Gneissic Rocks Research Articles

Origin of radon concentration of Csalóka Spring in the Sopron Mountains (West Hungary)

We examined the Csalóka Spring, which has the highest radon concentration in the Sopron Mountains (West Hungary) (, yearly average of 227 ± 10 Bq L−1). The main rock types here are gneiss and micaschist, formed from metamorphism of former granitic and clastic sedimentary rocks respectively. The aim of the study was to find a likely source of the high radon concentration in water.During two periods (2007–2008 and 2012–2013) water samples were taken from the Csalóka Spring to measure its radon concentration (from 153 ± 9 Bq L−1 to 291 ± 15 Bq L−1). Soil and rock samples were taken within a 10-m radius of the spring from debrish and from a deformed gneiss outcrop 500 m away from the spring. The radium activity concentration of the samples (between 24.3 ± 2.9 Bq kg−1 and 145 ± 6.0 Bq kg−1) was measured by gamma-spectroscopy, and the specific radon exhalation was determined using radon-chamber measurements (between 1.32 ± 0.5 Bq kg−1 and 37.1 ± 2.2 Bq kg−1). Based on these results a model calculation was used to determine the maximum potential radon concentration, which the soil or the rock may provide into the water. We showed that the maximum potential radon concentration of these mylonitic gneissic rocks (cpot = 2020 Bq L−1) is about eight times higher than the measured radon concentration in the water. However the maximum potential radon concentration for soils are significantly lower (41.3 Bq L−1) Based on measurements of radon exhalation and porosity of rock and soil samples we concluded that the source material can be the gneiss rock around the spring rather than the soil there.We determined the average radon concentration and the time dependence of the radon concentration over these years in the spring water. We obtained a strong negative correlation (−0.94 in period of 2007–2008 and −0.91 in 2012–2013) between precipitation and radon concentration.

MICROMORPHOLOGY AND PEDOGENESIS OF MOUNTAINOUS INCEPTISOLS IN THE MANTIQUEIRA RANGE (MG)

ABSTRACTUnderstanding soil formation processes across different landscapes is needed to predict how soil properties will respond to land use change. This study aimed to characterize mountainous Inceptisols (Cambisols) under high altitude subtropical climate in southeastern Brazil, by soil physical, chemical and micromorphological analyses, under native forest and pasture. The soil under pasture had a greater bulk density than under forest, resulting in a severe reduction of macroporosity. At two depths, coarse quartz grains are angular, suggesting absence of transportational processes, thus confirming an autochthonous pedogenesis from the underlying gneissic rock. Most feldspars were weathered beyond recognition, but mineral alteration was commonly seen across cleavage plans and edges of micas. The micromorphological results suggest an intermediate stage of mineral weathering and soil development, which is in accordance with properties expected to be found in Inceptisols.

The installation campaign of 9 seismic stations around the KTB site to test anisotropy detection by the Receiver Function Technique

Abstract. The project at hand is a field test around the KTB (Kontinentale Tiefbohrung) site in the Oberpfalz, Southeastern Germany, at the northwestern edge of the Bohemian Massif. The region has been extensively studied through the analysis of several seismic reflection lines deployed around the drilling site. The deep borehole had been placed into gneiss rocks of the Zone Erbendorf-Vohenstrauss. Drilling activity lasted from 1987 to 1994, and it descended down to a depth of 9101 m. In our experiment, we aim to recover structural information as well as anisotropy of the upper crust using the receiver function technique. This retrieved information is the basis for comparing the out-coming anisotropy amount and orientation with information of rock samples from up to 9 km depth, and with high-frequency seismic experiments around the drill site. For that purpose, we installed 9 seismic stations, and recorded seismicity continuously for two years from June 2012 to July 2014.

Solos: Subsídio Para Estudos de Geologia de Engenharia

The objective of this paper was to discuss in simplified and multidisciplinary terms and through an engineering geology point of view the different variables related to the development of residual, transported, organic, expansive and lateritic soils, contributing to standardize concepts of geotechnical interest mineralogical and chemical data from five profiles whose respective saprolitic soils were formed by the action of weathering processes on gneissic metamorphic rocks in tropical and subtropical climatic environment were presented and discussed. The residual soils developed from these rock, besides the great abundance in the state of Rio de Janeiro, have thicknesses greater than 10 meters, being associated with large landslides and mass movements occurred in the last 50 years both in that state and in others. The article emphasizes finally that the presence of relict heterogeneities in saprolitic soils and saprock inherited from their source rocks should not be discarded in the analysis of slope stability and foundations projects.

