Hornblende Biotite Gneiss Research Articles

Determination of the utility of groundwater with respect to the geochemical parameters: a case study from Tuticorin District of Tamil Nadu (India)

In modern living, rapid development has created an increase in demand for groundwater. An endeavor has been made to understand the hydrogeochemical parameters to determine the utility of groundwater. This situation is severe in coastal hard rock aquifers due to the influence of salinity ingression and other anthropogenic influence. A total of 135 groundwater samples were collected from the coastal aquifer of the Tuticorin district and analyzed for major cations and anions during premonsoon (PRM) and postmonsoon (POM). The ions analyzed were used to determine the drinking, agricultural and domestic utility of groundwater. The electrical conductivity (EC) contour shows that the groundwater quality is poor along the coast. The parameters were compared with WHO (Guidelines for drinking water quality recommendations, WHO, Geneva, 2004) standard for drinking purpose. A groundwater classification method has been developed for groundwater in the area using a dynamic water quality index (WQI). On the basis of the WQI so computed, groundwater in the area has been spatially classified into “excellent,” “good,” “poor” and “very poor” to “Unsuitable” water types variation lithologywise. Corrosivity ratio and hardness were noted to be higher and found to be unsuitable in majority of the regions for domestic purpose. Higher fluoride concentration was noted in the central part of the study area represented by complex geology comprising of the hornblende biotite gneiss and charnockite. Sodium percentage (Na%), sodium absorption ratio, residual sodium carbonate, Wilcox (Classification and use of irrigation waters, US Department of Agriculture, Washington, 1955), permeability index, residual sodium bicarbonate, magnesium hazard, Kelly’s ratio and potential salinity also indicate that most of the groundwater samples are not suitable for irrigation purposes.

Landslide Hazard Zonation in and around Thodupuzha–Idukki–Munnar Road, Idukki District, Kerala: A Geospatial Approach

Abstract Landslide hazard zonation in and around Thodupuzha – Idukki – Munnar road (TM Road) in Idukki district, Kerala, India has been carried out using geospatial techniques. Being a landslide prone area a hazard zonation is attempted using terrain fragility concept. Based on the traverse mapping, slide prone areas and palaeo-slides along the TM road were identified. Precambrian crystallines consisting of hornblende-biotite gneiss, biotite gneiss, granite gneiss, charnockite and pink granites form the main rock types. Factor maps of various terrain parameters such as slope, landuse, relative relief, drainage pattern, drainage density, landform, and surface material were prepared and their integration carried out on a GIS platform. Based on geospatial analyses, the study area (438 sq. km) is ranked into four classes of relative fragility viz. highly fragile (8.25 sq. km), fragile (41.25 sq. km), moderately fragile (232 sq. km) and stable (156.5 sq. km). The first two categories together form 11% of the area, the most hazardous regions, which require immediate mitigation measures for slope protection. The study forms a basis for evolving a strategy for the development of the entire TM road of Idukki district. The fragility concept used in this study is a fast and cost effective model for identifying landslide prone areas, especially in the Western Ghats.

The Feiran–Solaf metamorphic complex, Sinai, Egypt: Geochronological and geochemical constraints on its evolution

