Kinematic Plate Models of the Neoproterozoic

Plate tectonic reconstructions traditionally use a combination of palaeomagnetic and geological data to model the changing positions of continents throughout Earth history. Plate reconstructions are particularly useful because they provide a framework for testing a range of hypotheses pertaining to climate, seawater chemistry, evolutionary patterns and the relationship between mantle and surface. During the Mesozoic and Cenozoic these are underpinned by data from the ocean basins that preserve relative plate motions, and data from hotspot chains and tomographic imaging of subducted slabs within the mantle to constrain absolute plate motions. For earlier times, neither ocean basins nor subducted slabs are preserved to assist with constructing plate models. Previously published plate models are usually built around times that have high quality palaeomagnetic data and between these times, the motion of continental crust is usually interpolated. Alternatively, regional tectonic models are developed predominantly from using geological data but without integrating the model into a global context. Additionally, until now all global plate models for the Neoproterozoic model only describe the configurations of continental blocks and do not explicitly consider the spatial and temporal evolution of plate boundaries. In this thesis, I present the first topological plate model of the Neoproterozoic that traces the dynamic evolution and interaction of tectonic plates, which encompass the entire earth. This model synthesises new geological and palaeomagnetic data, along with conclusions drawn from kinematic data to help discriminate competing continental configurations of the western area of the Neoproterozoic supercontinent, Rodinia. The thesis concludes by analysing the supercontinent cycle from 1000 to 0 Ma, by extracting the rift length, subduction zone length and perimeter-to-area ratio of continental crust to better understand the long-term evolution of our planet

Kinematic constraints on the Rodinia to Gondwana transition

Earth's plate tectonic history during the breakup of the supercontinent Pangea is well constrained from the seafloor spreading record, but evolving plate configurations during older supercontinent cycles are much less well understood. A relative paucity of available palaeomagnetic and geological data for deep time reconstructions necessitates innovative approaches to help discriminate between competing plate configurations. More difficult is tracing the journeys of individual continents during the amalgamation and breakup of supercontinents. Typically, deep-time reconstructions are built using absolute motions defined by palaeomagnetic data, and do not consider the kinematics of relative motions between plates, even for occasions where they are thought to be ‘plate-pairs’, either rifting apart leading to the formation of conjugate passive margins separated by a new ocean basin, or brought together by collision and orogenesis. Here, we use open-source software tools (GPlates/pyGPlates) to assess quantitative plate kinematics inherent within alternative reconstructions, such as rates of relative plate motion. We analyse the Rodinia-Gondwana transition during the Neoproterozoic, investigating the proposed Australia-Laurentia configurations during Rodinia, and the motion of India colliding with Gondwana. We find that earlier rifting times provide more optimal kinematic results. The AUSWUS and AUSMEX configurations with rifting at 800 Ma are the most kinematically supported configurations for Australia and Laurentia (average rates of 57 and 64 mm/a respectively), and angular rotation of ∼1.4°/Ma, compared to a SWEAT configuration (average spreading rate ∼76 mm/a) and Missing-Link configuration (∼90 mm/a). Later rifting, at, or after, 725 Ma necessitates unreasonably high spreading rates of >130 mm/a for AUSWUS and AUSMEX and ∼150 mm/a for SWEAT and Missing-Link. Using motion paths and convergence rates, we create a kinematically reasonable (convergence below 70 mm/a) tectonic model that is built upon a front-on collision of India with Gondwana, while also incorporating sinistral strike-slip motion against Australia and East Antarctica. We use this simple tectonic model to refine a global model for the breakup of western Rodinia and the transition to eastern Gondwana. © 2017 Elsevier B.V.This manuscript is a contribution to IGCP projects 628 (Gondwana Map) and 648 (Supercontinent Cycles and Global Geodynamics). This research was supported by the Science Industry Endowment Fund (RP 04-174) Big Data Knowledge Discovery Project, Australian Research Council grant DP130101946 (RDM) and the AuScope NCRIS project. ASM is supported by a CSIRO-Data61 Postgraduate Scholarship. ASC's contribution forms TRaX Record #379 and was funded by an Australian Research Council Future Fellowship FT120100340

