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Investigation of parental magma and eruption history of olivine-rich picritic crystal mush near Margi, Troodos ophiolite

Ri Cao^1^ , Lee M. Saper1,2, Leonid. Danyushevsky3, Geoffrey Bromiley1

  • Affiliations: 1 School of GeoSciences, Grant Institute, King's Buildings, University of Edinburgh, Edinburgh, UK, EH9 3FE 2 Division of Geological and Planetary Sciences, Caltech, Pasadena, USA 3 Friendly Solutions, Australia      \email: r.cao-4@sms.ed.ac.uk 

  • Presentation type: Poster

  • Presentation time: Thursday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 232

  • Programme No: 1.1.18

  • Theme 1 > Session 1

Abstract

The Troodos ophiolite is one of the supra-subduction ophiolite complexes. Ascending from the base, the Troodos massif comprises tectonised harzburgite, layered intrusive rocks such as dunite, wehrlite, pyroxenite, and gabbro, followed by sheeted dykes and capped with extrusive rocks. Within the extrusive sequence, two distinct lava suites have been identified: (1) a relatively enriched suite comprising andesites, dacites and rhyodacite, called Lower Pillow Lavas (LPL), (2) a more depleted suite, basalt-basaltic andesite, corresponding to the former Upper Pillow Lavas (UPL). The area around Margi is within the UPL, which also contains unusually high crystal-rich (40 to 70 vol.%) picrites. This study aims to establish the parental compositions and eruption mechanisms of such crystal-rich picrites. To explore the parental magmas for the picritic bodies, we conducted fieldwork near Margi to (1) sample a suite of picritic and other olivine-bearing UPL rocks, and (2) observe field relations. Fieldwork was followed by electron beam microanalysis of a representative set of small picritic bodies to determine the crystal chemistry of olivine and abundant spinel inclusions in hosts. To probe the potential parental compositions of picrite, we modelled reverse crystallisation using the most primitive UPL glass compositions and applied a post-entrapment correction to glassy MIs for diffusive Fe loss using Petrolog4. Petrolog4 modelling constrains conditions of fractionation based on parental melt compositions modelled from olivine MI, revealing that crystal-rich magmas are likely formed by magma recharging and repetitive fractionation and concentration of olivine crystals within magmatic systems less than 0.5 GPa (i.e., ~12 km depth).