Showing papers on "Gondwana published in 2020"

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

Abstract: 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.

Toward an integrated model of geological evolution for NE Brazil-NW Africa: The Borborema Province and its connections to the Trans-Saharan (Benino-Nigerian and Tuareg shields) and Central African orogens

Abstract: Both the Borborema Province of NE Brazil and the geological provinces of NW Africa (the Trans-Saharan Orogen consisted of the Tuareg and Benino-Nigerian shields and the Central African Orogen of Cameroon, Chad, and Central African Republic) are complex geological regions with superposition of distinct deformational, metamorphic and magmatic events and final structural configuration during the Brasiliano/Pan-African Orogeny (ca. 625-510 Ma). These provinces represent the site of major mountain building processes in the Ediacaran/Cambrian transition that culminated in the amalgamation of West Gondwana after the collision of the West African-Sao Luis, Sao Francisco-Congo, and Saharan paleocontinents. In the last years, discovery and characterization of key tectonic units such as ophiolites, eclogites, HP/UHP rocks, and both oceanic and continental magmatic arcs are helping to clarify these processes and propose tectonic models for the geological evolution of NE Brazil-NW Africa. Connections of the marginal belts that frame these provinces, bordering the eastern margin of the West African-Sao Luis Craton (Medio Coreau-Dahomeyides-Gourma-West Tuareg Shield) and the northern margin of the Sao Francisco-Congo Craton (Rio Preto-Riacho do Pontal-Sergipano-Yaounde-Central African) are progressively better constrained, while correlations within the interior, highly reworked and sectioned portions of both the Borborema Province, the Benino-Nigerian Shield, the Central and East Tuareg Shield, Western Cameroon, and Adamawa-Yade domains are more complicated and demand further investigation. Some of the questions of prime importance in this context are the continuation or not of the 1000-920 Ma Cariris Velhos Belt of NE Brazil into NW Africa, and if the basement-dominated North Borborema/Benino-Nigerian (NOBO-BENI) and Alto Pajeu-Alto Moxoto-Rio Capibaribe-Pernambuco-Alagoas/Adamawa-Yade (APAMCAPAY) domains could represent major decratonized blocks (such as LATEA in the Central Tuareg Shield), perhaps developed due to hyperextension and detachment of a Greater Sao Francisco-Congo paleocontinent northern margin. In this case, the Goias-Pharusian and Transnordestino-Central African oceanic realms along with restricted internal oceans such as the hypothetical Pianco-Alto Brigida/Western Cameroon (PAB-WECA) Seaway probably separated these ancient paleocontinental blocks during the Neoproterozoic. The development of subduction zones and the docking of Neoproterozoic juvenile terranes welded the hyperextended Archean/Paleoproterozoic lithospheric fragments together and they became squeezed and reworked in between the major cratonic landmasses during the Brasiliano/Pan-African Orogeny. The quest for the sites of ancient oceans and continents that once composed NE Brazil and NW Africa goes on and tentative scenarios will surely benefit from novel geological, isotopic, and geochronological data put forward in the near future.

The geological history and evolution of West Antarctica

Abstract: West Antarctica has formed the tectonically active margin between East Antarctica and the Pacific Ocean for almost half a billion years, where it has recorded a dynamic history of magmatism, continental growth and fragmentation. Despite the scale and importance of West Antarctica, there has not been an integrated view of the geology and tectonic evolution of the region as a whole. In this Review, we identify three broad physiographic provinces and present their overlapping and interconnected tectonic, magmatic and sedimentary history. The Weddell Sea region, which lays furthest from the subducting margin, was most impacted by the Jurassic initiation of Gondwana break-up. Marie Byrd Land and the West Antarctic rift system developed as a broad Cretaceous to Cenozoic continental rift system, reworking a former convergent margin. Finally, the Antarctic Peninsula and Thurston Island preserve an almost complete magmatic arc system. We conclude by briefly summarizing the geologic history of the West Antarctic system as a whole, how it provides insight into continental margin evolution and what key topics must be addressed by future research. Understanding the complex geologic history of West Antarctica provides insight into the formation of continental margins across Earth. In this Review, we detail the magmatism, continental growth and fragmentation of West Antarctica over the past 500 million years.

