U‒Pb ages and Hf isotopic composition of zircons in Austrian last glacial loess: constraints on heavy mineral sources and sediment transport pathways

Loess sediments in Austria deposited ca. 30‒20 ka ago yield different zircon age signatures for samples collected around Krems (SE Bohemian Massif; samples K23 and S1) and Wels (half-way between the Bohemian Massif and the Eastern Alps; sample A16). CL imaging reveals both old, multi-stage zircons with complex growth histories and inherited cores, and young, first cycle magmatic zircons. Paleoproterozoic ages between 2200 and 1800 Ma (K23 and S1), an age gap of 1800- 1000 Ma for S1 and abundant Cadomian grains indicate NW African/North Gondwanan derivation of these zircons. Also A16 yields ages between 630-600 Ma that can be attributed to 'Pan-African' orogenic processes. Significant differences are seen for the <500 Ma part of the age spectra with major age peaks at 493-494 Ma and 344-335 Ma (K23 and S1), and 477 and 287 Ma (A16). All three samples show negative initial ɛHf signatures (‒25 to ‒10, except one grain with +9.4) implying zircon crystallization from magmas derived by recycling of older continental crust. Hf isotopic compositions of 330-320 Ma old zircons from S1 and K23 preclude a derivation from Bavarian Forest granites and intermediate granitoids. Rather all the data suggest strong contributions of eroded local rocks (South Bohemian pluton, Gföhl unit) to loess material at the SE edge of the Bohemian Massif (K23 and S1), and sourcing of zircons from sediment donor regions in the Eastern Alps for loess at Wels (A16). We tentatively infer primary fluvial transport and secondary aeolian reworking and re-deposition of detritus from western/southwestern directions. Finally, our data highlight that loess zircon ages are fundamentally influenced by fluvial transport, its directions, the interplay of sediment donor regions through the mixing of detritus and zircon fertility of rocks, rather than paleo-wind directions

Geochemistry and Petrogenesis of the Banded and Granitic Gneisses in Parts of Kushaka Schist Belt, Northwestern Nigeria

The Kushaka schist belt in the Kwona Mutua and Kushaka areas is one of the 12 well recognized N-S trending belts composed of igneous, metamorphic and metasedimentary rocks in varying proportion. The major rocks of the belt comprise the Migmatite-Gneiss-Quartzite Complex, schists and Pan-African granitoids. Banded and granite gneisses constitute the bulk of the Migmatite-Gneiss-Quartzite Complex. Banded gneiss consists of paleosome and leucosome of dioritic, tonalitic, granodioritic and granitic composition while granite gneiss is composed of biotite, staurolite–biotite and staurolite-muscovite gneiss. Major mineral constituents of these rocks are quartz, orthoclase, plagioclase, pyroxene, biotite, muscovite, orthoclase, microcline and staurolite while the accessory minerals are titanite, apatite and iron oxides. Metamorphism may have reached grannulite facies locally with pyroxenes crystallizing in the dioritic and granodioritic rock. Analysis of geochemical data reveals marked variation in the abundance of SiO2 (60.77-77.53 wt %), Al2O3 (12.9-15.99 wt %), Fe2O3 (0.78-7.04 wt%), Na2O (1.67-5.15 wt%) and K2O (1.64-6.13 wt %), typical of rocks of hybrid sedimentary–igneous protoliths. Igneous protolith reveals decreasing P2O5 content with increasing silica content, low K2O/ Na2O ratio (0.24 – 0.87), low K2O values (&lt; 2.5 wt %) displaying mixed tholeiitic and calc-alkaline, metaluminous and peraluminous, ferroan and magnesian character, and high-K calc-alkaline to shoshonitic affinities. By contrast, the rocks of sedimentary protolith shows high K2O/ Na2O ratio (1.19 – 2.5), high Na2O values (&gt; 3 wt %) and staurolite mineral. Their pelitic and mafic attributes were derived essentially from a quartz-diorite, granodiorite and granite-quartz monzonite source. Fractional crystallization and partial melting of older dioritic-granodioritic-tonalitic source rock derived from upper mantle materials contaminated by continental crust played important roles during their genesis. They are enriched in Large Ion Lithophile Elements (LILE) but depleted in Nb, P and Ti typical of volcanic arc and syn-collisional settings. Keywords: Banded gneiss, Pan-African, sedimentary, igneous, granodiorite, protolith, Kushaka, Nigeria DOI: 10.7176/JEES/11-4-05 Publication date: April 30th 202

