Academic literature on the topic 'Rodinia (continent)'

One hundred years of geological research in and around Antarctica since Scott's Discovery expedition of 1901–1904 have seen the continent move from a great unknown at the margins of human knowledge to centre stage in the development of plate tectonics, continental break-up and global climate evolution. Research in Antarctica has helped make the Gondwana supercontinent a scientific fact. Discoveries offshore have provided some of the key evidence for plate tectonics and extended the evidence of global glaciation back over 30 million years. Studies of Antarctica's tectonic evolution have helped elucidate the details of continental break-up, and the continent continues to provide the best testing ground for competing scientific models. Antarctica's deep past has provided support for the “Snowball Earth” hypothesis, and for the pre-Gondwana, Rodinia supercontinent. Current research is focusing on Antarctica's subglacial lakes and basins, the possible causes of Antarctic glaciation, the evolution of its surrounding oceanic and mantle gateways, and its sub-ice geological composition and structure. None of this would have been possible without maps, and these have provided the foundation stone for Antarctic research. New mapping and scientific techniques, and new research platforms hold great promise for further major contributions from Antarctica to Earth system science in the twenty-first century.

ABSTRACTScotland has a magmatic record covering much of the period 3100–50 Ma. In this review, we pull together information on Scotland's igneous rocks into a continuous story, showing how magmatic activity has contributed to the country's structural development and assessing whether the effects of older magmatic events can be recognised in later episodes.The oldest igneous rocks are part of supracrustal sequences within the Lewisian Gneiss Complex, formed when Scotland was part of the supercontinent Kenorland. The supracrustal rocks were intruded between 3100 and 2800 Ma by granodiorites and tonalites, which were metamorphosed and deformed in a major tectonothermal event between 2700 and 2500 Ma. The break-up of Kenorland (2400–2200 Ma) was marked by the intrusion of mafic dyke swarms of tholeiitic affinity. The convergence of continental masses to form the supercontinent Columbia resulted, at ∼1900 Ma, in a series of subduction-related volcanic rocks and gabbro–anorthosite masses. Subsequent continent–continent collision formed a series of granite–pegmatite sheets at ∼1855 Ma and ∼1675 Ma and reworked much of the earlier rocks in the amphibolite facies. Columbia was breaking up by 1200 Ma, an event marked by remnants of basaltic magmatism in the NW of the country. Re-assembly of the continental fragments to form the supercontinent Rodinia resulted in the Grenville Orogeny, which in Scotland was marked by basement reworking but no confirmed magmatic activity. Early attempts to split Rodinia produced a rift-related, bimodal, mafic–felsic sequence in the Moine Supergroup of the Northern Highlands, at least some of the mafic rocks having mid-ocean ridge basalt affinities. Crustal thickening during a disputed orogenic event, the Knoydartian, may have caused regional migmatisation. The final break-up of Rodinia occurred in Scotland at ∼600 Ma, when very extensive tholeiitic magmatism characterised the later parts of the Dalradian Supergroup, while a series of granites intruded the Moine and Dalradian successions.Ordovician and Silurian times saw the closure of the Iapetus Ocean and the convergence of Laurentia, Avalonia and Baltica. The collision of a major arc system with Laurentia caused the Grampian event (480–465 Ma) of the Caledonian Orogeny, marked by ophiolite obduction, the generation of (largely) anatectic granites, volcanism in the Midland Valley and Southern Uplands, and intrusion of a major gabbro–granite suite in the NE. The late-Caledonian events (435–420 Ma) were largely post-collisional and were marked by the emplacement of alkaline igneous intrusions in the NW, calc-alkaline granitic intrusions over much of the country, widespread volcanic activity and regional dyke swarms. Laurentia, Avalonia and Baltica amalgamated to form the supercontinent Laurussia. Magmatic activity recommenced at 350 Ma, when intra-plate alkaline magmatism affected much of southern Scotland, in particular, through into Permian times. The alkaline magmatism was interrupted at ∼295 Ma by a short-lived event in which tholeiitic magmas were intruded as sills and dykes in a swarm ∼200 km wide. In the early Palaeogene, lithospheric attenuation related to proto-North Atlantic formation and the splitting of Pangaea was complemented by the arrival of the Iceland mantle plume. Huge volumes of mafic magma were emplaced as lava fields, central complexes and regional swarms, locally increasing crustal thickness by 30%