Precambrian Basement Complex of Egypt

Abstract: Surface exposure of the Egyptian Precambrian basement complex covers ca. 100 000 km2. Outcrops of the basement rocks extend over extensive areas in southern Sinai, the Eastern Desert south of latitude 29°N and the Western Desert south of latitude 24°N between the Nile valley at Aswan in the east to Gabal Uweinat, near the Egyptian-Libyan-Sudanese border, in the west. Apart from the rejuvenated Paleoproterozoic to Archean rocks of Gabal Uweinat-Gabal Kamil inlier (charnockitic, TTG and gabbro-diorite gneisses), belonging to the Saharan Metacraton, the Precambrian basement complex of Egypt, in Sinai and the Eastern Desert, belongs to the juvenile Neoproterozoic (550–900 Ma) crust of the Arabian-Nubian Shield (ANS). The Uweinat-Kamil inlier rocks have been reworked by several events at 3.1–2.55 Ga ago and 2.0 Ga ago. In the southern Western Desert, midway between Aswan and Uweinat-Kamil inliers, there exist three Precambrian inliers; Gabal-Umm-Shagir, Gabal-El-Asr and Bir Safsaf that contain Neoproterozoic Pan-African granitoids and remnants of the pre-Pan-African crust, probably representing the eastern transition between the Paleoproterozoic to Archean terranes of the Sahara Metacraton (i.e. Uweinat-Kamil inlier) and the juvenile Neoproterozoic terranes of the Arabian-Nubian Shield. The evolution of the ANS juvenile crust took place during most of the Neoproterozoic time (900–600 Ma) throughout three major stages, namely: (1) accretion stage (~870–670 Ma) including the formation of island arc volcano-sedimentary sequences and plutonic rocks and amalgamation of these accreted terrains onto east Gondwana continental block; (2) collision (~650–640 Ma) between the juvenile accreted ANS crust with the older pre-Neoproterozoic continental margin of West Gondwana (Saharan Metacraton) along arc-arc and arc–continental sutures, which prompt crustal thickening, and (3) post-collisional stage (630–550 Ma), which commenced after termination of collision, and encompassed extensional collapse of the thickened lithosphere, inducing extension and thinning of the ANS crust, which lasted until about 550 Ma. The main lithologies of the Egyptian part of the ANS include low- to medium-grade metamorphosed volcanosedimentary successions, dismembered ophiolite sequences, metagabbro–diorite complexes and calc-alkaline granitoids formed during the island arc (i.e. subduction) stage. Also, a substantial volume of undeformed late-collisional more evolved calc-alkaline granitoids were emplaced, subsequent to crustal thickening phase and preceding the onset of crustal extensional phase (630–590 Ma). A major period of mafic to felsic, high-K, Dokhan volcanics (610–580 Ma) and high-silica A-type granites and rhyolites (610–560 Ma) is associated with escape tectonics and crustal extension in the post-collisional stage.

Skeleton of a Cretaceous mammal from Madagascar reflects long-term insularity

Abstract: The fossil record of mammaliaforms (mammals and their closest relatives) of the Mesozoic era from the southern supercontinent Gondwana is far less extensive than that from its northern counterpart, Laurasia1,2. Among Mesozoic mammaliaforms, Gondwanatheria is one of the most poorly known clades, previously represented by only a single cranium and isolated jaws and teeth1–5. As a result, the anatomy, palaeobiology and phylogenetic relationships of gondwanatherians remain unclear. Here we report the discovery of an articulated and very well-preserved skeleton of a gondwanatherian of the latest age (72.1–66 million years ago) of the Cretaceous period from Madagascar that we assign to a new genus and species, Adalatherium hui. To our knowledge, the specimen is the most complete skeleton of a Gondwanan Mesozoic mammaliaform that has been found, and includes the only postcranial material and ascending ramus of the dentary known for any gondwanatherian. A phylogenetic analysis including the new taxon recovers Gondwanatheria as the sister group to Multituberculata. The skeleton, which represents one of the largest of the Gondwanan Mesozoic mammaliaforms, is particularly notable for exhibiting many unique features in combination with features that are convergent on those of therian mammals. This uniqueness is consistent with a lineage history for A. hui of isolation on Madagascar for more than 20 million years. Adalatherium hui, a newly discovered gondwanatherian mammal from Madagascar dated to near the end of the Cretaceous period, shows features consistent with a long evolutionary trajectory of isolation in an insular environment.

Isotopic systematics of zircon indicate an African affinity for the rocks of southernmost India.

