Showing papers on "Gondwana published in 2003"

Development of the Arabian-Nubian Shield: perspectives on accretion and deformation in the northern East African Orogen and the assembly of Gondwana

Abstract: Abstract The Arabian-Nubian Shield froms the suture between East and West Gondwana at the northern end of the East African Orogen (EAO). The older components of the shield include Archaean and Palaeoproterozoic continental crust, and Neoproterozoic (c.870–670Ma) continental-marginal and juvenile intraoceanic magmatic-arc terranes that accumulated in an oceanic environment referred to as the Mozambique Ocean. Subduction, starting c. 870 Ma, and initial arc-arc convergence and terrane suturing at c. 780 Ma, marked the beginning of ocean-basin closure and Gondwana assembly. Terrane amalgamation continued until c. 600 Ma, resulting in the juxtaposition of East and West Gondwana across the deformed rocks of the shield, and final assembly of Gondwana was achieved by c. 550 Ma following overlapping periods of basin formation, rifting, compression, strike-slip faulting, and the creation of gneiss domes in association with extension and/or thrusting. Most post-amalgamation basin contain molasse deposits, but those in the eastern Arabian Shield and Oman have marine to glaciomarine deposits, which indicate that seaways penetrated the orogen soon after orogeny. The varied character of the post-amalgamation events militate against any simple tectonic model of final Gondwana convergence at the northern end of the EAO, and requires that models accommodate alternating periods of Late Neoproterozoic extension and shortening, uplift and depression, deposition and erosion.

The Saghand Region, Central Iran: U-Pb geochronology, petrogenesis and implications for Gondwana Tectonics

Abstract: The Saghand area of East-Central Iran exposes rocks that comprise the substratum of the Central Iranian continental terrane, as part of the larger Alpine-Himalayan orogenic system. Our new U-Pb ages and geochemical data from the magmatic, metamorphic and siliciclastic rocks of the Saghand area unravel three main episodes of orogenic activity in the latest Neoproterozoic-Early Cambrian, the Late Triassic, and the Eocene. Geologic events in the oldest episode include in chronological order, low- to medium-grade metamorphism, calc-alkaline plutonism, rhyolitic to andesitic volcanism, and widespread trondhjemite emplacement, from 547 Ma to 525 Ma. The Late Triassic event (approximately 220-213 Ma) is characterized by the emplacement of granite-tonalite plutons. The extensive, high-grade metamorphic rocks, migmatites and post-kinematic intrusions of Eocene age (47-44 Ma) occur in a distinct domain, in the western part of the Saghand area. These rocks previously were thought to represent the Precambrian basement of the Central Iranian Terrane. The terminal Neoproterozoic-Early Cambrian orogeny in central Iran was related to a broad-scale magmatic arc that developed along the Proto-Tethyan margin of the Gondwanaland supercontinent. The fragmented remains of that margin occur as displaced terranes, including the Central Iranian Terrane, now embedded within the Alpine-Himalayan orogenic system. The newly recognized Late Triassic intrusions of the Saghand area are indicative of a tectonomagmatic episode of possible collisional nature, in accord with the previously identified Early Kimmerian (Cimmerian) event in the region. The extensive Eocene metamorphic and magmatic activities correspond to the early Alpine Orogeny, which resulted from the convergence between Arabian and Eurasian plates, and the Cenozoic closure of the Tethys oceanic tract(s) by subduction.

