# Quaternary Evolution of Ischia: A Review of Volcanology and Geology
## 3 Results
### Review of the Volcanology and Geochemistry of Ischia
The geological constraints in the laccolith model are the rate of tectonic uplift of Epomeo Mt, the bulk of the erupted products, the period of quiescence between the different volcanic phases, the frequency of the eruptions in geological time and the geochemical data relative to the erupted magma [30]. The laccolith hypothesis [30] initiates with the premise that the low crustal layer of Ischia (two kilometers in depth), which has experienced tectonic uplift and fracturing during the last 55 ky B.P., reposes a laccolith (Figure 5). The increment in pressure of this magmatic body, which has displayed resurgence, was achieved with the placement of a resurgent block wide 4 \(\times\) 4 km (Epomeo Mt), then further uplifted (piston phase, about 33 ky B.P. up to 10 ky B.P). The resurgence during the last two stages of quiescence (33-29 ky B.P. and 18-10 ky B.P.) and the ensuing eruptions are genetically related to the action of new magma [10]. During the resurgence, the island has been affected by gravitational  
Figure 5: The laccolith model of Ischia constructed by [PERSON] [30] (**a,b,c**) and [PERSON] et al. [19] (**d**). w: plate uplift; p\({}_{0}\): laccolith pressure; p\({}_{\rm x}\). laccolith pressure at phase x; q: average magma influx; L: length of the elastic plate; h: thickness of the elastic plate; \(\alpha\)3: minimum principal stress [30]. instabilities in the southern sector (large debris avalanches) and by seismic activity in the northern sector. The issues on the lacolith model have been reassessed by [PERSON] et al. [73], focusing on the volcano-tectonics of the northern portion of Ischia and with the relationships with the resurgence, the subsidence and the earthquakes. In particular, the seismogenic fault genetically related with the historical and recent destructive earthquakes of Ischia (Casamicciola 2017 earthquake) has been identified, and interpreted as formed in the northern portion of the island during the later phases of the caldera resurgence. A volcano-tectonic model of northern Ischia has been constructed [73], showing the down throwing of the fault zones offshore and the processes of stress loading and release onshore, which have been triggered by the subsidence of the Mt. Epomeo block. The geochemical information has proved the divergences in the magmatic development and has unveiled the value of the magma mixing [10]. Three chief rounds have been differentiated in the magmatic past times of the last 55 ky. The first round (55-33 ky; trachyte and alkali-trachyte) is marked by explosive eruptions, and by minor contamination. During the second round (28-18 ky B.P. ), initiating with the arrival of trachy-basaltic magma in the system of rules, the magmatic chamber transformed to an open system and was marked by mixing processes between the new magma participating the magmatic chamber and the resident magma and by processes of contamination with the fluids. The volcanic deposits of the third round (10 ky-1302 AD) vary in composition from latite to alkali-trachyte and exhibit a negative correlation between the rate of differentiation and the Sr isotopic ratios. The isotopic changes are evidence for a magmatic chamber, chemically zoned, and mixing procedures, before or during the eruption [6,10]. Table 1 summarizes the geological data on the volcanic deposits, on the tectonic activity and on the volcano-tectonic evolution of Ischia during the last 55 ky B.P. [10]. The periods from 10 to 18 ky B.P. and from 28 to 33 ky B.P. correspond with hiatuses of the volcanic activity and of the volcanic products. Ischia's volcanic history displays two cycles of activity (PRES and POES, Pre-Epomeo and Post-Epomeo lavas), separated by an important explosive phase, producing the Monte Epomeo Green Tuffs [9]. The geochemical data has specified three main magmatic sequences (A, B, C). The first sequence (sequence C) is in the PRES and is constituted of lava fluxes, domes and other pyroclastic products, which together make the volcanic basement of the island.