Granite Massif Research Articles

U-Pb age and trace elements composition of titanite from granites of Belokurikhinsky massif, Gorny Altai

As a result of isotope-geochemical study, the age data (U-Pb method, ID-TIMS) of titanite from the first phase granites of the Belokurikhinsky granite massif, Gorny Altai, were obtained for the first time. The concordant value of the titanite age of 255 ± 2 Ma coincides within the margin of error with the previously published results of dating micas from granites of the second and third phases of the Belokurikha massif by the Ar-Ar method (250 ± 3 Ma). At the same time, the results of dating differ significantly from the previously published age values for the granites of the Belokurikha massif (232 ± 5 Ma, U-Pb method for the monofraction of zircon grains; 245 ± 8 Ma, Rb-Sr method for the whole rocks). Therefore, there is every reason to narrow the time interval of the formation of the Belokurikha granite massif to 255-250 Ma. The study of the trace element composition of titanite by SIMS demonstrated their zonal structure. The central part of the titanite grain differs from the rim by a noticeably higher content of REE, Cr, Y, and Nb. The content of V, Zr and Ba decreases to a lesser extent towards the rim, the content of Sr and U remains constant. At the same time, the REE distribution spectra in the central and rim parts are conformal to each other, having a convex spectrum for LREE and a concave one for HREE. Titanite is characterized by a negative Eu-anomaly, the depth of which decreases to the rim of the grain. A negative Eu-anomaly indicates the co-crystallization of titanite and plagioclase. The REE distribution spectra in titanite from the Belokurikha massif correspond to the characteristics of a typical magmatic titanite from granitoids and differ significantly from the distribution spectra in metamorphic titanite.

EXTRACTION OF MINERAL RAW MATERIALS OF A GIVEN SIZE AND DENSITY FROM ROCK MASS BY THE VIBRATION METHOD

Vibration processes are widely used in technology in the processing of bulk materials to improve the efficiency of such operations as transportation, mixing, separation by size and material composition and compaction. Theoretical studies of the processes of vibration displacement of particles in granular media under the influence of vibration are presented by a large number of mathematical models, but many of them need to be compared with experimental data. Practical interest is the determination of the time of ascent of relatively large or densest particles to the surface of a layer of crushed rock mass under the action of the vertical vibration component. The article presents the results of an experimental study of this process. A set of experiments on the extraction of basalt particles from tuff rock mass (waste from basalt quarries), ferruginous quartzites from the mass of dump rock, and relatively large granite particles from crushed granite mass was performed. Processing of the experiments using the SPSS Statistics program allowed us to analyze the process and obtain regression models for determining the time of ascent of a particle of a given size and density from the rock mass, including two generalized regression models. In the first of them, the variables were the amplitude and frequency of vibration, the particle size of the medium was 25 mm, the particle density of the medium was 1.6-2.8 g/cm3, the particles floating under the action of vibration have a particle size of 50 mm, their density varies from 2.5 to 5.1 g/cm3. In the second model for А= 5 мм, w=30 Гц, an additional variable factor is the size of the floating particle, which varies from 50 to 25 mm The resulting equations allow us to determine the time of ascent and predict the extraction of particles of a given size and density under the influence of vibration, for example on the conveyor belt, without conducting cumbersome experiments.

New data on the granite pedestal of the monument to Peter the Great “The Bronze Horseman” in Saint Petersburg

