ORCID Profile
0000-0001-9699-2769
Current Organisation
James Cook University
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Publisher: Geological Society of America
Date: 28-06-2016
DOI: 10.1130/G37972.1
Publisher: Informa UK Limited
Date: 04-08-2023
Publisher: Elsevier BV
Date: 12-2020
Publisher: Elsevier BV
Date: 10-2020
Publisher: Geological Society of America
Date: 06-03-2014
DOI: 10.1130/B30817.1
Publisher: Geological Society of America
Date: 30-06-2017
DOI: 10.1130/B31620.1
Publisher: Oxford University Press (OUP)
Date: 2007
Publisher: Elsevier BV
Date: 11-2020
Publisher: Elsevier BV
Date: 09-2020
Publisher: Elsevier BV
Date: 12-2021
Publisher: Elsevier BV
Date: 03-2015
Publisher: Elsevier BV
Date: 03-2008
Publisher: Copernicus GmbH
Date: 03-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-752
Abstract: & & C' shear bands are common structures in ductile shear zones but their development is poorly understood. They occur in rocks with a high mechanical strength contrast so we used numerical models of viscoplastic deformation to study the effect of the proportion of weak phase and the phase strength contrast on C' shear band development. We employed simple shear to a finite strain of 18 in 900 steps and recorded the microstructure, stress and strain distribution at each step. We found that C' shear bands form in models with & #8805 % weak phase when there is a moderate or high phase strength contrast, and they occur in all models with weak phase proportions & #8805 %. Contrary to previous research, we find that C' shear bands form when layers of weak phase parallel to the shear zone boundary rotate forwards. This occurs due to mechanical instabilities that are a result of heterogeneous distributions of stress and strain rate. C' shear bands form on planes of low strain rate and stress, not in sites of maximum strain rate as has previously been suggested. C' shear bands are ephemeral and they either rotate backwards to the C plane once they are inactive or rotate into the field of shortening and thicken to form X- and triangle- shaped structures.& &
Publisher: Elsevier BV
Date: 12-2020
Publisher: Wiley
Date: 24-11-2021
DOI: 10.1111/JMG.12641
Abstract: Deciphering the tectono‐metamorphic evolution of Precambrian terranes can be difficult due to reworking by later superimposed events. Whole‐rock elemental and isotopic geochemistry and zircon U–Pb geochronology are often employed in those studies, but these approaches are often not sensitive to the presence of multiple events and medium‐grade metamorphic episodes. The Rio Apa Terrane (RAT), an allochthonous fragment of the Amazonian Craton, is a crustal block with a well‐characterized crustal evolution but with no detailed thermal constraints for its tectono‐metamorphic evolution. In contrast to previous studies, we show the existence of four tectono‐metamorphic events at c . 1,780, c . 1,625, c . 1,420–1,340, and c . 1,300–1,200 Ma on the basis of apatite, titanite, and rutile U–Pb, in situ white‐mica Rb–Sr, and in situ garnet Lu–Hf geochronology combined with mineral chemistry and phase‐equilibria modelling. The c . 1,780 Ma event is recorded in the basement of the Western domain, representing an extensional event coeval with the development of its Eastern domain in response to the retreat stage of the accretionary system. This is followed by juxtaposition of the Western and Eastern domains along a major crustal boundary at c . 1,625 Ma, which is defined by the magnetic profiles and zircon U–Pb–Hf data across the boundary. The third and fourth events correspond to progressive high‐pressure/medium‐temperature (HP/MT) metamorphism, characterized by an anticlockwise P–T path, suggesting a convergent‐to‐collisional tectonic setting. The RAT was accreted to the adjoining Paraguá Terrane at c . 1,420–1,340 Ma under an isobaric P–T evolution spanning ~530°C to 600°C and ~10.0 kbar. Subsequently, the combined Rio Apa and Paraguá terranes collided with the SW Amazonian Craton at c . 1,300–1,200 Ma, reaching P–T conditions of ~560–580°C and ~10.9–11.7 kbar during crustal thickening. This study reveals for the first time the existence of a HP/MT metamorphic evolution related to the growth of the SW Amazonian Craton as part of an accretionary orogenic system during Rodinia assembly in the Palaeoproterozoic to Mesoproterozoic.
