Assembly, configuration, and break-up history of Rodinia: A synthesis

The gradual discovery that late Neoproterozoic ice sheets extended to sea level near the equator poses a palaeoenvironmental conundrum. Was the Earth’s orbital obliquity > 60� (making the tropics colder than the poles) for 4.0 billion years following the lunar-forming impact, or did climate cool globally for some reason to the point at which runaway ice-albedo feedback created a ‘snowball’ Earth? The high-obliquity hypothesis does not account for major features of the Neoproterozoic glacial record such as the abrupt onsets and terminations of discrete glacial events, their close association with large (> 10&) negative d 13 C shifts in seawater proxies, the deposition of strange carbonate layers (‘cap carbonates’) globally during post-glacial sea-level rise, and the return of large sedimentary iron formations, after a 1.1 billion year hiatus, exclusively during glacial events. A snowball event, on the other hand, should begin and end abruptly, particularly at lower latitudes. It should last for millions of years, because outgassing must amass an intense greenhouse in order to overcome the ice albedo. A largely ice-covered ocean should become anoxic and reduced iron should be widely transported in solution and precipitated as iron formation wherever oxygenic photosynthesis occurred, or upon deglaciation. The intense greenhouse ensures a transient post-glacial regime of enhanced carbonate and silicate weathering, which should drive a flux of alkalinity that could quantitatively account for the world-wide occurrence of cap carbonates. The resulting high rates of carbonate sedimentation, coupled with the kinetic isotope effect of transferring the CO2 burden to the ocean, should drive down the d 13 C of seawater, as is observed. If cap carbonates are the ‘smoke’ of a snowball Earth, what was the ‘gun’? In proposing the original Neoproterozoic snowball Earth hypothesis, Joe Kirschvink postulated that an unusual preponderance of land masses in the middle and low latitudes, consistent with palaeomagnetic evidence, set the stage for snowball events by raising the planetary albedo. Others had pointed out that silicate weathering would most likely be enhanced if many continents were in the tropics, resulting in lower atmospheric CO2 and a colder climate. Negative d 13 C shifts of 10–20& precede glaciation in many regions, giving rise to speculation that the climate was destabilized by a growing dependency on greenhouse methane, stemming ultimately from the same unusual continental distribution. Given the existing palaeomagnetic, geochemical and geological evidence for late Neoproterozoic climatic shocks without parallel in the Phanerozoic, it seems inevitable that the history of life was impacted, perhaps profoundly so.

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The snowball Earth hypothesis: testing the limits of global change

Orogenic gold and geologic time: a global synthesis

A synopsis of events related to the assembly of eastern Gondwana

Iron formations are economically important sedimentary rocks that are most common in Precambrian sedimentary successions. Although many aspects of their origin remain unresolved, it is widely accepted that secular changes in the style of their deposition are linked to environmental and geochemical evolution of Earth. Two types of Precambrian iron formations have been recognized with respect to their depositional setting. Algoma-type iron formations are interlayered with or stratigraphically linked to submarine-emplaced volcanic rocks in greenstone belts and, in some cases, with volcanogenic massive sulfide (VMS) deposits. In contrast, larger Superior-type iron formations are developed in passive-margin sedimentary rock successions and generally lack direct relationships with volcanic rocks. The early distinction made between these two iron-formation types, although mimimized by later studies, remains a valid first approximation. Texturally, iron formations were also divided into two groups. Banded iron formation (BIF) is dominant in Archean to earliest Paleoproterozoic successions, whereas granular iron formation (GIF) is much more common in Paleoproterozoic successions. Secular changes in the style of iron-formation deposition, identified more than 20 years ago, have been linked to diverse environmental changes. Geochronologic studies emphasize the episodic nature of the deposition of giant iron formations, as they are coeval with, and genetically linked to, time periods when large igneous provinces (LIPs) were emplaced. Superior-type iron formation first appeared at ca. 2.6 Ga, when construction of large continents changed the heat flux at the core-mantle boundary. From ca. 2.6 to ca. 2.4 Ga, global mafic magmatism culminated in the deposition of giant Superior-type BIF in South Africa, Australia, Brazil, Russia, and Ukraine. The younger BIFs in this age range were deposited during the early stage of a shift from reducing to oxidizing conditions in the ocean-atmosphere system. Counterintuitively, enhanced magmatism at 2.50 to 2.45 Ga may have triggered atmospheric oxidation. After the rise of atmospheric oxygen during the GOE at ca. 2.4 Ga, GIF became abundant in the rock record, compared to the predominance of BIF prior to the Great Oxidation Event (GOE). Iron formations generally disappeared at ca. 1.85 Ga, reappearing at the end of the Neoproterozoic, again tied to periods of intense magmatic activity and also, in this case, to global glaciations, the so-called Snowball Earth events. By the Phanerozoic, marine iron deposition was restricted to local areas of closed to semiclosed basins, where volcanic and hydrothermal activity was extensive (e.g., back-arc basins), with ironstones additionally being linked to periods of intense magmatic activity and ocean anoxia.

