The nature and origin of the ~1880 Ma Circum-Superior Large Igneous Province

The Circum-Superior Large Igneous Province (LIP) consists predominantly of ultramafic-mafic lavas and sills with minor felsic components distributed as various segments along the margins of the Superior Province craton. Ultramafic-mafic dykes and carbonatite complexes of the LIP also intrude the more central parts of the craton. Most of this magmatism occurred at ∼1880 Ma. New major and trace element and Sr-Nd-Pb-Hf-Os isotopic data reveal that the segments of the Circum-Superior LIP can be treated as a single entity formed in the same tectonomagmatic environment. In contrast to most previous studies, the Circum-Superior LIP is interpreted to have formed from a single mantle plume and this is consistent with the high MgO and Ni contents of magmas, oceanic-plateau-like incompatible trace element profiles, ocean-island-like positive Nb-Ta anomalies, Icelandic plume-like Nb/Y and Zr/Y ratios, oceanic-plateau-like Zr/Nb and Nb/Th ratios and Nd-Hf isotopic compositions which differ from that of the estimated depleted upper mantle at ∼1880 Ma. Further support for a mantle plume origin comes from calculated high degrees of partial melting, high mantle potential temperatures and the presence of a radiating dyke swarm. The location of most of the magmatic rocks along the Superior Province margins probably represents the deflection of plume material by the thick cratonic keel toward regions of thinner lithosphere at the craton margins. There is no obvious geochemical distinction between segments of the Circum-Superior LIP which host ore deposits and those which do not. The geochemistry of the Circum-Superior LIP differs markedly from that of other ∼1880 Ma igneous provinces on other cratons which questions the validity of the formation of a very large LIP and the occurrence of a superplume event at ∼1880 Ma.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

A helium, oxygen and rhenium-osmium isotope study of some intraplate magmatism

Intraplate magmatism provides important constraints on the evolution, dynamics and composition of the Earth's mantle. Uncertainties remain, however, in understanding the mantle sources related to intraplate magmatism. For example, the influence or existence of mantle stratification, core-mantle interaction and recycling of subducted components are poorly understood. The extent to which geochemical signatures of intraplate magmas are modified during melt transportation, eruption and emplacement also requires better definition. This thesis employs He, O and Re-Os isotope systematics on selected volcanic and intrusive rocks from a number of oceanic and continental intraplate settings to address some of these key issues. New constraints on the effect of syn-eruptive degassing and post-emplacement mobility processes on intraplate magmas are presented. Ocean Island Basalts (OIB) from the Western Canary Islands and Coppermine Continental Flood Basalts (CFB) suggest that Re degassing for both modem and ancient alkaline and tholeiitic sub-aerially empted lavas are similar in extent. Crustal contamination is shown to explain some low δ(^18)O (≤5%(_0) in central Icelandic lavas and low (^3)He/'(^4)He ( 50 ppt) Western Canary OIB indicate that recycled oceanic crust forms part of the mantle source for these basalts, a theme also common to low δ(^18)O measured in central Icelandic glasses with (^3)He/(^4)He ratios similar to those of mid ocean ridge basalts. Decoupling of lithophile (Sr, Nd, Pb) and siderophile (Os) isotope tracers from He in both settings provides evidence for (^3)He-recharge with (^3)He/(^4)He up to 11.8R(_A) for the Western Canary Islands and 34.3R(_A) for central Icelandic lavas. There is evidence in Western Canary Island lavas, and in OIB globally, that a common or 'universal' mantle component is present with a near-chondritic (^187)Os/(^188)Os (≥0.127), mantle-like δ(^18)O (~5.2%(_0)) and elevated (^206)Pb/(^204)Pb (≥19.1) with respect to the depleted mantle; the so-called FOZO (Focus Zone), PHEM (Primary He mantle), or C (Common) components. Coppermine Re-Os isochron ages (1284 ± 13 Ma) are within error of the accepted 1270 ± 4 Ma U-Pb age for the Muskox Intrusion. γOs initials derived from both the Coppermine CFB (+2.0) and Muskox Intmsion (+1.3) lie on an enstatite or ordinary chondritic Os isotopic evolution curve for the Earth's mantle indicating derivation from a source similar to the universal component recognised in modem-day OIB. These results can be interpreted in the context of a veined or banded peridotite-pyroxenite mantle. Small amounts of partial melting of a heterogeneous mantle source leads to great isotopic variability whilst larger degrees of partial melting will lead to more homogeneous mantle-derived compositions. Pyroxenite sources might also explain the correlated isotopic and elemental compositions, including the possibility of (^186)Os-(^187)Os enrichment in OIB through high Re/Os and Pt/Os ratios. Ultimately, a universal mantle component appears to be present in all intraplate magmatism. This universal component is not always related to high (^3)He/(^4)He and appears to provide an endmember component to all intraplate mantle melting signatures from the Archaean to the present-day

The nature and origin of the -1880 Ma Circum-Superior Large Igneous Province.

