ORCID Profile
0000-0002-5270-3985
Current Organisation
University of St Andrews
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
Publisher: Informa UK Limited
Date: 21-03-2022
Publisher: Wiley
Date: 26-09-2007
Publisher: Wiley
Date: 16-09-2008
Publisher: Geological Society of America
Date: 16-02-2023
DOI: 10.1130/B36332.1
Abstract: Metamorphic core complexes are classically interpreted to have formed during crustal extension, although many also occur in compressional environments. New U−(Th)−Pb allanite and xenotime geochronologic data from the structurally highest Zas Unit (Cycladic Blueschist Unit) of the Naxos metamorphic core complex, Greece, integrated with pressure−temperature−time (P−T−t) histories, are incorporated into a thermal model to test the role of crustal thickening and extension in forming metamorphic core complexes. Metamorphism on Naxos is diachronous, with peak metamorphic conditions propagating down structural section over a ∼30−35 m.y. period, from ca. 50 Ma to 15 Ma. At the highest structural level, the Zas Unit records blueschist-facies metamorphism (∼14.5−19 kbar, 470−570 °C) at ca. 50 Ma, during northeast-directed subduction of the Adriatic continental margin. The Zas Unit was subsequently extruded toward the SW and thrust over more proximal continental margin and basement rocks (Koronos and Core units). This contractional episode resulted in crustal thickening and Barrovian metamorphism from ca. 40 Ma and reached peak kyanite-sillimanite−grade conditions of ∼10−5 kbar and 600−730 °C at 20−15 Ma. Model P−T−t paths, assuming conductive relaxation of isotherms following overthrusting, are consistent with the clockwise P−T−t evolution. In contrast, extension results in exhumation and cooling of the crust, which is inconsistent with key components of the thermal evolution. Barrovian metamorphism on Naxos is therefore interpreted to have resulted from crustal thickening over a ∼30−35 m.y. time period prior to extension, normal faulting, and rapid exhumation after a thermal climax at ca. 15 Ma.
Publisher: Wiley
Date: 07-05-2007
Publisher: Wiley
Date: 2002
Publisher: Elsevier BV
Date: 2013
Publisher: Medknow
Date: 2017
Abstract: Epidemiological studies on the extent of the interaction and/or influence of stroke severity on clinical outcomes are important. The aim of the present study was to investigate the putative (and degree of) impact of initial stroke severity in predicting the overall functional outcome, in-hospital placement, and mortality in acute ischemic stroke (AIS) in comparison with age, admission to the stroke unit and thrombolytic treatment. The John Hunter Hospital acute stroke register was used to collect a retrospective cohort of AIS patients being assessed for reperfusion therapy and admitted between January 2006 and December 2013. Univariate and multivariate logistic regression and receiver operating characteristics analyses were used to assess associations with functional outcome, in-hospital placement, and mortality at 90 days. 608 AIS patients with complete datasets were included in the study. On univariate analysis, initial stroke severity showed the strongest independent association to the risk of death within 90 days (Odds ratio (OR) =1.15 P < 0.001 95% confidence interval (CI) = [1.11, 1.18]) age was a less significant independent influence (OR = 1.02 P = 0.049 95% CI = [1.00, 1.03]). Multivariate logistic regression analysis demonstrated that initial stroke severity independently predicted the 90 day mortality (OR = 1.16 95% CI = [1.12, 1.2] P < 0.0001) and unfavorable outcome (OR = 1.16 95% CI = [1.13, 1.2] P < 0.0001). Higher National Institute of Health Stroke Scale at admission was significantly associated with longer in-hospital placement (P < 0.0001). In this acute stroke cohort, initial stroke severity had a major impact on the likelihood of death following an AIS and appears to be the dominant influence on the overall stroke outcome and in-hospital placement.