Late Paleoproterozoic iron formations and Paleozoic ironstones were deposited at the redoxcline where biological and nonbiological oxidation occurred. In contrast, older iron formations were deposited in anoxic oceans, where ferrous iron oxidation by anoxygenic photosynthetic bacteria was likely an important process. Endogenic and exogenic factors contributed to produce the conditions necessary for deposition of iron formation. Mantle plume events that led to the formation of LIPs also enhanced spreading rates of midocean ridges and produced higher growth rates of oceanic plateaus, both processes thus having contributed to a higher hydrothermal flux to the ocean. Oceanic and atmospheric redox states determined the fate of this flux. When the hydrothermal flux overwhelmed the oceanic oxidation state, iron was transported and deposited distally from hydrothermal vents. Where the hydrothermal flux was insufficient to overwhelm the oceanic redox state, iron was deposited only proximally, generally as oxides or sulfides. Manganese, in contrast, was more mobile. We conclude that occurrences of BIF, GIF, Phanerozoic ironstones, and exhalites surrounding VMS systems record a complex interplay involving mantle heat, tectonics, and surface redox conditions throughout Earth history, in which mantle heat unidirectionally declined and the surface oxidation state mainly unidirectionally increased, accompanied by superimposed shorter term fluctuations.

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Iron Formation: The Sedimentary Product of a Complex Interplay among Mantle, Tectonic, Oceanic, and Biospheric Processes

