Early Mesoproterozoic (>1.4 Ga) ages from granulite basement inliers of SE Mexico and their implications on the Oaxaquia concept – Evidence from U-Pb and Lu-Hf isotopes on zircon

Abstract

Four isolated lower crustal complexes also referred to as “Oaxaquia” are exposed in E and SE Mexico. U-Pb zircon dating by laser ablation MC-ICPMS and single-grain Lu-Hf analysis by solution MC-ICPMS were applied to zircon from ortho- and paragneiss samples. Two orthogneiss samples from the Huiznopala Gneiss yield igneous protolith ages of 1411 ± 27 Ma and 1412 ± 59 Ma, respectively. A similar age of 1444 ± 16 Ma was obtained from the “El Catrín” migmatite of the Oaxacan Complex. Hafnium isotope compositions indicate that zircon crystallized from a depleted mantle source with varying amounts of recycled crustal material. The early Mesoproterozoic crust was partially remelted during ~1.25 to 1.2 Ga arc magmatism. Paragneisses contain mainly detrital zircon sourced from these ~1.25 to 1.2 Ga igneous rocks, indicating the basin received detritus from the arc. None of the Huiznopala and Oaxacan Complex paragneiss samples contained any early Mesoproterozoic or older zircon, which implies an absence of the older protolith material during sedimentation. However, differences in Hf-isotope compositions of some detrital zircons indicate provenances from both typical Oaxaquia (juvenile Mesoproterozoic crust) and more evolved crustal precursors of the same age. Paragneiss from the Guichicovi Complex, instead, contains both early Mesoproterozoic and Paleoproterozoic zircon indicating cratonic sources. The results are interpreted in terms of a “proto-Oaxaquia” oceanic arc system that was active over early Mesoproterozoic times (1.5–1.4 Ga) during the breakup of the Columbia supercontinent. These data further suggest that this arc system was accreted to Amazonia contemporaneously with the ~1.25 to 1.2 Ga granitic arc magmatism reported in Oaxaquia and the Eastern Cordillera of Colombia. Stacking of these arc rocks along the continental margin may have caused additional migmatization around 1.1 Ga.