Depositional age and tectonic setting of the Dimunalike iron formation in southeast Tarim Craton: Implications for the resurgence of Neoproterozoic iron formations

Abstract

Proterozoic iron formations (IFs) largely formed during the Paleoproterozoic and Neoproterozoic eras. It remains unclear why IFs reappeared in Neoproterozoic successions globally after a depositional gap of more than one billion years. Tonian IFs can help clarify this ambiguity as they were deposited during a transitional period when IFs reemerged. In this study, we report new geochronological and geochemical data of metavolcanic rocks interbedded with a Tonian IF — the Dimunalike IF — in the southeast portion of the Tarim Craton to i) constrain the depositional age and tectonic setting of this IF, and ii) provide new insights into the resurgence of IF deposition in the Neoproterozoic. Zircons from metavolcanic rocks yield a U–Pb weighted mean age of 745.2 ± 1.6 Ma (MSWD = 0.81), indicating that the Dimunalike IF formed in the late Tonian. The metavolcanic rocks exhibit geochemical signatures similar to within-plate alkalic basalts, being characterized by high Zr contents (233–254 ppm) and Zr/Y ratios (6.62–7.08). Considering the Hf isotope composition of zircons from the metavolcanic rocks, as well as igneous rocks throughout the Tarim Craton, it is suggested that the Dimunalike IF was deposited in a rift basin related to the breakup of the Rodinia supercontinent. With an age of approximately 745 Ma and no signs of glacial influence, the Dimunalike IF demonstrates that extensive IF deposition occurred prior to the Cryogenian. Our new data support the idea that, rather than glaciations, hydrothermal processes and mafic volcanism were crucial to the resurgence of Neoproterozoic IFs by enhancing ferruginous conditions in oceans.