Int J Earth Sci (Geol Rundsch) DOI 10.1007/s00531-017-1520-7

ORIGINAL PAPER

A ~565 Ma old glaciation in the Ediacaran of peri‑Gondwanan West Africa

Ulf Linnemann1 · Agustín Pieren Pidal2 · Mandy Hofmann1 · Kerstin Drost3 · Cecilio Quesada4 · Axel Gerdes5 · Linda Marko5 · Andreas Gärtner1 · Johannes Zieger1 · Jens Ulrich6 · Rita Krause1 · Patricia Vickers‑Rich7,8,9,10 · Jana Horak11

Received: 28 February 2017 / Accepted: 16 July 2017 © Springer-Verlag GmbH Germany 2017

Abstract In the Cadomian orogen of the NE Bohemian (“Bügeleisen-Geschiebe”), facetted pebbles, dreikanters, and Massif and of SW Iberia, a post-Gaskiers glacial event zircon grains afected by ice abrasion. For age and prov- dated at c. 565 Ma has been detected. Such Ediacaran-aged enance determination, LA–ICP–MS U–Pb ages (n = 1124) glaciomarine deposits occur in the Weesenstein and Clan- and Hf isotope (n = 446) analyses were performed. The zschwitz groups of the Saxo-Thuringian zone (Bohemia) maximum age of the glaciomarine deposits within a Cado- and in the Lower Alcudian group of the southern Central mian back-arc basin based on U–Pb analytics resulted in Iberian zone (Iberia). Both areas are parts of Cadomia the youngest detrital zircon populations showing ages of situated in the Western and Central European Varisci- 562–565 Ma and of c. 566–576 Ma old zircon derived from des. Glaciomarine sedimentary rocks are characterized granitoid pebbles within the diamictites. The youngest age by such features as dropstones, fat iron-shaped pebbles recorded was 538–540 Ma based on zircon from the plu- tons which had intruded the previously deformed Ediacaran metasedimentary rocks. Previously described glaciomarine Electronic supplementary material The online version diamictites of Cadomia (Weesenstein, Clanzschwitz, and of this article (doi:10.1007/s00531-017-1520-7) contains Orellana diamictites) are most defnitely younger than the supplementary material, which is available to authorized users.

* Ulf Linnemann Rita Krause [email protected] [email protected] Agustín Pieren Pidal Patricia Vickers‑Rich [email protected] [email protected]; [email protected] Mandy Hofmann Jana Horak [email protected] [email protected] Kerstin Drost 1 Senckenberg Naturhistorische Sammlungen Dresden, [email protected] Museum für Mineralogie und Geologie, GeoPlasmaLab, Cecilio Quesada Königsbücker Landstraße 159, 01109 Dresden, Germany [email protected]; [email protected] 2 Departmento de Estratigrafía, Universidad Complutense, Axel Gerdes 28040 Madrid, Spain [email protected]‑frankfurt.de 3 Department of Geology, School of Natural Sciences, Trinity Linda Marko College Dublin, Dublin 2, Ireland [email protected]‑frankfurt.de 4 Instituto Geológico y Minero de España, Ríos Rosas 23, Andreas Gärtner 28003 Madrid, Spain [email protected] 5 Institut für Geowissenschaften, Mineralogie, Johannes Zieger Goethe-Universität Frankfurt, Altenhöferallee 1, [email protected] 60438 Frankfurt am Main, Germany Jens Ulrich 6 G.U.B. Ingenieur AG, Niederlassung Freiberg, Halsbrücker jens.ulrich@gub‑ing.de Straße 34, 09599 Freiberg, Germany

Vol.:(0123456789)1 3 Int J Earth Sci (Geol Rundsch) c. 579–581 Ma Gaskiers glaciation in Newfoundland (Gaski- (Macdonald et al. 2010; Rooney et al. 2015). Cryogenian ers) and in SE New England (Squantum). We propose the global glacial events were followed by a mid-Ediacaran term Weesenstein–Orellana glaciation for this new Ediaca- Gaskiers glaciation aged between c. 581 and 579 Ma (Pu ran glacial event, named after the most relevant regions of et al. 2016). The global nature of the Gaskiers ice age is still exposure. Palaeogeographically, these glaciomarine diam- under debate. It is noteworthy that elements of the Ediacaran ictites and related sedimentary deposits lie on the periphery biota are frst recorded about 5 Ma after the Gaskiers glacio- of the West African Craton (western peri-Gondwana), and marine deposition of the Drook Formation, exposed on the evidence has been provided by detrital zircon U–Pb ages and Avalon Peninsula (Newfoundland) and hosting the Avalon their Hf isotope composition. Correlation with similar gla- assemblage, the oldest known community of large multicel- ciomarine deposits in the Anti-Atlas (Bou Azzer) and Saudi lular organisms on Earth (Narbonne et al. 2012, 2014). Arabia suggests a continued distribution of post-Gaskiers Here, we introduce a new post-Gaskiers glacial event glacial deposits along the Gondwana margin of Northern recorded in upper Ediacaran-aged strata occurring in the Africa. The Weesenstein–Orellana glaciation correlates in Cadomian orogen of Gondwanan Europe (Fig. 1). We pre- part with the Shuram–Wonoka δ13C anomaly. sent evidence for glaciomarine sedimentation in late Neo- proterozoic evidenced in strata from the Saxo-Thuringian Keywords Glaciation · Ediacaran · Weesenstein– zone of the Central European Variscides (Germany) and Orellana glaciation · Neoproterozoic palaeoclimate · peri- from the Central Iberian zone of the Variscides in Spain. Gondwana · West African craton · Cadomian orogeny · These sedimentary units are characterized by glaciomarine U–Pb zircon ages · Hf isotopes sedimentary features. Their maximum age is provided by U–Pb dates of youngest detrital zircon populations and of magmatic zircon from granitoid pebbles within the diamic- Introduction tites. U–Pb ages and Hf isotopes of detrital zircon were used as provenance indicators. We integrate all new data with the Glaciations have a major impact on the evolution of life and previous records and proposed the existence of a new late afect the entire planet Earth (Hofman 2009). Neoprote- Ediacaran glacial episode. rozoic glaciations played a major role as a bottleneck, and upon melting a major driver, for the origin of frst large multicellular life, and the rise of the Ediacaran biota (Nar- Geological setting bonne and Gehling 2003; Vickers-Rich and Fedonkin 2007). Cryogenian (c. 850–635 Ma) strata record the most extreme The Cadomian orogeny culminating at the end of the Pre- climate episodes in Earth’s history. The widespread occur- cambrian and the earliest Cambrian is the principal pre- rence of low-latitude glacial deposits globally together with Variscan orogenic event in both the Bohemian Massif and the unusual geochemistry and sedimentology of cap car- Iberia (Fig. 1). Cadomian orogenic processes are character- bonates (Hofman et al. 1998; Bao et al. 2008) inspired the ized by a wide range of geotectonic events that took place hypothesis of Snowball Earth (Kirschvink 1992, Kirschvink in a marginal setting at the periphery of NW and N Africa et al. 2000). Timing of Cryogenian glaciations is well estab- from c. 750 to 540 Ma (e.g., Linnemann et al. 2000, 2014; lished, represented by the Marinoan and Sturtian Snowball Gutiérrez-Alonso et al. 2003; Drost et al. 2011). The type Earth events. The Marinoan Snowball Earth (Hofman et al. area for the Cadomian orogeny is the Armorican massif in 1998) is bracketed between c. 635 and 639 Ma (Hofmann north-western France (e.g., Graindor 1957). Rocks related et al. 2004; Prave et al. 2016). Its predecessor, the Sturtian to the Cadomian orogeny are commonly referred to by the snowball, began around 717 Ma and ended at c. 660 Ma collective term “Cadomian basement”.

7 Department of Chemistry and Biotechnology, Faculty Glacial deposits in the Saxo‑Thuringian zone of Science, Swinburne University of Technology, (Bohemian massif) Melbourne (Hawthorn), VIC 3122, Australia 8 School of Earth, Atmosphere and Environment, Monash Our study focuses on rocks from the passive margin of the University, Melbourne (Clayton), VIC 3800, Australia Cadomian arc–back-arc system (Linnemann 2007; Linne- 9 School of Environmental Sciences, Deakin University, mann et al. 2014), best preserved in the Elbe zone and the Melbourne (Burwood), VIC, Australia North Saxon antiform in the southeastern part of the Saxo- 10 Palaeontology Department, Museum Victoria, Carlton Thuringian zone (NE Bohemian massif) (Fig. 2). In par- Gardens, Melbourne, VIC 3001, Australia ticular, we investigated the Ediacaran-aged Weesenstein 11 National Museum Cardif, Mineralogy and Petrology, and Clanzschwitz groups (Linnemann 2007). Furthermore, Cathays Park, Cardif CF10 3NP, UK we included in our research the granodiorites of Laas and

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Fig. 1 Location of Variscan massifs in Central and Western Europe. AM Armorican massif, BM Bohemian massif, FCM French Central massif, IM Iberian massif, M Moravo-Sile- sian unit, S Sudetes. Variscan zones: CIZ Central Iberian, CZ Cantabrian, GTOM Galicia-Tras os Montes, MZ Moldanubian, OMZ Ossa-Morena, PL Pulo do Lobo, SPZ South Portu- guese, SXZ Saxo-Thuringian, TBU Teplá-Barrandian unit, WALZ West asturian–Leonese. Ediacaran glaciomarine deposits in the Cadomian orogen: a Weesenstein and Clanzschwitz, b Orellana

