Petrogenetic link between amphibolites and the banded iron formation of the Yishui region in the North China Craton: implications for Neoarchean plume tectonics

ABSTRACT

Amphibolites have a genetically close relationship with banded iron formations (BIFs) in the North China Craton (NCC). The Yishui amphibolites in the NCC occur interbedded with Algoma–type Yishui BIFs as related wall rocks. A reconstruction of the amphibolite protolith was conducted based on the results of petrologic, mineralogic, and geochemical analyses. The Yishui amphibolites consist of actinolite, ferrohornblende, albite, orthoclase, biotite, quartz, magnetite with minor pyrite, titanite, and ilmenite. Their chemical compositions are mainly SiO₂, Fe₂O₃^T, CaO, and Al₂O₃ with subordinate TiO₂, MgO, Na₂O, K₂O, P₂O₅, and MnO. The chondrite–normalized rare earth element diagram, characterized by enriched light rare earth elements (La/Yb_CN = 19.51–24.05) with insignificant Eu and Ce anomalies, shows coherent trends. The primitive mantle–normalized multi–element spider diagram is enriched in large ion lithophile elements, high field strength elements, and light rare earth elements which are related to a mantle source. The results of this study, combined with previous literature data, indicate that the Yishui amphibolite protoliths had intraplate alkaline basalt affinities and were derived from an ocean island basalt–type mantle source with no contamination. The results also suggest that the basalts were primarily the product of small amounts of partial melting. Based on the results, it is considered that a mantle plume model is the most appropriate tectonic model as it better explains the amphibolite geochemical signature. Furthermore, this model can provide crucial information regarding the Archaean NCC tectonic evolution and can demonstrate the temporal and spatial relationships between the BIFs and wall rocks.