Kinematic constraints on the Rodinia to Gondwana transition

Earth's plate tectonic history during the breakup of the supercontinent Pangea is well constrained from the seafloor spreading record, but evolving plate configurations during older supercontinent cycles are much less well understood. A relative paucity of available palaeomagnetic and geological data for deep time reconstructions necessitates innovative approaches to help discriminate between competing plate configurations. More difficult is tracing the journeys of individual continents during the amalgamation and breakup of supercontinents. Typically, deep-time reconstructions are built using absolute motions defined by palaeomagnetic data, and do not consider the kinematics of relative motions between plates, even for occasions where they are thought to be ‘plate-pairs’, either rifting apart leading to the formation of conjugate passive margins separated by a new ocean basin, or brought together by collision and orogenesis. Here, we use open-source software tools (GPlates/pyGPlates) to assess quantitative plate kinematics inherent within alternative reconstructions, such as rates of relative plate motion. We analyse the Rodinia-Gondwana transition during the Neoproterozoic, investigating the proposed Australia-Laurentia configurations during Rodinia, and the motion of India colliding with Gondwana. We find that earlier rifting times provide more optimal kinematic results. The AUSWUS and AUSMEX configurations with rifting at 800 Ma are the most kinematically supported configurations for Australia and Laurentia (average rates of 57 and 64 mm/a respectively), and angular rotation of ∼1.4°/Ma, compared to a SWEAT configuration (average spreading rate ∼76 mm/a) and Missing-Link configuration (∼90 mm/a). Later rifting, at, or after, 725 Ma necessitates unreasonably high spreading rates of >130 mm/a for AUSWUS and AUSMEX and ∼150 mm/a for SWEAT and Missing-Link. Using motion paths and convergence rates, we create a kinematically reasonable (convergence below 70 mm/a) tectonic model that is built upon a front-on collision of India with Gondwana, while also incorporating sinistral strike-slip motion against Australia and East Antarctica. We use this simple tectonic model to refine a global model for the breakup of western Rodinia and the transition to eastern Gondwana. © 2017 Elsevier B.V.This manuscript is a contribution to IGCP projects 628 (Gondwana Map) and 648 (Supercontinent Cycles and Global Geodynamics). This research was supported by the Science Industry Endowment Fund (RP 04-174) Big Data Knowledge Discovery Project, Australian Research Council grant DP130101946 (RDM) and the AuScope NCRIS project. ASM is supported by a CSIRO-Data61 Postgraduate Scholarship. ASC's contribution forms TRaX Record #379 and was funded by an Australian Research Council Future Fellowship FT120100340

A tectonic-rules-based mantle reference frame since 1 billion years ago - implications for supercontinent cycles and plate-mantle system evolution

Understanding the long-term evolution of Earth\u27s plate-mantle system is reliant on absolute plate motion models in a mantle reference frame, but such models are both difficult to construct and controversial. We present a tectonic-rules-based optimization approach to construct a plate motion model in a mantle reference frame covering the last billion years and use it as a constraint for mantle flow models. Our plate motion model results in net lithospheric rotation consistently below 0.25g g€Myr-1, in agreement with mantle flow models, while trench motions are confined to a relatively narrow range of -2 to +2g€cmg€yr-1 since 320g€Ma, during Pangea stability and dispersal. In contrast, the period from 600 to 320g€Ma, nicknamed the zippy tricentenary here, displays twice the trench motion scatter compared to more recent times, reflecting a predominance of short and highly mobile subduction zones. Our model supports an orthoversion evolution from Rodinia to Pangea with Pangea offset approximately 90g eastwards relative to Rodinia - this is the opposite sense of motion compared to a previous orthoversion hypothesis based on paleomagnetic data. In our coupled plate-mantle model a broad network of basal mantle ridges forms between 1000 and 600g€Ma, reflecting widely distributed subduction zones. Between 600 and 500g€Ma a short-lived degree-2 basal mantle structure forms in response to a band of subduction zones confined to low latitudes, generating extensive antipodal lower mantle upwellings centred at the poles. Subsequently, the northern basal structure migrates southward and evolves into a Pacific-centred upwelling, while the southern structure is dissected by subducting slabs, disintegrating into a network of ridges between 500 and 400g€Ma. From 400 to 200g€Ma, a stable Pacific-centred degree-1 convective planform emerges. It lacks an antipodal counterpart due to the closure of the Iapetus and Rheic oceans between Laurussia and Gondwana as well as due to coeval subduction between Baltica and Laurentia and around Siberia, populating the mantle with slabs until 320g€Ma when Pangea is assembled. A basal degree-2 structure forms subsequent to Pangea breakup, after the influence of previously subducted slabs in the African hemisphere on the lowermost mantle structure has faded away. This succession of mantle states is distinct from previously proposed mantle convection models. We show that the history of plume-related volcanism is consistent with deep plumes associated with evolving basal mantle structures. This Solid Earth Evolution Model for the last 1000 million years (SEEM1000) forms the foundation for a multitude of spatio-temporal data analysis approaches

Dynamic redox and nutrient cycling response to climate forcing in the Mesoproterozoic ocean

