## 3 Results  
### Bulk Rock and Mineral Chemistry  
The sampling location and major and trace-elemental compositions of the samples are presented in Table S1. For the Telica volcano, the major oxide description of the samples selected for this volcano was taken from [72]. Whole-rock compositions at Telica range from basaltic to andesitic (SiO\({}_{2}\) = 50.9-58.6 wt%; K\({}_{2}\)O = 0.84-1.43 wt%) and plot in the field of calc-alkaline (CA) to high-potassium calc-alkaline (HKCA) rocks [72]. These fall within the compositional ranges reported in the literature (50.8-53.5 wt% SiO\({}_{2}\); 0.9-1.1 wt% K\({}_{2}\)O; e.g., [20; 81; 82]). The basalts and basaltic andesites are enriched in large ion lithophile elements (LILE: Cs, Rb, Ba, La, etc.) relative to N-MORBs (Table S1). Most samples have moderate to strong high field strength element depletion (HFSE: Ta, Nb, Zr, Hf), and display generally lower Hf, Zr and Ti contents than N-MORB and E-MORB averages [83]. The normalised pattern also exhibits Ti and Zr anomalies relative to N-MORB [68].  
The Baru volcanic rock samples are basaltic andesites of the CA series (Table S1) [12]. Samples from La Cuesta are characterised by high Mg# [13]; within the high magnesium andesite field of 55-70 Mg#. The basaltic andesites are less enriched in large ion lithophile elements LILE relative to N-MORBs. Most samples have moderate to strong high field strength elements depletion (HFSE: Ta, Nb, Zr, Hf), with Nb = 5-11 ppm and Ta = 0.5-0.8 ppm, in line with adakitic characteristics (Supplementary Material S5).  
Mg# and Forsterite (Fo) contents for both Telica and Baru are illustrated in Figure S1. At Telica volcano, green clinopyroxenes on thin sections are identified as augite (W\({}_{036}\)-En\({}_{44}\)Fs\({}_{19}\)) with Mg# values (Mg/(Mg + Fe) of 71%. In sample TEL02, Px has dark green translucid tones, distinct cleavage, and is <4 mm. On thin sections, these were identified as augite (W\({}_{041-42}\)En\({}_{38}\)Fs\({}_{20}\)) with Mg# values (Mg/(Mg + Fe) = 71-72% and also contain iron oxides and Oi. The Oi is of a green transparent to pale green tone (some yellow in TEL02), generally <2 mm in size and with small plagioclase intergrowths. At Baru, only one out of 11 crystals of a quites from sample LCI recorded strong normal zoning from core-to-rim (81 to 78% Mg#). These aquites are observed in intergrowth with plagioclase phenocrysts of the same size, occasionally grouped with glomerulyic textures. The Oi have Fo\({}_{74-90}\) compositions, and two are normally zoned (Fo\({}_{85}\) to Fo\({}_{81}\) and Fo\({}_{76}\) to Fo\({}_{74}\)). The Mg# value of Px decreases from LCS and LCI to Bambito (Mg# 60-70). Px are slightly more variable in LCS (W\({}_{042-48}\)En\({}_{41-49}\)Fs\({}_{6-13}\)) with Mg# of 74-89%. Normal zonation was recorded in 3/13 while reverse zoning was recorded in 2/13 crystals. In sample BAM, some green clinopyroxenes on thin sections were identified as augites (W\({}_{040-45}\)En\({}_{41-48}\)Fs\({}_{8-13}\)) with Mg# values (Mg/(Mg + Fe) = 77-85%. Most of the augite crystals are present as phenocrysts of the large diameter (>2-4 mm) and contain concentric oxides and glass inclusions.