Geochemical characterization of Archaean amphibolites from the eastern part of Anshan–Benxi iron producing area, northeastern China: implication for tectonic setting of BIFs

The Anshan-Benxi iron producing area, which is located at the northeastern margin of the North China Craton, is the main distribution area of Archaean BIFs in China. In their eastern part, including the Gongchangling and Waitoushan deposits, BIFs mainly are hosted in the Archaean middle Anshan Group. Amphibolites are widely distributed in the iron-bearing rock series, reflecting the tectonic setting of BIFs. Amphibolites not only have MORB-like compositional characteristics, but also have island arc-like ones, and they are consistent with back-arc basin basalts (BABB). In the study area, the protolith of amphibolites belongs to Okinawa-type BABB; it indicates that tectonic setting of BIFs is the intra-continental back-arc basin. In the study area, the formation of sedimentary basins for BIFs had been associated with oceanic plate subduction. Amphibolites from Gongchangling deposit are characterized by relative enrichments in LILE and LREE, and depletions in HFSE. This indicates that they had a relatively large influence of subduction in their formation. Amphibolites from Waitoushan deposit are characterized by relative enrichments in LILE without conspicuous depletions in HFSE, indicating relatively low subduction rates. Copyright (c) 2015 John Wiley & Sons, Ltd.