Eighty-five detrital zircon grains from Mesoproterozoic and/or Neoproterozoic to Middle Cambrian sedimentary strata in
northwest Sonora, Mexico, have been analyzed to determine source terranes and provide limiting depositional ages of the units.
The zircon suites from the Mesoproterozoic and/or Neoproterozoic El Alamo Formation and El Aguila unit yield ages between
1.06 Ga and 2.67 Ga, with predominant ages of 1.1 to 1.2 Ga. Zircons from the Lower? and Middle Cambrian Bolsa Quartzite
show age groups from 525 Ma to 1.63 Ga, with a dominant population of 1.1 to 1.2 Ga grains. Grains older than 1.2 Ga in the
samples were most likely derived from basement terranes and ~1.4 Ga granitic bodies of the southwest U.S. and northwest
Mexico. It is also possible that the sediments were transported from the south, although source rocks of the appropriate age are not
presently exposed south of the study area in northern Mexico. Three possibilities for the dominant 1.1 to 1.2 Ga grains include
derivation from: (1) exposures of the Grenville belt in southern North America, (2) local 1.1-1.2 Ga granite bodies, or (3) a
southern source, such as the Oaxaca terrane, that was subsequently rifted away. Sampling of additional units in the western U.S.
and northern Mexico may help resolve the ambiguity surrounding the source of the 1.1 to 1.2 Ga grains.