Abstract Paleoproterozoic arc and backarc assemblages accreted to the south Laurentian margin between 1800 Ma and 1600 Ma, and previously thought to be indigenous to North America, more likely represent fragments of a dismembered marginal sea developed outboard of the formerly opposing Australian-Antarctic plate. Fugitive elements of this arc-backarc system in North America share a common geological record with their left-behind Australia-Antarctic counterparts, including discrete peaks in tectonic and/or magmatic activity at 1780 Ma, 1760 Ma, 1740 Ma, 1710–1705 Ma, 1690–1670 Ma, 1650 Ma, and 1620 Ma. Subduction rollback, ocean basin closure, and the arrival of Laurentia at the Australian-Antarctic convergent margin first led to arc-continent collision at 1650–1640 Ma and then continent-continent collision by 1620 Ma as the last vestiges of the backarc basin collapsed. Collision induced obduction and transfer of the arc and more outboard parts of the Australian-Antarctic backarc basin onto the Laurentian margin, where they remained following later breakup of the Neoproterozoic Rodinia supercontinent. North American felsic rocks generally yield Nd depleted mantle model ages consistent with arc and backarc assemblages built on early Paleoproterozoic Australian crust as opposed to older Archean basement making up the now underlying Wyoming and Superior cratons.

Abstract During the Grenvillian assembly of Rodinia, the Namaqua-Natal Metamorphic Province (NNMP) was formed as a result of the convergence of the Laurentia and Kalahari cratons. A detailed model for this accretion along the south-eastern margin of the Kalahari Craton has been established, but the tectonic history of the NNMP along the western margin of the Kalahari Craton has remained highly controversial. U-Pb SHRIMP zircon age dating of gneiss in the Kakamas Domain of the NNMP, as well as U-Pb SHRIMP age dating of detrital zircons and 40Ar/39Ar dating of metamorphic muscovite from sediments overlying the gneiss, confirms the presence of at least two separate events during the Namaqua-Natal Orogeny at ~1 166 Ma and 1 116 Ma. These events occurred after the Areachap Terrane was accreted onto the western margin of the Proto-Kalahari Craton during the Kheis Orogeny. 40Ar/39Ar ages derived from metamorphic muscovite formed in the metasediments of the Kheis terrane does not provide evidence for the timing of the Kheis Orogeny but suggests that it most likely only occurred after ~1 300 Ma and not at 1 800 Ma as commonly accepted. A U-Pb concordia age of ~1 166 Ma was derived from granitic gneiss in the Kakamas Domain of the Bushmanland Subprovince, possibly reflecting subduction and the initiation of continent-continent collision between the Proto-Kalahari Craton and the Bushmanland Subprovince. This granitic gneiss is nonconformably overlain by the metasediments of the Korannaland Group that contains metamorphic muscovite with 40Ar/39Ar ages of ~1 116 Ma. This age suggest that complete closure of the ocean between the Proto-Kalahari Craton and Bushmanland Subprovince probably occurred about 50 Ma after the intrusion of the ~1 166 Ma granitic gneisses.

AbstractWe present updated U–Pb ages and Hf isotopic compositions of detrital zircons and whole-rock geochemical data to investigate the provenance and tectonic setting of late Neoproterozoic and early Cambrian sandstones from the Cathaysia Block, in order to offer new constraints on its tectonic evolution and its palaeo-position within the supercontinent. The source rocks for the studied sandstones were dominated by felsic–intermediate materials with moderate weathering history. U–Pb dating results show major populations atc. 2500 Ma, 1000–900 Ma and 870–716 Ma with subordinate peaks at 655–532 Ma, consistent with the global Neoarchean continental crust growth, assembly and break-up of Rodinia, and Pan-African Event associated with the formation of Gondwana. Zircon U–Pb ages and Hf isotopic data suggest that most derived from exotic terranes once connected to the Cathaysia Block. Using whole-rock geochemical analysis, it was determined that the studied sedimentary rocks were deposited in a passive continental margin and the Cathaysia and Yangtze blocks were part of the same continent; no Cambrian ocean existed between them. Compiling a detrital zircon dataset from Qiangtang, northern India, the Lhasa Terrane and Western Australia, the Cathaysia Block seems to be more similar to the Qiangtang and western part of the northern India margin, instead of having a direct connection with the Lhasa Terrane and Western Australia in the Gondwana reconstruction during the late Neoproterozoic and Cambrian eons.

