Tectono-magmatic evolution of the Chihuahua-Sinaloa border region in northern Mexico: Insights from zircon-apatite U–Pb geochronology, zircon Hf isotope composition and geochemistry of granodiorite intrusions

Abstract

We present the whole-rock geochemistry, LA–ICP–MS zircon-apatite U–Pb ages and zircon Hf isotope composition of the granodioritic plutons at the southwestern boundary of Chihuahua with the states of Sinaloa and Sonora. These granodiorites are exposed in the north and south of the Rio El Fuerte in southwest Chihuahua and northern Sinaloa. The magmatism spans over a time period of 37Ma from 90 to 53Ma. Zircons are exclusively magmatic with strong oscillatory zoning. No inheritance of any age has been observed. Our new U–Pb dating (~250 analyses) does not support the involvement of older basement lithologies in the generation of the granitic magmas. The U–Pb apatite ages from granodiorites in southwest Chihuahua vary from 52 to 70Ma. These apatite ages are 1 to 20Ma younger than the corresponding zircon U–Pb crystallization ages, suggesting variable cooling rates from very fast to 15°C/Ma (~800°C to 500°C) and shallow to moderate emplacement depths. In contrast, U–Pb apatite ages from the Sinaloa batholith are restricted from 64 to 61Ma and are indistinguishable from the zircon U–Pb ages range from 67 to 60Ma within the error, indicating rapid cooling and very shallow emplacement. However, one sample from El Realito showed a larger difference of ~20Ma in zircon–apatite age pair: zircon 80±0.8Ma and apatite 60.6±4Ma, suggesting a slower cooling rate of ~15°C/Ma. The weighted mean initial εHf (t) isotope composition (2σ) of granodiorites varies from +1.8 to +5.2. The radiogenic Hf isotope composition coupled with previous Sr–Nd isotope data demonstrates a significant shift from multiple crustal sources in the Sonoran batholithic belt to the predominant contribution of the mantle-derived magmas in the southwest Chihuahua and northern Sinaloa. Based on U–Pb ages, the absence of inheritance, typical high Th/U ratio and radiogenic Hf isotope composition, we suggest that the Late Cretaceous–Paleogene magmatic rocks in this region are not derived from melting of a felsic older crust, neither evolved North American Proterozoic basement nor Jurassic metasedimentary rocks of the Guerrero terrane. Instead, the magma was primarily derived from partial melting of mantle related sources, possibly in the subcontinental mantle wedge above the Farallon plate. Our younger U–Pb zircon–apatite ages are well correlated with the late-stage cogenetic porphyry Cu–Au mineralization at 57 to 59Ma. If the origin of ore mineralization is related to the magma sources of host batholiths, then a minimal input from crustal melt is suggested in the genesis of Cu–Au porphyry system.