PREFACE -- ACKNOWLEDGEMENTS -- 1 INTRODUCTION -- 1.1 Subject matter and organization -- 1.2 Investigated area and time span -- 1.3 Major structural units or geological provinces -- 1.3.1 The Amazonian craton and adjacent fold belts -- 1.3.2 The West-Afdcan craton and adjacent fold belts -- 1.3.3 The Congo or Zaire-Sao Frangisco craton and adjacent fold belts -- 1.3.4 The Kalahari craton and adjacent fold belts -- 1.3.5 The Rio de la Plata craton and adjacent fold belts -- 1.3.6 The particular case of Northeast Brazil and its African Extension -- 1.4 Geodynamic evolution of Western Gondwana -- 1.5 Location of Pan-African-Brasiliano sutures -- PART 1: THE PAN-AFRICAN-BRASILIANO CRATONS -- 2 THE BASEMENT OR INFRASTRUCTURE OF THE PAN-AFRICAN-BRASILIANO CRATONS -- 2.1 The West-African craton -- 2.1.1 The Reguibat block -- 2.1.2 The Man-Leo block and its extension in Brazil -- 2.1.3 Conclusions -- 2.2 The Amazonian or Amazon craton -- 2.2.1 The Guyana or Rio Branco block -- 2.2.2 The Guapore or Central Brazil block -- 2.2.3 Conclusions -- 2.3 The Congo (Zaire)-Sao Francisco craton -- 2.3.1 The Sao Francisco massif or craton -- 2.3.2 The Congo or Zaire block or craton -- 2.4 The Rio de la Plata craton -- 2.5 The Kalahari or South-African craton -- 3 LATE EARLY-MIDDLE PROTEROZOIC COVER AND METASEDIMENTARY SEQUENCES 3.1 The West-African craton -- 3.1.1 The Adrar of Mauritania -- 3.1.2 TheGourma -- 3.1.3 The Volta Basin -- 3.1.4 Conclusions to the study of the Pan-African cover rocks of the West-African craton -- 3.2 The Amazonian or Amazon craton -- 3.2.1 The cover rocks of the Amazonian craton north of the 13 Degrees south parallel -- 3.2.2 The southern extension of the Guapore block south of the 13 Degrees south parallel -- 3.2.3 Conclusions to the study of the late Early-Middle-Late Proterozoic sequences -- 3.3 The Congo (Zaire)-Sao Francisco craton -- 3.3.1 The Sao Francisco block or craton (Brazil) -- 3.3.2 The Congo or Zaire block or craton -- 3.3.3 Conclusions to the study of the Late-Early-Middle-Proterozoic sequences -- 3.4 The Rio de la Plata craton -- 3.5 The Western portion ofthe Kalahari craton -- PART 2: THE PAN-AFRICAN-BRASILIANO FOLD BELTS -- 4 DEFINITION, PRESENTATION -- 5 THE TRANS-S AH ARAN MEGA-OROGEN -- 5.1 Recognition of a suture -- 5.2 The slightly tectonized passive margin of the West-African craton -- 5.3 The highly tectonized passive margin and the active margin -- 5.3.1 The materials -- 5.3.2 Geodynamic evolution: Granitization and molassic deposits -- 5.4 Conclusions -- 5.5 Extension of the Trans-Saharan mega-fold belt into Brazil -- 6 THEWEST-CONGO-ARAgUAI AND RIBEIRAFOLD BELTS -- 6.1 The West-Congo-Araguai fold belt -- 6.1.1 The metasediments ofthe external units -- 6.1.2 The materials of the granitized and highly metamorphosed central zone -- 6.1.3 The structure of the Araguai-West-Congo fold belt and conclusions -- 6.2 The Ribeira-Mantiqueira fold belt -- 6.2.1 The materials -- 6.2.2 The structure -- 6.2.3 Conclusion: The geodynamic evolution -- 7 THE BRASILIA FOLD BELT: THE COLLISION BETWEEN THE CONGO-S AO FRANCISCO ANDAMAZONPLATES -- 7.1 The materials -- 7.1.1 The basement -- 7.1.2 The late Early-Middle Proterozoic metasediments -- 7.1.3 The late Middle and Late Proterozoic metasediments -- 7.2 Structure and geodynamic evolution -- 7.3 Conclusions -- 8 THE DOM FELICIANO, KAOKO (ATLANTIC DAM ARA), GARIEP AND MALMESBURY FOLDBELTS -- 8.1 TheSouthAmericanDomFelicianofoldbelt -- 8.1.1 The northern segment or Tyucas fold belt -- 8.1.2 The median segment in Rio Grande do Sul -- 8.1.3 The southern segment in Uruguay -- 8.2 The Kaoko or Atlantic branch of the Damara fold belt -- 8.3 The Gariep fold belt -- 8.4 The Malmesbury fold belt -- 8.5 Conclusions on South-Atlantic Pan-African-Brasiliano fold belts -- 9 THE DAMARA (S .L.) FOLD BELTS: THE INTERNAL AND THE ATLANTIC OR KAOKO BRANCHES -- 9.1 The filling of the internal Damara 'geosyncline' -- 9.2 Structure, metamorphism, and granitoids -- 9.3 Dynamic evolution: proposed models -- 9.4 The Kaokoveld fold belt or Atlantic branch of the Damara -- 10 THE E-W OUBANGUIDE-SERGIPE MEGA-OROGEN -- 10.1 The Sergipane(s.L) or Sergipe fold belt -- 10.1.1 The general structure -- 10.1.2 Thematerials -- 10.1.3 The geodynamic evolution -- 10.2 The Oubanguide fold belt -- 10.2.1 The general structure -- 10.2.2 Thematerials -- 10.2.3 The geodynamic evolution -- 10.3 Conclusions -- 11 THE FESTOON OF WEST-AFRICAN TRANS SOUTH-AMERICAN FOLD BELTS -- 11.1 The Pan-African Bassaride and Rokelide fold belts -- 11.2 The Araguaia and Paraguay fold belts -- 11.2.1 The Paraguay fold belt -- 11.2.2 The Araguaia fold belt -- 11.2.3 Conclusions: Geodynamic models -- 11.3 The Sierras Pampeanas fold belt in Argentina -- 11.4 Conclusions -- PART 3: AMOSAIC OF PAN-AFRICAN-BRASILIANO MEMI-CRATONS AND MINI-FOLD BELTS: NORTHEAST BRAZIL AND THE CENTRAL-WESTERN PORTION OF AFRICA -- 12 NORTHEAST BRAZIL AND ITS AFRICAN CONTINUATION: STRUCTURE AND INVOLVED MATERIALS -- 12.1 The southern lateral or frontal zone -- 12.2 The central fan -- 12.2.1 The Serido fold belt, NE Brazil: A type Brasiliano metasedimentaiy sequence? -- 12.2.2 The Ceara Group, NE Brazil -- 12.2.3 The'Schist Belts'of Western Nigeria -- 12.2.4 The central and eastern Hoggar -- 12.3 The lateral western zone -- 12.4 The Pemambuco-Patos shear band and its African extension -- 12.5 The molassic deposits -- 12.6 The granitoids -- 12.7 Conclusions -- PART 4: C ONCLUSIONS AND DISCUSSIONS -- 13 THE AMALGAMATION OF WESTERN GONDWANA(~ 600 Ma): ITS SUTURING (~ 500 Ma) WTTHEASTERNGONDWANA -- 13.1 Pre-Pan-African Brasiliano geological evolution -- 13.1.1 The example of the West-Africa, Amazon and Rio de la Plata mega-craton -- 13.1.2 The example of the Congo (Za5fre)-Sao Francisco craton -- 13.1.3 The infrastructure of some Pan-African-Brasiliano fold belts -- 13.1.4 Diversity of geodynamic evolution in Western Gondwana -- 13.2 The Pan-African-Brasiliano sedimentation -- 13.2.1 Variable ages of metasedimentaiy fills: Comparison with cratonic cover sequences -- 13.2.2 Rifting, glaciation, and ferruginous sedimentation during the late Proterozoic -- 13.3 Hie Pan-African-Brasiliano orogeny -- 13.3.1 The Trans-Saharan mega-fold belt -- 13.3.2 The set of fold belts fringing the South- Adantic Ocean -- 13.3.3 The Oubanguide-Seigipe mega-fold belt -- 13.3.4 The NE-Brazil-Central west-Africa Plate -- 13.3.5 The festoon of the West-Afncan Trans South-American fold belts -- 13.3.6 The amalgamation of West Gondwana and its collision with East Gondwana -- 13.4 Tectonic inheritance in the opening of the South Atlantic -- REFERENCES -- INDEX.

