Biotite Granitoids Research Articles

Deciphering groundwater pollution in the Lower Anayari Catchment: insights from using δ2H, δ18O, PMF, and APCS-MLR receptor model.

This research provides a comprehensive analysis of groundwater pollution in the Lower Anayari Catchment (LAC) through δ2H and δ18O isotopic analysis, along with positive matrix factorization (PMF) and PCS-MLR receptor models. Forty groundwater samples were collected from hand-dug wells and equipped boreholes across the LAC. Flame photometry for Na+ and K+, complexometric titration for Ca2+, ion chromatography for Cl-, F-, NO3-, SO42-, and PO43-, and atomic absorption spectrometry for Mg2+, Fe, Pb, Cd, As, and Ni were analytical techniques/instruments employed. In regard to cations, Na+ has the highest average concentration of 63.0 mg/L, while Mg2+ has the lowest at 2.58 mg/L. Concerning the anions and nutrients, Cl- has the highest mean concentration of 18.7 mg/L, and Fl- has the lowest at 0.50 mg/L. Metalloids were detected in trace amount with Fe displaying the highest mean concentration of 0.077 mg/L whereas Cd and As recorded lowest (0.001 mg/L). The average values for groundwater δ18O and δ2H were - 3.64‰ and - 20.7‰, respectively; the average values for rainwater isotopic composition were - 3.41‰ for δ18O and - 17.4‰ for δ2H. It is believed that natural geological features, particularly biotite granitoid and volcanic flow/subvolcanic rocks from the Birimian Supergroup, significantly influence groundwater mineralisation. Additionally, the impact of anthropogenic activities on water quality, with urban development and agricultural practices, may be attributed to increasing levels of certain contaminants such as Fe, Ni, NO3-, and PO43-. This research contributes to the broader field of hydrological study and provides practical implications for managing and conserving water resources in similar contexts. The innovative combination of isotopic and statistical analyses sets a new standard for future studies in groundwater quality assessment, emphasising the need for comprehensive approaches that consider both geological characteristics and human impacts for sustainable water resource management.

The Neoproterozoic Agudos Grandes granitic batholith, SE Brazil: Inferences on source areas from elemental and Sr-Nd-Pb isotope geochemistry

I-type, K-rich calc-alkaline hornblende-biotite granitoids (HKCA) suites are typical of both pre- and post-collisional tectonic settings, and their petrogenesis is challenging, since they are dominated by rocks with intermediate composition (e.g., 60–68 wt% SiO2; 10–20 vol % mafic mineral) that are neither typical products of crust nor of mantle partial melting. These granitoids are particularly abundant as the main components of Ediacaran batholiths intruding the Neoproterozoic Ribeira Fold Belt in SE Brazil, e.g. constituting ∼70% of the exposition of the Agudos Grandes Batholith, where they were emplaced at 620-610 Ma, as indicated by U–Pb zircon dating from our previous work and new data presented here. Two types of coeval granitoids comprise an expanded suite of mafic to felsic titanite and allanite-rich biotite granitoids (Itapevi-type) and a single occurrence of biotite-muscovite leucogranite (Turvo-type). Elemental and isotope whole-rock data indicate that different sources were involved in the genesis of their parent magmas, with crust with old residence predominating for the HKCA and Itapevi types, as indicated by very negative (−16 to −20) εNd(t) and low initial 206Pb/204Pb (16.4–16.7), and younger metasedimentary rocks as the source of the Turvo leucogranite (εNd(t) (∼-14); initial 87Sr/86Sr = 0.717). This “syn-orogenic” magmatism was immediately followed, as demonstrated by field and geochronological data, by ∼605-600 Ma circumscribed plutons dominated by more fractionated (±muscovite)-biotite granites that derive from melts generated in the middle crust from sources that are slightly younger than those of the HKCA granitoids, as indicated by slightly less negative (εNd(t) (similar to those of the Turvo leucogranite) and higher 206Pb/204Pb (17.1–17.3). After a ∼15 Myr lull, A-type plutons were emplaced in a post-orogenic setting, probably from mantle and crust sources. The syn-to late-orogenic (620-600 Ma) magmatism of the Agudos Grandes was produced by a thermal anomaly, probably associated with a continental arc. A combination of elemental and isotope geochemistry and inherited zircon data suggests that crustal melting was probably induced by ascension of mantle-derived basic magmas, and initiated in hot zones at the lower portions of a previously thickened crust, formed by old Paleoproterozoic to Archean material (the basement of the Apiaí-São Roque Domain of the Ribeira Belt?), and progressed to the middle portions of the crust, where it provoked partial melting of a different crustal domain with younger age and crustal residence (Embu Complex orthogneisses and metasediments).

Petrography and geochemistry of the Sanaga river sediments, central Cameroon: Constraints on weathering, provenance, and tectonic setting

The Sanaga River (SR), central Cameroon, flows predominantly over metasediments (2.1 Ga), Paleoproterozoic amphibolites and orthogneisses, granitoids from the Adamawa-Yade batholith (AYB), sedimentary clastic rocks of Cretaceous age, and Cenozoic rocks of the Cameroon Volcanic Line. To infer the origin of alluviums and tectonic setting of source rocks, the texture, heavy mineral, major, trace, and rare earth element concentrations of stream sediments were investigated. The very high SiO2/Al2O3 ratios and the ZTR (Zircon-Tourmaline-Rutile) index of SR sediments suggested a high maturity. This interpretation was additionally confirmed by the Th/Sc vs Zr/Sc plot. The Plagioclase- and Chemical Index of Alteration (PIA and CIA) values, the (A-K)-C-N and A–CN–K triangular plots show an intense degree of weathering in the source area. Numerous discrimination diagrams, based on trace elements, indicate that sediments were derived from felsic source rocks mainly granodiorites, granites, and biotite granitoids exposed in the SR watershed. This shows that the metamorphic and volcanic rocks do not significantly contribute to the stream sediments. Paleotectonic investigations using multi-element discrimination plots indicate passive and rift settings for the SR drainage basin. Rift settings were also inferred from downstream sediments of the SR. They are probably related to Proterozoic events including opening of large oceanic basins. The passive and rifted margin settings are supported by the occurrence of rare ophiolitic rocks, which indicate an old oceanic crust.