Ion-microprobe U–Th–Pb geochronological data are presented for fourteen samples from the Feiran–Solaf metamorphic complex in the Sinai Peninsula, Egypt. These data reveal a succession of magmatic and metamorphic events from ca. 1000Ma to <600Ma. The oldest age of ∼1.0Ga is obtained from zircon in Solaf zone metapsammites, representing the age of a locally restricted acidic igneous source which eroded and was deposited as arkose sometime after ∼975±10Ma. A similar ∼1.0Ga age from granodioritic biotite gneisses is interpreted as dating its crystallization. A biotite gneiss sample bordering the Solaf granodioritic gneiss yields an age of 792±7Ma, suggesting at least two phases of arc development over ca. 200Ma. While detrital zircon from migmatitic metapelites indicates input of material as old as ∼1.0Ga, the probable maximum sedimentation age for their immature pelitic protolith, which was likely deposited in an active continental marginal basin within a continental arc, is 656±6Ma. These metapelites were metamorphosed at 603±6Ma.Leucosome and mesosome samples from migmatitic biotite-hornblende gneisses of the Feiran zone yield polyphase zircon with ca. 700Ma cores interpreted as dating igneous crystallization, while overgrowths of 627±7Ma and 592±10Ma define the time of high-grade metamorphism. A biotite-hornblende gneiss sample from the Feiran-zone contains zircon that defines a protolith crystallization age at 623±6Ma, with rim overgrowths defining a metamorphic age of 587±7Ma. Zircon from the diorite body separating the Feiran and Solaf zones yields crystallization ages of 617±4Ma and 602±4Ma for samples collected from the periphery and core, respectively, while zircon from a late-tectonic granodiorite sample intruding the metapsammitic gneisses yields a crystallization age of 589±6Ma.High spatial resolution age dating from the Feiran–Solaf metamorphic complex and intruding magmatic rocks thus reveals four episodes of arc magmatism at 799–785Ma, 713–692Ma, 629–613Ma, and 606–583Ma. The timing of regional high-grade metamorphism is constrained by the zircon rims in the migmatitic metapelites and migmatized biotite-hornblende gneisses which record two distinct events at 627±7Ma and 592±10Ma, interpreted to represent peak and isothermal decompressional metamorphic events, synchronous with heat flow from concurrent young magmatism.

Late Neoproterozoic metamorphic assemblages along the Pan-African Hamisana Shear Zone, southeastern Egypt: Metamorphism, geochemistry and petrogenesis

A variety of Late Neoproterozoic gneisses and amphibolites are distributed along the N–S trending Hamisana Shear Zone (HSZ), in southeastern Egypt. The HSZ originated after the accretion of the Arabian–Nubian Shield (ANS) and covers an area of about 1500km2 in southeastern Egypt and northeastern Sudan. The architecture of the northern part of the HSZ is best explained as a tectono-stratigraphic column, in which allochthonous ophiolitic mélange was thrusted onto metamorphosed island-arc assemblages (gneisses and amphibolites). The latter rock units were generally subjected to two successive phases of amphibolite facies metamorphism, followed by a thermal phase and retrograde overprint. The early penetrative, low- to medium-pressure metamorphism (M1) was synchronous with D1-gneissosity and N–S trending lineation, demarcating the high strain HSZ. The mineral assemblages formed during the M1 phase include quartz+andesine+hornblende (I)+biotite (I) in hornblende–biotite gneiss, quartz+andesine+pargasitic hornblende (I)+ferroan pargasitic hornblende (I)+edenitic hornblende (I) in hornblende-schist, quartz+plagioclase+biotite+muscovite in psammopelitic gneiss, and diopside+tremolite+calcite+sphene±garnet in calc-silicates, being characteristic for amphibolite facies with metamorphic conditions of 600±50°C and 5–6.5kbar. The second metamorphic phase (M2) is related to the crystallization of biotite and/or hornblende in S2 foliation demarcating the NE–SW trending dextral shear deformation (D2). The calculated temperature for this M2 phase is about 592°C. Subsequent thermal events are documented by growth of spinel and scapolite in calc-silicate rocks and of cordierite in psammopelitic gneiss in response to uplift, decomposition and heat provided by the nearby late-formed igneous intrusions. Finally, the rocks reached a temperature of about 530°C during the cooling retrogressive stage. Based on geological, petrological and geochemical investigations, the island arc assemblages are grouped into: (a) meta-igneous rocks (hornblende–biotite gneiss, biotite gneiss and amphibolites) and (b) metasedimentary rocks (psammopelitic gneiss, hornblende-schist and calc-silicates). Geochemical inspection revealed the non-consanguineous nature of these rock units. They represent subduction-related, theoleiitic and calc-alkaline magmatic rocks and their concomitant sedimentary derivations as well as minor continental shelf calcareous sediments. In terms of maturity, the geochemical signatures of these subduction-related rocks point to an immature volcanic arc origin.

