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  • 1.
    Anders, Bebhinn
    et al.
    Earth and Ocean Sciences, School of Natural Sciences, NUI Galway, University Road, Galway, Ireland;Sediment Origins Research Team (SORT), NUI Galway, Ireland.
    Tyrrell, S.
    Earth and Ocean Sciences, School of Natural Sciences, NUI Galway, University Road, Galway, Ireland;Sediment Origins Research Team (SORT), NUI Galway, Ireland;Irish Centre for Research in Applied Geosciences (iCRAG), Ireland.
    Chew, D.
    Department of Geology, Trinity College Dublin, College Green, Dublin 2, Ireland;Irish Centre for Research in Applied Geosciences (iCRAG), Ireland.
    Mark, C.
    Swedish Museum of Natural History, Department of Geology. UCD School of Earth Sciences, University College Dublin, Belfield, Dublin 4, Ireland.
    O'Sullivan, G.
    UCD School of Earth Sciences, University College Dublin, Belfield, Dublin 4, Ireland.
    Murray, J.
    Earth and Ocean Sciences, School of Natural Sciences, NUI Galway, University Road, Galway, Ireland;Irish Centre for Research in Applied Geosciences (iCRAG), Ireland.
    Graham, J.R.
    Department of Geology, Trinity College Dublin, College Green, Dublin 2, Ireland.
    Badenszki, E.
    Irish Centre for Research in Applied Geosciences (iCRAG), Ireland;UCD School of Earth Sciences, University College Dublin, Belfield, Dublin 4, Ireland.
    Spatial variation in provenance signal: identifying complex sand sourcing within a Carboniferous basin using multiproxy provenance analysis2022In: Journal of the Geological Society, ISSN 0016-7649, E-ISSN 2041-479X, Vol. 179, no 1, article id jgs2021-045Article in journal (Refereed)
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  • 2. Augustsson, Carita
    et al.
    Rüsing, Tobias
    Niemeyer, Hans
    Kooijman, Ellen
    Swedish Museum of Natural History, Department of Geology.
    Berndt, Jasper
    Bahlburg, Heinrich
    Zimmermann, Udo
    0.3 byr of drainage stability along the Palaeozoic palaeo-Pacific Gondwana margin; a detrital zircon study2015In: Journal of the Geological Society, ISSN 0016-7649, E-ISSN 2041-479X, Vol. 172, p. 186-200Article in journal (Refereed)
    Abstract [en]

    The palaeo-Pacific margin of Gondwana in the present-day south–central Andes is marked by tectonic activity related to subduction and terrane accretion. We present detrital zircon U–Pb data encompassing the Palaeozoic era in northern Chile and northwestern Argentina. Cathodoluminescence images reveal dominantly magmatic zircon barely affected by abrasion and displaying only one growth phase. The main age clusters for these zircon grains are Ediacaran to Palaeozoic with an additional peak at 1.3–0.9 Ga and they can be correlated with ‘Grenvillian’ age, and the Brasiliano, Pampean, and Famatinian orogenies. The zircon data reveal main transport from the nearby Ordovician Famatinian arc and related rocks. The Silurian sandstone units are more comparable with Cambrian units, with Brasiliano and Transamazonian ages (2.2–1.9 Ga) being more common, because the Silurian deposits were situated within or east of the (extinct) Famatinian arc. Hence, the arc acted as a transport barrier throughout Palaeozoic time. The complete suite of zircon ages does not record the accretions of exotic terranes or the Palaeozoic glacial periods. We conclude that the transport system along the palaeo-Pacific margin of Gondwana remained stable for c. 0.3 byr and that provenance data do not necessarily reflect the interior of a continent. Hence, inherited geomorphological features must be taken into account when detrital mineral ages are interpreted.