Petrogenetic links between rare metal-bearing pegmatites and TTG gneisses in the West African Craton: The Mangodara district of SW Burkina Faso

We describe the geological context of rare metal-bearing pegmatites from the Mangodara district (South-West Burkina Faso, Paleoproterozoic West African Craton) and discuss their petrogenesis and links with the host rocks. The Mangodara district exposes a gneiss-granitoid complex structured in a regional-scale dome, mantled by granodioritic gneiss enclosing rafts of amphibolite, micaschist and paragneiss, and cored by tonalitic to trondhjemitic gneisses. These gneisses enclose granitoid plutons, and four populations of rare metal-bearing pegmatites: titanite-allanite-, apatite-zircon-, garnet-columbite (Li, Nb) and garnet-REE (Ti, Y, HREE)-bearing varieties.Rafts of migmatitic amphibolite, micaschist and paragneiss are chemically equivalent to nearby Birimian greenstone belts. An origin of the gneiss-granitoid complex by partial melting is suggested by diffuse contacts of rafts with the gneisses as well as the presence of garnet-bearing or hornblende-bearing leucosome in paragneiss and in amphibolites, respectively. Textural continuity between pegmatites and granitic veins concordant to the foliation of the gneisses point to syntectonic segregation of the pegmatite-forming magmas.The compositions of gneisses and plutonic rocks spread between a Na-rich pole and a K-rich pole. Granodioritic gneiss, hornblende-biotite granodiorite and potassic biotite granitoids define a K-rich series attributed to relatively low-pressure high-degree partial melting of dominantly paragneiss, which accounts for low to absent LILE and HFSE fractionation compared to the paragneiss. Tonalitic-trondhjemitic gneiss, a biotite trondhjemite and a peraluminous two-mica trondhjemite belong to a Na-rich series characterized by low K content and strong depletion in REE and HFSE, which might reflect plagioclase clustering after partial melting at a relatively high pressure of amphibolite, and fractionation of HFSE-REE-bearing minerals. Thermodynamic and mass balance modeling further corroborate these propositions implying that partial melting of paragneiss and amphibolite at about 5 to 10 kbars for a temperature of 780 to 850 °C followed by melt/solid segregation and fractional crystallization are susceptible to generate the Na- and K-rich series.U-Pb dating of zircon from a titanite-allanite-bearing pegmatite at 2094.3 ± 8.8 Ma and of apatite from tonalitic-trondhjemitic gneiss, apatite-zircon-bearing pegmatite and granodioritic gneiss at 2094 ± 21 Ma, 2055 ± 20 Ma, and 2041 ± 33 Ma respectively, confirm that partial melting, melt segregation and crystallization-cooling occurred during the Eburnean orogeny.Based on these data, we propose that (i) titanite-allanite- and apatite-zircon-bearing pegmatites result from syntectonic segregation of residual melt during crystallization of the tonalitic-trondhjemitic gneiss, (ii) garnet-columbite-bearing pegmatites originate from syntectonic melt segregation from the migmatitic paragneiss, and (iii) garnet-REE-bearing pegmatites derive from segregation of a residual melt within the granodioritic gneiss.

Hydrogeochemical and isotopic controls on the source of fluoride in groundwater within the Vea catchment, northeastern Ghana

Groundwater consumption is considered as a major exposure route to fluoride in humans. Therefore, this study unraveled the sources and sinks of groundwater fluoride in the Vea catchment of northeastern Ghana using an integration of litho-petrography, hydrogeochemical analysis, multivariate statistical analysis, and stable isotope analysis. In this regard, 70 groundwater samples were collected from boreholes and analyzed for major ions and stable isotopes using standard procedures whilst 10 rock samples were collected from the crystalline basement rocks of the Birimian Supergroup and used for the petrographic studies. The petrographic results revealed the dominance of quartz, microcline, plagioclase (albite), biotite, muscovite and hornblende in the lithological units. The order of dominance of fluoride in the various lithologies is K-feldspar-rich granitoid > hornblende-biotite granitoid > basaltic flow > hornblende-biotite tonalite > hornblende biotite granodiorite > biotite granitoid. The groundwater fluoride concentrations varied from 0.35 to 3.95 mg/L with a mean concentration of 1.68 mg/L. Almost 61% of the samples have fluoride concentrations above the World Health Organization's maximum permissible limit of 1.5 mg/L. Groundwater is supersaturated with respect to albite due to silicate weathering and undersaturated with respect to fluorite and calcite. This enhanced ion exchange and fluoride mobilization in the groundwater from progressive calcite precipitation. The fluoride concentrations show positive correlations with Na+, Mg2+, HCO3−, and SO42−, confirming that fluoride enrichment is due to silicate weathering and ion exchange reactions. The δ18O and δ2H values with respect to V-SMOW vary between −4.15 and −2.75‰ and −22.49 and −13.74‰, respectively suggesting considerable isotopic variation of the groundwater. Enriched isotopic composition is observed with low fluoride concentration whilst depleted isotopic composition is observed with a higher concentration of fluoride in groundwater. The stable isotopic compositions of the groundwater also indicated meteoric origin with an evaporative effect, which partly influences the groundwater chemistry.