In order to expand and popularize knowledge about the stone decoration of Saint Petersburg, we present new data on the mineralogy and petrography of the famous Thunder-Stone, the parts of which were the basis for the monument to Peter the Great – the legendary “Bronze Horseman”. In the course of studying geological documentation of the monument's granite base, we examined the mineral composition and internal structure of granite, as well as the fragments of a pegmatite vein and veinlets found in it. 25 single-mineral samples were collected from the available micro-scaled shear fractures within the pedestal surface and studied by electron microscopy, electron probe and X-ray phase analysis. It was established that K-Na feldspar in the granite composition was represented by microcline, whereas micas were represented by annite-siderophyllite and muscovite. Accessory minerals included monazite, xenotime, thorite, zircon, rutile, apatite, fluorite, Ti-, Nb-, Ta-bearing minerals, uranium phosphates. The presence of topaz is characteristic of pegmatites. The revealed structural and textural features of four granite boulders in the monument pedestal, as well as mineralogical and chemical composition of their rock-forming and accessory minerals, showed the similarity of this rock to Precambrian biotite-muscovite granites and topaz-containing pegmatites (stockscheiders) of the late formation phase of the Vyborg rapakivi granite massif. The research results are considered as the basis for further geological and mineralogical study of the Thunder-Stone origin and determining the place of its separation from the primary source.

Application of the Finite Element Method (FEM) through GFAS Software to the study of a tunnel

Computational simulation is widely used in companies to perform analysis and improve the quality of products and projects. Most of these analyses are carried out using software that uses the Finite Element Method, which allows to obtain answers to numerous engineering problems. In this study, two examples of application to the study of tunnels of the Finite Element Method using the Geostru Software "GFAS - Geotechnical F.E.M. Analysis System" are proposed. The case of a tunnel excavated inside a granite rock massif was analyzed, first determining the state of stresses in the cavity contour through a theoretical method and comparing these results with those obtained in the software. Then, by means of finite element modeling, the settlements induced by the excavation were determined. Finally, the problem of tunnel excavation in a viscoplastic rock mass is presented and the authors propose a comparison of the analytical and numerical method.

New Insights into Crust and upper Mantle Structure in Guangdong Province, China and Its Geothermal Implications

Southeast Asia contains significant natural geothermal resources. However, the mechanism for generating geothermal anomalies by the crust–mantle structure still needs to define. In this study, we focused on Guangdong Province, China. We conducted three magnetotelluric profiles to interpret the crust and upper mantle structure beneath the Guangdong Province and its geothermal implications. Based on data analysis results, a two-dimension inversion was conducted on the dataset. The inversion model revealed that there is a presence of upwelling channels, and some channels are connected with shallow crustal fault zone; the thickness of crust and lithosphere in Guangdong Province is relatively thin. Such a special crust and upper mantle structure form high surface heat flow. Merged with previous research, our results imply that massive Late Mesozoic granites, which contain high radioactive heat generating elements, are distributed on the surface and underground of Guangdong Province. Based on the correlation between high radioactive Late Mesozoic granites, crust-upper mantle structure, surface heat flow, and locations of natural hot springs, we established a geothermal conceptual model to visualize the origin of a current geophysical and geothermal anomaly in Guangdong Province.

Environmental isotopes and noble gas ages of the deep groundwater with coupled flow modelling in the Baltic artesian basin

In this study, modelled groundwater actual flow times in intermediate and deep aquifers, covered by regional scale impermeable aquitards, were compared with 4He and 81Kr age dating results. To improve the reliability of the steady state 3D groundwater flow model, the isotopic ages of deep groundwater were compared to the MODPATH modelled travel times. The highest helium values in groundwater reservoirs coincide with fault zones in the crystalline basement and sedimentary cover near Rapakivi granite massifs. Insights into isotope-geochemical anomalies of the Baltic Artesian Basin intermediate and deep groundwater support their main distribution peculiarities in the flow path towards the Baltic Sea coast lowland and seabed depression as the regional groundwater discharge area.