Relationship between groundwater chemistry and the Precambrian basement rocks on eastern Bornholm, Denmark

Bornholm is situated south of Sweden, in the Sorgenfrei–Tornquist Zone (Fig. 1). The Precambrian basement on northern and eastern Bornholm consists of different types of granitic and gneissic rocks with pegmatites, aplites and dolerite dykes (Callisen 1934). The age of the granite and gneiss is c. 1455 Ma (Waight et al. 2012).

Aquifer assessment for agriculture through geophysical, hydrochemical and hydrogeological approaches around Perumattunallur lake, Southern India

This study mainly focused on aquifer assessment using 2-D Electrical Resistivity Imaging (ERI), hydrochemical, Geographic Information System (GIS)-based analysis and aquifer yield test for agriculture around Perumattunallur lake, Southern India. It comprises on quantifying aquifer thickness and yields with groundwater quality. The 2-D ERI technique was an attempt to study the geological structural and compare with borewell lithologs. The litho units encompass clay, calcrete weathered gneiss rock and charnockites. It shows that the resistivity of the top layer covered by clay/calcrete with kankar ranges of 1–12 Ωm followed by fine sand with a resistivity range of (10–20 Ωm) and calcrete mixed with gneissic rocks with a resistivity range of 20–120 Ωm. The massive charnockite with a resistivity range of >200 Ωm is observed in the hill ranges, present in the NE–SW direction. The hydrochemical study was attempted for the parameters (i.e., TDS, pH, Na+, K+, Ca2+, Mg2+ and Cl−) from bore well water samples briefly displayed by GIS-based geospatial analysis. The geochemical facies analysis of rock–water interaction study was used for the groundwater quality for agriculture. The pumping test helped to determine the aquifer yields with exact determination of the estimation of groundwater supply for agricultural use. The NW side of the wall is a high yield of water discharge from the lake. The average water yield of the study area is about 245.8 m3/day in summer and 310.6 m3/day in winter through the selected 7 bore wells. The alluvium clay with a calcrete layer occurs at the SE part and the results show as a low yield due to poor porosity. The radius influence of each well to be taken as 150 m was identified using the pumping test. The pumping test gives details about an aquifer of leaky aquifer with complex structure of gneissic rock with fracture/fault zone help for aquifer types. The results of the geophysical, hydrochemical and water yield test are used for groundwater quality and quantity for agriculture purpose and domestic use for the sustainable development of groundwater resources in the surroundings of the lake.

Trace-element fingerprints of chromite, magnetite and sulfides from the 3.1 Ga ultramafic–mafic rocks of the Nuggihalli greenstone belt, Western Dharwar craton (India)

The 3.1 Ga Nuggihalli greenstone belt in the Western Dharwar craton is comprised of chromitite-bearing sill-like ultramafic–mafic rocks that are surrounded by metavolcanic schists (compositionally komatiitic to komatiitic basalts) and a suite of tonalite–trondhjemite–granodiorite gneissic rocks. The sill-like plutonic unit consists of a succession of serpentinite (after dunite)–peridotite–pyroxenite and gabbro with bands of titaniferous magnetite ore. The chromitite ore-bodies (length ≈30–500 m; width ≈2–15 m) are hosted by the serpentinite–peridotite unit. Unaltered chromites from massive chromitites (>80 % modal chromite) of the Byrapur and Bhaktarhalli chromite mines in the greenstone belt are characterized by high Cr# (100Cr/(Cr + Al)) of 78–86 and moderate Mg# (100 Mg/(Mg + Fe2+)) of 45–55. In situ trace-element analysis (LA-ICPMS) of unaltered chromites indicates that the parental magma of the chromitite ore-bodies was a komatiite lacking nickel-sulfide mineralization. In the Ga/Fe3+# versus Ti/Fe3+# diagram, the Byrapur chromites plot in the field of suprasubduction zone (SSZ) chromites while those from Bhaktarhalli lie in the MOR field. The above results corroborate our previous results based on major-element characteristics of the chromites, where the calculated parental melt of the Byrapur chromites was komatiitic to komatiitic basalt, and the Bhaktarhalli chromite was derived from Archean high-Mg basalt. The major-element chromite data hinted at the possibility of a SSZ environment existing in the Archean. Altered and compositionally zoned chromite grains in our study show a decrease in Ga, V, Co, Zn, Mn and enrichments of Ni and Ti in the ferritchromit rims. Trace-element heterogeneity in the altered chromites is attributed to serpentinization. The trace-element patterns of magnetite from the massive magnetite bands in the greenstone belt are similar to those from magmatic Fe–Ti–V-rich magnetite bands in layered intrusions, and magnetites from andesitic melts, suggesting that magnetite crystallized from an evolved gabbroic melt. Enrichments of Ni, Co, Te, As and Bi in disseminated millerite and niccolite occurring within chromitites, and in disseminated bravoite within magnetites, reflect element mobility during serpentinization. Monosulfide solid solution inclusions within pyroxenes (altered to actinolite) in pyroxenite, and interstitial pyrites and chalcopyrites in magnetite, retain primary characteristics except for Fe-enrichment in chalcopyrite, probably due to sub-solidus re-equilibration with magnetite. Disseminated sulfides are depleted in platinum-group elements (PGE) due to late sulfide saturation and the PGE-depleted nature of the mantle source of the sill-like ultramafic–mafic plutonic rocks in the Nuggihalli greenstone belt.

