The great escape: Petrogenesis of low-silica volcanism of Pliocene to Quaternary age associated with the Altiplano-Puna Volcanic Complex of northern Chile (21°10′-22°50′S)

Constraining the sub-arc, parental magma composition for the giant Altiplano-Puna Volcanic Complex, northern Chile

“…1). In this region, the ascending parental basaltic-andesite magma is thought to have avoided significant contamination by evolved melts from the APMB as demonstrated by the lowest 87 Sr/ 86 Sr and highest 143 Nd/ 144 Nd being towards the borders of the large felsic body 12,20 . The studied volcanoes ( Fig.…”

“…We aim to achieve this goal by analysing the δ 18 O values of single minerals from rare, weakly differentiated lavas with relatively low silica contents (SiO 2 = 54.6 to 57.2 wt% 12 ) and relatively low Sr and high Nd isotope ratios ( 87 Sr/ 86 Sr = 0.70554 to 0.70669; 143 Nd/ 144 Nd = 0.51234 to 0.51251; ref. 12 ). The samples selected for this study are from six individual volcanoes (La Poruña, San Pedro, Paniri, La Poruñita, Palpana and Chela), which were active at different times and are all located around the western margin of the Altiplano-Puna Magma Body (APMB) melt anomaly in the Altiplano-Puna Volcanic Complex (Fig.…”

“…Study area and sample selection. Common volcanic products in the Central Andes include stratovolcanoes and extensive ignimbrite deposits, but several monogenetic volcanoes of mafic character also exist 12,13 . Within the volcano-tectonic ignimbrite province of the Altiplano-Puna Volcanic Complex 14 , the location of mafic volcanism is largely confined to the borders of the partial melt anomaly termed the Altiplano-Puna Magma Body (APMB 12 ; Fig.…”

“…[16][17][18] ). In this region, volcanoes outside the limits of the APMB are composed of lava that is more primitive than the volcanoes situated directly above the APMB 12 .…”

“…Olivine-and pyroxene-phyric lava and scoria are ubiquitous at La Poruña, San Pedro, Paniri, La Poruñita, Palpana and Chela and vary from basaltic-andesite to andesite in composition, with whole-rock elemental and Sr and Nd isotope compositions that range from e.g., SiO 2 = 54.6 to 62.9 wt%, MgO = 1.6 to 6.1 wt%, Sr = 389 to 885 ppm, Cr = 5 to 625 ppm, 87 Sr/ 86 Sr = 0.705541(10) to 0.707656 (10), and 143 Nd/ 144 Nd = 0.512337(12) to 0.512513(50) (see 12,22,23 ). Recent work on these volcanoes utilised whole-rock elemental and Sr and Nd isotope data to construct an evolutionary model, in which limited magmatic differentiation occurred at mid-upper crustal levels 12,22 . Lavas of these selected volcanoes may thus represent the composition of parental magmas feeding volcanism within the Altiplano-Puna Volcanic Complex, as the magmas feeding these mafic eruptions largely escaped assimilation of APMB felsic melts during ascent 12 .…”