Deep structure of the Salair fold-nappe terrane (NW CAOB) according to magnetotelluric sounding

The Salair fold-nappe terrane (a.k.a. Salair orogen, Salair) is the northwestern part of the Altai-Sayan folded area of the Central Asian Orogenic Belt. It is composed of Cambrian – Early Ordovician volcanic rocks and island-arc sedimentary deposits. In plan, Salair is a horseshoe-shaped structure with the northeast-facing convex side, which is formed by the outcrops of the Early Paleozoic folded basement. Its inner part is the Khmelev basin composed of Upper Devonian – Lower Carboniferous sandstones and siltstones. The Early Paleozoic volcanic rocks and sediments of Salair are overthrusted onto the Devonian-Permian sediments of the Kuznetsk basin. The Paleozoic thrusts, that were reactivated at the neotectonic stage, are observed in the modern relief as tectonic steps. Our study of the Salair deep structure was based on the data from two profiles of magnetotelluric sounding. These 175-km and 125-km long profiles go across the strike of the Salair structure and the western part of the Kuznetsk basin. Profile 1 detects a subhorizontal zone of increased conductivity (100–500 Ohm·m) at the depths of 8–15 km. At the eastern part of Profile 1, this zone gently continues upward, towards a shallow conducting zone that corresponds to the sediments of the Kuznetsk basin. Two high-resistance bodies (1000–7000 Ohm⋅m) are detected at the depths of 0–6 km in the middle of the section. They are separated by a subvertical conducting zone corresponding to the Kinterep thrust. The main features are the subhorizontal positions and the flattened forms of crustal conductivity anomalies. At the central part of Profile 2, there is a high-resistance block (above 150000 Ohm⋅m) over the entire depth range of the section, from the surface to the depths of about 20 km. In the eastern part of Profile 2, a shallow zone of increased conductivity corresponds to the sediments of the Kuznetsk basin. The subhorizontal mid-crust layer of increased conductivity, which is detected in the Salair crust, is typical of intracontinental orogens. The distribution pattern of electrical conductivity anomalies confirms the Salair thrust onto the Kuznetsk basin. The northern part of the Khmelev basin is characterized by high resistivity, which can be explained by abundant covered Late Permian granite massifs in that part of the Khmelev basin. The Kinterep thrust located in the northeastern part of the Khmelev basin is manifested in the deep geoelectric crust structure as a conducting zone, which can be considered as an evidence of the activity of this fault.

Tonalite-trondjemite-granodiorite formation of the Archaean. Special features of composition and conditions of formation, Ukrainian Shield as an example

Tonalite-trondjemite-granodiorite formation (TTG) produces the main volume of acidic rocks of the continental crust. Similar rocks are never met later. Therefore the problems of their production are directly connected with the problem of the crust and mantle formation.
 The structure of the Archean TTG formation of granite-gneiss area of the Bug megablock and granite-grrenstone area of the Middle Dnieper megablock (MDMB) has been considered. Similar and different features have been found. The analysis of these data resulted in a conclusion that within the MDMB, West Periazovian and Khashchevate-Zavalie block of the Middle Bug area the events of formation of the Archean granite-greenstone area were similar, however these three blocks of the Ukrainian Shield demonstrate different levels of erosion damage reflected in PT-conditions of metamorphic transformations.
 The rocks of TTG formation are a part of complex structured stratum appeared as a result of impregnation (migmatization) by quartz-albite melt of the primary crust and/or of more ancient strata of predominantly basic composition. In the middle-lower crust a partial replacement of the primary crust occurred and in the upper one — the deposition of new portions of the melt on the earlier ones, piercement of granite masses and migmatization of volcanogenic stratum. During the Archean these events happened repeatedly, that resulted in partial replacement of the primary crust with plagiogranites.
 Modern notions have been considered on the processes of producing of TTG granite formation. It has been shown that according to thermal model distribution of temperatures in the crust does not cross the line of basalt water solidus. That is why the appearance of granite melts could not be the result of submergence to big depths (ultrametamorphism). Chronological and genetic relation with mantle melting, of which komatiites and spilites of green-stone structures were crystallized, assumed convective flows in the mantle. To explain the formation of tonalite and trondjemite melt a model of two-leveled crystallization differentiation of ultrabasic melt has been used. However appearance of primary basalt replacement in such a scale and assimilation of green-stone roots by granite melt are possible only in case of interaction of mantle fluids with the rocks of primary crust. An assumption has been made that the composition of some part of these fluids could be close to composition of granite (trondjemite). According to the author’s opinion such assumption confirms a hypothesis of V. Griffin and N. Pirson about formation of crystalline mantle on the border between the Archean and Proterozoic.