The multi-stage tectonic evolution of the Xitieshan terrane, North Qaidam orogen, western China: From Grenville-age orogeny to early-Paleozoic ultrahigh-pressure metamorphism

The geodynamic evolution of the early Paleozoic ultrahigh-pressure metamorphic belt in North Qaidam, western China, is controversial due to ambiguous interpretations concerning the nature and ages of the eclogitic protoliths. Within this framework, we present new LA-ICP-MS U–Pb zircon ages from eclogites and their country rock gneisses from the Xitieshan terrane, located in the central part of the North Qaidam UHP metamorphic belt. Xitieshan terrane contains clearly different protolith characteristics of eclogites and as such provides a natural laboratory to investigate the geodynamic evolution of the North Qaidam UHP metamorphic terrane. LA-ICP-MS U–Pb zircon dating of three phengite-bearing eclogites and two country rock gneiss samples from the Xitieshan terrane yielded 424–427Ma and 917–920Ma ages, respectively. The age of 424–427Ma from eclogite probably reflects continental lithosphere subduction post-dating oceanic lithosphere subduction at ~440–460Ma. The 0.91–0.92Ga metamorphic ages from gneiss and associated metamorphic mineral assemblages are interpreted as evidence for the occurrence of a Grenville-age orogeny in the North Qaidam UHPM belt. Using internal microstructure, geochemistry and U–Pb ages of zircon in this study, combined with the petrological and geochemical investigations on the eclogites of previous literature’s data, three types of eclogitic protoliths are identified in the Xitieshan terrane i.e. 1) Subducted early Paleozoic oceanic crust (440–460Ma), 2) Neoproterozoic oceanic crust material emplaced onto micro-continental fragments ahead of the main, early Paleozoic, collision event (440–420Ma) and 3) Neoproterozoic mafic dikes intruded in continental fragments (rifted away from the former supercontinent Rodinia). These results demonstrate that the basement rocks of the North Qaidam terrane formed part of the former supercontinent Rodinia, attached to the Yangtze Craton and/or the Qinling microcontinent, and recorded a complex tectono-metamorphic evolution that involved Neoproterozoic and Early Paleozoic orogenies.

Hydrogeochemistry of high fluoride groundwater in hard rock aquifer in a part of Dharmapuri district, Tamil Nadu, India

Fluoride is one of the important ions that affect the groundwater quality. F− concentration above 1.5 mg/L in drinking water affects teeth and bones of humans. Usually the F− concentration in groundwater is controlled by local geological setting and climatic condition of an area. The present study aims to assess the hydrogeochemistry of groundwater in Vaniyar River basin, Dharmapuri district and to understand the F− abundance in groundwater. Forty four representative groundwater samples were collected for once in two months and analyzed for major cations and anions using ion chromatograph. The general order of the dominance of major cations is Na+ > Ca2+ > Mg2+ > K+ and that of major anions is Cl− > HCO 3 − > SO 4 2− > CO 3 − > F−. Most of the samples are Na-Cl type and few are Ca-Mg-Cl and Ca-Cl types. The F− concentration in groundwater of this region ranges from 0.15 to 6.48 mg/L and many of the residents are affected by dental and skeletal fluorosis. The arid climatic conditions of the region, dominance of gneissic rocks and the low freshwater exchange due to periodical drought conditions endorse the presence of high F− concentration in the groundwater of the area.

