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  • 1.
    Bezenjani, R. Nasiri
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Pease, Victoria
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Whitehouse, M. J.
    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)
    Abstract [en]

    Detrital zircon U-Pb SIMS dating is used to evaluate the provenance of two correlative basins in the Arabian-Nubian Shield (ANS). The Wadi Igla Formation in the Central Eastern Desert (CED) of Egypt and the Thalbah Group in the Midyan Terrane (MT) of NW Saudi Arabia are considered to be post-amalgamation terrestrial basins, developed during closure of the Mozambique Ocean and amalgamation of the ANS in Cryogenian-early Ediacaran time. The analytical results indicate that the upper-part of the Wadi Igla Formation has a maximum depositional age of 628 +/- 6 Ma, contains 98% Neoproterozoic zircon with ages between 815 and 628 Ma, and has two distinct peaks at 690 Ma and 652 Ma. A rhyolite clast from the upper-part of the Wadi Igla Formation gives a U-Pb age of 700 +/- 6 Ma. This age significantly predates Dokhan volcanism, indicating that the dominant rhyolitic clasts within the Wadi Igla Formation are not from the Dokhan Volcanics, as previously believed. Analytical results from the Thalbah Group suggest multiphase basin formation and development. The lower part of the Thalbah Group is intruded by monzogranites of the Liban complex, has a minimum depositional age of 635 +/- 5 Ma, resembling that of the Wadi Igla Formation. Its middle part has a maximum age of 612 +/- 7 Ma and is comprised of 90% Neoproterozoic zircon with ages ranging from 820 to 612 Ma. The upper part of the Thalbah Group has a maximum age of 596 +/- 10 Ma and contains a wider range of Neoproterozoic detritus with ages between 985 and 596 Ma. The basement of the Thalbah Group is represented by metasediments and metavolcanics of the Zaam Group. The sample collected from the uppermost part of the Zaam Group (Um Ashsh Formation) contains zircon of mostly Cryogenian age (ca. 812-697 Ma) and has a maximum age of 700 +/- 4 Ma, suggesting that the Zaam Group might be correlative with the subduction-related metavolcanic and metasedimentary rocks that are overlain unconformably by the Wadi Igla Formation in the CED. The Wadi Igla basin and the lower and middle parts of the Thalbah basin have similar provenance, record a Cryogenian-early Ediacaran age, and represent syn-subduction (rather than post-amalgamation) basins. The upper part of the Thalbah Group, in contrast, has a distinct provenance representing an Ediacaran syn-collisional basin. The narrow age range of the Wadi Igla Formation and the lower and middle parts of the Thalbah Group indicates a restricted source from the CED and MT island arc basement, whereas the wide age range for the upper part of the Thalbah Group indicates a contribution from other parts of the ANS. The sediment sources and the age patterns of detrital zircons change abruptly at ca. 596 Ma. This may coincide with the onset of collision of the CED and MT basements with the older Hijaz-Gebeit terrane (850-680 Ma) to the south along the Yanbu-Onib-Sol Hamed-Gerf-Allaqi-Heiani (YOSHGAH) suture in the ANS during the East African Orogeny.

  • 2.
    Boskabadi, Ahmad
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Pitcairn, Iairn K.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Stern, R. J.
    Azer, M. K.
    Broman, Curt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mohamed, F. H.
    Majka, J.
    Carbonatite crystallization and alteration in the Tarr carbonatite-albitite complex, Sinai Peninsula, Egypt2013In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. - 239, p. 24-41Article in journal (Refereed)
    Abstract [en]

