The onset of flysch sedimentation in the Kaoko Belt (NW Namibia) – Implications for the pre-collisional evolution of the Kaoko–Dom Feliciano–Gariep orogen

Detrital zircon provenance study of a metamorphosed sedimentary succession in the eastern part of the Kaoko Belt in Namibia has revealed two distinct sources for the Neoproterozoic sedimentation along the southwestern Congo Craton margin. The lower part of the succession shows detrital zircon ages consistent with erosion of Paleoproterozoic basement of the Congo Craton with an inferred Mesoproterozoic volcano-sedimentary cover. Within the middle part of the succession, which includes glaciogenic sediments correlated with the Sturtian (717–660 Ma) glaciation, the Mesoproterozoic zircon grains disappear and the signal is dominated by ages known from the Congo Craton basement. The sedimentation in these parts of the succession is interpreted as related to the early Neoproterozoic rifting. The sedimentary rocks in the top part of the profile contain only subordinate proportion of the Paleoproterozoic–Archaean zircon grains and the populations are dominated by three age groups of ca. 1.0–1.2 Ga, ca. 800–750 Ma and ca. 650 Ma, consistent with erosion of the Punta del Este–Coastal Terrane exposed in the centre of the Kaoko–Dom Feliciano–Gariep orogen. An associated glaciogenic horizon interpreted as reflecting the Marinoan (645–635 Ma) glaciation constrains the sedimentation in the upper part of the succession and suggests a short time span between the high-grade metamorphism/magmatism in the Punta del Este–Coastal Terrane and its exhumation. Sedimentary rocks with such detrital zircon pattern appear also in the Damara and Gariep belts. Their source in the western part of the Kaoko–Dom Feliciano–Gariep orogen suggests that they represent an early orogenic flysch that originated during early collision in the western part of the orogen. The short time span between the metamorphism/magmatism in the Punta del Este–Coastal Terrane and deposition of the early orogenic flysch derived from it suggests that the Coastal Terrane was never separated from the Congo Craton by an oceanic domain. The estimated time span between the end of lithospheric stretching and sedimentation of the early flysch suggests that the hypothetical Adamastor Ocean separating the western and eastern forelands of the Kaoko–Dom Feliciano–Gariep orogen must have been small.acceptedVersio

Combined garnet and zircon geochronology of the ultra-high temperature metamorphism: Constraints on the rise of the Orlica-Śnieżnik Dome, NE Bohemian Massif, SW Poland

Garnet and zircon geochronology combined with trace element partitioning and petrological studies provide tight constraints on evolution of the UHT-(U)HP terrain of the Orlica-Śnieżnik Dome (OSD) in the NE Bohemian massif. Lu-Hf dating of peritectic garnet from two mesocratic granulites constrained the time of its initial growth at 346.9 ± 1.2 and 348.3 ± 2.0 Ma recording peak 2.5 GPa pressure and 950 °C temperature. In situ, U-Pb SHRIMP dating of zircon from the same granulite gave a younger age of 341.9 ± 3.4 Ma. Ti-in-zircon thermometry indicates crystallization at 810–860 °C pointing to zircon formation on the retrograde path. Lu partitioning between garnet rim and zircon suggest equilibrium growth and thus U-Pb zircon age constrain the terminal phase of garnet crystallization which lasted about 6 Ma. All Sm-Nd garnet ages obtained for mesocratic and mafic granulites are identical and consistently younger than the corresponding Lu-Hf dates. They are interpreted as reflecting cooling of granulites through the Sm-Nd closure temperature at about 337 Ma. The estimated PTt path documents the ca. 10 Ma evolution cycle of the OSD characterized by two distinct periods: (1) 347 - > 342 Ma period corresponds to nearly isothermal decompression resulting from crustal scale folding and vertical extrusion of granulites, and (2) at > 342–337 Ma which corresponds to a fast, nearly isobaric cooling.This study was financed by Polish Ministry of Science and Higher Education grant No. N N307 057734 and financially supported by Polish Academy of Sciences, Institute of Geological Sciences grant No. HPT. R. Anczkiewicz acknowledges funding from internal IGS PAS grant. The research of J. Szczepanski was funded by the University of Wroclaw grant 1017/S/ING

Basement provenance revealed by U-Pb detrital zircon ages: A tale of African and European heritage in Tuscany, Italy