The affinity of Archean crust on the Yilgarn—Albany–Fraser Orogen boundary: Implications for gold mineralisation in the Tropicana Zone

Craton margins can be subject to a wide array of gold genesis and redistribution processes, although high-grade terrains on craton margins are frequently viewed as less prospective than lower-grade counterparts. In contrast to this, the high-grade Tropicana Zone, a newly defined Archean crustal component on the eastern margin of the Yilgarn Craton within the Albany–Fraser Orogen (AFO), contains a significant Proterozoic gold deposit. This deposit and zone comprise mid-amphibolite to granulite-facies gneissic rocks with evidence of partial melting and granite injection. The Tropicana Zone contains significant low-Si, LILE-enriched, granites classed as sanukitoids. Along with the distinctive compositions, the rarity of these rocks within any Archean craton suggests that the granitoid protoliths represent a single suite, emplaced during one event.Due to the intense granulite-facies overprinting of the Tropicana Zone rocks, determination of the magmatic protolith age for these sanukitoids is challenging. Nonetheless, the best age estimate for magmatism is 2692±16 Ma, based on the youngest zircons preserving textural evidence of growth within a viscous silicate melt. This age is older than compositionally similar magmatism found within the Yilgarn Craton, although a sanukitoid in the Northern Foreland of the AFO has a similar age. Furthermore, the granulite-facies metamorphic zircon growth in the Tropicana Zone at 2718–2554 Ma was prolonged compared to that in the Yilgarn Craton. Nonetheless, the Hf isotopic signature of the Tropicana Zone zircon shares strong similarity to that from the Eastern Goldfields Superterrane of the Yilgarn Craton. This implies that the Tropicana Zone reflects a deeper crustal level of the Yilgarn Craton, exhumed and thrust NW an unknown distance over the craton edge. In addition, we observe that the granulite-facies zircons have a less radiogenic Hf-isotope signature than the preserved pre-metamorphic zircon cores. Based on correlations with alpha dose, U and Th content and 176Hf/177Hf we suggest this reflects the preferential destruction and release of unradiogenic Hf from inherited zircon whereas the protolith sanukitoid zircon, with lower U and Th content, was more resistant to mobilisation during high-grade metamorphism. We note this situation may be a more general response of the Hf isotopic system, in which zircon grown in a more mafic melt is less likely to contribute to the metamorphic Hf reservoir than its felsic counterpart.Juvenile granitic veins dated at c. 1780 Ma intruded into the Tropicana Zone indicate that the Tropicana Zone was structurally emplaced at or before c. 1780 Ma, given similar Proterozoic magmatic events are well documented from (para)autochthonous adjacent units. Re–Os dating of pyrite coeval with one generation of gold in these rocks indicates model ages of c. 2100 Ma, supportive of a Palaeoproterozoic age of mineralisation. This mineralisation event is distinct from major Proterozoic tectonothermal events elsewhere in the AFO. Sanukitoid magmas are well-known for gold fertility and were likely the original source of gold in the Tropicana Zone, which was subsequently concentrated into brittle structures during several episodes. Gold mineralisation post-dated peak metamorphic conditions and is significantly younger than gold mineralisation within other parts of the adjoining Yilgarn Craton.

The Nickeliferous Archean Madziwa Igneous Complex, Northern Zimbabwe: Petrological Evolution, Magmatic Architecture, and Ore Genesis

