CENTA NERC DTP and BGS CASE PhD geology student.
My PhD project is entitled: 'Crust-mantle exchange in orogenic lower crust: the record in high temperature eclogites'.
My project aims to unravel the evolution of the Himalayan lower continental crust, in north-west Bhutan, during the continental collision between India and Asia. With no means for direct sampling of the lower orogenic crust, we are reliant on geophysical data and the mineralogical, geochemical and gechronological evidence encoded in rocks that have been exhumed to the surface. The project investigates role of deep crustal burial and exhumation on the exchange of various elements and the differentiation and evolution of the continental crust. These aims will be achieved by combining detailed observations of metamorphic petrology with geochronological and geochemical data.
The metamorphic history of a suite of high-pressure, high-temperature rocks collected from NW-Bhutan challenges some of our current tectonic models for the evolution of the Himalayan crust. These ‘hot’ eclogites, along with several other east Himalayan examples, record a history that shows the Indian crust experienced deep burial during continental collision. Young eclogitic ages of 13 Ma (U-Pb zircon) found in NW-Bhutan cannot be explained by current Himalayan exhumation models and neccessitate an alternate mechanism to explain the rapid crustal exhumation. Thermodynamic modelling of rock reactions and geochronological work, linking age to metamorphic stage, will be used to quantify the rates and timescales of rapid exhumation, in order to elucidate possible tectonic mechanisms.
The origins of the mafic boudins that host the evidence for eclogite metamorphism is currently a topic of debate. Some studies suggest that they could be Himalayan age mantle melts that were intruded into the base of the orogenic crust. It is critical to test this hypothesis, because the addition of mantle material to the lower crust during orogenesis (considering that most orogens are assumed to be closed systems) could have broad implications on the geochemical and thermal evolution of the lower crust. Sm-Nd and Lu-Hf dating of garnets in the boudins will be used to ascertain wether garnet growth occured early on the prograde path (i.e. pre-Himalayan protolith), or at peak pressure conditions (i.e. Himalayan age intrusion).
The project combines a number of observational, analytical and modelling methods to pursue these aims, including: geological fieldwork, metamorphic petrology, collection of mineral major element data (electron-microprobe analysis, EMPA), collection of in-situ mineral trace element (LA-ICP-MS), XRF bulk rock data collection, U-Pb monazite and zircon dating, Sm-Nd and Lu-Hf garnet dating and thermodynamical modelling using THERMOCALC and Perple_X.
I was recently involved in the STEM Matters 2016 lectures in December 2016, where I was invited to be a speaker and Q&A panel member for the programme of school lectures, that was jointly organised by the Open University and the Denbigh Teaching School Alliance.
The recording of the live webcast of my talk entitled 'Mountains under the microscope: unlocking the secrets of the Himalaya' can be found here.
Photo credit: Kate Bradshaw
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