Fluid-induced Dehydration of the Paleoarchean Sand River Biotite-Hornblende Gneiss, Central Zone, Limpopo Complex, South Africa

Fluid-induced Dehydration of the Paleoarchean Sand River Biotite-Hornblende Gneiss, Central Zone, Limpopo Complex, South Africa

Morphometrical analysis of two tropical mountain river basins of contrasting environmental settings, the southern Western Ghats, India

The morphometric analysis of river basins represents a simple procedure to describe hydrologic and geomorphic processes operating on a basin scale. A morphometric analysis was carried out to evaluate the drainage characteristics of two adjoining, mountain river basins of the southern Western Ghats, India, Muthirapuzha River Basin (MRB) in the western slopes and Pambar River Basin (PRB) in the eastern slopes. The basins, forming a part of the Proterozoic, high-grade, Southern Granulite Terrain of the Peninsular India, are carved out of a terrain dominantly made of granite- and hornblende-biotite gneisses. The Western Ghats, forming the basin divide, significantly influences the regional climate (i.e., humid climate in MRB, while semi-arid in PRB). The Survey of India topographic maps (1:50,000) and Shuttle Radar Topographic Mission digital elevation data were used as the base for delineation and analysis. Both river basins are of 6th order and comparable in basin geometry. The drainage patterns and linear alignment of the drainage networks suggest the influence of structural elements. The Rb of either basins failed to highlight the structural controls on drainage organization, which might be a result of the elongated basin shape. The irregular trends in Rb between various stream orders suggest the influence of geology and relief on drainage branching. The Dd values designate the basins as moderate- to well-drained with lower infiltration rates. The overall increasing trend of Rl between successive stream orders suggests a geomorphic maturity of either basins and confirmed by the characteristic Ihyp values. The Re values imply an elongate shape for both MRB and PRB and subsequently lower vulnerability to flash floods and hence, easier flood management. The relatively higher Rr of PRB is an indicative of comparatively steeply sloping terrain and consequently higher intensity of erosion processes. Further, the derivatives of digital elevation data (slope, aspect, topographic wetness index, and stream power index), showing significant differences between MRB and PRB, are useful in soil conservation plans. The study highlighted the variation in morphometric parameters with respect to the dissimilarities in topography and climate.

Redefinition of depositional ages of Neoarchean supracrustal rocks in western Shandong Province, China: SHRIMP U–Pb zircon dating

Western Shandong Province is an important terrane in the eastern part of the North China Craton where 2.75–2.5Ga tectono-thermal events are well recognized. Supracrustal rocks, named the Taishan “Group”, experienced greenschist- to amphibolite-facies metamorphism and occur as lenses and strips in granitoids and are subdivided into the Yanlingguan, Shancaoyu and Liuhang “Formations”. The Yanlingguan “Formation” is mainly composed of amphibolite but also contains fine-grained biotite-hornblende gneiss, komatiitic rocks and schist. The Liuhang “Formation” is similar in rock association to the Yanlingguan “Formation” but contains more metasedimentary rocks. The Shancaoyu “Formation” is mainly composed of fine-grained biotite gneiss (leptynite) preserving bedding and is interlayered with schist. Its protoliths are mainly sedimentary rocks with some mafic to felsic volcano-sedimentary varieties. We undertook SHRIMP zircon dating on eighteen metasedimentary and volcanic samples, mainly from the Shancaoyu “Formation” and the upper part of the Liuhang “Formation”. Ages of detrital and volcanic zircons vary from 2.75 to 2.54Ga and 2.55 to 2.525Ga, respectively, and the age distribution patterns vary in different samples. We conclude that the Shancaoyu “Formation” and the upper part of the Liuhang “Formation” were deposited in the late Neoarchean (2.55–2.525Ga) and not in the early Neoarchean (2.8–2.7Ga) as thought before. Western Shandong is the only terrane in the North China Craton where both early and late Neoarchean supracrustal rocks have been identified. A magmatic arc model may be applied to explain the tectono-thermal evolution at the end of the Neoarchean.