The nickeliferous Madziwa Igneous Complex consists of several lenticular, mafic-ultramafic enclaves within late Archean gneissic terrain. The lenses of igneous rock are locally deformed and metamorphosed to lower greenschist grade. They are here interpreted to be remnants of a large, composite, magmatic structure with two main components: (1) a set of narrow (10s–100s of meters wide) dikes intruding the gneissic foliation, and (2) a large lopolith made up of leuconorite. Some dikes contain a differentiated and vertically oriented layered suite comprising a central pyroxenite layer, plus norite as both a continuous marginal layer and intermittent layers within the pyroxenite. The pyroxenite-norite suite has a preliminary U-Pb zircon age of 2684 Ma. Other dikes are made up of diorite and/or ferrodiorite; in places, the dioritic rocks also intrude the pyroxenite-norite suite. The leuconorite lopolith transects both the dikes and the gneissic country rocks, its basal contacts with the pyroxenite-norite suite varying locally from intrusive to gradational to (magmatic) erosional. Although modified in places by secondary mobilization, disseminated Ni-Cu sulfides are primarily hosted within the central (ortho- to mesocumulate) pyroxenite adjacent to internal norite layers. Whole-rock geochemical data establish the comagmatic origin of the principal rock types and indicate an Archean, D-type, basaltic source magma with ca. 8% MgO, the two dioritic rock types representing late, immiscible, silica- and Fe-Ti-P-rich derivatives of pyroxenite-norite(-leuconorite) crystallization. In addition to the major rock types, peridotites occur in several outlying dikes and may represent fractionates of a komatiitic precursor to the basalt. Geologic and geochemical evidence points to bulk assimilation of country rock gneiss by the Madziwa magma and sulfide segregation triggered by felsic contamination. These processes did not occur locally within the dikes but rather in the conduit system prior to the emplacement of the magma charged with sulfide droplets. The unusual vertical layering of the pyroxenite-norite sequence and the localization of the sulfide ores are attributed to the strong outward, cooling gradient across such narrow dikes and to large-scale, lateral movement of sulfide droplets through the solidifying, pyroxene crystal framework ahead of an advancing postcumulus plagioclase crystallization front.

Multi-element variations in olivine as geochemical signatures of Ni-Cu sulfide mineralization in mafic magma systems—examples from Voisey’s Bay and Pants Lake intrusions, Labrador, Canada

Olivine from the olivine gabbro to troctolite intrusions at Voisey’s Bay and at Pants Lake, Labrador, was analyzed for multiple elements (Ca, Sc, Mg, Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Y, and Zr) with secondary ion mass spectrometry (SIMS). Both intrusions have similar lithologies and petrographic characteristics and are approximately coeval (1.34 and 1.32 Ga, respectively) members of the Mesoproterozoic Nain Plutonic Suite. The Voisey’s Bay intrusion hosts a producing economic Ni-Cu sulfide deposit, whereas the Pants Lake intrusion displays evidence of Ni-Cu sulfide mineralization, but, to date, a viable ore deposit has not been discovered. Olivine from both barren and mineralized lithologies was analyzed to assess the potential of the olivine composition for providing a record of silicate melt evolution and sulfide saturation related to formation of a massive sulfide deposit. Two detailed transects were sampled, using five diamond drill holes that laterally approach the basal massive sulfide in the Eastern Deeps portion of the Voisey’s Bay intrusion from the barren central part. Olivine displays distinct trace element distributions that vary coherently with host lithology and proximity to sulfide mineralization. In particular, olivine shows an increase in Fe (∼Fo80 to ∼Fo60), Mn (∼2500 to 5000 ppm), and Zn (∼280 to 700 ppm), generally coupled with a decrease in Ni (∼1600 to ∼900 ppm), Co (∼270 to ∼190 ppm), and Cr (∼110 to 45 ppm), from barren troctolite (normal troctolite—NT) and weakly mineralized troctolite (variable-textured troctolite—VTT) towards the heavily mineralized, brecciated basal succession (basal breccia sequence—BBS). The enrichment in Fe-Mn-Zn is most pronounced in samples that laterally approach, but do not directly intersect, the massive sulfide deposit at the base of the intrusion, particularly in samples from the lower variable-textured troctolite and the basal breccia. Olivine from gabbro lithologies within the basal gabbro (BG) and upper gabbro (UG) of the Pants Lake intrusion is fairly homogeneous (∼Fo60, ∼4300 ppm Mn, ∼460 ppm Zn, ∼340 ppm Ni, ∼50 ppm Cr), with a more evolved composition (∼2100 ppm Ca, ∼20 ppm Sc, ∼300 ppm Ti, ∼4 ppm Y) than the average olivine of the Voisey’s Bay intrusion (∼570 ppm Ca, ∼6 ppm Sc, ∼65 ppm Ti, ∼0.3 ppm Y). Pants Lake olivine also commonly lacks the mutually Mn-Zn-rich signature of olivine from the basal breccia at Voisey’s Bay that is characteristic of contamination of the parent magma by country rock gneiss, and there reflects a close proximity to massive sulfides. In conjunction with petrographic observation and the stratigraphic context, a multiple-element (V-Cr-Mn-Fe-Co-Ni-Zn) regression can be applied to calculate a lateral proximity of olivine to massive sulfide mineralization in the Eastern Deeps part of the Voisey’s Bay intrusion, over a distance exceeding 150 m. The compositional variations in olivine from the economic Voisey’s Bay intrusion (bimodal and primitive) and the mainly barren Pants Lake intrusion (homogeneous and evolved) provide potential as a regional-scale mineralogical fertility indicator for mafic intrusions with comparable types of sulfide mineralization.