  • 3.
    Bomfleur, Benjamin
    et al.
    Institute for Geology and Palaeontology, Westfälische Wilhelms-Universität Münster.
    Mörs, Thomas
    Swedish Museum of Natural History, Department of Paleobiology.
    Unverfärth, Jan
    Institute for Geology and Palaeontology, Westfälische Wilhelms-Universität Münster.
    Feng, Liu
    State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology.
    Läufer, Andreas
    Federal Institute for Geosciences and Natural Resources (BGR), Germany.
    Castillo, Paula
    Institute for Geology and Palaeontology, Westfälische Wilhelms-Universität Münster.
    Oh, Changhwan
    Department of Earth Sciences Education, Chungbuk National University, Republic of Korea.
    Park, Tae-Yoon, S.
    Division of Polar Earth-System Sciences, Korea Polar Research Institute, Republic of Korea.
    Woo, Jusun
    School of Earth and Environmental Sciences, Seoul National University, Republic of Korea.
    Crispini, Laura
    DISTAV, University of Genova.
    Uncharted Permian to Jurassic continental deposits in the far north of Victoria Land, East Antarctica2020In: Journal of the Geological Society, ISSN 0016-7649, E-ISSN 2041-479X, Vol. 178, article id jgs2020-062Article in journal (Refereed)
    Abstract [en]

    The remote lower reaches of the Rennick Glacier in the far north of Victoria Land hold some of the least-explored outcrop areas of the Transantarctic basin system. Following recent international field-work efforts in the Helliwell Hills, we here provide a comprehensive emendation to the regional stratigraphy. Results of geological and palaeontological reconnaissance and of petrographic, geochemical and palynostratigraphic analyses reveal a stack of three previously unknown sedimentary units in the study area: the Lower Triassic Van der Hoeven Formation (new unit, 115+ m thick) consists mainly of quartzose sandstone and non-carbonaceous mudstone rich in continental trace fossils. The Middle to Upper Triassic Helliwell Formation (new unit, 235 m thick) consists of coal-bearing overbank deposits and volcaniclastic sandstone and yielded typical plant fossils of the Gondwanan Dicroidium flora together with plant-bearing silicified peat. The succession is capped by c. 14 m of the sandstone-dominated Section Peak Formation (uppermost Triassic–Lower Jurassic). Our results enable more detailed correlation of the Palaeozoic–Mesozoic successions throughout East Antarctica and into Tasmania. Of particular interest is one section that spans the end-Permian mass extinction interval, which promises to allow detailed reconstructions of high-latitude vegetation dynamics across this critical interval in Earth history.

  • 4.
    Callegari, Riccardo
    et al.
    Faculty of Geology, Geophysics and Environmental Protection, AGH University of Science and Technology, Kraków, Poland;Department of Earth Sciences, Uppsala University, Uppsala, Sweden.
    Kośmińska, Karolina
    Faculty of Geology, Geophysics and Environmental Protection, AGH University of Science and Technology, Kraków, Poland.
    Barnes, Christopher J.
    Institute of Geological Sciences, Polish Academy of Sciences, Kraków, Poland.
    Klonowska, Iwona
    Faculty of Geology, Geophysics and Environmental Protection, AGH University of Science and Technology, Kraków, Poland;Department of Earth Sciences, Uppsala University, Uppsala, Sweden.
    Barker, Abigail K.
    Department of Earth Sciences, Uppsala University, Uppsala, Sweden.
    Rousku, Sabine
    Department of Earth Sciences, Uppsala University, Uppsala, Sweden.
    Nääs, Erika
    Department of Earth Sciences, Uppsala University, Uppsala, Sweden.
    Kooijman, Ellen
    Swedish Museum of Natural History, Department of Geology. Department of Geosciences, Swedish Museum of Natural History, Stockholm, Sweden.
    Witt-Nilsson, Patrik
    Rosmarus Enviro, Uppsala, Sweden.
    Majka, Jarosław
    Faculty of Geology, Geophysics and Environmental Protection, AGH University of Science and Technology, Kraków, Poland;Department of Earth Sciences, Uppsala University, Uppsala, Sweden.
    Early Neoproterozoic magmatism and Caledonian metamorphism recorded by the Mårma terrane, Seve Nappe Complex, northern Swedish Caledonides2023In: Journal of the Geological Society, ISSN 0016-7649, E-ISSN 2041-479X, Vol. 180, no 5Article in journal (Refereed)
    Abstract [en]