Publisher: Wiley
Date: 12-08-2016
DOI: 10.1111/JMG.12212
Publisher: Oxford University Press (OUP)
Date: 07-2007
Publisher: Elsevier BV
Date: 04-2021
Publisher: American Geophysical Union (AGU)
Date: 04-2019
DOI: 10.1029/2018GC008079
Publisher: Wiley
Date: 11-1994
Publisher: Wiley
Date: 21-07-2007
Publisher: Wiley
Date: 25-07-2014
DOI: 10.1111/JMG.12095
Publisher: Oxford University Press (OUP)
Date: 27-07-2012
Publisher: Wiley
Date: 12-01-2018
DOI: 10.1111/JMG.12298
Publisher: Wiley
Date: 31-08-2016
DOI: 10.1111/JMG.12211
Publisher: Geological Society of America
Date: 16-02-2023
DOI: 10.1130/B36489.1
Abstract: Granitoids of varying mineralogy are exposed on the Cycladic islands of Greece they include both hornblende-bearing I-type granites and garnet ± muscovite−bearing S-type granites, suggesting heterogeneous magma sources. In this contribution, we present new field observations, major- and trace-element geochemistry, Sr-Nd isotopes, and U-Pb geochronology of granitoids from Tinos, Delos, and Naxos that provide insight into these magma sources, along with the timing of adjacent extensional structures. I-type (biotite and hornblende-biotite) granites have initial 87Sr/86Sr = 0.70956−0.71065 and εNd(t) = −6.3 to −9.3, and S-type (garnet ± tourmaline-muscovite) leucogranites have overlapping initial εNd(t) = −7.5 to −10.1, with initial 87Sr/86Sr values overlapping as well as extending to higher values (0.70621−0.73180). These isotope signatures are comparable to those of the Variscan-age Cycladic basement, but not the Hellenic arc. We suggest that both I- and S-type granites were derived via crustal anatexis of variable sources, dominantly metaigneous and metasedimentary, respectively, during the climax of Barrovian metamorphism between ca. 17 and 12 Ma, and critically, they are not related to the Hellenic subduction zone. I-type granitoids were likely derived from dehydration melting of igneous Variscan- or Cadomian-aged basement protoliths, whereas S-type leucogranites formed by muscovite dehydration melting of sedimentary protoliths. Top-to-the-(N)NE shear zones on Naxos and Tinos were active from ca. 20 to 15 Ma and are folded and cut by later low- and high-angle normal faults. S-type leucogranites at Livada Bay, Tinos, dated at ca. 14 Ma, are cut by domino-style normal faults, placing a maximum age on the timing of extension. This is similar to ca. 15−14 Ma dates from NNE-SSW horizontally boudinaged S-type granites on Naxos. We propose that the concurrent intrusion of both I- and S-type granitoids with the onset of normal faulting marked the transition from an overall compressional to an extensional stress field associated with orogenic collapse at ca. 15 Ma.
Publisher: Wiley
Date: 06-12-2007
Publisher: Wiley
Date: 04-07-2006
Publisher: Mineralogical Association of Canada
Date: 02-2005
Publisher: Elsevier BV
Date: 08-2013
Publisher: Wiley
Date: 10-03-2008
Publisher: Wiley
Date: 20-05-2010
Publisher: Oxford University Press (OUP)
Date: 02-2020
DOI: 10.1093/PETROLOGY/EGAA029
Abstract: The evolution of crustal magmatic systems is incompletely understood, as most studies are limited either by their temporal or spatial resolution. Exposed plutonic rocks represent the final stage of a long-term evolution punctuated by several magmatic events with different chemistry and generated under different mechanical conditions. Although the final state can be easily described, the nature of each magmatic pulse is more difficult to retrieve. This study presents a new method to investigate the compositional evolution of plutonic systems while considering thermal and mechanical processes. A thermomechanical code (MVEP2) extended by a semi-analytical dike/sill formation algorithm, is combined with a thermodynamic modelling approach (Perple_X) to investigate the feedback between petrology and mechanics. Melt is extracted to form dikes while depleting the source region. The evolving rock compositions are tracked on markers using a different phase diagram for each discrete bulk-rock composition. The rock compositional evolution is thus tracked with a high precision by means of a database with more than 58 000 phase diagrams. This database describes how density, melt fraction, chemical composition of melt and solid fractions and mineralogical assemblages change over crustal to uppermost mantle P–T conditions for a large range of rock compositions. Each bulk rock composition is composed of the 10 major oxides (SiO2–TiO2–Al2O3–Cr2O3–MgO–FeO–CaO–Na2O–K2O–H2O) including an oxygen buffer. The combined modelling approach is applied to study the chemical evolution of the crust during arc magmatism and related melt extraction and magma mixing processes. Basaltic sills are periodically injected into the crust to model heat/magma influx from the mantle. We find that accumulated sills turn into long-lived mush chambers when using a lower rock cohesion or assuming a higher intrusion depth. Associated partial melting of crustal host rocks occurs around densely distributed dikes and sills. High silica rocks (e.g. granites) are generated by partial melting of the host rocks, melt segregation within dikes, and from fractional crystallization of basalts. Although the volume of these rocks is relatively small in our models compared to rocks with a mafic to intermediate composition, they provide important information about the processes of magma differentiation within arc continental crust.
