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

Du manteau à la croûte, dynamique de subduction et systèmes minéralisés en Méditerranée orientale

Subduction zones display a major economic interest, in terms of mineral resources, with mainly copper and gold deposits. While many studies focus on ore-forming physico-chemical mechanisms, the control of geodynamic processes on such deposits remains poorly investigated. In this study, I track tridimensional (3D) subduction-related mantle and crustal processes that promote ore genesis. The eastern Mediterranean subduction zone is a relevant study area to explore subduction-mineralization interactions, because of its complex tectonic and magmatic evolution and the large number of available metallogenic data. This work consisted in (1) performing a new kinematic reconstruction model of this region, (2) using this model, characterizing the spatial and temporal distribution of magmatic and ore occurrences, (3) evidencing, on the field, the relations between mineralization and large-scale tectonic structures and (4) providing physical constrains to proposed conceptual models, using 3D thermo-mechanical numerical modeling. Two main metallogenic provinces are evidenced: a late Cretaceous copper-rich and an Oligocene-Miocene lead-zinc- then gold-rich provinces emplaced in an arc and back-arc context, respectively. These metallogenic periods are controlled by the subduction zone retreat and associated asthenospheric flow that results in an extensional (or transtensional) tectonic regime in the overriding lithosphere, promoting ore genesis. Their metal content, as well as their typology then depend on (1) how much these processes affect the subduction kinematics and (2) the past geodynamic evolution of this subduction zone.Les zones de subduction présentent un intérêt majeur en termes de ressources minérales, notamment à cuivre et or. De nombreuses études se sont focalisées sur les mécanismes physico-chimiques de formation de ces minéralisations, mais très peu se sont intéressées aux processus géodynamiques qui contrôlent ces mécanismes. Dans cette étude, j’identifie les processus mantelliques et crustaux, liés à la dynamique tridimensionnelle (3D) de la subduction, qui favorisent la genèse de ces concentrations métalliques. La zone de subduction est-Méditerranéenne présente une évolution tectonique et magmatique complexe, avec de nombreuses données métallogéniques disponibles, ce qui en fait une zone d’étude privilégiée afin d’étudier ces interactions entre subduction et minéralisations. Ce travail a consisté à (1) réaliser un nouveau modèle de reconstructions cinématiques de la région, (2) caractériser la distribution spatiale et temporelle des occurrences magmatiques et minéralisées à partir de ce modèle, (3) mettre en évidence, via une étude de terrain, le contrôle structural de ces minéralisations et (4) apporter des contraintes physiques aux modèles conceptuels alors proposés, à l’aide d’une étude de modélisation numérique thermo-mécanique 3D. Deux provinces métallogéniques ont ainsi été mises en évidence : (1) au Crétacé supérieur, une province riche en cuivre qui s’est développée dans un environnement d’arc et (2) à l’Oligocène-Miocène, une province riche en plomb-zinc puis en or, qui s’est mise en place dans un contexte d’arrière-arc. Ces épisodes fertiles sont contrôlés par le retrait de la zone de subduction et les flux asthénosphériques associés qui permettent l’instauration d’un régime tectonique extensif (ou transtensif) dans la lithosphère, favorisant la genèse de ces systèmes minéralisés. Leur contenu métallique ainsi que leur typologie est alors fonction (1) de l’intensité avec laquelle ces processus influent sur la cinématique de subduction et (2) de l’histoire géodynamique antérieure de cette zone de subduction

Malignant melanoma of the urethra: a rare histologic subdivision of vulvar cancer with a poor prognosis

Malignant melanoma of the urethra is a rare tumour that is difficult to diagnose and treat, resulting in a poor prognosis. In this paper, we present the case of a 65-year-old woman who was referred to a gynaecologist because of a urethral mass that mimicked a caruncle. The tumour was removed by local excision, and a pathological analysis revealed a malignant melanoma. Distal urethrectomy was performed after three months with no evidence of residual tumour. There was no evidence of disease at a six-year followup. In this paper, we compare the epidemiology, treatment, staging, and prognosis of vulvar cancer in general to malignant melanoma of the vulva in particular

