Radiometric dating and temperature history of banded iron formation–associated hematite, Gogebic iron range, Michigan, USA

摘要: Newly developed techniques were used to characterize the age, origin, and temperature history of coarse hematite contained in high-grade iron ore. Three botryoidal specimens from two different mines Gogebic range near Ironwood, Michigan (USA), yielded (U-Th)/^(21)Ne ages concordant with plateau ^4He/^3He ages. These data reveal that while grew at ca. 772 ± 41 Ma, third formed 300 m.y. later (453 14 Ma). polydomain thermochronometry indicates formation >80 °C for older ∼60 younger. Fe mobilization recrystallization open cavities 3–5 km subsurface has occurred episodically or possibly continuously over hundreds millions years despite a quiescent tectonic setting throughout this interval. While analyzed are distinct typical ore, their along structural relationships constrain onset enrichment between 1060 770 Ma. Cooling ∼0.5 °C/m.y. ensued 800 550 declining ∼0.1 last suggest an erosion rate ∼6 m/m.y. ∼5 total Superior Upland province through Phanerozoic, limit unroofing associated Pleistocene glaciation <1 km.