Many geologists believe that the Precordillera terrane of western Argentina was transferred from Laurentia, the ancestral craton of North America, to Gondwana in the early Paleozoic, although considerable disagreement exists on the method and time of transfer. While studying stratigraphic successions in the Precordillera, the PIs by chance analyzed detrital zircons from two quartz sandstone beds, one of Early Cambrian age, the other of early Late Ordovician age. The results were surprising, and led them to conclude that the Precordillera terrane was never part of Laurentia, but instead migrated from a location in tropical Gondwana in Cambrian time to its present location after Ordovician time. These results also lead the PIs to question all the basic, widely held assumptions supporting the Laurentian affinity of the Precordillera terrane. Because the implications of their preliminary data are 1) revolutionary, 2) require re-evaluation of a substantial body of evidence, and 3) are presently subject to challenge and dismissal, it is critical that their preliminary data be tested. They propose to collect samples from additional Cambrian sandstone beds in the Precordillera for U/Pb geochronology of detrital zircons. The objective is to demonstrate that the evidence from the single preliminary sample is not a fluke or an aberration but instead is truly representative.
