Geophysical Journal | 2003 volume 25 5

Tectonophysical conditions of forming crystallization schistosity

© Shevchuk V.V., Pavlov G.G.

This paper shows the possibility of forming crystallization schistosity revealed by plane - parallel orientation of foliated and tabular minerals under different dynamo-kinematic conditions. Along with empirically and experimentally proved orientation of minerals perpendicularly to coaxial compression, the possibility of oriented potassium feldspar porphyroblasts formation in migmatite and granite-gneiss complexes under conditions of transtention (combination of simple shear and additional extention normal to shear trend) is also argued. In the first case original crystals are rebuilt according to Rikke principle and schistosity shows recrystallizaton nature. In the second case the growth of new porphyroblasts occurs under conditions of augmenting the volume of mineral forming system and influx of necessary components. The shear component provides uniformity of tension and corresponding regularity of potassium feldspar porphyroblasts. Porphyroblast crystallization predates tension and creates, due to cristallization pressure, local stress fields. These stress fields determine orientation of porphyroblasts and cause the oriented growth of other minerals.

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