Discrimination of iron ore deposits of granulite terrain of Southern Peninsular India using ASTER data

This work describes a new image processing technique for discriminating iron ores (magnetite quartzite deposits) and associated lithology in high-grade granulite region of Salem, Southern Peninsular India using visible, near-infrared and short wave infrared reflectance data of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). Image spectra show that the magnetite quartzite and associated lithology of garnetiferrous pyroxene granulite, hornblende biotite gneiss, amphibolite, dunite, and pegmatite have absorption features around spectral bands 1, 3, 5, and 7. ASTER band ratios ((1 + 3)/2, (3 + 5)/4, (5 + 7)/6) in RGB are constructed by summing the bands representing the shoulders of absorption features as a numerator, and the band located nearest the absorption feature as a denominator to map iron ores and band ratios ((2 + 4)/3, (5 + 7)/6, (7 + 9)/8) in RGB for associated lithology. The results show that ASTER band ratios ((1 + 3)/2, (3 + 5)/4, (5 + 7)/6) in a Red–Green–Blue (RGB) color combination identifies the iron ores much better than previously published ASTER band ratios analysis. A Principal Component Analysis (PCA) is applied to reduce redundant information in highly correlated bands. PCA (3, 2, and 1 for iron ores and 5, 4, 2 for granulite rock) in RGB enabled the discrimination between the iron ores and garnetiferrous pyroxene granulite rock. Thus, this image processing technique is very much suitable for discriminating the different types of rocks of granulite region. As outcome of the present work, the geology map of Salem region is provided based on the interpretation of ASTER image results and field verification work. It is recommended that the proposed methods have great potential for mapping of iron ores and associated lithology of granulite region with similar rock units of granulite regions of Southern Peninsular India. This work also demonstrates the ability of ASTER’s to provide information on iron ores, which is valuable for mineral prospecting and exploration activities.

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.

Factors controlling fluoride contents of groundwater in north-central and northwestern Sri Lanka

Chemical characterization has been made of groundwater bodies at 294 locations in four village districts in north-central and northwestern Sri Lanka, with special focus on fluorine contamination. High fluoride contents in groundwater are becoming a major problem in the dry zone of Sri Lanka, and dental fluorosis and renal failures are widespread. Field measurements of temperature, pH, and electrical conductivity were made during sampling. Chemical analyses of the water samples were later made using atomic absorption spectroscopy, spectrophotometry, and titration. Fluoride concentrations in the study area vary from 0.01 to 4.34 mg/l, and depend on pH and the concentrations of Na, Ca, and HCO3−. Basement rocks including hornblende biotite gneiss, biotite gneiss, and granitic gneiss seem to have contributed to the anomalous concentrations of fluoride in the groundwater. Longer residence time in aquifers within fractured crystalline bedrocks may enhance fluoride levels in the groundwater in these areas. In addition, elevated fluoride concentrations in shallow groundwater in intensive agricultural areas appear to be related to the leaching of fluoride from soils due to successive irrigation.

Mapping of fluoride ions in groundwater of Dindigul district, Tamilnadu, India—using GIS technique

The accurate information through water quality analysis, scientific study on F − distribution in groundwater and geochemical knowledge with spatial information on geology and climate are necessary to understand the source/cause, type and level of F − contamination. The Dindigul district is a hard-rock terrain and marked as one of the fluoride-rich area in Tamilnadu due to occurrence of various rock types including fluoride-bearing minerals. The F − content of groundwater can thus originate from the dissolution of fluoride-bearing minerals in the bed rock. Eighty-six representative groundwater samples from Dindigul district was collected during two different seasons. Samples were analysed for F −, other major cations and anions. The study area is chiefly composed of hornblende biotite gneiss and charnockite, apart from this untreated tannery effluents also let from many places in the study area. Geographical Information System technique was adopted to study the sources of F −, and it was found that F − in the study is mainly attributed to geogenic source.

