Publication Date:
2015-09-30
Description:
The shallow transport of magma occurs through dikes causing surface deformation. Our understanding of the effects of diking at the surface is limited, especially on the long-term, for repeated intrusive episodes. We use analogue models to study the upper crustal deformation induced by dikes. We insert metal plates within cohesive sand with three setups: in A, the intrusion rises upward with constant thickness; in B and C, the intrusion thickens at a fixed depth, with final rectangular (B) or triangular (C) shape in section. Experiments A create a doming delimited by reverse faults, with secondary apical graben, without close correspondence in nature. In experiments B and C, a depression flanked by two uplifted areas is bordered by inward dipping normal faults propagating downward and, for deeper intrusions in B, also by inner faults, reverse at the surface; this deformation is similar to what observed in nature, suggesting a consistent physical behavior. Dikes in nature initially propagate developing a mode I fracture at the tip, subsequently thickened by magma intrusion, without any host-rock translation in the propagation direction (as in A). The deformation pattern in B and C depends on the intrusion depth and thickness, consistently to what observed along divergent plate boundaries. The early deformation in B and C is similar to that from single rifting episodes (i.e. Lakagigar, Iceland; Dabbahu, Afar), whereas the late stages resemble the structure of mature rifts (i.e. Krafla, Iceland), confirming diking as a major process in shaping divergent plate boundaries.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
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