Late Proterozoic Rodinia breakup in Mexico - A new approach using SIMS dating of zircon coronas and baddeleyite

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Earth's history has been dominated by cycles of supercontinent assemblage and breakup as a consequence of global geodynamic processes in the deep earth. Little is known about older, Precambrian supercontinents, since the relevant geologic units often are covered by younger rocks, or overprinted by later tectonothermal events. Mexico is situated at the suture between ancient continents (like Laurentia and Gondwana) that collided repeatedly to form supercontinents, first Rodinia (ca. 1000 Ma), and then Pangea (ca. 300 Ma). In Mexico, Rodinia breakup and opening of the Iapetus Ocean during the Neoproterozoic has not been constrained so far. Recent research, however, revealed that Neoproterozoic basaltic magmas (now amphibolite) probably intruded Precambrian basement units in southern Mexico as a consequence of crustal thinning during the opening of the Iapetus Ocean. Repeated metamorphic overprints during the Phanerozoic and the chemical composition of basalts thus far have precluded direct dating of this igneous event. Previous indirect evidence is derived from metasedimentary rocks that are intruded by basaltic magmas whose sedimentary age has been estimated on the basis of chemostratigraphic data at 600-580 Ma and from U-Pb ages of secondary zircon from anorthosite and associated ilmenite ores that yielded Neoproterozoic dates. The main goal of this proposal is to determine the exact age and origins of these Neoproterozoic basaltic magmas through high-spatial resolution SIMS dating of: (1) metamorphic zircon in contact-metamorphic coronas around rutile and ilmenite formed by Zr exsolution; targeted samples are from anorthosites and ilmenitites in contact with basaltic amphibolite dikes where thermal overprinting liberated Zr leading to new zircon growth. (2) Primary baddeleyite in amphibolite. U-Pb geochronology will be complemented by determining trace element and stable isotope (oxygen) compositions of zircon and baddeleyite, as well as radiogenic isotopes (Hf, Nd) in whole rock samples to elucidate the origin of crystals and their host rocks. This proposal aims at initiating a new collaboration between Heidelberg University and the proposed Mercator Fellow Prof. Dr. Bodo Weber (CICESE, Mexico) who is a renowned expert on the tectonic evolution of Mexico. The expected results are essential to redefine the complex tectonic correlations during the Neoproterozoic as well as to develop novel chronochemistry approaches for complex polymetamorphic rocks.