Partitioning of vorticity in bimineralic rocks

A model for the rotational behaviour of Row in bimineralic rocks based on t he concept of a multiphase continuum is developed here. An additive relatio n with respect to the vorticity is assumed. The ideal linear viscous bimine ralic rocks are defined such that (i) both the bulk rock and the constituen t phases have linear viscous rheology. (ii) the phases are uniformly mixed and distributed in the rock, and (iii) no segregation occurs during the def ormation. The model reveals the partitioning of vorticity between the two p hases: in the ideal linear viscous bimineralic rocks. The model shows that there are two modes of Row behaviour. In mode 1 there is neither partitioni ng of strain rate nor vorticity; in mode 2 partitioning occurs for strain r ate and vorticity. Mode 1 behaviour corresponds to upper bound behaviour an d mode 2 to the lower bound behaviour. There are two solutions for the part itioning of vorticity in mode 2: type I and type 2 partitioning. In the typ e 1 partitioning the more viscous phase is more rotational than the less vi scous phase. while in the type 2 partitioning the former is less rotational than the latter. In a special case where Row occurs by simple shearing and where the more viscous phase behaves as rigid particles. the following two cases occur: (1) the more viscous phase rotates at twice the rate of the b ulk rock (type i partitioning), (2) the more viscous phase does not rotate at all with respect to the external reference coordinate (type 2 partitioni ng). The present model alone cannot predict which type will occur and furth er theoretical and experimental work is needed. (C) 2001 Elsevier Science L td. All rights reserved.