Deformation and fluid-rock interaction along then reactivated Outer Hebrides fault zone, Scotland

The Outer Hebrides Fault Zone (OHFZ) is a major, moderately E- to ESE-dipping long-lived reactivated fault zone which is developed in, and cross-cuts, crystalline amphibolite to granulite grade Lewisian basement gneisses, NW Scotland. A complex assemblage of different fault rocks and structures is presently exposed along the OHFZ, which reflects deformation at a range of crustal depths and metamorphic (temperature, pressure, fluid activity) conditions. Detailed field and microstructural observations have demonstrated that segments of the fault zone which display evidence of repeated reactivation over long periods of geological time (movements range from late Laxfordian / Grenvillian to Oligocene in age) are characterised by intense, localised greenschist facies retrogression and the development of sericite- and chlorite-bearing phyllonitic shear zones. In contrast, phyllonite is absent from segments of the fault zone which have not suffered extensive reactivation. These observations are consistent with phyllonitisation at mid-crustal depths having caused profound long-term mechanical weakening of the OHFZ,Two phases of retrogression and phyllonitisation have been recognised along the OHFZ:Upper greenschist facies, Late Laxfordian / Grenvillian phyllonitisation, which occurred at between 15 and 17km depth (Lewis and Harris only), and Lower greenschist facies, Caledonian phyllonitisation, which occurred at between 8 and 9km depth (Lewis, Harris and the Uists).Microstructural and geochemical studies of selected phyllonites from reactivated segments of the OHFZ demonstrate that greenschist facies retrogression and phyllonitisation were promoted by the influx of warm (c.250 to 450 C), hydrous iron^ and magnesium-bearing, oxidising fluids into the fault zone. Fluid flow during upper greenschist facies phyllonitisation was focused into pre-existing bands of highly strained quartzo-feldspathic mylonite, whilst fluid flow during lower greenschist facies phyllonitisation was focused predominantly into pre-existing brittle fractures and cataclastic crush zones. Thus, the distribution and intensity of fluid flow, and hence the distribution and intensity of retrogression and phyllonitisation were ultimately governed by the nature of pre-existing permeability pathways through the fault zone. It is therefore concluded that the long-term rheological evolution of reactivated basement fault zones is inexorably linked to the mid-crustal permeability evolution of such structure

The role of pre-existing structures during rifting, continental breakup and transform system development, offshore West Greenland

Continental breakup between Greenland and North America produced the small oceanic basins of the Labrador Sea and Baffin Bay, which are connected via the Davis Strait, a region mostly comprised of continental crust. This study contributes to the debate regarding the role of pre-existing structures on rift development in this region using seismic reflection data from the Davis Strait data to produce a series of seismic surfaces, isochrons and a new offshore fault map from which three normal fault sets were identified as (i) NE-SW, (ii) NNW-SSE and (iii) NW-SE. These results were then integrated with plate reconstructions and onshore structural data allowing us to build a two-stage conceptual model for the offshore fault evolution in which basin formation was primarily controlled by rejuvenation of various types of pre-existing structures. During the first phase of rifting between at least Chron 27 (ca. 62 Ma; Palaeocene), but potentially earlier, and Chron 24 (ca. 54 Ma; Eocene) faulting was primarily controlled by pre-existing structures with oblique normal reactivation of both the NE-SW and NW-SE structural sets in addition to possible normal reactivation of the NNW-SSE structural set. In the second rifting stage between Chron 24 (ca. 54 Ma; Eocene) and Chron 13 (ca. 35 Ma; Oligocene), the sinistral Ungava transform fault system developed due to the lateral offset between the Labrador Sea and Baffin Bay. This lateral offset was established in the first rift stage possibly due to the presence of the Nagssugtoqidian and Torngat terranes being less susceptible to rift propagation. Without the influence of pre-existing structures the manifestation of deformation cannot be easily explained during either of the rifting phases. Although basement control diminished into the post-rift, the syn-rift basins from both rift stages continued to influence the location of sedimentation possibly due to differential compaction effects. Variable lithospheric strength through the rifting cycle may provide an explanation for the observed diminishing role of basement structures through time