    Petrology, geochronology and bulk-rock chemistry are combined to investigate the early Neoproterozoic magmatismand Cambrian–Ordovician metamorphism in the northern Swedish Caledonides. This work includes several lithologies of theMårma terrane in the Seve Nappe Complex exposed in the Kebnekaise region. U–Pb zircon geochronology yielded crystallizationages of 835 ± 8 Ma for a mylonitic orthogneiss, 864 ± 3 Ma for the Vistas Granite and 840 ± 7 Ma for an intruded granitic dyke,whereas a gabbro and a granodiorite intrusion gave U–Pb zircon crystallization ages of 856 ± 3 Ma and 850 ± 1 Ma, respectively.U–Pb monazite dating of the mylonitic orthogneiss gave an upper intercept age of 841 ± 7 Ma and a lower intercept age of443 ± 20 Ma. Pressure–temperature estimates derived for the mylonitic orthogneiss reveal metamorphic peak-pressure and peaktemperatureof 10.5–11.75 kbar and 550–610°C and 7.4–8.1 kbar at 615–675°C, respectively.Metamorphic pressure–temperatureestimates for the Vistas Granite yield 6.5–7.5 kbar at 600–625°C. Whole-rock chemistry coupled with U–Pb geochronologyindicates that bimodal magmatism was related to attempted rifting of Rodinia between 870 and 840 Ma.

  • 5.
    Carter, Isabel S. M.
    et al.
    Faculty of Geology, Geophysics and Environmental Protection, AGH University of Kraków, al. Mickiewicza 30, 30-059 Kraków, Poland;Department of Earth Sciences, Uppsala University, Villavägen 16, SE-752 36 Uppsala, Sweden.
    Cuthbert, Simon J.
    Faculty of Geology, Geophysics and Environmental Protection, AGH University of Kraków, al. Mickiewicza 30, 30-059 Kraków, Poland.
    Walczak, Katarzyna
    Faculty of Geology, Geophysics and Environmental Protection, AGH University of Kraków, al. Mickiewicza 30, 30-059 Kraków, Poland.
    Ziemniak, Grzegorz
    Institute of Geological Sciences, University of Wrocław, Pl. M. Borna 9, 50-204 Wrocław, Poland.
    Kooijman, Ellen
    Swedish Museum of Natural History, Department of Geology. Department of Geosciences, Swedish Museum of Natural History, Stockholm, Sweden.
    Majka, Jarosław
    Faculty of Geology, Geophysics and Environmental Protection, AGH University of Kraków, al. Mickiewicza 30, 30-059 Kraków, Poland;Department of Earth Sciences, Uppsala University, Villavägen 16, SE-752 36 Uppsala, Sweden.
    Cambrian ages for metavolcanic rocks in the Lower Köli Nappes, Swedish Caledonides: implications for the status of the Virisen arc terrane2023In: Journal of the Geological Society, ISSN 0016-7649, E-ISSN 2041-479X, Vol. 180, no 6Article in journal (Refereed)
    Abstract [en]

    The Köli Nappe Complex (KNC) of the Scandinavian Caledonide orogen originated as oceanic terranes within the Iapetus Ocean. These terranes have characteristics of magmatic arcs and associated forearc or back-arc basins and underwent several periods of rifting and magmatism prior to their accretion to the Baltican margin. We present new U–Pb zircon ages from the Lower Köli Ankarede Volcanite Formation in Västerbotten, Sweden. U–Pb ages of magmatic zircon grains from metamorphosed dacitic to andesitic rocks show ages of 512 ± 3.5, 497 ± 2, 491 ± 1 and 488 ± 4 Ma. The three younger ages fit with previous ages for Lower Köli volcanic rocks, but the 512 Ma age is older than any previous age for this unit. These dates constrain the age of magmatism in an ensimatic arc system within Iapetus. We compare this evolution with published information from the other Köli nappes. Magmatic ages within the KNC overlap with ages for an early episode of ultrahigh-pressure (UHP) metamorphism within the underlying Seve Nappe Complex (SNC), supporting the hypothesis that attributes UHP metamorphism within the SNC to subduction beneath the island arc now preserved within the Lower Köli Nappes.

  • 6.
    Di Rosa, Maria
    et al.
    Dipartimento di Scienze della Terra, Università di Pisa, Italy.
    Farina, Federico
    Dipartimento di Scienze della Terra Ardito Desio, Università di Milano Statale, Italy.
    Marroni, Michele
    Dipartimento di Scienze della Terra, Università di Pisa, Italy;Istituto di Geoscienze e Georisorse, CNR, Pisa, Italy.
    Jeon, Heejin
    Swedish Museum of Natural History, Department of Geology. NordSIMS, Naturhistoriska Riskmuseet, Stokholm, Sweden.
    Pandolfi, Luca
    Dipartimento di Scienze della Terra, Università di Pisa, Italy.
    U–PB ages from felsic rocks of the External Ligurian sedimentary mélange (Northern Apennine, Italy): tracing the pre-Jurassic history of the hyperextended Adria continental margin2023In: Journal of the Geological Society, ISSN 0016-7649, E-ISSN 2041-479XArticle in journal (Refereed)
  • 7. Harper, David
    et al.
    Hammarlund, Emma
    Topper, Timothy
    Swedish Museum of Natural History, Department of Paleobiology.
    Nielsen, Arne
    Rasmussen, Jan
    Park, Tae-Yoon
    Smith, Paul
    The Sirius Passet Lagerstätte of North Greenland: a remote window on the Cambrian Explosion2019In: Journal of the Geological Society, ISSN 0016-7649, E-ISSN 2041-479X, Vol. 176, p. 1023-1037Article in journal (Refereed)
    Abstract [en]

