DETRITAL ZIRCONS FROM THE CAROLINA TERRANE AS AN EXAMPLE FROM A WORLDWIDE RIVER SAND DATABASE: HOW U-PB DATING AND LU-HF AND OXYGEN ISOTOPES ON DETRITAL ZIRCON INFORM PALEOGEOGRAPHIC RECONSTRUCTIONS

In 1998 Ken Eriksson suggested collaboration on NeoProterzoic to Pennsylvania sedimentary rocks from PA to NC including the Carolina Terrane (CSB) to see how sources evolved with time (Eriksson et al., 2004). This led to sampling of active river sands in the US (Eriksson et al., 2003) and spurred 2 non-sedimentologists into examining continental growth through time as determined by dating detrital zircons from major rivers (Campbell and Allen, 2008). U-Pb dating simultaneously with analysis of some trace elements is now routinely supplemented by Lu-Hf and oxygen isotope analyses. The CSB sample (Aaron and Uwharrie formations) is used to show what can be gleaned from such datasets. CSB has a limited zircon age range (630-510 Ma), and has rimming of 610 Ma cores by 550 Ma rims. Earlier Nd-Sm work on CSB indicated an isotopically juvenile signal but this and 16 zircon Lu-Hf analyses indicate that while grossly oceanic in character, CSB contains a substantial and variable crustal component. Epsilon Hf values at ~550 Ma range from +11 to +1. Further oxygen isotope values range from the common mantle value of ~+5.3 ‰ to an unusual group at +3.6 ‰ that correlates strongly with Hf isotope composition. The primitive Hf correlates with the depleted oxygen. Such oxygen isotope compositions indicate “deep” high temperature hydrothermal interactions of polar waters with the zircon’s source rock. We interpret these data to align with models of Murphy et al. (2006) that CSB zircons were derived in an epicontinental setting near the south pole ~550Ma.

Campbell, I.H. and Allen, C.M., 2008, Formation of supercontinents linked toincreases in atmospheric oxygen: Nature Geoscience v.1, p. 554-558.

Eriksson K.A., Campbell, I.H., Palin, J.M., Allen, C.M., 2003, Predominance of Grenville magmatism recorded in detrital zircons from modern Appalachian Rivers: J. Geol.,v. 111, p. 707-717.

Eriksson, K.A., Campbell I.H., Palin, J.M., Allen, C.M., and Bock, B., 2004, Evidence for multiple recycling in Neoproterozoic through Pennsylvanian sedimentary rocks of the central Appalachian basin: J. Geol. v. 112, p, 261-276.

Murphy, J.B., Gutierrez-Alonso, G., Nance, R.D., Fernandez-Suarez, J., Keppie, D.J., Quesada, C., Strachan, R.A., and Dostal, J., 2006, Origin of the Rheic Ocean: Rifting along a Neoproterozoic suture?: Geology, v. 34, p. 325-328.