The eruptibility of magmas at Tharsis and Syrtis Major on Mars

Abstract

Magnetic and geologic data indicate that the ratio of intrusive to extrusive magmatism (the I/E ratio) is higher in the Tharsis and Syrtis Major volcanic provinces on Mars relative to most volcanic centers on Earth. The fraction of magmas that erupt helps to determine the effects of magmatism on crustal structure and the flux of magmatic gases to the atmosphere and also influences estimates of melt production inferred from the history of surface volcanism. We consider several possible controls on the prevalence of intrusive magmatism at Tharsis and Syrtis Major, including melt production rates, lithospheric properties, regional stresses and strain rates, and magmatic volatile budgets. The Curie temperature is the minimum crustal temperature required for thermal demagnetization, implying that if the primary magnetic mineral is magnetite or hematite, the crust was warm during the intrusive magmatism reflected in Tharsis and Syrtis Major I/E ratios. When wall rocks are warm, thermally activated creep relaxes stresses from magma replenishment and regional tectonics, and eruptibility depends on buoyancy overpressure. We develop a new one‐dimensional model for the development of buoyancy in a viscous regime that accounts for cooling, crystallization, volatile exsolution, bubble coalescence and rise, fluid egress, and compaction of country rock. Under these conditions, we find that initial water and CO2 contents typically <1.5 wt % can explain the observed range of intrusive/extrusive ratios. Our results support the hypothesis that warm crust and a relatively sparse volatile budget encouraged the development of large intrusive complexes beneath Tharsis and Syrtis Major.

Lava Flow Eruption Conditions in the Tharsis Volcanic Province on Mars

“…% water and Martian basalts are thought to be particularly dry with estimates of <1.5 wt. % water (e.g., Black & Manga, 2016). On the other hand, crystallization increases with increasing distance from the vent as the flow cools which increases the flows viscosity by orders of magnitude along its length (e.g., Crisp & Baloga, 1994).…”

Volatiles and the tempo of flood basalt magmatism

“…We describe our treatment of these magmatic processes in detail in the Supplementary Materials and in Black and Manga (2016). We model equilibrium crystallization of an initial melt with constant composition using Rhyolite-MELTS (Ghiorso and Sack, 1995;Gualda et al, 2012).…”

“…In our Rhyolite-MELTS calculations, we adopt the most magnesian primary melt composition computed by Sobolev et al (2009) and compositional gradients within the chamber could account for the contributions of crystal segregation to differentiation and increased buoyancy. We compute bubble size distributions using empirically and theoretically validated expressions for collision frequency (Manga and Stone, 1995), and from the bubble size distributions obtain rise velocities and the vertical distribution of exsolved volatiles within the chamber (Black and Manga, 2016). The fluid densities are calculated with a parameterized equation of state (Degruyter and Huber, 2014).…”

Magma Chamber Growth During Intercaldera Periods: Insights From Thermo‐Mechanical Modeling With Applications to Laguna del Maule, Campi Flegrei, Santorini, and Aso

“…Field studies of plutons (C. F. Miller et al, ; R. B. Miller & Paterson, ; Paterson & Miller, ; Wiebe, ; Wiebe & Collins, ) and eruptive deposits (Chamberlain et al, ; Charlier et al, ; Matthews et al, ), analogue experiments (Snyder & Tait, ), and numerical models (Annen, ; Jellinek & DePaolo, ; Karlstrom et al, ) have illuminated the physical processes by which magma chambers are assembled, typically by the episodic injection of magma via dikes ascending from deeper reservoirs. However, we do not yet understand what determines the proportion of magma that ultimately remains in the crust relative to the amount erupted (Black & Manga, ; White et al, ) and how this relates to the long‐term growth of eruptible portions of the reservoir, referred to here as magma chambers. Thermal and mechanical models (Annen, ; Degruyter & Huber, ; Jellinek & DePaolo, ) suggest that for a given rate of magma supply, smaller chambers are more likely to erupt and freeze, while larger chambers favor magma storage, which begs the question: How do magma chambers grow to the volumes required to sustain the largest eruptions on Earth?…”