Dohna (earliest Cambrian). These plutonic rocks intruded group (Figs. 2, 3) is fault-bounded against Palaeozoic rocks the Ediacaran sedimentary units at c. 540 Ma after their along its southwestern limit by the southern branch of the deformation (Linnemann et al. 2010a). West Lausitz fault. The strip of Cadomian rock units con- The Weesenstein group is exposed in the Elbe zone, tinues towards the northwest and is represented north of the which forms an NW–SE trending Variscan shear zone Meißen massif by the Rödern group and the Großenhain exhibiting a strong dextral strike-slip movement of at least orthogneiss (Fig. 2). The Cadomian basement of the Elbe 80–120 km sub-horizontal displacement (Linnemann 1994). zone continues further to the northwest into the North Saxon Strike-slip movements took place in a time interval from c. antiform. In that area, the Cadomian basement units of the 335 to 327 Ma (Hofmann et al. 2009). The Elbe zone divides Clanzschwitz group and the Laas granodiorite are present the Variscan nappe pile of the Erzgebirge in the SW from the (Fig. 2). The complex pluton of the Meissen massif intruded Lausitz Block in the NE (Fig. 2). While the latter consists into the strike-slip regime of the Elbe zone at 334 ± 3 Ma mainly of Cadomian basement rocks (Lausitz Greywacke (Hofmann et al. 2009), emplaced into the southern branch complex, and Lausitz Granodiorite complex, Linnemann of the West Lausitz fault, a distinct zone of weakness at that et al. 2010a), the Erzgebirge is composed of a complex Vari- time (Linnemann 1994). Variscan strike-slip movements scan nappe pile of at least four separate nappes characterized had ceased by 327 ± 3 Ma, the timing of intrusion of the by low pressure, and high and ultra-high pressure rocks (e.g. Markersbach granite (Hofmann et al. 2009) that crosscuts Sebastian 2013 and references therein). After reaching crus- all faults and cleavage planes in country rocks and thus pro- tal levels at c. 340 Ma, and exhumation a short time later, a vides a perfect time marker for the cessation of the Variscan top-to-NW directed fnal emplacement was responsible for strike-slip movement and the end of Variscan deformation the origin of the dextral strike-slip movements along the in the region (Hofmann et al. 2009). At the beginning of the Elbe zone (Linnemann 1994; Linnemann et al. 2010b and Permian, subsidence and felsic volcanism began in the Elbe references therein). The Elbe zone is fault-bounded against zone resulting in formation of the Döhlen basin during the the Erzgebirge nappe pile by the Mid Saxon fault, whereas Rotliegend (Fig. 2) (Hofmann et al. 2009; Zieger 2015). This the northern limit is the northern branch of the West Lausitz is the region in which the Weesenstein group and Dohna fault (Fig. 2). Variscan basement rocks of the Elbe zone show granodiorite outcrop were mapped in detail by Linnemann a protolith age range from the Ordovician to the Early Car- (1990, 1991). In the c. 2500 m-thick Weesenstein group, boniferous and crop out in the Elbtalschiefergebirge (SE of the older Seidewitz formation (c. 1500 m) occurs in the SW, Dresden) as well as in the Nossen-Wilsdruf Schiefergebirge while the younger Müglitz formation (c. 1000 m) is located (Fig. 2). Cadomian basement rocks form a narrow strip on in the NE. The section is rootless and fault-bounded at the the northeastern fank of the Elbe zone. In the Elbtalschief- base of the Seidewitz formation by the southern branch of ergebirge (Figs. 2, 3), outcrops of the Weesenstein group the Westlausitz fault (Fig. 4). The Müglitz formation is lim- and the Dohna granodiorite occur. Here, the Weesenstein ited by the intrusive contact with the Dohna granodiorite

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Fig. 2 Geological map of the Elbe zone and adjoining geological of Dohna and Laas (c. 540 Ma, Elbe zone), 12 Großenhain orthog- units showing the position of the Weesenstein, Clanzschwitz, and neiss, 13 Meißen massif (c. 335 Ma, not subdivided, monzonites, Rödern groups (Ediacaran) (modifed from Pietzsch 1927; Linne- diorites, granites), 14 Upper Carboniferous volcanic and sub-volcanic mann 2007). 1 diamictites, quartzites, greywackes, and other silici- rocks, 15 granulites of the Granulitgebirge (“Saxonian Granulites”, clastic metasedimentary rocks of the Weesenstein, Clanzschwitz, and Variscan metamorphic core complex), 16 schist belt on the periph- Rödern groups (Ediacaran), 2 greywackes and mudstones (Ediaca- ery of the Granulitgebirge, 17 fasergabbro, 18 greenschists (prasin- ran, Lausitz Greywacke complex), 3 Cambro-Ordovician quartzites ites), 19 orthogneiss (c. 490 Ma) of the Frankenberg Zwischengebirge and quartz schists, 4 Palaeozoic rocks not subdivided (Ordovician to (Variscan nappe complex), 20 gneisses and other lithologies of the Early Carboniferous), 5 Phyllitic Unit of the Elbe zone (Mühlbach- Erzgebirge nappe pile (high- and ultra-high-pressure rocks, not sub- Nossen group, Cambro-Ordovician, to Devonian protoliths), 6 Early divided), 21 phyllites and other lithologies of the Erzgebirge nappe Variscan molasses of Hainichen (upper Viséan), 7 Rotliegend (Early pile (low pressure rocks, not subdivided), 22 Variscan granitoids (c. Permian Variscan molasses), 8 Late Cretaceous, 9 granodiorites and 335–320 Ma), 23 major fault anatexites (c. 540 Ma, Lausitz Granitoid complex), 10 Granodiorites

(Figs. 3, 4). The latter is dated at c. 538 Ma (Pb–Pb age, the sedimentary pile is the Purpurberg quartzite member Gehmlich 2003). The general metamorphic overprint is (Fig. A), a sedimentary sequence of medium-to-thick-bed- characterized by a mid-to-high greenschist grade (in part ded quartzites (“Purpurberg quartzite”, Figs. 4, 5a, b) with biotite grade). Bedding is sub-vertical with two pronounced quartz schist intercalations in the middle and conglomerate cleavages (Cadomian, Variscan, Linnemann 1990). The at the top (Fig. 5d). Primary sedimentary features, such as older Seidewitz formation represents a pre-glacial deposit, cross bedding and ripple marks (Fig. 5b), indicate that the while the younger Müglitz formation contains glaciomarine lower part of the section is distributed in the SW, while the sedimentary rocks (Fig. 5). younger top in a transition to the overlying Müglitz forma- The Seidewitz formation is composed primarily of shelf tion occurs towards the NE (Fig. 4). The Purpurberg quartz- deposits, such as quartz schist, quartzite, quartz wacke, ite member represents the marine part of a fan delta deposit, greywacke, and mudstone (Fig. 5a–d). A prominent part of which pinches out along strike towards the SE and to the

