Showing papers by "Chris D. Clark published in 2012"
TL;DR: In this paper, the authors reconstruct the demise of the British-Irish Ice Sheet (BIIS) and present palaeo-glaciological maps of retreat stages between 27 and 15 ka BP.
471 citations
TL;DR: The Madurai Block of southern India is rich in granitic orthogneiss, much of which is orthopyroxene-bearing (charnockite) as mentioned in this paper.
153 citations
TL;DR: In this article, the authors used a Geographic Information System (GIS) to produce the best estimate of ice extent during the global Last Glacial Maximum (gLGM) and, to a lesser degree, during earlier phases of glaciation.
69 citations
TL;DR: Garnet grains from an intensely metasomatized mid-crustal shear zone in the Reynolds Range, central Australia, exhibit a diverse assortment of textural and compositional characteristics that provide important insights into the geochemical effects of fluid-rock interaction.
Abstract: Garnet grains from an intensely metasomatized mid-crustal shear zone in the Reynolds Range, central Australia, exhibit a diverse assortment of textural and compositional characteristics that provide important insights into the geochemical effects of fluid–rock interaction. Electron microprobe X-ray maps and major element profiles, in situ secondary ion mass spectrometry oxygen isotope analyses, and U–Pb and Sm–Nd geochronology are used to reconstruct their thermal, temporal and fluid evolution. These techniques reveal a detailed sequence of garnet growth, re-equilibration and dissolution during intracontinental reworking associated with the Ordovician–Carboniferous (450–300 Ma) Alice Springs Orogeny. A euhedral garnet porphyroblast displays bell-shaped major element profiles diagnostic of prograde growth zoning during shear zone burial. Coexisting granulitic garnet porphyroclasts inherited from precursor wall rocks show extensive cation re-equilibration assisted by fracturing and fragmentation. Oxygen isotope variations in the former are inversely correlated with the molar proportion of grossular, suggesting that isotopic fractionation is linked to Ca substitution. The latter generally show close correspondence to the isotopic composition of their precursor, indicating slow intergranular diffusion of O relative to Fe2+, Mg and Mn. Peak metamorphism associated with shearing (∼550 °C; 5.0–6.5 kbar) occurred at c. 360 Ma, followed by rapid exhumation and cooling. Progressive Mn enrichment in rim domains indicates that the retrograde evolution caused partial garnet dissolution. Accompanying intra-mineral porosity production then stimulated limited oxygen isotope exchange between relict granulitic garnet grains and adjacent metasomatic biotite, resulting in increased garnet δ18O values over length scales <200 μm. Spatially restricted oxygen interdiffusion was thus facilitated by increased fluid access to reaction interfaces. The concentration of Ca in channelled fracture networks suggests that its mobility was enhanced by a similar mechanism. In contrast, the intergranular diffusion of Fe2+, Mg and Mn was rock-wide under the same P–T regime, as demonstrated by a lack of local spatial variations in the re-equilibration of these components. The extraction of detailed reaction histories from garnet must therefore take into account the variable length- and time-scales of elemental and isotopic exchange, particularly where the involvement of a fluid phase enhances the possibility of measureable resetting profiles being generated for slowly diffusing components such as Ca and O, even at low ambient temperatures and relatively fast cooling rates.
41 citations
TL;DR: In situ high precision U-Pb analysis of rutile by secondary ion mass spectrometry (SIMS) reveals that instrumental bias for isotope ratios and count rates vary due to crystal orientation Electron backscatter diffraction (EBSD) techniques have been combined with SIMS data to show consistent and systematic crystal orientation effects as mentioned in this paper.
40 citations
TL;DR: In this article, the authors provide a synthesis of subglacial lake types that have been identified or may theoretically exist beneath contemporary or palaeo-ice sheets, and propose diagnostic criteria for identifying palaeoencave-subglacial lakes in the geological record.
40 citations
TL;DR: In this paper, the authors used a laser ablation ICP-MS analysis of trace elements to determine the ages of migmatitic and mylonitic gneisses from the Day Nui Con Voi massif in northern Vietnam.
36 citations
TL;DR: The Vestfold Hills terrane in East Antarctica is a granulite facies terrane that preserves a record of sedimentation, magmatism and metamorphism that differs significantly from the other Archaean terranes exposed in Antarctica.
36 citations
TL;DR: The marine-based Atlantic periphery of the last NW European Ice Sheet experienced significant advances and retreats of its marine sector during its existence as discussed by the authors, and therefore had considerable potentia...
25 citations
TL;DR: In this paper, the authors address what theories, methods and procedures practitioners should adopt in order to resolve ethical problems in service practice and identify several approaches from several approaches identified from the literature.
Abstract: • Summary: This article addresses what theories, methods and procedures practitioners ought to adopt in order to resolve ethical problems in service practice. Several approaches are identified from...
24 citations
TL;DR: In this paper, the integration of zircon U-Pb ages and trace element chemistry with structural and petrologic relations from a range of sample types provides important temporal constraints on the tectono-metamorphic evolution of the southern Parry Sound domain (PSD), Ontario, Canada, and the processes attending development of the underlying Twelve Mile Bay shear zone (TMBSZ).
TL;DR: In this article, the authors presented a total dataset of 8414 moraines, which almost quadrupled the inventory of the Barr and Clark map and the one presented in this paper.
Abstract: Barr and Clark published a series of maps depicting the distribution of end moraines across Far NE Russia. These moraines outlined the former distribution and dimensions of glaciers, and were identified through the analysis of Landsat ETM+ satellite images (15- and 30-m resolution). Now, a number of freely available digital elevation model (DEM) datasets are available, which cover the entire ∼4 million km2 of Far NE Russia. These include the 30-m resolution ASTER GDEM and the 90-m resolution Viewfinder Panorama DEM. Here we use these datasets, in conjunction with Landsat ETM+ images, to complete the process of systematically and comprehensively mapping end moraines. With the aid of the DEMs described above, here we present a total dataset of 8414 moraines, which almost quadruples the inventory of Barr and Clark. This increase in the number of moraines is considered to reflect the utility of the DEMs for mapping glacial landforms. In terms of moraine distribution, the Barr and Clark map and the one present...
TL;DR: The authors argued that, rather than offering any significantly new principles or policies, the drift of the Changing Lives process was mainly to refurnish the discourse in which statutory social work is conducted, shifting that discourse away from a long-standing Scottish concern to promote social welfare on a community basis towards an individualised conception of well-being.
Abstract: In 2004 the then Scottish Executive launched the 21st Century Social Work Review. The review report, Changing Lives, addressed perceived shortcomings in statutory social work services, claiming to offer a fundamental review of the profession. This paper argues that, rather than offering any significantly new principles or policies, the drift of the Changing Lives process was chiefly to refurnish the discourse in which statutory social work is conducted. Specifically it shifts that discourse away from a long-standing Scottish concern to promote social welfare on a community basis towards an individualised conception of well-being. Central to that process is the Review's advocacy of personalisation of services. It is argued therefore that Changing Lives is best understood as an exercise in the ‘problematics of government’—a reassertion of control by reshaping expectations, rather than a substantive reform of services.
16 Jul 2012