High magnesian granitoids in the Precambrian continental crust: Implication for the continuum between ferro–potassic and magnesio–potassic rock suites

Ferro-potassic (Fe–K) to magnesio-potassic (Mg–K) hornblende–biotite granitoids (HBGs) with a wide range of SiO2 from 52 to 77 wt% are typical of Precambrian continental crust, and are generally related to late- and post-collisional orogenic events. Despite their broadly uniform mineralogy and tectonic environment, the chemical compositions of these granites suggest different sources from lower crust for the Fe-K suites to enriched mantle for the Mg–K counterparts. Here we propose a classification of the magnesian rocks into moderate-Mg, high-Mg and ultra-Mg, with corresponding examples from various parts of the world such as the Closepet-type, sanukitoids, and their high-Mg counterparts of the Elan-type. The Elan-type granitoids are characterized by the highest MgO, Cr, Ni, εNd(T) and lowest TiO2, FeOt/(FeOt + MgO) contents among all the Precambrian HBGs, and are hence close to a true end-member. The Precambrian HBGs show common features such as a wide range of SiO2 contents, enrichment in LILE (K, Ba, Sr), LREE, Nb-Ti negative primitive-mantle normalized anomalies and weak negative or no Eu-anomalies in intermediate suites. The Mg# of magmatic and cumulus/ relict amphiboles displays a compositional array of ultra-Mg to Fe granites and shows positive correlation with the whole-rock Mg#. Continuum between the compositions of Mg–K and Fe–K granitoids is reflected in a gradual decrease in Mg, Cr, Ni of the rocks and Mg of the mafic silicates, increase in Ti, P, Zr, Y, Zn, U, total REE, and decrease of the Nd initial isotopic composition, together with a change in the paragenesis of Fe–Ti-oxides. We interpret these features to result from mixing of metasomatized mantle and crustal magmas and their homogenization at the lower crust level. The lower-crustal source component increases from the Mg–K to Fe–K series. During their passage to higher crustal levels, the magmas underwent fractional crystallization and crustal contamination leading to the wide range in silica content.

Свойства и минералогический состав темногумусовой квазиглеевой солончаковой солонцеватой криотурбированной мерзлотной почвы Баргузинской котловины (Бурятия)

Morphological, physical-chemical properties, texture, salt composition mineralogical composition of the particle-size fractions 5 mkm of dark-humus quasigleyic solonchakous solonetzic cryoturbated deeply permafrost loamy-sandy soil developed from alluvial sediments (Salic Mollic Reductaquic Turbic Cryosol (Eutric, Loamic, Calcaric, Fluvic, Sodic)) are presented. The soil is situated at the northern-eastern part of Barguzin Depression in the impact zone of dumping of nitrogen siliceous thermal underground waters of Kuldur type (Kuchiger springs). The soil forms from materials of disintegration of high-content-potassium calcareous-alkali granites of Barguzin complex of Angara-Vitim Batholith. It was found soil salinity of weak to very strong degree, presumably sulfate-sodium with gypsum. There is a net of gypsum filaments in the solum that is observed by morphological analysis. Low amount of rectorite was found in clay fraction of undisturbed layers of alluvium at the depth of 54-145 cm in the studied soil profile. Regular structure of rectorite comprised mica (A) and smectite (B) packets with alternation motive ABAB… is transformed into irregular structure of mica-smectite interstratifications by impact of soluble sodium salts and cryoturbation of soil material in soil horizons at the depth of 0-54 cm formed from the alluvium. Regional peculiarity of studied soil is small shear of quartz in silt and sand fractions that is a result of mineral composition of biotite and amphibole-biotite granites and granitoids. Irregular mica-smectite interstratifications with high shear (>50%) of smectite packets are destroyed by impact of sodium sulfate and hydrocarbonates hydrogenic accumulation in the solum and are partially illuviated into middle part of soil profile with formation of humus-clay cutans on the lateral sides of aggregates by infiltration of rain waters. Existence of humus-clay cutans is an evidence of weak degree of solonetzic process.

Evaluate best-mixing model for estimating thermal conductivity for granitoids from mineralogy: A case study for the granitoids of the Bundelkhand craton, central India

Granitoid is an important part of the upper continental crust, and therefore its thermal conductivity (TC) plays an important role in understanding the lithospheric thermal structure in a region and for geotechnical or geoengineering purposes. In above context, due to the lack of TC data or absence of proper sample for its measurements, TC values are assumed which can lead to erroneous results. In such scenario, when direct measurements are not possible, TC can be estimated by indirect methods with proper precautions. An attempt is made here to arrive at the best mixing model for granitic rocks by using TC of the individual minerals and compare the deviation between the measured and calculated values. The considered mean models are: arithmetic, geometric, harmonic, effective, Voigt-Reuss-Hill and Hashin-Shtrikman along with its lower and upper bound. Studied rocks are potassic granitoid (PG), biotite granitoid (BG), sodic granitoid (GG) and gneisses (BnG) from the Bundelkhand craton, central India. Measurements of TC are done in the laboratory on 21 samples using steady-state method. Data show wide variations in TC values for granitoids (PG: 2.7 − 3.2, BG: 2.6 − 2.9, GG: 2.9 − 3.0 Wm−1 K−1) and gneisses (2.9 − 3.7 Wm−1 K−1). Modal mineralogy of the rocks are determined using petrological and geochemical data through modal analysis and normative (CIPW-NORM) methods. The calculated TC arrived by both the methods provide a satisfactory agreement for the harmonic mean model, showing deviation from −10.9 to 17.6% for modal analysis and −16.1 to 11.5% for NORM method. Deviations from the above methods decrease further (−23.3 to 2.8% and −27.7 to −3.1%, respectively) using minimum mineral TC. Therefore, we suggest that, in the case of non-availability of the proper sample for direct measurement, the TC of very low porous granitoids could be satisfactorily determined by assessing their modal mineralogy and considering the harmonic mean model.

