Low-δ18O and negative-Δ199Hg felsic igneous rocks in NE China: Implications for Early Cretaceous orogenic thinning

Changzhou DENG, Anzong FU, Hongyan GENG*, Deyou SUN, Guochun ZHAO, Guangzhou MAO, Frédéric MOYNIER, Bernd LEHMANN, Runsheng YIN

*Corresponding author for this work

Research output: Journal PublicationsJournal Article (refereed)peer-review

2 Citations (Scopus)

Abstract

Magmatic rocks carry key information to understand the processes of material cycling in the Earth's interior and record crucial clues to reconstruct the important tectonic evolution of the Earth. Therefore, it is of great importance to constrain the magma source (such as origin from crust or mantle, oceanic crust or continental crust, lower or upper continental crust) accurately, which however remains to be unraveled because of the variety magmatic sources and complex magmatic processes. High-precision stable isotopic analyses provide new tools to decipher the genesis of igneous rocks and to reconstruct their associated tectonic settings. Here, we report a pioneering work using integrated O-Hg-Hf-Nd isotopes to understand the genesis of the Early Cretaceous A-type granites and rhyolites from the Paleozoic-Mesozoic accretionary orogen in NE China. Low δ18O zircon values (3.2–5.7‰) of the A-type rocks reveal a magma source affected by meteoric fluids. Their whole-rock negative Δ199Hg values (−0.24 to −0.01‰), which are similar with the terrestrial systems but clearly different from the marine systems, indicate that hydrothermal alteration took place in the continental setting. Positive zircon εHf(t) (4.2–10.7) and mainly positive whole-rock εNd(t) (−0.5 to 2.4, mean = 1.2 ± 1.0, 1SD) values indicate that the magma source was dominated by juvenile crustal materials. This study suggests an elevated geothermal gradient due to the lithospheric thinning triggered by rollback and foundering of a Paleo-oceanic slab. The specific thermal anomaly caused the remelting of the altered upper continental crust, resulting in the formation of the A-type granites and rhyolites, with the characters of low-δ18O and negative-Δ199Hg values. Our study shows that Hg isotope, coupled with O and Nd–Hf isotopes, is a promising tool for petrogenetic studies.

Original languageEnglish
Article number121569
JournalChemical Geology
Volume633
DOIs
Publication statusPublished - 5 Sept 2023

Bibliographical note

Funding Information:
We would like to thank Editor Sonja Aulbach, professor Stephen Grasby and anonymous reviewers for the constructive suggestions of the manuscript. This study was supported by the Department of Natural Resources of Heilongjiang Province ( 201701 ) and the Croucher Chinese Visitorships from Croucher Foundation (2020−2021). Professor Guosheng Sun is thanked for their help during fieldwork. Professor Min Sun is thanked for the constructive comments on the preparation of the manuscript.

Publisher Copyright:
© 2023 Elsevier B.V.

Keywords

  • East China
  • Low-δO
  • Magmatism
  • Negative-ΔHg
  • Orogenic thinning

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