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We carried out SHRIMP zircon U-Pb dating on A-type granitic intrusions from the Namaqua-Natal Province, South Africa, Sverdrupfjella, western Dronning Maud Land, Antarctica and the Nampula Province of northern Mozambique. Zircon grains in these granitic rocks are typically elongated and oscillatory zoned, suggesting magmatic origins. Zircons from the granitoid intrusions analyzed in this study suggest ∼1025–1100 Ma ages, which confirm widespread Mesoproterozoic A-type granitic magmatism in the Namaqua-Natal (South Africa), Maud (Antarctica) and Mozambique metamorphic terrains. No older inherited (e.g., ∼2500 Ma Achean basement or ∼1200 Ma island arc magmatism in northern Natal) zircon grains were seen. Four plutons from the Natal Belt (Mvoti Pluton, Glendale Pluton, Kwalembe Pluton, Ntimbankulu Pluton) display 1050–1040 Ma ages, whereas the Nthlimbitwa Pluton in northern Natal indicates older 1090–1080 Ma ages. A sample from Sverdrupfjella, Antarctica has ∼1091 Ma old zircons along with ∼530 Ma metamorphic rims. Similarly, four samples analysed from the Nampula Province of Mozambique suggest crystallization ages of ∼1060–1090 Ma but also show significant discordance with two samples showing younger ∼550 Ma overgrowths. None of the Natal samples show any younger overgrowths. A single sample from southwestern Namaqualand yielded an age of ∼1033 Ma.Currently available chronological data suggest magmatism took place in the Namaqua-Natal-Maud-Mozambique (NNMM) belt between ∼1025 Ma and ∼1100 Ma with two broad phases between ∼1060–1020 Ma and 1100–1070 Ma respectively, with peaks at between ∼1030–1040 Ma and ∼1070–1090 Ma. The age data from the granitic intrusions from Namaqualand, combined with those from Natal, Antarctica and Mozambique suggest a crude spatial-age relationship with the older >1070 Ma ages being largely restricted close to the eastern and western margins of the Kalahari Craton in northern Natal, Mozambique, Namaqualand and WDML Antarctica whereas the younger

The Saharan Metacraton is a poorly known tract of pre-Neoproterozoic continental crust that occupies the area between the juvenile Arabian Nubian Shield, in the east, and the Tuareg Shield to the west. Neoproterozoic orogenesis (i.e. Ouban guides and East African orogenies) affect the west, the south and the east of the metacraton, respectively, which led to deformation, emplacement of igneous bodies, and localised episodes of rift-related magamatism. Details about interior regions of the Saharan Metacraton are poorly known, with much of it covered by Phanerozoic rocks. The basement outcrops in Sudan, Chad, Algeria and Libya have been the subject of few modern geochronological studies. Here we present results from the first zircon geochronology and in-situ zircon hafnium isotope investigations from both the Sudanese Butana and central Chad. The terranes in Butana, formed to the east of pre-Neoproterozoic continental crust of the Saharan Metacraton, with the oldest juvenile magmatism (ƐHf(t) of +4.89 to +7.89) at ca. 839 Ma, followed by subsequent magmatism at ca. 787 Ma. The ca. 787 Ma event (seen elsewhere in the East African Orogen) is interpreted to represent volcanic-arc collision and accretion with the kernel of the Saharan Metacraton. The ca. 839 Ma magmatism is contemporaneous with the accretion of the Tonian (ca. 850 Ma) arc terranes of the Arabian Nubian Shield and marks subduction to the east of the Saharan Metacraton. The magmatic history of the Ouaddaï region in Chad begins in the late Mesoproterozoic, with localised rifting, resulting in the emplacement of juvenile granites (ca. 1030 Ma). The Cryogenian and Ediacaran in the Saharan Metacraton reveal a complicated history of magmatism and deformation. Age data from Chad show the emplacement of granites (from melting of Mesoproterozoic crust: ƐHf(t) = +2.04 and −4.07) at ca. 665–654 Ma, coeval with the main East African Orogeny and accretion of the other ANS terranes to the Saharan Metacraton at ca. 650–580 Ma. The youngest tectonothermal event within the Saharan Metacraton is recorded by emplacement of granites between 580 and 550 Ma (ƐHf(t) values of −17 to −31) in southern Chad. Refereed/Peer-reviewed

The geological timescale before 720 Ma uses rounded absolute ages rather than specific events recorded in rocks to subdivide time. This has led increasingly to mismatches between subdivisions and the features for which they were named. Here we review the formal processes that led to the current timescale, outline rock-based concepts that could be used to subdivide pre-Cryogenian time and propose revisions. An appraisal of the Precambrian rock record confirms that purely chronostratigraphic subdivision would require only modest deviation from current chronometric boundaries, removal of which could be expedited by establishing event-based concepts and provisional, approximate ages for eon-, era- and period-level subdivisions. Our review leads to the following conclusions: (1) the current informal four-fold Archean subdivision should be simplified to a tripartite scheme, pending more detailed analysis, and (2) an improved rock-based Proterozoic Eon might comprise a Paleoproterozoic Era with three periods (early Paleoproterozoic or Skourian, Rhyacian, Orosirian), Mesoproterozoic Era with four periods (Statherian, Calymmian, Ectasian, Stenian) and a Neoproterozoic Era with four periods (pre-Tonian or Kleisian, Tonian, Cryogenian and Ediacaran). These proposals stem from a wide community and could be used to guide future development of the pre-Cryogenian timescale by international bodies. Publisher PDF

The Borborema Province is an important Precambrian orogenic system in Northeastern Brazil. It was formed during the assembly of Western Gondwana in the Brasiliano-Pan-African Orogeny. The Neoproterozoic Sergipano Belt is part of the Province and occupies a large area of its southern portion. Investigation of provenance and tectonic environment of the metavolcanic-sedimentary complexes in this belt are of regional amplitude and may reveal important aspects of the evolution of the province. In this study new whole-rock geochemistry, isotope Nd data and U-Pb geochronological data on detrital zircon of the metavolcanic-sedimentary Araticum Complex within the northeastern part of the Sergipano Belt, in order to contribute to the understanding the role of the Sergipano Belt in amalgamation of Western Gondwana. The related data indicate provenance from eroded island arcs and back-arc-relate settings during the Neoproterozoic. Detrital zircon grains indicate populations of Ediacaran-Cryogenian (ca. 660-620 Ma) and Tonian-Stenian ages (around ca. 1047 Ma) suggesting that source areas represent extinct volcanic arcs of the Pernambuco-Alagoas Domain to the north. Based on this study, it is suggested that sediments of the Araticum paleobasin were deposited in an oceanic environment during the arc exhumation over the Brasiliano-Pan African Orogeny, but also with strong contributions from Stenian island arcs, which are attributed to the Cariris Velhos Orogeny. Our results support that major supracrustal sequences of the Sergipano Fold Belt were deposited in the Neoproterozoic, such as indicated by previous studies.

