Age and petrogenesis of the Lundy granite: Paleocene intraplate peraluminous magmatism in the Bristol Channel, UK

This is the author accepted manuscript. The final version is available from Geological Society via the DOI in this record.The Lundy granite forms part of the Lundy Igneous Complex, which is the southernmost substantive expression of magmatism within both the British Cenozoic Igneous Province and the wider North Atlantic Igneous Province. Its Qz + Pl + Kfs + Bt ± Grt ± Tpz mineralogy and peraluminous character contrast with other British Cenozoic Igneous Province granites farther north but are similar to the granites of the adjacent Early Permian Cornubian Batholith. We present the results of mapping, petrographical and mineral chemical analysis, and the first U–Pb zircon ages for the granite (59.8 ± 0.4 – 58.4 ± 0.4 Ma) and cross-cutting basic dykes (57.2 ± 0.5 Ma), which confirm a Paleocene age for magmatism. Zircon inheritance is limited but two cores imply the presence of Early Palaeozoic igneous rocks in the unexposed basement of SW England. The anomalous southerly location of the Lundy Igneous Complex is a consequence of mantle melting arising from the superimposition of localized lithospheric extension, related to intraplate strike-slip tectonics, with the distal ancestral Icelandic plume. Granite generation primarily reflects crustal partial melting during the emplacement of mantle-derived melts. The change in geochemical character between the Lundy granite (peraluminous) and other British Cenozoic Igneous Province granites (metaluminous or subalkaline) indicates a fundamental crustal source control between contrasting peri-Gondwanan and Laurentian basement provinces.Financial assistance was received from University College Oxford, the Geologists’ Association, the Lundy Field Society and the Burdett-Coutts fund

The Jurassic–Cretaceous depositional and tectonic evolution of the southernwestern margin of the Neotethys Ocean, Northern Oman and United Arab Emirates

The concept that the autochthonous, parautochthonous and allochthonous Permian–Cretaceous sequences in the United Arab Emirates (UAE) and Oman record the transition from platform, slope to basin sedimentation within the southern part of Neotethys has been fundamental to the interpretation of the geological history of the region. The results of a major geological mapping programme of the UAE, carried out by the British Geological Survey for the Federal Government of the UAE, coupled with the detailed examination of key sections within northern Oman has led to a re-evaluation of the geological evolution of this region. This detailed study has led to a greater appreciation of the sedimentology and depositional setting of the sediments laid down along the northeastern Arabian continental margin during the Jurassic to Cretaceous, allowing a more refined model of Neotethys Ocean basin evolution to be established. The model charts the progressive breakup of the Arabian continental margin and closure of Neotethys during the mid to late Cretaceous and is divided into three main stages: Stage 1—Initial rifting and formation of the Neotethys Ocean, followed by a prolonged period of stable, passive margin sedimentation which extended from the Permian to Late Jurassic times; Stage 2—Uplift and erosion of the shelf margin during the Late Jurassic to Early Cretaceous, coincident with increased carbonate-clastic sedimentation in the outer ramp, distal slope and basinal areas; Stage 3—Increased instability during the Late Cretaceous leading to the breakup of the platform margin and foreland basin sedimentation accompanying the obduction of the Oman-UAE ophiolite. Data obtained for the upper part of the platform and platform margin to slope successions has revealed that the topography of the “shelf”-slope-basinal margin was more subdued than previously thought, with this more gentle ramp margin morphology persisting until early to mid-Cretaceous times when the platform margin started to become unstable during ophiolite obduction. The thrust-repeated allochthonous sedimentary rocks of the Hamrat Duru Group were deposited on the outer platform margin/lower slope rise to basinal plain of this basin margin and includes the dismembered remains of two turbidite fan systems which fed carbonate-rich detritus into deeper parts of the ocean. A re-evaluation of the chert-rich sequences, previously equated with deposition on the abyssal plain of Neotethys, has led to the conclusion that they may record sedimentation at a much shallower level within a starved ocean basin, possibly in a mid-ramp (above storm wave base) to outer ramp setting. A marked change in basin dynamics occurred during the mid-Cretaceous leading to the development of a shallow ramp basin margin in Oman with terrestrial to shallow marine sedimentary rocks interdigitating with red siliceous mudstones. By contrast, the contemporaneous succession in the Dibba Zone of the UAE indicates considerable instability on a steep shelf break. This instability is recorded by the presence of several major olistostrome deposits within the Aruma Group of the UAE which are thought to have been generated in advance of the rapidly obducting Oman-UAE ophiolite