A new data set of ca. 500 LA-ICP-MS U-Pb detrital zircon ages for six metasedimentary units from the Tuscan basement (Apuan Alps, Monti Pisani, Monticiano-Roccastrada), along with a precise SHRIMP U-Pb crystallization age of a metavolcanic unit (Apuan Alps) have been collected to determine their depositional ages and provenance. These results have been integrated with the recently published ca. 900 U-Pb detrital zircon ages from Elba Island to draw a complete picture of the Paleozoic journey of the Tuscan basement. A major change in the sources supplying sediments to the Tuscan basins is shown to occur during this journey. Detrital zircon ages of early Cambrian to middle Ordovician metasediments mirror those of coeval northern Africa sediments: most samples were sourced in western Africa, while one sample is derived material from central northern Africa. The Tuscan block was therefore located at the peri-Gondwana margin, close to central northern Africa. The prominent mid-Ordovician magmatic arc activity (ca. 460. Ma) at the northern Gondwana margin and its detritus, characterise the zircon age distribution of Ordovician and Silurian volcano-sedimentary rocks, that were therefore generated at the northernmost Gondwana margin during subduction and subsequent initial Paleotethys rifting. The Carboniferous-Permian metasediments are dominated by populations of Ordovician and Variscan-age zircons, with a minor occurrence of Neoarchean and Paleoproterozoic zircons that is best explained by recycling of European Neoproterozoic-Cambrian metasediments. In summary, the main sources supplying the Tuscan basins were located in northern Africa throughout Cambrian-Ordovician times, shifting to the volcanic arc active at the northern Gondwana margin during the middle Ordovician. During Variscan and post-Variscan times, detrital zircon sources were mostly located in European terrains, witnessing the shift of Tuscany from Africa to Europe

Morphotectonic evidence for chronodynamics of uplift in the East Nepal Himalaya

The integration of a geomorphological and geological data from the Makalu-Barun region (Photo 1) and from the adjacent areas point to a rapid exhumation of deep crustal rocks during the mature stages of collisional orogeny. Our observations from the years 1971, 1973, 1976 and 2002 suggest a signi6cant feedback between the rate of tectonic exhumation of deep rocks and the intensity of climate-driven morphogenetic processes. High-mountain landform patterns in the relief section between the Mount Everest, Makalu and the Arun valley are the result of morphotectonic processes, denudation and erosion efficiency in different paleoclimatic conditions during the Late Cenozoic14916

Linking the basement geology along the Africa-South America coasts in the South Atlantic

The match of geological units of the dissected Kaoko-Dom Feliciano-Gariep orogenic system exposed along the coasts of the South Atlantic is poorly understood. Two suites of intrusive rocks crop out in the Angra Fria Bay area, a part of the Coastal Terrane of the Kaoko Belt in Namibia. U–Pb zircon dating of three samples from the younger suite provided ages of 574 ± 6, 586 ± 3 and 584 ± 7 Ma, similar to the ages of the oldest syn-collisional granitoids in the area. Three samples of the older suite gave ages of 626 ± 5, 622 ± 5 and 620 ± 6 Ma respectively, which have not previously been recorded in intrusive rocks of the Kaoko Belt, but which coincide with those from the Florianópolis Batholith in the Dom Feliciano Belt in Brazil. Zircon ages, Sr–Nd isotopic composition and tectonic position of these granitoids suggest that this magmatic complex could be a continuation of the Florianópolis Batholith on the African side of the Atlantic Ocean. Consequently, the Angra Fria intrusions and the Florianópolis Batholith may represent suitable localities for spatial reconstruction of the Gondwana supercontinent in the area, where the robust pre-Mesozoic connecting points are scarce

New U-Pb zircon and ⁴⁰Ar/³⁹Ar muscovite age constraints on the emplacement of the Lizio syn-tectonic granite (Armorican Massif, France)

LA-ICP-MS U-Pb analyses performed on zircon grains from the Lizio granite yielded an emplacement age of 316 ± 6 Ma. Typical S-C structures show that the Lizio granite was emplaced contemporaneously with dextral shearing along the northern branch of the South Armorican Shear Zone and that it was therefore active at that time. 40Ar/39Ar analyses performed on muscovite grains yielded plateau dates ranging between 311.5 and 308.2 Ma. Muscovite chemistry is typical of primary magmatic muscovite, which precludes a late fluidsinduced resetting of the K-Ar isotopic system. 40Ar/39Ar dates thus likely correspond to the cooling ages below the argon closure temperature. Considering the uncertainties on the measured ages, we can propose that either the Lizio granite cooled down quickly in less than a million of years or that it remained in a hot environment for several millions of years after its emplacement. This latter scenario could have been sustained by shear heating during dextral shearing along the northern branch of the South Armorican Shear Zone