Putting the geology back into Earth models

New digital methods for data capture can now provide photorealistic, spatially precise, and geometrically accurate three-dimensional (3-D) models of rocks exposed at the Earth's surface [Xu et al., 2000; Pringle et al., 2001; Clegg et al., 2005]. These “virtual outcrops” have the potential to create a new form of laboratory-based teaching aids for geoscience students, to help address accessibility issues in fieldwork, and generally to improve public awareness of the spectacular nature of geologic exposures from remote locations worldwide. This article addresses how virtual outcrops can provide calibration, or a quantitative “reality check,” for a new generation of high-resolution predictive models for the Earth's subsurface

STFC - Roadmap for Solar System Research 2022

This is a report to the Science Technology and Facilities Council (STFC) UK by their Solar System Advisory Panel (SSAP) on the status and direction of UK research in the field of solar system studie

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb carbonate geochronology: strategies, progress, and limitations

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb geochronology of carbonate minerals, calcite in particular, is rapidly gaining popularity as an absolute dating method. The high spatial resolution of LA-ICP-MS U–Pb carbonate geochronology has benefits over traditional isotope dilution methods, particularly for diagenetic and hydrothermal calcite, because uranium and lead are heterogeneously distributed on the sub-millimetre scale. At the same time, this can provide limitations to the method, as locating zones of radiogenic lead can be time-consuming and “hit or miss”. Here, we present strategies for dating carbonates with in situ techniques, through imaging and petrographic techniques to data interpretation; our examples are drawn from the dating of fracture-filling calcite, but our discussion is relevant to all carbonate applications. We review several limitations to the method, including open-system behaviour, variable initial-lead compositions, and U–daughter disequilibrium. We also discuss two approaches to data collection: traditional spot analyses guided by petrographic and elemental imaging and image-based dating that utilises LA-ICP-MS elemental and isotopic map data

Hadley circulation and precipitation changes control black shale deposition in the Late Jurassic Boreal Seaway

New climate simulations using the HadCM3L model with a paleogeography of the Late Jurassic [155.5 Ma], and proxy-data corroborate that warm and wet tropical-like conditions reached as far north as the UK sector of the Jurassic Boreal Seaway [~35oN]. This is associated with a northern hemisphere Jurassic Hadley cell and an intensified subtropical jet which both extend significantly polewards than in the modern (July-September). Deposition of the Kimmeridge Clay Formation [KCF] occurred in the shallow, storm-dominated, epeiric Boreal Seaway. High resolution paleo-environmental proxy data from the Kimmeridge Clay Formation [KCF; ~155–150 Ma], UK are used to test for the role of tropical atmospheric circulation on meter-scale heterogeneities in black shale deposition. Proxy and model data show that the most organic-rich section [eudoxus to mid-hudlestoni zones] is characterised by a positive δ13Corg excursion and up to 37 wt% total organic carbon [%TOC]. Orbital-modulation of organic carbon burial primarily in the long eccentricity power band combined with a clear positive correlation between %TOC carbonate-free and the kaolinite/illite ratio supports peak organic carbon burial under the influence of very humid climate conditions, similar to the modern tropics. This re-interpretation of large-scale climate relationships, supported by independent modelling and geological data, has profound implications for atmospheric circulation patterns and processes affecting marine productivity and organic carbon burial further north along the Boreal Seaway, including the Arctic

Bioethics, Suffering, and the Culture Wars

This article provides an analysis of the enduring disagreements among bioethicists over the divide between secular and religious boundaries that are reflected in liberal, libertarian, and conservative approaches to medicine as a profession and vocation. At the beginning of the twentieth century, the most authoritative voices to address the problem of suffering were Protestants, Strict Calvinists, hydropaths, and homeopaths. Other religious and medical groups had regularly confronted pain and suffering in the nineteenth century in light of the discovery and increasing use of anesthesia. Rationalizations for suffering were first and foremost indebted to strong beliefs about divine will and about the seemingly inevitable course of nature. Did physical pain reflect the wrongdoing of one individual or of an entire community? What was the appropriate way to respond to the natural circumstances of growth, decay, and healing? Such questions produced a varied rhetoric of suffering that emerged in new ways in the second half of the twentieth century. Questions and concerns about the ethical foundations of medical practice—what should and should not be permitted—illustrate the present cultural struggles