The Maurice Ewing Bank is located east of the Falkland/Malvinas Islands and is one of the most intriguing regions of southern Gondwana. The interaction of several microplates with major cratonic areas resulted in complex displacements between Paleozoic and Cretaceous times. Here, we present combined U-Pb and Lu-Hf zircon isotopic analyses of the Maurice Ewing Bank basement to constrain the age and tectonic setting to aid in paleogeographic reconstruction. The high-grade paragneisses in the bank present dominant Late Mesoproterozoic detrital zircon age distributions with populations at 1032 ± 12 Ma, 1068 ± 16 Ma and 1233 ± 8 Ma and juvenile signature (positive εHf[t] values). The gneisses are cutting by anatectic pink granite crystallized at 1006 ± 13 Ma which formed after syn-collisional high-grade metamorphism and shows juvenile and some crustal component (εHf[t] = +1.6 to −3). The Maurice Ewing Bank basement rocks have same Stenian age and dominant juvenile signature as the arc-related basement rocks from the Falkland/Malvinas Islands and are probably part of the same continental plateau of the South America continent. This new finding enables future reconstructions in paleogeographic models where the basement of the Falkland/Malvinas Islands and the Maurice Ewing Bank formed a single block during the Mesoproterozoic and were partly separated by crustal stretching during the opening of the Atlantic Ocean in the Late Jurassic-Cretaceous. The block played a major role in the deformation of the Cape Fold Belt from the Late Paleozoic through the Mesozoic. Fil: Chemale, Farid. Universidade do Vale do Rio dos Sinos. Programa de Pós-Graduação em Geologia; Brasil Fil: Ramos, Victor Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina Fil: Naipauer, Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina Fil: Girelli, Tiago J.. Universidade do Vale do Rio dos Sinos. Programa de Pós-Graduação em Geologia; Brasil Fil: Vargas, Mateus. Universidade do Vale do Rio dos Sinos. Programa de Pós-Graduação em Geologia; Brasil

The Ossa-Morena Zone in Iberia, and equivalent terranes in northern France and Central Europe, are thought to be paleogeographically linked to the West African Craton at Ediacaran to early Paleozoic times. Evidence is mainly based on metasedimentary rock detrital zircon age spectra, characterized by two dominant populations of Paleoproterozoic and Cryogenian-Ediacaran ages, with a systematic lack of late Stenian – early Tonian zircon grains. We report here U-Pb-Hf results on detrital zircon grains from six Ordovician-Devonian metasedimentary rocks from the Ossa-Morena Zone. In addition to the Cryogenian-Ediacaran and Paleoproterozoic populations already recognized in previous studies on uppermost Ediacaran and lower Cambrian rocks, the samples ubiquitously show a late Stenian – early Tonian population centered at ≈1 Ga and representing ≈20% of the concordant dates. The eHf versus age plot of the studied samples mainly depicts two vertical arrays corresponding to the Cryogenian-Ediacaran and Stenian-Tonian detrital zircon populations, which spread from eHf values of ≈10 down to ≈−20. The detrital zircon age distribution and Hf isotope signature of the studied rocks point to the Sahara metacraton as the most plausible sediment source. The eastward translation of the continental ribbon represented by the Ossa-Morena Zone and equivalent domains of the Variscides from an original position close to the West African Craton to an Ordovician-Devonian location close to the Sahara metacraton probably occurred at latest Ediacaran – earliest Cambrian times in a dextral strike-slip tectonic setting that post-dated Pan-African collision and Cadomian subduction.

The Lajeado Group is a Stenian-Tonian metasedimentary unit comprising a thick carbonate succession that was involved in the Brasiliano – Pan-African Ribeira orogenesis in Southeast Brazil. The carbonate rocks record significant carbon isotope variations, which provide further information about the Mesoproterozoic Earth system. The δ13C values obtained along a composite vertical section vary between −5 and +5‰ with two negative isotope excursions with magnitudes higher than 6‰. The coincidence between the isotopic trend of the Lajeado carbonate succession with equivalent units studied worldwide suggests that the deposition of the lower and middle parts of the unit may have occurred at 1.2–1.1 Ga, which is in agreement with recently published geochronological data. Despite the similarities, the Lajeado Group displays larger carbon isotope variations and negative isotope excursions of higher magnitudes when compared to coeval marine settings. We argue that the basin conditions may have been more favourable to build up large particulate (POC) and dissolved organic carbon (DOC) reservoirs. When oxidized they significantly impacted the dissolved inorganic carbon (DIC) pool, causing the negative excursions. If our scenario holds, the Lajeado Group may be considered an example of record of fluctuations in atmospheric pO2 levels and the oxidation state of the planet during the late Mesoproterozoic.

The Río de la Plata Craton is one of the three major cratons of South America. The craton is largely covered by sedimentary basins where its most exposed area is Buenos Aires-Piedra Alta Province (Chernicoff et al., 2014). This province includes the Martín García Island in the confluence of Uruguay River and the Río de la Plata estuary. Despite to be a reference area for the craton the Martín García Island lacks modern geological investigation. We present U-Pb SIMS (secondary ion mass spectrometer) geochronological data on zircon and titanite, as well as Hf isotope determinations on zircon, from rocks of Martín García Island (Argentina), Sola and Dos Hermanas Islands (Uruguay) and from Paso Severino Formation (Uruguay). We investigated: 1) Rhyacian intermediate-to acidic plutonic, arc-type rocks of the Florida Belt dated between 2090 Ma and 2115 Ma, derived from juvenile Neoarchean crust (TDMHf: 2.52 Ga; average εHf: +3.62); 2) Rhyacian metadacite (San José metamorphic belt) of 2127 Ma; 3) Statherian metagabbros of 1724–1734 Ma, with Transplatense inheritance; 4) Early Ectasian metagabbro of 1392 Ma, with Rhyacian inheritance; and 5) Stenian metagabbros of 1193 Ma (TDMHf: 2.00 Ga, εHf: 0.1). Most of the dated orthogneisses show Brasilian-age (from 778 to 550 Ma) Pb loss in the zircons, interpreted to be caused by shearing or uplifting during Neoproterozoic. The results show that the area is not exclusively Rhyacian in age but encompasses Statherian, Ectasian, and Stenian gabbros. The last two are interpreted as distal intrusions associated to the Sunsás Orogen. All post-Transplatense metagabbros have geochemical signature of island arc basalt derived from primitive mantle with enrichment of LILE and depletion of HFSE. These characteristics point to the recurrence of magma chambers intermittently active during the Rhyacian, Statherian, Ectasian, and Stenian, all with a similar source. The term “Transplatense” is used to replace “Trans-Amazonian” events that occurred within the craton. Fil: Santos, João O. S.. University of Western Australia; Australia Fil: Chernicoff, Carlos Jorge. Curtin University; Australia. Secretaría de Industria y Minería. Servicio Geológico Minero Argentino; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Zappettini, Eduardo Osvaldo. Curtin University; Australia Fil: McNaughton, Neal J.. Macquarie University; Australia Fil: Gréau, Yoann. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

In situ monazite geochronological data yield the timing of migmatitic metamorphism in southern Ubendian Belt. The mineral assemblage of garnet-biotite- sillimanite- K–feldspar- plagioclase-quartz- ilmenite, in migmatitic metapelitic gneisses was achieved during the Ediacaran metamorphic episode between 565 ± 4 Ma and 559 ± 8 Ma as manifested by dating of monazite grains that include garnet. The Ediacaran metamorphic event in the southern Ubendian Belt overprinted the Paleoproterozoic metamorphic event established at 1808 ± 9 Ma and the Mesoproterozoic metamorphic event at 944 ± 4 Ma (Tonian Period). The Stenian - Tonian and Ediacaran metamorphic imprints in the southern Ubendian Belt fall within the time window of metamorphism and deformation of the neighboring Irumide, southern Irumide, and Unango/Marrupa Complexes. The ca. 560 Ma old granulite facies imprinting in the southern Ubendian Belt is coeval with shear zone patterns in the neighboring Nyika Terrane in NE Malawi the event that was followed by eclogite facies metamorphism during the last stage of Gondwana amalgamation.