Detrital Mineral U/Pb Age Dating and Geochemistry of Magmatic Products in Basin Sequences

Dating and geochemical analyses of detrital minerals (mainly zircons) combined with traditional methods, such as heavy minerals and sandstone modes, are a powerful tool in paleogeographic and paleotectonic research and industrial applications

Quantification of an Archaean to Recent Earth Expansion Process Using Global Geological and Geophysical Data Sets

Global geological and geophysical data, while routinely used in conventional plate tectonic studies, has not been applied to models of an expanding Earth. Crustal reconstructions on Archaean to Recent models of an expanding Earth presented here are the first time that reconstructions have been extended back to the Archaean, and the first time that continental and oceanic geology has been utilised to constrain plate assemblage and palaeoradius of the Earth. A set of twenty four spherical models have been constructed, twenty three covering the Archaean to Recent and one projected to five million years into the future. Construction of these spherical models relies on the fundamental premise that crustal lithosphere is cumulative with time, and historical markers preserved in the oceanic and continental geology accurately constrain both palaeoradius and plate reconstruction from the Archaean to Recent. Post-Triassic reconstructions of oceanic lithosphere demonstrate a plate fit together along each plate margin at better than 99% fit. During the Triassic, continents envelope the Earth as a complete continental shell at a reduced Earth radius, and marginal and epi- continental sedimentary basins merge to form a global network surrounding continental cratons and orogenic zones. Continental crust is reconstructed on Pre-Jurassic models using the primary crustal elements of cratons, orogens and basins, with expansion primarily manifested as crustal extension within an established network of epi-continental rifts, orogens and sedimentary basins. By removing all basin and pre-orogenic sediments a primordial proto-Earth at a palaeoradius of approximately 1700 kilometres is achieved during the Mesoproterozoic, comprising assembled cratons and Proterozoic basement rocks.For all models, an intracratonic to intracontinental spatial integrity is maintained throughout Earth history during processes of Precambrian and Palaeozoic continental crustal extension, Late Palaeozoic crustal rupture, Permo-Triassic continental break-up, and Mesozoic and Cenozoic continental dispersal to the Recent. Palaeomagnetic pole data delineate diametrically opposed palaeomagnetic pole clusters for each era back to the Archaean, without the need to consider random crustal dispersion-amalgamation-dispersal cycles. The palaeopole data is further supported by palaeogeographic, palaeobiogeographic, and palaeoclimatic indicators, which define palaeoequators and palaeoclimatic zones consistent with palaeomagnetic determinations. The distribution of latitude dependent lithofacies including glacigenic strata, carbonates, coal, and faunal and floral species is shown to coincide precisely with established palaeopoles and palaeoequators for all expanding Earth models. For climatic and biotic indicators a distinct latitudinal zonation paralleling the established palaeoequator is evident and a distinct northward shift in climatic zonation suggests that an inclined Earth rotational axis, inclined to the pole of the ecliptic, was well established during the Palaeozoic and persists to the Recent. Coastal geography on expanding Earth models shows that large Panthallassa, Tethys and Iapetus Oceans are not required during reconstruction. Instead, epi-continental Panthallassa and lapetus Seas represent precursors to the modem Pacific and Atlantic Oceans and the Tethys Sea represents a precursor of the present Eurasian continent.Emergent land surfaces during the Precambrian and Phanerozoic equate to the conventional Rodinia, Gondwana and Pangaea supercontinents and smaller subcontinents, and demonstrate a spatial intracratonic and intracontinental integrity throughout Earth history. On each spherical model constructed proto-continental development is evolutionary and defined by a progressive extension of epi-continental sedimentary basins, pulsed orogenesis, eustatic and transgression-regression of epi-continental seas, and opening of modem oceans during the Mesozoic to Recent. Metallogenic modelling of Precambrian and Phanerozoic metal deposits shows a broad global Precambrian metallogenic provinciality coinciding with cratons and intracratonic settings, to regional provinces clustering as specific metal associations. The Phanerozoic metallogenic distribution highlights the abundance of porphyry and granite associated metals concentrated within Phanerozoic orogenic belts, and orogenic belts are shown to crosscut and displace pre-existing Palaeozoic and Precambrian metallogenic provinces. A proposed causal model for Earth expansion has expansion due to an exponential increase in mass with time. Earth expansion then involves an increase in mass by condensation, or segregation of new matter from the Earth's core. This new matter accumulates at the core-mantle interface and the increase in volume results in a swelling of the mantle, which is then manifested in the outer crust as crustal extension. Matter generation within the Earth's core is seen as an endothermic reaction, which will ultimately result in a decay of the matter formation process and cessation of expansion with time