The onset of flysch sedimentation in the Kaoko Belt (NW Namibia) – Implications for the pre-collisional evolution of the Kaoko–Dom Feliciano–Gariep orogen

Detrital zircon provenance study of a metamorphosed sedimentary succession in the eastern part of the Kaoko Belt in Namibia has revealed two distinct sources for the Neoproterozoic sedimentation along the southwestern Congo Craton margin. The lower part of the succession shows detrital zircon ages consistent with erosion of Paleoproterozoic basement of the Congo Craton with an inferred Mesoproterozoic volcano-sedimentary cover. Within the middle part of the succession, which includes glaciogenic sediments correlated with the Sturtian (717–660 Ma) glaciation, the Mesoproterozoic zircon grains disappear and the signal is dominated by ages known from the Congo Craton basement. The sedimentation in these parts of the succession is interpreted as related to the early Neoproterozoic rifting. The sedimentary rocks in the top part of the profile contain only subordinate proportion of the Paleoproterozoic–Archaean zircon grains and the populations are dominated by three age groups of ca. 1.0–1.2 Ga, ca. 800–750 Ma and ca. 650 Ma, consistent with erosion of the Punta del Este–Coastal Terrane exposed in the centre of the Kaoko–Dom Feliciano–Gariep orogen. An associated glaciogenic horizon interpreted as reflecting the Marinoan (645–635 Ma) glaciation constrains the sedimentation in the upper part of the succession and suggests a short time span between the high-grade metamorphism/magmatism in the Punta del Este–Coastal Terrane and its exhumation. Sedimentary rocks with such detrital zircon pattern appear also in the Damara and Gariep belts. Their source in the western part of the Kaoko–Dom Feliciano–Gariep orogen suggests that they represent an early orogenic flysch that originated during early collision in the western part of the orogen. The short time span between the metamorphism/magmatism in the Punta del Este–Coastal Terrane and deposition of the early orogenic flysch derived from it suggests that the Coastal Terrane was never separated from the Congo Craton by an oceanic domain. The estimated time span between the end of lithospheric stretching and sedimentation of the early flysch suggests that the hypothetical Adamastor Ocean separating the western and eastern forelands of the Kaoko–Dom Feliciano–Gariep orogen must have been small

U–Pb zircon provenance of Moldanubian metasediments in the Bohemian Massif

<p>Detrital zircon U–Pb age data from the Moldanubian part of the Bohemian Massif obtained by laser ablation inductively coupled plasma mass spectrometry show variations between the lithotectonic units and point to their formation in spatially close but separated basins that were supplied by detritus from somewhat different source areas, possibly over different periods of time. The youngest detrital zircon component in metasediments of the Monotonous and Varied Units is Early Ordovician and Mid- to Late Devonian in age, respectively, suggesting their deposition in Palaeozoic times. Reliable interpretation of the Mid- to Late Devonian zircons recovered from metasediments of the Gföhl Unit is precluded by their high metamorphic grade and presence of anatectic melt. The Early Carboniferous zircons from the Gföhl Unit are interpreted as being of metamorphic origin. Comparison of detrital zircon age spectra from the Moldanubian, Teplá–Barrandian and Moravo-Silesian metasediments suggests that these were deposited in separate basins but the overall similarity of the Neoproterozoic and Palaeoproterozoic age maxima and sparse Neo- and Mesoarchaean ages suggest that the three crustal segments must have been spatially related prior to the Variscan orogeny. Future tectonic models of the Variscan assembly of the Bohemian Massif must account for nearly synchronous evolution of the Moldanubian, Teplá–Barrandian and Moravo-Silesian Palaeozoic sedimentary basins that shared a common crust and most of their sedimentary sources, as well as for a rapid burial of the Moldanubian sediments to mid- and lower crustal levels that was followed by their rapid exhumation to the upper crust in Mid-Devonian to Early Carboniferous times. </p