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NW (Fig. 4) (Linnemann 2007). The depositional centre is rocks, such as rhyolite, felsite porphyry (andesite), and kera- located at the Purpurberg and the Hallstein regions (Fig. 5a) tophyre (22.7%). Only 15.0% are igneous in origin includ- along both fanks of the valley of the Bahra River (Fig. 4) ing granodiorite, aplitic granite, and granite. The remaining (Linnemann 1990). The Purpurberg member is thin-bedded 15.1% of the pebbles are vein quartz and quartz derived from in the more distal parts of the fan delta and perfectly vis- pegmatites (Schmidt 1960). The dominance of sedimentary ible in the outcrops of the “Röhrsdorfer Park” (Figs. 4, 5c). rocks among the loose pebbles in the diamictite is an addi- The Seidewitz formation is limited in completeness at the tional argument for its glaciomarine origin, because glaciers base by the tectonic contact of the southern branch of the erode mainly the shelf deposits in the source area before West Lausitz fault (Fig. 4). In that part of the formation, the became foating ice. geological situation becomes further complicated by intru- In addition to the observations of glaciomarine features sion of a Variscan hornblende granodiorite (Fig. 4), which in the macro-scale, we carried out studies on zircon surfaces is part of the Meissen massif (c. 335 Ma; Hofmann et al. recovered from the diamictites of the Müglitz formation and 2009). Due to the contact-metamorphic overprint, most of compared them with such surfaces derived from a sub-recent the older part of the Seidewitz formation has been altered Quarternary lodgement till from Germany (Isle of Rügen, into an andalusite hornfels (Pietzsch 1917; Linnemann coastline north of Saßnitz, Fig. 7). Features indicative of 1990). In its northwesternmost part, the Seidewitz forma- glacial transport for detrital grains include high angularity, tion was afected by partial melting and magmatization due fresh faces, conchoidal breaks, and arc-step-like fractures to a contact-metamorphic overprint by the emplacement of reported by Immonen (2013). SEM backscatter images of the Meissen massif and strong shearing during the dextral investigated zircon grains show clear efects of ice abra- strike-slip movements along the Elbe zone (Fig. 2) (Linne- sion in the Quarternary lodgement till (Fig. 7a–f), similar mann 1990). Within the Seidewitz formation, a number of to such surfaces on the zircons recovered from the glacio- amphibolites and meta-basalts occur (Fig. 4). In addition, marine rainout deposit of the Weesenstein group (Fig. 7g–q, one very badly exposed chert layer is known only from loose sample WST 1, Müglitz formation). Zircons from both sam- blocks found close to “Röhrsdorfer Park” (Pietzsch 1917) ples exhibit scratches, fatiron shapes with relatively sharp (Fig. 4). top and stump end, and rip-up structures generated in the The transition of the Seidewitz formation into the overly- pressure shadows during ice abrasion. Edges of rip-ups ing (younger) Müglitz formation is gradual. The transitional had been sub-rounded subsequently during sedimentation interval is best exposed on the eastern fank of the Müglitz processes and demonstrate that they are not formed during valley (Fig. 4) in the area northeast of the Weesenstein heavy mineral separation by the jaw crusher. Some zircon castle. Quartzite and quartz schist grade into greywacke, grains exhibit shortening by compression characterized mudstone, and quartz wacke of the Müglitz formation. An by a release band running vertical to compressive strain additional, characteristic feature of the Weesenstein forma- (Fig. 7f, p). Cathodoluminescence images of zircons from tion is occurrence of diamictites and conglomerates (Figs. 4, the Weesenstein diamictite refect a wide range of diferent 5e–g). The diamictites crop out mainly along the fanks of tectonomagmatic settings from which such zircon grains the Müglitz Valley (Fig. 4). A few exposures are known were derived (Fig. 8). Most zircons show normal magmatic in the valley of the Lockwitz River (Fig. 4) (Linnemann zoning, and this points to a felsic provenance. Complex zir- 1990). Isolated diamictite pebbles of granitoids, quartzite, cons with core and rim are common. Other grains seem to and greywacke “swim” in a matrix of greywacke and mud- have been derived from mafc melts or rocks which under- stone (Fig. 5e, f), varying in size between 5 mm and 30 cm. went ultra-high-pressure metamorphism. Some of the pebbles are rounded and deformed due to Late Within the Elbe zone and the North Saxon antiform, Carboniferous tectonic overprint (Fig. 5e). rock units exist, which are related to the Weesenstein group. In some units, the diamictite is less deformed, particularly Towards the northeast, the Cadomian basement of the Elbe those cropping out around the railway station of Weesen- zone continues into the Radeburg area, bound by the north- stein. Here, diamictites which escaped penetrative deforma- ern and southern branches of the Westlausitz fault (Fig. 2). tion in the pressure shadows of more competent rock units, Here, Cadomian rocks are preserved in a narrow strip of such as thick quartz wacke layers, can reach a thickness of meta-greywackes (Rödern group). Bedding and cleavage run more than 50 m. Glaciomarine features are documented by sub-vertical. Locally layers of diamictite occur at Brotberg dropstones (Fig. 6a), dreikanters (Fig. 6b), fatiron-shaped Mountain near Rödern (Schmidt 1960). The metasediments pebbles (“Bügeleisen-Geschiebe”) (Fig. 6c, d), and facetted of the Rödern group exhibit a metamorphic overprint gener- pebbles (Fig. 6d, e). Typical rainout deposits, formed by ated under greenschist facies conditions (biotite grade) and melting icebergs, also occur (Fig. 6f), with randomly ori- were intruded at c. 540 Ma by a protolith of the Großen- ented and predominantly quartzite and greywacke pebbles hain orthogneiss (Fig. 4) (Schmidt 1960; Gehmlich 2003). (47.2%). The second-largest group represented is volcanic During the Variscan strike-slip movements along the Elbe

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zone, the Cadomian basement strip was intruded by the c. The entire group is about 850 m thick and shows sub-vertical 335 Ma old Meißen massif magma (Hofmann et al. 2009) bedding and cleavage. Member 1 is composed of mudstones (Fig. 2). The Rödern group is a strongly deformed equiva- and quartz schists, and was intruded by the Laas granodiorite lent of the Weesenstein group, while the Großenhain orthog- in the Early Cambrian. The strong contact metamorphism neiss is a highgrade overprinted continuation of the Dohna led to the origin of up to ~1 cm andalusite crystals. The granodiorite. second member of the Clanzschwitz group is composed of In the North Saxon antiform, about 30 km to the NW, quartzite and quartz schist. Member 3 hosts diamictite (Clan- there is a third area of importance with a Cadomian base- zschwitz diamictite) and conglomerate layers (Fig. 5g). The ment unit (Fig. 2). The metasedimentary Clanzschwitz Clanzschwitz group was intruded by the Laas granodiorite group is subdivided into three un-named members (Fig. 9). at c. 533 Ma (Pb–Pb age, Gehmlich 2003), and underwent

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◂Fig. 3 Geological map of the Elbtalschiefergebirge at Dresden by granodiorites of a similar age (c. 533–540 Ma, Pb–Pb (modifed from Linnemann et al. 2008). 1 Weesenstein group contain- ages by Gehmlich 2003). All in all, the Cadomian basement ing the older Seidewitz formation including the Purpurberg Quartz- ite member and the younger Müglitz formation (Ediacaran), 2 Pur- units of the Elbe zone share striking similarities. Thus, purberg quartzite member and its equivalents (Seidewitz formation, we assume that these units formed a single pre-Variscan Weesenstein group, Ediacaran), 3 Quartz schists often under- and rock unit along the southern margin of the Lausitz block. overlying the Purpurberg quartzite member (Seidewitz formation, The formerly coherent unit of Cadomian passive margin Weesenstein group, Ediacaran), 4 Isolated pebbles and conglomer- ates of glaciomarine origin (Müglitz formation, Weesenstein group, sequences, including diamictite levels, was later sliced into Ediacaran), 5 Meta-basalts (Weesenstein group, Ediacaran), 6 Dohna the described three sub-units at Weesenstein, Rödern, and granodiorite (Early Cambrian), 7 Cadomian metasediments of the Clanzschwitz due to dextral strike-slip movements along the Erzgebirge block overprinted under upper greenschist to amphibo- Elbe zone (Linnemann 1994; Linnemann et al. 2010a, b) lite facies conditions during Variscan orogenic processes, 8 Ordovi- cian, Silurian and Devonian metasediments and volcanic rocks of in the c. 335–327 Ma time interval (Hofmann et al. 2009). the Elbtalschiefergebirge overprinted under greenschist facies condi- tions during Variscan orogenic processes (so-called “Phyllitic unit” Glacial deposits in the Central Iberian zone (Iberian of the Elbe zone or Mühlbach-Nossen group), 9 Ordovician granite massif) (Tourmaline granite, 485 ± 6 Ma, Linnemann et al. 2000), 10 Early Carboniferous metasediments, 11 Devonian volcano-sedimentary complex of the Elbtalschiefergebirge, 12 Devonian “diabase-lime- Lotze (1945) proposed a division of the Iberian massif into stone series” of the Elbtalschiefergebirge, 13 Early Carboniferous six tectonostratigraphic zones, which still forms the basis of siliciclastic fysch deposits of the Elbtalschiefergebirge, 14 Variscan present subdivisions. Lotze’s Eastern Lusitanian–Alcudian (Early Carboniferous) granitoids of the Meissen massif (c. 335 Ma) and the Markersbach granite (c. 320 Ma, Hofmann et al. 2009), 15 Zone is a 100–150 km-wide band that stretches from Coim- Permian and younger sedimentary cover, 16 major faults and dextral bra–Castelo Branco–Cáceres to Ciudad Real and contains shear zones of the Elbtalschiefergebirge originated during Variscan the glaciomarine diamictites dealt with herein. It was later orogenic processes, 17 Limit of Permian (Rotliegend) sedimentary merged with the Galician–Castillian Zone into the Central rocks, 18 Limit of Cretaceous (Cenomanian–Turonian) sedimentary rocks, P-Top of the Purpurberg Mtn., type locality for the Purpurberg Iberian Zone by Julivert et al. (1972). Neoproterozoic rocks quartzite member occur in most tectonostratigraphic domains of the Variscan orogen in Iberia interpreted to have once belonged to peri- Gondwanan Cadomia (Quesada 1990, 1991). The various a high greenschist facies and biotite grade regional meta- divisions are thought to represent an arc/back-arc system morphism. After a gap of sedimentation, the Cadomian (Ossa-Morena zone) accreted to a passive margin of West basement in the North Saxon antiform was transgressed by Africa on which a retro-arc basin developed (Central Iberian, Lower Ordovician sediments, preserved as quartzites and West Asturian–Leonese, and Cantabrian zones) as a conse- mudstones of the Collmberg formation (Pietzsch 1962), quence of such arc accretion in late Neoproterozoic-earliest cropping out south of Clanzschwitz (Fig. 2). Cambrian time (Quesada 1990, 1991, 1996, 2006). Defor- The three described Cadomian basement exposures host mation associated with this arc-continent event character- the same geological unit which forms a ca. 60 km-long strip izes the Cadomian orogeny in this part of peri-Gondwana along the northeastern fank of the Elbe zone and at the and variably afected the various parts involved (Gutiérrez- southeastern margin of the North Saxon antiform (Fig. 2). Alonso et al. 2003). Among the different tectonostrati- The sedimentary and igneous parts of all three Cadomian graphic zones in Iberia, the Central Iberian zone is by far basement units exhibit striking similarities. Both the older the one of the largest and thickest exposures of Cadomian parts of the Clanzschwitz (members 1 and 2) and Weesen- basement rocks (commonly known as Schist and Greywacke stein groups (Seidewitz formation, Purpurberg quartzite Complex in this area). member) consist of quartzite and quartz schists. In the Ovtracht and Tamain (1970) studied the Proterozoic younger parts, both groups are composed of diamictites, rocks of the Schist and Graywacke complex in the core of greywackes, and conglomerates, also similar to the Müglitz the Alcudia anticline. They subdivided the Ediacaran-aged formation (Weesenstein group) and member 3 of the Clan- sedimentary rocks into Lower and Upper Alcudian groups zschwitz group. In addition, the package of greywacke and (Fig. 10) and subsequently integrated into the so-called mudstone in the Rödern group hosts diamictite horizons, Alcudian supergroup (San José et al. 1990) (Fig. 11). These poorly exposed at the Brotberg area near the village of rocks have also been called the Extremenian Dome group Rödern (Schmidt 1960). The occurrence of facetted peb- (Álvarez-Nava Oñate et al. 1988), a name which unfortu- bles and the c. 60 km-wide distribution of diamictites in the nately has no relation to the investigated area. Therefore, Weesenstein, Clanzschwitz, and Rödern areas at the same the terms Lower and Upper Alcudian group are preferred lithostratigraphic level supports a glaciomarine nature of here. In the area around Orellana, Ediacaran and lower Pal- the diamictites (Linnemann 2007). All three sedimentary aeozoic strata were mapped and studied in detail by Pieren units of Cadomian basement in the Elbe zone were intruded (2000). The exposed Lower Alcudian group is about 4000 m

