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Article Dans Une Revue Precambrian Research Année : 2024

Late Ediacaran iron formations in NW Iran: Origin, depositional age, tectonic and climatic significance

Résumé

The late Neoproterozoic Takab banded iron formation (BIF) occurs in one of the most important part of the Iranian plateau containing Precambrian crustal segments, now embedded in the Alpine-Himalayan orogenic system. The Takab BIF is hosted by low to medium grade metamorphic sequence including schist, quartzite and marble and its structure is dominated by bands or streaks. The ore body is mostly composed of quartz and iron oxides (magnetite, hematite, maghemite, goethite in different proportions), occurring as alternating iron- and silica-rich laminates. LA-ICP-MS U–Pb dating on zircons in schists from both the lower and upper layers of the orebody indicate a depositional age of ca. ∼560 Ma for iron deposits. Major, trace and rare earth elements of the ore body support the mixing of seawater and hydrothermal fluids through iron precipitation and up to ca. 20 % incorporation of terrigenous materials into the chemical precipitate of the original BIF. The provenance indicators as well Nd isotopic data, point towards the Neoproterozoic felsic-to-intermediate crystalline basement of the Takab area as the main sediment source. Fe isotope data together with Ce anomalies suggest that suboxic conditions prevailed in Ediacaran seawater at the time of deposition of the ore body. Combined with geochronological and geochemical data from other Neoproterozoic formations and crystalline rocks on the Iranian plateau, as well as supportive evidence for the occurrence of glacial sediments and bimodal volcanism in the studied area, we propose that the formation of the Takab BIF occurred in a back-arc basin environment, hence corresponding to a Rapitan-type iron ore. The co-occurrence of late Ediacaran BIFs and glaciogenic metasedimentary formations suggest the presence of active-magmatic marine anoxic basins at ca. ∼560 Ma, equivalent to the Ediacaran post-Gaskiers glaciation time.
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hal-04549373 , version 1 (17-04-2024)

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Maryam Honarmand, Ghasem Nabatian, Christiane Wagner, Iman Monsef, Guillaume Delpech, et al.. Late Ediacaran iron formations in NW Iran: Origin, depositional age, tectonic and climatic significance. Precambrian Research, 2024, 406, pp.107382. ⟨10.1016/j.precamres.2024.107382⟩. ⟨hal-04549373⟩
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