Petrogenesis of the Zoned Laacher See Tephra

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Abstract
The late Quaternary Laacher See phonolitic tephra deposit (East Eifel, W. Germany) is mineral-ogically and chemically zoned from highly evolved, volatile-rich and crystal-poor at its base towards a mafic, crystal-rich phonolite at the top (Wörner & Schmincke, 1984). This zonation is interpreted as the result of a continuous eruption from a zoned magma column. Major and trace element evidence shows that the last erupted mafic ULST (Upper Laacher See Tephra) phonolite can be derived from a basanite parent magma via fractional crystallization of 30 per cent clinopyroxene, 24 per cent amphibole, 4 per cent phlogopite, 3.8 per cent magnetite, 2.5–3.0 per cent olivine and 1 per cent apatite, leaving a derivative of 30 per cent evolved magma.

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