Zoom link<\/a><\/p>\nSupervisors:<\/strong>
\nProfessor Robert Frei, IGN
\nSenior researcher Nynke Keulen, GEUS
\nAssociate Professor Vincent J. van Hinsberg, Mcgill University – Canada
\nProfessor Jochen Kolb, Karlsruher Institut f\u00fcr Technologie – Germany<\/p>\nAssessment committee:<\/strong>
\nProfessor John C. Schumacher, Portland State University – US
\nAssociate Professor Thomas Ulrich, Aarhus University
\nProfessor Tod Waight (chair), IGN<\/p>\nSummary:<\/strong>
\nPlumasite-type corundum in ultramafic rocks from the Nattivit area (Isertoq Terrane), in SouthEast Greenland formed during convergence and continent collision. The continental crust in\u00a0Isertoq Terrane, consist of 3.0-2.9 Ga (\u03b5Nd TDM model) mafic to ultramafic rock and TTG sheets with intrusion ages of U\/Pb zircon 2841\u00b111 to 2651\u00b17 Ma. The geochemical data for the\u00a0mafic to ultramafic rocks in Isertoq Terrane indicate a continental arc tectonic setting. Peak metamorphism in Isertoq Terrane occurred at 1891\u00b19 to 1871\u00b19 Ma at 700-740\u00b0C and 7-9 kbar.
\nPegmatite intrusion occurred in three episodes between 1855\u00b116 and 1735\u00b127 Ma. The pegmatite triggered corundum formation at 1843\u00b14Ma (U\/Pb zircon age) at the contact with\u00a0ultramafic rocks, at 680-700\u00b0 and 7-9 kbar, during the collisional phase. The pegmatites are peraluminous, calc-alkaline and have a granitic to granodioritic composition. The Rb-Sr, SmNd, Pb and oxygen isotopes indicate the pegmatite are derived from partial melts from mafic\u00a0granulite or subducted plate. A typical setting for plumasite-type corundum appears to be in the upper plate of a convergent geotectonic setting. The desilication of the pegmatite and\u00a0metasomatism of lherzolite causes an increase in Ca, Mg, K, Mn, Al and Fe towards the centre of the metasomatic reaction zone, where there additionally is observed an increase in Cr, Ni,\u00a0Mg, Fe, Sc, Co, V, Zn, Ti, and Mn, derived from the lherzolite. The thermodynamic fluid composition modelling with the Perple_X suite of programs for a metasomatic reaction zone in\u00a0lherzolite, show that the pegmatite fluid have pH of 0.7 units above neutral and thus is alkaline.
\nThe pegmatite had a maximum X(CO2) of 0.1, and raised the oxygen fugacity level in the lherzolite from NNO-3 to NNO-2. The fluid in equilibrium with the metasomatic mineral\u00a0assemblage contains Fe and Al as major cations, additionally components of K, Si and Ca were also present, and Na, Mg and Cr as minor ligands. The pegmatite fluid was F-rich, where the\u00a0fluid F and Cl content is estimated to 121-161 ppm from F contents in apatite and biotite, and Cl is between 0.5 and 5 mass%. (Hydr)oxide and carbonate species dominate the fluid, and cation\u00a0concentrations are not sensitive to the Cl-content of the fluid. The combination of reduced and alkaline conditions results in high Al mobility, and this is enhanced by the elevated F-content in\u00a0the fluid. Saturation in corundum in the lherzolite is proposed to be a result of a combination of active Al addition from the lherzolite and residual enrichment of Al from the pegmatite, and the\u00a0Fe-enrichment in the corundum a result of high Fe and low Cr mobility in the metasomatic fluid.<\/p>\nA digital version of the PhD thesis can be obtained from the PhD secretary Mikala Heckscher at<\/em> mikala@ign.ku.dk<\/p>\n","protected":false},"excerpt":{"rendered":"Majken Djurhuus Poulsen defends her thesis, Controls on element exchange during plumasite-type corundum formation in ultramafic rocks Zoom link Supervisors: Professor Robert Frei, IGN Senior researcher Nynke Keulen, GEUS Associate Professor Vincent J. van Hinsberg, Mcgill University – Canada Professor Jochen Kolb, Karlsruher Institut f\u00fcr Technologie – Germany Assessment committee: Professor John C. Schumacher, Portland […]<\/p>\n","protected":false},"author":0,"featured_media":133926,"template":"","class_list":["post-133925","event","type-event","status-publish","has-post-thumbnail","hentry","event_category-phd-thesis-defense"],"acf":[],"aioseo_notices":[],"yoast_head":"\n
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