Models of Rodinia assembly and fragmentation

Abstract: Amongst existing palaeogeographic models of the Rodinia supercontinent, or portions thereof, arguments have focused upon geological relations or palaeomagnetic results, but rarely both. A new model of Rodinia is proposed, integrating the most recent palaeomagnetic data with current stratigraphic, geochronological and tectonic constraints from around the world. This new model differs from its predecessors in five major aspects: cratonic Australia is positioned in the recently proposed AUSMEX fit against Laurentia; East Gondwanaland is divided among several blocks; the Congo-Sao Francisco and India-Rayner Cratons are positioned independently from Rodinia; Siberia is reconstructed against northern Laurentia, although in a different position than in all previous models; and Kalahari-Dronning Maud Land is connected with Western Australia. The proposed Rodinia palaeogeography is meant to serve as a working hypothesis for future refinements. There is general agreement that the Earth's continental crust may have been assembled to form the supercontinent, Rodinia, in the Late Mesoproterozoic and Early Neoproterozoic. Rodinia is thought to have been produced by collisional events of broadly Grenvillian (Late Mesoproterozoic) age, and to have been relatively long-lived (c. 1100-750Ma) (McMenamin & McMenamin 1990; Hoffman 1991). Nonetheless, there are several versions of its composition and configuration (e.g. Hoffman 1991 ; Dalziel 1997; Weil et al. 1998). Laurentia is thought to have formed the core of Rodinia because it is surrounded by passive margins formed during Late Neoproterozoic breakup of the supercontinent (Bond et at. 1984). Most Rodinia models propose that Australia, Antarctica and possibly South China (Li et al. 1999) may have been situated along Laurentia's western margin (unless otherwise stated, all geographic references are in present coordinates); Baltica and Amazonia, and the Rio de la Plata Craton may have lain along its eastern margin. The precise position of Siberia is disputed, but it is generally shown as lying along either the northern or the western margin of Laurentia. The position of the Congo and Kalahari Cratons is uncertain, with at least four reconstructions having been shown for Kalahari in the last few years (Powell et al. 2001). An alternative Neoproterozoic supercontinent, Palaeopangaea, was proposed by Piper (2000), based mainly on palaeomagnetic data. This model is similar to earlier reconstructions by the same author (Piper 1987 and refs cited therein), which were criticized by both Van der Voo & Meert (1991) and Li & Powell (1999). In addition, the recent publication about Palaeopangaea (Piper 2000) contains no references for the poles employed, making the model difficult to assess. For these reasons, it will not be discussed further in this paper. Several important results have been published recently that provide new geological, geochronological and palaeomagnetic constraints on Mesoproterozoic-Early Neoproterozoic palaeogeography. Palaeomagnetic data are necessary for quantitative constraints on Precambrian reconstructions. Unfortunately, these data are distributed very non-uniformly in time and space (Meert & Powell 2001 table 1). The majority of palaeomagnetic results for the interval during which Rodinia may have existed (c. ll00-750Ma) come from Laurentia and Baltica, and fragments of apparent polar wander paths (APWP) can be constructed for these two blocks. Data from other cratons are sparse, making it impossible to construct an APWP for each block. The palaeopositions of these blocks are based on comparisons of individual palaeopoles, hence relative palaeolongitudes are not constrained. The objective of this paper is to create a new model of the Rodinia supercontinent. Palaeomagnetism has been used to determine permissible fits for Rodinia; geological constraints, such as continuity of tectonic belts, and the presence of passive or active continental margins have been used to refine permissible fits into plausible reconstructions. There is also the global balance of Late Neoproterozoic rifted margins that needs to be accounted for in any acceptable reconstruction. Selection of reliable palaeomagnetic data is the key issue for many MesoproterozoicNeoproterozoic reconstructions (e.g. Powell et at. From YOSHIDA, M., WINDLEY, B. F. & DASGUPTA, S. (eds) 2003. Proterozoic East Gondwana: Supercontinent Assembly and Breakup. Geological Society, London, Special Publications, 206, 35-55. 0305-8719/03/$15 © The Geological Society of London. 36 SERGEIA. PISAREVSKY ET AL. 1993; Torsvik et al. 1996; Smethurst et al. 1998; Weil et al. 1998; Piper 2000). In the present synthesis (Table 1), only palaeomagnetic results with Q~4 are used (Van der Voo 1990). There are fewexceptions where less reliable data is referred to and all such cases are explained individually. However, existing data are insufficient to provide robust reconstructions for all cratons except Laurentia and Baltica. In addition, there are no reliable palaeomagnetic data for Amazonia, West Africa and Rio de la Plata in the interval 11 00-700 Ma. In attempting to reconstruct Rodinia, available information from the majority of Precambrian continental blocks was used. Because very little is known about the Rodinian connections of North China, NE Africa and Arabia, Avalonia, Cadornia, Omolon, and other fragments of continental crust from the Russian Far East, northern Alaska and southeastern Table 1. Palaeomagnetic poles at 1100-700 Ma

Proterozoic East Gondwana: Supercontinent Assembly and Breakup

Abstract: This volume focuses on Late Mesoproterozoic to early Cambrian events related to Gondwana assembly and break up. The nineteen papers provide a comprehensive review including advanced knowledge and new data from all critical areas of East Gondwana. The recent knowledge of the evolution of East Gondwana, which was regarded as an integral part of the Mesoproterozoic supercontinent Rodinia, is the major theme of the volume, which is reinforced by highlighting this radical and new understanding of the evolution of this region. This volume is of use as both a text and reference book for Earth Science postgraduates, and should appeal worldwide to professional geologists with an interest in Rodinia, Gondwana and that important transition from the Proterozoic to the Phanerozoic Earth.

