A Large Magma Reservoir Beneath the Tengchong Volcano Revealed by Ambient Noise Adjoint Tomography
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Abstract The Tengchong volcano (TCV) is a large active volcano system in the southeastern Tibetan Plateau. It is characterized by large‐volume magmatic gas emission, active hydrothermal circulation, and intense volcanic and earthquake activities, posing a threat of near future eruptions. However, there is still no available model of the magmatic plumbing system beneath the volcano system, limiting the quantitative assessments of the eruption hazards. Here, we present a high‐resolution 3D model of the TCV constructed using ambient noise adjoint tomography. Our 3D model reveals a large basaltic magma reservoir with a volume of ∼7,000 km 3 at depths of 20–35 km, which has a melt fraction of ∼2%–4.5%. Our results suggest that the deep crustal magma reservoir is fed by partial melting in the uppermost mantle and is recharging the shallow magma chambers beneath the TCV. Our results are key to understanding the volcanic activities and assessing future eruption hazards.Keywords:
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The 2014 and 2015 eruptions of Kuchinoerabujima Volcano followed a ~15-year precursory activation of the hydrothermal system induced by a magma intrusion event. Continuous heat transfer from the degassing magma body heated the hydrothermal system and the increase of the fluid pressure in the hydrothermal system caused fracturing of the unstable edifice, inducing a phreatic explosion. The 2014 eruption occurred from two fissures that traced the eruption fissures formed in the 1931 eruption. The explosive eruption detonated the hydrothermally-altered materials and part of the intruding magma. The rise of fumarolic activities before the past two activities in 1931-35 and 1966-1980 also suggest activation of the hydrothermal system by magmatic intrusions prior to the eruption. The long-lasting precursory activities in Kuchinoerabujima suggest complex processes of the heat transfer from the magma to the hydrothermal system.
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Abstract In the continental crust, the probability of dike propagation out of magma chambers is governed by thermal, rheological, and pressure conditions of magma chamber‐wall rock systems. Incremental injection of melt into an average‐size, laccolith‐shaped, midcrustal magma chamber produces a volume of mobile magma at the bottom of the chamber that has the potential to escape as dikes through the upper, immobile portion of the chamber and the roof. Here we numerically model the conditions needed for dike propagation out of a magma chamber during continuous and episodic injections of melt into the chamber. The roles of magma buoyancy and overpressure from melt injections in generating dikes are explored within 1.78 × 10 4 to 1.78 × 10 8 Pa·s range of magma viscosities ( μ mag ), 10 to 40 GPa range of elastic moduli ( E ) of the immobile top portion of the magma chamber, and 10 and 20 kyr durations of chamber growth. During episodic, high‐flux melt injections (tens of km 3 /yr), magma overpressure can reach >100 MPa and initiate dike propagation even when μ mag and E are near the high ends of the examined ranges. The probability of generating dikes diminishes when the injection flux is lower. Continuous low‐flux injections favor magma accumulation because injection overpressure never exceeds 20 MPa. During either continuous or episodic growth of magma chamber, there is never a sufficient amount of mobile magma in the chamber for dikes to be induced by magma buoyancy alone.
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Assessing volcano hazard and forecasting eruptions require knowledge of the geometry and properties of a volcano's magma chamber. However, there are few high‐resolution seismic imagery studies of magma chambers. Paulatto et al. used seismic tomography along with numerical models of magma chamber growth to get a better picture of the magma chamber beneath the active Soufrière Hills volcano on the island of Montserrat. Their approach reveals details of the magma system that have not been shown in previous studies. The authors' analysis shows that the magma chamber contains about 13 cubic kilometers of magma, with more than 30% melt faction between about 5.5‐ and 7.5‐kilometer depth. The researchers suggest that the magma chamber could have formed through sill intrusion over several thousand years. ( Geochemistry, Geophysics, Geosystems (G 3 ), doi:10.1029/2011GC003892, 2012)
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