    Carbonate dykes occurring in the Arabian-Nubian Shield (ANS) are clearly intrusive in origin and carbonatites according to the IUGS classification, yet previous investigations refer to them as “intrusive carbonates”, due mainly to their low Sr, Ba, Nb, Y, Th and rare earth element (REE) contents. The Tarr carbonatite albitite complex (TCA) in SE Sinai, Egypt contains a series of small (<1.2 km2) albitite intrusions surrounded by small veins and dykes of carbonatite, which occur predominantly in a narrow zone of brecciation surrounding the intrusions. Fennitic alteration surrounding TCA has been reported but there is little consensus on the extent and origin of this alteration. Fennitic alteration surrounding the TCA carbonatites is not abundant. Alteration is dominated by precipitation of carbonates in the breccia zone surrounding the albitite intrusion with associated actinolite, chlorite, sericite and epidote. Geochemical compositions are consistent with addition of carbonates and associated secondary minerals because the altered rocks contain higher CaO, MgO, Fe2O3 and MnO and lower SiO2, Al2O3, Na2O and K2O compared to their less altered rocks. Fluid inclusion investigations show that the carbonatite magma contained a high-salinity H2O–CO2–NaCl–CaCl2 fluid, although the lack of fennitic alteration implies that this fluid was not abundant. The crystallization conditions of the carbonatite dykes and carbonatite matrix in the breccia zones have been constrained using Zr-in-rutile thermometry and fluid inclusion microthermometry. Crystallization of the carbonatite in the dykes and in the breccia zone occurred between 565 ± 38 °C and 420–480 °C, respectively and at 0.75–1.3 kbar, which corresponds to a depth of 2.8–4.9 km. Rutile hosted within the carbonatite crystallized earlier at high temperature and the carbonate matrix crystallized later after cooling. Immiscible fluid from carbonatite magma would have altered the surrounding country rocks at lower temperature (between 400 °C and 150 °C deduced from the fluid inclusion thermometry) after the intrusion of the carbonatite melt.

  • 3. Hoffmann, J. Elis
    et al.
    Svahnberg, Henrik
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Schersten, Anders
    Muenker, Carsten
    The geodynamic evolution of Mesoarchean anorthosite complexes inferred from the Naajat Kuuat Complex, southern West Greenland2012In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 196, p. 149-170Article in journal (Refereed)
    Abstract [en]

    Layered anorthosite complexes are typical components of Archean crustal domains. However, the geodynamic settings in which they were emplaced are still discussed as geological relationships are often ambiguous. Here we report major, trace element and high-precision high-field-strength-element (HFSE) data for the recently discovered well preserved Naajat Kuuat Anorthosite Complex from the inner Ameralik fjord region, southern West Greenland. The dataset is complemented by the first combined Hf-Nd isotope analyses for Archean layered anorthosite complexes and U-Pb zircon geochronology. The data contribute to the small database on Archean layered anorthosite complexes and are used to unravel the origin of these complexes and the tectonic regime involved. Fractional crystallisation of olivine, pyroxene, plagioclase and possibly amphibole controls major and trace element variations in the layered intrusion. There are two groups of amphibolites: (1) a group with primitive mantle normalized trace element patterns are similar to those of MORB-like basalts and (2) typical island-arc tholeiites (IAT), apparently indicating an island-arc setting. Lu-Hf regression lines yield an age of 2985 +/- 59 Ma (MSWD 4) within the error of the Sm-Nd regression age of 2929 110 Ma (MSWD 17). The initial epsilon Hf(2985) for the Naajat Kuuat rocks range from +1.6 to +5.8 and the initial epsilon Nd(2985) range from +0.4 to +3.9, either indicating variably depleted mantle sources or variable degrees of crustal contamination. In contrast to most mafic assemblages, ratios of Nb/Ta are highly variable (7.85 to 18.6), reflecting fractionation and accumulation of amphibole, ilmenite and pyroxene. The MORB-like parental liquids have the highest Nb/Ta of ca. 18, consistent with a mantle source overprinted by melt-like components from subducting oceanic crust with high Nb/Ta. The accumulation of plagioclase forming the anorthosites and the primary fractionation of amphibole as well as the occurrence of high-Al basalts within the Naajat Kuuat complex argue for hydrous parental liquids in support of an island-arc related setting. Zircon U-Pb geochronology from the anorthosite and adjacent tonalites reveal major tonalite intrusion into the complex at ca. 2802 Ma and a second regional event at ca. 2710 Ma, in accord with crustal heating due to micro-continent amalgamation and crustal thickening. Altogether, the geochemical data can be interpreted with a geodynamic model, where anorthosite-complex associated rocks intrude into tectonically thickened island-arc crust. Crustal thickening is possibly triggered by island-arc accretion, leading to the emplacement of TTG bodies that further thickened the crustal pile. Further collision and amalgamation with other proto-crustal assemblages might have led to enhanced crustal magmatism and granulite facies metamorphism.

