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Isla El Tigre volcano is located in the Gulf of Fonseca (Honduras) along the Central America volcanic front, where a significant change in the strike of the volcanic chain is observed. The studied samples of this poorly investigated volcano are mainly subalkaline basic to intermediate lavas (basalts and basaltic andesites) and subordinate subalkaline/alkaline transitional basalts, both having the typical mineralogical and geochemical characteristics of arc volcanic rocks. On the basis of petrographic and geochemical features, two groups of rocks have been distinguished. Lavas from the main volcanic edifice are highly porphyritic and hy-qz normative, and have lower MgO contents (< 5 wt.%). They show significant LILE and LREE enrichments and Nb-Ta depletions, and have a strong slab signature as well as incompatible element contents similar to those of the main front of the adjacent volcanoes in El Salvador and Nicaragua (e.g., Ba/La up to 80). In contrast, lavas from the parasitic cones have higher MgO contents (> 5 wt.%), are ol-hy normative and show lower HFSE depletions relative to LILE and LREE, with lower Ba/La, Ba/Nb and Zr/Nb ratios. This suggests that mantle-derived magmas were not produced by the same process throughout the activity of the volcano. The bulk rock geochemistry and 87Sr/86Sr (0.70373-0.70382), 143Nd/144Nd (0.51298-0.51301), 206Pb/204Pb (18.55-18.58), 207Pb/204Pb (15.54-15.56) and 208Pb/204Pb (38.23-38.26) isotopic data of Isla El Tigre compared with the other volcanoes of the Gulf of Fonseca and all available literature data for Central America suggests that this stratovolcano was mainly built by mantle-derived melts driven by slab-derived fluid-flux melting, while magmas erupted through its parasitic cones have a clear signature of decompression melting with minor slab contribution. The coexistence of these two different mantle melting generation processes is likely related to the complex geodynamic setting of the Gulf of Fonseca, where the volcanic front changes direction by ca. 30° and two fundamental tectonic structures of the Chortis continental block, mainly the N-S Honduras Depression and the NE-SW Guayape Fault Zone, cross each other.

The Estancia Glencross Area (EGA) volcanic rocks form a series of five isolated buttes located at the southern end (∼52°S) of the discontinuous belt of Cenozoic basaltic lava formations occurring in the extra-Andean Patagonia. EGA volcanics are subalkalinebasaltsand basalticandesiteserupted at 8.0–8.5 Ma in a region closely behind the Andean Cordillera. EGAvolcanismpredated by about 4–5 my the onset of the volcanism in the nearby Pali Aike Volcanic Field, which produced highly primitive, alkaline lavas. Incompatible trace-element distributions and Sr–Nd isotope compositions of EGA rocks are those typical of within-plate OIB-type basalts and are indicative of minimal interaction of sub-lithosphericmagmaswith enriched reservoirs. The geochemical characteristics of EGA volcanics, as well as their age and location are consistent with a model of slab window opening beneath this region. The high silica content and thegarnetsignature of the estimated EGA primary magma are explained by a two-stage process involving the initial production of melts from a garnetlherzolitesource followed by the reaction of these melts withharzburgitecountry rocks during their ascent through the mantle lithosphere. The melt/harzburgite reaction, favoured by a slow melt ascent rate, as well as the low magma production at EGA, are likely related to the dominantly compressive stress regime operating in this area during LateMiocene.