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<jats:title>Abstract</jats:title> <jats:p> Shale rock core from the Bowland Shale Formation, UK was analysed in the laboratory using Rock-Eval(6) pyrolysis and Fourier Transform Infrared Spectroscopy (FTIR). These methods are used to characterise the organic constituents of soil and rock. This research is a proof-of-concept study to investigate whether regression models developed using FTIR and Rock-Eval data for the same length of core can be used to estimate selected Rock-Eval parameters. The accuracy of the regression models was assessed using statistical methods, the results of which were used to choose preferred models for each Rock-Eval parameter. Models produced were shown to have an acceptable level of uncertainty for Total Organic Carbon, S1, S2 and S3 outputs which led us to conclude these are potentially suitable for estimating unknown down-core Rock-Eval parameter values. Conversely, the T <jats:sub>max</jats:sub> model had a higher variability in the cross-validation data above the acceptable level of uncertainty which could lead to erroneous estimates. Down-core interpolations of selected Rock-Eval parameters could be practically achieved by modelling FTIR data by maintaining standard sample frequencies for Rock-Eval while supplementing with higher frequencies for FTIR and chemometric analysis. </jats:p>

<jats:title>Abstract</jats:title> <jats:p> The Neoarchaean to Palaeoproterozoic Betsiboka Suite of Madagascar mainly consists of granitoid orthogneiss and migmatite variably metamorphosed to amphibolite and granulite facies during the late Neoproterozoic. New U-Pb zircon data yielded emplacement ages of 2512 ± 17 Ma, 2507 ± 17 Ma, 2493 ± 14 Ma, and 2485 ± 16 Ma. Zircon d <jats:sup>18</jats:sup> O data indicate involvement of the continental crust during magma genesis. Mostly positive ε <jats:sub>Hf</jats:sub> (t) values plot slightly below the depleted-mantle curve. The isotopic data favour mixing between an older Archaean crustal source and a juvenile depleted-mantle source. Possible local crustal candidates for the older component in the exposed Malagasy basement are Neoarchaean mafic gneisses in the Tsaratanana Complex and the ca. 3200 Ma Nosy Boraha orthogneiss in the Antongil Domain. The new isotopic data support interpretations from previous studies investigating the genesis of Tonian plutonic rocks advocating crustal melting of a Mesoarchaean crustal source in the Antananarivo Domain. In addition, detrital zircon in the Proterozoic Ambatolampy Group and Itremo Group likely had a local source with the same isotopic composition as the Betsiboka Suite. Our study demonstrates the significance of multi-isotopic data from zircon for constraining the sources of detrital zircon grains in sedimentary provenance studies. </jats:p> <jats:p content-type="supplementary-material"> Supplementary material at <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="uri" specific-use="dataset is-supplemented-by" xlink:href="https://doi.org/10.6084/m9.figshare.c.6282672">https://doi.org/10.6084/m9.figshare.c.6282672</jats:ext-link> </jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Sierra de Juárez Complex (SJC) of southern Mexico contains an extensive geological record from Precambrian to Cenozoic, involving Rodinia, NW-Gondwana, western equatorial Pangea, and eastern peninsular Mexico. It is thus critical for palinspastic reconstructions and lithotectonic correlations, mainly between the Mexican and NW South America terranes. In this contribution, we investigate the tectonic evolution of the northern SJC from Silurian to the Lower Cretaceous on the basis of fieldwork, petrography, and zircon U-Pb geochronology by LA-ICPMS. Our results allow us to constrain five main geologic events. (1) Middle Paleozoic sedimentation along NW-Gondwana during transtensional tectonics. (2) Volcanosedimentary activity between 292-281 Ma in NW-Gondwana during Rheic Ocean closure. (3) Early Permian metamorphism related to flat-slab subduction postdating Pangea assembly. (4) Early-Middle Jurassic anatexis and magmatism coeval with regional shearing at ca. 175 Ma influenced by transtensional tectonics along eastern peninsular Mexico during Pangea tenure. (5) Intermediate to acid magmatism between ca. 136-129 Ma, correlated with the Zongolica continental arc in southern Mexico, followed by deep-crustal shearing related to either the formation of the extensional Chivillas basin or the Upper Cretaceous-Cenozoic contractional episode documented in the Cuicateco Terrane.</jats:p> <jats:p content-type="supplementary-material"> Supplementary material at <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="uri" specific-use="dataset is-supplemented-by" xlink:href="https://doi.org/10.6084/m9.figshare.c.6282721">https://doi.org/10.6084/m9.figshare.c.6282721</jats:ext-link> </jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Ordovician rocks of the conterminous United States (US) have a complex history, spanning multiple ancient basins, shifting palaeoclimate and evolving tectonic regimes. The US portion of the palaeocontinent of Laurentia occupied a relatively stable and isolated position around the southern tropics during the Ordovician. In general, Lower Ordovician rocks form a vast autochthonous blanket of fine-grained (tropical) carbonates that covered much of Laurentia, named the ‘Great American Carbonate Bank’. Outboard, ribbon carbonates and graptolitic shales are found in allochthonous fragments of the ancient continental margin. Middle Ordovician strata are more lithologically diverse, including the addition of several regionally distributed sandstones of the inner detrital belt, mostly overlying the Sauk–Tippecanoe unconformity. Upper Ordovician strata show the greatest lithologic and faunal diversity, reflecting steepening topography resulting from regional compression along the south Laurentian (Appalachian) margin. Recent advances in the interpretation of the US Ordovician come primarily from studies of carbon and oxygen stable isotopes, sequence stratigraphy, palaeoecology, tephrochronology, redox geochemistry, strontium isotopes and geochronology.</jats:p>

