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  • 1. Ali, K.A.
    et al.
    Surour, A.A:
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Andresen, A.
    Single zircon Hf-O isotope constraints on the origin of A-type granites from the Jabal Al-Hassir ring complex, Saudi Arabia.2015In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 256, p. 131-147Article in journal (Refereed)
    Abstract [en]

    The Jabal Al-Hassir ring complex in the southern Arabian Shield is an alkaline granite complex comprising an inner core of biotite granite that outwardly becomes a porphyritic sodic-calcic amphibole (ferrobarroisite–katophorite) granite. A combined study of mineral chemistry and single zircon Hf–O zircon isotope analyses was carried out to infer the magma sources of the Neoproterozoic post-collisional A-type granitoids in Saudi Arabia. The granitic rocks show high positive initial ɛHf(t) values of +7.0 to +10.3 and δ18O values of +5.8‰ to +7.4‰ that are consistent with melting of a juvenile crustal protolith that was formed during the Neoproterozoic assembly of the Arabian-Nubian Shield (ANS). Crustal-model ages (Hf-tNC) of 0.71–0.94 Ga indicate minor contribution from an older continental crust in the formation of the Jabal Al-Hassir granitic rocks (crystallization age = 620 ±3 Ma), but any such component is likely to be Neoproterozoic in age. Temperature and oxygen fugacity (ƒO2) estimates suggested that the Jabal Al-Hassir A-type granite magma was generated at high temperature (820–1050 °C) and low ƒO2. Geochemical characteristics (e.g., low ƒO2), geochronological data, and Hf and O isotope compositions, indicate that the magmas of the Neoproterozoic A-type granites of the Jabal Al-Hassir ring complex were likely generated by crustal partial melting of a juvenile Neoproterozoic lower crustal tholeiitic rocks, following collision between East and West Gondwana in the final stages of the evolution of the Arabian Shield.

  • 2. Andersson, Joel B.H.
    et al.
    Logan, Leslie
    Martinsson, Olof
    Chew, David
    Kooijman, Ellen
    Swedish Museum of Natural History, Department of Geology. Department of Geosciences Swedish Museum of Natural History Stockholm Sweden.
    Kielman-Schmitt, Melanie
    Swedish Museum of Natural History, Department of Geology.
    Kampmann, Tobias C.
    Bauer, Tobias E.
    U-Pb zircon-titanite-apatite age constraints on basin development and basin inversion in the Kiruna mining district, Sweden2022In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 372, p. 106613-106613, article id 106613Article in journal (Refereed)
  • 3.
    Babechuk, Michael
    et al.
    Isotope Geochemistry Group, Department of Geosciences, Eberhard Karls University of Tübingen, Tübingen, Germany.
    Weimar, Nadine
    Isotope Geochemistry Group, Department of Geosciences, Eberhard Karls University of Tübingen, Tübingen, Germany.
    Kleinhanns, Ilka
    Isotope Geochemistry Group, Department of Geosciences, Eberhard Karls University of Tübingen, Tübingen, Germany.
    Eroglu, Suemeyya
    Isotope Geochemistry Group, Department of Geosciences, Eberhard Karls University of Tübingen, Tübingen, Germany.
    Swanner, Elizabeth
    Department of Geological & Atmospheric Sciences, Iowa State University, Ames, USA.
    Kenny, Gavin
    Swedish Museum of Natural History, Department of Geology.
    Kamber, Balz
    Department of Geology, Trinity College Dublin, Dublin, Ireland.
    Schoenberg, Ronny
    Isotope Geochemistry Group, Department of Geosciences, Eberhard Karls University of Tübingen, Tübingen, Germany.
    Pervasively anoxic surface conditions at the onset of the Great Oxidation Event: New multi-proxy constraints from the Cooper Lake paleosol2019In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 323, p. 126-163Article in journal (Refereed)
    Abstract [en]

    Oceanic element inventories derived from marine sedimentary rocks place important constraints on oxidativecontinental weathering in deep time, but there remains a scarcity in complementary observations directly fromcontinental sedimentary reservoirs. This study focuses on better defining continental weathering conditions nearthe Archean-Proterozoic boundary through the multi-proxy (major and ultra-trace element, Fe and Cr stableisotopes, μ-XRF elemental mapping, and detrital zircon U-Pb geochronology) investigation of the ca. 2.45 billionyear old (giga annum, Ga) Cooper Lake paleosol (saprolith) developed on a sediment-hosted mafic dike withinthe Huronian Supergroup (Ontario, Canada).Throughout the variably altered Cooper Lake saprolith, ratios of immobile elements (Nb, Ta, Zr, Hf, Th, Al, Ti)are constant, indicating a uniform pre-alteration dike composition, lack of extreme pH weathering conditions,and no major influence from ligand-rich fluids during weathering or burial metasomatism/metamorphism. Theloss of Mg, Fe, Na, Sr, and Li, a signature of albite and ferromagnesian silicate weathering, increases towards thetop of the preserved profile (unconformity) and dike margins. Coupled bulk rock behaviour of Fe-Mg-Mn and colocalizationof Fe-Mn in clay minerals (predominantly chlorite) indicates these elements were solubilized primarilyin their divalent state without Fe/Mn-oxide formation. A lack of a Ce anomaly and immobility of Mo, V, and Cr further support pervasively anoxic weathering conditions. Subtle U enrichment, if primary, is the onlygeochemical evidence that could be consistent with oxidative element mobilization. The leaching of ferromagnesiansilicates was accompanied by variable mobility and depletion of transition metals with a relativedepletion order of Fe≈Mg≈Zn > Ni > Co > Cu (Cu being significantly influenced by secondary sulfideformation). Mild enrichment of heavy Fe isotopes (δ56/54Fe from 0.169 to 0.492‰) correlating with Fe depletionin the saprolith indicates open-system loss of isotopically light aqueous Fe(II). Minor REE+Y fractionation withincreasing alteration intensity, including a decreasing Eu anomaly and Y/Ho ratio, is attributed to albitebreakdown and preferential scavenging of HREE > Y by clay minerals, respectively. Younger metasomatismresulted in the addition of several elements (K, Rb, Cs, Be, Tl, Ba, Sn, In, W), partly or wholly obscuring theirearlier paleo-weathering trends.The behavior of Cr at Cooper Lake can help test previous hypotheses of an enhanced, low pH-driven continentalweathering flux of Cr(III) to marine reservoirs between ca. 2.48–2.32 Ga and the utility of the stable Crisotope proxy of Mn-oxide induced Cr(III) oxidation. Synchrotron μ-XRF maps and invariant Cr/Nb ratios revealcomplete immobility of Cr despite its distribution amongst both clay-rich groundmass and Fe-Ti oxides.Assuming a pH-dependent, continental source of Cr(III) to marine basins, the Cr immobility at Cooper Lakeindicates either that signatures of acidic surface waters were localized to uppermost and typically unpreservedregolith horizons or were geographically restricted to acid-generating point sources. However, given detritalpyrite preservation in overlying fluvial sequences, it is probable that the oxidative sulfide corrosion required todrive surface pH < 4 lagged behind in this region relative to other early Proterozoic sequences. The entiresaprolith exhibits a consistently light stable Cr isotope composition (δ53/52Cr: −0.321 ± 0.038‰, 2sd, n=34)that cannot be linked to Cr(III) oxidation and is instead interpreted to have a magmatic origin.

  • 4. Bezenjani, R. Nasiri
    et al.
    Pease, V.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Shalaby, M. H.
    Kadi, K. A.
    Kozdroj, W.
    Detrital zircon geochronology and provenance of the Neoproterozoic Hammamat Group (Igla Basin), Egypt and the Thalbah Group, NW Saudi Arabia: Implications for regional collision tectonics2014In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 245, p. 225-243Article in journal (Refereed)
  • 5. Brengman, Latisha A.
    et al.
    Fedo, Christopher M.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Jabeen, Iffat
    Banerjee, Neil R.
    Textural, geochemical, and isotopic data from silicified rocks and associated chemical sedimentary rocks in the ~ 2.7 Ga Abitibi greenstone belt, Canada: Insight into the role of silicification2020In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 351Article in journal (Refereed)
    Abstract [en]

    Silica-rich Precambrian rocks often preserve geochemical information and microfossil remnants from the early biosphere and could play a critical role in the formation of early crust. Because these rocks are important geochemical and paleontological archives, we need to better constrain their geochemical and isotopic attributes and generate a refined picture of the evolving Archean silica cycle. Here, we investigate a series of sub- to greenschist facies Si-rich Archean rocks from the ~ 2.7 Ga Abitibi greenstone belt, Canada, that represent chemical sedimentary rocks and rocks formed via silica-addition through the process of silicification. We report data for major and trace element geochemistry, multi-crystal silicon and oxygen isotopes of quartz using isotope ratio mass spectrometry, and texture-specific silicon isotope values measured using secondary ion mass spectrometry on Neoarchean chemical sedimentary rocks, their silicified equivalents, and associated silicified volcanic rocks. We find that in such a well-preserved terrane we can utilize petrographic textures and geochemical attributes to establish rock origin, distinguishing siliceous rocks that form via chemical sedimentation from those that form via silicification. Chemical sedimentary rocks display a wide range of 30Si-depleted silicon isotopes values that vary with stratigraphy similar to other Archean iron formation. Silicified volcanic rocks possess 30Si-enriched values, similar to Archean silicified basalts. We conclude that because silicon isotope values of iron formation shift toward 30Si-enriched values up stratigraphy, basinal changes in the composition of the silicon isotope reservoir may be preserved. Silicon isotope values of silicified volcanic rocks by contrast, likely represent precipitation from an isotopically heavy silicon reservoir, influenced by downward percolating seawater and upward moving convecting fluids interacting with host volcanic rock (basalt or andesite). Overall, we confirm that Neoarchean silicified rocks are 30Si-enriched like their Paleoarchean counterparts.