The biogeographic and tectonic history of India

Abstract: Aim To present an up to date account of the Mesozoic history of India and its rela-tionship to the other Gondwana continents and to Eurasia.Location Continents surrounding the Western Indian Ocean.Methods Utilization of recent evidence of continental relationships based upon researchin stratigraphy, palaeomagnetism, palaeontology, and contemporary biotas.Results The physical data revealed a sequence of events as India moved northward: (1)India–Madagascar rifted from east Africa 158–160 Ma (million years ago), (2) India–Madagascar from Antarctica c. 130 Ma, (3) India–Seychelles from Madagascar84–96 Ma, (4) India from Seychelles 65 Ma, (5) India began collision with Eurasia 55–65 Ma and (6) final suturing took place c. 42–55 Ma. However, data from fossil andcontemporary faunas indicate that, throughout the late Cretaceous, India maintainedexchanges with adjacent lands. There is an absence in the fossil record of peculiaranimals and plants that should have evolved, had India undergone an extended period ofisolation just before its contact with Eurasia.Main conclusions The depiction of India in late Cretaceous as an isolated continent is inerror. Most global palaeomaps, including the most recent one, show India, as it movesnorthward, following a track far out in the Indian Ocean. But the evidence now indicatesthat India’s journey into northern latitudes cannot have taken place under such isolatedcircumstances. Although real breaks among the lands were indicated by the physicaldata, faunal links were maintained by vagile animals that were able to surmount minormarine barriers. India, during its northward journey, remained close to Africa andMadagascar even as it began to contact Eurasia.KeywordsIndia, biogeography, Gondwana, late Cretaceous, palaeontology, tectonics.INTRODUCTIONIt has now been more than 40 years since the theory of platetectonics has found general acceptance and more than30 years since Dietz & Holden (1970) published their mapsillustrating the breakup of Pangea and the dispersal of con-tinents through time. Although many palaeomaps by variousauthors have been published since 1970, the predominantmodern series is that produced by the Palaeomap Project atthe University of Texas (Arlington). The latest edition enti-tled ‘Atlas of Earth History’ (Scotese, 2001) is a beautiful,colour rendition with artistic representations of sea floor,shorelines, and mountains.The Palaeomap Project produces a variety of educationalmaterials including a CD ROM map series with computeranimations and Palaeo-Globe kits for constructing physicalmodels of the earth at different periods of time. The Projecthas a web site advertising its products (http://www.scote-se.com) and offers special discounts to primary and secon-dary schools. On one hand, there is no doubt that thisproject performs an important educational service providingan attractive introduction to plate tectonics for a broadaudience; on the other hand, it must be asked if the maps andvirtual reality simulations are accurate representations ofcurrent scientific knowledge. The information is presented ina factual manner with no indication that some of it may notbe on firm ground.In the case of India, the Project supplies a virtual realitysequence in which that continent is shown as separatingfrom Madagascar 90 Ma, moving through the middle of the

Timing and geometry of early Gondwana breakup

Abstract: The Mesozoic opening history of the southern ocean between South America, Africa and Antarctica is one of the largest gaps in knowledge on the evolution of this region. Competing geodynamic models were published during the last two decades to explain the geophysical and geological observations. Here we report on aeromagnetic data collected along the East Antarctic coast during five seasons. These data provide new constraints on the timing and geometry of the early Gondwana break-up. In the Riiser-Larsen Sea/Mozambique Basin, the first oceanic crust between Africa and Antarctica formed around 155 Ma. In the west the Weddell Rift propagated from west to east with a velocity of 63 km/Myr between chrons M19N and M17N. At chron M14N South America and Africa finally were split off the Antarctic continent. Stretching in the area of the South Atlantic started at the latest from 155 Myr onwards. The different spreading velocities and directions of South America and Africa created at chron M9N the first oceanic crust in the South Atlantic. A new model indicates that the Karoo and Dronning Maud Land magmatism occurred well before any new ocean floor was created and, therefore, the first formation of new oceanic crust cannot directly be related to a plume interaction.

