DETRITAL ZIRCON U-PB GEOCHRONOLOGY OF THE UPPER NEOPROTEROZOIC JACOBSVILLE SANDSTONE EASTERN UPPER PENINSULA, MICHIGAN, USA

Recent detrital zircon studies on the Neoproterozoic Jacobsville Sandstone in the upper peninsula of Michigan revealed that the deposition of the Jacobsville postdates volcanism associated with the Midcontinent Rift. Moreover, these data indicate that the provenance of the Jacobsville was variable in space and time. We present detrital zircon U-Pb age results for the upper Jacobsville Sandstone east near Munising, MI. Samples were collected at Au Sable Point (n=308), west of Munising (n=302) and near Deer Lake (n=213), sites . K-S statistical analysis indicates that these age spectra are statistically similar. The detrital zircon age spectra of the three sample groups were dominated (>60%) by Midcontinent Granite-Rhyolite (MGR) province grains and have an age peak about 1450 Ma. Grenville age grains (980-1200 Ma) comprise 16-30% of the age spectra with the peaks at ~1150 to 1250 Ma. Archean and Yavapai- Mazatzal ages are rare. The Deer Lake sample has a significant Penokean (~10%) peak at 1880 Ma. These data indicate that the eastern occurrences of the upper Jacobsville Sandstone were derived from the Grenville highlands and the adjacent MGR province more than 1000 km to the east and south. Thus, these strata may represent the distal clastic wedge of the Grenville foreland basin. The ubiquitous MGR zircons may have been derived from the south, and transported to the north along the arm of the MCR that occurs beneath southern Michigan. Keweenawan volcanic rocks of the MCR were not an important sediment source during upper Jacobsville deposition in the eastern Upper Peninsula of Michigan. Some of the ubiquitous MGR grains may have been transported north through the arm of the MCR that exists beneath the Michigan Basin.