  • 4. Jarrar, Ghaleb H.
    et al.
    Theye, Thomas
    Yaseen, Najel
    Whitehouse, Martin
    Pease, Victoria
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Passchier, Cees
    Geochemistry and P-T-t evolution of the Abu-Barqa Metamorphic Suite, SW Jordan, and implications for the tectonics of the northern Arabian-Nubian Shield2013In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 239, p. 56-78Article in journal (Refereed)
    Abstract [en]

    The Abu Barqa Metamorphic Suite (ABMS) represents the oldest part of the Arabian-Nubian Shield in southern Jordan. It comprises tonalitic gneiss, metasediments including schist and paragneiss, and granitic gneiss, intruded by later granitic bodies. Geochemically, the majority of the schist samples have shale and Fe-shale protoliths, while the paragneisses represent metagreywacke. Tectonic discrimination diagrams indicate that the protolith of the ABMS was deposited at an active continental margin/island arc setting. U-Pb zircon (SIMS) ages from metamorphic and igneous rocks of the ABMS indicate that it evolved between similar to 800 and similar to 610 Ma. A tonalitic gneiss has a crystallization age of 787 +/- 3 Ma. Detrital zircon from the metasediment has a range of concordant ages from 680 to 860 Ma. The entire metamorphic complex was intruded by calc-alkaline granitoids (similar to 615-610 Ma) and quartz diorite dated (similar to 600 Ma). Field and petrographic investigations of ABMS metasediment elucidate the development of three metamorphic zones, from north to south: (1) andalusite-staurolite (andalusite + staurolite + biotite + muscovite + plagioclase +/- garnet + quartz +/- chlorite + fibrolitic sillimanite + accessories), (2) garnetsillimanite (sillimanite + garnet + biotite + plagioclase + quartz + K-feldspar + cordierite (pinitized) +/- rutile +/- ilmenite), and (3) cordierite-sillimanite (sillimanite + biotite + plagioclase + cordierite + hercynite + quartz + accessories). The maximum metamorphic conditions (M1) were attained in the garnet-sillimanite zone (5-6 kbar, similar to 700 degrees C), while peak conditions of similar to 3.2 kbar and 540 degrees C were obtained for the andalusite-staurolite zone (using both forward-pseudosection modeling and inverse-modeling with multi-equilibrium approach). Compositional isopleth calculations of small relics of garnet yield about 3.5 kbar and 600 degrees C for the sillimanite-cordierite zone. These values are in agreement with results obtained by TWQ inverse modeling. The M1 event most probably occurred around similar to 625 and was followed by a decompressional thermal phase (M2) contemporaneous with post-tectonic granitoid emplacement at similar to 615-610 Ma; and lastly went through a retrograde cooling phase (M3) accompanying uplift of the whole complex to the surface at similar to 605 Ma.

  • 5.
    Kielman, Ross B.
    et al.
    Swedish Museum of Natural History, Sweden.
    Nemchin, Alexander A.
    Whitehouse, Martin J.
    Pidgeon, Robert T.
    Bellucci, Jeremy J.
    U-Pb age distribution recorded in zircons from Archean quartzites in the Mt. Alfred area, Yilgarn Craton, Western Australia2018In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 310, p. 278-290Article in journal (Refereed)
    Abstract [en]