Radioelemental, petrological and geochemical characterization of the Bundelkhand craton, central India: implication in the Archaean geodynamic evolution

We have carried out radioelemental (232Th, 238U, 40K), petrological and geochemical analyses on granitoids and gneisses covering major rock formations of the Bundelkhand craton, central India. Our data reveal that above characteristics are distinct among granitoids (i.e. pink, biotite and grey granitoids) and gneisses (i.e. potassic and sodic types). Pink granitoid is K-feldspar-rich and meta-aluminous to per-aluminous in character. Biotite granitoid is meta-aluminous in character. Grey granitoid is rich in Na-feldspar and mafic minerals, granodiorite to diorite in composition and meta-aluminous in character. Among these granitoids, radioelements (Th, U, K) are highest in pink granitoid (45.0 ± 21.7 ppm, 7.2 ± 3.4 ppm, 4.2 ± 0.4 %), intermediate in biotite granitoid (44.5 ± 28.2 ppm, 5.4 ± 2.8 ppm, 3.4 ± 0.7 %) and lowest in grey granitoid (17.7 ± 4.3 ppm, 4.4 ± 0.6 ppm, 3.0 ± 0.4 %). Among gneisses, potassic-type gneisses have higher radioelements (11.8 ± 5.3 ppm, 3.1 ± 1.2 ppm, 2.0 ± 0.5 %) than the sodic-type gneisses (5.6 ± 2.8 ppm, 1.3 ± 0.5 ppm, 1.4 ± 0.7 %). Moreover, the pink granitoid and the biotite granitoid have higher Th/U (6 and 8, respectively) compared to the grey granitoid (Th/U: 4), implying enrichment of Th in pink and biotite granitoids relative to grey granitoid. K/U among pink, biotite and grey granitoids shows little variation (0.6 × 104, 0.6 × 104, 0.7 × 104, respectively), indicating relatively similar increase in K and U. Therefore, mineralogical and petrological data along with radioelemental ratios suggest that radioelemental variations in these lithounits are mainly related to abundances of the radioactive minerals that have formed by the fractionation of LILE from different magma sources. Based on present data, the craton can be divided into three distinct zones that can be correlated with its evolution in time and space. The central part, where gneisses are associated with metavolcanics of greenstone belt, is characterized by lowest radioelements and is the oldest component. The southern part, dominated by pink granitoid, is characterized by highest radioelements and is the youngest part. The northern part, dominated by grey and biotite granitoid, is characterized by moderate radioelements.

Source-derived heterogeneities in the composite (charnockite-granite) ferroan Farsund intrusion (SW Norway)

The Sveconorwegian late-orogenic magmatism of southern Norway (970–916Ma) consists of two magmatic suites: the Hornblende–Biotite–Granitoids (HBG) suite and the Anorthosite–Mangerite–Charnockite (AMC) suite of the Rogaland Anorthosite Province (RAP), characterized by opx-bearing lithologies. The Farsund body comprises elements of both suites that display mingling relationships. The main facies, mostly charnockitic, contains orthopyroxene whereas a subordinate granitic facies comprises hornblende and biotite. U–Pb (zircon) isotopic data show overlapping ages of 931±2Ma for the charnockitic facies and 926±4Ma for the granitic facies. Both facies display similar extent of differentiation demonstrating that the granitic facies was not derived by fractionation from the charnockitic one. Mineralogical, geochemical and petrological data indicate that the charnockitic facies belongs to the AMC suite and the granitic facies, to the HBG suite. Strontium, Nd and Pb isotopic data show that the Farsund intrusion was emplaced at the boundary between two different lithotectonic units that are separated by the Farsund-RAP shear zone. This shear zone likely favored the emplacement of the magmas. Most of the assimilation occurred in the lower crust whereas limited differentiation likely took place in the upper crust.

Ion Probe U-Pb Dating of the Central Sakarya Basement: A peri-Gondwana Terrane Intruded by Late Lower Carboniferous Subduction/Collision-related Granitic Rocks