Features of the Structure and Formation Conditions of the Far Eastern Seas Foundation

The authors presented the results of tectonogeodynamic paleoreconstructions and numerical spatio-temporal basin modelling, which allowed to reveal the structural features and formation conditions of the base of the Far Eastern seas of the Russian Federation, as well as the occurrence of crystalline protrusions in the pre-Cenozoic bases at the stage of prototectonics and posthumous tectonics, which are primarily due to heterogeneity of the viscous properties of various layers of the earth’s crust, i.e. its tectonic and material stratification. A large-scale lateral redistribution of the substance, its outflow out of the areas of increased compression and injection into areas of geodynamic shelters has taken place at this stage. Mechanisms of the formation of a void space within protrusions have been considered. A conceptual model of the formation of petroleum deposits within the granite massifs of the base has been proposed.

A preliminary study of the siliceous and femic rock blocks in the Neoproterozoic diatexitic granite at Fuhu Hill in southwestern Guangdong, China

The crystalline basement of Cathaysia Block is commonly believed to have formed before the Middle Neoproterozoic; however, the basement rock has seldom been reported in the eastern Cathaysia. Recently, numerous siliceous and femic rock blocks distributed in the diatexitic host granite were observed on the rocky beach of Fuhu Hill in the southwestern Guangdong, China. The results of geological and geochemical investigations of these rock blocks revealed that the protolith of siliceous rock blocks (SRBs) was marine silicalite deposited in a pelagic environment between the ridge‐proximal and continental margin, and the femic rock blocks (FRBs) geochemically corresponded to trachybasalt and monzogabbro, pertaining to OIB/E‐MORB types in the Ce/Y‐Zr/Nb and Zr/Y/Nb systems. 206Pb/238U ages of 995 and 1,002 Ma were obtained from zircon U–Pb dating of the FRBs. The host rocks of the SRBs and FRBs were mainly diatexitic granite that was intruded and sometimes hosted by massive granite. The zircon 206Pb/238U age gained from the diatexitic granite was 991 Ma whereas that from the massive granite was 239 Ma. It may be concluded that SRBs and FRBs were derived from a spilite‐keratophyre formation formed during 1,005–995 Ma and disintegrated around 991 Ma due to crustal anataxis. These SRBs, FRBs, and their diatexitic host granite blocks might have been brought up to the shallow crust by granitic magma in the Indosinian period or due to fault activity in the late stage. Moreover, the southwest part of the eastern Cathaysia possessed a similar basement as the western Cathaysia.

On the genesis of aluminum-rich speleothems in a granite cave of NW Spain

Granite massifs often contain caves, with dimensions ranging from a few meters up to 1,000 m, also referred to as pseudokarst. The speleothems in such caves are mostly composed of either Si-rich (commonly opal-A) or Al-rich authigenic mineraloids. Whereas the formation and geochemical composition of opal-A biospeleothems have been studied and are fairly well understood, knowledge on the Al-rich analogues is scarce. This work reports for the first time a study on the composition, accretion process, age and growth rate of an Al-rich speleothem type flowstone from the A Trapa Cave System (Galicia, NW Spain), developed in a granite cave. To understand the growth process, trickling water was analyzed and the deposition environment inside the cave was characterized. We found that the speleothems are alternating Si- and Al-rich layered deposits formed between 1,635 ± 75 and 1,243 ± 58 cal BP by percolating water that carries underground mineral grains, dissolved ions, and organic matter from soil and the weathered bedrock above the cave.