The Circum-Superior Large Igneous Province (LIP) consists predominantly of ultramafic-mafic lavas and sills with minor felsic components distributed as various segments along the margins of the Superior Province craton. Ultramafic-mafic dykes and carbonatite complexes of the LIP also intrude the more central parts of the craton. Most of this magmatism occurred at 1880 Ma. New major and trace element and Sr-Nd-Pb-Hf-Os isotopic data reveal that the segments of the Circum-Superior LIP can be treated as a single entity formed in the same tectonomagmatic environment. In contrast to most previous studies, the Circum-Superior LIP is interpreted to have formed from a single mantle plume and this is consistent with the high MgO and Ni contents of magmas, oceanic-plateau-like incompatible trace element profiles, ocean-island-like positive Nb-Ta anomalies, Icelandic plume-like Nb/Y and Zr/Y ratios, oceanic-plateau-like Zr/Nb and Nb/Th ratios and Nd-Hf isotopic compositions which differ from that of the estimated depleted upper mantle at ∼1880 Ma. Further support for a mantle plume origin comes from calculated high degrees of partial melting, high mantle potential temperatures and the presence of a radiating dyke swarm. The location of most of the magmatic rocks along the Superior Province margins probably represents the deflection of plume material by the thick cratonic keel toward regions of thinner lithosphere at the craton margins. There is no obvious geochemical distinction between segments of the Circum-Superior LIP which host ore deposits and those which do not. The geochemistry of the Circum-Superior LIP differs markedly from that of other 1880 Ma igneous provinces on other cratons which questions the validity of the formation of a very large LIP and the occurrence of a superplume event at 1880 Ma

A petrological study of the appenite suite associated with the Ardara pluton, Co. Donegal, Ireland

Appinites are enigmatic rocks commonly associated with major I-type plutons in the Caledonian orogen, a number of different models have been proposed for the origin of their parental magmas and unusual textural characteristics. The appinite cluster associated with the Ardara pluton has been studied using petrological techniques with the aim of understanding these features as well as their relationships to the main pluton. The approach of this study has been to select a few appinite bodies considered to be representative of the whole Ardara appinite suite, and to study each in detail in parallel with a limited study of the main pluton. The techniques adopted include field mapping, petrography, mineral chemistry, whole rock major and trace element geochemistry. The detailed aims were to constrain the origin of the magma, its emplacement history and differentiation, for each selected body. In one case (Portnoo) the role of fluids was investigated in detail using stable isotope geochemistry. The Ardara appinite suite comprises a wide variety of generally amphibole-rich rocks typically including hornblendite, meladiorite, diorite, granodiorite and granite. There is one case of cortlandtite. Most have evidence of a significant volatile phase at crystallisation. The intrusions display a wide range in form and emplacement mechanism and most were emplaced prior to, or coeval with, the diapiric granite pluton of Ardara. They have a history of tectonic control on emplacement and are associated with major shear zones acting as potential magma pathways. Mineral geobarometry and geothermometry indicate that the appinites crystallised at 5-8 kb, and selected mineral pairs equilibrated between 800 and 976°C. G1 and G2 of the Ardara pluton crystallised at 5 kb and amphibole-plagioclase equilibrated at around 800°C. These pressures are high if the appinites are high-level diatremes, and this apparent inconsistency is discussed. Variations in bulk geochemistry are considerable and attempts are made to model these as the products of crystal-liquid processes using mass balance major oxide and Rayleigh trace element techniques. The results tend to be dominated by solutions involving amphibole, other mafic minerals and plagioclase, although in many cases no satisfactory result was obtained which suggests that crystal fractionation is not always the sole cause of differentiation. Stable isotope studies of delta18O, delta13C and 5D from the appinites and country rocks at Portnoo indicate that the dominant fluid in this appinite was magmatic in origin, although crustal contamination had occurred, while 6D data also indicate role for meteoric fluids. The data show that fluids from the appinite penetrated the limestone aureole to about 40m. The compositional characteristics of the Ardara appinite suite support a model of derivation of a hydrous basic magma from a mantle source. These magmas undergo differentiation by multiple processes, including crystal-liquid fractionation, as well as contamination by crustal assimilation and possibly by other magmas. The source of G1 & G2 of the main pluton is relatively primitive and could be immature lower crust. It is possible to derive G1 from G2 by crystal fractionation, but probably not in situ. The central G3 granite was almost certainly derived from a distinct, rather more mature crustal source

