Silicic Dome Volcanic Complexes

Abstract

Silicic Dome Volcanic Complexes are very well represented in Puna Norte and represent the initial manifestations of Cenozoic magmatism in the region. Their eruption, 100–200 km east of the actual frontal arc, began at the end of the Upper Oligocene–Lower Miocene and extended to the Middle Miocene in two pulses: 25–15 Ma and 13–11.8 Ma. They correspond to conical bodies with tumulus forms (0.1–4 km²) composed by silicic lavas and shallow intrusive bodies, together or not with pyroclastic facies. They have been extruded in several episodes of Pelean to Vulcanian type with strong hydromagmatic characteristics. The domes of the first pulse are dacitic, metaluminous to weakly peraluminous, with minor andesites and trachydacytes, and the second pulse rhyodacitic–rhyolitic and peraluminous. They show LILE and LREE enrichment relative to the HREE and negative spikes in Nb, Ta, and Ti. The REE pattern slope increases from the first to the second pulse rocks (Sm/Yb = 2–3.3 to = 3.5–5) and the isotopic composition varies between⁸⁷Sr/⁸⁶Sr $\sim$ 0.706 to $\sim$0.713, $\in \mathrm{Nd}$_T-3 to –7 in rocks of the first cycle to the second, link with crustal thickening previous or concomitant to the second pulse and with an increase of hybridization depth of the magmas at that time. Epithermal systems (Pb-Zn) rich in Ag-Au of intermediate sulphidation are associated with the dome complexes of the second pulse.