First Precambrian palaeomagnetic data from the Mawson Craton (East Antarctica) and tectonic implications

A pilot palaeomagnetic study was conducted on the recently dated with in situ SHRIMP U-Pb method at 1134 ± 9 Ma (U-Pb, zircon and baddeleyite) Bunger Hills dykes of the Mawson Craton (East Antarctica). Of the six dykes sampled, three revealed meaningful results providing the first well-dated Mesoproterozoic palaeopole at 40.5°S, 150.1°E (A95 = 20°) for the Mawson Craton. Discordance between this new pole and two roughly coeval poles from Dronning Maud Land and Coats Land (East Antarctica) demonstrates that these two terranes were not rigidly connected to the Mawson Craton ca. 1134 Ma. Comparison between the new pole and that of the broadly coeval Lakeview dolerite from the North Australian Craton supports the putative ~40° late Neoproterozoic relative rotation between the North Australian Craton and the combined South and West Australian cratons. A mean ca. 1134 Ma pole for the Proto-Australia Craton is calculated by combining our new pole and that of the Lakeview dolerite after restoring the 40° intracontinental rotation. A comparison of this mean pole with the roughly coeval Abitibi dykes pole from Laurentia confirms that the SWEAT reconstruction of Australia and Laurentia was not viable for ca. 1134 Ma

A tectonically driven Ediacaran oxygenation event.

The diversification of complex animal life during the Cambrian Period (541-485.4 Ma) is thought to have been contingent on an oxygenation event sometime during ~850 to 541 Ma in the Neoproterozoic Era. Whilst abundant geochemical evidence indicates repeated intervals of ocean oxygenation during this time, the timing and magnitude of any changes in atmospheric pO₂ remain uncertain. Recent work indicates a large increase in the tectonic CO₂ degassing rate between the Neoproterozoic and Paleozoic Eras. We use a biogeochemical model to show that this increase in the total carbon and sulphur throughput of the Earth system increased the rate of organic carbon and pyrite sulphur burial and hence atmospheric pO₂. Modelled atmospheric pO₂ increases by ~50% during the Ediacaran Period (635-541 Ma), reaching ~0.25 of the present atmospheric level (PAL), broadly consistent with the estimated pO₂ > 0.1-0.25 PAL requirement of large, mobile and predatory animals during the Cambrian explosion

Extreme variability in atmospheric oxygen levels in the late Precambrian

This is the final version. Available on open access from AAAS via the DOI in this recordData and materials availability: The datasets required to run the model and the code for NEOCARBSULF, which is constructed in MATLAB, can be accessed via the DOI: 10.5281/zenodo.6954788 or can be found at https://github.com/Alexjkrause/NEOCARBSULF.Mapping the history of atmospheric O2 during the late Precambrian is vital for evaluating potential links to the animal evolution. Ancient O2 levels are often inferred from geochemical analyses of marine sediments, leading to the assumption that the Earth experienced a stepwise increase in atmospheric O2 during the Neoproterozoic. However, the nature of this hypothesized oxygenation event remains unknown, with suggestions of a more dynamic O2 history in the oceans, and major uncertainty over any direct connection between the marine realm and atmospheric O2. Here we present a continuous quantitative reconstruction of atmospheric O2 over the last 1.5 billion years, using an isotope mass balance approach that combines bulk geochemistry and tectonic recycling rate calculations. We predict that atmospheric O2 levels during the Neoproterozoic oscillated between ~1% and ~50% PAL (Present Atmospheric Level). We conclude that there was no simple unidirectional rise in atmospheric O2 during the Neoproterozoic, and the first animals evolved against a backdrop of extreme O2 variability.Natural Environment Research Council (NERC)Royal SocietyLeverhulme TrustDeep Energy Community of the Deep Carbon ObservatoryRichard Lounsbery FoundationMSCA-I

Evolving marginal terranes during Neoproterozoic supercontinent reorganization: constraints from the Bemarivo Domain in northern Madagascar