Precambrian basement rocks exposed within tectonic windows in the North American Cordillera help to define the Precambrian crustal structure of western North America and possible reconstructions of the Late Proterozoic supercontinent Rodinia. New geologic mapping and U-Pb dating in the infrastructure of the Priest River metamorphic complex, northern Idaho, documents the first Archean basement (2651 ± 20 Ma) north of the Snake River Plain in the North American Cordillera. The Archean rocks are exposed in the core of an antiform and mantled by a metaquartzite that may represent the nonconformity between basement and the overlying Hauser Lake gneiss, which is correlated with the Prichard Formation of the Belt Supergroup. A structurally higher sheet of augen gneiss interleaved with the Hauser Lake gneiss yields a U-Pb zircon crystallization age somewhat greater than 1577 Ma. The slivers of augen gneiss were tectonically interleaved with the surrounding Hauser Lake gneiss near the base of the Spokane dome mylonite zone, which arches across this part of the Priest River complex. We conclude that the Spokane dome mylonite zone lies above the Archean basement-cover contact and that it was, in part, equivalent to the basal décollement of the Rocky Mountain fold and thrust belt. New U-Pb dates on metamorphic monazite and xenotime reveal peak metamorphism at ca. 72 Ma, compatible with movement along the Spokane dome mylonite zone at that time. The Archean basement could be interpreted as the western extension of the Hearne province, or a new Archean basement terrane separated from the Hearne province by an Early Proterozoic suture. The unique assemblage of 2.65 Ga basement, ~1.58 Ga felsic intrusive rocks, and the Middle Proterozoic Belt Supergroup can be used as a piercing point for the identification of the conjugate margin to Laurentia. Our new dating supports previous correlations of Australia's Gawler craton (2.55-2.65 Ga) and its 1590 Ma plutons with the Priest River complex basement gneisses. The Priest River complex basement may be a piece of eastern Australia stranded during rifting of the supercontinent Rodina in the Late Proterozoic.

AbstractNeoproterozoic–Cambrian rocks of the Windermere Supergroup and overlying units record the breakup of Rodinia and formation of the northwestern Laurentian ancestral continental margin. Understanding the nature and timing of this transition has been hampered by difficulty correlating poorly dated sedimentary successions from contrasting depositional settings across Mesozoic structures. Here we present new litho- and chemo-stratigraphic data from a Cryogenian–lower Cambrian succession in east-central Yukon (Canada), establish correlations between proximal and distal parts of the upper Windermere Supergroup and related strata in the northern Canadian Cordillera, and consider implications for the formation of the northwestern Laurentian margin. The newly defined Nadaleen Formation hosts the first appearance of Ediacaran macrofossils, while the overlying Gametrail Formation features a large negative carbon isotope anomaly with δ13Ccarb values as low as –13‰ that correlates with the globally developed Shuram-Wonoka anomaly. We also define the Rackla Group, which includes the youngest (Ediacaran) portions of the Windermere Supergroup in the northern Cordillera. The top of the Windermere Supergroup is marked by an unconformity above the Risky Formation that passes into a correlative conformity in the Nadaleen River area. This surface has been interpreted to mark the top of the rift-related succession, but we draw attention to evidence for tectonic instability through the early-middle Cambrian and argue that the transition from rifting to post-rift thermal subsidence is marked by a widespread unconformity that underlies upper Cambrian carbonate rocks. This is younger than the interpreted age of the rift to post-rift transition elsewhere along the ancestral western Laurentian continental margin.

