Geochemistry of the Start Complex greenschists: Rhenohercynian MORB?

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Abstract
The meta-igneous greenschists of the Start Complex, SouthDevon, are composed of a mineralogically uniform, but texturally variable, actinolite-epidote-albite assemblage with retrogressed variants containing chlorite, muscovite, sphene, carbonate and oxidized opaque minerals. Geochemically they represent a suite of relatively primitive tholeiites, exhibiting mild differentiation, depleted incompatible element abundances, and variable light rare-earth-element-depletion patterns comparable to modern basalts from normal spreading ridge segments (N-MORB). As the Start greenschistsexhibit a number of chemical similarities to the nearby Upper Palaeozoic Lizard ophiolite, and MORB-type clasts within the Rhenohercynian Zone generally, they may also represent local Variscan ocean crust, which floored smalloceanic basins that separated the Old Red Sandstone continent from the Armorican microplate to the south. The Start Complex could thus represent a previously unrecognized oceanic component to the Variscan orogenic belt (Rhenohercynian Zone) of Northwest Europe.