Trans-crustal structural control of CO2-rich extensional magmatic systems revealed at Mount Erebus Antarctica

Abstract

Erebus volcano, Antarctica, with its persistent phonolite lava lake, is a classic example of an evolved, CO2-rich rift volcano. Seismic studies provide limited images of the magmatic system. Here we show using magnetotelluric data that a steep, melt-related conduit of low electrical resistivity originating in the upper mantle undergoes pronounced lateral re-orientation in the deep crust before reaching shallower magmatic storage and the summit lava lake. The lateral turn represents a structural fault-valve controlling episodic flow of magma and CO2 vapour, which replenish and heat the high level phonolite differentiation zone. This magmatic valve lies within an inferred, east-west structural trend forming part of an accommodation zone across the southern termination of the Terror Rift, providing a dilatant magma pathway. Unlike H2O-rich subduction arc volcanoes, CO2-dominated Erebus geophysically shows continuous magmatic structure to shallow crustal depths of < 1 km, as the melt does not experience decompression-related volatile supersaturation and viscous stalling.

Insights on the Interplay of Rifting, Transcrustal Magmatism and Formation of Geothermal Resources in the Central Segment of the Ethiopian Rift Revealed by 3‐D Magnetotelluric Imaging

“…O. Rooney et al, 2011). This interpretation of the transcrustal magma system is in agreement with recent concepts and subsurface models, where magma storage occurs in form of multiple interconnected magmatic mush systems and at different levels, rather than in isolated voluminous magma chambers (e.g., Cashman et al, 2017;Hill et al, 2022).…”

“…At Mt. Erebus the transcrustal magma distribution has a vertically oblique geometry and lower crustal melt fractions of 10 vol% (Hill et al, 2022), both features that are comparable to the CMER, as imaged by us with an estimated lower crustal melt fraction of 7 vol%. However, Oppenheimer et al (2011) suggest that CO 2 streaming dehydrates magma at Mt.…”

“…Erebus and the resulting low water content (H 2 O: ∼0.1 wt%) allows magma storage at very shallow depths (≤1 km) below Mt. Erebus (Hill et al., 2022), which is apparently not the case for Aluto, where the dissolved volatile fraction in the melt is larger (C2: ≥4 km, H 2 O: ∼4.7 wt% from Samrock et al. (2021)).…”

“…The number of geophysical models imaging transcrustal magmatic mush systems at this scale (e.g., Cashman et al., 2017) is still limited (e.g., Bedrosian et al., 2018; Comeau et al., 2016, 2021; Hill et al., 2009; Huang et al., 2015; Käufl et al., 2020), especially in the setting of active continental rifts (e.g., Hill et al., 2022; Wannamaker et al., 2008). Our study (Figure 7) provides previously missing geophysical evidence for the hypothesized conceptual model of the Central Main Ethiopian Rift (e.g., T. O. Rooney et al., 2011).…”

Magnetotelluric Evidence for Lithospheric Alteration Beneath the Wuyi‐Yunkai Orogen: Implications for Thermal Structure of South China

“…Likewise, Figure 3b shows the ellipses of the phase tensor with the values of Φ 1 , which denotes the geometric mean of the maximum (Φ max ) and minimum (Φ min ) phases and represents the variation in resistivity with depth (Hill et al., 2009, 2022). In the Cathaysia Block and Wuyi‐Yunkai Orogen, the Φ 1 values of short‐period data increase with the period at most MT sites, which corresponds with the presence of shallow magmatic rocks with highly resistivity.…”