  • 6.
    Claesson, Stefan
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Bibikova, Elena V.
    Vernadsky Institute of Geochemistry and Analytical Chemistry, R.A.S., Moscow, Russia.
    Shumlyanskyy, Leonid
    M.P Semenenko Institute of Geochemistry, Mineralogy and Ore Formation, Palladina Ave. 34, 03680 Kyiv, Ukraine.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Billström, Kjell
    Swedish Museum of Natural History, Department of Geology.
    Can oxygen isotopes in magmatic zircon be modified by metamorphism? A case study from the Eoarchean Dniester-Bug Series, Ukrainian Shield2016In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 273, p. 1-11Article in journal (Refereed)
    Download full text (pdf)
    Claesson O Odesa PRECAM text and figures accepted 151108
  • 7. Ghanem, Hind
    et al.
    Jarrar, Ghaleb H.
    McAleer, Ryan J.
    Passchier, Cees W.
    Theye, Thomas
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Wintsch, Robert P.
    Drowned in granite - retrieving the tectono-metamorphic history of the Janub metamorphic complex, the northernmost part of the Arabian-Nubian Shield2022In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 383, p. 106903-106903, article id 106903Article in journal (Refereed)
  • 8. Ghanem, Hind
    et al.
    McAleer, Ryan J.
    Jarrar, Ghaleb H.
    Al Hseinat, Mu'ayyad
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    40Ar/39Ar and U-Pb SIMS zircon ages of Ediacaran dikes from the Arabian-Nubian Shield of south Jordan2020In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 343, article id 105714Article in journal (Refereed)
    Abstract [en]

    A spectacular feature of the Arabian-Nubian Shield (ANS) is the abundance of well-exposed and extensive Neoproterozoic dike swarms of variable compositions. Most of these dikes are late to post-orogenic with respect to the East African Orogen (EAO) and are unmetamorphosed. We dated a composite dike with latite margins and a rhyolite core (607 ± 6 Ma, U-Pb), a biotite rhyolite dike (600 ± 4 Ma, 40Ar/39Ar age of biotite), an andesite dike (594 ± 3, 40Ar/39Ar age of amphibole) and a dolerite dike (~579 Ma, 40Ar/39Ar whole rock total gas age). We propose that the first three dikes represent one generation that was emplaced at different episodes extending between 607 and 590 Ma. Time and composition equivalent dikes are common in the northern ANS. The dikes crosscut late collisional granitoids and geochemically display a subduction-related character as evidenced by a negative Nb-Ta anomaly. These dikes are absent in the alkali feldspar A-type Humrat Syenogranite dated at 586 ± 5 Ma in Jordan and equivalent rocks in the northern ANS, which are crosscut only by the (~579 Ma) dolerite dikes. The within-plate character of the dolerite dikes is supported by the absence of the Nb-Ta anomaly and high field strength element geochemistry. We propose that the dolerite dikes are a generation, distinct from the ~607–590 Ma dikes, that reflects a change in tectonic regime and represents the last magmatic activity of the Neoproterozoic in the northern ANS. The ages of the dikes dated in this study agree with the published age range of the transitional stage from late orogenic calc-alkaline to extensional alkaline tectono-magmatic setting for the ANS. We propose that the magmatic activity was terminated ~50 m.y. before the age of the Cambrian unconformity at ~530 Ma. Correlation with ages of dikes and magmatic rocks in the northern ANS favors this supposition. The dike geochemistry and geochronology are compatible with a tectonic model that involves mantle lithosphere delamination from below the northern ANS after a significant crust-mantle thickening caused by the EAO, followed by thermal relaxation, subsidence and gradual denudation until the age of the unconformity at ~530 Ma.

  • 9. Guitreau, Martin
    et al.
    Blichert-Toft, J.
    Billström, Kjell
    Swedish Museum of Natural History, Department of Geology.
    Hafnium isotope evidence for early-Proterozoic volcanic arc reworking in the Skellefte district (northern Sweden) and implications for the Svecofennian orogeny2014In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 252, p. 39-52Article in journal (Refereed)
    Abstract [en]

    The Skellefte district is a seemingly juvenile and heavily mineralized crustal domain in northern Sweden that formed between 1.90 and 1.87 Ga. It is commonly interpreted as a volcanic arc deposited on a basement (known variously as the Bothnian or the Knaften-Barsele group) that could be represented by older rocks (1.96-1.94 Ga) found in the vicinity. In order to understand the potential genetic relationship between the arc and the basement, Hf and Pb isotopes in magmatic zircons from key lithologies were measured by solution multi-collector inductively-coupled plasma mass spectrometry. It is shown that both geological groups display similar Hf isotope compositions, which translate into decreasing εHf with time. Overall, the data are compatible with reworking of the Knaften-Barsele arc to produce the Skellefte rocks over a short time interval from 1.90 to 1.87 Ga in a context of crustal extension with ongoing subduction. When the data presented here are integrated with general models of tectonic evolution of the Svecofennian orogen, they fit a scenario in which the juvenile Knaften-Barsele arc formed between 1.96 and 1.94 Ga and became accreted onto the Karelian continent located further north at about 1.92-1.91 Ga. Systematic north to south variations in Pb, Nd, and Hf isotope compositions throughout the Svecofennides, interpreted as resulting from an increase in Archean crust involvement towards the south, indicate a genetic link between the Proterozoic crustal domains of Sweden and Finland.

  • 10.
    Johansson, Åke
    Swedish Museum of Natural History, Department of Geology.
    Comments to ”Detrital zircon signatures of the Baltoscandian margin along the Arctic Circle Caledonides in Sweden: The Sveconorwegian connection” by Gee et al. (2015).: Letter to the Editor2016In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 276, p. 233-235Article in journal (Other academic)
  • 11.
    Johansson, Åke
    Swedish Museum of Natural History, Department of Geology.
    From Rodinia to Gondwana with the ‘SAMBA’ model—A distant viewfrom Baltica towards Amazonia and beyond2014In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 244, p. 226-235Article in journal (Refereed)
    Abstract [en]

    A refined model of the late Mesoproterozoic to Neoproterozoic supercontinent Rodinia is presented, with Baltica, Amazonia and West Africa attached to eastern Laurentia as in the SAMBA model (Johansson, 2009), East Antarctica, Australia and India to western Laurentia in a SWEAT configuration (Moores, 1991), and northern Siberia attached to northern Laurentia as proposed by Condie and Rosen (1994). In such a model, the Proto-Andean margin of South America would form the conjugate margin of Laurentia’s Grenville margin. With the Kalahari craton attached to SW Laurentia and East Antarctica, as proposed by Loewy et al. (2011), followed by the Congo and Tanzania cratons in Africa and the Sao Fransisco and Rio de la Plata cratons in South America, all these cratons would be part of Rodinia, but would still be separated from Amazonia by a wide Brasiliano (Clymene) ocean embayment. By rotating the African and eastern South American cratons ca 90° counterclockwise around a pole located close to the Laurentia – Kalahari junction, and East Antarctica, Australia and India ca 120° counterclockwise around a pole located inside the Kalahari craton, all relative to a fixed Laurentia, these cratons will move from a Rodinia to a Gondwana configuration. These rotations will open up the Proto-Pacific ocean, close the Brasiliano (Clymene) ocean, and both open and close the intervening Adamastor and Mozambque oceans, creating the various Brasiliano and Pan-African fold belts in the ensuing collisions. The maximum plate velocity, ca 7.5 cm/year (15 000 km in 200 m.y.), will occur along the outer periphery of this rotation, thereby explaining the formation of large amounts of juvenile Neoproterozoic continental crust within the oceanic Arabian – Nubian sector of the Pan-African Orogen. Rather than being an example of ‘introversion’ or ‘extroversion’, the change from Rodinia to Gondwana in this model would be more like the 90º ‘orthoversion’ model proposed by Mitchell et al. (2012).