Temperature and pH dependent geochemical modeling of fluoride mobilization in the groundwater of a crystalline aquifer in southern India

The present research should assess the high F− concentration evaluating geochemical parameters such as pH and T, in Tirupattur groundwater, South India. For this purpose, groundwater samples were collected from the shallow wells in the study area and analyzed to detect the concentrations of the fluoride and major ions. Results show that a high percentage (60%) of samples has F− concentration greater than 1.5mg/L. The major aqueous species in groundwater are Na+ and HCO3−. The observed positive correlation for F− with pH, Na+, and HCO3− and the negative correlation with Ca suggest their influence on fluoride geochemistry. Evaluation source of these ions indicates that silicate minerals present in the granitic and gneissic rocks are the major origin of F−. The effect of dissolution of evaporates and carbonate is found to be insignificant. However, cation exchange is influencing the Na/Ca ratio in few samples. Aqueous speciation modeling has been developed using PHREEQC. Results indicate that groundwater dissolves more F− minerals provided by Na excess. Further geochemical modeling with variable temperature and pH proved that increase in these parameters changes the chemical kinetics in favor of F− enrichment in groundwater. Considering the temperature range (18.2 to 36.8°C) and alkaline pH along the study area, the high concentrations of Na+ and HCO3− are the major factors determining the release of F− from minerals such as amphibole, biotite, fluorite and apatite in the crystalline formations.

The influence of bedrock geology and slip surface characteristics on failure mode and mobility: a comparative study of instability patterns in Nigeria

The correlation among bedrock, regolith properties, groundwater table, and slip surface character and their combined effects on the mode and scale of landslides were evaluated. Standard penetration test, laboratory, and DEM-based analyses were integrated to study igneous, metamorphic, and sedimentary areas where instability was common. A clear pattern of the distribution of translational and rotational slides, and their pre- and post-failure mechanisms were established. It was found that factors such as climate, vegetation types and density, tectonic setting, and catchment area were generally similar. The key differences were in the dissimilar underlying bedrock types which weathered to yield soils with distinctive engineering property and in the nature of the sliding surfaces. Whereas the weathering of granitic and gneissic rocks (where groundwater table was 7 m) produced less compressible, fairly-sorted, porous materials. The hydraulic conductivity of the granitic and gneissic-derived soils decreased with depth. At saturation levels above a threshold, the soils derived from the igneous and metamorphic rocks contracted and generated positive pore pressure. Movement on discrete, planar, slicken-sided, fractured, and foliated slip surfaces transformed the slides to flow (translational failures). On the contrary, pronounced dilation and negative pore-water developed in the more porous, less crushable soils from the sedimentary area leading to the dominance of rotational slumps in this region of active erosion.

Functional ecology as a missing link for conservation of a resource-limited flora in the Atlantic forest

The Atlantic forest is among the hottest hotspots for biodiversity conservation. Within this biome, inselbergs are isolated granitic and gneiss rocks that rise sharply above the lowland surrounding forests. Due to prevailing stressful conditions and resource paucity of inselbergs, distinguished plant communities are formed in these rocky-associated vegetation, which comprise unusually high levels of endemic and threatened species. Here, we evaluated the importance of competitiveness:stress-tolerance:ruderalism ecological strategies in different vegetation patches on the inselberg, tested for a connection between patch structure and functional traits, and compared the variation in functional traits between native and an exotic species, which represents a major threat to inselberg communities. Despite the stressful conditions of inselbergs, we found a relatively high diversity of ecological strategies, but most species and patches lied between the S and C strategy. The invasive Melinis repens, in turn, was functionally distinctive from native communities, with the predominance of traits associated with ruderalism. We also found that most functional traits significantly correlated with at least one environmental driver, highlighting their role in structuring plant communities in this heterogeneous environment. Since inselberg patches were spatially heterogeneous, and the variation in resource availability implies in favouring different ecological strategies, some patch types were more invasive-prone than others. Our data provide significant advances for identifying the environmental drivers of biological invasion in resource-limited environments. We argue that further trait-based approaches will become critical for developing conservation and management strategies for inselberg plant communities, especially in the context of rapid habitat loss and fragmentation of the Atlantic forest.

Coupling geomorphology parameters with lithology for micro-level groundwater resource assessment: a case study from semi-arid hard rock terrain in Tamil Nadu, India

The standard procedure of groundwater resource estimation in India till date is based on the specific yield parameters of each rock type (lithology) derived through pumping test analysis. Using the change in groundwater level, specific yield, and area of influence, groundwater storage change could be estimated. However, terrain conditions in the form of geomorphological variations have an important bearing on the net groundwater recharge. In this study, an attempt was made to use both lithology and geomorphology as input variables to estimate the recharge from different sources in each lithology unit influenced by the geomorphic conditions (lith-geom), season wise separately. The study provided a methodological approach for an evaluation of groundwater in a semi-arid hard rock terrain in Tirunelveli, Tamil Nadu, India. While characterizing the gneissic rock, it was found that the geomorphologic variations in the gneissic rock due to weathering and deposition behaved differently with respect to aquifer recharge. The three different geomorphic units identified in gneissic rock (pediplain shallow weathered (PPS), pediplain moderate weathered (PPM), and buried pediplain moderate (BPM)) showed a significant variation in recharge conditions among themselves. It was found from the study that Peninsular gneiss gives a net recharge value of 0.13 m/year/unit area when considered as a single unit w.r.t. lithology, whereas the same area considered with lith-geom classes gives recharge values between 0.1 and 0.41 m/year presenting a different assessment. It is also found from this study that the stage of development (SOD) for each lith-geom unit in Peninsular gneiss varies from 168 to 230 %, whereas the SOD is 223 % for the lithology as a single unit.

Geochemistry of PGE in mafic rocks of east Khasi Hills, Shillong Plateau, NE India

The mafic rocks of east Khasi Hills of the Meghalaya Plateau, northeastern India, occur as an intrusive body which cut across the weakly metamorphosed Shillong Group of rocks. Other than Shillong Group of rocks, high grade Archaean gneissic rocks and younger porphyritic granites are also observed in the study area. The studied mafic rocks of east Khasi Hills cover an area of about 4 km 2 and represent structurally controlled intrusion and varying grades of deformation. Structurally, these mafic rocks can be divided into massive type of mafic rocks, which are more or less deformation free and foliated type of mafic rocks that experienced deformation. Petrographically, this massive type can be classified as leuco-hornblende-gabbro whereas foliated type can be designated as amphibolite. On the basis of major oxide geochemistry, the investigated mafic rocks can be discriminated into high titanium (HT) (TiO 2>2 wt%) and low titanium (LT) types (TiO 2<2 wt%). Use of several geochemical variation diagrams, consideration of chondrite-normalized and mantle-normalized REE and PGE plots suggest role of magmatic differentiation (with almost no role of plagioclase fractionation) in a subduction controlled tectonic environment. The PGE trends of the studied rocks suggest relative enrichment of palladium group of PGE (PPGE) compared to iridium group PGE (IPGE). Critical consideration of Sm vs. La, Cu vs. La, Pd vs. La and Cu/Pd vs. La/Sm plots strongly favours generation of the parent magma at a columnar melting regime with batch melting of cylindrical column of the parent mantle to the tune of ∼25%. The characteristic PGE behaviours of the presently investigated mafic rocks of east Khasi Hills can be typically corroborated as ‘orogenic’ (discordant) type. These rocks have an enriched mantle affinity with a co-magmatic lineage and they have been generated by slab-dehydration, wedge-melting and assimilation fractional crystallization process at a continental margin arc setting.