Publisher: Elsevier BV
Date: 12-2016
Publisher: Wiley
Date: 08-03-2006
Publisher: Wiley
Date: 06-2003
Publisher: Wiley
Date: 06-2003
Publisher: Wiley
Date: 25-08-2005
Publisher: Elsevier BV
Date: 03-2019
Publisher: Wiley
Date: 08-2004
Publisher: Elsevier BV
Date: 03-2014
Publisher: Wiley
Date: 06-04-2016
DOI: 10.1118/1.4944871
Abstract: The feasibility of radiation therapy treatment planning using substitute computed tomography (sCT) generated from magnetic resonance images (MRIs) has been demonstrated by a number of research groups. One challenge with an MRI-alone workflow is the accurate identification of intraprostatic gold fiducial markers, which are frequently used for prostate localization prior to each dose delivery fraction. This paper investigates a template-matching approach for the detection of these seeds in MRI. Two different gradient echo T1 and T2* weighted MRI sequences were acquired from fifteen prostate cancer patients and evaluated for seed detection. For training, seed templates from manual contours were selected in a spectral clustering manifold learning framework. This aids in clustering "similar" gold fiducial markers together. The marker with the minimum distance to a cluster centroid was selected as the representative template of that cluster during training. During testing, Gaussian mixture modeling followed by a Markovian model was used in automatic detection of the probable candidates. The probable candidates were rigidly registered to the templates identified from spectral clustering, and a similarity metric is computed for ranking and detection. A fiducial detection accuracy of 95% was obtained compared to manual observations. Expert radiation therapist observers were able to correctly identify all three implanted seeds on 11 of the 15 scans (the proposed method correctly identified all seeds on 10 of the 15). An novel automatic framework for gold fiducial marker detection in MRI is proposed and evaluated with detection accuracies comparable to manual detection. When radiation therapists are unable to determine the seed location in MRI, they refer back to the planning CT (only available in the existing clinical framework) similarly, an automatic quality control is built into the automatic software to ensure that all gold seeds are either correctly detected or a warning is raised for further manual intervention.
Publisher: Mineralogical Society of America
Date: 25-07-2011
Publisher: Mineralogical Society of America
Date: 02-2018
Publisher: Wiley
Date: 17-09-2012
DOI: 10.1111/JMG.12001
Publisher: Wiley
Date: 02-2001
Publisher: Wiley
Date: 28-12-2012
Publisher: Wiley
Date: 14-05-2012
Publisher: Springer Science and Business Media LLC
Date: 02-01-2019
DOI: 10.1007/S00586-018-05868-0
Abstract: Lateral atlantoaxial (LAA) joint meniscoid composition may have clinical significance in patients following neck trauma. However, the existing method of radiologically assessing meniscoid composition has an inherent element of subjectivity, which could contribute to measurement variability. The present study sought to investigate the accuracy of two-point Dixon fat/water separation MRI as a quantitative assessment of LAA joint meniscoid composition. Sixteen LAA joint meniscoids were excised from four cadavers (mean [SD] age 79.5 [3.7] years one female) following cervical spine MRI (two-point Dixon, T1-weighted VIBE and T2-weighted SPACE sequences). Composition of LAA joint meniscoids was undertaken by (1) histological examination by light microscopy, (2) calculation of fat fraction by Dixon MRI (both in-phase/opposed-phase and fat/water methods), and (3) the existing method of considering VIBE and SPACE signal intensities. Analysis was performed using the kappa statistic with linear weighting. Microscopy revealed three, five, and eight meniscoids to be composed of adipose, fibroadipose, and fibrous tissues, respectively. Dixon sequence MRI classified 11 of these meniscoids correctly, with 'substantial' level of agreement (In-phase/Opp-phase kappa statistic = 0.78 [95% CI 0.38, 1.17] fat/water kappa statistic = 0.72 [95% CI 0.32, 1.11]). Level of agreement between microscopy and the VIBE and SPACE method was 'slight' (kappa statistic = 0.02 [95% CI - 0.34, 0.38]). Findings suggest that Dixon fat/water separation MRI may have superior utility in the assessment of LAA joint meniscoid composition than the existing method of considering VIBE and SPACE signal intensities. These slides can be retrieved under Electronic Supplementary Material.