  • 12.
    Johansson, Åke
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Bingen, Bernard
    Huhma, Hannu
    Waight, Tod
    Vestergaard, Rikke
    Soesoo, Alvar
    Skridlaite, Grazina
    Krzeminska, Ewa
    Shumlyanskyy, Leonid
    Holland, Mark E.
    Holm-Denoma, Christopher
    Teixeira, Wilson
    Faleiros, Frederico M.
    Ribeiro, Bruno V.
    Jacobs, Joachim
    Wang, Chengcheng
    Thomas, Robert J.
    Macey, Paul H.
    Kirkland, Christopher L.
    Hartnady, Michael I.H.
    Eglington, Bruce M.
    Puetz, Stephen J.
    Condie, Kent C.
    A geochronological review of magmatism along the external margin of Columbia and in the Grenville-age orogens forming the core of Rodinia2022In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 371, p. 1-43, article id 106463Article in journal (Refereed)
    Abstract [en]

    A total of 4344 magmatic U-Pb ages in the range 2300 to 800 Ma have been compiled from the Great Proterozoic Accretionary Orogen along the margin of the Columbia / Nuna supercontinent and from the subsequent Grenvillian collisional orogens forming the core of Rodinia. The age data are derived from Laurentia (North America and Greenland, n = 1212), Baltica (NE Europe, n = 1922), Amazonia (central South America, n = 625), Kalahari (southern Africa and Dronning Maud Land in East Antarctica, n = 386), and western Australia (n = 199). Laurentia, Baltica, and Amazonia (and possibly other cratons) most likely formed a ca. 10 000-km-long external active continental margin of Columbia from its assembly at ca. 1800 Ma until its dispersal at ca. 1260 Ma, after which all cratons studied were involved in the Rodinia-forming Grenvillian orogeny. However, the magmatic record is not smooth and even but highly irregular, with marked peaks and troughs, both for individual cratons and the combined data set. Magmatic peaks typically range in duration from a few tens of million years up to around hundred million years, with intervening troughs of comparable length. Some magmatic peaks are observed on multiple cratons, either by coincidence or because of paleogeographic proximity and common tectonic setting, while others are not. The best overall correlation, 0.617, is observed between Baltica and Amazonia, consistent with (but not definitive proof of) their being close neighbours in a SAMBA-like configuration at least in Columbia, and perhaps having shared the same peri-Columbian subduction system for a considerable time. Correlation factors between Laurentia and Baltica, or Laurentia and Amazonia, are below 0.14. Comparison between the Grenville Province in northeastern Laurentia and the Sveconorwegian Province in southwestern Fennoscandia (Baltica) shows some striking similarities, especially in the Mesoproterozoic, but also exhibits differences in the timing of events, especially during the final Grenville-Sveconorwegian collision, when the Sveconorwegian evolution seems to lag behind by some tens of million years. Between the other cratons, the evolution before and during the final Grenvillian collision is also largely diachronous. After 900 Ma, magmatic activity had ceased in all areas investigated, attesting to the position of most of them within the stable interior of Rodinia. 

    Download full text (pdf)
    Geochronological review
  • 13.
    Johansson, Åke
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Waight, Tod
    University of Copehagen.
    Andersen, Tom
    University of Oslo.
    Comment to “The cause for Nuna breakup in the Early to Middle Mesoproterozoic” by Huang et al. (2021)2021In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 367, p. 1-2, article id 106461Article in journal (Other academic)
  • 14. Klausen, Martin
    et al.
    Nilsson, Mimmi
    Swedish Museum of Natural History, Department of Geology.
    The Melville Bugt Dyke Swarm across SE Greenland: A closer link to Mesoproterozoic AMCG-complexes2019In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 329, p. 88-107Article in journal (Refereed)
  • 15.
    Krzeminska, Ewa
    et al.
    Polish Geological Institute.
    Johansson, Åke
    Swedish Museum of Natural History, Department of Geology. Swedish Museum of Natural History.
    Krzeminski, Leszek
    Polish Geological Institute.
    Wiszniewska, Janina
    Polish Geological Institute.
    Williams, Ian S.
    Australian National University, Canberra.
    Petecki, Zdzislaw
    Polish Geological Institute.
    Salwa, Sylwester
    Polish Geological Institute.
    Basement correlation across the southernmost Baltic Sea: Geochemical and geochronological evidence from onshore and offshore deep drill cores, northern Poland.2021In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 362, p. 1-20, article id 106300Article in journal (Refereed)
    Abstract [en]

    New zircon U-Pb age measurements, whole rock major and trace element geochemistry, and Sr and Nd isotopicanalyses of samples from fourteen deep drill holes that penetrated the hidden Precambrian basement of the southernmost Baltic Sea and the coastal area of northern Poland (Pomerania), make it possible to identify a two episodes of Proterozoic magmatism in that area. The basement consists of late Palaeoproterozoic deformed calc-alkaline, magnesian, I-type to A-type diorites to granites of volcanic arc affinity. U-Pb zircon geochronology documents their magmatic crystallization ages to be between 1791 ± 8 Ma and 1750 ± 5 Ma, with an episode of syn- to late-magmatic deformation recorded in thin overgrowths on zircons at about 1740 Ma. These rocks from Pomerania and its offshore area broadly correlate with the bedrock of Blekinge in southern Sweden, where most of the crust was formed at 1.77–1.75 Ga. They may thus be part of the same geological domain, extending on both sides of the present-day southern Baltic Sea, formed along a late Palaeoproterozoic active continental margin. A subordinate suite of undeformed, significantly younger A-type granites was emplaced at 1477 ± 6 Ma, 1449 ± 7 Ma and 1450 ± 9 Ma. This time interval is concurrent with emplacement of A-type granitoids on the Danish island of Bornholm as well as in Blekinge and other parts of southern Fennoscandia. However, their geochemical and isotopic data highlight a genetic diversity of these granites.

  • 16. Käpyaho, A.
    et al.
    Molnár, F.
    Sorjonen-Ward, P.
    Mänttäri, I.
    Sakellaris, G.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    New U-Pb age constraints for the timing of gold mineralization at the Pampalo gold deposit, Archaean Hattu schist belt, Eastern Finland, obtained from hydrothermally altered and recrystallised zircon.2017In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 289, p. 48-61Article in journal (Refereed)
    Abstract [en]

    In this paper we present new U-Pb data on zircon and titanite from the host rocks of the Pampalo gold deposit located within the Neoarchaean Hattu schist belt in eastern Finland. We also present new U-Pb data on nearby plutonic rocks. Plagioclase porphyries at the mine site demonstrate inheritance from 2.82–2.83 Ga sources while a suggestive intrusive age is at c. 2.76 Ga. Zircon grains extracted from the altered felsic units hosting the gold ore show complex alteration and recrystallisation textures and demonstrate Zr mobility. This mobility is most probably related to the alteration event although direct link to gold mineralization remains to be shown. The preserved or recrystallized parts of the altered zircon grains, texturally homogeneous grain aggregates and some overgrowths yield heterogeneous ages which cluster between ca. 2.73 and 2.70 Ga, with a mean age of 2.71 Ga. This age is considered to place a new constraint on the timing of mobility of Au at the Pampalo. This event postdates the known crustal formation event at 2.76–2.73 Ga in the area as recorded by the adjacent plutonic rocks and volcanoclastic rocks within the Hattu schist belt. The Naarva tourmaline granite, 10 km NW of Pampalo, is 2.69 Ga and is thus temporally associated with known regional crustal anatexis and metamorphism in the Archaean of eastern Finland. Whether this crustal reworking event played a role in the genesis of the gold in eastern Finland needs to be further studied.

