Mg-Ba-Sr-Nd isotopic evidence for a mélange origin of early Paleozoic arc magmatism

• Published in: Earth and planetary science letters 2022-01, Vol.577, p.117263, Article 117263
• Main Authors: Hao, Lu-Lu, Nan, Xiao-Yun, Kerr, Andrew C., Li, Si-Qi, Wu, Yuan-Bao, Wang, Hao, Huang, Fang
• Format: Article
• Language: English
• Subjects: arc magmas; Mg-Ba isotopes; mélange model; slab component transport; subduction zones
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/j.epsl.2021.117263

•Ba-Mg isotope data of mafic igneous rocks in a paleo-subduction zone are reported.•High δ26Mg values suggest subducted serpentinite components in their arc source.•Low δ138/134Ba values indicate contributions of subducted sediment.•A high δ138/134Ba value suggests contributions of subducted altered oceanic crust.•Arc magmas in paleo-subduction zones can be produced by mélange processes. In recent years, the mélange model has been increasingly considered as an important way to transfer slab components to arc sources in modern subduction zones. This model differs from the classic slab fluid/melt metasomatism model in that it invokes physical mixing of bulk sediment, altered oceanic crust (AOC), serpentinite, and mantle wedge at the slab-mantle interface. However, due to the lack of subducted sediment compositions, the mélange model has not been applied to any significant extent in paleo-subduction zones. The lack of evidence for bulk AOC and serpentinite components in mélange sources also hinders our understanding of any mélange origin for arc-type magmas. Here, we report Mg-Ba-Sr-Nd isotope compositions of the early Paleozoic Fushui mafic rocks in the Qinling orogen of central China, to trace their origin and constrain slab component transfer. The Fushui mafic rocks show typical arc-type geochemical features and enriched Sr-Nd isotope compositions, indicating the likely contribution of subducted sediments. They have low Rb/Ba ratios (