title: Earth's oldest mantle fabrics indicate Eoarchaean subduction.
abstract: The extension of subduction processes into the Eoarchaean era (4.0-3.6 Ga) is controversial. The oldest reported terrestrial olivine, from two dunite lenses within the ∼3,720 Ma Isua supracrustal belt in Greenland, record a shape-preferred orientation of olivine crystals defining a weak foliation and a well-defined lattice-preferred orientation (LPO). [001] parallel to the maximum finite elongation direction and (010) perpendicular to the foliation plane define a B-type LPO. In the modern Earth such fabrics are associated with deformation of mantle rocks in the hanging wall of subduction systems; an interpretation supported by experiments. Here we show that the presence of B-type fabrics in the studied Isua dunites is consistent with a mantle origin and a supra-subduction mantle wedge setting, the latter supported by compositional data from nearby mafic rocks. Our results provide independent microstructural data consistent with the operation of Eoarchaean subduction and indicate that microstructural analyses of ancient ultramafic rocks provide a valuable record of Archaean geodynamics.
authors.affiliation: Institute of Earth Sciences, University of Lausanne, UNIL-Mouline, Building Geopolis, CH-1015 Lausanne, Switzerland.|Department of Applied Geology, ARC Centre of Excellence for Core to Crust Fluid Systems (CCFS) and the Institute For Geoscience Research (TIGeR), Curtin University, GPO Box U1987, Perth, Western Australia 6845, Australia.
authors.forename: Mary-Alix
authors.initials: MA
authors.lastname: Kaczmarek
authors.affiliation: Department of Applied Geology, ARC Centre of Excellence for Core to Crust Fluid Systems (CCFS) and the Institute For Geoscience Research (TIGeR), Curtin University, GPO Box U1987, Perth, Western Australia 6845, Australia.
authors.forename: Steven M
authors.initials: SM
authors.lastname: Reddy
authors.affiliation: GeoQuEST Research Centre, School of Earth and Environmental Sciences, University of Wollongong, Wollongong, New South Wales 2522, Australia.|Beijing SHRIMP Centre, Institute of Geology, Chinese Academy of Geological Sciences, 26 Baiwanzhuang Road, Beijing 100037, China.
authors.forename: Allen P
authors.initials: AP
authors.lastname: Nutman
authors.affiliation: Beijing SHRIMP Centre, Institute of Geology, Chinese Academy of Geological Sciences, 26 Baiwanzhuang Road, Beijing 100037, China.|Glendale, Oxon OX9 2LQ, UK.
authors.forename: Clark R L
authors.initials: CR
authors.lastname: Friend
authors.affiliation: Research School of Earth Sciences, The Australian National University, Mills Road, Canberra 0200, Australia.
authors.forename: Vickie C
authors.initials: VC
authors.lastname: Bennett