  • 17. Ng, S.W.P.
    et al.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Tam, P.Y.
    Jayasingha, P.
    Wong, J.P.-M.
    Denyszyn, S.
    Yiu, J.S.-Y.
    Chang, S.-C.
    Ca. 820-640 Ma SIMS U-Pb age signal in the peripheral Vijayan Complex, Sri Lanka: Identifying magmatic pulses in the assembly of Gondwana.2017In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 294, p. 244-256Article in journal (Refereed)
    Abstract [en]

    Sri Lanka comprises three roughly north-south trending amphibolite- to granulite-facies lithotectonic complexes, from west to east the Highland Complex, the Wanni Complex, and the Vijayan Complex. These terranes were correlated with other East Gondwana continental terranes with similar lithologies forming at similar ages. The Wanni Complex and the Vijayan Complex have been interpreted as volcanic arc terranes brought together by a double-sided subduction. The Highland Complex represents the metamorphosed accretionary prism within the suture when the Wanni and Vijayan Complexes were juxtaposing against each other. In contrast to the Wanni and Highland Complexes, the Vijayan Complex has yielded only a few geochronological data with satisfactory precision. Previous studies suggested that the Vijayan Complex comprises ∼1100–924 Ma granitic gneisses, which were metamorphosed during ∼590–456 Ma. More recently, ∼772–617 Ma mafic intrusions have been identified. This study divides the Vijayan granitic gneisses and the associated melt products geochemically into a low-Nb series and a more primitive high-Nb series. Our SIMS U-Pb zircon data suggested that both series have protolith magmatic ages of ∼1062–935 Ma, and metamorphic ages of ∼580–521 Ma, which is consistent with previous work. However, some of the Vijayan granitic gneisses and granitic anatectic melt products at the Highland-Vijayan tectonic mixed zone preserve an additional Tonian-Cryogenian (∼820–630 Ma) age signal. This age signal suggested that felsic magmatism also occurred when mafic granulites were emplaced along the Highland-Vijayan boundary, which is broadly coeval with to the bimodal magmatism occurring along the Highland-Wanni boundary. This study also suggests that charnockitisation in the Vijayan Complex occurred at 562 ± 6 Ma during the Neoproterozoic regional metamorphism. The Tonian-Cryogenian signal preserved in the Highland-Vijayan tectonic mixed zone can also be found in the alkaline intrusion hosted by the Namuno Terrane and the Lurio Belt in Mozambique. This indicates a relationship between the Vijayan granitic gneisses and the Lurio foreland metagranitic basement, while the Namuno Terrane and the Lurio Belt are correlated with the Highland-Vijayan tectonic mixed zone. The ages and the isotope signatures of these granitic bodies further suggest a genetic relationship of these granitic bodies with various magmatic intrusions in East Antarctica.

  • 18.
    Nilsson, Mimmi
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Klausen, Martin
    Petersson, Andreas
    Swedish Museum of Natural History, Department of Geology.
    Break-up related 2170–2120 Ma mafic dykes across the North Atlantic craton: Final dismembering of a North Atlantic-Dharwar craton connection?2019In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433Article in journal (Refereed)
  • 19. Petersson, A.
    et al.
    Scherstén, A.
    Andersson, J.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Baronoski, M.T.
    Zircon U-Pb, Hf and O isotope constraints on growth versus reworking of continental crust in the subsurface Grenville orogen, Ohio, USA.2015In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 265, p. 313-327Article in journal (Refereed)
    Abstract [en]

    Combined U-Pb, O and Hf isotope data in zircon allows discrimination between juvenile and reworked crust, and is therefore a useful tool for understanding formation and evolution of the continental crust. The crustal evolution of basement rocks in central North America (Laurentia) is poorly constrained, as it is almost entirely overlain by Palaeozoic cover. In order to improve our understanding of the evolution of this region we present U-Pb, O and Hf isotope data from zircon in drill-core samples from the subsurface basement of Ohio. The Hf isotope data suggests juvenile crust formation at similar to 1650 Ma followed by continued reworking of a single reservoir. This similar to 1650 Ma reservoir was tapped at similar to 1450 Ma during the formation of the Granite-Rhyolite Province and subsequently reworked again during the Grenvillian orogeny. The similar to 1650 Ma crust formation model age for the suite of samples along with the presence of similar to 1650 Ma magmatic rocks suggests an eastward extension of the Mazatzal Province (or Mazatzal-like crust) and makes it a possible protolith to the subsurface basement of Ohio and surrounding Mesoproterozoic (i.e. Grenville-age) rocks. The eastward extension of this similar to 1650 Ma crustal reservoir into Ohio requires a revision of the crustal boundary defined by Nd isotopic data to be located further east, now overlapping with the Grenville front magnetic lineament in Ohio. In fact, the easternmost sample in this study is derived from a more depleted reservoir. This limits the extent of >1.5 Ga basement in subsurface Ohio and constrains the location of the crustal boundary. Further, syn-orogenic magmatism at similar to 1050 Ma suggests a potential extrapolation of the Interior Magmatic Belt into Ohio. Oxygen isotopic data in zircon suggests that during Grenvillian metamorphism, zircon recrystallisation occurred in the presence of heavy delta O-18 fluids resulting in zircon with elevated delta O-18 values.

  • 20. Petersson, A.
    et al.
    Scherstén, A.
    Bingen, B.
    Gerdes, A.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Mesoproterozoic continental growth: U-Pb-Hf-O zircon record in the Idefjorden Terrane, Sveconorwegian Orogen.2015In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 261, p. 75-95Article in journal (Refereed)
    Abstract [eo]

    The Idefjorden Terrane of the Sveconorwegian Orogen, Fennoscandia, is known to be an area of comparatively juvenile Mesoproterozoic continental growth. Here we provide an improved model of crustal growth based on new coupled zircon U-Pb-O-Lu-Hf isotopic data on thirteen samples of mafic to intermediate plutonic rocks from different domains of the Idefjorden Terrane. The new data support a retreating volcanic arc system, with shorter pulses of accretion. A gradual increase of radiogenic Hf (mean slif from 3.5 to 5.4) in plutonic rocks intruded between ca. 1630 Ma and 1560 Ma reflects an increase in juvenile mantle-derived magma in the genesis of the plutonic suites. This trend is consistent with development of an extensional back-arc rift geotectonic setting, accommodating deposition of the Stora Le-Marstrand greywacke dominated metasediment sequence. Combined isotopic information and the detrital zircon record of the Stora Le-Marstrand Formation support the interpretation that the Idefjorden Terrane was separated from the Fennoscandian Shield before the Sveconorwegian Orogeny.

  • 21.
    Petersson, Andreas
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Söderlund, Ulf
    Scherstén, Anders
    Waight, Tod
    Nilsson, Mimmi K.M.
    Vervoort, Jeff
    The robustness of the Lu-Hf and Sm-Nd isotopic systems during metamorphism – A case study of the Åker metabasite in southern Sweden2023In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 394, p. 107122-107122, article id 107122Article in journal (Refereed)
    Abstract [en]

    While whole-rock Lu-Hf isotope analysis remains one of the only ways to obtain initial Hf isotope signatures of old mafic rocks, Hf isotope analyses of more robust accessory zircon in intermediate to silicic rocks have largely replaced whole-rock analyses during the last decade. This has led to a discrepancy in the amount of existing data from mafic and felsic lithologies. However, especially in mafic, Si-poor rocks with a metamorphic imprint, Hf isotope data rely on whole-rock analysis since baddeleyite, commonly used for U-Pb age analyses of mafic rocks, is sensitive to alteration and metamorphism. Hence, to accurately evaluate the trace element and isotope signatures of altered mafic rocks, it is important to understand the mechanisms of element mobility during metamorphism. Here, we report whole-rock trace element compositions, Lu-Hf and Sm-Nd isotope data from variably deformed and metamorphosed samples of a mafic intrusion in southern Sweden, the Åker metabasite. These data suggest that trace elements were undisturbed on a whole-rock sample scale during deformation at upper amphibolite facies (at least 1000 MPa and 600 °C) metamorphism under hydrated conditions. Despite redistribution of Zr associated with the breakdown of baddeleyite and other igneous phases, the Åker metabasite has retained its chemical and isotopic integrity since igneous crystallisation at ca. 1565 Ma. This study demonstrates and strengthens the feasibility of whole-rock analyses of (meta-)mafic rocks for determining initial εNd and εHf values, despite deformation and metamorphism under hydrated amphibolite-grade metamorphic conditions. Testing the coherence of the calculated initial Nd and Hf isotope ratios by examining variably deformed and metamorphosed varieties of a rock in a single outcrop, could be used as a model for research on more complex Archean rocks.

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  • 22. Qu, Y
    et al.
    Wang, J.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Engdahl, A.
    Wang, G.
    McCloughlin, N.
    Carbonaceous biosignatures of diverse chemotrophic microbial communities from chert nodules of the Ediacaran Doushantuo Formation.2017In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 290, p. 184-196Article in journal (Refereed)
    Abstract [en]

    The Ediacaran Doushantuo Formation (DST) is renowned for exceptionally preserved Precambrian fossils including metazoans. Some of these fossils, particularly microfossils such as multicellular algae and acanthomorphic acritarchs, are preserved in DST chert nodules. To better understand the geomicrobiological processes that contributed to the authigenic formation of DST chert nodules and facilitated exceptional fossil preservation, we analyzed organic matter in these chert nodules and the surrounding matrix (calcareous mudstone) using multiple in-situ techniques: confocal laser Raman spectroscopy, micro-Fourier transform infrared spectroscopy (FTIR), and secondary ion mass spectroscopy (SIMS). We found strong ultrastructural, chemical, and isotopic heterogeneities in the organic matter as indicated by the Raman spectral parameter I-1350/1600 ranging from 0.49 to 0.88, the infrared spectral index R3/2 from 0.12 to 0.90, and an estimated δ13Corg-SIMS range of 44‰ (V-PDB). These micron-scale heterogeneities imply that the organic matter preserved in the DST chert nodules is derived from different carbonaceous sources in a diverse microbial ecosystem, including eukaryotic and/or prokaryotic photoautotrophs, as well as chemotrophs involved in the fermentation and probably anaerobic oxidation of organic remains. Thus, the microbial ecosystems in Ediacaran ocean waters and sediments were more complex than previously thought, and these microbial processes controlled dynamic micro-environments in DST sediments where chert nodules were formed and fossils were mineralized. The results also show that variations in the relative abundances, activities, and interactions of co-existing microorganisms in DST sediments may have modulated δ13Corg shifts, causing local decoupling between δ13Corg and δ13Ccarb as measured in bulk samples.

