Sublithospheric Triggers for Episodic Silicic Magmatism in Subduction Zones

Abstract:

The melt source and ascent mechanisms for crustal-scale silicic magmatism in subduction zones remain a matter of debate. Recent petrological-thermo-mechanical numerical experiments suggest that important physical controls of this process can be of sublithospheric origin. Firstly, deep sources of silicic magma can be related to episodic development of positively buoyant diapiric structures in the mantle wedge originated from deeply subducted rock mélanges (Gerya and Yuen, 2003; Castro and Gerya, 2008). Partial melting of these rapidly ascending lithologically mixed structures can produce silicic magmas with a relatively constant major element composition and variable time-dependent isotopic ratios inherited from the mélange (Vogt et al., 2013). Secondly, episodic injections of subduction-related mantle-derived mafic magmas into a partially molten hot zone of the arc lower crust can drive ascents of pre-existing felsic crustal magmas toward upper crustal levels. The injection of mafic magma induces overpressure in the lower crustal magma reservoir, which increases crustal stresses and triggers development of brittle/plastic fracture zones serving as conduits for the rapid episodic ascent of felsic magmas (Shubert et al., 2013). Our numerical results thus imply that subduction-related sublithospheric magma intrusions into the lower arc crust may both be the prime source for the generation of silicic magmas and the major physical driving mechanism for their episodic ascent toward upper crustal levels.

References:

Castro, A., and Gerya, T.V., 2008. Magmatic implications of mantle wedge plumes: experimental study. Lithos 103, 138–148.

Gerya, T.V., and Yuen, D.A., 2003. Rayleigh–Taylor instabilities from hydration and melting propel “cold plumes” at subduction zones. Earth and Planetary Science Letters 212, 47–62.

Schubert, M., Driesner, T., Gerya, T.V., Ulmer, P., 2013. Mafic injection as a trigger for felsic magmatism: A numerical study. Geochemistry, Geophysics, Geosystems, 14, 1910–1928.

Vogt, K., Castro, A., and Gerya, T., 2013. Numerical modeling of geochemical variations cause by crustal relamination. Geochemestry Geophysics Geosystems 14, 470–487.