Immiscible Transition from Carbonate-rich to Silicate-rich Melts in the 3 GPa Melting Interval of Eclogite + CO2 and Genesis of Silica-undersaturated Ocean Island Lavas |
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| Authors: | DASGUPTA RAJDEEP; HIRSCHMANN MARC M; STALKER KATHRYN |
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| Institution: | DEPARTMENT OF GEOLOGY AND GEOPHYSICS, UNIVERSITY OF MINNESOTA, 310 PILLSBURY DRIVE SE, MINNEAPOLIS, MN 55455, USA |
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| Abstract: | We explore the partial melting behavior of a carbonated silica-deficienteclogite (SLEC1; 5 wt % CO2) from experiments at 3 GPa and comparethe compositions of partial melts with those of alkalic andhighly alkalic oceanic island basalts (OIBs). The solidus islocated at 1050–1075 °C and the liquidus at  1415 °C.The sub-solidus assemblage consists of clinopyroxene, garnet,ilmenite, and calcio-dolomitic solid solution and the near solidusmelt is carbonatitic (<2 wt % SiO2, <1 wt % Al2O3, and<0·1 wt % TiO2). Beginning at 1225 °C, a stronglysilica-undersaturated silicate melt (34–43 wt % SiO2)with high TiO2 (up to 19 wt %) coexists with carbonate-richmelt (<5 wt % SiO2). The first appearance of carbonated silicatemelt is 100 °C cooler than the expected solidus of CO2-freeeclogite. In contrast to the continuous transition from carbonateto silicate melts observed experimentally in peridotite + CO2systems, carbonate and silicate melt coexist over a wide temperatureinterval for partial melting of SLEC1 carbonated eclogite at3 GPa. Silicate melts generated from SLEC1, especially at highmelt fraction (>20 wt %), may be plausible sources or contributingcomponents to melilitites and melilititic nephelinites fromoceanic provinces, as they have strong compositional similaritiesincluding their SiO2, FeO*, MgO, CaO, TiO2 and Na2O contents,and CaO/Al2O3 ratios. Carbonated silicate partial melts fromeclogite may also contribute to less extreme alkalic OIB, asthese lavas have a number of compositional attributes, suchas high TiO2 and FeO* and low Al2O3, that have not been observedfrom partial melting of peridotite ± CO2. In upwellingmantle, formation of carbonatite and silicate melts from eclogiteand peridotite source lithologies occurs over a wide range ofdepths, producing significant opportunities for metasomatictransfer and implantation of melts. KEY WORDS: carbonated eclogite; experimental phase equilibria; partial melting; liquid immiscibility; ocean island basalts |
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| Keywords: | : carbonated eclogite experimental phase equilibria partial melting liquid immiscibility ocean island basalts |
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