We have targeted the southern side of the Dronning Maud Land (DML) mountains in search of moraine material that might reveal the geology in the ice-covered region of the East Antarctic polar plateau. Nine samples of unconsolidated moraine material, carried by the northward flowing East Antarctic ice sheet to the southern side of the DML escarpment, were collected and processed for U-Pb zircon analyses. The analyses resulted in ca. 1100 new U-Pb zircon spot ages between ca. 2000 and 500 Ma. The oldest, Palaeoproterozoic rocks come from the easternmost localities with a probable source region between the Sor Rondane Mountains and Dome Fuji. The samples have major Stenian and early Tonian age peaks. Early Tonian rocks are well known from the SW Terrane in the Sor Rondane Mountains and characterise the major Tonian Oceanic Arc Super Terrane (TOAST). Stenian ages are far less common in the outcropping region. Although Stenian ages are common in both the Maud Province of western-central DML as well as in the Rayner Complex, our samples differ with respect to composition and/or isotope geochemistry; they are juvenile, subduction-related and resemble an early phase of oceanic arcs that was so far unknown in this region. In the westernmost sample, the oldest age peak is ca. 800–720 Ma with possible counterparts in the Schirmacher Oasis. All samples show a protracted Late Neoproterozoic/Early Palaeozoic metamorphic overprint, accompanied by igneous addition, most likely related to the East African-Antarctic Orogen. This overprint appears most intense in clasts collected from the westernmost locality, lasted for ca. 150 Ma and an eastward younging of metamorphic ages is observed. The new moraine samples together with previous outcrop studies reveal that this region has undergone two major phases of oceanic arc/terrane accretion; the first one from ca. 1100 to 900 Ma is probably related to accretion tectonics outboard of Rodinia, the second one from ca. 850 to 580 Ma occurred as a result of ocean closure and finally Gondwana amalgamation. No significant old components are found, but the high proportion of Late Neoproterozoic/Early Palaeozoic ages confirms that the East African-Antarctic Orogen transects DML and East Antarctica.

The precursor basin of the Aracuai – West Congo Orogenic System (AWCO) formed a large gulf within the Sao Francisco – Congo Paleocontinent (SFCP), where sedimentary successions ascribed to the Jequitinhonha Complex and Macaubas Group were deposited in the Neoproterozoic. This precursor basin system comprises an aborted continental rift of Early Tonian age and a Cryogenian rift that evolved to ocean-floor spreading up to the Early Ediacaran. The Jequitinhonha Complex is an extensive metasedimentary unit located in the northeastern Aracuai Orogen, consisting of Al-rich paragneiss (kinzigite), sillimanite-graphite gneiss and associated economic deposits of flake graphite, quartzite and lenses of calc-silicate rock, metamorphosed variably to upper amphibolite or granulite facies around 570–550 Ma. U-Pb (LA-MC-ICP-MS) data of 110 detrital zircon grains from the paleosome of a migmatitic paragneiss yield five main age peaks at 2564 ± 35 Ma (5% of the grains), 2012 ± 21 Ma (7%), 1807 ± 19 Ma (12%), 960 ± 8 Ma (29%) and 662 ± 6 Ma (48%), with the youngest grains around 630–609 Ma, and a major age gap from the Statherian to Stenian. The U-Pb age spectrum coupled with Lu-Hf in zircon (LA-MC-ICP-MS) data for 106 zircon grains suggest the following sources: Neoarchean to Orosirian grains were sourced from the SFCP basement, Early Tonian grains from the anorogenic magmatic province, and Cryogenian to Early Ediacaran grains were provided by the Southern Bahia Alkaline Province and Rio Doce magmatic arc. The eHf(t) values show a predominant contribution from evolved crust, with minor involvement of moderately juvenile crust. The sedimentation of Jequitinhonha Complex protoliths developed on the SFCP margin from the Cryogenian to Early Ediacaran, within anoxic marine environments favorable to the preservation of organic matter. This deposit formed the huge graphite deposits and lots of smaller occurrences found in the region, accumulating probably more than one billion tons of raw graphite. The youngest detrital zircon population suggests that the deposition record of the Jequitinhonha Complex covers the Cryogenian continental rifting event followed by the development of oceanic crust to the onset of subduction and building of the Rio Doce magmatic arc in the Early Ediacaran. The regional accumulation and preservation of carbon-rich sediments (now graphite-rich gneiss) most probably represent one of the largest storages of Ediacaran carbon around the world.

The first data on the Middle Riphean (Stenian) age of the Isherim Formation developed in the synonymous anticlinorium of the North Urals and U–Pb age of detrital zircons from its arkosic sandstones are discussed.

The transition to the diverse and complex biosphere of the Ediacaran and early Paleozoic is the culmination of a complex history of tectonic, climate, and geochemical development. Although much of this rise occurred in the middle and late intervals of the Neoproterozoic Era (1000–541 million years ago [Ma]), the foundation for many of these developments was laid much earlier, during the latest Mesoproterozic Stenian Period (1200–1000 Ma) and early Neoproterozoic Tonian Period (1000–720 Ma). Concurrent with the development of complex ecosystems, changes in the composition, configuration, and tectonic interaction between continental plates have been proposed as major shapers of both climate and biogeochemical cycling, but there is little support in the geologic record for overriding tectonic controls. Biogeochemical evidence, however, suggests that an expansion of marine oxygen concentrations may have stabilized nutrient cycles and created more stable environmental conditions under which complex, eukaryotic life could gain a foothold and flourish. The interaction of tectonic, biogeochemical, and climate processes, as described in this paper, resulted in the establishment of habitable environments that fostered the Ediacaran and early Phanerozoic radiations of animal life and the emergence of complex, modern-style ecosystems.

The Neoproterozoic–Ordovician Central Ribeira Orogen (southeastern portion), in SE Brazil, presents two contrasting tectonic domains in its southern portion: (a) the arc domain constituted of Neoproterozoic to Paleozoic magmatic rocks and low P-high T metamorphic para (Sao Fidelis Group)- and ortho-derived units (in Oriental Terrane); and (b) the basement domain, constituted of a Paleoproterozoic and Neoproterozoic medium P-high T metamorphic para (Palmital–Buzios succession)- and ortho-derived units (in Cabo Frio Tectonic Domain). Our work focuses on paraderived rocks sequences from both domains. The provenance analysis using U–Pb and Lu–Hf in zircon grains is presented here as an effective tool to unravel the paleogeography and nature of the pre-collisional sedimentary basins. We performed 505 analyses (U–Pb) on detrital zircon grains and some metamorphic overgrowths from six paragneiss samples. Besides, 141 analyses (Lu–Hf) in six samples only on the detrital zircon grains domains. All samples present a main peak from Neoproterozoic sources (750–570 Ma) and the other minor peak in the Stenian/Tonian periods (1200–850 Ma), this indicate an orogenic contribution for this basin. Scarce register from the Mesoproterozoic and two peaks in the Archean/Paleoproterozoic (2.6 and 1.9 Ga) are recognized as a contribution from an ancient continent. The Lu–Hf data reveals a juvenile source for the detrital zircon grains from Buzios succession while Palmital and Sao Fidelis Group units show a main crustal signature for their detrital zircon population. Based on the U–Pb and Lu–Hf data presented here, plus petrological data, geological correlations, and compilation of data from literature, we propose a tectonic model for the origin of para-derived rocks from the eastern part of the Ribeira Orogen. In at least two stages, starting with an extensional environment of ca. 600 Ma in a back-arc basin (Buzios succession deposition) and continuing as an active margin between 570 and 550 Ma in the fore-arc and prism basin (Sao Fidelis Group and Palmital succession).