Geochemistry and Petrogenetic Features of Metasediments in Northern Part of Kushaka and Birnin Gwari Schist Belts NW Nigeria

The Kushaka and Birnin Gwari metasediments and associated banded iron formations constitute important lithological units within the Precambrian Basement Complex. They were studied to evaluate their compositional characteristics and petrogenesis in order to contribute further to the understanding of the geodynamic evolution of Nigeria’s Schist belts. The Kushaka metasediments comprise quartzite, graphite and sulphur bearing staurolite-muscovite quartz schist interbedded with Banded Iron Formations (BIFs) while the Birnin Gwari schist comprise staurolite-biotite quartz schists with lithic (angular to rounded clastic quartz, schistose, volcanic and quartzo-feldspathic) sandstones. These schists are associated with fissile and ferruginous quartzite, banded and granitic gneisses, basalts and amphibolites. Petrographic work revealed varying proportions of quartz, staurolite, biotite and muscovite with subordinate iron-oxide minerals.  Geochemically the metasediments in the Kushaka are enriched in SiO2 (61.23 to 65.99 wt %) with elevated values of Al2O3 (16.53 – 20.93 wt %), Ba, V, W, La, Nb, Nd, Rb, Th and Zr; while  the Birnin Gwari schists, even though enriched in SiO2 (63.03 to 65.13 wt %), has moderately elevated Al2O3 (15.4 – 15.16 wt %) values  but is depleted these trace elements. Field and geochemical characterization of the Kushaka metasediments suggests peraluminous, tholeiite and calc-alkaline character; arkosic and shale-greywacke sedimentary protoliths derived from quartzose sedimentary and granite-quartz monzonite provenance. Calculated ICV values of 0.52 - 0.99 and occurrences of graphite and sulphur in the Kushaka metasediment suggests shallow stable shelf-type sediment of carbonate and iron formations in a reducing environment with matured sedimentary protolith. The Birnin Gwari metasediments on the other hand have a peraluminous and calc-alkaline character, inherited from shale-greywacke and quartzose sedimentary protoliths derived from granodioritic and granite-quartz monzonite provenance. ICV values of 1.12 – 1.18 and angular and volcanic clasts suggest rapid subsidence of basin during genesis and / or tectonic instability in the surrounding environment with immature sedimentary protolith. This is an indication of two contrasting environment in an arc setting with contribution from basaltic and andesitic detritus. Available geochronological data on granite and granitic gneisses have ascribed the Kushaka schist belt to Kibaran and the Birnin Gwari schist belt a Pan-African age. Keywords: Metasediments, protolith, Kushaka, Birnin Gwari, quartzite, provenance, shale, greywacke. DOI: 10.7176/JEES/11-16-05 Publication date:June 30th 202

Field Occurrence, Petrography and Structural Characteristics of the Basement Rocks in the Northern Part of Kushaka and Birnin Gwari Schist Belts, Northwestern Nigeria