Ion probe dating is used to determine the relative ages of amphibolite-facies meta-clastic sedimentary rocks and crosscutting granitoid rocks within an important 'basement' outcrop in northwestern Turkey. U-Pb ages of 89 detrital zircon grains separated from sillimanite-garnet micaschist from the Central Sakarya basement terrane range from 551 Ma (Ediacaran) to 2738 Ma (Neoarchean). Eighty five percent of the ages are 90-110% concordant. Zircon populations cluster at ~550-750 Ma (28 grains), ~950-1050 Ma (27 grains) and ~2000 Ma (5 grains), with smaller groupings at ~800 Ma and ~1850 Ma. The first, prominent, population (late Neoproterozoic) reflects derivation from a source area related to a Cadomian-Avalonian magmatic arc, or the East African orogen. An alternative Baltica-related origin is unlikely because Baltica was magmatically inactive during much of this period. The early Neoproterozoic ages (0.9-1.0 Ga) deviate significantly from the known age spectra of Cadomian terranes and are instead consistent with derivation from northeast Africa. The detrital zircon age spectrum of the Sakarya basement is similar to that of Cambrian-Ordovician sandstones along the northern periphery of the Arabian-Nubian Shield (Elat sandstones). A sample of crosscutting pink alkali feldspar-rich granitoid yielded an age of 324.3±1.5 Ma, whilst a grey, well-foliated biotite granitoid was dated at 327.2±1.9 Ma. A granitoid body with biotite and amphibole yielded an age of 319.5±1.1 Ma. The granitoid magmatism could thus have persisted for ~8 Ma during late Early Carboniferous time, possibly related to subduction or collision of a Central Sakarya terrane with the Eurasian margin. The Central Sakarya terrane is likely to have rifted during the Early Palaeozoic; i.e. relatively early compared to other Eastern Mediterranean, inferred 'Minoan terranes' and then accreted to the Eurasian margin, probably during Late Palaeozoic time. The differences in detrital zircon populations suggest that the Central Sakarya terrane was not part of the source area of Lower Carboniferous clastic sediments of the now-adjacent İstanbul terrane, consistent with these two tectonic units being far apart during Late Palaeozoic-Early Mesozoic time.

Geochemistry and 207Pb/206Pb zircon ages of granitoids from the southern portion of the Tamboril–Santa Quitéria granitic–migmatitic complex, Ceará Central Domain, Borborema Province (NE Brazil)

The Tamboril–Santa Quitéria Complex is an important Neoproterozoic granitic–migmatitic unit from the Ceará Central Domain that developed from ca. 650 to 610 Ma. In general the granitoids range in composition from diorite to granite with predominance (up to 85%) of granitic to monzogranitic composition with biotite as the main mafic AFM phase. Geochemical and 207Pb/206Pb evaporation zircon geochronology studies were applied in a group of these abundant monzogranitic rocks from the region of Novo Oriente in the southern portion of the Ceará Central Domain. In this area the granitoids are weakly peraluminous biotite granitoids and deformed biotite granitoids of high-K calc-alkaline and ferroan composition, which we interpreted as primary magmas (segregated diatexites) derived from the partial melting of crustal material. The close temporal relation of this magmatism with local eclogitic and regional high temperature metamorphism in Ceará Central Domain point out to an orogenic setting, arguably emplaced during the collisional stage. Subordinate coeval juvenile mantle incursions are also present. This crustally derived magmatism is the primary product of the continental thickening that resulted from the collision between the rocks represented by the Amazonian-West African craton (São Luiz cratonic fragment) to the northwest and the Paleoproterozoic–Archean basement of the Borborema Province to the southeast along the Transbrasiliano tectonic corridor.

Age of ferroan A-type post-tectonic granitoids of the southern part of the Keimoes Suite, Northern Cape Province, South Africa

The granitoids of the Keimoes Suite represent part of a complex group of late Mesoproterozoic intrusions of granodioritic to potassic granite composition that occupy an outcrop belt striking approximately NW–SE to the immediate west of Upington, Northern Cape Province, South Africa. The intrusions are believed to mark the contact between the Kaapvaal Craton and the Namaqua Sector of the Namaqua-Natal Province. Published geological, geochemical and geochronological knowledge of the Keimoes Suite is poor in general, with most data restricted to the central portion of the outcrop belt. In this contribution new ages and geochemical data for three granitoids of the southeastern Keimoes Suite in the Putsonderwater – Van Wykspan area, the Klip Koppies, Gemsbokbult and a member of the Kleinbegin Subsuite, are presented. All three intrusions show petrological and geochemical characteristics that agree well with literature data for the central and northern outcrop portions of the Keimoes Suite. They are weakly foliated to unfoliated, medium- to coarse-grained ferroan, alkali-calcic late- to post-tectonic A-type biotite granitoids intruded within a collisional within-plate tectonic setting. Zircon U–Pb SHRIMP ages for the intrusion of the three granitoids are within error of one another at ca. 1100 Ma. Marked differences between the three granitoids include the abundance and age of inherited zircons and Sm–Nd isotope systematics. With an ε Nd(t) value of 1.83, the Gemsbokbult Granite is dominantly sourced from partial melting of material with a mantle derivation with a minor crustal component. The other two intrusions, on the other hand, show a strong crustal source component, as indicated by ε Nd(t) values of −2.03 for the Klip Koppies Granite and −8.46 for the Kleinbegin Granite. The Keimoes Suite granitoids provide important clues as to the timing and tectonic evolution of the western margin of the Kaapvaal Craton at its junction with the Proterozoic Namaqua Sector of the Namaqua-Natal Province. A contribution to these melts from the host rocks, the ∼1.24–1.30 Ga Areachap Group volcanic belt is traced through the presence of inherited zircon cores of this age that is particularly evident in the Klip Koppies Granite. Inheritance also reflects the major tectono-magmatic events which affected the western margin of the Kaapvaal Craton during Mesoproterozoic times, with the bulk of the inheritance in the zircon populations due to peak metamorphism and partial melting caused by continental collision between the Kaapvaal Craton and the Kakamas Terrane and Bushmanland Subprovince to the west at approximately 1.18–1.2 Ga. Post 1.1 Ga ages reflect isotopic disturbance due to a later collisional event to the west at ∼1.08 Ga and subsequent exhumation of the western margin of the Kaapvaal Craton.

