FINGERPRINTING GONDWANA VIA BIVARIATE QUANTITATIVE ANALYSIS OF JOINT ZIRCON U-PB AND HF GLOBAL ARCHIVES

Compilations of initial Hf in zircon during crystallization (εHfT) are commonly used as a proxy for crustal growth and recycling. Many studies assume temporal trends in εHfT are representative of global phenomena rather than representing regional tectonic events modulated by the assembly and breakup of supercontinents. We present new quantitative comparison methods applied to a global database of 114,311 εHfT values to evaluate the geochronological and geochemical correspondence between eight paleocontinents defined by Paleozoic sutures: Africa, Antarctica, Asia, Australia, Baltica, North America, Peri-Gondwana, and South America. New data analysis methods are bivariate (2D) extensions of univariate (1D) quantitative comparison methods commonly employed in detrital provenance research: Cross-correlation, Likeness, and Similarity of kernel density estimates; and K-S and Kuiper tests of cumulative distribution functions. Results show that detrital zircon εHfT distributions are similar to their igneous zircon counterparts for individual paleocontinents, and that specific orogenic belts dominate the global signal at different times. We highlight one example of the latter which shows that the Ediacaran–Cambrian εHfT negative excursion, previously attributed to Snowball Earth erosion and related to a late Neoproterozoic onset of modern plate tectonics, is restricted to paleocontinents involved in the assembly of Gondwana (Africa, Antarctica, Australia, South America, and several Peri-Gondwanan terranes). We propose that the εHfT negative excursion is the product of remobilization of large volumes of Archean and Proterozoic crust during the Tonian to Cryogneian rifting of Rodinia, which formed new passive margins on old radiogenic crust. These passive margins and underlying continental crust were subsequently subducted in Pan-African collisional orogenies, without an extended intervening period of juvenile arc formation and accretion. Zircon in melts extracted from these thickened ancient crustal domains had highly evolved εHfT and were subsequently exhumed and distributed throughout Gondwana, providing a detrital geochemical fingerprint of this spatiotemporally limited tectonic event rather than a global Earth process.