DYNAMIC MINGLING OF MAGMA AND LIQUEFIED SEDIMENTS

Abstract

Hydrodynamic mingling of magma and liquefied sediments is generally accepted to represent the key process in the formation of some peperites. Experimental studies on simulant liquids and calculations based on recent empirical findings in the field of polymer research were undertaken to investigate the effectiveness of this process. These studies show that for a wide range of shear rates a laminar flow behaviour of the system magma-liquefied sediment can be expected, i.e. turbulent mingling is not a realistic scenario. Formation of peperitic fabrics with grain sizes on a cm scale can hydrodynamically be explained under realistic intrusion velocities. In addition to the hydrodynamics, cooling processes must also be considered during peperite formation. Calculations of the cooling history of the juvenile magmatic component under realistic cooling conditions demonstrate a significant limitation of the hydrodynamic mingling time. The consequence for peperite formation under normal intrusion conditions is that domains of magmatic melt and domains of liquefied sediment smaller than 10 cm are not probable. However, as smaller domain sizes (peperitic grain sizes) exist in nature, we conclude that either those peperites represent the products of explosive events or that hydrodynamic mingling was accompanied by additional fragmentation processes.