SHRIMP Zircon U-Pb Dating of Sapphirine-Bearing Granulite and Biotite-Hornblende Gneiss in the Schirmacher Hills, East Antarctica: Implications for Neoproterozoic Ultrahigh-Temperature Metamorphism Predating the Assembly of Gondwana

Abstract We applied SHRIMP zircon U-Pb age dating to ultrahigh-temperature (UHT) sapphirine-bearing orthopyroxene garnet (SOG) granulite and biotite-hornblende (Bt-Hbl) gneiss in the Schirmacher Hills, East Antarctica. In the Bt-Hbl gneiss, concordant ages of and Ma were obtained from zircon overgrowth rims and zircon cores, with oscillatory and irregular zoning, respectively. The zircon overgrowth rims ( Ma) with low Th/U ratios from the Bt-Hbl gneiss are interpreted as having a metamorphic origin. Oscillatory-zoned and/or irregularly zoned zircon cores may have crystallized during an igneous event at Ma; 800-Ma igneous events have not previously been recognized in central Dronning Maud Land (DML) inland nunatak. Zircons in the SOG granulite yielded a concordant age of Ma, using analyses of sector-zoned and simple-zoned grains. These zircons have relatively high Th/U ratios with a narrow range, and they occur in association with garnet breaking down to form cordierite. The -Ma age obtained from these zir...

Measurement of gamma radiation levels in soil samples from Thanjavur using γ-ray spectrometry and estimation of population exposure

This study assesses the level of terrestrial gamma radiation and associated dose rates from the naturally occurring radionuclides 232Th, 238U and 40K in 10 soil samples collected from Thanjavur (Tamil Nadu, India) using γ-ray spectrometry. The activity profile of radionuclides has clearly showed the existence of low level activity in Thanjavur. The geometric mean activity concentrations of 232Th, 238U and 40K is 42.9±9.4 Bq.kg−1, 14.7±1.7 Bq.kg−1 and 149.5±3.1 Bq.kg−1 respectively are derived from all the soil samples studied. The activity concentration of 232Th, 238U and 40K in soil is due to the presence of metamorphic rocks like shale, hornblende-biotite gneiss and quartzofeldspathic gneiss in these areas. Gamma absorbed dose rates in air outdoors were calculated to be in the range between 32 nGy.h−1 and 59.1 nGy.h−1 with an arithmetic mean of 43.3 ±9 nGy.h−1. This value is lesser than the population weighted world-averaged of 60 nGy.h−1. Inhabitants of Thanjavur are subjected to external gamma radiation exposure (effective dose) ranging between 39.2 and 72.6 μSv.y−1 with an arithmetic mean of 53.1±11 μSv.y−1. The values of the external hazard index determined from the soil radioactivity of the study area are less than the recommended safe levels.

Geoquímica dos ortognaisses do Complexo Região dos Lagos, Araruama-Cabo Frio, Rio de Janeiro, Brasil

The study area is situated on the mid-east part of the Rio de Janeiro state, Brazil, in the Cabo Frio Terrane. This terrane is located on the southeastern extremity of the Ribeira belt, which corresponds to a NE-SW structure composed of thrusts and folds generated during the Brasiliano Orogeny. In this research, the units that constitute the basement of the Cabo Frio terrane, orthogneisses and orthoamphibolites of Região dos Lagos Complex, of Palaeoproterozoic age, were studied based on petrography and geochemistry of the orthogneisses. These are hornblende-biotite gneisses of granodioritic to monzogranitic composition, leucogneisses of granitic composition and biotite gneisses of tonalitic and monzogranitic composition. Chemical data reveal that the orthogneisses have a subalkaline, calc-alkaline character and can be divided into two groups: a) gneisses of intermediate composition and lower K2O values, covering hornblende-biotite gneisses and biotite gneisses of diverse compositions; b) gneisses of acid compositions and relatively higher K2O values, including, predominantly, the granitic leucogneiss. Rare earth element data indicate that not all the samples of the Região dos Lagos Complex are cogenetic, but four different suites can be considered. The four identified groups have geochemical signatures similar to the suites generated in modern compressive tectonic environments, particularly those from the volcanic arcs in Chile. The orthogneisses of the Região dos Lagos Complex are interpreted as the result of mature magmatic arc construction, generated during the Palaeoproterozoic

