TY - JOUR
T1 - An impact melt origin for Earth’s oldest known evolved rocks
AU - Johnson, Tim E.
AU - Gardiner, Nicholas J.
AU - Miljković, Katarina
AU - Spencer, Christopher J.
AU - Kirkland, Christopher L.
AU - Bland, Phil A.
AU - Smithies, Hugh
N1 - T.E.J. acknowledges financial support from the State Key Lab for Geological Processes and Mineral Resources, China University of Geosciences, Wuhan (Open Fund GPMR210704), and from the Office of Research and Development (ORD) and The Institute of Geoscience Research (TIGeR), Curtin University. K.M. acknowledges Australian Research Council (ARC) funding and the developers of the iSALE hydrocode. H.S. publishes with the permission of the Executive Director, Geoscience and Resource Strategy. P.A.B. acknowledges support from ARC DP170102529.
PY - 2018/10
Y1 - 2018/10
N2 - Earth’s oldest evolved (felsic) rocks, the 4.02-billion-year-old Idiwhaa gneisses of the Acasta Gneiss Complex, northwest Canada, have compositions that are distinct from the felsic rocks that typify Earth’s ancient continental nuclei, implying that they formed through a different process. Using phase equilibria and trace element modelling, we show that the Idiwhaa gneisses were produced by partial melting of iron-rich hydrated basaltic rocks (amphibolites) at very low pressures, equating to the uppermost ~3 km of a Hadean crust that was dominantly mafic in composition. The heat required for partial melting at such shallow levels is most easily explained through meteorite impacts. Hydrodynamic impact modelling shows not only that this scenario is physically plausible, but also that the region of shallow partial melting appropriate to formation of the Idiwhaa gneisses would have been widespread. Given the predicted high flux of meteorites in the late Hadean, impact melting may have been the predominant mechanism that generated Hadean felsic rocks.
AB - Earth’s oldest evolved (felsic) rocks, the 4.02-billion-year-old Idiwhaa gneisses of the Acasta Gneiss Complex, northwest Canada, have compositions that are distinct from the felsic rocks that typify Earth’s ancient continental nuclei, implying that they formed through a different process. Using phase equilibria and trace element modelling, we show that the Idiwhaa gneisses were produced by partial melting of iron-rich hydrated basaltic rocks (amphibolites) at very low pressures, equating to the uppermost ~3 km of a Hadean crust that was dominantly mafic in composition. The heat required for partial melting at such shallow levels is most easily explained through meteorite impacts. Hydrodynamic impact modelling shows not only that this scenario is physically plausible, but also that the region of shallow partial melting appropriate to formation of the Idiwhaa gneisses would have been widespread. Given the predicted high flux of meteorites in the late Hadean, impact melting may have been the predominant mechanism that generated Hadean felsic rocks.
U2 - 10.1038/s41561-018-0206-5
DO - 10.1038/s41561-018-0206-5
M3 - Article
AN - SCOPUS:85052511433
SN - 1752-0894
VL - 11
SP - 795
EP - 799
JO - Nature Geoscience
JF - Nature Geoscience
IS - 10
ER -