  • 23. Qu, Yuangao
    et al.
    Lepland, Aivo
    van Zuilen, Mark A.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Črne, Alenka E.
    Fallick, Anthony E.
    Sample-scale carbon isotopic variability and diverse biomass in the Paleoproterozoic Zaonega Formation, Russia2018In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 315, p. 222-231Article in journal (Refereed)
    Abstract [en]

    The stratigraphic record of organic matter in the c. 1.97 Ga Zaonega Formation (ZF), Onega Basin, northwestern Russia, exhibits a distinct negative δ13C excursion (δ13Corg from −25 to −40‰ VPDB), which was previously interpreted either to reflect a disturbance in the global carbon cycle after the Great Oxidation Event, or to have been caused by an increase in basinal methanotrophic activity. In order to assess the nature of primary biomass and the effects of post-depositional alteration, we here report the sample-scale carbon isotopic characteristics of organic matter in two drill cores from the ZF, covering 500 m of stratigraphy, by using secondary ion mass spectrometry (SIMS). The results confirm that the organic matter has to a large extent preserved the primary isotopic signatures, whereas secondary effects are limited (<4‰). The sample-scale isotopic heterogeneity, defined as the difference between the maximum and minimum δ13C values obtained by SIMS from every individual sample, increases from typically <5‰ in the lower part of stratigraphy to systematically larger values (up to 11‰) in the upper part, which coincides with the decreasing trend of δ13Corg of bulk samples from −25 to −40‰. Samples with either relatively high (c. −25‰) or low (c. −40‰) δ13Corg values have small sample-scale isotopic heterogeneities, while samples with intermediate δ13Corg values (between −25 and −40‰) have significantly larger heterogeneities. These observations imply the co-existence of photoautotrophic and methanotrophic biomass during deposition of the upper part of the stratigraphy. Our study provides insight into the carbon isotopic characteristics of organic matter and suggests that the negative excursion of δ13Corg in the ZF is induced by a methanotrophic microbial ecosystem sustained by seepage of thermogenic methane during the deposition of the ZF and contemporaneous igneous activities.

  • 24. Qu, Yuangao
    et al.
    Zhu, Shixing
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Engdahl, Anders
    McLoughlin, Nicola
    Carbonaceous biosignatures of the earliest putative macroscopic multicellular eukaryotes from 1630 Ma Tuanshanzi Formation, north China2018In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 304, p. 99-109Article in journal (Refereed)
    Abstract [en]

    The Paleo- and Mesoproterozoic fossil record of multicellular eukaryotes is scarce but extremely important in studying the evolution of life in the Precambrian Era. Typically, fossils heralded as ‘multicellular eukaryotes’ that are older than the Ediacaran are met with controversy. To confront such debates, we investigate the chemical, isotopic, and molecular structural characteristics of organic matter from carbonaceous compressions in the 1630 Ma Tuanshanzi Formation in northern China, some of the earliest putative macroscopic multicellular eukaryote fossils (Zhu and Chen, 1995). The large-size and relative complexity of these fossils and similar remains from the 1.56 Ga Gaoyuzhuang Formation have led to their interpretation as eukaryotes. Raman spectral parameters give an estimated peak-metamorphic temperature TMax in the range of 202–286 °C, confirming the good preservation of the organic remains. Two-dimensional Raman maps of the carbonaceous compressions show ultrastructural variations that suggest diverse subcellular compounds being consistent with multicellular eukaryotes. The organic matter has carbon isotopic composition δ13Corg-SIMS between −45.3 and −32.2‰, and a branching index of carbon chain measured by the micro-FTIR spectral parameter R3/2 between 0.17 and 0.31. Together with their large-size and morphology, the isotopic, geochemical and ultrastructural data supports an interpretation of the Tuanshanzi Formation carbonaceous compressions as derived from phototrophic, multicellular eukaryotic algae. Our data support the early evolution of macroscopic multicellular eukaryotes in the sulfidic and low-oxygen conditions that prevailed in the Paleo- and Mesoproterozoic oceans.

  • 25. Ravindran, Arathy
    et al.
    Mezger, Klaus
    Balakrishnan, S
    Kooijman, Ellen
    Swedish Museum of Natural History, Department of Geology.
    Schmitt, Melanie
    Swedish Museum of Natural History, Department of Geology.
    Berndt, Jasper
    Initial 87Sr/86Sr as a sensitive tracer of Archaean crust-mantle evolution: Constraints from igneous and sedimentary rocks in the western Dharwar Craton, India2020In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 337, p. 1-15, article id 105523Article in journal (Refereed)
    Abstract [en]

    Among the rocky planets of the solar system only the Earth has “granitic” continental crust. The timing and processes involved in the formation of Earth’s first extensive crust is still enigmatic. The chemical and isotope compositions of ancient crustal rocks preserve a record of their genesis. The Rb-Sr system proves to be an efficient proxy for the reconstruction of crust-mantle evolution since it can bring together information from seawater as preserved in chemical sedimentary rocks and information from magmatic rocks that can trace the time and extent of crust formation and concomitant mantle depletion during the Archaean eon. The Dharwar Craton in India preserves a suite of metamorphosed igneous and sedimentary rocks that record its early crustal evolution. To overcome the susceptibility for resetting and the difficulty in determining initial 87Sr/86Sr, the minerals barite and apatite are used to obtain precise and accurate 87Sr/86Sr, because these minerals preferentially incorporate Sr and exclude Rb and preserve the initial Sr isotope compositions at the time of their formation. Initial 87Sr/86Sr of apatite were obtained in situ using Laser Ablation Multi-Collector Inductively Coupled Plasma Mass Spectrometry. The robustness and only minor dispersion of the isotope ratios demonstratethe capability of matrix apatites in preserving initial Sr ratios. The least radiogenic value is used as the best estimate for the initial 87Sr/86Sr. The 87Sr/86Sr ratios of apatite from igneous rocks that formed from 3.5 Ga to 2.6 Ga constrain the Rb/Sr of the source over the whole time-span. A comparison of the Sr isotopes between seawater-derived barite and initial Sr isotope ratios in apatite from igneous rocks reveals that significant mafic to intermediate crust had formed by 3.2 Ga. Studying the entire Archaean time window, a dominantly mafic crust was the main source for the granitoid rocks in the Dharwar Craton from 3.5 to 3.1 Ga, whereas the rocks from 2.9t o 2.7 Ga were extracted dominantly from the depleted mantle.

  • 26. Ravindran, Arathy
    et al.
    Mezger, Klaus
    Balakrishnan, Srinivasan
    Kooijman, Ellen
    Swedish Museum of Natural History, Department of Geology.
    Schmitt, Melanie
    Swedish Museum of Natural History, Department of Geology.
    Berndt, Jasper
    Initial 87Sr/86Sr as a sensitive tracer of Archaean crust-mantle evolution: constraints from igneous and sedimentary rocks in the western Dharwar Craton, India2019In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433Article in journal (Refereed)
  • 27. Riley, T. R.
    et al.
    Flowerdew, M. J.
    Pankhurst, R. J.
    Millar, I. L.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    U-Pb zircon geochronology from Haag Nunataks, Coats Land and Shackleton Range (Antarctica): Constraining the extent of juvenile Late Mesoproterozoic arc terranes2020In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 340, article id 105646Article in journal (Refereed)
    Abstract [en]

    Understanding the accretionary stages of Rodinia evolution and the arrangement of cratons and arc terranes is dependent upon high-precision geochronology from key piercing points of Mesoproterozoic rocks. U-Pb zircon dating is presented here from the Mesoproterozoic Haag Nunataks gneiss complex of West Antarctica where the dominant granodiorite protolith was emplaced at 1238 ± 4 Ma, aplite/pegmatite sheets were intruded at 1064 ± 4 Ma and the final intrusive phase of microgranite sheets were emplaced at 1056 ± 8 Ma. A separate magmatic event at ~1170 Ma is recorded as inherited zircons in the later stage intrusions. Based on field relationships, the main phase of deformation at Haag Nunataks is thought to have developed prior to the emplacement of the microgranite sheet at ~1056 Ma but after the ~1064 Ma aplite/pegmatite intrusive phase. Potentially correlative units from the Shackleton Range and Coats Land of East Antarctica are also dated to test supposed correlations with arc terranes and crustal blocks at the margins of Laurentia and the proto-Kalahari craton. An ice-transported granite pegmatite sample recovered from the Brunt Ice Shelf is used as a partial proxy for unexposed rocks of the ice-covered Coats Land block and has been dated at ~1100 Ma. A diorite gneiss from the Shackleton Range was also analysed as it forms part of a magnetic domain shared with the Haag Nunataks crustal block. Core zircon ages of ~2470 Ma were determined, and the age of migmatisation is interpreted at ~1740 Ma and rules out any potential correlation with the Haag Nunataks gneiss complex. The magmatic precursors of the Haag Nunataks orthogneisses were emplaced in a juvenile arc setting. We argue that this arc was located in the Natal Embayment region, contiguous with the Namaqua-Natal-Maud belt of arc terranes typified by enhanced magmatism at ~1240 Ma and ~1170 Ma not associated with any significant deformation events. The later magmatic events at Haag Nunataks at ~1060 Ma are more closely associated with collision of Laurentia with the proto-Kalahari craton and the associated deformation is correlated with the Ottawan phase of the Grenville orogeny.