Geoquímica dos ortognaisses do Complexo Região dos Lagos, Araruama-Cabo Frio, Rio de Janeiro, Brasil

The study area is situated on the mid-east part of the Rio de Janeiro state, Brazil, in the Cabo Frio Terrane. This terrane is located on the southeastern extremity of the Ribeira belt, which corresponds to a NE-SW structure composed of thrusts and folds generated during the Brasiliano Orogeny. In this research, the units that constitute the basement of the Cabo Frio terrane, orthogneisses and orthoamphibolites of Regiao dos Lagos Complex, of Palaeoproterozoic age, were studied based on petrography and geochemistry of the orthogneisses. These are hornblende-biotite gneisses of granodioritic to monzogranitic composition, leucogneisses of granitic composition and biotite gneisses of tonalitic and monzogranitic composition. Chemical data reveal that the orthogneisses have a subalkaline, calc-alkaline character and can be divided into two groups: a) gneisses of intermediate composition and lower K 2 O values, covering hornblende-biotite gneisses and biotite gneisses of diverse compositions; b) gneisses of acid compositions and relatively higher K 2 O values, including, predominantly, the granitic leucogneiss. Rare earth element data indicate that not all the samples of the Regiao dos Lagos Complex are cogenetic, but four different suites can be considered. The four identified groups have geochemical signatures similar to the suites generated in modern compressive tectonic environments, particularly those from the volcanic arcs in Chile. The orthogneisses of the Regiao dos Lagos Complex are interpreted as the result of mature magmatic arc construction, generated during the Palaeoproterozoic.

Metamorphic evolution of Neoproterozoic metapelites and gneisses in the Sinai, Egypt: Insights from petrology, mineral chemistry and K–Ar age dating

Petrology, mineral chemistry, and age dating of the metapelitic schists and gneisses in three metamorphic complexes of Sinai have been studied and reported with the aims of characterizing the nature, type, and age of metamorphism as well as the metamorphic evolution of the Sinai metamorphic complexes. Nine representative samples of metapelitic schists, migmatites, and gneisses from the Taba Metamorphic Complex (TMC), the Kid Metamorphic Complex (KMC) and the Feiran-Solaf Metamorphic Complex (FSC) in southern Sinai Peninsula have been analyzed by electron microprobe for their mineral assemblages and K–Ar geochronological methods for biotite separates. Garnet from the metapelites and migmatites are almandine-rich and usually show zoning with variable X Fe values. The estimated P–T metamorphic conditions of the TMC range from 560–578 °C/3–4.5 kbar for the metapelitic schists, to 685 °C/5.3 kbar for the migmatites, while those for the metapelitic schists in the KMC are 590 °C/4–5.9 kbar in the Umm Zariq Formation, and 636 °C/4.7 kbar in the northern part of the Malhaq Formation. The P–T metamorphic conditions of the hornblende–biotite gneisses from the SZ of the FSC are 634–641 °C/4–5 kbar. These P–T conditions and mineral assemblages indicate amphibolite facies conditions of the LP/HT-type of metamorphism. The K–Ar biotite cooling ages range from 594 to 617 Ma for the TMC, from 593 to 609 Ma for the KMC, and from 589 to 602 Ma for the FSC. It could be suggested that the cooling metamorphic ages of all complexes lie at approximately 600 Ma, and thus point to a uniform and single metamorphic event for the whole complexes in the southern Sinai Peninsula. The estimated geothermal gradient is in the range of 30–50 °C/km. Such a steep gradient and the LP/HT mineral assemblages suggest that they were formed in an extensional setting and a heat flow was transferred from nearby granite intrusions.

