Age constraints for Paleoproterozoic glaciation in the Lake Superior Region: detrital zircon and hydrothermal xenotime ages for the Chocolay Group, Marquette Range Supergroup

Abstract

A geochronological study of the Chocolay Group at the base of the Paleoproterozoic Marquette Range Supergroup in Michigan, Lake Superior Region, is attempted for the first time. Age data from detrital zircon grains and hydrothermal xenotime from the basal glaciogenic formation, the Enchantment Lake Formation, and the stratigraphically higher Sturgeon Quartzite and its equivalent, the Sunday Quartzite, provide maximum and minimum age constraints for the Chocolay Group. The youngest detrital zircon population in the Enchantment Lake Formation is 2317 ± 6 Ma; in the Sturgeon Quartzite, it is 2306 ± 9 Ma, and in the Sunday Quartzite, it is 2647 ± 5 Ma. The oldest hydrothermal xenotime age in the Enchantment Lake Formation is 2133 ± 11 Ma; in the Sturgeon Quartzite, it is 2115 ± 5 Ma, and in the Sunday Quartzite, it is 2207 ± 5 Ma. The radiometric age data in this study implies the depositional age of the Chocolay Group is constrained to ~2.3–2.2 Ga, which proves its correlation with part of the Huronian Supergroup in the Lake Huron Region, Ontario, and reveals the unconformity that separates the Chocolay Group from the overlying Menominee Group is up to 325 million years in duration. The source(s) of the ~ 2.3 Ga detrital zircon populations in the Enchantment Lake Formation and Sturgeon Quartzite remains an enigma because no known rock units of this age are known in the Michigan area. It is speculated that once widespread volcano-sedimentary cover sequences in Michigan were removed or concealed prior to Chocolay Group deposition. The hydrothermal xenotime ages probably reflect basinal hydrothermal fluid flow associated with the period of extension, involving rifting and major dyke formation, that affected the North American provinces between 2.2 and 2.1 Ga.

7.2 Huronian-Age Glaciation

“…In spite of early suggestions such as those of Young (1966) and Young and Church (1966) and that of Ojakangas (1988) and Ojakangas et al (2001b), correlation between the Palaeoproterozoic successions of the Lake Huron and Lake Superior regions was not generally accepted. New geochronological work on detrital zircons and xenotime cements from rocks of the Chocolay Group in northern Michigan (Vallini et al 2006) provided convincing data in support of the old correlations. The new age data showed that the depositional age of the Chocolay Group, including the glaciogenic diamictites at its base, is probably between about 2.3 and 2.2 Ga, thus validating the lithostratigraphic correlation proposed 40 years earlier.…”

“…Early attempts at lithostratigraphic correlation of these ancient glacial deposits were frustrated by spurious age data and erroneous interpretations of these data but as geochronological techniques have become more sophisticated, new results are showing that many of the early lithostratigraphical correlations are correct. Correlation of the Gowganda Formation with thinner glaciogenic deposits in Northern Michigan is now supported by modern geochronology (Vallini et al 2006). Deposition of Palaeoproterozoic sedimentary rocks in the N. Michigan area was initiated at the time of deposition of the Gowganda Formation so that the earlier glaciogenic formations and associated rocks are not preserved there.…”

Anomalous negative excursion of carbon isotope in organic carbon after the last Paleoproterozoic glaciation in North America

“…The Chocolay Group of the Marquette Range Supergroup consists of diamictite (Enchantment Lake Formation), sandstone (Mesnard Formation), and carbonate (Kona Dolomite) in ascending stratigraphic order (Figure 1b). The depositional age of the Enchantment Lake Formation has been constrained to between 2.29 and 2.13 Ga [ Vallini et al , 2006]. Positive δ 13 C carb excursions that may represent the onset of the Lomagundi event have been observed in the Kona Dolomite [ Bekker et al , 2006].…”

“…The age constraints for the Huronian Supergroup are from Young et al [2001] and Bekker et al [2006, and references therein]. The age constraint for the Enchantment Lake Formation is given by Vallini et al [2006].…”

Climatic catastrophes in Earth history: two great Proterozoic glacial episodes

“…Lithostratigraphical correlation between Palaeoproterozoic rocks on the north shore of Lake Huron and the south shore of Lake Superior. Note that there is only one glacial formation in each of the sections in the Lake Superior area and these are correlated with the Gowganda Formation of the Huronian Supergroup, as validated by recent geochronological studies (Vallini et al ., ). The glacial deposits of both regions are followed by quartz arenites.…”