Madagascar is a key area for unraveling the geodynamic evolution of the transition between the Rodinia and Gondwana supercontinents as it contains several suites of c. 850–700 Ma magmatic rocks that have been postulated to correlate with other Rodinian terranes. The Bemarivo Domain of northern Madagascar contains the youngest of these units that date to c. 750–700 Ma. We present zircon Hf and O isotope data to understand northern Madagascar's place in the Neoproterozoic plate tectonic reconfiguration. We demonstrate that the northern component of the Bemarivo Domain is distinct from the southern part of the Bemarivo Domain and have therefore assigned new names—the Bobakindro Terrane and Marojejy Terrane, respectively. Magmatic rocks of the Marojejy Terrane and Anaboriana Belt are characterized by evolved εHf(t) signatures and a range of δ18O values, similar to the Imorona-Itsindro Suite of central Madagascar. These magmatic suites likely formed together in the same long-lived volcanic arc. In contrast, the Bobakindro Terrane contains juvenile εHf(t) and mantle-like δ18O values, with no probable link to the rest of Madagascar. We propose that the Bobakindro Terrane formed in a juvenile arc system that included the Seychelles, the Malani Igneous Suite of northwest India, Oman, and the Yangtze Belt of south China, which at the time were all outboard from continental India and south China. The final assembly of northern Madagascar and amalgamation of the Bobakindro Terrane and Marojejy Terrane occurred along the Antsaba subduction zone, with collision occurring at c. 540 Ma.</p

Transient mobilization of subcrustal carbon coincident with Palaeocene–Eocene Thermal Maximum

Plume magmatism and continental breakup led to the opening of the northeast Atlantic Ocean during the globally warm early Cenozoic. This warmth culminated in a transient (170 thousand year, kyr) hyperthermal event associated with a large, if poorly constrained, emission of carbon called the Palaeocene–Eocene Thermal Maximum (PETM) 56 million years ago (Ma). Methane from hydrothermal vents in the coeval North Atlantic Igneous Province (NAIP) has been proposed as the trigger, though isotopic constraints from deep sea sediments have instead implicated direct volcanic carbon dioxide (CO2) emissions. Here we calculate that background levels of volcanic outgassing from mid-ocean ridges and large igneous provinces yield only one-fifth of the carbon required to trigger the hyperthermal. However, geochemical analyses of volcanic sequences spanning the rift-to-drift phase of the NAIP indicate a sudden ~220 kyr-long intensification of magmatic activity coincident with the PETM. This was likely driven by thinning and enhanced decompression melting of the sub-continental lithospheric mantle, which critically contained a high proportion of carbon-rich metasomatic carbonates. Melting models and coupled tectonic–geochemical simulations indicate that >104 gigatons of subcrustal carbon was mobilized into the ocean and atmosphere sufficiently rapidly to explain the scale and pace of the PETM

Rodinian devil in disguise: correlation of 1.25-1.10 Ga strata between Tasmania and Grand Canyon

Locating the continuation of the ca. 1.30–1.00 Ga Grenville orogen on continents formerly adjacent to Laurentia is central to resolving the paleogeography of the supercontinent Rodinia. Here we emphasize a correlation of late Mesoproterozoic foreland basins that, prior to truncation by Neoproterozoic rift margins, may have extended west of Laurentia within Rodinia. We propose correlation of the Unkar Group (Grand Canyon, Arizona, USA) with the upper Rocky Cape Group (Tasmania, southeast Australia) based on their similar stratigraphy, 1.25–1.10 Ga depositional age, and detrital zircon U-Pb age distribution and Hf isotope composition. This correlation places Tasmania adjacent to southwest Laurentia in the late Mesoproterozoic, which supports a new paleogeographic model for Rodinia. In this model, Tasmania and crustal fragments of Laurentia comprising the South Tasman Rise and the Coats Land block form key links between the Grenville orogen in southwest Laurentia and the Maud orogen (East Antarctica). A 1.14–1.07 Ga connection between the combined Grenville-Maud orogen and the Musgrave orogen of central Australia is compatible with paleomagnetic data but requires ∼4000 km of relative motion between Australia-Antarctica and Laurentia prior to the final assembly of Rodinia at ca. 0.90 Ga. We hypothesize that the final assembly of Rodinia was achieved by dextral motion between the crust of Australian and Laurentian affinity along a plate boundary concealed beneath ice cover in East Antarctica

