GEOCHRONOLOGICAL CONSTRAINTS ON THE EMPLACEMENT OF THE FRANKLIN LIP: TESTING HYPOTHESES FOR THE ONSET OF THE STURTIAN SNOWBALL EARTH

The establishment of time-correlative glacial deposits around the world, coupled with paleomagnetic data and climate modeling, has shown that ice at the poles reached equatorial latitudes at least twice during the Cryogenian Period. The cause for such a catastrophic change in climate remains uncertain, and explanations for the onset of the earlier Sturtian snowball Earth have invoked chemical weathering of the Franklin large igneous province (LIP) in the preceding millions of years, or the radiative forcing from its immediate sulfur aerosol emissions. High precision geochronology has the potential to resolve these questions, and a recent baddeleyite age closely linked the emplacement of the Franklin LIP to the timing of onset of the Sturtian glaciation; however, new high precision ages obtained from zircon in other Franklin sill samples using the chemical abrasion-isotope dilution-thermal ionization mass spectrometry (CA-ID-TIMS) technique differ from the previously published baddeleyite age by a few million years. This difference between the baddeleyite and zircon ages either illustrates an episodic and/or long-lived emplacement for the Franklin LIP that should be considered in future models of LIP climatic impacts, or calls for a reevaluation of baddeleyite geochronology.