<jats:title>Abstract</jats:title> <jats:p> To examine the impact of the heat generated by high-level radioactive waste on Boom Clay, two heater tests have been launched in the HADES underground research facility: the small-scale ATLAS Heater Test and the large-scale PRACLAY Heater Test. The major objective of these tests is to confirm and refine the thermo-hydro-mechanical (THM) constitutive models and associated parameter values obtained from a laboratory characterization programme. This paper presents the observations from the ATLAS and PRACLAY heater tests and the combined numerical modelling of these tests. To characterize the excavation damaged zone in the clay around these tests, a mechanical model with a strain-dependent elastic modulus is introduced for the Boom Clay. The consistency between the observations from laboratory tests and <jats:italic>in-situ</jats:italic> tests and the outcomes from the numerical models strengthen the confidence in our understanding of the THM behaviour of Boom Clay. They also enabled us to validate the mechanical model and produce a set of anisotropic THM property values for both intact and damaged Boom Clay. </jats:p>

<jats:title>Abstract</jats:title> <jats:p> The Ordovician was a key period in the biological and geological history of the planet. ‘A Global Synthesis of the Ordovician System’ is presented in two volumes of <jats:italic>The Geological Society, Special Publications</jats:italic> . This first volume (SP532) charts the history of the Ordovician System and explores significant advances in our understanding of the period's biostratigraphy, including more precise calibration of its timescale with tephra chronology and regional alignments using astrochronology and cyclostratigraphy. Changes in the world's oceans, their shifting currents and sea levels, the biogeography of their biotas and the ambient climate are described and discussed against a background of changing palaeogeography. This first volume also includes syntheses of Ordovician geology of most European countries, including historical key areas, such as the British Isles, Baltoscandia and Bohemia. </jats:p>

<jats:title>Abstract</jats:title> <jats:p> The location of the Meso-Tethyan suture in SE Asia is ambiguous due to the strong overprint by the later India–Asia collisional tectonics. For the SE Asian extension of the Meso-Tethyan Bangong–Nujiang Suture (BNS) in Tibet, the two main candidates are the Longling–Ruili Suture (between the Tengchong and Baoshan blocks) and the Myitkyina ophiolite belt. Here, we present new detrital zircon U–Pb ages from high-grade metasedimentary rocks of the Gaoligong Group, which is considered to be the basement of the Tengchong Block located between the Longling–Ruili Suture and Myitkyina ophiolite belt. Our data suggest that the Gaoligong Group contains Cambrian, Triassic and Cretaceous zircons and is not a Precambrian basement, with a diagnostic age population peak at <jats:italic>c.</jats:italic> 1110 Ma. This peak is comparable to the <jats:italic>c.</jats:italic> 1170 Ma peak reported in the Australia-derived blocks (e.g. Lhasa and West Australia). Such similarities, as well as the similarities in the stratigraphy, palaeobiogeography and magmatic history of the Tengchong Block, suggest that the Tengchong Block was located adjacent to the northern Australia margin in Gondwana, and was most likely to have been linked with the Lhasa Block (southern Tibet) since the Early Paleozoic. Thus, the Longling–Ruili Suture is likely to represent a continuation of the Meso-Tethyan BNS in SE Asia. </jats:p>