Paleoproterozoic to Mesoproterozoic cratonic basins in the Sao Francisco Craton are classified into three megasequences: Statherian, Calymmian–early Ectasian, and Stenian–early Tonian sequences. The location, depositional age, and provenance of these sequences are reflected in their detrital zircon U–Pb age distributions. A minimum of five detrital zircon age distributions are distinguishable: i) the Archean and Rhyacian distribution, which is restricted to the Calymmian interval at Chapada Diamantina; ii) the Rhyacian distribution, which occurs in the Statherian, Calymmian, and Stenian intervals and generally precedes the Proterozoic distribution; iii) the Proterozoic distribution, which always succeeds the Rhyacian distribution and appears in the Brasilia Belt and Southern Espinhaco; iv) the mixed Archean and Proterozoic distribution, restricted to the Stenian interval at the Southern Brasilia Belt; and v) the Statherian distribution, which is present in the Statherian interval at Espinhaco Basin and is recycled into the Calymmian and Stenian intervals at Chapada Diamantina. Based on the Hf isotope compositions of the detrital zircons, most of the sequences are predominantly sourced from Archean juvenile terrains and from Archean and Paleoproterozoic evolved terrains. The exception is the Paranoa Group, western Sao Francisco Craton, whose positive ɛHf(t) values suggest juvenile Paleoproterozoic sources such as the Goias Massif. The Archean zircons from Chapada Diamantina have Hf depleted mantle model ages ranging from Paleoarchean to Neoarchean and are mainly derived from the Gaviao Block within northeastern Sao Francisco Craton. The model unify a dataset spanning hundreds of millions of years of the depositional record over a large area of central and eastern Brazil. The records will assist researchers in unraveling the sedimentary and tectonic history of the Archean and Paleoproterozoic continents from new data collected regionally and in other continents.

International audience; Assessment of sediment redistribution by end-Ordovician ice sheets is crucial for the reconstruction of Lower Paleozoic source-to-sink patterns. Focusing on the ice-distal, deepwater Tazekka depocenter (Moroccan Meseta), we performed a provenance study that combined whole-rock geochemistry, petrography and insights from high-resolution detrital zircon ages. The results show that the glacigenic sediments are compositionally — mineralogically and geochemically — more mature than preglacial strata. This observation points to a preferential cannibalization of the “great Lower Paleozoic quartz-rich sandstone sheet”, with a limited input of first-cycle, far-travelled clastic sediments. Differentiation of glacial units is not straightforward, yet the glaciation acme is typified by a highly mature sedimentary source and an age spectrum lacking Mesoproterozoic zircon grains, both features strongly indicating derivation from the Cambrian–Lower Ordovician cover of the Tuareg Shield. More regional sources are expressed during the earlier glaciation stages, during which lowstand remobilizations unrelated to subglacial erosion are also suspected. Subordinate but notable late Tonian (∼0.8 Ga) and latest Stenian to early Tonian (∼1 Ga) zircon populations are also evidenced in Morocco, which may have implications for future paleogeographic reconstructions.

The ‘Purana’ basins were long considered Neoproterozoic basins until geochronology and palaeomagnestism showed parts of the Chattisgarth and lower Vindhyan basins to be a billion years older. Historically, the successions in the Chattisgarth Basin are correlated with similar successions in the Pranhita–Godavari and Indravati basins. In India, differentiating between early–late Mesoproterozoic rocks and those spanning the Mesoproterozoic–Neoproterozoic boundary is possible by comparing magnetic declination and inclination; palaeomagnetism is therefore a very useful correlation tool. Here we report a new Stenian-aged palaeopole (50.1°N, 67.4°E, radius of cone of 95% confidence A 95 = 12.4°, precision K = 30.1) from carbonate and shale successions of the Pranhita–Godavari and Chattisgarth basins (the C+/– magnetization). In addition, an early diagenetic remagnetization (component A) was identified. No primary or early diagenetic magnetizations were identified from the Indravati Basin. Here, as well as in stratigraphically higher parts of the other two successions, widespread younger magnetic overprints were identified (B+ and B– magnetic components). Our C+/– palaeopole is constrained by palaeomagnetic stability field tests, is different from known 1.4 Ga and 1.0 Ga Indian palaeopoles, but similar to a 1.19 Ga palaeopole. Penganga Group (Pranhita–Godavari Basin) deposition was probably initiated at around 1.2 Ga. A similar palaeomagnetic signature confirms its correlation with the Raipur Group (Chattisgarth Basin), of which the deposition spans most of the Stenian period ( c . 1.2–1.0 Ga). Sedimentation in these groups began significantly later than c . 1.4 and c . 1.6 Ga, as suggested by ages reported from below the Raipur and Penganga groups, respectively.

Na região norte da faixa Araçuaí, no domínio fisiográfico do Espinhaço Central, existem registros de bacias sedimentares superpostas instaladas sobre o embasamento do cráton São Francisco. Nesse contexto, a morfoestrutura da Serra Central, norte de Minas Gerais, é sustentada por uma sucessão siliciclástica do Supergrupo Espinhaço superposta a oeste por diamictitos da base do Grupo Macaúbas, representando os registros de rifteamento superpostos ao final do Esteniano e do Toniano Superior, respectivamente. No bordo oeste da Serra Central, são descritas estrias de média a alta obliquidade desenvolvidas sobre os planos de acamamento da sucessão do Grupo Sítio Novo, incompatíveis com a tectônica compressional Brasiliana, que afeta essas rochas. Essas estrias são associadas a degraus e definem vetores de deslizamento interestratais indicativos de movimentação normal a normal destral. Associados a essas lineações, ocorrem veios que também apontam para a atuação de um campo de esforço extensional, com componente destral associada. A análise cinemática e dinâmica dessas estruturas permitiu a interpretação de um regime tectônico distensivo de natureza transtrativa destral e, possivelmente, relacionado ao evento de rifteamento Macaúbas. Nesse cenário, o bloco de capa regional do rifte Macaúbas, representado pela sucessão esteniana do Grupo Sítio Novo, foi deformado sob a atuação de um cisalhamento antitético, com desenvolvimento de um rollover associado. No flanco frontal do rollover, as camadas experimentaram significativa magnitude de rotação, revelando elevado mergulho próximo à borda de falha e favorecendo o desenvolvimento do deslizamento interestratal. In the northern area of Araçuaí belt, in the central Espinhaço physiographic domain, there are records of superimposed sedimentary basins installed over the São Francisco cratonic basement. In this context, the morphostructure of the Central ridge, north of Minas Gerais, is supported by a siliciclastic succession of Espinhaço Supergroup that are superimposed to the west by the diamictic base of Macaúbas Group. These groups represent two overlapping rifting events in the end of Stenian and upper Tonian respectively. On the western edge of the Central range, high obliquity striated marks, incompatible with the Brasiliano compressional tectonics affecting these rocks, are described on bedding planes of the Sítio Novo Group succession. These marks are associated with orthogonal steps and define sliding vectors indicative of normal to normal destral movement. Associated with these lineations, veins occur, suggesting an extensional stress field, with an associated destral component. The kinematic and dynamic analysis of these structures accords the interpretation of an extensional tectonic regime, presenting a destral-transtensional nature, possibly related to the Macaúbas rifting event. In this scenario, the regional hanging wall of Macaúbas rift, represented by the Stenian succession of the Sítio Novo Group, indicates deformation under the action of an antithetic shear, with development of an associated rollover. The frontal limb layers of the rollover experienced significant magnitude of rotation, revealing high angle dip on the edge of the master fault and, then, favoring the development of interestratal slip.