    The U-Th-Pb isotopic data from detrital zircon grains from five samples of Archean quartzite from the Mt. Alfred area of the Illaara greenstone belt in the Yilgarn Craton of Western Australia are presented in this study. The zircon grains are typically fractured and contain both irregular and oscillatory zoned internal structures as revealed by cathodoluminescence imaging. Concordant 207Pb/206Pb ages range between 3109 ± 17 and 3918 ± 16 Ma (2σ), with three main age peaks at ca. 3640, 3690 and 3760 Ma. Older 207Pb/206Pb ages up to 4067 ± 5 Ma are strongly affected by at least one recent disturbance event, however one single-grain discordia yields an upper intercept age of 4107 ± 12 (MSWD = 1.2). A further sixteen zircon grains with multiple analyses define discordia that suggest U-Pb disturbance events in the Neoarchean and the Mesozoic, the latter as a result of invasive low temperature weathering solutions. The notable lack of grains with ages less than ∼3.6 Ga in the Mt. Alfred detrital zircon population differentiates it from other quartzite samples from both the Illaara Formation and the Eoarchean zircon-bearing metasedimentary rocks of the Narryer Terrane. Also, the limited spread of zircon ages between 3640 and 3760 Ma suggests a relatively uniform and possibly local source region. However, no rocks of this age have been found in the Youanmi Terrane. This implies either the distal transport of similarly aged clastic sediments at 3.1 Ga from the Narryer Gneiss Complex (NGC) to the Mt. Alfred area, or the previous existence of NGC-like rocks near the Illaara greenstone belt that are either not currently recognised or have since been destroyed.

  • 6. Petersson, Andreas
    et al.
    Schersten, Anders
    Andersson, Jenny
    Whitehouse, Martin J.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Swedish Museum of Natural History, Sweden.
    Baranoski, Mark T.
    Zircon U-Pb, Hf and O isotope constraints on growth versus reworking of continental crust in the subsurface Grenville orogen, Ohio, USA2015In: 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.

  • 7.
    Pettersson, Carl-Henrik
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Pease, Victoria
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Frei, Dick
    U-Pb zircon provenance of metasedimentary basement of the Northwestern Terrane, Svalbard: Implications for the Grenvillian–Sveconorwegian orogenyand development of Rodinia2009In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 175, no 1-4, p. 206-220Article in journal (Refereed)
    Abstract [en]

    Svalbard is pivotal for defining the northern extent of the Grenville/Sveconorwegian orogenic belt. Consequently, to constrain the origin of Svalbard’s Northwestern Terrane (NWT), detrital zircon populations from samples of the Krossfjorden Group and Smerenburgfjorden complex, northwestern Svalbard, were analyzed by U-Pb Laser ablation ICP-MS. These data indicate that the NWT’s metasedimentary basement, the Krossfjorden Group, was deposited between c. 1020-995 Ma and indicates that the Smerenburgfjorden complex may represent a migmatized and deformed part of the Krossfjorden Group. Statistically, the source area of the Krossfjorden Group can not be distinguished from other late Mesoproterozoic to early Neoproterozoic siliciclastic sequences exposed in the Caledonian orogenic belt and their detrital populations are compatible with derivation from the Eastern Grenville Province (EGP), dominated by ages coinciding with the Labradorian event (1710-1600 Ma). The diachronous tectonothermal evolution of these Meso-to Neoproterozoic metasedimentary sequences suggests deposition in a spatially linked peripheral foreland and remnant ocean basins located east of EGP, which migrated eastwards during the final suturing of Rodina. Thus, they do not represent a northern branch of the Grenvillian/Sveconorwegian Orogeny.

  • 8.
    Robinson, Frank A.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Pease, Victoria
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Whitehouse, M. J.
    Kooijman, E.
    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 (similar to 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 (similar to 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), delta O-18((V-SMOW)) ranging from 4.6 to 8.3 parts per thousand and epsilon(Hf) (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, delta O-18 and epsilon(Hf) (t) values ranging from 4.4 to 9.6 parts per thousand and -10.1 to +12.4, respectively; the later yields a concordia age of 645.8 [+/- 1.7] Ma (n = 29), delta O-18 ranging from 5.7 to 6.6 parts per thousand, and epsilon(Hf) (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 similar to 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.

