KEY PALEOMAGNETIC POLE FROM THE WOONGARRA / WEELI WOLLI LARGE IGNEOUS PROVINCE, PILBARA CRATON, AUSTRALIA: A LINK BETWEEN SUPERCRATONS?

Putative supercratons from the Archean-Proterozoic transition include the postulated entities Superia, Sclavia, and Vaalbara. The latter supercraton is characterized by an extensively preserved epicratonic cover succession, which includes a 2.45-Ga bimodal large igneous province represented by the Woongarra Rhyolite and Weeli Wolli mafic sill complex, emplaced over the entire southern half of the extant Pilbara craton. Sampling for the present study concentrated on localities as far north as possible, away from the Ophthalmian and Capricorn orogenies that were earlier shown to generate widespread remagnetization of pre-1.8 Ga rocks along the craton's southern margin. Sixteen sites show a single-polarity characteristic remanence direction (NW and very shallow upward) that is distinct from the orogenic overprint direction. The Woongarra / Weeli Wolli remanence passes an inverse baked-contact test on a Mesoproterzoic dyke and, more importantly, a conglomerate test on Woongarra clasts in the immediately overlying Boolgeeda diamictite. Rock-magnetic analyses suggest that low-Ti magnetite is the carrier of a primary thermoremanence in these rocks.

The near-equatorial position of Pilbara at 2.45 Ga allows, but does not require, a direct connection with the Superior craton as determined by data from the Matachewan dyke swarm in Canada. If geomagnetic polarity constraints are honored for the precisely coeval Woongarra / Weeli Wolli and Matachewan "N" poles at 2446-2449 Ma, then a direct connection is only permitted by the allowance of uncertainties in both results. If Pilbara and Kaapvaal were indeed connected in the Vaalbara supercraton, then a combined apparent polar wander path may be constructed from both regions when rotated into their original relative orientation. In this case, regardless of which Vaalbara reconstruction is considered among several published variations, a long-lived (2.45-2.22 Ga), direct connection with Superior is not permitted by the paleomagnetic data. This result is a telling example of how a single pole comparison may permit a "closest approach" connection between cratons, but often those allowable connections may be refuted by other paleomagnetic data when considered together in temporal context.