Neoproterozoic calc‐alkaline peraluminous granitoids of the Deleihimmi pluton, Central Eastern Desert, Egypt: implications for transition from late‐ to post‐collisional tectonomagmatic evolution in the northern Arabian–Nubian Shield

The widely distributed late‐collisional calc‐alkaline granitoids in the northern Arabian–Nubian Shield (ANS) have a geodynamic interest as they represent significant addition of material into the ANS juvenile crust in a short time interval (∼630–590 Ma). The Deleihimmi granitoids in the Egyptian Central Eastern Desert are, therefore, particularly interesting since they form a multiphase pluton composed largely of late‐collisional biotite granitoids enclosing granodiorite microgranular enclaves and intruded by leuco‐ and muscovite granites. Geochemically, different granitoid phases share some features and distinctly vary in others. They display slightly peraluminous (ASI = 1–1.16), non‐alkaline (calc‐alkaline and highly fractionated calc‐alkaline), I‐type affinities. Both biotite granitoids and leucogranites show similar rare earth element (REE) patterns [(La/Lu)N = 3.04–2.92 and 1.9–1.14; Eu/Eu* = 0.26–0.19 and 0.11–0.08, respectively) and related most likely by closed system crystal fractionation of a common parent. On the other hand, the late phase muscovite granites have distinctive geochemical features typical of rare‐metal granites. They are remarkably depleted in Sr and Ba (4–35 and 13–18 ppm, respectively), and enriched in Rb (381–473 ppm) and many rare metals. Moreover, their REE patterns show a tetrad effect (TE1,3 = 1.13 and 1.29) and pronounced negative Eu anomalies (Eu/Eu* = 0.07 and 0.08), implying extensive open system fractionation via fluid–rock interaction during the magmatic stage.Origin of the calc‐alkaline granitoids by high degree of partial melting of mafic lower crust with subsequent crystal fractionation is advocated. The broad distribution of late‐collisional calc‐alkaline granitoids in the northern ANS is related most likely to large areal and intensive lithospheric delamination subsequent to slab break‐off and crustal/mantle thickening. Such delamination caused both crustal uplift and partial melting of the remaining mantle lithosphere in response to asthenospheric uprise. The melts produced underplate the lower crust to promote its melting. The presence of microgranular enclaves, resulting from mingling of mantle‐derived mafic magma with felsic crustal‐derived liquid, favours this process. The derivation of the late‐phase rare‐metal granites by open system fractionation via fluid interaction is almost related to the onset of extension above the rising asthenosphere that results in mantle degassing during the switch to post‐collisional stage. Consequently, the switch from late‐ to post‐collisional stage of crustal evolution in the northern ANS could be potentially significant not only geodynamically but also economically. Copyright © 2011 John Wiley & Sons, Ltd.

Emplacement P-T conditions of Pan-African biotite-amphibole granitoids in the Nkambe area, Cameroon

Biotite- and amphibole-bearing monzogranite, quartz monzonite, and tonalite intrude into the biotite granitoids and biotite-hornblende gneisses of the Pan-African belt in the Nkambe area, northwestern Cameroon. The common mineral assemblage in these rocks is amphibole + biotite + plagioclase + K-feldspar + quartz + zircon + apatite; however, their modal composition varies in each rock-type. Most amphibole grains are relatively homogeneous and locally have slightly Al-rich rims. They are mostly ferro-edenite or ferropargasite, and in a tonalite sample, there is magnesiohornblende with less aluminous and more magnesian composition. The amphibole + biotite + plagioclase + K-feldspar + quartz assemblage was affected by several pressure-sensitive and H2O-free reactions. The ferro-edenite- and/or ferropargasite-bearing samples show similar pressure-temperature (P-T) ranges of 0.46-0.50 GPa/655-690 °C and 0.43-0.69 GPa/675-705 °C. In contrast, the magnesiohornblende-bearing tonalite records lower temperature conditions of 0.77 GPa/610 °C, which is attributed to subsolidus reequilibration during cooling. The P-T estimates for the biotite-amphibole granitoids in this and previous studies suggest that relatively high-pressure granitoids are widespread in the Nkambe area.

Paleoproterozoic structural evolution of the Man-Leo Shield (West Africa). Key structures for vertical to transcurrent tectonics

