Significance of Provenance Ages from the Chiapas Massif Complex (Southeastern Mexico): Redefining the Paleozoic Basement of the Maya Block and Its Evolution in a Peri-Gondwanan Realm

Abstract

Medium- to high-grade metasedimentary rocks are exposed as isolated domains in mostly metaigneous crystalline rocks of the Chiapas Massif Complex (CMC), which forms the basement of the southern Maya Block, southeastern Mexico. Laser ablation multicollector inductively coupled plasma mass spectrometry U-Pb isotope analyses on inherited detrital zircon cores show two principal age distributions: (a) Group I, with its highest peak at 500–650 Ma and smaller peaks at ∼380–400 Ma, 1.0–1.2 Ga, 1.5–2.0 Ga, and 2.6–3.1 Ga, and (b) Group II, with its highest peak at 1.0–1.2 Ga, a minor peak at 1.5–1.6 Ga (or ∼1.0-Ga zircon cores only), and a lack of 500–650-Ma zircons. The cores are commonly surrounded by metamorphic or anatectic overgrowths, and some zircon ages were reset by a tectonothermal event at ∼250 Ma. The age distribution of zircon cores from Group I metasediments are similar to detrital zircon ages in Carboniferous-Permian sediments (Santa Rosa Formation) in southeastern Chiapas, which were shed mostly from continental crust dominated by Pan-African–Brasiliano orogenic cycles. Group II metasediments have different sources, principally from Grenville orogens, such as the Oaxacan Complex, and early mid-Proterozoic sources, such as the Rio Negro–Juruena Province of western Amazonia. The lowest stratigraphic unit in the CMC (the Jocote Unit) is intruded by lower Ordovician S-type granite and contains only 1.5–1.6-Ga and older detrital zircons. The protoliths of the CMC can be correlated with Paleozoic strata across the southern Maya Block, and they show parallels with the geologic history and provenance patterns of protoliths from the Acatlán Complex (Mixteca Terrane) of central southern Mexico. The geologic history of the CMC and the Maya Block can be interpreted in terms of tectonothermal events accompanying accretion of the CMC and polarity reversal during formation of the western Pangea margin.