TIME CONSTRAINTS ON THE EVOLUTION OF THE TENNANT CREEK BLOCK, NORTHERN AUSTRALIA

Recent ion-microprobe U-Pb zircon age determinations on crustal components of the Palaeoproterozoic Tennant Creek Inlier have identified a relatively short (similar to 30 m.y.) history for the major magmatic events in the area, including those related to the Barramundi Orogeny. This work independently confirms the revisions of the Tennant Creek stratigraphy proposed by Donnellan et al. (1991). The oldest known rocks from the area are the volcaniclastic turbidites of the Warramunga Formation, which were deposited in a rapidly subsiding basin at 1862 +/- 9 to 1859 +/- 13 Ma. Subordinate zircon populations in the greywackes indicate earlier magmatic activity at 1930 +/- 12 and 1908 +/- 15 Ma. The regional shortening (D1) and contemporaneous intrusion of voluminous and chemically homogeneous granites (and associated felsic porphyry dykes), known across northern Australia as the Barramundi Orogeny, occurred here between 1858 +/- 12 and 1845 +/- 4 Ma. Following uplift, the felsic volcanics and volcaniclastics of the Flynn Subgroup were extruded between 1845 +/- 4 and 1827 +/- 9 Ma. During this interval, felsic porphyry dykes and minor granite bodies probably related to the Flynn Subgroup volcanism intruded the Warramunga Formation sediments. Magma source regions contain components as old as 3.0 Ga, as revealed by zircon inheritance in most of the analysed rocks. The youngest recognised igneous activity in the area are the intrusion of the ''Warrego granite'' at 1700-1650 Ma and the Gosse River East granite at 1712 +/- 5 Ma. The chronostratigraphy presented here is remarkably similar to that of parts of the well-exposed Palaeoproterozoic Trans-Hudson and Wopmay orogens of northern America.