The history of palaeocontinents alternates long fragmentation to drift periods with relatively short agglutination intervals. One of the products of a Rhyacian-Orosirian orogeny was a palaeocontinent that brought together the basement of the Araçuaí-West Congo orogen (AWCO) with regions now located in the São Francisco and Congo cratons. From ca. 2 Ga to ca. 0.7 Ga, this large region of the São Francisco-Congo palaeocontinent was spared of orogenic events, but underwent at least five taphrogenic events recorded by anorogenic magmatism and/or sedimentation. The taphrogenic events are well documented in the AWCO proximal portions and neighboring cratonic regions, but lack evidence in the AWCO high-grade core. Our studies on amphibolites intercalated in the Rhyacian Pocrane complex, basement of the Rio Doce magmatic arc, allowed to the recognition of two Mesoproterozoic taphrogenic episodes. The oldest one, a Calymmian episode, is recorded by amphibolites with a zircon magmatic crystallization age at 1529 ± 37 Ma (U-Pb SHRIMP), and lithochemical signature of basaltic magmatism related to continental intraplate settings. Another set of amphibolite bodies records the youngest taphrogenic episode, a Stenian event, with a zircon magmatic crystallization age at 1096 ± 20 Ma (U-Pb SHRIMP), and lithochemical signature similar to mature magmatism of continental rift setting. The Calymmian episode (ca. 1.5 Ga) correlates to the Espinhaço II basin stage and mafic dikes of the northern Espinhaço, Chapada Diamantina and Curaçá domains, while the Stenian episode (ca. 1.1 Ga) correlates to the Espinhaço III basin stage. We also present U-Pb data for 87 detrital zircon grains from a quartzite lens intercalated in the Pocrane complex, the Córrego Ubá quartzite. Its age spectrum shows main peaks at 1176 ± 21 Ma (35%), 1371 ± 30 Ma (18%), 1536 ± 22 Ma (19%), 1803 ± 36 Ma (17%) and 1977 ± 38 Ma (12%), suggesting a Stenian (ca. 1176 Ma) maximum depositional age (although only one zircon with low discordance shows an age of 955 ± 66 Ma). Comparing with data from the western sector of the Araçuaí orogen and São Francisco craton, it is noteworthy that no igneous zircon from the three samples yielded an age older than early Orosirian (~2.05 Ga), showing age spectra essentially limited in the range of ca. 1-2 Ga; i.e., younger than the Late Rhyacian orogeny that amalgamated the basement, and older than the main anorogenic event (930-870 Ma) associated with the Early Tonian precursor basin of AWCO. All together, these continental taphrogenic events testify the several unsuccessful fragmentation attempts that affected the long-lived São Francisco-Congo palaeocontinent, which remained preserved from a complete break-up associated with ocean spreading from the Early Orosirian to the Atlantic opening in Cretaceous time.

Facies analysis, aided by X-ray diffraction, QemScan analysis, U-Pb detrital ages and field geological data are used in a detailed sedimentary characterization of the Arkose Level, an immature sedimentary unit that occurs abruptly and discontinuously in the upper Paranoa Group, a sequence of mature marine rhythmites deposited in a shallow cratonic margin basin. This basin was developed during the Mesoproterozoic in the western margin of the Sao Francisco Craton, central Brazil. The study reveals three facies associations in the Arkose Level: (1) Facies Association I (C), (2) Facies Association II (MC) and (3) Facies Association III (FM). The lithofacies are characterized by plane-parallel lamination and planar cross-bedding, trough cross-stratification, channel-fills, overturned cross-stratification, and convoluted structures. The sedimentological and paleocurrent data acquired in this study leads to the interpretation that this unit represents a record of braided-river deposit, which was influenced by marine reworking in the uppermost portion. The depositional model comprises a transitional continental-marine environment, with channels in the continental domain interpreted as a high-energy braided river system around the margins of a shallow intracratonic basin during the Mesoproterozoic. Compiled and newly acquired LA-ICP-MS detrital zircon U-Pb ages reveal a new source area contribution of 1.1 Ga in the Upper portion of the Paranoa Group. The abrupt deposition of braided-river deposits amid the mature Paranoa basin is most probably associated with local faulting, responsible for exposing the crystalline basement and the sedimentary rocks of previous basins, providing new and near-source areas of crystalline basement rocks. The inferred faulting can be associated to a Stenian unsuccessful rifting event, or to the early stages of opening the Goias-Pharusian ocean, in the Tonian.

The basement of the Pelagonian zone of the Hellenides, in the Eastern Mediterranean realm, has been shaped by mid-Neoproterozoic (700 Ma) and Variscan (300 Ma) igneous activities. In the present study, detrital zircon U–Pb geochronology and Lu–Hf isotope geochemistry of ca. 700 Ma-aged granites and of pre-700 Ma metasediments from the Pelagonian zone allow a genuine perspective into the provenance and origin of this terrane which hosts one of the oldest sedimentary sequences known in SE Europe. Pelagonian crustal vestiges comprising 700 Ma granitoids and their hosting metasediments are termed here “Proto-Pelagonian”. Except from several concordant Tonian-aged detrital zircon grains (as young as 980 Ma), which set the Early Tonian as a maximum sedimentation age, a preponderance of the detrital zircon grains separated from four Proto-Pelagonian metasedimentary samples yielded Mesoproterozoic–Paleoproterozoic ages peaking at 1.5 Ga. Neoproterozoic-aged detrital zircon grains are generally absent. The detrital zircon isotopic data is thus consistent with an Amazonian source for this sequence. In terms of their detrital zircon age spectra, Proto-Pelagonian metasediments exhibit close similarity to pre-Avalonian metasedimentary sequences (e.g. Gamble Brook Formation) which underlie Late Neoproterozoic "typical Avalonian" successions in Atlantic Canada. The detrital zircon age signal obtained from the pre-700 Ma metasediments is however markedly different from that previously obtained from African-derived terranes which are imbricated with the Pelagonian zone in the Eastern Mediterranean region and which are usually devoid of Mesoproterozoic detrital zircon grains (other than Stenian). Likewise, the Proto-Pelagonian basement also differs from Avalonian-type terranes previously identified in the Eastern Mediterranean–SE European region (Istanbul block of the Pontides, Pirgadikia terrane of the Internal Hellinides, North and Central Dobrogea and Danubian basement), which alongside abundant Mesoproterozoic zircon grains contain also Neoproterozoic-aged detrital zircons. Thus, from the point of view of the pre-Variscan geological history, the Pelagonian zone is exotic with respect to surrounding terranes of both, North African and Avalonian origins.