In the Man-Leo Shield, Paleoproterozoic (Birimian) belts crop out in nine countries of West Africa. Dominant domains include: (i) greenstone belts composed of plutono-volcanic, volcano-clastic and sedimentary rocks, deformed and weakly metamorphosed under regional greenschist facies conditions; (ii) widespread granitoid batholiths. The domains display a basin and dome-like architecture, and are overprinted by partitioned structures from successively shallower crustal depth. Analyses of key ductile and brittle structures has shown that the structural evolution of Man-Leo Shield is characterized by early vertical magmato-tectonics and subsequently, horizontal transcurrent tectonics with progression from ductile to brittle behavior. Basin and dome-like architectures, and the formation of an ubiquitous vertical foliation (MF) formed during emplacement of early amphibole-bearing (PAG) granite plutons at ca. 2.2 Ga by diapirism during NW–SE crustal shortening. Subsequent to a late stage of predominantly NW–SE shortening that created steeply-dipping mylonite zones (Mz1), transcurrent faults became predominant. The formation of transcurrent faults began transpressively, with development of N–S trending regional-scale mylonite zones (Mz1), and a steeply-plunging stretching lineation that probably formed during emplacement of PAG-type granitoids ca. 2.15 Ga. NNE–SSW transpressive sinistral horsetail faults and many NW–SE trending tension veins are interpreted to have formed at this stage. After cooling of the upper crust ca. 2.1 Ga, transcurrent faults became strike-slip in character with formation of dominantly NE–SW dextral faults (Mz2) and the passive emplacement of biotite (PBG) granitoids. Clockwise rotation of the extensional stress axis ( σ 3) from NNE–SSW trending to ENE–SSW trending assisted the propagation of dextral NE–SW and sinistral NW–SE extensional en echelon horsetail faults. WNW–ESE trending extension jogs (Egz) are interpreted to have been initiated under the same stress conditions. Displacements on strike-slip/transcurrent faults are interpreted as the product of rotation of rigid nuclei blocks producing faults’ re-activation. On the Man-Leo Shield Paleoproterozoic rocks are poorly exposed, but the tectonic model proposed in this study can help to shed light on the structural setting in areas of the shield which are poorly exposed, and in particular, why regional-scale structures do not display significant horizontal displacements. For practical use, key structural criteria can help to identify mylonite zones and transcurrent faults at different scales of investigation.

Geochronological constraints on multiple deformations of the Honam Shear Zone, South Korea and its tectonic implication

The NE-trending Honam Shear Zone, South Korea, is a tectonic-scale shear zone, consisting of several parallel mylonite zones: Jeonju, Sunchang and Yecheon shear zones. Here we report the sensitive high-resolution ion microprobe (SHRIMP) U–Pb zircon ages from the mylonitic Precambrian orthogneiss and hornblende–biotite granitoid near the Myeongho area within the Yecheon Shear Zone, a representative segment of the Honam Shear Zone. The core and overgrowth parts of the zircons from the foliated hornblende–biotite granitoid yielded ca. 187 Ma and ca. 178 Ma, respectively. The former is interpreted as a timing of emplacement, whereas the latter as a timing of subsequent mylonitization, which is similar to zircon overgrowth age of ca. 179 Ma obtained from mylonitized quartz–feldspar orthogneiss. Muscovite and biotite K–Ar ages of mylonitized Precambrian rocks and foliated granitoids range from 162–168 Ma, 148–155 Ma, and 136 Ma. Our geochronological results, combined with those of previous geochronological and structural studies, suggest that the Honam Shear Zone is a tectonic element created during Middle Jurassic Daebo (or early Yanshanian) Orogeny and lasted possibly as late as at Early Cretaceous in relation to the subduction of the Izanagi Plate under the Asian continent.

Geochemistry of the Bafoussam Pan-African I- and S-type granitoids in western Cameroon

The Bafoussam area in western Cameroon is part of the Central African Orogenic Belt. It is dominated by granitoids which belong to the Pan-African syn- to post-collisional post-650 Ma group. Syenogranites are predominant, but alkali-feldspar granite, monzogranite, quartz-monzonite and quartz-monzodiorite occur as well. Four granitoid suites, biotite granitoids and deformed biotite granitoids with amphibole, megafeldspar granitoids with megacrysts and two-mica granitoids with primary muscovite and igneous garnet are distinguished. The granites can be assigned to high-K calc-alkalic to shoshonitic series. The partly shoshonitic biotite granitoids are metaluminous to weakly peraluminous and can be labelled as a highly fractionated I-type suite. The megafeldspar granitoids are weakly peraluminous with I-type character whereas the two-mica granitoids are weakly to strongly peraluminous and belong to an S-type suite. Emplacement ages at 558–564 Ma for the two-mica granitoids have been dated from monazite by the EMP Th–U–Pb method. The REE in the biotite granitoids are moderately fractionated with (La/Lu) N = 23–38. Enrichment of Nb and Ta varies by one order of magnitude. The megafeldspar granitoids show homogeneous and strongly fractionated REE patterns with (La/Lu) N = 27–42. The primitive mantle-normalized element patterns are homogeneous with marked negative Ba, Nb, Ta, Sr, Eu and Ti anomalies. The two-mica granitoids are characterized by low to moderate total REE contents with strongly fractionated REE expressed by (La/Lu) N ranging from 7 to 59. The negative Nb and Ta anomalies are less significant. Nd and Sr whole-rock isotope data confirm different sources for the granitoid suites. The source of the I-type biotite granitoids was probably a juvenile mantle which has been variably metasomatized. The source of the I-type megafeldspar granitoids is characterized by juvenile mantle and lower crust components. Anatectic melts of the upper continental crust with variable contribution of lower continental crust or mantle melts can explain the heterogeneous isotopic signatures of the S-type two-mica granitoids. It is suggested that the melting of these sources was successively initiated by the rising isotherms during a syn- to post-collisional setting which followed a subduction.

