Dallas Abbott and Ann Isley
Oceanic upwelling and mantle-plume activity; paleomagnetic tests of ideas on the source of the Fe in early Precambrian iron formations (in Mantle plumes; their identification through time )
Special Paper - Geological Society of America( 2001), 352:323-339
Index Terms/Descriptors: algoma-type deposits; Archean; banded iron formations; Canadian Shield; chemically precipitated rocks; chlorophyll; emplacement; global; hydrothermal alteration; iron; iron formations; iron ores; lava; mantle; mantle plumes; marine environment; metal ores; metals; metamorphic rocks; metasedimentary rocks; metasomatism; modern analogs; North America; organic compounds; paleogeography; paleomagnetism; pigments; Precambrian; productivity; sedimentary rocks; structural controls; Superior Province; superplumes; transport; upwelling
Latitude & LongitudeN46°00'00'' - N61°40'00'' and W99°00'00'' - W66°00'00''
In previous work, a cross-correlation analysis between time series of globally distributed occurrences of pre-1.6 Ga plume lavas and iron formations showed that the two events correlated at the 99% confidence level. These results fit two possible models for deposition in water depths from wave base to 2000 m-depths at which Superior-type iron formations were deposited. (1) The Fe could have traveled horizontally from a shallow-water, mantle-plume source, implying that iron formations should have median and mean paleolatitudes of approximately 30 degrees + or - 0.5 degrees (random-walk model). (2) Alternatively, the Fe traveled horizontally from a deep mid-ocean ridge source until it reached a coastal upwelling zone, implying that iron formations should have median and mean paleolatitudes of 44 degrees + or - 11 degrees and 43 degrees + or - 2 degrees , respectively (upwelling model). In order to test these models, we have used paleomagnetic data to determine the median and mean paleolatitudes of Superior-and Algoma-type iron formations. The median and mean paleolatitudes of six Superior-type banded iron formations are 37 degrees + or - 12 degrees and 35 degrees + or - 10 degrees , respectively. The median and mean paleolatitudes of nine Algoma-type banded iron formations are 20 degrees + or - 11 degrees and 21 degrees + or - 12 degrees , respectively. This result is expected for the Algoma-type iron formations, providing a test of the methodology. Our result is equivocal for the Superior-type iron formations, which contain over two-thirds of all fe deposited in iron formations. In order to fully test the upwelling hypothesis, more high-quality paleomagnetic data must be collected from iron formations and/or temporally associated rocks.