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Fig. 4 Lithostratigraphic columns of the Weesenstein group (Elbe ite); 8 greywacke; 9 mudstone; 10 andalusite quartzfels; 11 metasedi- zone, Elbtalschiefergebirge, Saxo-Thuringian zone) (from Linne- ments strongly sheared and overprinted by contact metamorphism, mann 1990, 1991). 1 conglomerate with pebbles of quartz and horn- often partial anatectic melting initialized by contact metamorphism fels (diameter of pebbles up to 3 cm); 2 conglomerate with pebbles is indicated; 12 meta-basalts; 13 Dohna granodiorite (538 ± 2 Ma, of quartz and rarely hornfels (diameter of pebbles up to 1 cm); 3 this study); 14 Hornblende diorite of the Meißen massif (334 ± 3 Ma, quartzite of the Purpurberg quartzite member (PBQM) and related Hofmann et al. 2009); 15 sample location; PBQM Purpurberg quartz- quartzite horizons of the Seidewitz formation; 4 quartz schist; 5 chert; ite member 6 glaciomarine Weesenstein diamictite of the Müglitz formation (“Weesenstein tillite”); 7 quartz wacke (immature greenish quartz- thick, but its base is nowhere exposed (Fig. 11). The group afnity to a continental island arc which matches with the is characterized by a monotonous succession of turbidites paleogeographic/paleotectonic interpretations mentioned composed of greywacke and mudstones (Fig. 11). Accord- above (Quesada 1991, 1996, 2006; Pieren 2000). ing to García-Hidalgo et al. (1993) and Pieren (2000), the The Lower Alcudian group was folded and locally cleaved Lower Alcudian group from bottom to top is composed of during the Cadomian orogenic activity. Generally, a vertical (1) shales and greywackes (“La Coronada Shales forma- and sub-vertical L­ 1 lineation is present, which was generated tion”), (2) greywacke, microconglomerate, and shale (“Saint by a (in the area) non-schistose gentle folding in the late Mary of Zújar chapel greywackes and conglomerates forma- Ediacaran (“intra-Alcudian” or Cadomian deformation). In tion”), and (3) shale, diamictite (pebbly mudstones), and addition, a Variscan schistose ­F1 exists. Most cobbles were greywacke (“Orellana matrix supported conglomerates for- oriented parallel to a 70ºN dipping L­ 1 lineation. Some of mation”) (Fig. 11). Some greywacke turbidite beds are up them were not oriented or almost normal to the ­L1 lineation. to 6 m thick and have been used as marker horizons during The Lower Alcudian group is unconformably overlain geological mapping of the region. Fuenlabrada et al. (2016) by the Upper Alcudian group (Fig. 11; Pieren 2000). This analyzed major and trace elements, REE, and Sm–Nd iso- lithostratigraphic unit begins with conglomerates and coarse topes of greywacke samples of the second unit. Their geo- sandstones followed upsection by fne-grained sandstones chemical results point to an active margin setting as the most and mudstones. Further upsection, shale and dolomite lay- reasonable source for the deposition of the Ediacaran–Early ers occur (Fig. 11). The basal unit of the Upper Alcudian Cambrian sequences of the Central Iberian zone. Trace ele- group is considered to be latest Ediacaran. However, based ment diagrams of the Ediacaran greywackes indicate a clear on contained ichnofossils (Pieren 2000) and detrital zircons

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Fig. 5 Outcrops and lithologies of the Weesenstein and Clan- A E zschwitz groups. a Purpurberg quartzite member (Weesenstein group, Seidewitz formation) sub-vertically dipping and forming a ridge (clifs of the Hallstein, Bahra valley, Elbtal- schiefergebirge). b Purpurberg quartzite member, proximal thick-bedded facies, bedding is sub-vertical and shows ripple marks and cross bedding (Pur- purberg near Friedrichswalde, Elbtalschiefergebirge, c cross bedding, b bedding plane), c Purpurberg quartzite member, distal thin-bedded facies, bed- ding is steeply dipping (outcrop B in the “Röhrsdorfer Park” close to Röhrsdorf, Elbtalschief- ergebirge). d Polished hand specimen of the conglomerate from the top-most part of the Purpurberg Quartzite mem- ber, white pebbles consist of quartzite, and black pebbles are composed of tourmaline hornfels (Purpurberg near F Friedrichswalde, Elbtalschiefer- gebirge), e Isolated and tectoni- cally stretched granitoid pebble in a matrix of greywacke and G mudstone (Weesenstein group, Müglitz formation, “Weesen- stein diamictite”, klippen at the railway station Weesenstein, Müglitz valley, Elbtalschiefer- gebirge), f Isolated and tectoni- cally stretched granitoid pebbles in a matrix of greywacke and mudstone (Weesenstein group, C Müglitz formation, “Weesen- stein diamictite”, klippen at the footpath from Weesenstein D to Köttewitz, Müglitz valley, Elbtalschiefergebirge), g Con- glomerate of the Clanzschwitz group (member 3, North Saxon antiform)

studied elsewhere in the region (Talavera et al. 2015), the to the generalized rift event recorded everywhere in Iberia upper part could be earliest Cambrian in age. during the Cambrian–Lower Ordovician (Quesada 1991; A second deformation affected both the Lower and Sánchez-García et al. 2003, 2008, 2010). Subsequent sub- Upper Alcudian groups. The Upper Alcudian group may sidence, interpreted in response to opening of the Rheic well represent a Cadomian remnant or successor basin Ocean as a culmination of rifting, allowed the area to be deformed during the latest stage of the Cadomian orogeny. transgressed in the Lower Ordovician establishing a new After fnal Cadomian deformation, a time of uplift, intense passive margin of Gondwana that survived until Variscan weathering, and erosion may represent the local response collision in the Devonian (Quesada 1991, 2006). The Lower

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Fig. 6 Images from the glacio- marine deposits of the Weesen- stein group (Müglitz formation, A klippen at the railway station Weesenstein, Müglitz val- ley, Elbtalschiefergebirge). a Granitoid dropstone in a rainout deposit, b dreikanter, c bullet shaped clast (fat iron-shaped pebble) in a rainout deposit (upper part sharp top formed by ice abrasion, lower part stump end in the pressure shadow during ice abrasion) (“Büge- B leisen-Geschiebe”), d facetted and striated pebble (fat iron- shaped pebble = “Bügeleisen- D Geschiebe”), e sharp facetted pebble from a rainout deposit, f rainout sediment showing isolated pebbles with diferent orientations “swimming” a fne- grained matrix C

E

F

Ordovician-aged reddish sandstone and mudstone and the sediments (Fig. 12c), fat iron-shaped pebbles (“Bügeleisen- Armorican quartzite formation were the frst to be deposited Geschiebe”) (Fig. 12d), and facetted pebbles (Fig. 12e). Pebble during this passive margin stage (Fig. 11; Pieren 2000). size varies between a few millimetres and 20 cm. Glaciomarine Diamictites in the uppermost part the Lower Alcudian diamictite occur in c. 10–50 m-thick beds in the region of Orel- group (Figs. 11, 12) show distinct features indicative of a lana la Vieja, Orellana de la Sierra, and the Orellana reservoir glaciomarine origin, including dropstones (Fig. 12b), rainout (Embalse de Orellana; Pieren 2000).