Geochemical and K–Ar age constraints on the Late Neoproterozoic (?) gneisses at Um Tenassib area, north Eastern Desert, Egypt

Wadi Um Tenassib metamorphic rocks consist mainly of biotite gneiss and biotite-hornblende gneiss with subordinate intercalations of amphibolite, migmatitic gneiss, and aplitic granite. Biotite-hornblende gneiss, biotite gneiss, and aplitic granite are geochemically characterized and their cooling ages are determined by using the K–Ar method on biotite. The Um Tenassib gneisses (UTG) range in composition from quartz diorite/monzodiorite to granodiorite. They were derived from igneous rocks that pertain to calc alkaline and metaluminous to weakly peraluminous affinities and were generated in continental volcanic arc setting. REE patterns of the UTG are moderately fractionated (La N/Lu N = 5.9–7.5) relative to those of the aplitic granite (La N/Lu N = 33). The similarity in the geochemical characteristics and REE patterns of both gneiss types indicate their magmatic consanguinity. Amphiboles of the UTG biotite-hornblende gneisses are mainly hornblende, together with few paragasitic hornblende and edenite. Plagioclase composition is oligoclase to andesine (An 21–46) in the biotite-hornblende gneiss, and oligoclase (An 11–26) in the biotite gneiss. Mineral chemistry of amphibole and plagioclase indicate that the gneisses were metamorphosed under low- to medium-pressure of 2.6–6.4 kbar and at medium to high temperatures of 660–755 °C. The K–Ar biotite cooling ages (seven samples) range from 585 ± 12 Ma to 598 ± 12 Ma for the UTG, except one biotite-hornblende gneiss sample gives age of 577 ± 11 Ma. These ages suggest a latest metamorphic cooling event at ca. 585–600 Ma time span, which is consistent with the proposed cooling ages of ∼600 Ma for the Elat metamorphic rocks [Cosca, M.A., Shimron, A., Caby, R., 1999. Late Precambrian metamorphism and cooling in the Arabian–Nubian Shield: petrology and 40Ar/ 39Ar geochronology of metamorphic rocks of the Elat area (southern Israel). Precamb. Res. 98, 107–127]. It may indicate that the metamorphism of the UTG might have been contemporaneous with the suggested regional metamorphism at 620 ± 10 Ma for Sinai metamorphic rocks (Cosca et al., 1999) and/or the emplacement age at 614 Ma for the granodiorite in the study area [Stern, R.J., Hedge, C.E., 1985. Geochronological and isotopic constraints on the Late Precambrian crustal evolution in the Eastern Desert of Egypt. Am. J. Sci. 285, 97–127]. These ages also lie within the range of magmatic activity of the Younger Granites in the North Eastern Desert (575–600 Ma).

Delineation of ground water potential zones in a hard rock terrain of Mysore district, Karnataka using IRS data and GIS techniques

In the present study, the ground water prospect of Mysore district has been delineated using remotely sensing data, base map of GSI, ground truth data, and geographic information system. Based on these integrated studies, it has been noticed that the lithology of the area mainly represents by amphibolite schists, hornblende-biotite gneiss, chamockite, quartzite and granite belonging to Archean to Lower Proterozoic. Resent alluvial deposits mainly occur as valley fills. Major lineaments are mainly confined to valley regions. Structurally the erosional and depositional landforms are occurring as hills, ridges, weathered pediments, weathered pediplains and valley fills. Geonaorphology, lineaments, drainage density, type of lithology and surface water bodies are directly influencing the ground water conditions and it is very good iu valley regions and in remaining area, it is moderate to poor.