Uranium-Lead Age of Granites of Kirovohrad Massif of the Inhul Megablock of the Ukrainian Shield

The porphyry-like biotite-garnet granites (sample KВ-5-1) of the Sokolivkа quarry were studied. The quarry is located in the Kirovohrad granite massif on the southwest of Kropyvnytsky city. The aim of our geochronology investigation is to determine the age of granites of the Kirovohrad massif by the U-Pb isotope method using monazite. The age of granites from Kirovohrad massif by the U-Pb method using monazite has not been determined yet. According to our data, the porphyry granites of the Kirovohrad massif (Sokolivkа quarry) were formed 2034 million years ago. This U-Pb data of the porphyry-like granites is significantly lower than the U-Pb age of the granites from other parts of this massif. This may be due to the multistage formation of the Kirovohrad massif, for example, the Novoukrainskiy and some granite massifs of the Zhytomyr complex from Volyn’ megablock.

Nature And Age of Granites in the Central Part of the Western Siberian Platform (Case Study of the Krivolutskii Batholith)

The study of granites in the basement of the Western Siberian platform is highly relevant since they are associated with hydrocarbon deposits, which are located not only above the granite massif, but also within the metasomatically altered upper layer of granites. At the same time, granites are most easily and reliably dated by zircon, which makes the geological structure of the area easier to examine, especially when the latter is overlapped by a thick sedimentary cover. The composition of granitoids from the basement of the Traigorod–Kondakovskii licensed site of the Western Siberian megabasin, located in the northwestern part of Tomsk Region, near the border with the Khanty-Mansi Autonomous Okrug, about 40 km east of the village of Aleksandrovskoye, has been studied. This license area is located within the Aleksandrovskii arch, which is bounded by the Ust-Tymsk Depression in the southeast and the Koltogorskii Trough in the northwest. The Aleksandrovskii Arch has a complex structure, which includes the large Krivolutskii granite batholith enclosed in the Carboniferous–Devonian sedimentary (mainly carbonate) rocks and Ordovician–Silurian shales. It has been established that batholith rocks are leucogranites and granites of normal alkalinity and have undergone metasomatic alterations in the form of propylitization and argillization. Granites belong to the I-type and were probably formed from the island arc substrate. Their age, according to the results of U–Pb zircon dating, is approximately 268 Ma; i.e., the generation and intrusion of granites took place during the beginning of the formation of the Koltogorsk–Urengoi Rift, the central rift of Western Siberia (which, according to Ar–Ar basalt dating, was also formed 268 million years ago).

Uranium-Lead Geochronology on Monacite of Granites of the Lypnyazka Massif and its Framing (Ingul Megablock of the Ukrainian Shield)

The Lipnyazka massif is located in the Dobrovelychkivsky district of the Kirovohrad region, v. Lipnyazka and further south. Structurally, it is located within the Bratskyy Synclinorium of the Ingul megablock and coincides with the Mikhailovsky anticline. The main petrotype of the massif rocks are porphyry-like granites, often with a gneiss-like texture, aplito-pegmatoid, pegmatoid granites and pegmatites. The latter most often form secant vein bodies. Uranium-lead isotopic dating of granitoids of the Lipnyazka granite massif has been performed, with which a number of deposits and ore occurrences of rare elements, primarily lithium, are spatially and probably genetically connected. The age of porphyry-like granites (2032 ± 6 million years), which is the main petrotype of rocks distributed in the area of the village of Limestone and pegmatoid granites (2027 ± 1 million years), which cut porphyry-like in the form of vein bodies. Aplithoid framed granites (2046 ± 8 million years old), common in the area of the mouth of the Sukhyi Tashlyk River (Dobryanka village), are somewhat older. Based on the results of determining the isotopic composition of strontium in the accessory apatite of granites, a conclusion was made about the upper crust source of granites of the Lipnyazka massif (87Sr/86Sr – 0.730-0.785).

