Outcrop-scale manifestations of reactivation during multiple superimposed rifting and basin inversion events: the Devonian Orcadian Basin, northern Scotland

The Devonian Orcadian Basin in Scotland hosts extensional fault systems assumed to be related to the initial formation of the basin, with only limited post-Devonian inversion and reactivation. However, a recent detailed structural study across Caithness, underpinned by published Re–Os geochronology, shows that three phases of deformation are present. North–south- and NW–SE-trending Group 1 faults are related to Devonian ENE–WSW transtension associated with sinistral shear along the Great Glen Fault during the formation of the Orcadian Basin. Metre- to kilometre-scale north–south-trending Group 2 folds and thrusts are developed close to earlier sub-basin-bounding faults and reflect late Carboniferous–early Permian east–west inversion associated with dextral reactivation of the Great Glen Fault. The dominant Group 3 structures are dextral oblique NE–SW-trending and sinistral east–west-trending faults with widespread syndeformational carbonate mineralization (± pyrite and bitumen) and are dated using Re–Os geochronology as Permian (c. 267 Ma). Regional Permian NW–SE extension related to the development of the offshore West Orkney Basin was superimposed over pre-existing fault networks, leading to local oblique reactivation of Group 1 faults in complex localized zones of transtensional folding, faulting and inversion. The structural complexity in surface outcrops onshore therefore reflects both the local reactivation of pre-existing faults and the superimposition of obliquely oriented rifting episodes during basin development in the adjacent offshore areas

A revised age, structural model and origin for the North Pennine Orefield in the Alston Block, northern England: intrusion (Whin Sill)-related base metal (Cu–Pb–Zn–F) mineralization

Mineralization and associated fluid migration events in the c. 1500 km2 North Pennine Orefield (NPO) are known to be associated with tectonic activity, but the age of these tectonic events and origins of the base metal sulfide mineralization remain unresolved. New fieldwork in the Alston Block shows that mineralization post-dates a weakly developed phase of north–south shortening consistent with far-field Variscan basin inversion during the late Carboniferous. New observations of field relationships, coupled with microstructural observations and stress inversion analyses, together with Re–Os sulfide geochronology show that the vein-hosted mineralization (apart from barium minerals) was synchronous with a phase of north–south extension and east–west shortening coeval with emplacement of the Whin Sill (c. 297–294 Ma). Thus the development of the NPO was related to an early Permian regional phase of transtensional deformation, mantle-sourced hydrothermal mineralization and magmatism in northern Britain. Previously proposed Mississippi Valley Type models, or alternatives relating mineralization to the influx of Mesozoic brines, can no longer be applied to the development of the NPO in the Alston Block. Our findings also mean that existing models for equivalent base metal sulfide fields worldwide (e.g. Zn–Pb districts of Silesia, Poland and Tennessee, USA) may need to be reassessed

A geological explanation for intraplate earthquake clustering complexity: the zeolite-bearing fault/fracture networks in the Adamello Massif (Southern Italian Alps)

Interconnected networks of faults and veins filled with hydrothermal minerals such as zeolite are widespread in many orogenic terrains. These fractures commonly form at relatively low temperatures (e.g. < 200°C) late in the tectonic history and represent significant phases of fluid flow and mineralisation during exhumation. Zeolite-bearing fractures spatially associated with the Gole Larghe Fault Zone in the Southern Italian Alps are preserved along an interconnected network of variably orientated pre-existing structures. They show evidence of repeated episodes of hydraulic tensile fracturing and small magnitude (total offsets <5m) shear displacements. We use geological observations and Coulomb stress modelling to propose that repeated seismogenic rupturing of larger offset faults led to local stress transfer and reactivation of widely distributed smaller pre-existing structures in the wall rocks. The differing orientations of the pre-existing features within what is assumed to have been a single regional stress field led to the simultaneous development of reverse, strike-slip and extensional faults. The kinematic diversity and cyclic nature of the hydraulically-assisted deformation suggest that the mineralised fracture systems represent a geological manifestation of intraplate micro-earthquake clusters associated with fluid migration episodes in the upper crust. Our observations highlight the role of crustal fluids and structural reactivation during earthquakes

New structural and Re–Os geochronological evidence constraining the age of faulting and associated mineralization in the Devonian Orcadian Basin, Scotland

The Devonian Orcadian Basin in northern Scotland belongs to a regionally linked system of post-Caledonian continental basins extending northwards to western Norway and eastern Greenland. Extensional fault systems that cut the Orcadian Basin sequences are commonly assumed to be Devonian, with some limited inversion and reactivation proposed during the Carboniferous and later times. We present a detailed structural study of the regionally recognized fault systems exposed in the Dounreay area of Caithness, which host significant amounts of authigenic mineralization (carbonate, base metal sulphides, bitumen). Structural and microstructural analyses combined with Re–Os geochronology have been used to date syndeformational fault infills (pyrite) suggesting that faulting, brecciation and fluid flow events are likely to have occurred during the Permian (267.5 ± 3.4 [3.5] Ma). Stress inversion of fault slickenline data associated with mineralization suggest NW–SE regional rifting, an episode also recognized farther west in Sutherland. Thus a dominant set of Permian age brittle faults is now recognized along the entire north coast of Scotland, forming part of the regional-scale North Coast Transfer Zone located on the southern margin of the offshore West Orkney Basin

The enigma of evaluation: Benefits, costs and risks of IT in Australian small-medium-sized enterprises

The evaluation of information technology (IT) is fraught with misconception and there is a lack of understanding of appropriate IT evaluation methods and techniques. The benefits, costs and risks of IT need to be identified, managed, and controlled if businesses are to derive value from their investments. This paper presents findings from an exploratory study that used a questionnaire survey to determine the benefits, costs and risks of IT investments from 130 small-to-medium-sized enterprises (SMEs) in Australia. The analysis revealed that organizations from different industry sectors significantly differ in the amount they invest in IT but that firm size (in terms of turnover and number of employees) does not influence IT investment levels. Second, strategic benefits vary across different industry sectors. Third, the way employees adapt to change as a result of IT implementation depends on the size of the organization. Based upon the findings, a series of benchmark metrics for benefits, costs, and risks of IT are presented. It is posited that these can serve as a reference point for initiating a quality evaluation cycle in which benchmarking forms an integral component of the strategic process

Assessment, disability, student engagement and responses to intervention

Assessment is central to the provision of meaningful and productive learning experiences for all students. The majority of students in today’s classroom benefit from core instruction; however, for a small percentage of students with a disability, learning requires more intensive instruction. It is this cohort of learners that we consider in this chapter. While the needs of these learners are diverse, they have in common some teaching and learning challenges that have direct implications for assessment practices. We consider three major challenges: (1) the various learning priorities for students in need of intensive instruction, and how to maximise the connection between current and targeted skills and knowledge; (2) how to measure change through skill or knowledge acquisition when the rate and magnitude of change may be achieved in small increments; and (3) how to determine whether change that does occur is attributable to our teaching, and what to do when teaching is not effective in achieving change. In the absence of this information, there is a serious risk that instruction will be less than effective, will lack social validity and that learners will fail to make progress and achieve positive learning outcomes. Within the context of a cycle typical of intensive instruction, we examine how assessment can play a key role in enhancing and facilitating teaching and learning in the classroom by addressing these three major challenges. We also review the practical challenges that teachers in regular classrooms face in utilising systematic assessment and programming strategies to meet the needs of all the students in their classrooms