Field, studies and geological mapping on a scale of 1:50000 were carried out to determine the lithologic framework and structural features of the Basement Complex rocks in northern parts of the Kushaka and Birnin Gwari schist belts (Kushaka Sheet 122). The area is underlain predominantly by five main rock types mainly (i) Migmatite-Gneiss-Quartzite suite comprising dioritic, granodioritic and granitic gneisses with fissile and ferruginous quartzites and banded iron formations (BIF); (ii) Kushaka graphite and sulphur bearing biotite and muscovite quartz schist inter-banded in places with iron formations; (iii) Birnin Gwari biotite-staurolite quartz schist; iv) the Kushaka Gneiss Complex composed of basalts (which is being reported for the first time), staurolite and muscovite gneisses and banded iron formations (BIF), and (v) syn-tectonic and late-orogenic biotite-hornblende syenite (BHS) and biotite-hornblende granite (BHG) in the Kushaka schist belt and biotite muscovite granite (BMG) in the Birnin Gwari schist belt area. Petrographic studies have revealed that essential minerals are quartz, K-feldspars (orthoclase, microcline), plagioclase, pyroxene, epidote, hornblende, biotite and muscovite while the accessory minerals are titanite, zircon, apatite, iron oxide (magnetite and hematite). With pyroxenes occurring in the dioritic and granodioritic rocks, metamorphism may have locally reached grannulite facies. Imprints of Pan-African thermo-tectonic events have shown observable migmatization as the first thermo-tectonic event resulting in plastic deformation D1 and regional S1 foliation, demostrated by presence of tight isoclinals fold, compositional banding and N – S preferred orientation of mafic minerals. The D2 deformation is co-axial with D1 and resulted in the formation of decimeter sized F2 isoclinal folds, B2 boudins and eye ball structures that are parallel to S1 plane schistocity. Strike-slip faults with dextral sense of movements were mapped in a number of places. D3 deformation is concentrated in the Kushaka Gneiss Complex with near circular deep fractures south of the Kalangai fault. Here granitization and fragmentation of proto-mylonitic staurolite resulted in brittle deformation and F3 open fold that refolded or transposed the earlier tight isoclinal F2 folds. The D4 deformation resulted in N-S and NW-SE quartz veins and pegmatite dykes which serve as channels for epigenetic gold-sulphide and rare metal bearing ore fluids. Keywords: Basement Complex, Pan-African, metamorphism, deformation, Kushaka, Birnin Gwari, Nigeria DOI: 10.7176/JNSR/12-12-02 Publication date:June 30th 202

Petrochronological study of chloritoid schist from Medvednica Mountain (Zagorje Mid-Transdanubian zone, Croatia)

The metamorphic conditions and evolution of the Palaeozoic-Mesozoic metamorphic complex of Medvednica Mountain (Zagorje-Mid-Transdanubian zone, Croatia) are still a matter of debate. The results of the investigation of five samples of metapelitic schists with the mineral association of quartz, white mica and chlorite are presented. The studied schists are part of the continental margin of Adria and were metamorphosed under upper greenschist- to amphibolite-facies conditions. The focus of this study is a sample representing the highest metamorphic grade that additionally contains chloritoid blasts. Pressure-temperature pseudosection modelling together with classical geothermobarometric calculations yielded peak metamorphic conditions of 0.94 ± 0.05 GPa and 550 ± 20 °C for chloritoid schist. Monazite in-situ U-Th-total Pb electron microprobe dating indicates two metamorphic events at 167 ± 2 Ma and 143 ± 2 Ma, which are interpreted as the time of monazite growth during two distinct metamorphic phases. The formation of the chloritoid paragenesis is related to the older event (around 167 Ma) and linked with the Middle Jurassic subduction-accretion processes of Neotethys-derived ophiolitic lithologies. The younger metamorphic event (around 143 Ma) is related to the obduction of ophiolites onto the continental margin of Adria

Late Triassic acidic volcanic clasts in different Neotethyan sedimentary mélanges: paleogeographic and geodynamic implication