Petrogenesis of the Puerto Edén Igneous and Metamorphic Complex, Magallanes, Chile: Late Jurassic syn-deformational anatexis of metapelites and granitoid magma genesis

A suite of schists, gneisses, migmatites, and biotite granitoids from the Puerto Edén Igneous and Metamorphic Complex (PEIMC) and biotite–hornblende granitoids of the South Patagonian batholith (southern Chile) has been studied. For that purpose, the chemistry of minerals and the bulk rock composition of major and trace elements including Rb–Sr and Sm–Nd isotopes were determined. Mineralogical observations and geothermobarometric calculations indicate high-temperature and low-pressure conditions (ca. 600–700 °C and 3 to 4.5 kbar) for an event of metamorphism and partial melting of metapelites in Late Jurassic times (previously determined by SHRIMP U–Pb zircon ages). Structures in schists, gneisses, migmatites and mylonites indicate non-coaxial deformation flow during and after peak metamorphic and anatectic conditions. Andalusite schists and sillimanite gneisses yield initial 87Sr/ 86Sr ratios of up to 0.7134 and εNd 150 values as low as − 7.6. Contemporaneous biotite granitoids and a coarse-grained orthogneiss have initial 87Sr/ 86Sr ratios between 0.7073 and 0.7089, and εNd 150 values in the range − 7.6 to − 4.4. This indicates that metamorphic rocks do not represent the natural isotopic variation in the migmatite source. Thus, a heterogeneous source with a least radiogenic component was involved in the production of the biotite granitoids. The PEIMC is considered as a segment of an evolving kilometre-sized and deep crustal shear zone in which partial melts were generated and segregated into a large reservoir of magmas forming composite plutons in Late Jurassic times. A biotite–hornblende granodiorite and a muscovite–garnet leucogranite show initial 87Sr/ 86Sr ratios of 0.7048 and 0.7061, and εNd 100 values of − 2.6 and − 1.8, respectively, and are thus probably related to Early Cretaceous magmas not involved in the anatexis of the metasedimentary rocks.

The geology, SHRIMP U–Pb geochronology and metallogenic significance of the Ankisatra-Besakay District, Andriamena belt, northern Madagascar

The Ankisatra-Besakay District (A-BD), located about 200 km north of Antananarivo and 75 km east of Maevatanana in central-northern Madagascar, hosts two historical mines, the Ankisatra Pb–Zn ± Au and Besakay Pb–Ag mines. These shear-hosted en echelon quartz veins at Besakay and deformed tensional quartz veins at Ankisatra produced a total of 4446 t of lead and 156 t of zinc in the early 1940s. In addition, there is Pb–Zn–Cu mineralisation in both quartz-feldspar leucosome veins/bands and metasomatised granulite-facies mafic orthogneiss, Cu–Zn and associated Fe–Mn mineralisation in magnetite–pyrite enderbite breccia, and Cu–Zn mineralisation in retrograde shear zones in granulite-facies paragneiss in the A-BD. The country rocks in the A-BD consist of amphibolite to granulite-facies mafic and granitoid orthogneisses and paragneisses with horizons of silicate-facies BIF. The paragneissic rocks in the district tectonically overlie the biotite–granitoid hornfels and sub-volcanic mangeritic rocks, which are separated from amphibolite-facies alkali-feldspar granitoid and enderbitic rocks by a major structure. The A-BD is structurally characterised by: (1) E–W-trending tensional fractures, quartz veins and dolerite dykes; (2) buckling-related axial-planar fractures; and (3) N–S, NE–SW and NNE–SSW trending dextral strike-slip shear zones, dolerite sills and quartz veins in transpressional extensional zones. Uranium–Pb SHRIMP II geochronology of zircon constrains the peak of magmatic, metamorphic, deformational and metasomatic events in the A-BD. An important constraint is whether hosting terranes contain signatures of the ca. 1690–1590 Ma critical age window for world-class BHT Pb–Zn–Ag deposits elsewhere in the world. At least two magmatic events are recorded from the A-BD. An early magmatic event is recorded by a 2725 ± 12 Ma single xenocrystic magmatic zircon in the >2676 ± 6 Ma precursor to the granulite-facies mafic orthogneiss. A ca. 2503–2460 Ma event is recorded by a 2465 ± 6 Ma minimum age of magmatism for the precursor to metasomatised granulite-facies mafic orthogneiss and 2483 ± 20 Ma for the precursor to biotite–granitoid hornfels. Zircons extracted from both the metasomatised and unaltered granulite-facies mafic orthogneisses record peak metamorphic ages of 2465 ± 12 and 2390 ± 10 Ma, probably representing compressional deformation, partial melting, and associated local magmatic events within the ca. 2475–2380 Ma period. Inherited zircons from the quartzo-feldspathic granulite-facies paragneisses return ages of protolithic supracrustal rocks ranging from ca. 2870 to 1700 Ma. A widespread period of rifting, anatectic magmatism, basic-ultrabasic and mangerite magmatism, and related granulite-facies metamorphism occurred between ca. 820 and 780 Ma. The possible exhalative units (silicate-facies BIF and metasomatic, garnet–quartz–plagioclase rock) are of late-Archaean to early-Palaeoproterozoic, rather than Mesoproterozoic age. The terrane lacks the critical evolution age window of ca. 1770–1550 Ma, characteristic of well-documented BHT Provinces in the Broken Hill Block and Mt. Isa Block, Australia and ca. 1959–1135 Ma from the Bushmanland Ore District, South Africa. This suggests that either such an event did not occur in the crust now forming the A-BD or that the equivalent supracrustal rocks containing these age signatures were eroded during Proterozoic times. It is less likely that the intense 780–820 Ma event destroyed evidence for their prior existence. The galenas from the Ankisatra and Besakay deposits have signatures characteristic of small-scale mineralised systems which derived most of their lead from local crustal rocks older than ca. >2.7 Ga. They are thus atypical of BHT deposits and associated vein-style mineralisation from well-endowed terranes. It is concluded that there are neither direct signs nor indirect temporal signals of giant stratiform/stratabound BHT Pb–Zn–Ag mineralisation, nor clear evidence for the presence of characteristic transitional sequences and alteration styles associated with BHT mineralisation in the A-BD, thus downgrading its prospectivity.