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The Chivillas Formation is the easternmost record of Mesozoic marine volcanism in Mexico. It consists of thick intervals of pillow lavas interbedded with siliciclastic turbidites, and debrites, containing clasts derived from metamorphic, sedimentary and volcanic sources. Clast composition and detrital zircon geochronology indicate a continental provenance, with sources located south of the studied rocks. Detrital zircon ages range from 1573 ± 60 to 125 ± 1.6 Ma. The probability curves have peaks at 124 to 130 Ma (mean 126 Ma); 188 Ma and 921–1236 Ma (the latter with peaks at ∼ 1022 and ∼ 1157 Ma). Subordinate peaks at 277, 419 and 535 Ma are also present. We interpret the youngest zircon population ∼ 126 Ma (Barremian), as the maximum depositional age. Other peaks suggest Grenvillian-type basement and Permo-Triassic arc sources. Late Jurassic detrital zircons were probably derived from the Sierra de Juarez Mylonitic belt. Pillow lavas are mostly alkaline basalts, with SiO2 46%–53%, and alkali oxide (K2O + Na2O) 5–8 wt.%; all samples have low-TiO2 ( |
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