New U–Pb in situ zircon dating provides a new approach for the study of the Espinhaco Supergroup units exposed in the Sao Francisco Craton and Aracuai Orogen. Located in Southern Espinhaco, Minas Gerais, the following two basins were formed in intraplate conditions: (i) the Lower Espinhaco Basin is marked by a volcano-sedimentary sequence with alluvial, fluvial and eolian deposits that were formed from 1.68 Ga to 1.80 Ga; (ii) the overlying sequence, called the Upper Espinhaco Basin, is a rift-sag basin that presents basal diamond-bearing continental deposits (the Sopa–Brumadinho Formation) with a younger zircon peak at 1192 Ma, which is the maximum age for deposition of the upper units. The obtained U–Pb detrital zircon data of the studied units show age groupings related to the orogenic cycles of Jequie (Neoarchean) and Transamazonian (Paleoproterozoic), which are associated with the stability period from 1.8 Ga to 0.91 Ga in the Sao Franscico Craton, and record deposition during at least the three basinal cycles. The Stenian–Tonian ages of the Upper Espinhaco Basin units (906 Ma to 1192 Ma) suggest a direct link with the evolution of the Rodinia Supercontinent and represent a marker for Mesoproterozoic to Early Neoproterozoic evolution in the Sao Franscico Craton and adjacent areas.

In the structure of west Kyrgyz Ridge (North Tien Shan), a great role is played by complexly dis� located Upper Precambrian-Cambrian terrigenouscarbona te and shale strata, as well as by granitoids that comprise several coupled WNWstriking synforms and anti forms, the largest of which is the Makbal antiform. Southeast of the core of this antiform, granitoids comprise the large Kara Dzhilga massif and several massifs that are of lesser size and have tectonic correlations with the hosting terrigenouscarbonate strata. In the Kara Dzhilga massif, the rocks of three penetration phases are distinguished; contacts between rocks are often of tectonic character. The early phase is presented by monzonite and monzodiorite; the main one, by largepor� phyric biotitic granites; and the additional one, by aplitic granites and pegmatites. By the chemical compo� sition, granites of Kara Dzhilga massif of the main phase correspond to subalkaline granites of highpotas� sium calcalkali series. The age of their crysta llization (zirconbased U-Pb method) is 1131 ± 4 Ma (Ste� nian). The formation of Stenian granitoids in the North Tien Shan may be related to development of Grenville fold belts, whose fragments were identified in the units of the Central Asian Belt. Tectonic correla� tions between these granitoids and hosting terrigenouscarbonate strata appeared as a result of immersion to significant depths and subsequent exhumation into the upper crustal horizons in the Early Ordovician.

A biostratigraphic model of the temporal distribution of distinctive Proterozoic microfossil assemblages is suggested, based on studies of upper Precambrian chert-embedded and compression-preserved organic-walled microfossils from the reference sections of Eurasia, North America and Australia. Microfossils from 2.0 to 0.542 Ga can be divided into seven successive informal global units which can be compared to standard units of the International and Russian time scales. Each unit is characterized by a particular association of taxa, typified by the fossil assemblage that gives it its name. These form broad biostratigraphic units comparable to assemblage zones of Phanerozoic successions; in general (but with minor differences) they correspond to chronostratigraphic units accepted by the Internal Commission on Stratigraphy. The units are: (1) Labradorian, the upper part of the Paleoproterozoic (Orosirian and Statherian), 2.0–1.65 Ga; (2) Anabarian, lower Mesoproterozoic (Calymmian–Ectasian)/Lower Riphean–lower Middle Riphean, 1.65–1.2 Ga; (3) Turukhanian, upper Mesoproterozoic (Stenian)/upper Middle Riphean, 1.2–1.03 Ga; (4) Uchuromayan, lower Neoproterozoic (late Stenian–Tonian)/lower Upper Riphean, 1.03–0.85 Ga; (5) Yuzhnouralian, upper Neoproterozoic (Cryogenian)/upper Upper Riphean, 0.85–0.63 Ga; (6) Amadeusian, lower Ediacaran/lower Vendian, 0.63–0.55 Ga; (7) Belomorian, upper Ediacaran/upper Vendian, 0.55–0.542 Ga.

The large (more than 200000 km 2 ) Uchur-Maya Meso- and Neoproterozoic intracontinental basin is delineated for the first time in the southeastern Siberian Platform, including the territory overlapped by the Ediacaran to Cambrian plate complex. The tectonic elements of higher orders—uplifts, domes, and deeps formed during the Neoproterozoic and Late Mesozoic tectonomagmatic activity—are outlined. The tectonic nappes of Paleoproterozoic rocks from 200 to 400 m thick were established between the Calymmian and Ecta- sian to Stenian rocks in the southeastern portion of the basin. The thickness of sedimentary rocks increases toward the Yudoma-Maya Aulacogen. The considerable thickness of Meso- and Neoproterozoic rocks and bitu- men contents in sedimentary rocks are favorable factors testifying to the petroleum resource potential of the basin. The southern part of the basin is promising for ore deposits (primarily, uranium and gold) in zones of structural and stratigraphic unconformities and within the sedimentary cover itself. This study may serve as a background for further, more detailed tectonic investigations and substantiation of strategic lines of geological exploration.

The Late Paleoproterozoic–Neoproterozoic (1800–541 Ma) sedimentation, volcanism and igneous events, and rifting in the North China Craton can be categorized into different stages: (1) Stage 1 (1800–1730 Ma, Early Statherian): It is represented by the Taihang (1780–1770 Ma) and Miyun (~1730 Ma) dyke swarms, the Xiong’er volcanic province (~1780 Ma), and a little clastic sedimentation related to the evolution of the Xiong’er rift. (2) Stage 2 (1730–1600 Ma, Late Statherian): It is represented by the Damiao–Shachang anorthosite–rapakivi granite–dyke complexes (1710–1680 Ma), the Laiwu (~1680 Ma) and Taishan (~1620 Ma) dyke swarms, the Dahongyu lavas (~1620 Ma), and some clastic rocks and a little limestone related to the Yan-Liao rift, the Xiong’er rift, and probably the Bayan Obo rift. (3) Stage 3 (1600–1400 Ma, Calymmian/Jixian): It is represented by the dolomite-dominated strata in the Yan-Liao rift, the Xiong’er rift, and probably the Bayan Obo rift, with little volcanism and magmatism. (4) Stage 4 (1400–1200 Ma, Ectasian): It is represented by the ~1320 Ma dykes–sills–granites and ~1230 Ma Licheng dyke swarm, and the sedimentation dominated by clastic rocks with a little marlstone and limestone possibly limited in the Yan-Liao rift. (5) Stage 5 (1200–1000 Ma, Stenian): It is unclear whether there were any magmatism and deposition during this period. (6) Stage 6 (1000–800 Ma, Tonian): It is represented by the Dashigou (~925 Ma) and Qianlishan (~810 Ma) dyke swarms, the Sariwon (Dalian–Chulan–Zenghekou) sills (925–890 Ma), and clastic rocks/carbonate-dominated sediments within the Xuhuai rift. (7) Stage 7 (800–541 Ma, Cryogenian–Ediacaran): It is uncertain yet if there were any igneous events or sedimentation during this period, although some strata in Henan province are candidates. Multiple stages of rifting indicate a prolonged and stepwise rifting lasting for 1000 Ma, with the center of the rifts shifted from the south (the Xiong’er rift, 1780–1730 Ma) to the north (the Yan-Liao rift, 1730–1200 Ma) and to the southeast (the Xuhuai rift, 1000–800 Ma) of the North China Craton.

