Contrasting Hydrothermal Processes at Teide Summit and in the Las Cañadas Caldera Wall, Teide National Park, Tenerife

Sammanfattning

Hydrothermal alteration in volcanic systems modifies mineralogy, isotope signatures and rock physical properties, although studies that integrate mineralogy, stable isotopes and rock-physics to fully characterize different alteration facies remain limited. This study investigates hydrothermal alteration types at the Teide-Las Cañadas complex based on multiparameter approach that links alteration types to petrological facies and associated mechanical behavior. To accomplish this goal, I combine field petrography, powder X-ray diffraction (XRD), whole-rock oxygen isotopes (δ18Ο), hydrogen isotopes (δD), connected porosity, thermal conductivity and P-wave velocity, but with an emphasis on the stable isotope part within this thesis. Sampling targets summit and flank areas at Teide (Teide Summit, Old Teide Cone, Old Teide Base, Lavas Negras/ Rajadas) and distal caldera-wall exposures (Siete Cañadas and the Ucanca sector). The XRD results show argillic and mixed alteration along the Las Cañadas caldera wall and acid-sulfate alteration around the Teide edifice. Isotopically, δD values span -82 to 34‰ and δ18O values span 0.03 to 12‰. The δD values show dominance of meteoric fluids, whereas δ18O values show temperature-dependent water-rock exchange, decoupling from δD. Thermal conductivity decreases with increasing porosity, while P-wave velocities cluster in an intermediate range. These data resolve five alteration types on Teide-Las Cañadas complex: (1) high-T meteoric, acid sulfate (2) low-T meteoric, acid sulfate (3) magmatic like δ18O, acid sulfate (4) low-T meteoric, argillic (5) high-T meteoric, mixed (argillic + silicified). One caldera-wall specimen shows Liesegang-type banding with a V-shaped δ18O profile (minimum in the inner ring) and δD more negative in the outer rings than in the inner, consistent with localized diffusion-reaction controlled fluid-rock exchange. Based on physical properties and mineralogy, we identify weak zones along the Ucanca sector (low-T argillic) and Teide flank (low-T acid sulfate) with high porosity, low thermal conductivity and low velocity and strong zone near Siete Cañadas (high-T mixed) with moderate porosity, high thermal conductivity and high velocity. This small-scale, integrated interpretation offered insight into how alteration may appear at larger scales across the Teide-Las Cañadas complex and may help identify weak zones and associated hazards at Teide and similar volcanoes.