EVOLUTION OF THE SUBCONTINENTAL LITHOSPHERE DURING MESOZOIC TETHYAN RIFTING: CONSTRAINTS FROM THE EXTERNAL LIGURIAN MANTLE SECTION (NORTHERN APENNINE, ITALY)

Our study is focussed on mantle bodies from the External Ligurian ophiolites, within the Monte Gavi and Monte Sant'Agostino areas. Here, two distinct pyroxenite-bearing mantle sections were recognized, mainly based on their plagioclase-facies evolution. The Monte Gavi mantle section is nearly undeformed and records reactive melt infiltration under plagioclase-facies conditions. This process involved both peridotites (clinopyroxene-poor lherzolites) and enclosed spinel pyroxenite layers, and occurred at 0.7–0.8 GPa. In the Monte Gavi peridotites and pyroxenites, the spinel-facies clinopyroxene was replaced by Ca-rich plagioclase and new orthopyroxene, typically associated with secondary clinopyroxene. The reactive melt migration caused increase of TiO2 contents in relict clinopyroxene and spinel, with the latter also recording a Cr2O3 increase. In the Monte Gavi peridotites and pyroxenites, geothermometers based on slowly diffusing elements (REE and Y) record high temperature conditions (1200-1250 °C) related to the melt infiltration event, followed by subsolidus cooling until ca. 900°C. The Monte Sant'Agostino mantle section is characterized by widespread ductile shearing with no evidence of melt infiltration. The deformation recorded by the Monte Sant'Agostino peridotites (clinopyroxene-rich lherzolites) occurred at 750–800 °C and 0.3–0.6 GPa, leading to protomylonitic to ultramylonitic textures with extreme grain size reduction (10–50 μm). Compared to the peridotites, the enclosed pyroxenite layers gave higher temperature-pressure estimates for the plagioclase-facies re-equilibration (870–930 °C and 0.8–0.9 GPa). We propose that the earlier plagioclase crystallization in the pyroxenites enhanced strain localization and formation of mylonite shear zones in the entire mantle section. We subdivide the subcontinental mantle section from the External Ligurian ophiolites into three distinct domains, developed in response to the rifting evolution that ultimately formed a Middle Jurassic ocean-continent transition: (1) a spinel tectonite domain, characterized by subsolidus static formation of plagioclase, i.e. the Suvero mantle section (Hidas et al., 2020), (2) a plagioclase mylonite domain experiencing melt-absent deformation and (3) a nearly undeformed domain that underwent reactive melt infiltration under plagioclase-facies conditions, exemplified by the the Monte Sant'Agostino and the Monte Gavi mantle sections, respectively. We relate mantle domains (1) and (2) to a rifting-driven uplift in the late Triassic accommodated by large-scale shear zones consisting of anhydrous plagioclase mylonites. Hidas K., Borghini G., Tommasi A., Zanetti A. & Rampone E. 2021. Interplay between melt infiltration and deformation in the deep lithospheric mantle (External Liguride ophiolite, North Italy). Lithos 380-381, 105855