Pb-Pb Zircon Dating by Direct Evaporation: Method Development and Selected Geological Applications

Abstract

<p>The zircon evaporation method requires no chemical treatment of the zircon grain in the form of acid dissolution or isotopic spiking. In a test of this method, the derived Pb-Pb age is consistent with conventional U-Pb age of zircons from the Battersea Pluton.</p> <p>Zircons from the Britt Domain reveal a variety of ages from a complete isotopic resetting to the time of the Grenville orogeny (approx. 1100 Ma) to ages of plutons at approx. 1330 Ma and 1450 Ma. An orthoquartzite, CBQ, contained zircons from a Penokean aged terrain and an Archean aged terrain. This may be evidence for a collision of a Penokean aged island arc onto the Superior Province. The age of the Pine Cove Pluton constrains minimum age of the Penokean suture. Its minimum age of approx. 1330 Ma constrains the time of last movement of the French River suture line.</p> <p>Zircons from the Cedar Lake and Lac Seul gneiss from the Winnipeg River Belt of the Superior Province show evidence of the last major metamorphic event, the Kenoran orogeny at 2700 Ma, and its age of crystallization at 3170 Ma. One zircon from the Cedar Lake tonalite results an age of 3391±2 Ma. This may be a xenocryst from older crust mixed into the tonalite.</p>The zircon evaporation technique is ideal for reconnaissance work due to the ease of sample preparation and the large number of zircons that can be tested quickly.</p>