    The lower Cambrian Lagerstätte of Sirius Passet, Peary Land, North Greenland, is one of the oldest of the Phanerozoic exceptionally preserved biotas. The Lagerstätte evidences the escalation of numbers of new body plans and life modes that formed the basis for a modern, functionally tiered ecosystem. The fauna is dominated by predators, infaunal, benthic and pelagic, and the presence of abundant nekton, including large sweep-net feeders, suggests an ecosystem rich in nutrients. Recent discoveries have helped reconstruct digestive systems and their contents, muscle fibres, and visual and nervous systems for a number of taxa. New collections have confirmed the complex combination of taphonomic pathways associated with the biota and its potentially substantial biodiversity. These complex animal-based communities within the Buen Formation were associated with microbial matgrounds, now preserved in black mudstones deposited below storm wave base that provide insight into the shift from late Neoproterozoic (Ediacaran) to Cambrian substrates and communities. Moreover, the encasing sediment holds important data on the palaeoenvironment and the water-column chemistry, suggesting that these animal-based communities developed in conditions with very low oxygen concentrations.

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  • 8. Heinonen, A.
    et al.
    Andersen, T.
    Rämö, O.T.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    The source of Proterozoic anorthosite and rapakivi granite magmatism: evidence from combined in situ Hf–O isotopes of zircon in the Ahvenisto complex, southeastern Finland.2015In: Journal of the Geological Society, ISSN 0016-7649, E-ISSN 2041-479X, Vol. 172, p. 103-112Article in journal (Refereed)
    Abstract [en]

    The isotope compositions of massif-type anorthosites in Proterozoic anorthosite–mangerite–charnockite–granite (AMCG) complexes are commonly dominated by crustal values. Olivine-bearing anorthositic rocks in several AMCG suites have, however, been shown to display juvenile character, suggesting that variably depleted mantle reservoirs were involved in their genesis. A coupled in situ zircon Hf–O isotope dataset from the 1.64 Ga Ahvenisto AMCG complex in the 1.54–1.65 Ga Fennoscandian rapakivi granite–massif-type anorthosite province reveals correlated juvenile isotope signals (δ18Ozrn = 5.4–6.6‰; initial ϵHf = −1.1 to +3.4) in the most primitive gabbroic rock type of the suite suggesting a depleted mantle origin for the anorthositic rocks. This signal is not as prominent in the more evolved co-magmatic anorthositic rocks (δ18Ozrn = 6.3–7.8‰; initial ϵHf = −0.8 to +2.0), most probably owing to contamination of the mantle-derived primary magma by crustal material. A rapakivi granite associated with the anorthositic rocks has different isotope composition (δ18Ozrn = 7.4–8.6‰; initial ϵHf = −2.1 to +0.5) that points to a crustal source.

  • 9.
    Kenny, Gavin
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Mänttäri, Irmeli
    Schmieder, Martin
    Whitehouse, Martin
    Nemchin, Alexander
    Bellucci, Jeremy
    Merle, Renaud
    Age of the Sääksjärvi impact structure, Finland: reconciling the timing of small impacts in crystalline basement with regional basin development2020In: Journal of the Geological Society, ISSN 0016-7649, E-ISSN 2041-479X, Vol. 177, p. 1231-1243Article in journal (Refereed)
    Abstract [en]

