia. The obtained geochemical and isotope data can be reconciled in a model of deep mantle-plume activity at 3.1 Ga causing mantle underplating, extension of the Palaeoarchaean crust and high-T magmatism. [ABSTRACT FROM AUTHOR]