Postmagmatic tectonics of basement granites of the Far Eastern seas of Russia

The article contains the results of tectonogeodynamic paleoreconstructions and numerical spatio-temporal basin modelling, which allowed to reveal the structural features and formation conditions of the base of the Far Eastern seas of the Russian Federation, as well as the occurrence of crystalline protrusions in the pre-Cenozoic bases at the stage of prototectonics and posthumous tectonics, which are primarily due to heterogeneity of the viscous properties of various layers of the earth’s crust, i.e. its tectonic and material stratification. A large-scale lateral redistribution of the substance, its outflow out of the areas of increased compression and injection into areas of geodynamic shelters has taken place at this stage. Mechanisms of the formation of a void space within protrusions have been considered. A conceptual model of the formation of petroleum deposits within the granite massifs of the base has been proposed.

A Review on Petrology and Geochemistry of the Neoproterozoic Malani Igneous Suite and Related Rocks (Northwestern Peninsular India)

This paper reports new mineral and whole-rock geochemical data on the acid volcano-plutonic rocks of the Tusham Ring Complex (TRC) from the Neoproterozoic Malani Igneous Suite (MIS), northwestern Peninsular India and discusses their magmatic evolution, tectonic implication, and geodynamic history. Geochemically, the investigated rocks have the characteristics of hypersolvus, high-K calc-alkaline to shoshonitic, peraluminous and A-type granitoids and they are enriched in SiO2, (Na2O + K2O), Fe/ Mg, Ga/Al, Th, U, REE (except Eu), LILE + HFSE, halogens (F and Cl) and depleted in CaO, MgO, Sr, Cr, Ni, P, Ti and Eu abundances. They also show high heat production (HHP) affinity and high mineralization potential. The high abundances of fluorine (0.80–7.11 wt %) and chlorine (0.44–1.56 wt %) in biotite and the geochemistry of the studied rock types indicate that the acid volcanics and granite massifs of TRC were derived from a halogen-enriched magmatic source under low degree partial melting of crustal protolith. The field, petrography, mineral chemistry, whole-rock geochemistry of the rocks under study, in combination with their tectonic and petrogenetic signatures have proposed that the rift-related Neoproterozoic magmatism of MIS has close linkage with geodynamic evolution of Nagarparkar, Seychelles and Madagascar A-type granitoids during Rodinia breakup.

Ambient gamma dose rate as an indicator of geogenic radon potential

Radon is the second cause of lung cancer after smoking, therefore is acknowledged as a major indoor air pollutant. Geogenic radon potential indicates regions where for natural reasons elevated indoor radon levels or elevated probability of their occurrence can be expected. The most common procedure for establishing geogenic radon potential includes measurements of soil permeability and soil gas radon concentrations. These measurements are time-consuming and expensive therefore a limited number of measurements is carried out and their results are extrapolated to the specific area. Our research aimed to analyse the usefulness of ambient gamma dose rate survey to assess radon concentration in the environment and therefore geogenic radon potential. The measurements were carried out on two granite massifs with higher (Karkonosze) and lower (Strzelin) radioactive elements contents. Seasonal variations of atmospheric radon concentrations and ambient gamma dose rates were registered with higher values during warmer and lower during colder seasons. The opposite seasonal variations were observed for soil gas radon concentrations. No distinctive seasonal variations were recorded in results of uranium, thorium and potassium contents in soil measured in situ by the gamma-ray spectrometer. The correlation coefficients were calculated on the base of annual average data. The correlations between ambient gamma dose rate and radon concentration in soil and in the atmosphere were 0.83 and 0.62 respectively, which may suggest that ambient gamma dose rate can be a useful parameter to indicate geogenic radon potential.