Abstract On the last page of his 1937 book “Our Wandering Continents” Alex Du Toit advised the geological community to develop the field of “comparative geology”, which he defined as “the study of continental fragments”. This is precisely the theme of this paper, which outlines my research activities for the past 28 years, on the continental fragments of the Indian Ocean. In the early 1990s, my colleagues and I were working in Madagascar, and we recognized the need to appreciate the excellent geological mapping (pioneered in the 1950s by Henri Besairie) in a more modern geodynamic context, by applying new ideas and analytical techniques, to a large and understudied piece of continental crust. One result of this work was the identification of a 700 to 800 Ma belt of plutons and volcanic equivalents, about 450 km long, which we suggested might represent an Andean-type arc, produced by Neoproterozoic subduction. We wondered if similar examples of this magmatic belt might be present elsewhere, and we began working in the Seychelles, where late Precambrian granites are exposed on about 40 of the >100 islands in the archipelago. Based on our new petrological, geochemical and geochronological measurements, we built a case that these ~750 Ma rocks also represent an Andean-type arc, coeval with and equivalent to the one present in Madagascar. By using similar types of approaches, we tracked this arc even further, into the Malani Igneous Province of Rajasthan, in northwest India. Our paleomagnetic data place these three entities adjacent to each other at ~750 Ma, and were positioned at the margins, rather than in the central parts of the Rodinia supercontinent, further supporting their formation in a subduction-related continental arc. A widespread view is that in the Neoproterozoic, Rodinia began to break apart, and the more familiar Gondwana supercontinent was assembled by Pan-African (~500 to 600 Ma) continental collisions, marked by the highly deformed and metamorphosed rocks of the East African Orogen. It was my mentor, Kevin Burke, who suggested that the present-day locations of Alkaline Rocks and Carbonatites (called “ARCs”) and their Deformed equivalents (called “DARCs”), might mark the outlines of two well-defined parts of the Wilson cycle. We can be confident that ARCs formed originally in intracontinental rift settings, and we postulated that DARCs represent suture zones, where vanished oceans have closed. We also found that the isotopic record of these events can be preserved in DARC minerals. In a nepheline syenite gneiss from Malawi, the U-Pb age of zircons is 730 Ma (marking the rifting of Rodinia), and that of monazites is 522 Ma (marking the collisional construction of Gondwana). A general outline of how and when Gondwana broke apart into the current configuration of continental entities, starting at about 165 Ma, has been known for some time, because this record is preserved in the magnetic properties of ocean-floor basalts, which can be precisely dated. A current topic of active research is the role that deep mantle plumes may have played in initiating, or assisting, continental fragmentation. I am part of a group of colleagues and students who are applying complementary datasets to understand how the Karoo (182 Ma), Etendeka (132 Ma), Marion (90 Ma) and Réunion (65 Ma) plumes influenced the break-up of Gondwana and the development of the Indian Ocean. Shortly after the impingement of the Karoo plume at 182 Ma, Gondwana fragmentation began as Madagascar + India + Antarctica separated from Africa, and drifted southward. Only after 90 Ma, when Madagascar was blanketed by lavas of the Marion plume, did India begin to rift, and rapidly drifted northward, assisted by the Marion and Deccan (65 Ma) plumes, eventually colliding with Asia to produce the Himalayas. It is interesting that a record of these plate kinematics is preserved in the large Permian – Eocene sedimentary basins of western Madagascar: transtensional pull-apart structures are dextral in Jurassic rocks (recording initial southward drift with respect to Africa), but change to sinistral in the Eocene, recording India’s northward drift. Our latest work has begun to reveal that small continental fragments are present in unexpected places. In the young (max. 9 Ma) plume-related, volcanic island of Mauritius, we found Precambrian zircons with ages between 660 and 3000 Ma, in beach sands and trachytic lavas. This can only mean that a fragment of ancient continent must exist beneath the young volcanoes there, and that the old zircons were picked up by ascending magmas on their way to surface eruption sites. We speculate, based on gravity inversion modelling, that continental fragments may also be present beneath the Nazareth, Saya de Malha and Chagos Banks, as well as the Maldives and Laccadives. These were once joined together in a microcontinent we called “Mauritia”, and became scattered across the Indian Ocean during Gondwana break-up, probably by mid-ocean ridge “jumps”. This work, widely reported in international news media, allows a more refined reconstruction of Gondwana, suggests that continental break-up is far more complex than previously perceived, and has important implications for regional geological correlations and exploration models. Our results, as interesting as they may be, are merely follow-ups that build upon the prescient and pioneering ideas of Alex Du Toit, whose legacy I appreciatively acknowledge.

AbstractDifferent parts of a Tonian–Early Devonian sedimentary succession, covering Proterozoic crystalline basement, occur along the erosional front to the Caledonide orogen, as outliers and coastal strips on land, and as more continuous strata in offshore areas. Rift-related Tonian–Cryogenian siliciclastic sedimentation preceded the break-up of the supercontinent Rodinia, the birth of Baltica and surrounding oceanic realms during the Ediacaran, and a marine transgression across Baltica during the Cambrian. An Ediacaran alkaline and carbonatite intrusive complex in central Sweden formed in connection with the extensional activity. Subsequently, during the Cambrian–Early Devonian, Baltica drifted northwards in the southern hemisphere to the equator, and six different lithofacies associations containing both siliciclastic and carbonate sedimentation were deposited in platformal shelf and Caledonian foreland basin settings. Bentonites in Ordovician and early Silurian successions were coupled to closure of the surrounding oceanic realms. Tectonic processes during the Caledonian orogeny around the margins to Baltica, the distance to different crustal components in this continent and climatic changes steered variations in lithofacies. Resultant fluctuations in sea-level gave rise to hiatuses and palaeo-karsts. Uranium and other metals in kerogen-rich black shales (Cambrian–Early Ordovician), hydrocarbons, stratabound Pb–Zn sulphide deposits in Cambrian (–Ediacaran?) sandstone, and limestone constitute the main resources.