  • 9. Yaseen, Najel
    et al.
    Pease, Victoria
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jarrar, Ghaleb H.
    Whitehouse, Martin
    U-Pb detrital zircon provenance of the Saramuj Conglomerate, Jordan, and implications for the Neoproterozoic evolution of the Red Sea region2013In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 239, p. 6-23Article in journal (Refereed)
    Abstract [en]

    The latest stage in the evolution of the northernmost Arabian-Nubian Shield is characterized by the development of volcano-sedimentary successions. In Jordan the Saramuj Conglomerate Formation is considered to be one of these post-tectonic basins. It is polymict and poorly sorted with wide range of clast compositions, roundness and size. We present the first SIMS U-Pb dating of detrital zircons from two sandstone samples representative for the conglomerate matrix and of four clasts from the Saramuj Conglomerate for provenance and age determinations. The relative probability curve for the matrix samples indicates a major contribution (85%) from c. 600 to 650 Ma, subclusters at 624 and 640 Ma, a minor source from 700 to 750 Ma, and a clear gap between 650 and 700 Ma. These ages are consistent with those obtained from andesitic, rhyodacitic, granitic and gneiss clasts (624, 642,650 and 734 Ma respectively). In contrast to the adjacent volcano-sedimentary successions in the Elat area, Sinai and the Eastern Desert, no ages older than 750 Ma were found. The good match between the known ages of the nearby exposed basement with the matrix ages and the immature nature of the sediments implies that the principal input was locally derived erosional detritus. The age of the youngest 10 detrital zircons at C. 615 Ma represents the maximum age of deposition, which is consistent with the stratigraphic position of the Saramuj Conglomerate. Clast ages of 642 Ma and 650 Ma are interpreted as evidence for a magmatic source that has not been recognized in SW Jordan. This study implies that the volcano-sedimentary successions in the northernmost Arabian-Nubian shield may be broadly coeval but have distinct provenance and therefore evolved as isolated basins. Furthermore, U-Pb zircon provenance analysis allows us to recognize igneous products that are no longer preserved and/or exposed in the region.

  • 10.
    Yeshanew, Fitsum G.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Swedish Museum of Natural History, Sweden.
    Pease, Victoria
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Whitehouse, Martin J.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Swedish Museum of Natural History, Sweden.
    Al-Khirbash, Salah
    Zircon U-Pb geochronology and Nd isotope systematics of the Abas terrane, Yemen: Implications for Neoproterozoic crust reworking events2015In: 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 epsilon(Nd)(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.

  • 11.
    Zhang, Wen
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Chinese Academy of Geological Sciences, China.
    Roberts, D.
    Pease, Victoria
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Provenance characteristics and regional implications of Neoproterozoic, Timanian-margin successions and a basal Caledonian nappe in northern Norway2015In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 268, p. 153-167Article in journal (Refereed)
    Abstract [en]

    The autochthonous/parautochthonous lithostratigraphic successions of Varanger Peninsula, NE Norway, range in age from Tonian to Cambrian and constituted a passive (Baltican) margin depositional system throughout most of the Neoproterozoic. Sediment sources were mainly from the south on the Fennoscandian Shield. U-Pb zircon age spectra from sandstones of eight formations show significant input of Late Palaeoproterozoic and Mesoproterozoic age, as well as a prominent Neoarchaean peak. These mostly reflect derivation from rock complexes and terranes that are exposed on the present-day Baltic Shield, although the abundance of Mesoproterozoic zircon grains is less easy to explain. Possible sources may represent (i) possible basement of this age now concealed beneath the Caledonian nappes, (ii) a northward continuation of the Sveconorwegian orogen, (iii) recycling of a sandstone-dominated thrust sheet derived from the Rodinian margin and emplaced in the Tonian or (iv) recycled material from pre-existing extensive river systems farther south on the Fennoscandian Shield. One major exception to the above age-spectral pattern is provided by the Late Ediacaran to earliest Cambrian Stahpogieddi Formation in the immediately overlying Gaissa Nappe Complex. Sandstones in this unit are derived from a northeasterly source, and show a major zircon age peak at c. 550 Ma. The formation is considered to represent deposition in a foreland basin ahead of the rising Timanian orogen.

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