Geophysical constraints on upper crustal structure in the Midland Valley of Scotland

The Midland Valley Investigation by Seismology (MAVIS) consists of three refraction lines of c. 80 km length across the Carboniferous basins of the Midland Valley of Scotland, Two lines trend approximately east-west (MAVIS I north and south), the latter crossing a major gravity and magnetic anomaly near Bathgate, The third line (MAVIS II) trends north-south, crossing the MAVIS I lines and Bathgate anomaly and extends into Lower Old Red Sandstone outcrop to the north and south of the OchiI and Wilsontown Faults respectively, These data are supplemented by lines recorded using quarry-blast sources, Two profiles trend east-west across the Bathgate anomaly (Sola north and south), A third profile (MAVIS III) trends north-south across the Lothian oil-shaIe fieIds. Three refractors are recognised defining four crustal layers, The first layer has velocities between 3.0 and 5.0 km/s and extends to depths between 0.5 and 3.0 km, This layer is interpreted as the Carboniferous and Upper Old Red Sandstone, The second layer has velocities between 5.3 and 5.9 km/s and occurs between depths of 0.5 to 3.0 km and 4.0 to 6.0 km, This layer is interpreted as the Lower Old Red Sandstone and Lower Palaeozoic, Therefore, the topmost refractor is interpreted as the unconformity between the Upper and Lower Old Red Sandstone mapped at the surface in the Midland Valley, The third layer occurs at between 4.0 to 6.0 and 7.0 and 8.5 km depth with velocities between 6.0 and 6.1 km/s, This layer is interpreted as crystalline basement. The deepest layer occurs at depths greater than 7.0 to 8.5 km and is interpreted as a higher velocity crystalline basement, The interface between the two basement layers may mark the transition from amphibolite to granulite facies metamorphism. Velocity data from layer 1 show Poisson's ratio for this layer to be 0.29 ± 0.06, and the ratio of horizontal to vertical P-wave velocity to be 1.15 +0.12 -0.15. Both values are consistent with the sands tone/Iimestone/shaIe sequence mapped at the surface. The Bathgate gravity anomaly was modelled within the constraints imposed by the seismic data. The results of earlier magnetic modelIing were confirmed, with deep and shallow end members of a series of possible solutions being modelled. The shallow model satisfies the anomaly with a thickened sequence of Carboniferous lavas within the seismic layer 1. The deep model is for a gabbroic intrusion within the crystalline basement extending from 10 to 15 km depth. Gravity modelIing across the OchiI Fault show this fracture to dip to the south. ReIief on the Old Red Sandstone unconformity is found to mirror structures mapped at the surface, whilst the underlying basement is virtually planar. A detachment is postulated between these horizons with the surface structures forming by thin-skinned tectonic processes. The detachment horizon is probably either within the Lower Palaeozoic sequence of seismic layer 2, or at the ductiIity contrast to be anticipated at the interface between Lower Palaeozoic and crystalline rocks. A detailed structural interpretation of the Lothian oil-shale fields suggests there may be several levels of such detachment with the Midland Valley. A model is presented for the development of the Ochil fault as an en echelon fracture resulting from reactivation of a basement lineament

The use of pXRF for light element geochemical analysis: a review of hardware design limitations and an empirical investigation of air, vacuum, helium flush and detector window technologies

Light element data are required for robust and accurate lithogeochemical interpretations and are important components in the study of hydrothermal alteration and mineralization processes. In this contribution we review the latest available portable energy dispersive X-Ray Fluorescence (pXRF) technologies exclusively in the context of light element analysis, with focus on the acquisition of data for Na, Mg, Al and Si. We discuss pXRF hardware design limitations, quantify variables that attenuate X-ray energies through numerical modelling, including common pXRF configurations, and empirically investigate modern pXRF technologies used to mitigate X-ray attenuation and improve light element analysis. The void between the sample and detector is a key issue regarding the success of pXRF light element analysis. Dry-air (normal conditions), vacuum purge and helium flush systems are evaluated. Modelled data that use a nominal sample-detector void of 10 mm show that using helium in lieu of air improves X-ray transmission effectiveness from ≈2% to ≈99% for Na and ≈10% to ≈100% for Mg. Modelled detector window data show that using a graphene detector window in lieu of a traditional beryllium detector window improves X-ray transmission effectiveness for Na from ≈38% to ≈64% and ≈57% to ≈77% for Mg. Progressive X-ray transmission effectiveness equates to ≈63% Na and ≈76% Mg when using a helium-graphene pXRF configuration v. ≈1% for Na and ≈6% Mg when using a traditional in-air beryllium pXRF arrangement (i.e. without sample or X-ray entrance window media). Empirically determined improvements of the resolved signal are more modest than those of modelled X-ray transmission effectiveness data. Instrument noise, spectral overlaps and random counting errors are unavoidable and inherent with the limitations of modern detector technologies. However, the employment of helium with graphene detector window technology allows very precise data to be obtained at significantly shorter scan times (i.e. 20 s, instead of the traditional 60–180 s, i.e. 3–9 times faster): a scan time of 20 s can achieve a precision of ≈18% @ ≈0.4% Na and ≈8% @ ≈0.3% Mg for elemental interference-free samples. Precision will improve with increasing analyte concentration

Learning and Expertise in Mineral Exploration Decision-Making: An Ecological Dynamics Perspective

The declining discovery rate of world-class ore deposits represents a significant obstacle to future global metal supply. To counter this trend, there is a requirement for mineral exploration to be conducted in increasingly challenging, uncertain, and remote environments. Faced with such increases in task and environmental complexity, an important concern in exploratory activities are the behavioural challenges of information perception, interpretation and decision-making by geoscientists tasked with discovering the next generation of deposits. Here, we outline the Dynamics model, as a diagnostic tool for situational analysis and a guiding framework for designing working and training environments to maximise exploration performance. The Dynamics model is based on an Ecological Dynamics framework, combining Newell’s Constraints model, Self Determination Theory, and including feedback loops to define an autopoietic system. By implication of the Dynamics model, several areas are highlighted as being important for improving the quality of exploration. These include: (a) provision of needs-supportive working environments that promote appropriate degrees of effort, autonomy, creativity and technical risk-taking; (b) an understanding of the wider motivational context, particularly the influence of tradition, culture and other ‘forms of life’ that constrain behaviour; (c) relevant goal-setting in the design of corporate strategies to direct exploration activities; and (d) development of practical, representative scenario-based training interventions, providing effective learning environments, with digital media and technologies presenting decision-outcome feedback, to assist in the development of expertise in mineral exploration targeting

Stirring dangerous waters: dilemmas for critical participatory research with young people

This article explores dilemmas of critical, participatory research with young people, illustrating examples from research in the UK and the US and highlighting issues of access, participation, dissemination and the misuse of findings.The authors stress the need for new field strategies including more participatory approaches and attention to transgression of power through research. © 2009 BSA Publications Ltd

Seismic structure of the Yilgarn Craton, Western Australia

The deep crustal and upper mantle structure of the Yilgarn Craton is investigated in this study using receiver-function analysis of teleseismic earthquake records from temporary stations. Two lines of stations were deployed, the main transect ran betwee

Nonlocal problems for elliptic equations in dihedral angles and the Green formula

SIGLEAvailable from TIB Hannover: ZS 808(247) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman