Cas, R.

El Barronal complex consists of a succession of andesite lavas and andesite volcaniclastic facies interbeddedwith carbonate and siliciclastic sedimentary rocks. Carbonate and siliciclastic rocks were deposited in a shallow- marine environment during periods of volcanic quiescence. Lavas consist of an inner coherent core grading out- ward into hyaloclastite brecciamade of dense clasts that in turn grade into hyaloclastite brecciamade of vesicular clasts, in massive to layered zones. Volcaniclastic facies contain clasts produced during explosive eruptions and reworked clasts from sources above wave base. Volcaniclastic facies were deposited from cold granular flows with different grain size populations. Stratigraphy and facies architecture at El Barronal suggest that a succession of several discrete eruptive events occurred with a similar cyclic pattern made of an initial explosive phase followed by effusive emplacement of lavas, in turn followed by a period of quiescence of volcanic activity. Hyaloclastic fragmentation of magma took place in the final stages of lava emplacement, allowing only for local disorganization of the jigsaw-fit texture.

Panarea is a largely submarine to partly subaerial Quaternary lava dome complex-stratovolcano with a long-lived, active, shallow hydrothermal system, located in the Aeolian Islands volcanic arc of southern Italy. The emergent top of the volcano forms a small archipelago, made up of calc-alkaline basaltic andesite to rhyolite lava domes (ca. 150–20 ka). We document the facies outcropping on Lisca Bianca islet, Panarea archipelago, based on grain size, clast fabric, and degree of hydrothermal alteration, identifying coherent facies, boulder breccia facies, cobble breccia facies, pebble breccia facies, and pervasively altered andesite facies (alunite-marcasite-sulfur). The breccias all have ubiquitous jigsaw-fit clast textures, and are variably hydrothermally altered. The breccias are interpreted as hydrothermal breccias and are distinguished from primary volcanic facies based on their distinguishing characteristics. The breccias formed through a cyclical process, involving the following: stage 1: progressive build-up of fluid pressure toward the level of the tensile strength of the host andesite; stage 2: incipient fracturing of the andesite when fluid pressure approaches and then exceeds the tensile strength of the andesite under critical fracturing conditions; stage 3: pervasive fracturing of the host andesite, leading to an increase in permeability as a network of fractures develops; stage 4: declining pressure, with fluid flow rates that lead to infilling and sealing of fractures by natroalunite, thereby reducing permeability, leading to progressive build-up of fluid pressure again, and the beginning of a new cycle.