Mafic injection as a trigger for felsic magmatism: A numerical study

Abstract

[1] The origin of crustal-scale silicic magmatism remains a matter of debate, and notable uncertainty exists concerning the physical mechanisms that drive ascent and emplacement of felsic magmas in upper crustal regions. A 2-D numerical model demonstrates that injection of mantle-derived mafic magma into a partially molten hot zone in the lower crust can drive felsic magma ascent and intrusion into upper crustal levels. The injection of mafic magma induces overpressure in the reservoir, which increases crustal stresses and triggers development of brittle/plastic shear zones, and can drive significant surface uplift. The emerging topography causes a nonuniform overpressure distribution in the reservoir and can trigger felsic magma ascent along crustal shear zones. Based on systematic numerical experiments, we investigate the influence of crustal strength and injection rate. The initial upper crustal strength controls the degree of crustal faulting and surface uplift and therefore whether felsic magma ascent can be initiated or not. The final upper crustal strength influences the depth and final style of felsic intrusion. The injection rate of mafic magma determines the time scale of overpressure growth and surface uplift stage. In contrast, the duration of the subsequent felsic ascent and intrusion emplacement stages remains nearly constant. Our results imply that mafic underplating and intrusion into the lower crust may not only be a prime control for the generation of felsic magmas in the lower crust but may also be an important physical driving mechanism for felsic magma ascent and intrusion into upper crustal levels.

Relamination Styles in Collisional Orogens

“…The relaminant tends to spread spontaneously below the strong lithosphere and later inside the low‐viscosity ductile crust below the stronger brittle/plastic middle to upper crust. A similar effect is observed during magma intrusion into the crust (e.g., Gerya & Burg, ; Keller et al, ; Schubert et al, ). The relaminant emplacement also resembles the buoyancy‐driven flattening of exhumed HP material arrested by the Moho as predicted in Norwegian Caledonides (Walsh & Hacker, ).…”

Rhyolites—Hard to produce, but easy to recycle and sequester: Integrating microgeochemical observations and numerical models

“…Furthermore, plutons may undergo doming and upward motion on the order of 10 5 -10 6 m.y. time scales, creating internal density redistribution (Ramberg, 1970;Petford, 2003;Schubert et al, 2013 …”

Intrusion of Magmatic Bodies Into the Continental Crust: 3‐D Numerical Models

“…In regions of active melt transport the friction coefficient might be as low as 0 if the fluid pressure is close to the total pressure (Gerya & Burg, ; Schubert et al, , and references therein). In this case, the yield strength is defined by the cohesion only and independent of depth.…”

“…The initial yield strength of the crust controls the degree of crustal faulting and surface uplift and is therefore the principle rheological control on magma ascent and emplacement within the crust. Crustal strength counteracts magma ascent driven by the buoyancy of the magma and the pressure difference between the deep mafic magma reservoir (SMSR) and the base of the crust (Schubert et al, ).…”

“…Little is known about the dynamic interplay between magma and crust. Only a few studies have stressed the importance of magma and host rock rheology upon emplacement using numerical formulations that allow for ductile (viscous), elastic, and brittle (plastic) deformation in two dimensions (Burov et al, ; Cao et al, ; Gerya & Burg, ; Schubert et al, ). However, intrusion dynamics and emplacement histories are intrinsically three‐dimensional phenomena.…”