    We report a new age for the Sääksjärvi impact structure, Finland, a 6 km diameter feature that formed in crystalline rocks of the Precambrian Baltic Shield. Two previous studies reported 40Ar/39Ar data for Sääksjärvi and suggested conflicting formation ages of ≤330 Ma or c. 560 Ma. The former age represents a possible complication for models which indicate that the region was covered by sediments of the Caledonian foreland basin throughout much of the Phanerozoic. We conducted a study combining imaging, microstructural analysis and U–Pb dating of shocked zircon from Sääksjärvi. The U–Pb dataset indicates a c. 600 Ma impact into predominantly c. 1850 Ma target rocks. A concordia age of 608 ± 8 Ma (2σ) confirms Sääksjärvi as the first known Ediacaran impact structure in the Baltic Shield and only the second worldwide. Our data indicate that the Sääksjärvi impact structure formed in exposed crystalline basement rocks of the Baltic Shield prior to the development of the Caledonian foreland basin. Given that most impact structures on Earth are relatively small features, radiometric dating of small impact structures in crystalline basement may place boundaries on the timing and spatial extent of palaeobasins that might otherwise be difficult to constrain.

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  • 10. Riley, T.R.
    et al.
    Flowerdew, M.J.
    Pankhust, R.J.
    Curtis, M.L.
    Fanning, C.M.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Early Jurassic magmatism on the Antarctic Peninsula and potential correlation with the Subcordilleran plutonic belt of Patagonia.2017In: Journal of the Geological Society, ISSN 0016-7649, E-ISSN 2041-479X, Vol. 174, p. 365-376Article in journal (Refereed)
    Abstract [en]

    Early Jurassic silicic volcanic rocks of the Chon Aike Province (V1: 187 – 182 Ma) are 30 recognised from many localities in the southern Antarctic Peninsula and northeast Patagonia and are 31 essentially coeval with the extensive Karoo (182 Ma) and Ferrar (183 Ma) large igneous provinces of 32 pre-breakup Gondwana. Until recently, plutonic rocks of this age were considered either rare or 33 absent from the Antarctic Peninsula batholith, which was thought to have been mainly constructed 34 during the Middle Jurassic and the mid-Cretaceous. New U-Pb zircon geochronology from the 35 Antarctic Peninsula and recently published U-Pb ages from elsewhere on the Peninsula and 36 Patagonia are used to demonstrate the more widespread nature of Early Jurassic plutonism. Eight 37 samples are dated here from the central and southern Antarctic Peninsula. They are all moderately 38 to strongly foliated granitoids (tonalite, granite, granodiorite) and locally represent the crystalline 39 basement. They yield ages in the range 188 – 181 Ma, and overlap with published ages of 185 – 180 40 Ma from granitoids from elsewhere on the Antarctic Peninsula and from the Subcordilleran plutonic 41 belt of Patagonia (185 – 181 Ma). Whilst Early Jurassic plutons of the Subcordilleran plutonic belt of 42 Patagonia are directly related to subduction processes along the proto-Pacific margin of Gondwana, 43 coeval volcanic rocks of the Chon Aike Province are interpreted to be directly associated with 44 extension and plume activity during the initial stages of Gondwana break-up. This indicates that 45 subduction was ongoing when Chon Aike Province volcanism started. The Early Jurassic plutonism on 46 the Antarctic Peninsula is transitional between subduction-related and break-up related 47 magamatism.

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  • 11. Stern, Robert J.
    et al.
    Ali, Kamal
    Asimow, Paul D.
    Azer, Mokhles K.
    Leybourne, Matthew I.
    Mubarak, Heba S.
    Ren, Minghua
    Romer, Rolf L.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    The Atud gabbro–diorite complex: Glimpse of the Cryogenian mixing, assimilation, storage and homogenization zone beneath the Eastern Desert of Egypt2020In: Journal of the Geological Society, ISSN 0016-7649, E-ISSN 2041-479X, Vol. 177, no 5, p. 965-980Article in journal (Refereed)
    Abstract [en]

    We analysed gabbroic and dioritic rocks from the Atud igneous complex in the Eastern Desert of Egypt to understand better the formation of juvenile continental crust of the Arabian–Nubian Shield. Our results show that the rocks are the same age (U–Pb zircon ages of 694.5 ± 2.1 Ma for two diorites and 695.3 ± 3.4 Ma for one gabbronorite). These are partial melts of the mantle and related fractionates (εNd690 = +4.2 to +7.3, 87Sr/86Sri = 0.70246–0.70268, zircon δ18O ∼ +5‰). Trace element patterns indicate that Atud magmas formed above a subduction zone as part of a large and long-lived (c. 60 myr) convergent margin. Atud complex igneous rocks belong to a larger metagabbro–epidiorite–diorite complex that formed as a deep crustal mush into which new pulses of mafic magma were periodically emplaced, incorporated and evolved. The petrological evolution can be explained by fractional crystallization of mafic magma plus variable plagioclase accumulation in a mid- to lower crustal MASH zone. The Atud igneous complex shows that mantle partial melting and fractional crystallization and plagioclase accumulation were important for Cryogenian crust formation in this part of the Arabian–Nubian Shield.Supplementary material: Analytical methods and data, calculated equilibrium mineral temperatures, results of petrogenetic modeling, and cathodluminesence images of zircons can be found at https://doi.org/10.6084/m9.figshare.c.4958822

