Mechanisms and orientation of melt segregation paths during pure shearing of a partially molten rock analog (norcamphor-benzamide)

In-situ deformation experiments were performed on partially molten analog m aterials (norcamphor in the presence of a benzamide-norcamphor melt) underg oing pure shearing at a constant melt fraction of 0.13. Melt in the samples induces a strain-dependent transition from purely dislocation creep to dis location creep associated with minor intergranular fracturing and grain bou ndary sliding (GBS). Intergranular fractures drain the melt from initially isotropic melt pockets to grain boundaries. Along such boundaries, grain-bo undary migration recrystallization is inhibited, while GBS occurs. Intergra nular melt pockets occur along grain boundaries oriented subparallel to the shortening direction, but melt must have migrated parallel to the elongati on direction of the samples, as indicated by melt accumulations at both ext ruding ends of the sample. Intergranular melt pockets parallel to the elong ation direction were only rarely observed, because melt was rapidly expelle d from these sites. Nevertheless, these grain boundaries are the pathways o f melt segregation in the samples. (C) 2001 Elsevier Science Ltd. All right s reserved.