U/Pb zircon dating and trace element geochemical analysis were performed on rhyolite clasts of different Middle Jurassic sedimentary mélanges from the Western Carpathian and Dinaric orogen. These igneous clast-bearing sedimentary successions were deposited on the westernmost passive margin of the Neotethys Ocean. During the latest Jurassic and Cretaceous, they became parts of different nappe stacks forming now the Inner Western Carpathians and some inselbergs within the Pannonian Basin. The Meliata nappe was stacked on the northern passive margin, while the Telekesoldal and Mónosbél nappes were part of the imbricated western - south-western margin. U/Pb dating of the 100m-sized blocks and redeposited smaller clasts and fine-grained sediments formed two age groups: 222.6±6.7 and 209.0±9 Ma. Trace element geochemistry suggested within plate continental volcanism as magma source. However, the measured ages are definitely younger than the classic, rift-related Anisian - Ladinian (238-242 Ma) magmatism, which was widespread along the western and south-western margin of the Neotethys Ocean (e.g. Dolomites, different Dinaridic units). On the other hand, similar, Late Triassic ages are reported from tuff intercalations from the Outer Dinarides and Western Carpathians, along with even more sparse effusive rocks of the Slovenian Trough. Trace element (incl. rare earth element) analysis showed positive correlation between the mélange clasts and the in situ Late Triassic rhyolites of the Slovenian Trough. This newly established link between the mélange nappes in NE Hungary and the in situ Late Triassic rhyolites in the Slovenian Trough make a good opportunity to reconsider both Middle Jurassic paleogeography, and later tectonic deformations, which led to the separation of the source area and the redeposited clasts

Variscan post-collisional cooling and uplift of the Tatra Mountains crystalline block constrained by integrated zircon, apatite and titanite LA-(MC)-ICP-MS U-Pb dating and rare earth element analyses

LA-ICP-MS U-Pb dating of apatite, titanite and zircon from the metamorphic cover of the Western Tatra granite was undertaken to constrain the timing of metamorphic events related to the final stages of Variscan orogenesis and subsequent post-orogenic exhumation. Zircon was found only in one sample from the northern metamorphic envelope. U-Pb ages from the outermost rims of zircons define a concordia age of 346 ± 6 Ma, while the inner rims yield a concordia age of 385 ± 8 Ma. Apatite from three samples from the northern metamorphic envelope yield U-Pb ages of 351.8 ± 4.4 Ma, 346.7 ± 5.9 Ma and 342.6 ± 7.1 Ma. Titanite from an amphibolite from the southern metamorphic envelope yields a U-Pb age of 345.3 ± 4.5 Ma. The age of c. 345 Ma is interpreted to represent the climax of metamorphism and the onset of simultaneous exhumation of the entire Tatra Mountains massif, and is recorded mainly in the northern part of the metamorphic cover. In the southern metamorphic envelope, distinct populations of apatite can be recognized within individual samples based on their rare earth element (REE) and actinide contents. One population of apatite (Ap1) yields a relatively imprecise U-Pb age of 340 ± 31 Ma. This population comprises apatite grains with very similar trace element compositions to apatite in the northern amphibolite samples, which suggests they crystallized under similar metamorphic conditions to their northern counterparts. A second apatite population (Ap2) yields an age of c. 328 ± 22 Ma, which is interpreted as neocrystalline apatite that formed during a late-Variscan (hydrothermal?) process involving (P, F, Ca, REE)-rich fluid migration. The youngest generation of apatite (Ap3) yields a U-Pb age of 260 ± 8 Ma and may have resulted from thermal resetting associated with the regional emplacement of Permian A-type granites. The proposed tectonic model assumes that rapid uplift (and cooling) of the Tatra block initiated at ca. 345 Ma, contemporaneous with anatexis. Subsequent fluid migration, possibly facilitated by extension related to the opening of Paleo-Tethys, affected only the southern part of the Tatra block

Die kombinierte Wirkung von spezialisierten wurzelbohrenden Insekten und Pflanzenkonkurrenz reduziert das Wachstum von Rumex obtusifolius

Die kombinierte Wirkungen von wurzelbohrenden Larven des europäische Schmetterling Pyropteron chrysidiforme (Massenausbringung) auf dem Stumpfblättrigen Ampfer wurden für zwei Gruppen von anfänglich kleinen und großen Pflanzen mit oder ohne Konkurrenz von dem Englischen Raygras bewertet