The Mesoproterozoic Conselheiro Mata Group is the uppermost sequence of the Proterozoic intracontinental Espinhaço basin that developed on the Congo-São Francisco Paleoplate. This sequence is represented by amarine shallow-water platform that experienced a sag phase followed by a rift phase in the Upper Espinhaço.We used combined sedimentological-stratigraphic descriptions of sections, whole-rock (WR) geochemistry and U-Pb detrital zircon dating to develop a regional paleogeographic evolution model of the sag phase. The succession corresponds to transgressive-regressive cycles in the following ascending order: 1) offshore to lower shoreface facies represented by quiescent periods and episodic sediment supply (Santa Rita Formation); 2) upper shoreface to foreshore and coastal desert facies with a reworking of the underlying units (Córrego dos Borges Formation); 3) lower shoreface with fallout of suspended fine sediments and a combination of unidirectional and oscillatory flows generated by storm waves (Córrego da Bandeira Formation); 4) tidal-influenced upper shoreface to foreshore facies with the migration of subaqueous dunes, wave swash in a beach environment and cycles of neap-spring tides (Córrego Pereira Formation); and 5) the resumption of lower-shoreface sedimentation and the subsequent development of a stromatolitic carbonate-siliciclastic platform (Rio Pardo Grande Formation). The geochemical data indicate that the studied units contain input from felsic rocks and sedimentary rocks. The basal marine to eolian sediments of the Galho do Miguel Formation are dominated by Rhyacian sources (2.1 Ga). The basal and intermediate units of the Conselheiro Group contain Archean, Rhyacian, Statherian and Calymmian-Ectasian (1.6–1.33 Ga) zircon grains, whereas Orosirian (1.9–2.0 Ga) sources dominate in the upper strata of the group. The study of this Stenian (Mesoproterozoic) intracratonic sequence provides clues to understanding the history of sedimentation and the potential source areas on the São Francisco Craton and adjacent areas, which are very useful for comparison to Phanerozoic intracratonic basins and the reconstruction of Paleoproterozoic and Mesoproterozoic supercontinents.

QUANTOS EVENTOS DE RIFTEAMENTO PRECEDERAM O DESENVOLVIMENTO DO ORÓGENO ARAÇUAÍ-CONGO OCIDENTAL? A edificação do Orógeno Araçuaí-Congo Ocidental teve início por volta de 630 Ma, como indicam as idades U-Pb mais antigas até agora obtidas de rochas do seu arco magmático. Esta orogenia foi precedida de, pelo menos, seis eventos de rifteamento e/ou magmatismo anorogênico que afetaram a região ocupada pelo Orógeno Araçuaí-Congo Ocidental, bem como o domínio cratônico São Francisco-Congo a ele adjacente. São eles os eventos E1 (Estateriano, 1,77-1,7 Ga), E2 (Calimiano, 1,57-1,5 Ga), E3 (Esteniano, 1,18 - ? Ga), E4 (no limite Esteaniano-Toniano, ca. 1 Ga), E5 (Toniano, 930-850 Ma) e E6 (Criogeniano, 750-670 Ma). O evento E1, chamado de Tafrogênese Estateriana, teve lugar entre 1,77 e 1,70 Ga e tem como registros mais importantes a deposição rifte das unidades sedimentares e vulcânicas da base do Supergrupo Espinhaço, bem como o alojamento dos plutons anorogênicos das suítes Borrachudos e Lagoa Real. O evento E1 é sucedido por uma nova fase de distensão durante o período Calimiano, em torno de 1,57 Ga, que é representada no Espinhaço Setentrional e Chapada Diamantina por rochas sedimentares e vulcânicas da porção média do Supergrupo Espinhaço. Manifestações do evento E3 (Esteniano) tiveram início em torno de 1,18 Ga com a deposição da Formação Sopa-Brumadinho (Supergrupo Espinhaço), exposta na Faixa Araçuaí. Os três primeiros eventos (E1, E2 e E3) parecem não ter ocorrido na Faixa Congo Ocidental. Nesta faixa, os granitos Noqui (999 ± 7 Ma) e rochas vulcânicas associadas representam um magmatismo anorogênico do limite Esteniano-Toniano, registrando um evento provavelmente local (E4), mas que pode ser correlacionável aos diques máficos de idade similar que ocorrem no sul da Bahia, no extremo oriental do Cráton São Francisco. As espessas sucessões de rochas vulcânicas bimodais dos grupos Zadiniano e Mayumbiano (930-910 Ma) constituem os principais registros do evento E5 na Faixa Congo-Ocidental. O magmatismo anorogênico representado pela Suíte Salto da Divisa e enxames de diques máficos tonianos (e.g., Pedro Lessa e Espinhaço Setentrional), assim como, muito provavelmente, os depósitos pré-glaciais da bacia Macaúbas são manifestações de E5, em terrenos do Orógeno Araçuaí e Cráton do São Francisco. O evento criogeniano, E6, é evidenciado pela Província Alcalina do Sul da Bahia entre 735 e 675 Ma, e, muito provavelmente, pelas formações diamictíticas do Grupo Macaúbas e unidades correlativas na Faixa Congo Ocidental, e pelo vulcanismo félsico La Louila (≤ 713 Ma) do sudoeste do Gabão. O evento E6 evoluiu para espalhamento oceânico no setor centro-sul da Bacia Macaúbas, mas este processo não afetou a parte norte desta bacia e, por isto, deixou íntegra a ligação continental (a ponte Bahia-Gabão) entre a Península São Francisco e o Continente Congo. De fato, nenhum dos eventos distensionais mencionados logrou levar à ruptura a placa São Francisco-Congo que, aglutinada na transição Riaciano-Orosiriano (ca. 2,05 Ga), permaneceu íntegra até o Cretáceo Inferior quando, então, o rifte Atlântico finalmente conseguiu desmembrá-la.Palavras-chave: rifte, magmatismo anorogênico, Orógeno Araçuaí-Congo Ocidental, Cráton São Francisco-Congo ABSTRACT: The development of the Araçuaí-West Congo orogen (AWCO) started around 630 Ma, as suggested by U-Pb ages from the oldest rocks yet found in its pre-collisional magmatic arc. This orogeny was preceded by at least six events of rifting and/or anorogenic magmatism, which affected the area occupied by the AWCO and the adjacent São Francisco-Congo craton, namely: the Statherian E1 (1.77-1.7 Ga), Calymmian E2 (1.57-1.5 Ga), Early Stenian E3 (1.18 - ? Ga), Stenian-Tonian E4 (ca. 1 Ga), Tonian E5 (930-850 Ma) and Cryogenian E6 (750-670 Ga) events. The E1 event, currently referred to as the Statherian taphrogenesis, took place between ca. 1.77 Ga and 1.7 Ga. It is recorded by the rift-related sedimentary and volcanic rocks of the basal section of the Espinhaço Supergroup, as well as the anorogenic plutons of the Borrachudos and Lagoa Real suites. The E1 event was followed by a Calymmian episode, the E2 (ca. 1.57 Ga), recorded in the northern Espinhaço range and Chapada Diamantina by sediments and volcanics of the middle portion of the Espinhaço Supergroup. The manifestations of the Stenian E3 event started around 1.18 Ga with the syn-rift deposition of the Sopa-Brumadinho Formation (Espinhaço Supergroup), exposed in the Araçuaí belt. The first three events (E1, E2 and E3) are so far not found in the West Congo belt. In this belt, a magmatism took place at the Stenian-Tonian time boundary, the anorogenic Noqui granites (ca. 999 ± 7 Ma) and related volcanic rocks, recording a probably local extensional event, E4, which can be correlated to mafic dykes of similar age found in southern Bahia (eastern tip of the São Francisco craton). The thick bimodal volcanic pile of the Zadinian and Mayumbian groups and related intrusions are the main records of the Tonian E5 event in the West Congo belt. The A-type Salto da Divisa Suite and Tonian mafic dykes (e.g., Pedro Lessa and Northern Espinhaço range), as well as the deposition of the pre-glacial formations of the Macaúbas basin are manifestations of the E5 event in the Araçuaí orogen and São Francisco craton. Records of the Cryogenian E6 event include the Southern Bahia alkaline province (ca. 735-675 Ma) and, probably, the La Louila felsic volcanism in SW Gabon (≤ 713 Ma), as well as the deposition of the diamictitic formations of the Macaúbas Group and correlatives. The E6 event evolved to oceanic spreading in the central-southern Macaúbas basin, but this process died out toward north keeping unbroken the continental link between the São Francisco peninsula and Congo continent (the Bahia-Gabon bridge). In fact, all those extensional events were unsuccessful in splitting the São Francisco-Congo plate, which amalgamated in the Rhyacian-Orosirian time boundary (ca. 2.05 Ma) and remained as such until the Lower Cretaceous, as the Atlantic rifting then successfully broke through the old continental mass.Keywords: rift, anorogenic magmatism, Araçuaí-West Congo orogen, São Francisco-Congo craton

