Two Carboniferous Ages<subtitle>A Comparison of Shrimp Zircon Dating with Conventional Zircon Ages and 40Ar/39Ar Analysis</subtitle>

Abstract

Abstract Using replicate measurements of a homogeneous reference zircon, the discrimination of Pb +and UO +ions relative to U +observed in zircon analysis with the SHRIMP ion microprobe has been established as a power law relationship. This relationship minimizes uncertainty in comparative measurement of 206Pb/ 238Uages in zircons. Ages thus obtained have been compared with isotope dilution thermal ionisation mass spectrometric (1DTIMS) analysis of zircons in the Paterson Volcanics (Carboniferous, Australia) and 40Ar/ 39Ar dating of sanidines in the Z1 tonstein (Carboniferous, Germany). No bias can be detected between the three dating methods, confirming that SHRIMP zircon 206Pb/ 238U ages are accurate and comparable with other well-measured Phanerozoic ages. The age of the Westphalian B Stage of Europe is constrained by the Z1 tonstein; SHRIMP zircon analysis supports the 40Ar/ 39Ar age of 311 Ma and improves on its precision by a factor of two. The Paterson Volcanics mark both the Australian base of the Kiaman magnetic superchron and onset of the major, Late Palaeozoic period of Gondwana glaciation; SHRIMP and 1DTIMS zircon dating reassign these processes to the Namurian from the late Westphalian assignment used until now for global correlations.