Caracterização hidrogeológica e hidroquímica das águas subterrâneas da região de São Gabriel, RS

O presente estudo trata da caracterização hidrogeológica e hidroquímica das águas subterrâneas do município de São Gabriel, RS. Foram analisadas 55 amostras de água provenientes de 55 poços tubulares profundos de diversas localidades e variados contextos hidrogeológicos. A maior parte do território do município de São Gabriel é constituída por rochas sedimentares da Bacia do Paraná. Assim, os principais aquíferos possuem águas com composições químicas bastante diversificadas, refletindo variados ambientes deposicionais e composições mineralógicas. Subordinadamente, aquíferos fraturados formados por rochas granítico-gnáissicas do Escudo Sul- -rio-grandense ocorrem na porção sul do município. Desta forma, a qualidade das águas subterrâ- neas do município varia de acordo com as condições geológicas de cada unidade aquífera e com as relações entre elas. Na área, os elementos Flúor e Sódio são os parâmetros que comprometem a utilização das águas subterrâneas para fins de consumo humano, dessedentação de animais e irrigação. Cerca de 30 % das análises apresentam águas impróprias para consumo com relação a estes íons, conforme parâmetros máximos permitidos pelo Ministério da Saúde do Brasil. Os principais aquíferos da região, em termos quantitativos e qualitativos, são o Aquífero Rio Bonito (ARB) e o Sistema Aquífero Guarani (SAG), localizados, respectivamente, na porção sul e nordeste do município. As águas dos poços que captam destes aquíferos são de boa qualidade, potáveis e as vazões podem ser consideradas como as melhores da região .

Polyphase evolution of Pelagonia (northern Greece) revealed by geological and fission-track data

Abstract. The Pelagonian zone, situated between the External Hellenides/Cyclades to the west and the Axios/Vardar/Almopias zone (AVAZ) and the Rhodope to the east, was involved in late Early Cretaceous and in Late Cretaceous–Eocene orogenic events whose duration and extent are still controversial. This paper constrains their late thermal imprints. New and previously published zircon (ZFT) and apatite (AFT) fission-track ages show cooling below 240 °C of the metamorphic western AVAZ imbricates between 102 and 93–90 Ma, of northern Pelagonia between 86 and 68 Ma, of the eastern AVAZ at 80 Ma and of the western Rhodope at 72 Ma. At the regional scale, this heterogeneous cooling is coeval with subsidence of Late Cretaceous marine basin(s) that unconformably covered the Early Cretaceous (130–110 Ma) thrust system from 100 Ma. Thrusting resumed at 70 Ma in the AVAZ and migrated across Pelagonia to reach the External Hellenides at 40–38 Ma. Renewed thrusting in Pelagonia is attested at 68 Ma by abrupt and rapid cooling below 240 °C and erosion of the gneissic rocks. ZFT and AFT in western and eastern Pelagonia, respectively, testify at ~40 Ma to the latest thermal imprint related to thrusting. Central-eastern Pelagonia cooled rapidly and uniformly from 240 to 80 °C between 24 and 16 Ma in the footwall of a major extensional fault. Extension started even earlier, at ~33 Ma in the western AVAZ. Post-7 Ma rapid cooling is inferred from inverse modeling of AFT lengths. It occurred while E–W normal faults were cutting Pliocene-to-recent sediment.

The mechanisms and characteristics of a complex rock-debris avalanche at the Nigeria–Cameroon border, West Africa

We describe a rock-debris avalanche which occurred on steep, symmetrical ridges resulting from fracture-controlled erosion in the valley. The fractures were partially filled with clayey materials, probably derived from the weathering of feldspar. Major fault lines trending N–S were located less than 7km from the landslide location. Exposed sections revealed that the basal rock units were migmatites and gneisses, while the upper section consisted of porphyritic granites. A failure of the residual clay-rich soil, composed of visible crystals of feldspar and mica, is thought to have triggered a long chain of events that led to the development of a rock-debris avalanche, which diverted the course of the rivers in the valley. The area was characterised by a shallow water table in the dry season (2 to 3m) and this might have facilitated the formation of a slip surface at the regolith–rock interface. Field observations and laboratory analysis showed that the regolith probably failed first because of high pore pressure build-up and rapid reduction in shear resistance; this then triggered the failure of the fractured rock units. The slope movement was perpendicular to the foliation of the gneissic rocks, which probably contributed to landslide mobility. Of interest was that changing saturation level at constant relative density of about 32% resulted in either complete or limited liquefaction, indicating that the mechanism of failure depended on the moisture content of the regolith.