Self accommodating shear strain dating advice when to become exclusive
These observations highlight that the end-member rheological assumptions of the current theoretical, laboratory, and numerical models of magma emplacement have limited physical validity because the host-magma interaction is too simplified.
Moreover, field observations in the host rock of thin laccoliths in the Henry Mountains, Utah, evidence significant plastic shear failure and ductile deformation of the overburden (Román-Berdiel et al., 1995; de Saint Blanquat et al., 2006; Wilson et al., 2016), in contrast to the elastic assumptions of the theoretical models (e.g., Pollard, 1973; Bunger and Cruden, 2011).
The experiments were run in a polariscope, which highlighted birefringence patterns related to deformation structures within the gel.
Our experiments show a strong correlation between intrusion shapes and host matrix deformation modes: (1) thin intrusions dominantly propagate by tensile failure and elastic deformation of the host, (2) rounded “diapiric” intrusions dominantly propagate by viscous flow of the host, and (3) irregular “hybrid” intrusions propagate by coeval brittle (tensile and shear) and ductile deformation of the host.
The oil intrusion in the elastic gel is a thin conduit with a sharp tip, like magmatic dykes, whereas the oil intrusion in the viscous gel is rounded, like diapirs.
In addition, the oil intrusion in gels of intermediate properties exhibits complex, hybrid shapes.
(A) A diapir (viscous end-member) indents and displaces the surrounding host rock extensively, making the host rock viscosity a fundamental parameter for governing ascent rate.