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Samples for U–Pb dating and Hf isotope analyses from the matrix of the diamictite in member 3 (greywacke, Kleiner Steinberg near Clanzschwitz, coordinates: N For our investigation to determine absolute age and prov- 51°20′47.9″; E 13°09′41.5″. A second sample (CL2) came enance, we collected ten samples of clastic sedimentary from the quartzite of member 2 (Großer Steinberg near Clan- rocks, six granodiorites, four granitoid pebbles, and one zschwitz, coordinates, N 51°21′1.17″; E 13°09′39.58″. A quartzite pebble. Pebbles were sourced from the glacioma- granitoid pebble (Cla 1n) from the diamictite (member 3) rine diamictite layers in the Weesenstein and Clanzschwitz was sampled at the Schlangenberg near Wellerswalde (coor- groups. One sample was taken from the Lower Alcudian dinates: N 51°20′44.01″; E 13°09′42.75″). From the Laas group (Iberia) near Orellana. U–Pb LA–SF–ICP–MS* dat- granodiorite that intruded the Clanzschwitz group, one sam- ing was carried out on zircons from all samples (*Laser ple was taken (Laas 1n, forest 1.5 km north of Clanzschwitz, ablation and inductively coupled plasma combined with a N 51°21′34.34″; E 13°09′22.60″). sector feld mass spectrometer). Analysis of Hf isotopes by From the Lower Alcudian group, one sample of a diamic- LA–MC–ICP–MS** was undertaken on zircon grains from tite matrix was taken from a road cut in the surroundings of Weesenstein and Clanzschwitz only (six sedimentary rock Orellana (sample OR1, N 39°00′4.6″; W5°34′11.9″). samples, three granitoid pebbles, one quartzite sample, and Hf isotope analysis by LA-MC- ICP-MS carried out on six granodiorite samples) (**Laser ablation and inductively zircon grains from of fve sedimentary rock samples (WST1, coupled plasma combined with a multicollector mass spec- W63d, P-Pur-1b-2-LA10, CL1, and CL2), one quartzite trometer). The sample locations are marked in the columns pebble (WeG4), three granitoid pebbles (WeG2n, WeG5, and map of Figs. 4, 9 and 11. Exact location details are given Cla1n), and six granodiorite samples (Dohna 2, 3, 4, DG1n, in the headings of Table 1 (U–Pb ages) and Table 2 (Hf Laas1). isotopes) (supplementary data). The following sedimentary samples have been collected from the Müglitz formation of the Weesenstein group: WST1 Methods (diamictite matrix, greywacke, Müglitz valley near Weesen- stein, coordinates: N 50°56′09.77″; E 13°51′47.42″), GWQ1 Zircon concentrates were separated from 2 to 4 kg samples (quartz wacke, Müglitz valley opposite to the castle in at the Senckenberg Naturhistorische Sammlungen Dres- Weesenstein, coordinates: N 50°56′01.90″; E 13°51′34.80″), den (Museum für Mineralogie und Geologie) by crushing and W63d (conglomerate, Müglitz valley at the Fuchshü- (jaw crusher), sieving, heavy mineral separation by heavy bel, coordinates: N 50°56′23.21″; E 13°51′36.31″). From the liquid (LST), and by making use of a magnetic separator. Seidewitz formation (Purpurberg quartzite member) of the Final selection of the zircon grains for U–Pb dating was Weesenstein group, the quartzite sample P-Pur-1n-2-LA10 achieved by hand-picking under a binocular microscope. Zir- was collected (quartzite, top of the Purpurberg, coordinates: con grains of all grain sizes and morphological types were N 50°54′48.64″; E 13°54′23.03″). In addition, one quartzite selected, mounted in resin blocks, and polished to half their pebble (WeG4) from the Müglitz formation was sampled thickness. Concerning stratigraphic ages, the stratigraphic (quartzite pebble, Müglitz valley at railway station Weesen- time scale of Ogg et al. (2016) has been used. stein, N 50°56′12.55″; E 13°51′49.67″). Furthermore, three granitoid pebbles from the diamictite in the Müglitz forma- U–Th–Pb isotopes tion (Weesenstein group) were sampled: WeG2n, WeG3n, and WeG5 (granitoid pebbles, Müglitz valley at railway sta- Zircons (n = 1124) were analyzed for U, Th, and Pb iso- tion Weesenstein, N 50°56′12.55″; E 13°51′49.67″). From topes by LA–SF ICP–MS techniques at the Museum für the Dohna granodiorite, which is intrusive into the Weesen- Mineralogie und Geologie (GeoPlasma Lab, Senckenberg stein group, fve samples were collected: Dohna1 (Müglitz Naturhistorische Sammlungen Dresden), using a Thermo- valley, Köttewitzer Wehr, coordinates: N 50°56′29.12″; E Scientifc Element 2 XR sector feld ICP-MS coupled to 13°51′38.83″), Dohna2 (Müglitz valley, Köttewitzer Wehr, a New Wave UP-193 Excimer Laser System. A teardrop- coordinates: N 50°56′29.28″; E 13°51′39.41″), Dohna 3 shaped, low-volume laser cell was used to enable sequential (Köttewitz, Müglitz valley on the foot path to Weesenstein, sampling of heterogeneous grains (e.g., growth zones) dur- coordinates: N 50°56′33.25″; E 13°52′03.36″), Dohna 4 ing time resolved data acquisition. Each analysis consisted (roadcut near Dresden-Nickern and Goppeln, SE of the of approximately 15 s background acquisition followed Gamighübel, temporary outcrop during road construction, by 30 s data acquisition, using a laser spot size of 25 and coordinates: N 50°59′44.67″; E 13°46′28.07″), and DG1n 35 µm, respectively. A common Pb correction based on the (Bahra valley, coordinates: N 50°55′2.61″; E 13°54′41.60″. interference- and background-corrected 204Pb signal and a From the Clanzschwitz group, two metasedimentary rock model Pb composition (Stacey and Kramers, 1975) was car- samples were sourced. The frst sample (CL1) was taken ried out if necessary. The necessity of the correction was

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judged on whether the corrected 207Pb/206Pb lies outside of uncertainties were propagated by quadratic addition of the the internal error of the measured ratios. Discordant analy- external reproducibility obtained from the standard zircon ses were interpreted with care. Raw data were corrected for GJ-1 (~0.6 and 0.5–1% for the 207Pb/206Pb and 206Pb/238U, background signal, common Pb, laser induced elemental respectively) during individual analytical sessions and the fractionation, instrumental mass discrimination, and time- within-run precision of each analysis. According to the rec- dependant elemental fractionation of Pb/Th and Pb/U using ommendation of Horstwood et al. (2016), a secondary zir- an Excel­ ® spreadsheet program developed by Axel Gerdes con standard (Plesovice zircon) was analyzed. Sequences (Institute of Geosciences, Johann Wolfgang Goethe-Uni- started with the analysis of fve GJ1, one Plesovice, and ten versity Frankfurt, Frankfurt am Main, Germany). Reported unknowns followed by a repetition of a succession of three

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◂Fig. 7 SEM backscatter images of zircon grains afected by ice abrasion from a Quaternary glacial diamictite (a–f Germany, Isle of Rügen, coastline north of Saßnitz) and from a glaciomarine rainout deposit of the Weesenstein group (g–q sample WST 1, Müglitz for- mation). “p” indicates the assumed maximum pressure during ice abrasion and “s” the pressure shadow. Arrows show the resulting movement of the ice during abrasion processes. Images show exam- ples of typical glacial features like high angularity, fresh faces, con- choidal breaks, and arc-step like fractures. a Scratches in a zircon grain. b Enlargement of a, c fat iron-shaped zircon grain. d zircon grain showing a more conic and a more stump end. e Scratches in the zircon grain shown in d. f Zircon grain illustrating shortening by compression, note the releasing band running perpendicular to the strain. g Zircon showing scratches (left) and rip-up structures (right), h enlargement of g. i Zircon showing rip-ups on the right side, which are sub-rounded by subsequent transport (see enlargement in j). j Enlargement of i, scratched zircon surface and sub-rounded edges of rip-ups, which rule out an origin during heavy mineral separation (e.g., by jaw crusher). k Zircon with relatively sharp top and stump end in the pressure shadow produced during ice abrasion., l zircon with rip-up showing sub-rounded edges. Similar to k, this grain hosts a sharp top and stump end in the pressure shadow produced during ice abrasion. m Zircon with rip-ups in the pressure shadow during ice abrasion. n Enlargement of M, zircon with rip-ups generated in the pressure shadow produced during ice abrasion; edges had been sub-rounded subsequently. o Zircon with scratches generated by ice abrasion. p Zircon grain showing shortening by compression, note the releasing band running perpendicular to the strain. q Flatiron-shaped zircon grain

