CONSTRAINTS FROM THE LIP BARCODE RECORD AND ASSOCIATED GIANT DYKE SWARMS FOR SUPERCONTINENT RECONSTRUCTIONS: PROGRESS REPORT ON THE LIPS-SUPERCONTINENT PROJECT

The breakup history of Pangaea, Earth’s most recent supercontinent, teaches us that large igneous provinces (LIPs) play a pivotal role in continental breakup, typically leaving remnants of flood basalts and their giant feeder dyke swarms on conjugate rifted margins. As was realized by Du Toit, as early as 1920 in relation to the extensive Karoo sills and dispersed southern continents, LIPs thus provide a key tool in reconstructing past continental aggregations. In the older record, many of the flood basalt sequences are no longer preserved, but their giant tholeiitic dyke swarms and sill complexes provide a rich proxy record for the waxing and waning of LIP activity in deep geological time, very strongly correlating with the putative supercontinent cycle.

A detailed survey of many ancient (Archean) cratons or (Proterozoic) composite cratons shows that they are riddled with numerous giant dykes swarms that can be tracked to magmatic "focal regions" along cratonic margins—a picture entirely analogous to LIPs decorating the margins of modern continents (e.g., the Indian subcontinent). Discrete, short duration, LIP events first weakened cratonic lithosphere and then accompanied final breakup. Reconstructing ancient supercontinents could thus be as simple as dating and matching the magmatic LIP records ("barcodes") of all remaining (~50) large cratonic pieces. In this respect, giant dyke swarms are of particular interest because 1) not only are they an integral part of LIPs, but 2) they have very large footprints (300-3000 km); 3) they were emplaced in short time pulses that can now be dated precisely; 4) they are relatively insensitive to uplift; and 5) project far back into cratonic hinterlands; 6) they contain rich geometrical and paleo-stress information; and 7) provide superior "piercing points"; finally, they provide 8) the target rocks of choice for high-quality, precisely dated, paleomagnetic poles (“key poles”).

Thus, we have established an industry-academia-government collaborative project "Reconstruction of Supercontinents Back to 2.7 Ga Using the Large Igneous Province Record" (www.supercontinent.org). Our project team has so far obtained >100 new targeted U-Pb ages on ancient LIPs from around the world and we aim to triple that. In this talk we will present some first results and implications.