Publisher: Cambridge University Press (CUP)
Date: 05-2000
DOI: 10.1017/S0016756800004027
Abstract: Layered orthogneisses of the Oygarden Islands preserve evidence for four high-grade deformation events (D 1 to D 4 ). Archaean D 1 and D 2 structures are only patchily preserved due to extensive recrystallization during D 3 and D 4 , which represent effects of the c . 1000 Ma Rayner Structural Episode. Ductile thrusting at middle to lower crustal levels occurred during D 3 , which is separated into two mutually cross-cutting phases based on structural geometry the two phases represent changes in finite strain that developed during progressive deformation. East-directed transport during D 3a developed subhorizontal thrusts that contain co-axial, east-trending F 3a folds and L 3a lineations. Buckling as a consequence of constriction in thrust duplexes developed upright F 3b folds coaxial to F 3a folds, and steeply south-dipping D 3b shear zones. Garnet–clinopyroxene- and garnet–orthopyroxene-bearing assemblages in mafic lithologies, and garnet–sillimanite-bearing assemblages in pelitic lithologies reflect D 3 conditions of P =9 kbar and T =800–850 °C. The well-exposed D 3 duplex structures indicate that shortening of the lower crust may be accommodated by extensive strain partitioning to develop contemporary kilometre-scale thrust stacking and ductile flow.
Publisher: Wiley
Date: 02-05-2019
DOI: 10.1111/JMG.12484
Abstract: This essay in honour of Mike Brown addresses aspects of chemical equilibrium and equilibration in rocks, with a focus on the role that chemical potentials play. Chemical equilibrium is achieved by diffusive flattening of chemical potential gradients. The idea of equilibration volume is developed, and the way equilibration volumes may evolve along a pressure–temperature path is discussed. The effect of the environment of an equilibration volume is key to understanding the evolution of the equilibration volume with changing conditions. The likely behaviour of equilibration volumes is used to suggest why preservation of equilibrium mineral assemblages and mineral compositions from metamorphism tends to occur. This line of logic then provides the conceptual support to conventional equilibrium thermodynamic approaches to studying rocks, using, for ex le, thermobarometry and pseudosections.
Publisher: Elsevier BV
Date: 2018
Publisher: Wiley
Date: 10-2011
Publisher: Wiley
Date: 14-05-2010
Publisher: Wiley
Date: 16-09-2008
Publisher: Wiley
Date: 04-2010
Publisher: Elsevier BV
Date: 09-2016
Publisher: Wiley
Date: 05-1998
Publisher: Wiley
Date: 19-03-2019
DOI: 10.1111/JMG.12478
Abstract: The development of thermodynamic models for tonalitic melt and the updated clinopyroxene and hibole models now allow the use of phase equilibrium modelling to estimate P–T conditions and melt production for anatectic mafic and intermediate rock types at high‐ T conditions. The Permian mid‐lower crustal section of the Ivrea Zone preserves a metamorphic field gradient from mid hibolite facies to granulite facies, and thus records the onset of partial melting in metabasic rocks. Interlayered metabasic and metapelitic rocks allows the direct comparison of P–T estimates and partial melting between both rock types with the same metamorphic evolution. Pseudosections for metabasic compositions calculated in the Na 2 O–CaO–K 2 O–FeO–MgO–Al 2 O 3 –SiO 2 –H 2 O–TiO 2 –O ( NCKFMASHTO ) system are presented and compared with those of metapelitic rocks calculated with consistent end‐member data and a–x models. The results presented in this study show that P–T conditions obtained by phase equilibria modelling of both metabasic and metapelitic rocks give consistent results within uncertainties, allowing integration of results obtained for both rock types. In combination, the calculations for both metabasic and metapelitic rocks allows an updated and more precisely constrained metamorphic field gradient for Val Strona di Omegna to be defined. The new field gradient has a slightly lower d P / d T which is in better agreement with the onset of crustal thinning of the Adriatic margin during the Permian inferred in recent studies.