Abstract: Southern India lies in an area of Gondwana where multiple blocks are juxtaposed along Moho-penetrating structures, the significance of which are not well understood. Adequate geochronological data that can be used to differentiate the various blocks are also lacking. We present a newly acquired SIMS U–Pb, Lu–Hf, O isotopic and trace element geochemical dataset from zircon and garnet from the protoliths of the Nagercoil Block at the very tip of southern India. The data indicate that the magmatic protoliths of the rocks in this block formed at c. 2040 Ma with Lu–Hf, O-isotope and trace element data consistent with formation in a magmatic arc environment. The zircon data from Nagercoil Block are isotopically and temporally distinct from those in all the other blocks in southern India, but remarkably correspond to rocks in East Africa that are exposed on the southern margin of the Tanzania–Bangweulu Block. The new data suggest that the tip of southern India has an African affinity and a major suture zone must lie along its northern margin. All of these blocks were finally brought together during the Ediacaran-Cambrian amalgamation of Gondwana where they underwent high to ultrahigh temperature metamorphism.

İzmir‐Ankara suture as a Triassic to Cretaceous plate boundary – data from central Anatolia

Abstract: The Izmir‐Ankara suture represents part of the boundary between Laurasia and Gondwana along which a wide Tethyan ocean was subducted. In northwest Turkey, it is associated with distinct oceanic subduction‐accretion complexes of Late Triassic, Jurassic and Late Cretaceous ages. The Late Triassic and Jurassic accretion complexes consist predominantly of basalt with lesser amounts of shale, limestone, chert, Permian (274 Ma zircon U‐Pb age) metagabbro and serpentinite, which have undergone greenschist facies metamorphism. Ar‐Ar muscovite ages from the phyllites range from 210 Ma down to 145 Ma with a broad southward younging. The Late Cretaceous subduction‐accretion complex, the ophiolitic melange, consists of basalt, radiolarian chert, shale and minor amounts of recrystallized limestone, serpentinite and greywacke, showing various degrees of blueschist facies metamorphism and penetrative deformation. Ar‐Ar phengite ages from two blueschist metabasites are ca. 80 Ma (Campanian). The ophiolitic melange includes large Jurassic peridotite‐gabbro bodies with plagiogranites with ca. 180 Ma U‐Pb zircon ages. Geochronological and geological data show that Permian to Cretaceous oceanic lithosphere was subducted north under the Pontides from the Late Triassic to the Late Cretaceous. This period was characterized generally by subduction‐accretion, except in the Early Cretaceous, when subduction‐erosion took place. In the Sakarya segment all the subduction accretion complexes, as well as the adjacent continental sequences, are unconformably overlain by Lower Eocene red beds. This, along with the stratigraphy of the Sakarya Zone indicate that the hard collision between the Sakarya Zone and the Anatolide‐Tauride Block took place in Paleocene.

New insights from low-temperature thermochronology into the tectonic and geomorphologic evolution of the south-eastern Brazilian highlands and passive margin

Abstract: The South Atlantic passive margin along the south-eastern Brazilian highlands exhibits a complex landscape, including a northern inselberg area and a southern elevated plateau, separated by the Doce River valley. This landscape is set on the Proterozoic to early Paleozoic rocks of the region that once was the hot core of the Aracuaf orogen, in Ediacaran to Ordovician times. Due to the break-up of Gondwana and consequently the opening of the South Atlantic during the Early Cretaceous, those rocks of the Aracuaf orogen became the basement of a portion of the South Atlantic passive margin and related southeastern Brazilian highlands. Our goal is to provide a new set of constraints on the thermo-tectonic history of this portion of the south-eastern Brazilian margin and related surface processes, and to provide a hypothesis on the geodynamic context since break-up. To this end, we combine the apatite fission track (AFT) and apatite (U-Th)/He (AHe) methods as input for inverse thermal history modelling. All our AFT and AHe central ages are Late Cretaceous to early Paleogene. The AFT ages vary between 62 Ma and 90 Ma, with mean track lengths between 12.2 mu m and 13.6 mu m. AHe ages are found to be equivalent to AFT ages within uncertainty, albeit with the former exhibiting a lesser degree of confidence. We relate this Late Cretaceous-Paleocene basement cooling to uplift with accelerated denudation at this time. Spatial variation of the denudation time can be linked to differential reactivation of the Precambrian structural network and differential erosion due to a complex interplay with the drainage system. We argue that posterior large-scale sedimentation in the offshore basins may be a result of flexural isostasy combined with an expansion of the drainage network. We put forward the combined compression of the Mid-Atlantic ridge and the Peruvian phase of the Andean orogeny, potentially augmented through the thermal weakening of the lower crust by the Trindade thermal anomaly, as a probable cause for the uplift. (C) 2019, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V.