  • 28. Robinson, Frank
    et al.
    Pease, Victoria
    Whitehouse, Martin
    Swedish Museum of Natural History, Department of Geology.
    Kooijman, Ellen
    Swedish Museum of Natural History, Department of Geology.
    Preliminary detrital zircon signatures from the southern Asir terrane, Saudi Arabia: A link to Yemen or the Nubian Shield?2018In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 311, p. 247-261Article in journal (Refereed)
    Abstract [en]

    The Arabian Shield comprises early Neoproterozoic to Cambrian (∼850–530 Ma) tectonostratigraphic terranes formed by the closure and accretion of juvenile volcanic arcs and back-arc basins associated with Gondwana assembly. Unlike the Nubian Shield which preserves crustal isotopic signatures, the Arabian Shield is distinctly juvenile with the exception of the Paleoproterozoic (∼1800–1670 Ma) Khida subterrane in Saudi Arabia and the terranes of Yemen. This study presents the first combined zircon U-Pb, O and Hf isotope data of metavolcanic and metasedimentary rocks from southwestern most Saudi Arabia, near the Yemen border – a region thought to contain some of the oldest (>815 Ma) lithologies in Saudi Arabia, including the Atura Formation and the Tayyah Belt. One volcaniclastic metasediment sample from the Atura Formation yields zircon U-Pb age peaks of 741, 672, 646 Ma (n = 131), δ18O(V-SMOW) ranging from 4.6 to 8.3‰ and ɛHf (t) from +7.7 to +12.5. Two samples from the Tayyah Belt include an older metasandstone and a late intruding granitic dyke which provides a minimum age for the Tayyah Belt. The former yields two significant U-Pb peaks of 812 (n = 8) and 999 (n = 6) Ma, δ18O and ɛHf (t) values ranging from 4.4 to 9.6‰ and −10.1 to +12.4, respectively; the later yields a concordia age of 645.8 [±1.7] Ma (n = 29), δ18O ranging from 5.7 to 6.6‰, and ɛHf (t) of +5.9 to +9.6. The zircon age and juvenile Hf signatures from the Atura Formation are consistent with the synorogenic phase in the Shield. Sedimentation was likely associated with arc volcanism during the previously documented eastward phase of accretion at ∼740–640 Ma and the closure of the Mozambique Ocean. In contrast, the data from the texturally more mature Tayyah Belt metasediment indicate a more distal, and more evolved crustal input at the time of sediment deposition which is unusual for the Saudi Arabian Shield. Consequently, the Tayyah metasediments are likely sourced from areas with greater continental affinity, such as the cratonic basement and/or reworked crust of the Sahara metacraton in NE Africa.

  • 29. Roerdink, D.L.
    et al.
    Mason, P.R.D.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Brouwer, F.M.
    Reworking of atmospheric sulfur in a Paleoarchean hydrothermal system at Londozi, Barberton Greenstone Belt, Swaziland2016In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 280, p. 195-204Article in journal (Refereed)
    Abstract [en]

    Anomalous fractionation of the minor isotopes of sulfur (Δ33S, Δ36S) in Archean pyrite is thought to reflect photochemical reactions in an anoxic atmosphere, with most samples falling along a reference array with Δ36S/Δ33S ≈ −1. Small deviations from this array record microbial sulfate reduction or changes in atmospheric source reactions. Here, we argue that reworking of atmospheric sulfur with distinct minor sulfur isotope ratios (Δ36S/Δ33S ≠ −1) produced additional variability in sulfide Δ33S and Δ36S-values in a 3.52 Ga hydrothermal barite deposit at Londozi, Barberton Greenstone Belt, Swaziland. In situ measurement of the four stable sulfur isotopes in pyrite revealed Δ36S–Δ33S relationships and a Δ36S/Δ33S trend (−3.2 ± 0.4), which is significantly different from the co-variation between Δ36S and Δ33S in the co-existing barite that reflects ambient Paleoarchean seawater sulfate. This argues against biological or thermochemical sulfate reduction at the time of barite deposition, and requires incorporation of sulfide generated in a chemically distinct atmosphere before 3.52 Ga. We propose a model that combines reworking of this sulfur by hydrothermal leaching, deep mixing with juvenile sulfur and surface mixing with biogenic sulfide to explain the observed variation in δ34S, Δ33S and Δ36S. These interactions between abiotic and biological processes in the Londozi hydrothermal system complicate the interpretation of biosignatures based on deviations in Δ33S and Δ36S from the Archean reference array.

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  • 30. Rowe, Matthew L.
    et al.
    Kemp, Anthony I.S.
    Wingate, Michael T.D.
    Petersson, Andreas
    Swedish Museum of Natural History, Department of Geology.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    van der Riet, Christiaan
    Cratonisation of Archaean continental crust: Insights from U–Pb zircon geochronology and geochemistry of granitic rocks in the Narryer Terrane, northwest Yilgarn Craton2022In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 372, p. 106609-106609, article id 106609Article in journal (Refereed)
  • 31. Sarlus, Zmar
    et al.
    Andersson, Ulf B.
    Martinsson, Olof
    Bauer, Tobias E.
    Wanhainen, Christina
    Andersson, Joel B.H.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Timing and origin of the host rocks to the Malmberget iron oxide-apatite deposit, Sweden2020In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 342, article id 105652Article in journal (Refereed)
    Abstract [en]

    The northern Norrbotten region in Sweden hosts abundant iron-oxide apatite (IOA) deposits including Kiirunavaara, the type locality for Kiruna-type deposits, and Malmberget. Felsic and intermediate metavolcanic rocks hosting the Malmberget IOA deposit contain oscillatory zoned zircon which yield magmatic U-Pb SIMS ages of 1885 ± 6 Ma and 1881 ± 6 Ma, respectively. Metamorphic rims on zircon from these rocks yield 1797 ± 7 Ma and 1775 ± 6 Ma, respectively, and record the age of the latest Svecofennian regional metamorphic event in the Gällivare area, tentatively interpreted as regional contact metamorphism. Two granite dikes that cut the ore yield U-Pb zircon emplacement ages of 1790 ± 6 Ma and 1791 ± 7 Ma, respectively, overlapping with the metamorphic overgrowths, and set a lower age limit for ore formation in the Malmberget IOA deposit. Rocks hosting the Malmberget IOA deposit have an alkalic to alkali-calcic affinity with a geochemical signature that favors a continental-arc, transitional to extensional setting. These rocks are suggested to have been generated in a back-arc region, in response to subduction beneath the craton margin retreating to the SW or W. The obtained ages and geochemical signatures of these rocks coincide well with the regionally defined Kiirunavaara group rocks, hosting several other IOA deposits in northern Sweden.

  • 32. Sałacińska, Anna
    et al.
    Kusiak, Monika A.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Dunkley, Daniel J.
    Wilde, Simon A.
    Kielman, Ross
    Swedish Museum of Natural History, Department of Geology.
    Complexity of the early Archean Uivak Gneiss: Insights from Tigigakyuk Inlet, Saglek Block, Labrador, Canada and possible correlations with south West Greenland2018In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 315, p. 103-119Article in journal (Refereed)
    Abstract [en]

    The Saglek Block of Labrador comprises Eoarchean to Neoarchean lithologies, metamorphosed at high temperature at ca. 2.7 Ga. Here, we investigate the gneisses of Tigigakyuk Inlet, previously identified as the locality exposing the most ancient rocks in the Saglek Block. New geochronological and geochemical results reveal a multistage history. Precise magmatic emplacement ages of 3.75 to 3.71 Ga refine the age of the Uivak Gneiss. Zircon rims and neoblastic grains with low Th/U record metamorphism at ca. 3.6 and 2.8-2.7 Ga. Magmatism between these tectono-metamorphic events is recorded by the presence of meta-mafic dykes in the gneisses, gabbroic enclaves in ca. 2.7 Ga syn-tectonic granitoids, as well as by a ca. 3.56 Ga age for monzonitic gneiss in which metamorphic zircon is present as xenocrysts. Felsic (TTG) magmatism between ca. 3.75 Ga and 3.71 Ga, as well as metamorphism at both ca. 3.6 Ga and 2.8-2.7 Ga, is also recognised in the Itsaq Gneiss Complex of south West Greenland, and is restricted to the Færingehavn Terrane. Our new data enable a more rigorous correlation between these formerly conjugate parts of the North Atlantic Craton.

