A set of experimental small-scale models of continental extension investigated the emplacement of orthogonal and oblique magma chambers, initially underplated at the base of the crust. The models are driven by a centrifugal body force which simulates the role of gravity in nature. The model represent crustal conditions analogous to relatively mature continental rifts and consider both symmetric and asymmetric extension. The experimental results suggest that magma emplacement is controlled by the interactions between tectonics and rheology of the crustal layer. In particular, extension is mainly accomodated by lateral flow and ductile doming in the viscous layer simulating the lower crust and by listric normal faults, in the overlying brittle layer, associated with a ductile domal uplift. Stretching of the continental crust induces a "reactive" migration of viscous lalayers into footwall of major normal faults, where magma accumulation at the core of the domes takes place. This behaviour suggests that widespread magmatism is expected to localise in the footwall of major normal faults, a situation that is often observed in core complex structures. Although the models presented here are intended to simulate magma emplacement during extension of a two-mayer brittle-ductile system, lateral flow and migration of magma initially underplated at the base of the crust beneath narrow rift (e.g., the Ethiopian rift) may also provide a similar mechanism and a possible explanation for the occurrence of important volcanoes on the plateaus flanking the rift zones. In the suggested model, such volcanoes are related to large basaltic magma reservoirs, located at the base of the crust, to accomodate the space vacuated by lateral flow and thinning of the ductile crust. The similarity in structure of the models with natural examples of continental extension modes (such as rift systems and core complexes) may suggest a close similarity of dynamic processes.
Dynamics of magma emplacement in centrifuge models of continental extension with implications for flank volcanism
Bonini M;Corti G;
2001
Abstract
A set of experimental small-scale models of continental extension investigated the emplacement of orthogonal and oblique magma chambers, initially underplated at the base of the crust. The models are driven by a centrifugal body force which simulates the role of gravity in nature. The model represent crustal conditions analogous to relatively mature continental rifts and consider both symmetric and asymmetric extension. The experimental results suggest that magma emplacement is controlled by the interactions between tectonics and rheology of the crustal layer. In particular, extension is mainly accomodated by lateral flow and ductile doming in the viscous layer simulating the lower crust and by listric normal faults, in the overlying brittle layer, associated with a ductile domal uplift. Stretching of the continental crust induces a "reactive" migration of viscous lalayers into footwall of major normal faults, where magma accumulation at the core of the domes takes place. This behaviour suggests that widespread magmatism is expected to localise in the footwall of major normal faults, a situation that is often observed in core complex structures. Although the models presented here are intended to simulate magma emplacement during extension of a two-mayer brittle-ductile system, lateral flow and migration of magma initially underplated at the base of the crust beneath narrow rift (e.g., the Ethiopian rift) may also provide a similar mechanism and a possible explanation for the occurrence of important volcanoes on the plateaus flanking the rift zones. In the suggested model, such volcanoes are related to large basaltic magma reservoirs, located at the base of the crust, to accomodate the space vacuated by lateral flow and thinning of the ductile crust. The similarity in structure of the models with natural examples of continental extension modes (such as rift systems and core complexes) may suggest a close similarity of dynamic processes.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