New U–Pb in situ zircon dating provides a new approach for the study of the Espinhaço Supergroup units exposed in the São Francisco Craton and Araçuaí Orogen. Located in Southern Espinhaço, Minas Gerais, the following two basins were formed in intraplate conditions: (i) the Lower Espinhaço Basin is marked by a volcano-sedimentary sequence with alluvial, fluvial and eolian deposits that were formed from 1.68 Ga to 1.80 Ga; (ii) the overlying sequence, called the Upper Espinhaço Basin, is a rift-sag basin that presents basal diamond-bearing continental deposits (the Sopa–Brumadinho Formation) with a younger zircon peak at 1192 Ma, which is the maximum age for deposition of the upper units. The obtained U–Pb detrital zircon data of the studied units show age groupings related to the orogenic cycles of Jequié (Neoarchean) and Transamazonian (Paleoproterozoic), which are associated with the stability period from 1.8 Ga to 0.91 Ga in the São Franscico Craton, and record deposition during at least the three basinal cycles. The Stenian–Tonian ages of the Upper Espinhaço Basin units (906 Ma to 1192 Ma) suggest a direct link with the evolution of the Rodinia Supercontinent and represent a marker for Mesoproterozoic to Early Neoproterozoic evolution in the São Franscico Craton and adjacent areas.

Mesoproterozoic (~ 1050 Ma; Stenian) zircon crystals from the Saranac Prospect, Bancroft, Ontario, contain up to ~ 1 wt.% U and ~ 0.15 wt.% Th and, correspondingly, they are for the most part extensively radiation-damaged (calculated total α-doses 2.3−35.3 × 1018/g). The crystals show textures of complex, intense chemical alteration that is attributed to multiple, low-T replacement events along fluid-controlled reaction fronts. Centers of crystals appear totally replaced; the primary zoning is virtually erased and the material has high porosity and numerous inclusions. Interior regions surrounding the central reworked areas still exhibit primary igneous-type zoning; in those regions the alteration emanates from fractures and then follows the more radiation-damaged growth zones. Altered areas are typically recognized by their high porosity, low BSE intensity, and deficient analytical totals. Those regions often have lost a significant fraction of their radiogenic Pb. They are in general somewhat depleted in Zr, Si, and U, and are notably enriched in Ca and Fe. Element maps reveal elevated concentrations of Al and Y within filled fractures. Our observations indicate that the fluid-driven ion exchange is mainly controlled by the accessibility of micro-areas with elevated levels of radiation damage to transporting fluids via “fast pathways”. Most importantly, there is apparent Zr−Si−U equilibrium between initially existing and newly formed zircon. The retention of U after the chemical replacement (94 ± 14% relative to the original U content in the respective zones) does not significantly fall below the retention of two major cations Zr (95 ± 4%) and Si (95 ± 2%). In spite of the partially extreme hydrothermal alteration overprinting, the original U zoning in the crystals is well preserved. These observations suggest that preferential chemical leaching of U from zircon is clearly not a general feature of this mineral. This in turn seems to question the general validity of hydrothermal experiments to low-T, fluid-driven alteration of zircon in geological environments. The observed apparent immobility of U may affect the interpretation of U−Pb discordance in zircon, and the performance assessment of this mineral as potential waste form for actinides.

Five tectonic periods can be distinguished in the tectonic evolution of Chinese continent during the Meso-Neoproterozoic and Early Cambrian: (1) the Changcheng Tectonic Period (Latest Paleoproterozoic-Early Mesoproterozoic, equal to the Statherian and Calymmian periods, 1, 800–1, 400 Ma); (2) the Jixian Tectonic Period (Middle-Late Mesoproterozoic, equal to the Ectasian and Stenian periods, 1, 400–1, 000 Ma); (3) the Qingbaikou Tectonic Period (or Jinning Period as it is called in South China, equal to the global Tonian Period, 1, 000–800 Ma); (4) the Nanhua Tectonic Period (Cryogenian Period, 800–680 Ma); (5) the Sinian Tectonic Period (Latest Neoproterozoic-Early Cambrian Epoch, 680–513 Ma) (National Commission on Stratigraphy of China, 2001; International Commission on Stratigraphy, 2004).

The orthotectonic Scottish Caledonides constitute only a small fragment of the Neoproterozoic to Paleozoic margin of Laurentia, albeit one which lies at a prominent bend in that margin. Sequences exposed in the Scottish outcrop include Mesoproterozoic, Neoproterozoic and Cambro-Ordovician strata which record sedimentation, volcanism and deformation related to the latter stages of the amalgamation of Rodinia, the subsequent breakout of Laurentia, and growth of the Iapetus Ocean. Metamorphic and tectonic overprints then record the destruction of that ocean through Ordovician arc accretion and mid-to-late Silurian collision of Laurentia, Baltica and Avalonia with the final closure of Iapetus by end-Silurian time. New isotopic data and recent advances in the understanding of the late Mesoproterozoic (Stenian) to Cambro-Ordovician stratigraphical framework now better constrain the sequence and timing of events across the ‘Scottish Corner’ and invite a dynamic comparison with the current research into the East Greenland Caledonides summarised in this volume. Although many broad similarities exist, the comparisons described here reveal for the first time a number of significant contrasts in the spatial arrangement of depocentres, location of rifting, patterns and timing of magmatism, metamorphism and contractional deformation. This expanded understanding of the late Neoproterozoic evolution of these adjacent sectors of Laurentia provides an important basis for reconstructions of the subsequent lower Paleozoic Caledonian orogenic evolution of the present North Atlantic region.