Hybrid phase equilibria modelling with conventional and trace element thermobarometry to assess the P–T evolution of UHT granulites: An example from the Highland Complex, Sri Lanka
Journal of Metamorphic Geology, vol. 39, pp. 209–246
Abstract
Abstract Here we attempt to constrain the P–T evolution of ultrahigh‐temperature granulites using textures coupled with multiple thermobarometric approaches. Sapphirine‐bearing granulites were collected from a quarry in the central part of the Highland Complex of Sri Lanka. Three sapphirine‐bearing domains were selected and petrographically studied. Homogeneous sample domains were thermodynamically modelled using their bulk compositions (forward phase equilibria modelling). One heterogeneous sample from a single domain, composed of irregularly distributed residuum and melt, was also used. The bulk composition of its residual part was calculated using mineral compositions and their respective modes. Equilibrium T–X(Fe2O3) phase diagrams were constructed in the chemical system NCKFMASHTO to estimate the bulk ferric/ferrous iron ratio, and conventional geothermometers (garnet–orthopyroxene and Al in orthopyroxene) were applied. The Ti in zircon trace element thermometer was also applied to calculate peak metamorphic conditions. Modal abundance isopleths of each mineral in equilibrium phase diagrams and textural observations were combined to constrain the retrograde P–T path. Our hybrid approach of forward and inverse phase equilibria modelling and conventional thermobarometric calculations indicate that the sapphirine‐bearing granulites have reached their peak T of 920–940°C at P ~10 kbar under relatively highly oxidizing conditions. Subsequently, the rocks followed a near‐isobaric cooling path down to 890–860°C, prior to near‐isothermal decompression up to 6 kbar. The results highlight the importance of dealing with Fe3+. Multiple thermobarometric approaches on carefully observed mineral textures are required to retrieve the most reliable P–T conditions of HT/UHT mineral assemblages.
Authors 12
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P.L. Dharmapriya corresponding
Affiliation as printed
Department of Geology Faculty of Science University of Peradeniya Peradeniya Sri Lanka
Department of Geology, Faculty of Science, University of Peradeniya, Peradeniya, Sri Lanka
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Sanjeewa P.K. Malaviarachchi corresponding
Affiliation as printed
Department of Geology Faculty of Science University of Peradeniya Peradeniya Sri Lanka
Department of Geology, Faculty of Science, University of Peradeniya, Peradeniya, Sri Lanka
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Affiliation as printed
Department of Earth Sciences ETH Zurich Zurich Switzerland
Department of Earth Sciences, ETH Zurich, Zurich, Switzerland
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Leo M. Kriegsman Aachen Department of Research & Education Naturalis Biodiversity Center Leiden The Netherlands
Naturalis Biodiversity Center · Utrecht University
Affiliation as printed
Department of Earth Sciences University of Utrecht Utrecht The Netherlands
Department of Research & Education Naturalis Biodiversity Center Leiden The Netherlands
Department of Earth Sciences, University of Utrecht, Utrecht, The Netherlands
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Affiliation as printed
Division of Earth Sciences Department of Environmental Changes Faculty of Social and Cultural Studies Kyushu University Fukuoka Japan
Division of Earth Sciences, Department of Environmental Changes, Faculty of Social and Cultural Studies, Kyushu University, Fukuoka, Japan
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Indian Institute of Science Bangalore
Affiliation as printed
Centre for Earth Sciences Indian Institute of Science Bangalore India
Centre for Earth Sciences, Indian Institute of Science, Bangalore, India
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Chinese Academy of Sciences · Institute of Geology and Geophysics
Affiliation as printed
Key Laboratory of Mineral Resources Institute of Geology and Geophysics Chinese Academy of Sciences Beijing China
Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China
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University of Tsukuba · University of Johannesburg
Affiliation as printed
Department of Geology University of Johannesburg Auckland Park South Africa
Faculty of Life and Environmental Sciences University of Tsukuba Ibaraki Japan
Department of Geology, University of Johannesburg, Auckland Park, South Africa
Faculty of Life and Environmental Sciences, University of Tsukuba, Ibaraki, Japan
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Affiliation as printed
Key Laboratory of Continental Dynamics of Northwest University Department of Geology Northwest University Xi’an China
Key Laboratory of Continental Dynamics of Northwest University, Department of Geology, Northwest University, Xi'an, China
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Affiliation as printed
Division of Earth Sciences Department of Environmental Changes Faculty of Social and Cultural Studies Kyushu University Fukuoka Japan
Division of Earth Sciences, Department of Environmental Changes, Faculty of Social and Cultural Studies, Kyushu University, Fukuoka, Japan
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Affiliation as printed
Department of Geology Faculty of Science University of Peradeniya Peradeniya Sri Lanka
Department of Geology, Faculty of Science, University of Peradeniya, Peradeniya, Sri Lanka
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National Institute of Fundamental Studies
Affiliation as printed
National Institute of Fundamental Studies Kandy Sri Lanka
National Institute of Fundamental Studies, Kandy, Sri Lanka
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