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Abstract:
Dykes during their ascent can mechanically stall in the heterogeneous crust, deflect through pre-existing fractures or at weak contacts forming a plethora of intrusive bodies. Yet, the conditions under which sill emplacement occurs in glacial regimes remain unclear. Here, we study the mechanical and geometrical conditions for sill emplacement by coupling field observations (the Stardalur cone sheet-laccolith system) with FEM numerical models. We modelled a heterogeneous crust, intruded by a dyke with varied overpressure (Po=1-30 MPa) and regional extension (Fext=0.5-3 MPa) loading conditions. We performed sensitivity tests to understand how the tip-contact distance responds to different loading conditions. We explored how inclined sheets form sills, or the thickness of soft (low Young’s modulus) layers encourage sill deflection. Finally, we added an ice cap above the setting as a boundary pressure load to explore dyking subject to unloading due to glacier thickness (0-1 km) and length (5-25 km) variations. Our results propose that a sill is encouraged by dyke overpressure (Po ≥ 5MPa) and varied layer thickness (W≥10 m) conditions. In glacial settings, instead, it is promoted when the thickness and the length of the glacier is decreasing.
