The scale-invariant nature of migmatite from the Oberpfalz, NE Bavaria and its significance for melt transport

Four examples of migmatite from the Moldanubian Zone in western Bohemia, which formed during the late Carboniferous, display fractal patterns of melt bodies over more than 1.5 orders of magnitude. Net-type migmatites have a fractal dimension of 1.80-1.85 (in two orthogonal planes), while that of a cross-stromatic migmatite is 1.60. This fractal quality allows the migmatitic structures to be simply quantified and modelled. For modelling purposes, the net-type migmatites are compared analogously to a Menger Sponge. Using a published theoretical model of magma flow in vertical channels, it is shown that melt with viscosities less than 10(6)-10(8) Pa s can escape from the Menger Sponge under the influence of gravity alone. (C) 1999 Elsevier Science B.V. All rights reserved.