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  • 33. Shumlyanskyy, Leonid
    et al.
    Hawkesworth, Chris
    Billström, Kjell
    Swedish Museum of Natural History, Department of Geology.
    Bogdanova, Svetlana
    Mytrokhyn, Oleksandr
    Romer, Rolf
    Dhuime, Bruno
    Claesson, Stefan
    Swedish Museum of Natural History, Department of Geology.
    Ernst, Richard
    Whitehouse, Martin
    Swedish Museum of Natural History, Department of Geology.
    Bilan, Olena
    The origin of the Palaeoproterozoic AMCG complexes in the Ukrainian shield: New U-Pb ages and Hf isotopes in zircon2017In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 292, p. 216-239Article in journal (Refereed)
  • 34. Shumlyanskyy, Leonid
    et al.
    Hawkesworth, Chris
    Dhuime, Bruno
    Billström, Kjell
    Swedish Museum of Natural History, Department of Geology.
    Claesson, Stefan
    Storey, Craig
    207Pb/206Pb ages and Hf isotope compositions of zircons from sedimentary rocks of the Ukrainian shield: Crustal growth of the south-western part of the East European craton from Archaean to Neoproterozoic2015In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 260, p. 39-54Article in journal (Refereed)
  • 35. Shumlyanskyy, Leonid
    et al.
    Wilde, Simon
    Nemchin, Alexander
    Claesson, Stefan
    Swedish Museum of Natural History, Department of Geology.
    Billström, Kjell
    Swedish Museum of Natural History, Department of Geology.
    Baginski, Boguslaw
    Eoarchean rock association in the Dniester-Bouh Domain of the Ukrainian Shield: A suite of LILE-depleted enderbites and mafic granulites2020In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433Article in journal (Refereed)
    Abstract [en]

    We present the results of a study of an Eoarchean rock assemblage in the Dniester-Bouh Domain of the Ukrainian Shield. This comprises granulite-facies granitoids intercalated with mafic and ultramafic granulites. Zircon U-Pb geochronology indicates enderbite crystallisation at 3786 ± 32 Ma, followed by a subsequent event at ca. 3500 Ma. Several events can be tentatively identified that affected these rocks between ca. 3000 and 2700 Ma. The last zircon growth event took place in response to granulite facies metamorphism and included two separate episodes at ca. 2000 and ca. 1900 Ma. The oldest two zircon populations in enderbites have εHf values around 0, indicating their crystallisation from a protolith with a short crustal residence time. Zircons that crystallised during the 3000–2700 Ma event(s) vary in Hf isotope systematics from εHf ~ 1 at ca. 3000 Ma to εHf ~ −14 at c. 2700 Ma. Paleoproterozoic zircons reveal even more significant variations in εHf value from +6 to –22. Such variations are indicative of juvenile input and mixing with old non-radiogenic Hf.

    All Eoarchean rocks are depleted in incompatible trace elements and have negative Ta-Nb, P, and Ti anomalies. Compared to the typical TTG associations, enderbites record depletion in felsic components (SiO2, Na2O, K2O, Rb, Th), and enrichment in mafic ones (TiO2, MgO, CaO, V), allowing them to be defined as “mafic” or “depleted” TTG.

    Geochemical data indicate that mafic and ultramafic rocks of the Dniester-Bouh Domain formed by shallow high-degree melting of the mantle, with the absence of garnet in their source, and the presence of residual Ti-bearing minerals and/or amphibole. In contrast, enderbites were formed from a mixed garnet-bearing amphibolite – eclogite source, i.e. melting over a range of pressures/depths. Our preferred model for the formation of the Eoarchean rock association involves the shallow melting of mantle and formation of basalts and accompanying ultramafic cumulates at a spreading centre, with subsequent underthrusting of one segment of oceanic crust beneath the other, and partial melting of hydrated metamorphosed (eclogitized) mafic rocks in the underthrust plate, leading to the formation of the TTG melts

  • 36.
    Skridlaite, Grazina
    et al.
    Vilnius University.
    Siliauskas, Laurynas
    Vilnius University.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Johansson, Åke
    Swedish Museum of Natural History, Department of Geology. Swedish Museum of Natural History.
    Rimsa, Andrius
    Loxus Consulting AB.
    On the origin and evolution of the 1.86–1.76 Ga Mid-Baltic Belt in the western East European Craton2021In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 367, p. 1-21, article id 106403Article in journal (Refereed)
    Abstract [en]

    A Mid-Lithuanian Domain (MLD) was distinguished by Bogdanova et al. (2015) as part of the large Mid-BalticBelt (MBB) in the western East European Craton. Zircon U-Pb dating by SIMS, Sr- and Nd-isotope systematics and a detailed geochemical study have allowed to subdivide the MLD into two parts: NW and SE. The NW magmatic rocks have been emplaced at 1.86 to 1.83 Ga from either an enriched mantle source or from a mantle magma with presence of older crustal material. The SE MLD magmatic rocks originated from a slightly depleted mantle source at 1.87 to 1.82 Ga. At 1.79 Ga, they were intruded by gabbronorites which at 1.76 Ga were crosscut by thin veinlets of microgabbronorite. The SE MLD magmatic series with their oceanic island arc affinity correlate well with the contemporaneous Fröderyd metavolcanics of the Vetlanda-Oskarshamn belt in Sweden, while the NW MLD rocks are similar to the TIB-0 Askersund granitoids in the southern Bergslagen area. The younger (1.81–1.79 Ga) intrusives in both areas are time-equivalents of the TIB-1 magmatism on the Swedish side. Thus, the MLD as well as its counterparts on the Swedish side of the Baltic Sea may belong to the same Mid-Baltic Belt, representing an active, south-facing continental margin established at ca. 1.86 Ga. The shape and outline of the belt was affected by the Fennoscandia-Sarmatia collision at ca. 1.82–1.80 Ga, as well as by later magmatism.

  • 37. Soderlund, Ulf
    et al.
    Bleeker, Wouter
    Demirer, Kursad
    Srivastava, Rajesh
    Hamilton, Michael
    Nilsson, Mimmi
    Swedish Museum of Natural History, Department of Geology.
    Pesonen, Lauri
    Samal, Amiya
    Jayananda, Mudlappa
    Ernst, Richard
    Srinivas, Madabhooshi
    Emplacement ages of Paleoproterozoic mafic dyke swarms in eastern Dharwar craton, India: Implications for paleoreconstructions and support for a ∼30° change in dyke trends from south to north2019In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433Article in journal (Refereed)
  • 38. Sundblad, Krister
    et al.
    Salin, Evgenia
    Claesson, Stefan
    Swedish Museum of Natural History, Department of Geology.
    Gyllencreutz, Richard
    Billström, Kjell
    Swedish Museum of Natural History, Department of Geology.
    The Precambrian of Gotland, a key for understanding the Proterozoic evolution in southern Fennoscandia2021In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433Article in journal (Refereed)
  • 39. Sundblad, Krister
    et al.
    Salin, Evgenia
    Claesson, Stefan
    Swedish Museum of Natural History, Department of Geology.
    Gyllencreutz, Richard
    Billström, Kjell
    Swedish Museum of Natural History, Department of Geology.
    The Precambrian of Gotland, a key for understanding the Proterozoic evolution in southern Fennoscandia2021In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 363, p. 106321-106321, article id 106321Article in journal (Refereed)
  • 40. Trevisan, Veronica G.
    et al.
    Hagemann, Steffen G.
    Loucks, Robert R.
    Xavier, Roberto P.
    Motta, João G.
    Parra-Avila, Luis A.
    Petersson, Andreas
    Swedish Museum of Natural History, Department of Geology.
    Gao, Jian-Feng
    Kemp, Anthony I.S.
    Assis, Rafael R.
    Tectonic switches recorded in a Paleoproterozoic accretionary orogen in the Alta Floresta Mineral Province, southern Amazonian Craton2021In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 364, p. 106324-106324, article id 106324Article in journal (Refereed)
  • 41.
    Tual, Lorraine
    et al.
    Department of Geology, Lund University, Sölvegatan 12, SE-223 62 Lund, Sweden.
    Piñán-Llamas, Aránzazu
    Department of Geosciences, IPFW University, 2101 E. Coliseum Blvd, Fort Wayne, IN 46805, USA.
    Möller, Charlotte
    Department of Geology, Lund University, Sölvegatan 12, SE-223 62 Lund, Sweden.
    High-temperature deformation in the basal shear zone of an eclogite-bearing fold nappe, Sveconorwegian orogen, Sweden2015In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 265, p. 104-120Article in journal (Refereed)
  • 42. Upadhyay, Dewashish
    et al.
    Chattopadhyay, Sabyasachi
    Kooijman, Ellen
    Swedish Museum of Natural History, Department of Geology.
    Mezger, Klaus
    Berndt, Jasper
    Magmatic and metamorphic history of Paleoarchean tonalite–trondhjemite–granodiorite (TTG) suite from the Singhbhum craton, eastern India2014In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 252, p. 180-190Article in journal (Refereed)
    Abstract [en]