Floristic Diversity of Insular Pine Forests of the Trans-Volga–Kazakh Steppe Province

The insular pine forests of the Trans-Volga–Kazakh province of the Black Sea–Kazakh steppe region have high biodiversity and are relict in nature. The problems of their study and conservation are relevant in the context of increasing anthropogenic impact and climatic changes. A comprehensive analysis was performed for the floristic composition of communities of pine forests from the Burabai, Karkaraly, and Buzuluk national parks, the Naurzum Reserve, the Kanonersky forestry enterprise (south of the Priishimsky altitudinal zone pine forests), the pine forests of the Ilmensky Reserve and the Burlinsky altitudinal zone located in forest–steppe regions near the northern border of the province based on our own field materials and published data. For the first time, the data on the floristic diversity of all large pine forests in the province (the geographical aspect) are summarized in a unified manner. The similarity in the taxonomic, geographical, ecological, morphological, and coenotic structure of the floristic composition of all isolated insular pine forests indicate the presence of historical links and their relic character. The results of the correlation and cluster analysis of floristic lists showed a different degree of similarity between pine forests in different parts of the province in connection with the specific physical and geographical conditions. Three groups of pine forests have been identified: (a) pine forests of the sandy massifs of the Naurzum Reserve and the Kanonersky forestry enterprise, which have the most xerophilic appearance and are poor in composition, with a predominance of steppe species and turf grasses; (b) pine forests of granite massifs of the Kazakh Uplands (Burabay and Karkaraly national parks) with an average species richness; (c) the Buzuluk and Burlinsky pine forests, which occupy the most northern, borderline position in the province, with high floristic diversity and increased participation of forest species.

Effects of high temperature on rock bulk density

ABSTRACT A deep understanding of the physico-mechanical characteristics of rocks undergoing thermal treatments has gained a great interest in deep rock projects. In this research, the size and mass of cylindrical granite samples were measured before, under and after a temperature up to 1000°C, and their bulk densities at different temperature levels were calculated. Under and after high temperature, the granite density decreased with temperature due to the increase of the granite volume and decrease of the granite mass, with the rock volume increase being the prominent factor driving this behaviour. Additionally, the rate at which density increased under high temperature was always larger than the rate after high temperature. The rock mass loss after thermal treatment was attributed to the evaporation of different types of water, thermal reactions of rock-forming minerals and generation of rock fragments, while the rock volume expansion was mainly caused by thermal expansion and reactions of the rock-forming minerals, which was in accordance with the optical microscope observation results. 400°C is considered as the threshold temperature for the relationship between the decrease rate of rock density and temperature. Two fitting equations were proposed as the two boundaries of the rock density decrease rates.

The Pan-African High-K I-Type Granites From Batié Complex, West Cameroon: Age, Origin, and Tectonic Implications

The Batié granitic massif in western Cameroon is NE-SW elongated, following the regional foliation and parallel to the Kekem-Fotouni shear zone, south-western extension of the Tcholliré-Banyo Fault (TBF). This massif comprises two petrographic units: biotite granite and amphibole granite. Major, trace, REE, Sr-Nd isotopic and new U-Pb data, are used to constrain their nature and origin. The results indicate that they are high-K alkali- calcic with shoshonite affinity. The amphibole granite is metaluminous, whereas biotite granite is weakly peraluminous. Both granites are high temperature I-type granites and crystallized under oxidizing conditions. Initial (87Sr/86Sr)620Ma ratios (0.706-0.708) and εNd620Ma (-12.58 to -8.89) indicate the parental magmas were produced by partial melting of deep old Paleoproterozoic crust and were mixed with felsic magma from upper continental crust. Their TDM typically vary from 1.68 to 1.96 Ga. The massif was mostly emplaced between 630 and 547 Ma; during the transitional period between the crustal thickening (ca. 630-620 Ma) and the development of the shear zones, which began with sinistral movements (613-585 Ma) and continued with dextral movements (585-540 Ma). Plutonism continued during the dextral movements. The Batié granite is geochemically and isotopically similar to other post-collisional pan-African granitic massifs located along TBF.