Melting mud in Earth's mantle

Melting of subducted sediment remains controversial, as direct observation of sediment melt generation at mantle depths is not possible. Geochemical fingerprints provide indirect evidence for subduction delivery of sediment to the mantle; however, sediment abundance in mantle-derived melt is generally low (0%–2%), and difficult to detect. Here we provide evidence for melting of subducted sediment in granite sampled from an exhumed mantle section. Peraluminous granite dikes that intrude peridotite in the Oman–United Arab Emirates ophiolite have U-Pb ages of 99.8 ± 3.3 Ma that predate obduction. The dikes have unusually high oxygen isotope (δ18O) values for whole rock (14–23‰) and quartz (20–22‰), and yield the highest δ18O zircon values known (14–28‰; values relative to Vienna standard mean ocean water [VSMOW]). The extremely high oxygen isotope ratios uniquely identify the melt source as high-δ18O marine sediment (pelitic and/or siliciceous mud), as no other source could produce granite with such anomalously high δ18O. Formation of high-δ18O sediment-derived (S-type) granite within peridotite requires subduction of sediment to the mantle, where it melted and intruded overlying mantle wedge. The granite suite described here contains the highest oxygen isotope ratios reported for igneous rocks, yet intruded mantle peridotite below the Mohorovičić seismic discontinuity, the most primitive oxygen isotope reservoir in the silicate Earth. Identifying the presence and quantifying the extent of sediment melting within the mantle has important implications for understanding subduction recycling of supracrustal material and effects on mantle heterogeneity over time.National Geographi

The Permian Cornubian granite batholith, SW England; Part 1: Field, structural, and petrological constraints

This is the author accepted manuscript. The final version is available from the Geological Society of America via the DOI in this recordThe Permian Cornubian granite batholith (295−275 Ma) in SW England includes seven major plutons and numerous smaller stocks extending for ∼250 km from the Isles of Scilly in the WSW to Dartmoor in the ENE. The granites are peraluminous and classified as crustal melt S-type, predominantly two-mica granites, and biotite or tourmaline monzo- and syenogranites, with subordinate minor topaz granite and lithium mica granite. The granites and their host rocks are pervasively mineralized with tin (cassiterite), tungsten (wolframite, ferberite), copper (chalcopyrite, chalcocite, bornite), arsenic (arsenopyrite), and zinc (sphalerite) mineralized lodes. Quartz-muscovite selvedges (greisen-bordered) also contain enrichment of lithophile elements such as boron (tourmaline), fluorine (fluorite), and lithium (lithium-micas such as lepidolite and zinnwaldite). They are derived from both muscovite and biotite dehydration melting of pelitic-psammitic rocks and intruded from a common source along the length of the batholith. Pressure estimates from andalusite and cordierite-bearing hornfels in the contact metamorphic aureole (150 ± 100 MPa) show that the granites intruded to 3 km depth. Cupolas around the Land’s End and Tregonning granites show aplite-pegmatite dikes and tourmaline + quartz + muscovite veins (greisen) that are frequently mineralized. Synchronous intrusions of lamprophyre dikes suggest an additional heat source for crustal melting may have been from underplating of alkaline magmas. The lack of significant erosion means that the source region is not exposed. In an accompanying paper (Part 2; Watts et al., 2024), gravity modeling reveals possible solutions for the shape and depth of the granite and the structure of the lower crust. We present a new model for the Land’s End, Tregonning, and Carnmenellis granites showing a mid-crustal source composed of amphibolite facies migmatites bounded by prominent seismic reflectors, with upward expanding dikes feeding inter-connected granite laccoliths that show inflated cupolas with shallow contact metamorphism. The Cornubian granites intruded >90 m.y. after obduction of the Lizard ophiolite complex, and after Upper Devonian−Carboniferous Variscan compressional, and later extensional, deformation of the surrounding Devonian country rocks. Comparisons are made between the Cornubian batholith and the Patagonian batholith in Chile, the Himalayan leucogranites, and the Baltoro granite batholith along the Karakoram range in northern Pakistan

Geophysical imaging of ophiolite structure in the United Arab Emirates.

The Oman-United Arab Emirates ophiolite has been used extensively to document the geological processes that form oceanic crust. The geometry of the ophiolite, its extension into the Gulf of Oman, and the nature of the crust that underlies it are, however, unknown. Here, we show the ophiolite forms a high velocity, high density, >15 km thick east-dipping body that during emplacement flexed down a previously rifted continental margin thereby contributing to subsidence of flanking sedimentary basins. The western limit of the ophiolite is defined onshore by the Semail thrust while the eastern limit extends several km offshore, where it is defined seismically by a ~40-45°, east-dipping, normal fault. The fault is interpreted as the southwestern margin of an incipient suture zone that separates the Arabian plate from in situ Gulf of Oman oceanic crust and mantle presently subducting northwards beneath the Eurasian plate along the Makran trench

Crustal and Mantle Deformation Inherited From Obduction of the Semail Ophiolite (Oman) and Continental Collision (Zagros)