measurements of the GJ1 standard, one measurement of the Plesovice standard, and ten unknowns. U–Pb ages were in the recommended range of Sláma et al. (2008). Concordia diagrams (2σ error ellipses) and Concordia Fig. 8 Cathodoluminescence (CL) images and U–Pb LA–ICP–MS ages (95% confdence level) were produced using Isoplot/Ex ages of zircon grains from the Purpurberg Quartzite member (Sei- 2.49 (Ludwig 2001) and frequency and relative probability dewitz formation, Weesenstein group) (sample Pur 2). Complex zir- plots using AgeDisplay (Sircombe 2004). The 207Pb/206Pb con grains are very common (spots b3–b4; b6–b7; c15–c16). Zircon grains which were afected by high pressure metamorphism are fre- age was taken for interpretation for all zircons >1.0 Ga, and 206 238 quent among the Eburnean-aged zircons (a52, c60). Very rare are zir- the Pb/ U ages for younger grains. For further details con grains which originated in mafc melts (b35) on analytical protocol and data processing, see Gerdes and Zeh (2006). Th/U ratios are obtained from the LA–ICP–MS measurements of investigated zircon grains. U and Pb con- instrumental mass bias for Hf isotopes was corrected using tent and Th/U ratio were calculated relative to the GJ-1 zir- an exponential law and a 179Hf/177Hf value of 0.7325. In con standard, and are accurate to approximately 10%. Ana- case of Yb isotopes, the mass bias was corrected using lytical results of U–Th–Pb isotopes and calculated U–Pb the Hf mass bias of the individual integration step mul- ages are given in Table 1 (supplementary data). tiplied by a daily βHf/βYb ofset factor (Gerdes and Zeh 2009). All data were adjusted relative to the JMC475 Lu–Hf isotopes of 176Hf/177Hf ratio = 0.282160 and quoted uncertain- ties are quadratic additions of the within-run precision Hafnium isotope measurements on zircons (n = 446) were of each analysis and the reproducibility of the JMC475 made using a Thermo-Finnigan Neptune multicollector (2SD = 0.0028%, n = 8). Accuracy and external reproduc- ICP-MS at Goethe Universität Frankfurt (GUF, Institut ibility of the method were verifed by repeated analyses of für Geowissenschaften, Mineralogie) coupled to RESOlu- reference zircon GJ-1 and Plesovice. Results are in perfect tion M50 193 nm ArF Excimer laser system (Australian agreement with previously published results (e.g., Gerdes Scientifc Instruments) following the method described in and Zeh 2006; Sláma et al. 2008) and with the LA-MC- Gerdes and Zeh (2006, 2009). Spots of 40 µm in diameter ICP MS long-term average of GJ-1 (0.282010 ± 0.000025; were drilled with a repetition rate of 5.5 Hz and an energy n > 800) and Plesovice (0.282483 ± 0.000025, n > 300) density of 6 J/cm2 during 50 s of data acquisition. The reference zircon at GUF.

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Fig. 9 Geological map with sample locations and a lithostratigraphic ber 2), 3 diamictite (glaciomarine diamictite, “Clanzschwitz tillite”) column of the Clanzschwitz group (North Saxon antiform). 1 Mud- (member 3), 4 quartzite and quartz schist (Ordovician, Collmberg stones and quartz schists afected by contact metamorphism of the formation), 5 Laas granodiotite, 6 Laas granodiorite with a gneissic Laas granodiorite with large andalusite crystals (up to 1 cm) (mem- texture, 7 fault, 8 roads, and 9 villages ber 1 of the Clanzschwitz group), 2 quartzite and quartz schist (mem-

The initial 176Hf/177Hf values are expressed as Results and discussion εHf(t), which is calculated using a decay constant value −11 −1 of 1.867 × 10 year , CHUR after Bouvier et al. Age constraints for glaciomarine sedimentation 176 177 176 177 (2008, Hf/ HfCHUR,today = 0.282785 and Lu/ Hf CHUR,today = 0.0336) and U–Pb and Pb–Pb ages obtained U–Pb ages of detrital zircons are represented in Figs. 13 for the respective domains (Table 2, supplementary and 14. Because ash beds and fossils have not been found data). For the calculation of Hf two stage model ages in the investigated sections, the maximum depositional age 176 177 ­(TDM) in billion years, the measured Lu/ Lu of (MDA) had to be used for the stratigraphic age determina- each spot (frst stage = age of zircon), a value of 0.0113 tion (Condon and Bowring 2011). for the average continental crust, and a juvenile crust The maximum depositional age for each sample was 176 177 176 177 Lu/ LuNC = 0.0384 and Hf/ Hf NC = 0.283165 calculated from the youngest zircon population for each (average MORB; Chauvel et al. 2008) were used. sandstone sample (Figs. 13, 14). For the Weesenstein diam- Cathodoluminescence (CL, supplementary data) and ictite (WST1, Müglitz formation, Weesenstein group), a backscatter images were made using an EVO 50 scanning maximum depositional age of 562 ± 5 Ma was obtained electron microscope (Zeiss) at Senckenberg Naturhistorische (Fig. 13). Underlying strata show similar maximum depo- Sammlungen Dresden. sitional ages of 562 ± 5 Ma for the Purpurberg quartzite

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Fig. 10 Geological map of a part of the Alcudia antiform at the roadcut near Orellana, sample location of OR-1 (images see Fig. 12), Orellana reservoir (Orellana region, Central Iberian zone, Iberia) N 39°00′4.6″; W5°34′11.9″. Red dots are towns. Inset map CIZ Cen- (from García-Hidalgo et al. 1993; Pieren 2000; Clariana García et al. tral Iberian zone, CZ Cantabrian zone, GTOM Galicia-Tras os Montes 2017). Locality 1: waterline of the sweetwater reservoir (images see zone, MZ Moldanubian zone, OMZ Ossa-Morena zone, PL Pulo do Fig. 12), N 39°00′8.4″; W5°31′18.9″. Locality 2: roadcut near Orel- Lobo zone, SPZ South Portuguese zone lana (images see Fig. 12), N 38°52′52.8″; W5°29′5.6″. Locality 3: member and 564 ± 5 Ma for quartz wacke sample GWQ1. age of the Laas granodiorite (537 ± 5, Fig. 16) offers Three granitoid pebbles from the diamictite horizons in the the minimum age for the deposition of the Clanzschwitz Müglitz formation exhibit ages of 576 ± 7, 572 ± 2, and diamictite. 566 ± 4 Ma (Fig. 15), and support the maximum deposi- The zircons from the Orellana diamictite (OR1) in the tional age obtained from detrital zircon. The upper limit Lower Alcudian group of the Central Iberian zone yielded (minimum age) for the deposition of the Weesenstein diam- a maximum depositional age of 565 ± 4 Ma (Fig. 14). ictite is estimated based on the age of intrusion of the Dohna In all three cases (Weesenstein, Clanzschwitz, and Orel- granodiorite (538 ± 2 Ma, Fig. 16). lana), the maximum depositional age for the diamictites is The Clanzschwitz diamictite (CL1, member 3, Clan- signifcantly younger than that for the Gaskiers glaciation zschwitz group) exhibits a maximum depositional age of in Newfoundland and in SE New England (Squantum). 570 ± 8 Ma supported by another age determination based Thus, the three diamictites should represent a post-Gask- on a zircon from the underlying member 2 (CL2), which iers glacial event during Ediacaran time. Alternatively, is 565 ± 5 Ma (Fig. 14). The age of a zircon in the grani- a shifting of the icecenter from Avalonia (Gaskiers gla- toid pebble taken from the diamictite (member 3, Cla1n) is ciation, c. 579–581 Ma) to West African peri-Gondwana 574 ± 5 Ma (Table 1, supplementary data). The intrusion (Weesenstein-Orellana glaciation, c. 565 Ma) over time

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Fig. 11 Idealized section of the Lower and Upper Alcudian groups stratigraphic log of the Lower Alcudian group) (from García-Hidalgo (Alcudian supergroup) and overlying Ordovician strata from the et al. 1993; Pieren 2000). For abbreviations of inset, see Fig. 10 Alcudia antiform near Orellana (Central Iberian zone, Spain). Left would be possible. However, this solution seems to be the paleolandscape in the hinterland at c. 600–610 Ma. The more unlikely because of the existence of contemporane- detrital zircon populations derived from the pebble exhibit a ous occurence of c. 565 Ma glacial deposits in Virginia dominant peak at 630 Ma and a number of secondary peaks (Hebert et al. 2010). of Neoproterozoic age at c. 710 and 790 Ma. No Tonian and Mesoproterozoic zircons were found. Palaeoproterozoic Provenance and crustal growth of the hinterland zircon dates range between c. 1769 ± 66 and 2471 ± 13 Ma, while the Archaean zircon population occupies the range U–Pb ages and Hf isotopes are classical tools for provenance of 2525 ± 59 to 3163 ± 26 Ma (Fig. 14). Such a pattern studies and analysis of tectonomagmatic events, important of the zircon population is typical for peri-Gondwanan for our understanding of patterns of crustal growth in the deposits originating in the periphery of the West African hinterland. Information of the pre-glacial hinterland can be craton (Linnemann et al. 2014). A pronounced peak ranging obtained from the detrital zircon of quartzite pebble WeG4 from 1942 ± 18 to 2168 ± Ma is coeval with the so-called taken from the Weesenstein diamictite, with a maximum age Eburnean orogeny. Neoproterozoic zircons came from one of deposition being 612 ± 7 Ma (Fig. 14). Because younger of the Pan-African orogens. The latter ones formed during zircons aged at c. 565–600 Ma are lacking, it could not continent–continent collision of the amalgamation of the have been derived from the Purpurberg quartzite member, Gondwana supercontinent at c. 610–630 Ma (Black et al. which underlies the diamictites of the Müglitz formation. 1994). All in all, the zircon population found in the quartzite Instead, the pebble must be derived from much older strata pebble from the Weesenstein tillite (Müglitz formation) rep- and, therefore, representative of the sedimentary cover of resents the composition of rocks in a pre-glacial hinterland,

