Misconceptions about Lu-Hf isotopic system: A comment on Gómez-Torres et al. (2025) “U-Pb, Hf isotopes and trace elements of zircon reveals a Mesoproterozoic crustal source for the Jurassic Caopas sub-volcanic intrusion: Northern part of the Nazas Igneous Province in Mexico”

Abstract

Gómez-Torres et al. (2025) [DOI: 10.1016/j.jsames.2024.105266] present geochemical data on major and trace elements in rocks and zircons, U-Pb zircon ages, and Lu-Hf zircon isotopic data from a limited sample set to investigate the petrogenesis of Middle Jurassic rhyolite in the subvolcanic Caopas intrusion. Their striking conclusion is that Mesoproterozoic crust (Oaxaquia-like rocks) served as the magma source for this intrusion through crustal reworking in a rift environment. However, I argue that there is no solid evidence to support this assumption. In this commentary, first, several formal issues, errors, and major omissions in the methodological procedures are pointed out, including a key point such as the handling of the zircon Hf model ages (TDM2_[Hf]). Then, a correct treatment of the Lu-Hf data and a more plausible interpretation of the TDM2_[Hf] are provided. This interpretation suggests that a mixing process was involved in the genesis of the Caopas intrusion between an undifferentiated basement (Oaxaquia-like, Permian, or Triassic crustal rocks) and juvenile material (fresh magma).