Tearing up Rodinia: the Neoproterozoic palaeogeography of South American cratonic fragments

Abstract: Rodinia was initially defined as a long-lived supercontinent that assembled all the continental fragments around Laurentia and remained stable from 1000 up to 750 Ma. Nonetheless, recent work has cast doubt on the Rodinia palaeogeography and even on the timing of its assembly and break-up. The geochronological and palaeomagnetic databases accumulated for South America and Africa in the last decade show that most of these continental fragments were not part of Rodinia. A wide Brasiliano Ocean separated most of the South American and African cratons from the Laurentia − Amazonia − Rio Apa −West Africa margin. This ocean was closed between 940 and 630 Ma along the Pampean–Paraguay–Araguaia–Pharusian mobile belts. Moreover, accretion along the South American and African platforms was a diachronous and long-lived process that involved several intra-oceanic and continental magmatic arcs and microcontinents. This evolution started at around 1000 Ma and ended at around 520 Ma with the final assembly of Gondwana.

Origin of northern Gondwana Cambrian sandstone revealed by detrital zircon SHRIMP dating

Abstract: Voluminous Paleozoic sandstone sequences were deposited in northern Africa and Arabia following an extended Neoproterozoic orogenic cycle that culminated in the assembly of Gondwana. We measured sensitive high-resolution ion microprobe (SHRIMP) U-Pb ages of detrital zircons separated from several Cambrian units in the Elat area of southern Israel in order to unravel their provenance. This sandstone forms the base of the widespread siliciclastic section now exposed on the periphery of the Arabian-Nubian shield in northeastern Africa and Arabia. Most of the detrital zircons we analyzed yielded Neoproterozoic concordant ages with a marked concentration at 0.55‐0.65 Ga. The most likely provenance of the Neoproterozoic detritus is the Arabian-Nubian shield; 0.55‐0.65 Ga was a time of posttectonic igneous activity, rift-related volcanism, and strike-slip faulting there. Of the zircons, 30% yielded pre-Neoproterozoic ages grouped at 0.9‐1.1 Ga (Kibaran), 1.65‐1.85 Ga, and 2.45‐2.7 Ga. The majority of the pre-Neoproterozoic zircons underwent Pb loss, possibly as a consequence of the Pan-African orogeny resetting their provenance. Rocks of the Saharan metacraton and the southern Afif terrane in Saudi Arabia (;1000 km south of Elat) are plausible sources of these zircons. Kibaran basement rocks are currently exposed more than 3000 km south of Elat (flanking the Mozambique belt), but the shape of the detrital zircons of that age and the presence of feldspar in the host sandstone are not fully consistent with such a long-distance transport. Reworking of Neoproteorozoic glacial detritus may explain the presence of Kibaran detrital zircons in the Cambrian of Elat, but the possibility that the Arabian-Nubian shield contains Kibaran rocks (hitherto not recognized) should also be explored.

Mesozoic-Cenozoic evolution of Australia's New Guinea margin in a west Pacific context

Abstract: The northern Australian margin includes the island of New Guinea, which records a complex structural and tectonic evolution, largely masked by Mio-Pliocene orogenesis and the Pleistocene onset of tectonic collapse. In thePalaeozoic, New Guinea contained the boundary between a Late Palaeozoic active margin in the east and a region of extension associated with Gondwana breakup along the western margin of Australia. In the Permian and Early Triassic, New Guinea was an active margin resulting in widespread Middle Triassic granite intrusions, The Mesozoic saw Triassic and Jurassic rifting followed by Cretaceous passive margin subsidence and renewed rifting in the Late Cretaceous and Paleocene. Since the Eocene, New Guinea tectonics have been driven by rapid northward movement of the Australian Plate and later sinistral oblique convergence with the Pacific Plate, resulting in Mio-Pliocene arc-continent collision. Neogene deformation along the margin, however, has been the result of direct interaction with the Philippine and Caroline Plates. Collision with the Philippine-Caroline Arc commenced in the Late Oligocene and orogenesis continues today. We suggest that the New Guinea Mobile Belt comprises a collision zone between a north-facing Cretaceous indented margin and a south-facing Palaeogene accretionary prism, subsequently cut by a Neogene strike-slip fault system with well over 1000 km sinistral displacement that has alternated between extension and compression. The change in character of the lithosphere in New Guinea, from thick and strong in the west to thin and weak north and east of the Tasman Line, was also an important influence on the style and location of Mesozoic and Cenozoic deformation.