Geomorphology from space: A global overview of regional landforms

This book, Geomorphology from Space: A Global Overview of Regional Landforms, was published by NASA STIF as a successor to the two earlier works on the same subject: Mission to Earth: LANDSAT views the Earth, and ERTS-1: A New Window on Our Planet. The purpose of the book is threefold: first, to serve as a stimulant in rekindling interest in descriptive geomorphology and landforms analysis at the regional scale; second, to introduce the community of geologists, geographers, and others who analyze the Earth's surficial forms to the practical value of space-acquired remotely sensed data in carrying out their research and applications; and third, to foster more scientific collaboration between geomorphologists who are studying the Earth's landforms and astrogeologists who analyze landforms on other planets and moons in the solar system, thereby strengthening the growing field of comparative planetology

1967-2016, celebrating 50 years of geoscience in the mid-continent guidebook for the 50th annual meeting of the Geological Society of America, North-Central Section, April 18-19, 2016

Field Trip 1: The Quaternary geology of the southern Chicago metropolitan area; the Chicago Outlet, morainic systems, glacial chronology, and Kankakee Torrent; Field Trip 2: Fluorite deposits within the Illinois-Kentucky fluorspar district and how they relate to the Hicks Dome cryptoexplosive feature, Hardin County, Illinois; Field Trip 3: Quaternary geology of the upper Sangamon River basin; glacial, postglacial, and postsettlement history; Field Trip 4: Provenance, age, and depositional mechanisms of the Grover Gravel; evidence for multiple erosion cycles, volcanic eruptions, and early glaciations; Field Trip 9: Project-based field trips to the Starved Rock area for geoscience educators, northern IllinoisOpe

Joint inversion of the magnetic anomaly due to a kimberlite pipe and its analytic signal

Diamonds and kimberlites -- Geophysical surveys for kimberlites -- Problem -- Main objectives -- Methodology -- Major concepts -- The progress of magnetic method and the historical development concerned of magnetic method survey for kimberlites -- Derivatives of the magnetic field -- Formulas of derivatives of the magnetic field -- Finite difference derivatives -- Comparison of the responses from two methods -- Inversion of the magnetic field -- Introduction of the magnetic field inversion -- The solutions -- Levenberg-marquardt method -- The convergence -- Tests for the magnetic inversion -- Inversion of the analytic signal -- Introduction of the analytic signal -- Forward modeling -- Method of inversion -- Tests -- Joint inversion of the magnetic field and its analytic signal -- Introduction of joint inversion -- The model of the joint inversion -- Forward modeling -- Fromulation of the joint inversion -- Normalization -- Weighting of the two sets of the data -- The convergence -- The technique of the joint inversion -- Application to the real data -- Conclusion and discussion

The provenance and thermal histories of the Carboniferous Midland Valley of Scotland