Publisher: Elsevier BV
Date: 07-2015
Publisher: Copernicus GmbH
Date: 04-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-13151
Abstract: & & Deformation of foliated rocks commonly leads to crenulation or micro-folding, with the development of cleavage domains and microlithons. We here consider the effect of mechanical anisotropy due to a crystallographic preferred orientation (CPO) that defines the foliation, for ex le by of alignment of micas. Mechanical anisotropy enhances shear localisation (Ran, et al., 2018 de Riese et al., 2019), resulting in low-strain domains (microlithons) and high-strain shear bands or cleavage domains. We investigate the crenulation patterns that result from moderate strain simple shear deformation, varying the initial orientation of the mechanical anisotropy relative to the shear plane. & & & & & We use the Viscoplastic Full-Field Transform (VPFFT) crystal plasticity code coupled with the modelling platform ELLE (www.elle.ws Llorens et al., 2017) to simulate the deformation of anisotropic single-phase material with an initial given CPO in dextral simple shear in low to medium strain. Deformation is assumed to be accommodated by glide along the basal, prismatic and pyramidal slip systems of a hexagonal model mineral. An approximately transverse anisotropy is achieved by assigning a small critical resolved shear stress to the basal plane. An initially point-maximum CPO at variable angles to the shear plane defines the initial straight foliation at different angles to the shear plane, limiting ourselves to orientations in which the foliation is in the stretching field. The resulting crenulation geometries strongly depend on the orientation of the foliation and we observe four types of localisation behaviour: (1) synthetic shear bands, (2) antithetic shear bands, (3) initial formation of antithetic shear bands and subsequent development of synthetic shear bands, and (4) distributed, approximately shear-margin parallel strain localisation, but no distinct shear bands.& & & & The numerical simulations not only show the evolving strain-rate field, but also the predicted finite strain pattern of existing visible foliations. We show the results for layers parallel to the foliation, but also cases where the visible layering is at an angle to the mechanical anisotropy (e.g. in case of distinct sedimentary layers and a cleavage that controls the mechanical anisotropy). A wide range of crenulation types form as a function of the initial orientation of the visible layering and mechanical anisotropy (comparable to C, C' and C'' shear bands and compressional crenulation cleavage). Most importantly, some of may be highly misleading and may easily be interpreted as indicating the opposite sense of shear.& & & & Reference& & & & de Riese, T., et al. (2019). Shear localisation in anisotropic, non-linear viscous materials that develop a CPO: A numerical study. Journal of Structural Geology, 124, 81-90. DOI: 10.1016/j.jsg.2019.03.006& & & & Llorens, M.-G., et al. (2017). Dynamic recrystallisation during deformation of polycrystalline ice: insights from numerical simulations. Philosophical Transactions of the Royal Society A, Special Issue on Microdynamics of Ice, 375: 20150346. DOI: 10.1098/rsta.2015.0346.& & & & Ran, H., et al. (2018). Time for anisotropy: The significance of mechanical anisotropy for the development of deformation structures. Journal of Structural Geology, 125, 41-47. DOI: 10.1016/j.jsg.2018.04.019& &
Publisher: Copernicus GmbH
Date: 24-09-2020
DOI: 10.5194/ADGEO-53-205-2020
Abstract: Abstract. Diversity and inclusion in the workplace optimise performance through the input of a range of perspectives and approaches that drive innovation and invention. However, gender inequity is prevalent throughout society and females remain underrepresented in geoscience careers. This study provides the current status of gender equity in geosciences throughout Australasia within the context of broader gender equity policy, frameworks and initiatives and suggests additional solutions and opportunities to improve gender equity and the retention of women in the geoscience workforce. At an in idual institutional level in academia, females make up between 23 %–52 % of the total geoscience departmental or school staff in Australia, 26 %–39 % of the total staff in New Zealand, 29 % of total staff at the University of Papua New Guinea and 18 % at the University of the South Pacific. Significant gender imbalance exists at more senior levels, with disproportionately more males than females, a pattern typical of many Science Technology Engineering and Maths (STEM) disciplines. Gender inequity is prevalent within the general membership, committee roles and in award recipients of Australasian geoscience professional associations. Within the Geological Society of Australia and Geoscience Society of New Zealand, only 4 % (n=47) and 18 % (n=161), respectively of past award recipients for national and general awards were female. All past awards considered in this study that are named in honour of a person were named in honour of a man (n=9). In recent years, women-focused networks have begun to play an invaluable role to support the retention and promotion of women in geosciences and provide a supportive mentoring environment to discuss challenges and share advice. The improved visibility of women in the geoscientific community is an ongoing issue that can in part be addressed through the development of public databases of women geoscientists. These provide a list of women geoscientists that encourages and supports the achievement of gender balance of invited talks, job shortlisting and on panels, as well as in the media. This work highlights that more must be done to actively reduce and eliminate sexual harassment and assault in university and field environments. We emphasise that particular efforts are required to make geoscience careers more inclusive and safer, through the establishment of specific codes of conduct for field trips. Shared learning of best practices from evidence-based approaches and innovative solutions will also be of value in creating positive change. Greater engagement from the wider geoscientific community, and society in general, is required for the success of gender equity initiatives. Identified solutions and opportunities must target all levels of education and career development. Additional data in future should be collected to look beyond gender to monitor and assess intersectionality. Improved efforts to understand why women leave STEM careers will help to address the “leaky pipeline” and determine the initiatives that will be most effective in creating long term sustainable change.
Publisher: Elsevier BV
Date: 09-2018
Publisher: Elsevier BV
Date: 12-2022
Publisher: Elsevier BV
Date: 08-2019
No related grants have been discovered for Melanie Finch.