Ordovician ferrosilicic magmas: Experimental evidence for ultrahigh temperatures affecting a metagreywacke source |
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| Authors: | A Castro A García-Casco C Fernndez LG Corretg I Moreno-Ventas T Gerya I Lw |
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| Institution: | A. Castro, A. García-Casco, C. Fernández, L.G. Corretgé, I. Moreno-Ventas, T. Gerya,I. Löw |
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| Abstract: | Peculiar magmatic rocks were erupted and emplaced at depth at the margin of the Gondwana supercontinent during the Cambro-Ordovician transition. These rocks are characterized by high contents in silica and iron but they do not have equivalents in the high-silica members of the calc-alkaline series. They have particular geochemical signatures, with Al saturation index, ASI > 1, FeO > 2.5 wt.%, MgO > 0.8 wt.% for very low contents in calcium (CaO < 2.0 wt.%), supporting a derivation from near-total melting (> 80 vol.% melt) of metagreywackes. The results from inverse experiments indicate that the most plausible conditions are within the range 1000 °C (excess water) and 1100–1200 °C (subsaturated and dry) at pressures of 1.5 to 2.0 GPa. A tectonic scenario implying melting of subducted sediments within an ascending mantle-wedge plume is suggested for the generation of primary ferrosilicic melts at the Gondwana continental margin during Upper Cambrian to Lower Ordovician times. |
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| Keywords: | Ferrosilicic magmatism Experimental petrology Mantle-wedge plumes Gondwana Cambro-Ordovician Crustal recycling |
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