Recycling of sediment into the mantle source of K-rich mafic rocks

Sr–Nd–Hf–O isotopic evidence from the Fushui complex in the Qinling orogen

Hao Wang, Yuan Bao Wu*, Chao Ran Li, Tian Yu Zhao, Zheng Wei Qin, Liu Qin Zhu, Shan Gao, Jian Ping Zheng, Xiao Ming Liu, Lian Zhou, Yang Zhang, Sai Hong Yang

*Corresponding author for this work

Research output: Contribution to journalArticle

30 Citations (Scopus)

Abstract

Potassium (K)-rich mafic rocks are viewed as being derived from partial melting of an enriched mantle source, but it is controversial about which processes cause the mantle enrichment. The Fushui intrusive complex is the largest early Paleozoic K-rich intrusive complex in the eastern Qinling orogen. Therefore, detailed studies on the Fushui complex can contribute not only to understanding of the petrogenesis of K-rich mafic rocks, but also to unraveling the Paleozoic evolution of the Qinling orogen. In this study, we provide an integrated investigation of in situ zircon U–Pb dating and Hf–O isotopes, in combination with whole-rock major and trace elements, as well as Sr–Nd–Hf isotopes, for the Fushui intrusive complex. In situ zircon secondary ion mass spectrometry (SIMS) / laser ablation induction coupled plasma mass spectrometry (LA-ICPMS) U–Pb dating reveals that different rock types of the Fushui complex have identical formation ages of 488–484 Ma. The Fushui complex belongs to the shoshonitic series, and is characterized by extreme large ion lithophile element (LILE, e.g., Ba, U, Th and Sr) and Pb enrichment and depletion of high field-strength elements (HFSEs, e.g. Nb, Ta, Zr, Hf, P and Ti). It shows high initial Sr isotopic ratios (0.7100–0.7151), negative whole-rock εNd(t) (−3.97 to −5.68) and negative to slight positive whole-rock (−2.24 to 2.38) and zircon (−2.85 to 0.34) εHf(t) values, as well as high zircon δ18O values (6.86 ± 0.13 ‰). The Hf–Nd isotopic systems are decoupled with positive ΔεHf values (3.85–5.37). These geochemical features indicate that the mantle source has incorporated subducted zircon–barren oceanic sediments. A simple two-end-members mixing model constrains the amount of subducted sediments in the Fushui mantle source to 5–8 %. The Fushui complex originated from 1 to 6 % equilibrium melting of a phlogopite-bearing garnet lherzolite by non-modal melting. As shoshonitic magmas have been discovered in modern nascent arcs, we suggest that the generation of the Fushui complex was induced by the subduction of the Paleotethyan Ocean, when it jumped from the northern to the southern boundary of the North Qinling microcontinent.

Original languageEnglish
Pages (from-to)1-19
Number of pages19
JournalContributions to Mineralogy and Petrology
Volume168
Issue number4
DOIs
Publication statusPublished - 1 Oct 2014
Externally publishedYes

Keywords

  • Geochemistry
  • K-rich mafic rock
  • Qinling orogen
  • Subducted sediment
  • Zircon Hf–O isotope

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