NEW PALEOMAGNETIC CONSTRAINTS ON RODINIA CONNECTIONS BETWEEN AUSTRALIA AND LAURENTIA

Reconstructions of Australia-Antarctica against either western Canada (SWEAT) or the western United States (AUSWUS) are based mainly on geological correlations, but have yet to receive quantitative support from precisely-dated paleopoles. Our studies of 1070 Ma mafic sills within the intracratonic Bangemall Superbasin of Western Australia have yielded a primary paleopole, BBS, that is significantly more reliable than previous results of this age for Australia. A reconstruction similar to SWEAT or AUSWUS between Australia (including the Mawson block of Antarctica) and Laurentia cannot be achieved by matching the BBS pole with the 1100 to 1020 Ma Laurentian apparent polar wander path, indicating that neither fit is viable at 1070 Ma.

Superimposing the BBS paleopole and an interpolated 1070 Ma pole position for Laurentia permits a reconstruction, AUSMEX (Australia-Mexico), that closely aligns late Mesoproterozoic orogenic belts in northeast Australia and southernmost Laurentia. However, paleomagnetic data for the 1235 Ma Sudbury dikes place Laurentia at low latitudes, whereas new paleomagnetic results for c. 1210 Ma dikes and metamorphic rocks place Australia at high latitudes. This makes any direct connection between the two continents at that time improbable, and implies that they moved independently during late Mesoproterozoic (Grenville) orogenic events. Imprecise data suggest that both continents occupied high latitudes at 1140 Ma. By 1070 Ma, Australia and Laurentia had moved to low-latitude positions, possibly in an arrangement similar to AUSMEX.

These results imply that: 1. Paleo- and early Mesoproterozoic geological similarities between Australia and Laurentia are fortuitous, 2. the Pacific Ocean did not form by separation of eastern Australia- Mawson from western Laurentia, and 3. up to 10,000 km of late Neoproterozoic passive margins in both continents need to matched with other continental blocks within any proposed Rodinia supercontinent.