Neoproterozoic–Early Paleozoic gravitational tectonic collapse in the southern part of the Arabian-Nubian Shield: The Bulbul Belt of southern Ethiopia

We present new structural and metamorphic data from the Bulbul Belt in southern Ethiopia indicating that the latest phase of the Neoproterozoic evolution of the southern part of the Arabian-Nubian Shield is characterized by the development of low-angle oblique normal-slip shear zones manifesting regional gravitational tectonic collapse. The ∼100 km long, ∼1–5 km wide, N-trending Chulul Shear Zone which represents the southern part of the Bulbul Shear Zone is characterized by the presence of moderately E-dipping mylonitic fabric, SE-plunging stretching lineation and kinematic indicators showing top-to-the-southeast tectonic transport. This shear zone separates the structurally and metamorphically contrasting Melka Guba Domain (the southern extension of the Alghe terrane) in the west from the Chulul Domain (the southern extension of the Bulbul terrane) to the east. The Melka Guba Domain comprises migmatites, hornblende–biotite gneisses and quartzo-feldspathic gneisses with metamorphic assemblages that indicate upper amphibolite metamorphism ( T of ∼650 °C and P of ∼6 kbar). In addition, the Melka Guba Domain preserves E-W trending relic gneissic and migmatitic layering that is not evident elsewhere in the region. This older planar fabric is discordantly overprinted by a regional gneissic and migmatitic layering that was subsequently folded about NNE-trending upright folds. The Chulul Domain, on the other hand, is dominated by amphibolite schist, mafic and ultramafic rocks and meta-diorites interpreted as an island arc-ophiolitic-plutonic assemblage. Metamorphic mineral assemblages in the Chulul Domain suggest greenschist facies metamorphism ( T of ∼450 °C and P of ∼3 kbar). Deformation in the Chulul Domain is dominated by N-trending schistosity similar in orientation to that in the Melka Guba Domain to the west. We explain these structural and metamorphic contrasts using a model of gravitational tectonic collapse (∼550–500 Ma) involving detachment along the Chulul Shear Zone. The collapse follows the collision between the Melka Guba and the Chulul Domains at ∼820–580 Ma after the consumption of a possibly E-dipping subduction zone. Our model offers little support to the theory that the Neoproterozoic N-trending belts in southern Ethiopia were roots of northward expulsion of the Arabian-Nubian Shield from the Mozambique Belt.

The Kwyjibo Cu-REE-U-Au-Mo-F Property, Quebec: A Mesoproterozoic Polymetallic Iron Oxide Deposit in the Northeastern Grenville Province

The Kwyjibo deposit is the most significant of a number of examples of the iron oxide-copper-gold class of deposits to have been found in the Grenville. It is a Mesoproterozoic Cu-REE-Mo-F-U-Au iron oxide occurrence located approximately 120 km northeast of Sept-Iles, Quebec. The deposit, which comprises different textural facies of magnetite and hematite mineralization, occurs along the southeast margin of the Canatiche granitic complex. Porphyroidal leucogranite and volcanic equivalents of the Canatiche Complex are the main hosts of the mineralization. Calc-silicate rock and hornblende-biotite gneiss, possibly belonging to the supracrustal Manitou Complex, flank the deposit to the southeast and south. Magnetite is ubiquitous in the Canatiche granitoids and generally occurs as disseminations and fine agglomerations. Near the deposit, magnetite becomes progressively more abundant, forming veinlets, veins, stockworks, and pseudobreccias, culminating in locally brecciated massive magnetite, the dominant type of iron oxide concentration. Specular hematite occurs locally as disseminations and veinlets. Mineralization at Kwyjibo is complex and multiphase and is divided into early granophile, magnetite, main polymetallic, and specular hematite stages. The main polymetallic mineralization, comprising chalcopyrite, pyrite, molybdenite, fluorite, and REE-bearing minerals, is superimposed on preexisting magnetite-rich rocks and shows little evidence of deformation. The Kwyjibo deposit has a number of features in common with other polymetallic iron oxide deposits around the world, including granitic host rocks of within-plate affinity, various textural facies of iron oxide mineralization styles, and sodic and potassic alteration zones. A close spatial association with a major deep seated structure is also postulated. The Grenville province hosts a major anorthosite belt and is a world-class titaniferous metallogenic province. The Proterozoic era, and especially its anorogenic periods, are the main metallogenic epochs both for iron oxide-copper-gold deposits and anorthosite-hosted Ti-rich iron oxide deposits. Empirical observations suggest a possible petrogenetic relationship between these two important ore deposit types.