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Fig. 12 Images from the glaciomarine deposits of the A Lower Alcudian group (“Orel- lana diamictite”, Alcudia antiform, Central Iberian zone, Spain). a Diamictite containing pebbles of sedimentary rocks (quartzite, greywacke) (Local- ity 2, Fig. 10), b dropstone in a rainout deposit, c rainout deposit with millimetre-sized D rock fragments, d faceted and fat iron-shaped pebble in a rainout deposit (fat faceted top and sharp left end formed by ice abrasion; stump right E end formed in the pressure shadow during ice abrasion (“Bügeleisen-Geschiebe”) (Locality 3, Fig. 10), e Facet- ted pebble from a rainout B deposit (fat iron-shaped peb- ble = “Bügeleisen-Geschiebe”) (Locality 3, Fig. 10), and f large fat iron-shaped pebble (=“Bügeleisen-Geschiebe”), a fne-grained diamictite matrix. (b, c, f images photographed in a roadcut at Casa el Canchal, N 38°52′52.8″; W5°29′5.6″)

F C

which consisted of eroded parts of the Pan-African orogen Neoproterozoic zircons (c. 565–950 Ma), the Palaeoprote- and the West African craton. In this region, no Mesoprote- rozoic zircons (c. 1800–2200 Ma), and the Archaean zircons rozoic zircon grains were found. (c. 2500–3600 Ma). In addition, some samples of siliciclas- All samples of clastic sediments from the Weesen- tic sedimentary rocks yielded a few Mesoproterozoic zircon stein, Clanzschwitz, and Orellana areas show a very simi- grains (c. 1000–1200 and c. 1550 Ma). The Palaeoprote- lar pattern of zircon populations (Figs. 13, 14) typical for rozoic and Archaean pattern is typical of a West African Cadomia and its West African hinterland (Linnemann Craton provenance (e.g., Linnemann et al. 2000, 2014; Abati et al. 2014). The U–Pb ages of the detrital zircons from et al. 2010, 2012). Neoproterozoic zircon populations are this study can be grouped in three major groups: (1) the diagnostic of provenance from the Cadomian orogen and

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◂Fig. 13 Combined binned frequency and probability density distribu- Zircons aged between ca. 540 and 700 Ma with negative tion plots of U–Pb LA–ICP–MS ages of detrital zircon grains from εHf, in the range of −7 to −21, and model ages between the Weesenstein group (Ediacaran of the Elbe zone) in the ranges of 400–1200 Ma (left) and 400 to 3800 Ma (right): W63d (conglom- c. 1.7 and 2.2 Ga can be explained by almost pure rework- erate, Müglitz formation), WST1 (diamictite matrix, greywacke, ing of older Eburnean crust (Fig. 17). Surprisingly, Müglitz formation), GWQ1 (quartz wacke, Müglitz formation), and eleven Neoproterozoic zircon grains show more negative P-Pur1b-2-LA10 (quartzite, Purpurberg quartzite member, Seidewitz εHf between −20 and −41. Such zircons lie on a linear formation); MDA maximum depositional age array with most Eburnean and Archaean zircons, and may have been formed by recycling of c. 2500–3800 Ma from the Pan-African basement of the Trans-Saharan Belt old Archaean crust (Fig. 17). The relatively abundant or a related area (Linnemann 2007, Linnemann et al. 2011; group with negative and moderate positive εHf (+8 to Drost et al. 2011). The scarce Mesoproterozoic zircons −8) is only compatible with mixing of the newly formed might well have been derived from the cratonic neighbours Cadomian crust at c. 540–700 Ma and of Eburnean and of the West African Craton, which were at c. 570 Ma the Archaean crust (see mixing field in Fig. 17). Zircons Amazonian or Sub-Saharan cratons (e.g., Gärtner et al. within the c. 537–540 Ma age group of old granodiorites 2013). of Laas and Dohna show a spread of the εHfi in the range The pre-glacial deposits of the Purpurberg quartzite of +2 to −17 and fall in the same mixing field. Thus, member (Seidewitz formation, Weesenstein group) and of Cadomian granitoid magmatism seems to be derived from member 2 of the Clanzschwitz group show a much stronger an evolved Cadomian crust (Fig. 17). sedimentary input from the cratonic hinterland indicated by From Mesoproterozoic zircon grains, only four anal- the strong Palaeoproterozoic and Archaean zircon popula- yses could be performed. Three of them point to the tions (Figs. 13, 14). recycling of a Palaeoproterozoic crust, and one could Detrital zircon populations in the range of c. 565–580 Ma be derived from the recycling of a true Mesoproterozoic in our samples of sedimentary rocks and granitoid pebbles crust (Fig. 17). Palaeoproterozoic zircons (c. 1.7–2.4 Ga), aged at c. 566–576 Ma indicate that the main peak of the in most cases, exhibit εHf of +8 to −10 and model ages Cadomian orogeny was over and the Cadomian orogen was of about 2.0 and 2.7 Ga (Fig. 17). Such grains document exposed during the time of glacial processes. a recycling of Palaeoproterozoic and Neoarchean crust. Similarities of the zircon populations of glacigenic and A number of zircon grains have positive εHf notations. related sedimentary rocks from Bohemia and Iberia docu- Some of them fall on the depleted mantle curve. These ment no diferences in the composition of the West Afri- zircons show a strong afnity to a juvenile Eburnean crust. can hinterland and a coeval plate tectonics evolution. The Other Palaeoproterozoic zircon grains are characterized by relative large distance of about 1800 km between the gla- εHf of −10 to −26 (Fig. 17). These zircons demonstrate cial diamictites in Bohemia and Iberia constrains a relative a recycling of a ca. 3.0–3.8 Ga old Archean crust. Two wide distribution of the glaciated area within the Cadomian Palaeoproterozoic zircons from the Purpurberg quartzite orogen. member are exceptional. These two zircons are 2056 ± 34 Neoproterozoic zircons of glacial deposits and related and 2103 ± 40 Ma old, and show a strongly negative εHf rocks from the Saxo-Thuringian zone show a wide vari- of −34 and −32 (Fig. 17). Calculated ­TDM model ages are ability of the epsilon Hf (εHf) values, in the range of 13 4.27 and 4.21 Ga, respectively. Both grains lie on a linear and −41 (Fig. 17). About 15% have positive (εHf). Such array parallel to the 176Lu/177Hf evolution of a continen- an initial epsilon Hf notation indicates that these zircons tal crust extracted from the depleted mantle during the crystallized either from magmas directly derived from Hadean that mirrors a Jack Hills Trend (Fig. 17), named a depleted mantle source (=juvenile magmas) contami- after the location of the oldest zircon on Earth (Wilde et al. nated with different amounts of older crust or by partial 2001). U–Pb ages combined with Hf isotope data demon- melting of a relatively juvenile crust of a Cadomian or strate that a c. 4.2–4.3 Ga old crust must have survived in Pan-African magmatic arc affinity, respectively (Fig. 17). the framework of the West African Craton at least until c. Zircons close to the depleted mantle array are very scarce 2.05–2.1 Ga ago. and about 660–690 Ma old (Fig. 17), which is in line Most Neo- to Palaeoarchaean zircon grains dated at with the early magmatic arc setting in the Pan-African 2.5 to 3.5 Ga exhibit εHf values between +4 and −18 orogens. Most zircon with ages of c. 540–700 Ma has with expecting model ages of 2.7–3.7 Ga (Fig. 17). Neo- lower εHf (up to −41), suggesting that juvenile magmas to Palaeoarchaean crustal evolution points to the recy- were contaminated by older crust or recycling of the juve- cling of late Neo- to Eoarchean crust of the West African nile island arcs together with some older crust (Fig. 17). Craton. T­ DM model ages indicate three different Archean About 85% of Neoproterozoic zircon show negative εHf. crustal domains, which would have been recycled. These

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◂Fig. 14 Combined binned frequency and probability density distribu- 1998). It is very obvious, that both, Liberian (c.3.0 Ga) tion plots of U–Pb LA–ICP–MS ages of detrital zircon grains from and Leonian (c. 3.4 Ga) crust, were recycled during the Weesenstein, Clanzschwitz, and Lower Alcudian groups (Ediaca- ran) in the ranges of 400–1200 Ma (left) and 400–3800 Ma (right): Archaean time. WeG4 (quartzite pebble from the Weesenstein diamictite, Ediacaran, Müglitz formation, Weesenstein group, Elbe zone), CL1 (diamictite matrix, Ediacaran, Clanzschwitz group, member 3, North Saxon anti- Conclusions form), CL2 (quartzite, Ediacaran, Clanzschwitz group, member 2, North Saxon antiform), and OR1 (greywacke, diamictite matrix, Edi- acaran, Orellana diamictite, Lower Alcudian group, Central Iberian Sedimentary features, aspects of basin development, plate zone, Spain) tectonics framework, U–Pb ages, and Hf isotope data together allow reconstruction of Ediacaran glacial pro- cesses, palaeogeography, timing of orogenic processes, and units are characterized by model ages of c. 3.0, 3.2–3.3, crustal growth of the piece of the Cadomian orogen pre- and 3.5–3.7 Ga, respectively. Most known West African served in the Elbe zone and the North Saxon antiform of Archean ages of granitoid magmatism fall between c. 2.7 the Saxo-Thuringian zone (NE Bohemian Massif) and from and 3.0 Ga (e.g. Rocci et al. 1991). Scarce occurrence the Alcudian group of the Central Iberian zone in Iberia. of 3.42–3.52 Ga old felsic rocks in the Amsaga area Sedimentary and other features of the deposits further allow (Mauritania) has been reported by Potrel et al. (1996, tracing a glacial event within sedimentary rocks related

