Emplacement of a large igneous province as a possible cause of banded iron formation 2.45 billion years ago

LATEST Archaean and earliest Palaeoproterozoic times (from 2.6 to 2.2 billion years ago) have generally been viewed as a largely quiescent period of Earth history; the geological record indicates the very slow deposition of pelagic and chemical sediments1,2, and bears only a limited record of magmatic and tectonic activity3–5. Such quiescence is consistent with the contention that the Earth's main banded iron formations (BIFs)—finely laminated chemical sedimentary rocks, rich in iron oxide—formed slowly as oxygen abundances in the oceans gradually increased, thus reducing the capacity of sea water to retain dissolved iron6–10. Here we show that a large igneous province, comprising >30,000km3 of dolerite, basalt and rhyolite, accompanied deposition of a Hamersley Province BIF 2,449 ±3 million years ago. This observation indicates that Hamersley BIFs formed during a major tectono-magmatic event and were deposited very much faster than previously thought, at similar rates to (or faster than) modern pelagic sediments. Thus the largest Palaeoproterozoic BIFs, rather than simply reflecting a gradual increase in the oxygen content of the oceans during a period of tectonic quiescence, are more likely to have formed as a result of an increased supply of suboxic iron- and silica-rich sea water upwelling onto continental shelves during a pulse (or pulses) of increased submarine magmatic and hydrothermal activity.