Controls on Mesoproterozoic ocean redox heterogeneity, and links to nutrient cycling and oxygenation feedbacks, remain poorly resolved. Here, we report ocean redox and phosphorus cycling across two high-resolution sections from the ~1.4 Ga Xiamaling Formation, North China Craton. In the lower section, fluctuations in trade wind intensity regulated the spatial extent of a ferruginous oxygen minimum zone, promoting phosphorus drawdown and persistent oligotrophic conditions. In the upper section, high but variable continental chemical weathering rates led to periodic fluctuations between highly and weakly euxinic conditions, promoting phosphorus recycling and persistent eutrophication. Biogeochemical modeling demonstrates how changes in geographical location relative to global atmospheric circulation cells could have driven these temporal changes in regional ocean biogeochemistry. Our approach suggests that much of the ocean redox heterogeneity apparent in the Mesoproterozoic record can be explained by climate forcing at individual locations, rather than specific events or step-changes in global oceanic redox conditions

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

Assembly of the basal mantle structure beneath Africa

International audiencePlate tectonics shapes Earth's surface, and is linked to motions within its deep interior1,2. Cold oceanic lithosphere sinks into the mantle, and hot mantle plumes rise from the deep Earth, leading to volcanism3,4. Volcanic eruptions over the past 320 million years have been linked to two large structures at the base of the mantle presently under Africa and the Pacific Ocean5,6. This has led to the hypothesis that these basal mantle structures have been stationary over geological time7,8, in contrast to observations and models suggesting that tectonic plates9,10, subduction zones11-14 and mantle plumes15,16 have been mobile, and that basal mantle structures are presently deforming17,18. Here we reconstruct mantle flow from one billion years ago to the present day to show that the history of volcanism is statistically as consistent with mobile basal mantle structures as with fixed ones. In our reconstructions, cold lithosphere sank deep into the African hemisphere between 740 and 500 million years ago, and from 400 million years ago the structure beneath Africa progressively assembled, pushed by peri-Gondwana slabs, to become a coherent structure as recently as 60 million years ago. Our mantle flow models suggest that basal mantle structures are mobile, and aggregate and disperse over time, similarly to continents at Earth's surface9. Our models also predict the presence of continental material in the mantle beneath Africa, consistent with geochemical data19,20

Closure of the Proterozoic Mozambique Ocean was instigated by a late Tonian plate reorganization event

International audiencePlate reorganization events involve fundamental changes in lithospheric plate-motions and can influence the lithosphere-mantle system as well as both ocean and atmospheric circulation through bathymetric and topographic changes. Here, we compile published data to interpret the geological record of the Neoproterozoic Arabian-Nubian Shield and integrate this with a full-plate tectonic reconstruction. Our model reveals a plate reorganization event in the late Tonian period about 720 million years ago that changed plate-movement directions in the Mozambique Ocean. After the reorganization, Neoproterozoic India moved towards both the African cratons and Australia-Mawson and instigated the future amalgamation of central Gondwana about 200 million years later. This plate kinematic change is coeval with the breakup of the core of Rodinia between Australia-Mawson and Laurentia and Kalahari and Congo. We suggest the plate reorganization event caused the long-term shift of continents to the southern hemisphere and created a pan-northern hemisphere ocean in the Ediacaran

Delineating driving mechanisms of Phanerozoic climate: building a habitable Earth

International audienceThe fundamental drivers of Phanerozoic climate change over geological timescales (10-100s of Ma) are well recognised: degassing from the deep-earth puts carbon into the atmosphere, silicate weathering takes carbon from the atmosphere and traps it in carbonate minerals. A number of variables are purported to control or exert influence on these two mechanisms, such as the motion of tectonic plates varying the amount of degassing, the palaeogeogrpahic distribution of continents and oceans, the colonisation of land by plants and preservation of more weatherable material, such as ophiolites. We present a framework, pySCION, that integrates these drivers into a single analysis, connecting solid earth with climate and biogeochemistry. Further, our framework allows us to isolate individual drivers to determine their importance, and how it changes through time. Our model, with all drivers active, successfully reproduces the key aspects and trends of Phanerozoic temperature, to a much greater extent than previous models. We find that no single driver can explain Phanerozoic temperature with any degree of confidence, and that the most important driver varies for each geological period

Author Correction: Assembly of the basal mantle structure beneath Africa (Nature, (2022), 603, 7903, (846-851), 10.1038/s41586-022-04538-y)

In the version of this article initially published, there were labeling errors in the x-axis tick mark labels for Fig. 3b–d. The Fig. 3b labels now reading “0.70, 0.80, 0.90” appeared initially as “0.65, 0.70, 0.75,” the Fig. 3c labels now reading “–5, 0” originally read “–6, –4”, and the Fig. 3d labels now reading “0, 1.0” originally read “0, 0.5”. The x-axis labels have been corrected in the HTML and PDF versions of the article