    Texturally controlled dating of zircon from Paleoarchean tonalite–trondhjemite–granodiorites of the Older Metamorphic Tonalitic Gneisses and the Singhbhum Granite batholith (Phases I, II, and III) from the Singhbhum craton in eastern India reveals a polycyclic evolution of the Archean crust. The granitoid suites were emplaced in two pulses at 3.45–3.44 Ga and 3.35–3.32 Ga. Tonalites and trondhjemites of the Older Metamorphic Tonalitic Gneisses were emplaced at ca. 3.45–3.44 Ga together with Phase III of the Singhbhum Granite pluton while granites belonging to the Older Metamorphic Tonalitic Gneisses were emplaced at ca. 3.35–3.32 together with Phase I and Phase II of the Singhbhum Granite pluton. Both crustal units underwent an early phase of relatively high-grade metamorphism at 3.30–3.28 Ga followed by extensive fluid-induced alteration during low-grade metamorphism at 3.19–3.12 Ga, and 3.02–2.96 Ga. The two units have also been marginally affected at ca. 2.52 Ga and 1.06 Ga by major metamorphic events in the North Singhbhum Mobile Belt and the Singhbhum shear zone at the northern margin of the craton. The zircon grains in granites have inherited cores with ages of ca. 3.61 Ga and 3.46–3.41 Ga and with well-developed oscillatory growth zonation which suggests the granitic magmas were derived by partial melting of an igneous precursor or sedimentary rocks derived from an igneous source. The emplacement of the expansive granitoids belonging to the Older Metamorphic Tonalitic Gneisses and the Singhbhum Granite was synchronous with the amphibolite-facies metamorphism (ca. 3.32 Ga) of older meta-igneous and metasedimentary rocks belonging to the Older Metamorphic Group. Major felsic crust formation in the craton occurred in a narrow time interval between 3.46 and 3.32 Ma with minor contributions of material as old as 3.6 Ga. The complex polycyclic evolution of the Paleoarchean crust in the Singhbhum craton can account for the wide range of often disparate ages obtained using whole rock isochron dating techniques with some of the isochron dates being geologically meaningful while others representing mixing lines or disturbance of the isotopic systems during metamorphism.

  • 43. van Schijndel, Valby
    et al.
    Cornell, David H.
    Frei, Dirk
    Simonsen, Siri Lene
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Crustal evolution of the Rehoboth Province from Archaean to Mesoproterozoic times: Insights from the Rehoboth Basement Inlier2014In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 240, p. 22-36Article in journal (Refereed)
  • 44. Wang, Cheng-Cheng
    et al.
    Wiest, Johannes D.
    Jacobs, Joachim
    Bingen, Bernard
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Elburg, Marlina A.
    Sørstrand, Thea S.
    Mikkelsen, Lise
    Hestnes, Åse
    Tracing the Sveconorwegian orogen into the Caledonides of West Norway: Geochronological and isotopic studies on magmatism and migmatization2021In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 362, p. 106301-106301, article id 106301Article in journal (Refereed)
  • 45. White, Alistair
    et al.
    Burgess, Ray
    Charnley, Norman
    Selby, David
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Robb, Laurence
    Waters, David
    Constraints on the timing of late-Eburnean metamorphism, gold mineralisation and regional exhumation at Damang mine, Ghana2014In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 243, p. 18-38Article in journal (Refereed)
  • 46.
    Whitehouse, Martin J.
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Dunkley, Daniel J.
    Kusiak, Monika A.
    Wilde, Simon A.
    On the true antiquity of Eoarchean chemofossils – assessing the claim for Earth’s oldest biogenic graphite in the Saglek Block of Labrador2019In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 323, p. 70-81Article in journal (Refereed)
    Abstract [en]

    A recent claim to have found traces of Earth’s earliest life (>3.95 Ga) utilising isotopically light carbon in graphite-bearing metapelites from the Saglek Block of northern Labrador, Canada, is re-evaluated applying rigorous geological and geochronological criteria. The establishment of these criteria in previous evaluations of early life claims from southern West Greenland and northern Canada is reviewed in order to provide a backdrop to discussion of the Saglek claim. In particular, we emphasise the importance of the scale of lithological continuity in determining the veracity of such claims, which are considerably easier to demonstrate from large, relatively less tectonised supracrustal remnants like the Isua Greenstone Belt than they are from smaller, isolated enclaves of the kind found on Akilia or the highly tectonised and imbricated unit that is found in the Saglek Block. Unambiguous field relationships between ca. 3.9 Ga tonalitic gneiss and the graphite-bearing metasediments have not been demonstrated in the literature that the Saglek claim relies upon, and earlier U-Pb-Hf isotopic studies on zircon from metasediments at one of the localities used in the claim indicate a Mesoarchean to Neoarchean time of deposition. We conclude that, irrespective of the validity of the carbon isotopic evidence, field relationships and geochronological evidence fail to demonstrate an age of >3.95 Ga for the potential traces of life.

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  • 47.
    Whitehouse, Martin J.
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Flowerdew, Michael J.
    Stoeser, Douglas B.
    Stacey, John S.
    The Khida terrane – Isotopic evidence for Paleoproterozoic to Neoarchean basement in the eastern Arabian Shield2023In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 399, p. 107222-107222, article id 107222Article in journal (Refereed)
  • 48.
    Yeshanew, Fitsum G.
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Pease, V.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Al-Khirbash, S.
    Zircon U–Pb geochronology and Nd isotope systematics of the Abas terrane, Yemen: Implications for Neoproterozoic crust reworking events.2015In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 267, p. 106-120Article in journal (Refereed)
    Abstract [en]

    High-spatial-resolution secondary-ion mass spectrometry (SIMS) U–Pb zircon ages, whole-rock Nd isotopic and geochemical data are reported for granites and granitic gneisses from a traverse across the Abas terrane, Yemen, a part of the Precambrian basement of southern Arabian Peninsula. SIMS U–Pb dating identifies two magmatic episodes, the first at c. 790–725 Ma represented by granitic gneisses, the second clearly post-tectonic at c. 625–590 Ma. The oldest sample in the post-tectonic group is slightly deformed while younger samples are undeformed indicating that penetrative deformation ceased at c. 625 Ma in the Abas region. Whole-rock Nd(t) values between −11 and +0.8, Nd model ages of 1.70–1.13 Ga indicate a significant contribution of evolved continental material in the genesis of the Abas granitoids, unlike most of the juvenile Arabian-Nubian Shield (ANS), although there are few inherited zircons. Secular variation in ɛNd(t) reflects a change in magma source with increasing juvenile magma and diminishing crustal input during post-tectonic (625–590 Ma) magmatism. The combination of subduction zone chemistry, absence of older rocks, paucity of inherited zircons, evolved Nd isotopic signatures and the I-type characteristics of the samples suggest that assimilation occurred at depth.

  • 49. Yin, Zongjun
    et al.
    Cunningham, John A.
    Vargas, Kelly
    Bengtson, Stefan
    Swedish Museum of Natural History, Department of Paleobiology.
    Zhu, Maoyan
    Donoghue, Philip C.J.
    University of Bristol.
    Nuclei and nucleoli in embryo-like fossils from the Ediacaran Weng’an Biota.2017In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 301, p. 145-151Article in journal (Refereed)
    Abstract [en]

    The embryo-like microfossils from the Ediacaran Weng’an Biota (ca. 609 million years old) are among the oldest plausible claims of animals in the fossil record. Fossilization frequently extends beyond the cellular, to preserve subcellular structures including contentious Large Intracellular Structures (LISs) that have been alternately interpreted as eukaryote nuclei or organelles, degraded remains, or abiological structures. Here we present new data on the structure, morphology, and development of the LISs in these embryo-like fossils, based on Synchrotron Radiation X-ray Tomographic Microscopy (SRXTM) and quantitative computed tomographic analysis. All the lines of evidence, including consistency in the number, shape, position, and relative size (LIS-to-cytoplasm ratio) of the LISs, as well as their occurrence within preserved cytoplasm, support their interpretation as cell nuclei. Our results allow us to reject the view that nuclei cannot be preserved in early eukaryote fossils, offering new potential for interpreting the fossil record of early eukaryote evolution.

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