Sedimentary basins are an important geological archive as they contain a wealth of information about the regions palaeogeographical setting, thermal evolution, and post depositional history, which are critical to many geological applications. However, establishing the source(s) of the sedimentary material stored within a basin, can be complicated by the refractory nature of some minerals often used as proxies for sediment provenance, meaning that a recycled component may be present and difficult to recognise. Thermal and burial history reconstructions based on the maturation of organic matter (vitrinite reflectance, VR) has been applied widely by the hydrocarbon industry to great success. However, due to the techniques inability to supply a quantification on time, its application in regions that lack post depositional constraints can lead to differing interpretations. In this thesis two geochronometers (zircon and apatite U-Pb geochronology) and one thermochronometer (apatite fission track, AFT) have been applied to the Carboniferous sedimentary strata of the central and eastern regions of the Midland Valley of Scotland. The aim of which is to provide a better understanding of the evolution of post-Caledonian sediment source(s) and pathways and to better constrain the post-Carboniferous thermal histories of the Midland Valley. This will reduce the geological uncertainties associated with the region, which is vital for Scotland to meet its future low carbon geo-energy commitments. A multi-proxy approach, applying U-Pb geochronology to detrital zircon and apatite has been utilised to investigate and constrain the provenance of the clastic material in Viséan to Westphalian B, Carboniferous sandstones of the Midland Valley of Scotland. The results of this provenance data clearly show three distinct sources for the sandstones: 1) Laurentian associated rocks (~900-2000 and ~2500-3100 Ma), 2) Caledonian orogeny associated rocks (395-475 Ma), and 3) Carboniferous volcanic associated rocks (~330-350 Ma). Applying U-Pb geochronology to both zircon and apatite from the same sandstone has allowed for the identification of recycled components, indicating that not all U-Pb age populations have been derived directly from their original source. Detrital zircon UPb age peaks that align with the Grenvillian (900-1200 Ma), Pinwarian (1450-1510 Ma), Labradorian (1600-1700 Ma), and Lewisian (2500-3100 Ma) orogenic events, lack equivalent apatite U-Pb counterparts. This suggests that Laurentian associated populations have been derived through the recycling of existing sedimentary and metasedimentary lithologies from the Devonian Old Red Sandstone, Grampian terrane, and Southern Uplands. Samples with complementary prominent Caledonian orogeny associated zircon and apatite U-Pb age peaks, are likely to be derived from first cycle sources from north of the Midland Valley, while Carboniferous ages are most likely derived from volcanic sources within the region. Spatial and temporal variation in the sample detrital spectra, indicates the provenance source did not remain constant over time. Early-mid Viséan (ArundianAsbian) U-Pb zircon samples are dominated by Proterozoic and Archean, Laurentian associated ages and lack a significant Caledonian peak, indicating recycling of Devonian Old Red Sandstone, Grampian terrane, and Southern Uplands dominated the sediment supply. U Pb apatite samples from the same time are dominated by a Caledonian peak suggesting either a very minor Caledonian associated source was actively supplying a limited amount of sediment or recycling of apatite through existing sedimentary lithologies is possible, as previous investigations have shown late Devonian Old Red Sandstone to be lacking in Caledonian aged U-Pb zircon. Late Viséan (Brigantian) samples in the eastern Midland Valley of Scotland have a marked increase in Palaeozoic Caledonian associated zircon ages, indicating the source region now included first cycle Caledonian associate rocks, although Laurentian associated components still dominate the spectra. A Brigantian sample collected to the west of the Bathgate Hills Volcanic Formation, located towards the centre of the study area, still shows a paucity in Caledonian related zircon ages, suggesting the volcanic high was a barrier or at least hindered sediment from the northeast being deposited across the region. Carboniferous peaks present in Brigantian zircon and apatite samples indicate the volcanic highs were also local sediment sources. A major change in sediment provenance occurs during the early Namurian (Pendleian) evidenced by the reversal in the dominant source signal, with Laurentian associated ages now relatively insignificant compared to Palaeozoic peaks, indicating first cycle Caledonian associated rocks now dominated the source area. A similar signal is recorded in Carboniferous strata in the Millstone Grit Formation in the Pennine Basin, attributed to a regional source to the north supplied via the Pennine delta. This distal source was also likely supplying material into the Midland Valley as well as proximal sources from Scottish Caledonian rocks, which combined to drown out the recycled component. Caledonian ages continue to dominate the Midland Valley samples in the Westphalian, contrary to Carboniferous basins to the south, which experience a reduction in the influence from the northern source during the Westphalian. Sources that dominated basins to the south were most likely prevented from entering the Midland Valley of Scotland by the Southern Upland high, which allowed the Caledonian sources to prevail. Undertaking detrital thermochronology is challenging due to the low yield of accessory minerals in some sedimentary rocks. However, results show AFT ages from the Midland Valley of Scotland reflect the geological structure of the region during the Carboniferous, with oldest ages located within the syncline cores and on structural highs. A complex series of forward and inverse modelling of individual and multi-sample profiles, combining outcrop and borehole samples, suggests the thermal histories can be sub-divided into three episodes: 1) Carboniferous Permian heating, 2) PermianMesozoic Cooling, and 3) Cenozoic cooling. . Inverse models also suggest initial heating was under the influence of an elevated geothermal gradient, supported by Carboniferous volcanic activity. These episodes are similar to those reported in other thermochronology investigations for onshore Scotland and show a contrast to those reported offshore, suggesting the onshore region was cooling as a coherent block from post Carboniferous times. Though the general trend observed in profile models is one of cooling through the Mesozoic, indicating an absence of significant burial under continued successions, some individual samples display an element of late Mesozoic reheating, which may be attributable to the Late Cretaceous transgression. The final Cenozoic cooling pulse, evident across the region, has been recognised in numerous investigations and has been attributed to processes associated with the emplacement of the proto-Icelandic plume or far field stresses related to compressional forces associated with the opening of the North Atlantic Ocean and Alpine collision. However, the temperature sensitivity of AFT is not enough to resolve this part of the thermal history. The results reported in this thesis reveal that the provenance of the Carboniferous sedimentary strata of the Midland Valley of Scotland did not remain constant through time and that post burial thermal maximum was attained following Carboniferous burial under an elevated geothermal gradient which was followed by episodes of cooling. These findings have important implications for assessing the future geo-energy potential within the Midland Valley of Scotland