Fluid Geochemistry of Tacaná Volcano-Hydrothermal System

Abstract

Tacaná hosts an active volcano-hydrothermal system, characterized by boiling temperature fumaroles, near the summit (3,600-3,800 m asl), and bubbling degassing thermal springs near its base (1,000-2,000 m asl). The magmatic signature of gases rising to the surface is attested by their high CO 2 contents (δ 13 C CO2 = −3.6 ± 1.3 ‰), and relatively high 3 He/ 4 He ratios (6.0 ± 0.9 R A ), with a CO 2 / 3 He ratio typical for the Central American Arc (2.3 × 10 10 -6.9 × 10 11 ). Such magmatic signature is practically identical for the near-summit fumaroles, and the bubbling gases at the base of Tacaná edifice. Besides the HCO 3 -enrichment in thermal spring waters, the springs (pH 5.8-6.7) show a SO 4 -and minor Cl-enrichment: a CO 2 and H 2 S + SO 2 -rich magmatic steam condenses into a deeper geothermal aquifer, and the resulting hydrothermal fluid mixes with meteoric waters near the surface. The recharge area for the thermal springs is located at higher elevations (>400 m higher than spring outlet elevation), as inferred from the δD-δ 18 O data for rivers, thermal and cold springs. These general insights of the Tacaná volcano-hydrothermal system serve as the baseline for future volcanic surveillance, and geothermal prospection. The main locus of hydrothermal activity is located inside the Tacaná horseshoe-shaped crater in the northwestern sector of the volcanic edifice. In terms of volcanic hazard, this sector can be considered the most probable site for future phreatic activity.

SO2 degassing at Tungurahua volcano (Ecuador) between 2007 and 2013: Transition from continuous to episodic activity

“…This approach allows a detailed geochemical and isotopic characterisation of the gas sample, giving strong constraints on the subsurface temperature of the volcanichydrothermal systems and the gas source (Allard et al, 1991;Ohba et al, 2008;Rouwet et al, 2009;Vaselli et al, 2010). Nevertheless, given the high risk implied by direct sampling, routine sampling and analysis are hard to sustain in a continuous way (Symonds et al, 1994).…”

Volcanic Lakes in Africa: The VOLADA_Africa 2.0 Database, and Implications for Volcanic Hazard

“…EAR, Figure 11), and to mafic magmas. Stratovolcanoes or (dome) complex volcanoes with welldeveloped hydrothermal systems that provide the prototype settings to develop crater lakes on volcano summits (wet volcanoes; Caudron et al, 2015;Rouwet et al, 2015b), are relatively scarce in Africa. The EAR volcanism is MORB-or OIB-type leading to predominantly basaltic (Mt Cameroon; Mbassa et al, 2012;Kervyn et al, 2014;Adams et al, 2015;Nyamulagira, Nyiragongo;Pouclet et al, 2016;Karthala, outside the EAR;Class et al, 2009;Pelleter et al, 2014), or sporadically carbonatitic volcanism (Oldoinyo Lengai; Kervyn et al, 2014;Keller and Zaitsev, 2012;Weidendorfer et al, 2017).…”

Solute fluxes and geothermal potential of Tacaná volcano-hydrothermal system, Mexico–Guatemala

“…As many active volcanoes of CAVA, it hosts a volcanohydrothermal system which is displayed as numerous thermal manifestations including thermal springs at lower altitudes and steam vents close to the volcano summit. The geochemistry of thermal waters and steam vents have been studied by Rouwet (2006) and Rouwet et al (2009Rouwet et al ( , 2014. It has been shown that the thermal water of Tacana are CO 2 -enriched, of a rare SO 4 -HCO 3 composition (up to 1 g L −1 of each anion), and that the steam vents discharge vapor of CO 2 -H 2 S composition without "magmatic" HCl and SO 2 , with low H 2 and relatively low 3 He/ 4 He ratio of~5.5 Ra, where Ra is the 3 He/ 4 He air ratio (1.4 × 10 −6 ).…”