Geology of Western Gondwana (2000 - 500 Ma) : Pan-African-Brasiliano Aggregation of South America and Africa

Neoproterozoic (∼600 Ma) aggregation of Western Gondwana: a tentative scenario

The Dahomeyide orogen is located along the southeastern margin of the West African craton, and is exposed throughout eastern Ghana, Togo, Benin, Nigeria and Cameroon (Fig. 1). The West African craton has remained tectnically stable since ca. 2000 Ma (Black 1985 a, b; Camil 1984). Western sectors of the craton are characterized by an Archean domain represented by grey gneisses and migmatitic complexes (amphibolite and granulite metamorphic facies), acid to basic granulites and charnockitic complexes, together with subordinate greenstone rocks, supracrustal metasedimentary and metavolcanoclastic rocks and granites. These rocks were affected by orogenic events at ca. 3000 Ma (Leonian) and ca. 2800 Ma (Liberian). Southeasternmost segments of the Archean domain were partially remobilized at ca. 1800 Ma during Eburnean orogenesis. Western sectors of this domain were variably affected by late Proterozoic (Pan-African) orogenic events.

Roland Trompette

Papers

Geology of Western Gondwana (2000 - 500 Ma) : Pan-African-Brasiliano Aggregation of South America and Africa

Neoproterozoic (∼600 Ma) aggregation of Western Gondwana: a tentative scenario

The Dahomeyide Orogen: Tectonothermal Evolution and Relationships with the Volta Basin

Pan-African tectonic evolution and glacial events registered in Neoproterozoic to Cambrian cratonic and foreland basins of West Africa

Geological evolution of the Neoproterozoic Corumbágraben system (Brazil). Depositional context of the stratified Fe and Mn ores of the Jacadigo Group