Extending full-plate tectonic models into deep time: Linking the Neoproterozoic and the Phanerozoic

Recent progress in plate tectonic reconstructions has seen models move beyond the classical idea of continental drift by attempting to reconstruct the full evolving configuration of tectonic plates and plate boundaries. A particular problem for the Neoproterozoic and Cambrian is that many existing interpretations of geological and palaeomagnetic data have remained disconnected from younger, better-constrained periods in Earth history. An important test of deep time reconstructions is therefore to demonstrate the continuous kinematic viability of tectonic motions across multiple supercontinent cycles. We present, for the first time, a continuous full-plate model spanning 1 Ga to the present-day, that includes a revised and improved model for the Neoproterozoic-Cambrian (1000-520 Ma) that connects with models of the Phanerozoic, thereby opening up pre-Gondwana times for quantitative analysis and further regional refinements. In this contribution, we first summarise methodological approaches to full-plate modelling and review the existing full-plate models in order to select appropriate models that produce a single continuous model. Our model is presented in a palaeomagnetic reference frame, with a newly-derived apparent polar wander path for Gondwana from 540 to 320 Ma, and a global apparent polar wander path from 320 to 0 Ma. We stress, though while we have used palaeomagnetic data when available, the model is also geologically constrained, based on preserved data from past-plate boundaries. This study is intended as a first step in the direction of a detailed and self-consistent tectonic reconstruction for the last billion years of Earth history, and our model files are released to facilitate community development

A full-plate global reconstruction of the Neoproterozoic

Neoproterozoic tectonic geography was dominated by the formation of the supercontinent Rodinia, its break-up and the subsequent amalgamation of Gondwana. The Neoproterozoic was a tumultuous time of Earth history, with large climatic variations, the emergence of complex life and a series of continent-building orogenies of a scale not repeated until the Cenozoic. Here we synthesise available geological and palaeomagnetic data and build the first full-plate, topological model of the Neoproterozoic that maps the evolution of the tectonic plate configurations during this time. Topological models trace evolving plate boundaries and facilitate the evaluation of "plate tectonic rules" such as subduction zone migration through time when building plate models. There is a rich history of subduction zone proxies preserved in the Neoproterozoic geological record, providing good evidence for the existence of continent-margin and intra-oceanic subduction zones through time. These are preserved either as volcanic arc protoliths accreted in continent-continent, or continent-arc collisions, or as the detritus of these volcanic arcs preserved in successor basins. Despite this, we find that the model presented here still predicts less subduction (ca. 90%) than on the modern earth, suggesting that we have produced a conservative model and are likely underestimating the amount of subduction, either due to a simplification of tectonically complex areas, or because of the absence of preservation in the geological record (e.g. ocean-ocean convergence). Furthermore, the reconstruction of plate boundary geometries provides constraints for global-scale earth system parameters, such as the role of volcanism or ridge production on the planet's icehouse climatic excursion during the Cryogenian. Besides modelling plate boundaries, our model presents some notable departures from previous Rodinia models. We omit India and South China from Rodinia completely, due to long-lived subduction preserved on margins of India and conflicting palaeomagnetic data for the Cryogenian, such that these two cratons act as 'lonely wanderers' for much of the Neoproterozoic. We also introduce a Tonian-Cryogenian aged rotation of the Congo-São Francisco Craton relative to Rodinia to better fit palaeomagnetic data and account for thick passive margin sediments along its southern margin during the Tonian. The GPlates files of the model are released to the public and it is our expectation that this model can act as a foundation for future model refinements, the testing of alternative models, as well as providing constraints for both geodynamic and palaeoclimate models