Geochronology and geochemistry of Early Cretaceous volcanic sequences in Northwestern Peru: implications for Farallon Plate subduction

ABSTRACT

The Early Cretaceous geology of Northwestern (NW) Peru was characterized by emplacement of voluminous felsic volcanic rocks (e.g. the Oyotún Fm.), which have important implications for the understanding of Early Cretaceous crust-mantle interactions in the Central Andes. We present U-Pb-Hf isotopic compositions and whole-rock and trace elemental compositions of a series of Early Cretaceous volcanic rocks from the Western Cordillera and the Eastern Cordillera of the Central Andes. The volcanic rocks outcrop sporadically with limited thickness and uniform volcanic lithofacies in the western region, while the eastern region has distributions of larger scale volcanic rocks with more complex volcanic lithofacies. LA-ICP-MS zircon U-Pb dating defines the age of the Oyotún Fm. range from 138.8 Ma to 131.0 Ma in the Western Cordillera, and from 139.7 Ma to 132.3 Ma in the Eastern Cordillera. In situ Hf isotope analysis on dated zircon yield an ε_Hf(t) range of +3.37 to +8.42 and a T_DM2(Hf) range from 983 Ma to 650 Ma with a peak at ca. 840 Ma. The Early Cretaceous felsic magmas are predominantly dacites and rhyolites with minor components of basalt and andesite, and show relatively homogeneous Hf isotopic compositions of zircon in single samples. Both the ε_Hf(t) of zircons and the magma temperature increase from the bottom to the top of the Early Cretaceous volcanic rocks in each studied area. All these facts imply an increasing contribution of contemporaneous underplated hot and dry mantle-derived magmas with time, both as a heat source inducing crustal melting and a source of material (melt) that variably mixed with the ancient continental crustal materials.

KEYWORDS:

• Geochemistry
• Zircon U-Pb-Hf isotopes
• volcanic rocks
• Early Cretaceous
• Farallon Plate
• NW Peru

Acknowledgments

We thank Prof. Robert J. Stern, Editor-in-Chief, the Reviewers Carlos Aizprua, Yamirka Rojas-Agramonte and an anonymous reviewer for their critical, careful, and very constructive reviews that have helped improve the clarity and interpretations of the manuscript. We also appreciate the assistance of J.L. Shen and N.C. Xu for ICP-MS and XRF analyses, Y.S. Liu for Lu-Hf isotopic analysis and P.J. Lin for LA-ICP-MS analysis, G.F. Xing, N. Chen, and Marco Chumpitaz for their helpful discussion and Leyla Guerrero for help in the field.

Disclosure statement

No potential conflict of interest was reported by the author(s).

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Funding

This work was supported by the National Natural Science Foundation of China [41302071] International Comparative Study of volcanic rocks in Yandangshan Global Geopark (Scientific Research) project [NJZX-K-2020-28]; China Geological Survey [DD20190603].