Neoarchaean banded iron formation within a ∼2620 Ma turbidite-dominated deep-water basin, Slave craton, NW Canada
| Autor: | Luke Ootes, Rasmus Haugaard, Kurt O. Konhauser |
|---|---|
| Rok vydání: | 2017 |
| Předmět: |
geography
Felsic geography.geographical_feature_category 010504 meteorology & atmospheric sciences Archean Metamorphic rock Geochemistry Geology Greenalite 010502 geochemistry & geophysics 01 natural sciences Craton Geochemistry and Petrology Clastic rock Banded iron formation Stilpnomelane 0105 earth and related environmental sciences |
| Zdroj: | Precambrian Research. 292:130-151 |
| ISSN: | 0301-9268 |
| Popis: | Banded iron formations (BIFs) are iron- and silica-rich chemical metasedimentary rocks that span much of the Archaean and early Palaeoproterozoic rock record. Given that BIFs precipitated from ambient seawater, they provide an important archive of Earth’s ancient marine environments. Within the Slave craton occurs one of the largest and well-preserved Achaean turbidite basins in the world. Interstratified within the greywacke-mudstone turbidites is BIF that is commonly associated with ferruginous sediments and locally with a felsic tuff bed. Field investigations were conducted at four BIF locations from west to east across the Slave craton. These BIFs are composed of micro- and mesobands of quartz and magnetite, with various amounts of metamorphic grunerite, ferro-actinolite, ferro-hornblende as well as greenalite and stilpnomelane, the latter two are interpreted as retrograde metamorphic phases. As the BIF was deposited in a deep-water turbidite-dominated basin(s), the chemical component was occasionally diluted by clastic detritus, as illustrated by highly variable Al2O3 content, and Al2O3/TiO2 and Cr/Ni that are similar to the clastic sediments. On a layer-by-layer basis, the iron content in the BIF ranges from as low as 4 wt.% and up to ∼75 wt.% Fe2O3, whereas the SiO2 content ranges from 20 wt.% to as high as ∼94 wt.%. This, together with a hyperbolic germanium/silicon distribution, suggests that continentally-sourced silica comprised the background precipitation, which was periodically interrupted by pulses of hydrothermally-sourced iron. High-temperature hydrothermal fluids contributed, with an average shale-normalized positive Eu anomaly of 1.92, which indicates input of reduced Eu2+ to the ambient seawater. The BIF shows characteristic aqueous fluid-derived rare earths + yttrium fractionation (Pr/Yb |
| Databáze: | OpenAIRE |
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