Seeking Earth’s oldest geological record: an unexpected discovery of well-preserved 3834 Ma metatonalite

Abstract

One of Greenland’s largest bodies of Archean (meta)sedimentary rocks occurs on the ∼5.5 by 2.0 km nunatak Isortup Nunataa (∼65°31′N 49°54′W) and is ∼35 km north of the Eoarchean Isua supracrustal belt with its world’s best record of early sedimentary and volcanic systems. The nunatak was visited to ascertain if its metasedimentary rocks are also Eoarchean and thereby provide extra insight into the early Earth. The metasedimentary rocks are derived from a ca 3060 Ma arc-like volcanogenic source and can be assigned to the Akia terrane that crops out immediately to the west. However, glacial erratics scattered over the nunatak indicate there are well-preserved Eoarchean rocks including 3834 Ma metatonalite hidden to the east under the Inland Ice. This demonstrates there are still occurrences of Eoarchean rocks out there to be found—by a mix of logic and luck. These findings will all enhance our knowledge of the early Earth, to help answer the big questions about the important early events that shaped our planet. KEY POINTS The nunatak Isortup Nunataa (West Greenland) is dominated by ca 3060 Ma arc-like volcanogenic metasedimentary rocks that are assigned to the Akia terrane, which crops out immediately to the west. Glacial erratics, including 3834 Ma metatonalite scattered over the nunatak, indicate there are well-preserved Eoarchean rocks hidden to the east under the Inland Ice. Any new findings of Eoarchean rocks will enhance our understanding of the early Earth.