Fig. 15 U–Pb LA–ICP–MS zircon ages of three granitoid pebbles from the Müglitz formation of the Weesenstein group (Weesenstein diamic- tite) and from one granitoid pebble from member 3 of the Clanzschwitz group (Clanzschwitz diamictite)

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with a glacial event recorded in Northwest Africa (Morocco) (Vernhet et al. 2012) and in Saudi Arabia (Vickers-Rich and Fedonkin 2007) is much more realistic and provides more information about the timing of this young Neoproterozoic glacial event. At Bou Azzer (Moroccan Anti-Atlas), Vern- het et al. (2012) describe glaciomarine structures (striated pavement on rhyolites) within the Ouarzazate group. The age of the latter is constrained by published U–Pb ages of the Ouarzazate group and can be placed in a time window between c. 570 and 562 Ma (Karaoui et al. 2015). In Saudi Arabia, another glaciomarine diamictite has been detected in Ediacaran sedimentary deposits of the Dhaiqa formation. An ash bed just below the diamictite provided a U–Pb age of 560 ± 4 Ma (Vickers-Rich and Fedonkin 2007). Further- more, an Ediacaran glacial deposit (Moelv diamictite) crops out in Baltica (Bingen et al. 2005). However, available age data are not sufcient to constrain an age younger than the Gaskiers glaciation (Bingen et al. 2005). All in all, Ediaca- ran diamictites of the Saxo-Thuringian zone are bracketed in a time range of 565–540 Ma. We correlate glacial deposits of Bohemia and Iberia with the closer occurrences of glacioma- rine diamictites in the Anti-Atlas (Bou Azzer) and in Saudi Arabia (Dhaiqa formation), which suggest a sedimentation age closer to 565 Ma for the Weesenstein, Clanzschwitz, and Orellana diamictites. Because of the clear post-Gaskiers age of all these glacial deposits, the data allow to defne a new Ediacaran glacial event younger than the Gaskiers glaciation. Because of the main occurrences, we propose to name the glacial event at c. 565 as Weesenstein–Orellana glaciation (Fig. 18). Existence of this Cadomian glaciation could be the reason for the negative excursion of the δ13C curve Fig. 16 U-Pb ages from the granodiorites of Laas (top) and Dohna (bottom). For the Dohna granodiorite, U-Pb LA–ICP–MS zircon (Shuram–Wonoka anomaly) (Fig. 18; Halverson et al. ages of fve diferent samples were used (DG1n, Dohna 1–4). In the 2005). The origin of the Shuram–Wonoka anomaly is under lower right diagram, a Concordia age of 538 ± 2 Ma is shown, which discussion. Le Guerroue et al. (2006) concluded that the was calculated from the youngest zircon population of all samples. anomaly was not related to glaciation, since it lasted 50 In addition, the diagram shows the large amount of inherited zircon grains occurring in the Dohna granodiorite Myr, and that it included the Gaskiers glaciation (i.e., it began before the Gaskiers). They also suggested that it did not end until 550 Ma, which suggests that it is not to the Cadomian orogen (Weesenstein and Clanzschwitz caused by glaciation. Halverson et al. (2005) suggest dura- groups, and Lower Alcudian group). Indicative for glacio- tion of the Shuram–Wonoka anomaly between c. 590 and marine deposition are dropstones, fatiron-shaped pebbles c. 560 Ma. A shorter time interval (581 ± 6–567 ± 6 Ma) (“Bügeleisen-Geschiebe”), facetted pebbles, dreikanters, is inferred by an age model of Retallack et al. (2014). rainout sediments, and zircon grains afected by ice abrasion. All in all, precise timing and the basic cause for the Pre-glacial and glaciomarine sedimentation took place in a Shuram–Wonoka anomaly are not well known, but Edi- time span between c. 565 and 540 Ma. Age constraints com- acaran glaciations certainly contributed to that negative pletely rule out a correlation of this glacial event recorded in anomaly, because glacial events require a response in the the Cadomian metasedimentary rocks of the Saxo-Thuring- ocean water chemistry. ian and Central Iberian zones with the Gaskiers glaciation, Glacigenic sedimentary and related rocks act as an archive which occurred around 579–581 Ma (Bowring et al. 2002; of evolution of the hinterland. The Hf isotope record of detri- Thompson et al. 2014; Pu et al. 2016). Instead, a correlation tal and magmatic zircons from investigated strata gives some

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Fig. 17 Hf isotope evolution diagrams summarizing the data of zircons from the studied metasedimentary rocks of the Weesenstein and Clanzschwitz groups. The probability plot of the zircon age populations is represented in grey. See text for discussion. Top Hf isotope evolution diagram of analyzed zircon grains in the age range of ca. 500–4000 Ma. Below Hf isotope evolution diagram of analyzed zircon grains in the age range of 500–1200 Ma. For details and references of depleted mantle evolution, see Gerdes and Zeh (2006) and Dhuime et al. (2011). Data were analyzed using the decay constant of 1.867 × 10−11 (Scherer et al. 2001) and the CHUR parameters of Bouvier et al. (2008)

clues about the nature of the major geologic events forming arc developed during the Neoproterozoic on stretched the Cadomian orogen and its West African hinterland. The Archaean and Palaeoproterozoic (Eburnean) crust. Cadomian crustal evolution is dominated by the recycling of For the West African hinterland, important episodes continental crust as suggested by the dominance of zircons of crustal growth and/or recycling can be defned: (1) a with negative εHfi values. Juvenile arc magmas became con- 2.2–4.3 Ga old basement became recycled in most cases taminated by the recycling of Eburnean and Archaean crust during Eburnean (c. 1.8–2.2 Ga) orogenic processes; (2) two during long Cadomian magmatic arc activity. A minority of Eburnean zircons found in the Purpurberg quartzite member the zircons consists of those derived from the depleted man- and aged at 2056 ± 34 and 2103 ± 40 Ma imply recycling tle array. Mixture with continental crust is always present. of pre-existing Hadean crust and show ­TDM model ages of The required geotectonic setting is a continental magmatic 4.21 and 4.27 Ga, respectively (Jack Hills trend). Hadean

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Fig. 18 Timing of the Weesenstein–Orellana glaciation and its rela- posite includes the diferent terranes of the Cadomian orogen dis- tion to the δ13C curve (Halverson et al. 2005) (left); palinspastic map tributed now in Western and Central Europe (peri-Gondwanan West showing palaeopositions of Ediacaran post-Gaskiers glacial deposits Africa) in peri-Gondwana, North Africa, and Arabia (right). Cadomia com- crust existed until c. 2.0 Ga; (3) juvenile zircons are scarce; Abati J, Aghzer AM, Gerdes A, Ennih N (2012) Insights on the (4) Archean magmas recycled a c. 2.7–3.8 Ga old crust; crustal evolution of the West African Craton from Hf isotopes in detrital zircons from the Anti-Atlas belt. Precambr Res and (5) zircons with ages of 3.2–3.3 and 3.4–3.5 Ga show 212–213:263–274 a juvenile trend. Álvarez-Nava Oñate H, García Casquero JL, Gil Toja A, Hernández Urroz J, Lorenzo Álvarez S, López Díaz F, Mira López M, Mon- Acknowledgements This is a contribution to IGCP project 648 teserín López V, Nozal Martín F, Pardo Alonso MV, Picart Boira “Supercontinent Cycles and Global Geodynamics”. Gregory J. Retal- J, Robles Casas R, Santamaría Casanovas J, Solé FJ (1988) Uni- lack (Eugene) and an unknown reviewer are thanked for their helpful dades litoestratigráfcas de los materiales Precámbrico-Cámbricos reviews. We thank the Australian IGCP Committee for their funding en la mitad suroriental de la zona Centro-Ibérica. II Congreso support for the work in Saudi Arabia as well as the UNESCO IGCP Geológico de España, Comunicaciones 1:19–22 Board for project IGCP587. Special thanks go to Fayek Kattan and Bao H, Lyons JR, Zhou C (2008) Triple oxygen isotope evidence for his team from the Saudi Geological Survey for facilitating our work elevated CO­ 2 levels after a Neoproterozoic glaciation. Nature in Saudi Arabia. 453(7194):504–506 Bingen B, Grifn WL, Torsvik TH, Saeed A (2005) Timing of Late Neoproterozoic glaciation on Baltica constrained by detrital zircon References geochronology in the Hedmark Group, south-east Norway. Terra Nova 17:250–258 Abati J, Aghzer AM, Gerdes A, Ennih N (2010) Detrital zircon ages Black R, Latouche L, Liégeois JP, Caby R, Bertrand JM (1994) Pan- of Neoproterozoic sequences of the Moroccan anti-atlas belt. Pre- African displaced terranes of the Tuareg Shield (central Sahara). cambr Res 181(1–4):115–128 Geology 22:641–644

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