Publisher: Elsevier BV
Date: 12-2020
Publisher: Elsevier BV
Date: 02-2014
Publisher: Wiley
Date: 22-04-2018
DOI: 10.1111/JMG.12311
Publisher: Oxford University Press (OUP)
Date: 10-1997
Publisher: Elsevier BV
Date: 05-2011
Publisher: Oxford University Press (OUP)
Date: 11-2003
Publisher: Geological Society of America
Date: 04-04-2016
DOI: 10.1130/G37595.1
Publisher: Springer Science and Business Media LLC
Date: 21-11-2014
DOI: 10.1007/S13246-014-0311-8
Abstract: Routine quality assurance (QA) is necessary and essential to ensure MR scanner performance. This includes geometric distortion, slice positioning and thickness accuracy, high contrast spatial resolution, intensity uniformity, ghosting artefact and low contrast object detectability. However, this manual process can be very time consuming. This paper describes the development and validation of an open source tool to automate the MR QA process, which aims to increase physicist efficiency, and improve the consistency of QA results by reducing human error. The OSAQA software was developed in Matlab and the source code is available for download from saqa-project/. During program execution QA results are logged for immediate review and are also exported to a spreadsheet for long-term machine performance reporting. For the automatic contrast QA test, a user specific contrast evaluation was designed to improve accuracy for in iduals on different display monitors. American College of Radiology QA images were acquired over a period of 2 months to compare manual QA and the results from the proposed OSAQA software. OSAQA was found to significantly reduce the QA time from approximately 45 to 2 min. Both the manual and OSAQA results were found to agree with regard to the recommended criteria and the differences were insignificant compared to the criteria. The intensity homogeneity filter is necessary to obtain an image with acceptable quality and at the same time keeps the high contrast spatial resolution within the recommended criterion. The OSAQA tool has been validated on scanners with different field strengths and manufacturers. A number of suggestions have been made to improve both the phantom design and QA protocol in the future.
Publisher: Wiley
Date: 16-09-2008
Publisher: Wiley
Date: 14-01-2008
Publisher: Wiley
Date: 29-07-2002
Publisher: Wiley
Date: 09-2000
Publisher: Wiley
Date: 2011
Publisher: Wiley
Date: 05-2005
Publisher: Wiley
Date: 11-02-2014
DOI: 10.1111/JMG.12070
Publisher: Wiley
Date: 09-07-2008
Publisher: Wiley
Date: 10-02-2014
DOI: 10.1111/JMG.12071
Publisher: Society of Economic Geologists
Date: 05-2007
Publisher: Geological Society of London
Date: 03-2013
DOI: 10.1144/JGS2012-096
Publisher: Wiley
Date: 24-08-2012
Publisher: Wiley
Date: 09-09-2003
Publisher: Geological Society of London
Date: 2011
Publisher: Springer Science and Business Media LLC
Date: 14-12-2016
DOI: 10.1038/NGEO2605
Publisher: Wiley
Date: 21-07-2007
Publisher: Elsevier BV
Date: 09-1993
Publisher: Wiley
Date: 27-01-2014
DOI: 10.1111/JMG.12069
Publisher: Elsevier BV
Date: 05-2011
Publisher: Wiley
Date: 06-08-2018
DOI: 10.1111/JMG.12428
Publisher: Wiley
Date: 24-11-2016
DOI: 10.1111/JMG.12227
Publisher: Wiley
Date: 12-2004
Publisher: Elsevier BV
Date: 06-2017
Publisher: Wiley
Date: 27-09-2005
Publisher: Wiley
Date: 09-1999
Publisher: Elsevier BV
Date: 07-2014
Publisher: Wiley
Date: 15-12-2020
DOI: 10.1111/JMG.12582
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Richard White.