Rb-Sr ages of the Archean rocks from the Vermilion district,northeastern Minnesota

The Vermilion district of northerneastern Minnesota is a classic example of a lower Precambrian greenstone-granite terrane. It is a complex volcanic-sedimentary pile, characterized by repeated periods of volcanism and the presence of intercalated pyroclastic, volcanoclastic and epiclastic rocks. The volcanic-sedimentary pile is surrounded and intruded by contemporaneous granitic batholiths. Several rock units from the district have been dated by the whole-rock Rb-Sr method. The isochron ages and the corresponding initial Sr⁸⁷/Sr⁸⁶ ratios (= I) are:

	$\text{t(}\text{in b.y.}\text{) ± 2σ}$	$\text{1 ± 2σ}$
Ely Greenstone	$\text{2.69 ± 0.08}$	$\text{0.70056 ± 0.00026}$
Newton Lake Formation	$\text{2.65 ±0.11}$	$\text{0.70086 ± 0.00024}$
Granitic pebbles	$\text{2.69 ± 0.28}$	$\text{0.70078 ± 0.00058}$
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