Abstract: A common deviation from typical subduction models occurs when thrust sheets of oceanic crust and upper‐mantle rocks are emplaced over more buoyant continental lithosphere. The archetypal example of ophiolite obduction is the Semail ophiolite in the United Arab Emirates (UAE)‐Oman orogenic belt, formed and obducted onto the Arabian continental margin during the Late Cretaceous. The Strait of Hormuz syntaxis, the northern extent of the UAE‐Oman mountains, marks the transition from ocean‐continent convergence in the Gulf of Oman to continental collision along the Zagros Mountains. Based on new seismic data from a focused recording network, we infer continental crustal and mantle deformation in the northeastern corner of the Arabian plate (including the southern Zagros and the UAE‐Oman mountains), using observations from anisotropic tomography and shear‐wave splitting (SWS) measurements. We recover a change of ∼90° (from approximately WNW to nearly NS) in the axis of fast‐anisotropic orientations in the crust from the Zagros to the UAE‐Oman mountain belt, consistent with the dominant strike of the orogenic belts. We also find evidence in our SWS parameters for localized fossil deformation in the lithospheric mantle underlying the UAE‐Oman mountain range, possibly related to stress‐induced tectonism triggered by north‐east oriented underthrusting of the proto‐Arabian continental margin beneath the overriding Semail ophiolite. Shear‐wave‐splitting anisotropy orientations along two transects across the northern Musandam peninsula, averaging 15° anticlockwise from the north, provide the first geophysical verification of previous geological evidence that suggests a NE polarity of the Late Cretaceous Oman subduction zone system

Magmatic, Metamorphic and Structural History of the Variscan Lizard Ophiolite and Metamorphic Sole, Cornwall, UK

This is the final version. Available on open access from Wiley via the DOI in this recordData availability statement: The field data, electron-microprobe analysis data, the CA-ID-TIMS and laser ablation U-Pb data and XRF data used for structural analysis, geochronology, geochemistry and thermobarometry in the study are currently being archived at Oxford Research Archive for Data (ORA-Data). It can be accessed here: https://doi.org/10.5287/bodleian:0zwDDM7QmThe Lizard ophiolite, Cornwall, South-West England, is the largest and best-preserved ophiolite within the Variscan orogenic belt. It forms part of the Rheic-Rhenohercynian suture zone, and was obducted northwestward onto the passive continental margin of Avalonia (Laurussia) during the Middle Devonian. It comprises an almost complete thrust slice of oceanic crust with sheeted dykes, gabbros, Moho transition sequence, and upper-mantle peridotites, underlain by a metamorphic sole. Despite the importance of the Lizard ophiolite in understanding Variscan tectonics, the origin and age of the Lizard ophiolite are debated. We present new field observations, structural maps and cross-sections of the Lizard ophiolite from extensive re-mapping, integrated with U–Pb geochronology, petrology, thermobarometry, and whole rock geochemistry. We report new U–Pb zircon (CA-ID-TIMS and LA-ICPMS) ages of 386.80 ± 0.25/0.31/0.52 Ma (Givetian) from a plagiogranite dyke intruding the Crousa Gabbros at Porthoustock, and 395.08 ± 0.14/0.22/0.47 Ma (Emsian) from partial melts of the metamorphic sole Landewednack Amphibolites at Mullion Cove. These ages, respectively, precisely date the formation of the Lizard ophiolite oceanic crust, and the age of cooling post peak-metamorphism of the sole. Petrological modeling on the Landewednack Amphibolites suggests peak metamorphic conditions of 10 ± 2 kbar and 600 ± 75°C. We demonstrate that the Lizard ophiolite formed as a supra-subduction zone ophiolite overlying an inverted metamorphic sole, and we combine our observations and data into a new geodynamic model for the formation and obduction of the ophiolite. The current data supports an induced subduction initiation model.Natural Environment Research Council (NERC)University of OxfordLeverhulme Trus

Personhood, consciousness, and god : how to be a proper pantheist

© Springer Nature B.V. 2018In this paper I develop a theory of personhood which leaves open the possibility of construing the universe as a person. If successful, it removes one bar to endorsing pantheism. I do this by examining a rising school of thought on personhood, on which persons, or selves, are understood as identical to episodes of consciousness. Through a critique of this experiential approach to personhood, I develop a theory of self as constituted of qualitative mental contents, but where these contents are also capable of unconscious existence. On this theory, though we can be conscious of our selves, consciousness turns out to be inessential to personhood. This move, I then argue, provides resources for responding to the pantheist’s problem of God’s person.Peer reviewedFinal Accepted Versio

Multi-domain clinical natural language processing with MedCAT: The Medical Concept Annotation Toolkit

Electronic health records (EHR) contain large volumes of unstructured text, requiring the application of information extraction (IE) technologies to enable clinical analysis. We present the open source Medical Concept Annotation Toolkit (MedCAT) that provides: (a) a novel self-supervised machine learning algorithm for extracting concepts using any concept vocabulary including UMLS/SNOMED-CT; (b) a feature-rich annotation interface for customizing and training IE models; and (c) integrations to the broader CogStack ecosystem for vendor-agnostic health system deployment. We show improved performance in extracting UMLS concepts from open datasets (F1:0.448-0.738 vs 0.429-0.650). Further real-world validation demonstrates SNOMED-CT extraction at 3 large London hospitals with self-supervised training over ∼8.8B words from ∼17M clinical records and further fine-tuning with ∼6K clinician annotated examples. We show strong transferability (F1 > 0.94) between hospitals, datasets and concept types indicating cross-domain EHR-agnostic utility for accelerated clinical and research use cases