<jats:title>Abstract</jats:title> <jats:p> Field relationships and new U–Pb geochronology data indicate a temporal link between the diverse high-K mafic–intermediate magmas of the Ossa–Morena Zone (OMZ). Ages of <jats:italic>c.</jats:italic> 338–335 Ma for the Vale de Maceiras gabbro and the Campo Maior microdiorite and quartz-diorite indicate that plutonism took place during a Variscan extensional D <jats:sub>2</jats:sub> deformation event in the OMZ. The syntectonic nature of the Vale de Maceiras pluton is attested to by the orientation of intrusive contacts, magmatic foliation and the growth of contact metamorphic minerals in relation to the Variscan extensional D <jats:sub>2</jats:sub> foliation. The Campo Maior microdiorite, quartz-diorite and orthomigmatites are temporally linked to high-temperature mylonitic gneisses formed simultaneously with the Variscan extensional D <jats:sub>2</jats:sub> deformation event. The geochemical features of the Vale de Maceiras and Campo Maior mafic–intermediate rocks show an affinity with the sanukitoid series. This finding suggests that the observed geochemical variability, from tholeiitic to calc-alkaline and sanukitoid, in the Visean OMZ plutonic rocks ( <jats:italic>c.</jats:italic> 349–335 Ma) may have been inherited from partially melted mantle domains that were previously contaminated by crustal melts during subduction. </jats:p>

<jats:title>Abstract</jats:title> <jats:p> Brittle structures are crucial for enabling several key natural processes in the Earth's upper crust. In addition, understanding the 3D characteristics and geological evolution of these features is equally important to support various developmental objectives, such as those, <jats:italic>inter alia</jats:italic> , linked to natural gas, groundwater, hydrothermal minerals and seismicity. In this study, we map various fractures of Gondwana based on the available geological information, satellite imagery and digital elevation data. The lengths and orientations of more than 10 000 fractures in their present-day position reveal four clearly defined patterns, with those striking NW being predominant. Archean–Paleoproterozoic domains are defined by fractures oriented north and NE, whereas the Mesoproterozoic has dominant NNW-striking fractures. In contrast, the Neoproterozoic has mostly NE-striking fractures and the Phanerozoic sequences are defined by a predominant NW and a subordinate west fracture pattern. The style and geometry of these structures can be linked to major geodynamic events that led to the formation of Gondwana building blocks during the Eburnean ( <jats:italic>c.</jats:italic> 2.2–1.8 Ga), Kibaran ( <jats:italic>c.</jats:italic> 1.4–1.0 Ga) and Pan African–Brasiliano ( <jats:italic>c.</jats:italic> 800–550 Ma) orogens, and amalgamation of Pangaea ( <jats:italic>c.</jats:italic> 350–250 Ma). Many structures were reactivated and new faults formed during opening of the Atlantic and Indian oceans ( <jats:italic>c.</jats:italic> 180–120 Ma), the India–Asia collision and rifting across East Africa since about 40 Ma. Although the changes in palaeogeography remain difficult to model with accuracy, major structural orientations are corroborated by the occurrence of major mineral deposits and seismicity. The spatial distribution of mapped patterns across the different continents also correlates well with large shale gas prospects and increased groundwater yields. Thus, Gondwana fractures need to be considered in more detail for informing future development related to water and energy use, especially across regions of Africa. </jats:p>

<jats:title>Abstract</jats:title> <jats:p> Time-lapse seismic monitoring is a key component in the geological sequestration of greenhouse gases. Currently, a lack of understanding of the influence of injected CO <jats:sub>2</jats:sub> on rocks’ geophysical signatures is reported. Using a novel ultrasonic experimental system, we measured the variations in the longitudinal (P) and transverse (S) elastic wave speeds of a CO <jats:sub>2</jats:sub> -saturated porous medium at different pressure and temperature conditions around the CO <jats:sub>2</jats:sub> critical point. The results show that both P- and S-wave speeds, corrected to seismic frequencies, decreased by more than 4.5% across the CO <jats:sub>2</jats:sub> gas to liquid and gas to supercritical states, primarily as a consequence of CO <jats:sub>2</jats:sub> density increase. This study provides a-20 firm basis for the use of seismological methods in monitoring sequestered CO <jats:sub>2</jats:sub> ; although the abruptness, and hence remote seismic detectability, depends on which phase boundary is crossed. Further, these measurements also allow us to compare observations to frequency-dependent wave propagation theory. The observed wave speeds mostly align with those calculated at 1 MHz using the Biot theory for both CO <jats:sub>2</jats:sub> and H <jats:sub>2</jats:sub> O saturated states. However, the observed and calculated wave speeds diverge above the phase transition in some of the tests, possibly due to the kinetics of the phase transition within a porous medium. As such, aside from the direct utility in providing information on the expected seismic responses, the CO <jats:sub>2</jats:sub> provides a highly tunable fluid that can be advantageous for experimental studies. </jats:p>