Cette thèse de doctorat se focalise sur la fin du Précambrien, le Néoprotérozoïque, une période charnière dans l'histoire de la Terre, par l'étude d'unités ophiolitiques datées entre 800 et 700 Ma. Les travaux présentés ici portent sur l'étude pétrographique, géochimique et magnétique des serpentinites de ces ophiolites. Associées à des sutures panafricaines en bordure des cratons ouest africain et amazonien, ces ophiolites sont des vestiges des subductions et de la lithosphère océanique associées à la dislocation du supercontinent Rodinia. L'étude de ces ophiolites permet de proposer des contextes de formation pour ces sections de lithosphère océanique. Une autre question à l'origine de ce travail était : L'étude de la serpentinisation et de l'hydrothermalisme associé permet-elle d'apporter des contraintes sur le paléoenvironnement océanique ?<br>This Doctoral thesis focus on the end of the Precambrian, the Neoproterozoic, a pivotal period in the Earth history, by the study of ophiolitic units dated between 800 and 700 Ma. This work essentially deals with the petrography, geochemistry and magnetism of serpentinites from these ophiolites. They are associated with Panafrican orogenic belts along the West African and the Amazonian cratons and witnesses the subductions and the oceanic lithosphere associated to the break-up of the supercontinent Rodinia. The study of these neoproterozoic ophiolites allowed us to propose the formation settings for these sections of oceanic lithosphere. Another question behind this work is: Does the study of serpentinization and associated hydrothermalism allows one to provide constraints on the oceanic paleoenvironment?

The configurations of Gondwana and Pangea are well known because the histories of oceans that opened to disperse Pangea can be reconstructed from their patterns of magnetic stripes (chapters 1 and 9). The configurations of older supercontinents cannot be easily determined because the oceanic lithosphere formed when they dispersed is so old that it has been completely subducted and destroyed. Thus the histories, and even existence, of these older continents must be inferred from indirect evidence. The four most widely used techniques for reconstructing old supercontinents are: paleomagnetic data; correlation of orogenic belts that developed during accretion of the supercontinent: correlation of extensional features that developed when the supercontinent fragmented; and recognition that sediment in one present continent was derived from a source now in another continent. Paleomagnetic information can be used in two ways. One is to compare APW curves for different continental blocks to determine whether there were periods of time when two or more blocks seem to have been joined (appendix C). If similar movements are found for several continental blocks that are now separated, then we can infer that they formed a single block, perhaps a supercontinent, during the period when they had identical APW paths. Another method of using paleomagnetic data is simply to compare the apparent latitudes of numerous continental blocks. Even though longitudes cannot be specified, latitudes can be used to infer proximity of different blocks, thus supporting other information that suggests the configuration of a supercontinent. Correlation of orogenic belts starts with identification of belts of different ages in present continents. Belts of the same age are now scattered all over the earth’s land surface because of fragmentation of supercontinents and movement of modern continents to their present positions. The configurations of older supercontinents can be inferred by placing modern continents into positions in which these orogenic belts line up to form a pattern that would be expected to develop during accretion of a supercontinent. We demonstrate this technique below in our discussion of the configurations of Rodinia and Columbia.

Chapter 6 observed the tendency of contemporary rights-talk to push all other moral considerations off the table—an observation adumbrated in Chapter 5, where contemporary defences of natural rights were seen to lack awareness that the exercise of such rights might be subject to moral obligations and even contingent upon duties of virtue. Chapter 1 observed the complaint of sceptics that natural, moral rights are often not distinguished from legal ones, with the consequence that the stability and security of the latter are smuggled into natural morality or ethics. Such smuggling is part of a cultural inclination to assimilate morality to law and replace conscience with procedures, in order to abolish the possibility of a failure of conscience. It expresses an aversion to risk and denial of tragedy, whose cost is a practical, moral rigidity that ranges from the imprudent to the absurd. This chapter displays the problem as it appears in ethics, by analysing David Rodin’s War and Self-Defense. Rodin’s attempt to justify killing in terms of a fundamental (natural) moral ‘right to life’, which can only be forfeited through culpable wrongdoing, fails. As he himself inadvertently acknowledges, that right is contingent on a range of moral factors external to the right-holder. Whether it exists at all depends on the situation as a whole and can only be determined at the end of a process of moral deliberation, not posited at the beginning as fundamental. Talk about a (natural) moral right, connoting stability and security, misleads.