The hydrothermally altered ankaramite basalts of Punta Poyata (Tenerife, Canary Islands)

Abstract

The features of hydrothermal mineral phases hosted in ankaramite basalts from the lower part of the Taganana area (northside Anaga, Tenerife) are studied in this work. This area, known as "Arco de Taganana", constitutes a volcanic rift zone that is overturned to the northwest and now identified by a dense NE-SW striking dyke swarm with a distinct SE dip. The most recent K-Ar data indicate a mid-upper Miocene age for the emplacement of the dykes. The rocks are intensely altered, usually brecciated, and are deeply eroded. This allows us to look at the roots of a volcanic edifice that has almost disappeared. Basaltic pyroclastic deposits and lava flows, as well as salic breccias, associated to the emplacement of salic domes, unconformably overly these rocks. Mineralogical and geochemical characteristics of the mineralization as well as isotopic data are reported in this paper. Some mineral paragenesis and isotopic data reflect submarine conditions of alteration. Mineralogy was studied by transmitted and reflected light microscopy, XRD, SEM and electron microprobe. In general terms, the mineralization consists of major jasper (quartz and opal) and celadonite, in association with minor hematite, magnetite, Fe ± Ca, Mg carbonates, Kaersutite, calcite and traces of ilmenite, which is always associated with magnetite. Four paragenetic stages were recognized in the studied area: two of them exhibit hydrothermal mineralization.