GEOCHRONOLOGY OF THE ALBION RANGE, IDAHO, AND ADJACENT NORTHERN ELKO COUNTY, NEVADA. FROM SHRIMP ANALYSIS OF DETRITAL ZIRCONS

Detrital zircon samples (sixty-random-grains each) from Raft River, Goose Creek, and Salmon Falls Creek, streams draining the Albion Mountains Core Complex of southern Idaho and adjacent northern Nevada, constrain the timing of Tertiary intrusive and eruptive events, and the stratigraphic affinity of the Meso- and Neoproterozoic Raft River and Mt. Harrison sedimentary sequences. Raft River drains the east side of the core complex, and contains Eocene (37 to 57 Ma) zircon grains from northern Nevada volcanics (Elko Formation and related strata), and Miocene (7.6 to 13.4 Ma) grains from the Twin Falls, Bruneau/Jarbidge, and Owyhee/Humboldt volcanic fields. Three detrital zircons (30.7 to 32.3 Ma) must have been derived from the Oligocene Almo granite exposed in the Silent City of Rocks 10 km upstream along Raft River from the sample locality. These 31 to 32 Ma ages are the first U-Pb ages on that pluton, and are consistent with U-Pb SHRIMP dates from the third stage of intrusion of the Emigrant Pass plutonic complex of the Grouse Creek Mountains to the south (A.E. Egger, et al., 2003, Int. Geol Rev. v.45, p. 497-532). Other zircon-grain populations in Raft River include 1009 to 1184 Ma “Grenville recycled” grains from Paleozoic or Proterozoic sandstones (Mt. Harrison succession), Paleoproterozoic “Yavapai-Mazatzal” grains (1686 to 1831 Ma) possibly recycled through the Elba Quartzite of the Raft River sequence, and scattered Archean grains back to 3300 Ma. In addition, Raft River contains intriguing small populations of 336 to 365 Ma western-assemblage “Antler” Devonian grains, 481 to 511 Ma Ordovician and Cambrian grains, and 688 to 742 Ma Neoproterozoic “Sturtian” grains, all with no obvious source. Goose Creek drains the west side of the core complex, and is flooded by Miocene 7.1 to 15.2 Ma Snake River Plain hotspot volcanic grains, in addition to sparse numbers of the same older populations. Salmon Falls Creek, the next drainage west, contains Jurassic (152 -172 Ma) grains from the Contact Pluton, late Eocene (42-35 Ma) magmatic grains, and McDermitt (15.9 +/- 0.3 Ma), Owyhee-Humboldt (13.5 +/- 0.8 Ma), and Bruneau-Jarbidge/Twin Falls (11.6 +/- 1.2 Ma) volcanic field grains. In each case the detrital zircons record the magmatic or recycled sedimentary zircon populations present in the source areas.