Table 1 Summary of petrographic features for the outcrop samples

Teziutlán andesite unit

(1.44–2.65 Ma)

LH8–LH12

dark gray; vesicular matrix, pores with 1–5 mm in diameter, relatively few phenocrysts ~ 0.5 × 1 mm in size; plagioclase, pyroxene, olivine, magnetite, ilmenite

LH13–LH17

medium gray; nonporous, occasionally fractured, porphyritic to glomerophyric texture with abundant, irregularly distributed subhedral to euhedral plagioclase phenocrysts (up to 10 mm long); plagioclase, pyroxene, magnetite, occasionally olivine

LH29–LH30

medium gray; few pores 1 to 3 mm in diameter, porphyritic to glomerophyric texture with comparatively few, unequally distributed phenocrysts with a size ranging between < 1 mm and 10 mm; plagioclase, pyroxene, olivine, some altered olivine in LH29

RLM1–RLM3

brownish–gray; RLM1 and RLM2: nonporous, RLM3: few pores with a diameter of < 1 mm to 2 mm partially plugged with secondary alteration minerals, fine cracks, and fissures with alteration rims along these cracks, porphyritic with large phenocrysts (up to 2–5 mm long); plagioclase, pyroxene (augite), olivine, magnetite

RLM9

dark gray; nonporous, fractured, porphyritic texture comprising relatively large plagioclase phenocrysts that are up to 10 mm long; plagioclase, pyroxene, magnetite

Cuyoaco andesite unit

(8.9–10.5 Ma)

LH33–LH35

medium gray; nonporous, porphyritic to glomerophyric texture with comparatively few and irregularly distributed subhedral to euhedral plagioclase phenocrysts (up to 10 mm long) as well as augite and olivine

LH40

medium gray; nonporous, occasionally fractures, porphyritic to glomerophyric texture with abundant phenocrysts up to ~ 1 × 2 mm in size, some alteration rims

LH41

light gray to beige; slightly reddish; nonporous, occasionally fractures, porphyritic to glomerophyric texture with abundant phenocrysts up to ~ 1 × 2 mm in size, weak alteration

LH50–LH51

beige; nonporous, microcrystalline matrix with plagioclase, quartz, pyroxene, hornblende, and biotite; interpreted as subvolcanic/hypabyssal rocks

LH72–OLH1

light gray to reddish; nonporous, abundant fractures, porphyritic texture with phenocrysts ~ 1 × 2 mm in size, weak alteration; plagioclase, pyroxene (augite), olivine, ilmenite