  • 12. Woodard, J.
    et al.
    Tuisku, P.
    Kärki, A.
    Lahaye, Y.
    Majka, J.
    Huhma, H.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Zircon and monazite geochronology of deformation in the Pielavesi Shear Zone, Finland: multistage evolution of the Archaean–Proterozoic boundary in the Fenoscandian Shield.2017In: Journal of the Geological Society, ISSN 0016-7649, E-ISSN 2041-479X, Vol. 174, p. 255-267Article in journal (Refereed)
    Abstract [en]

    The Raahe–Ladoga Shear Complex is a major crustal structure representing the Archaean–Palaeoproterozoic boundary in the Fennoscandian Shield. The complex developed during the Svecofennian Orogeny (c. 1.9 – 1.8 Ga) beginning with regional thrust tectonic phases D1 and D2, followed by large-scale shearing events D3 and D4. The Pielavesi Shear Zone is a vertical north–south-trending shear zone within the Raahe–Ladoga Shear Complex formed during regional D3 shearing and later reactivated during the regional D4 phase. Three north–south-trending elongate granitoid intrusions were selected as representative of silicic melts that intruded the transtensional Pielavesi Shear Zone during the regional D3 phase. The oriented magmatic fabric of the granitoids indicates that they intruded coeval to the deformation event. The zircon U–(Th)–Pb secondary ionization mass spectrometry (SIMS) ages of these intrusions (1888 ± 4, 1884 ± 6 and 1883 ± 5 Ma) overlap within error and provide a direct age for the regional D3 deformation. εHf(T)(−1.1 to +3.4) and εNd(T) (−1.2 to +0.4) values from these granitoids are both consistent with a predominantly juvenile source affected by a minor Archaean component. U–(Th)–Pb SIMS analyses of metamorphic monazite formed within a crosscutting blastomylonite provide an age for the regional D4phase and associated fluid activity of 1793 ± 3 Ma.

  • 13. Yashanew, F.G.
    et al.
    Pease, V.
    Abdelsalam, M.G.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Zircon U–Pb ages, δ18O and whole-rock Nd isotopic compositions of the Dire Dawa Precambrian basement, eastern Ethiopia: implications for the assembly of Gondwana2016In: Journal of the Geological Society, ISSN 0016-7649, E-ISSN 2041-479X, Vol. 172, p. 142-156Article in journal (Refereed)
    Abstract [en]

    New high spatial resolution secondary ion mass spectrometry (SIMS) zircon dating from the Dire Dawa Precambrian basement yields crystallization ages at c. 790 Ma and 600 – 560 Ma. Two of the youngest samples are pervasively deformed, indicating that orogenesis continued until c. 560 Ma. SIMS δ18Ozrn shows bimodality, with the oldest sample (c. 790 Ma) and inherited zircons of that age in the younger samples having values of 7.8 – 9.6‰, whereas the Ediacaran samples have δ18Ozrn values of 4.9 – 7.2‰. These δ18Ozrn ratios are higher than mantle values and indicate a supracrustal input to the source of the Dire Dawa granitoids. All samples have unradiogenic εNd(t) values of −10.3 to −5.8 and Nd model ages of 1.72 – 1.42 Ga. These attributes suggest that the Dire Dawa granitoids were mostly derived from reworking of long-lived crustal sources. The occurrence of c. 580 – 550 Ma orogenesis in both the Dire Dawa basement and the juvenile Western Ethiopian Shield and the confinement of c. 630 Ma metamorphism to only the latter indicate that these two lithospheric blocks of contrasting isotopic compositions amalgamated at c. 580 – 550 Ma. This suggests that the Mozambique Ocean, which separated these two lithospheric blocks, was completely consumed during the late Ediacaran to early Cambrian.

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