Proterozoic history of the Borborema province (NE Brazil): Correlations with neighboring cratons and Pan-African belts and implications for the evolution of western Gondwana

Abstract: [1] Geological and geochronological correlations between Borborema province (NE Brazil) and neighboring cratons and Brasiliano/Pan-African belts indicate that the Amazonian, West African, and Sao Francisco/Congo cratons and the basement of the Araguaia, Borborema, Nigerian, and Cameroon provinces were part of the Atlantica supercontinent This continent was established at the end of the Transamazonian/Eburnean cycle (∼20 Ga) and, apart from ubiquitous taphrogenesis in the 18–17 Ga interval, remained largely unaffected for the following 1 Ga Around 1 Ga an important magmatic event in Borborema province correlates with rifting episodes and anorogenic magmatism in the Sao Francisco, Congo, and Amazonian cratons These events are interpreted as failed attempts to break up Atlantica, which at this time may have been part of the larger Rodinia supercontinent Renewed extensional conditions in Borborema province during the middle and late Neoproterozoic are attributed to far-field stresses transmitted to the interior of Atlantica by outwardly dipping subduction zones that encircled its northern (present day coordinates) portion The rarity of petrotectonic assemblages typical of subduction zone environments indicates that extension did not evolve enough to form large oceans basins and thus that the Borborema province essentially includes reworked intracontinental domains Regional deformation and metamorphism, starting at 650–640 Ma, and shear zone development, beginning at 590–595 Ma, were continuously developed through time and were synchronous throughout most of the Borborema, Araguaia, Cameroon, and Nigerian provinces Postorogenic conditions were reached 540–530 Myr ago, while active deformation was still occurring in other belts that accreted around Atlantica to form western Gondwana

Archaean–Cambrian crustal development of East Antarctica: metamorphic characteristics and tectonic implications

Abstract: The East Antarctic Shield consists of a variety of Archaean and Proterozoic-Cambrian high-grade terranes that have distinct crustal histories and were amalgamated at various times in the Precambrian-Cambrian. High-grade Pan-African tectonism at 600–500Ma is recognized from four distinct belts: the Dronning Maud Land, Lutzow-Holm Bay, Prydz Bay and Denman Glacier Belts. These high-grade belts juxtapose distinct Mesoproterozoic and Neoproterozoic crustal provinces (Maud, Rayner and Wilkes), the Rauer Terrane, and have also marginally affected Archaean cratonic remnants in the Napier Complex and southern Prince Charles Mountains. The Wilkes Province experienced its principal tectonothermal events prior to 1130Ma and was not affected by the younger events that characterize the Maud Province (1150 and 1030–990Ma), the Rayner Province (990–920Ma) and the Rauer Terrane (1030–990Ma). These differences between the isotopic/event records of the basement provinces now separated by the Pan-African belts require that the older provinces were not formerly parts of a continuous ‘Grenville’ belt as proposed in the SW US-East Antartic model. East Antarctica was not a single unified crustal block within either East Gondwana or Rodinia until the Cambrian, which is now demonstrated to be the key phase of high-grade and ultrahigh-temperature (UHT) metamorphism associated with supercontinent assembly. The high-grade Pan-African tectonism is characterized by extensive infracrustal melting, clock-wise P-T paths, rapid post-peak exhumation along isothermal decompression paths to shallow- or mid-crustal levels by 500 Ma and the generation, at least locally, of UHT conditions. A significant flux of heat from the mantle into the deep and initially overthickened crust is required to produce these observed metamorphic effects. Whilst the thermal evolution can be explained by models that invoke the removal of most of the lithospheric mantle following crustal thickening and prior to rapid extension of the remaining crust, these one-dimensional models are inconsistent with present crustal thicknesses of 25–35km in the Pan-African domains of the East Antarctic Shield.

Evidence for Neoproterozoic continental arc magmatism in the Santa Quitéria batholith of Ceará State‚ NW Borborema Province‚ NE Brazil: implications for the assembly of West Gondwana

Abstract: Recent field investigations and geochronological studies of Neoproterozoic rocks in the northwestern part of the Borborema Province, Ceara State, NE Brazil provide important clues pertaining to the nature of convergence between the Borborema Province and the West African-Sao Luis craton during the assembly of West Gondwana. U-Pb zircon data indicate that the earliest evidence of convergent magmatism along the northwest margin of the Borborema Province occurred around 777 Ma, and was followed by the development of a large continental arc batholith (Santa Quiteria batholith) between ca. 665 and 591 Ma within the central part of Ceara State. These findings, along with supporting geophysical data, suggest that convergence between the Borborema Province and the West African-Sao Luis craton involved closure of an oceanic realm with subduction polarity to the southeast beneath the northwestern part of the province. Consequently, it seems likely that the Pharusian Ocean was continuous from the Hoggar Province in West Africa into South America during the late Neoproterozoic and additional data suggests that it may have even been connected with the Goianides Ocean of the Brasilia Belt farther to the southwest.