COMPLETING THE PLATE TECTONIC REVOLUTION USING THE LIP RECORD

Nearly five decades after the “plate tectonic revolution” of the 1960s, a detailed picture has emerged of the kinematics and dynamics of our planet in the context of the supercontinent Pangea. A much less detailed understanding exists for the pre-Pangea world, although there is substantial evidence for previous supercontinents (Rodinia, Nuna, etc) whose break-up severely fragmented and dispersed the older geological record. Only a full paleogeographic reconstruction of the approximately 35 main (and numerous minor) ‘puzzle’ pieces of preserved continental crust will allow a synthesis of the entire geological record. The strongest reconstruction constraints are coming from large igneous provinces (LIPs) and their plumbing systems of regional diabase dyke swarms. This is because LIPs and their dyke swarms: 1) are associated with continental break-up; 2) are emplaced in short pulses (typically 1 Myr or less); 3) have very large “footprints” (300- 3000 km); 4) are relatively insensitive to uplift (vertical dykes); 5) contain valuable geometrical information (e.g., radiating and linear dyke swarms) and yield superior ‘piercing points’; and 6) they are the target rocks of choice for high-quality paleomagnetic studies, commonly yielding stable results that can be tested for their primary nature. Also, advances in U-Pb geochronology, together with the realization that almost all mafic rocks contain baddeleyite (ZrO2), now allow precise dating of the short bursts of LIP magmatism. Multiple, precisely-dated events provide, in effect, magmatic ‘barcodes’ that can be compared among crustal blocks thus identifying original ‘nearest neighbours’. Also geometrical information (i.e., dyke trends) can constrain relative craton configurations, while primary paleomagnetic information can further constrain azimuthal orientation, latitude, and relative longitude. Using this approach, we are in year 2 of a 5-year project, sponsored by an industry-government-university consortium, to date all LIP events and their dyke swarms around the globe and produce robust reconstructions back to 2.7 Ga (www.supercontinent.org). We overview the Year 1 results of nearly 50 U-Pb baddeleyite ages from many cratons. Currently about 40+ scientists are involved; additional collaborators are welcome.