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.

A non–plate tectonic model for the Eoarchean Isua supracrustal belt

“…We speculate that the exclusivity of subduction tectonic interpretations for the Isua supracrustal belt is largely a function of relatively sparse structural study. Although the antiquity and significance of the belt have been recognized since the 1970s (Moorbath et al, 1972;Moorbath et al, 1973), and signal insights into early Earth processes have been derived from Isua since then (e.g., Allwood et al, 2018;Bennett et al, 2007;Cabral et al, 2013;Caro et al, 2003;Crowe et al, 2013;Frei et al, 2016;Hassenkam et al, 2017;Komiya et al, 1999;Moore and Webb, 2013;Naeraa et al, 2012;Nutman et al, 2016;Rizo et al, 2012;Rosing et al, 2010), only about 10 research groups have published structural information about the belt (Allwood et al, 2018;Appel et al, 1998;Bridgwater and McGregor, 1974;Crowley, 2003;Crowley et al, 2002;Fedo, 2000;Fedo et al, 2001;Friend and Nutman, 2005Friend et al, 2008;Hanmer and Greene, 2002;James, 1976;Kaczmarek et al, 2016;Keto and Kurki, 1967;Komiya et al, 1999;Kurki and Keto, 1966;Myers, 2001;Nutman, 1984;Nutman and Bridgwater, 1986;Friend, 2007, 2009;Nutman et al, 1997Nutman et al, , 2000…”

The Architecture and Evolution of the Singhbhum Craton

“…Basically there are two contending hypotheses; (1) plume-driven, and (2) subduction-driven lithospheric evolution. Some hold the view that some form of subduction and plate tectonics was an important process contributing to crust formation and it started from Eoarchean and even Hadean times (Polat et al, 1998(Polat et al, , 2002(Polat et al, , 2016Nutman et al, 2007;Reimink et al 2014;Kaczmarek et al, 2016 ). Others (Puchtel et al, 1998;Polat et al, 2006;van Kranendonk, 2010;Moyen, 2011;Johnson et al, 2014Johnson et al, , 2017van Kranendonk et al, 2004van Kranendonk et al, , 2015 suggest that plume-related processes are in the main responsible for the Archean crust formation.…”

Eoarchaean tectonics: New constraints from high pressure-temperature experiments and mass balance modelling

“…In a process slightly different to present-day subduction the subsequent hydrous melting of thick basaltic subducting plates generated magmas with ETT compositions that solidified into the first continental crust ( Fig. 2b) (Ernst et al 2016;Harrison et al, 2005;Steenfelt et al, 2005;Hopkins et al 2008;Chen et al, 2009;Jenner et al, 2009;, Foley et al, 2014, Polat et al, 2015Hastie et al 2016a, Kaczmarek et al, 2016 (Fig. 1: Model 2).…”

“…These ancient rocks are found in West Greenland (Baadsgaard et al, 1986, Crowley, 2003, Australia (Nutman et al, 1993, Kinny andNutman, 1996), Antarctica (Harley and Black 1997), China (Liu et al, 2007, Ge et al, 2018 and Canada (Bowring and Williams, 1999, Iizuka et al, 2007, O'Neill et al, 2007. Nevertheless, the tectonic processes responsible for generating this ancient continental material are poorly understood and rival hypotheses of a dominant horizontal vs. vertical geodynamic regime are still hotly debated (Ernst et al 2016;Hawkesworth et al, 2016, 2017, Hastie et al, 2016a, Kaczmarek et al, 2016, Rozel et al 2017, Cox et al 2018, Ge et al, 2018, Keller and Schoene 2018, Moyen and Laurent 2018, Wiemer et al, 2018. Accordingly, the timing of the initiation of plate tectonics resembling either modern subduction zone processes or atypical subduction, is also highly contentious with estimates ranging from <1.0 to >4.0 Ga (Harrison et al 2005;Jenner et al 2009, Dhuime et al 2012, Foley et al, 2014Nebel et al 2014, Hastie et al 2016a, Hawkesworth et al 2016, Stern et al 2016Keller andSchoene 2018, Ge et al 2018).…”

“…There is near universal agreement that the ETT are generated by the partial melting of metabasic source rocks (Sen and Dunn 1994, Wolf and Wyllie 1994, Rapp and Watson 1995, Drummond et al 1996, Nutman et al 1999, Hoffmann et al, 2011, Hastie et al 2016a), but the tectonic environment where this occurred is the subject of intense debate between primitive subduction zones (plate tectonics?) (Ernst et al 2016;, 2015, Foley et al, 2014, Hastie et al 2015, Polat et al 2015, Kaczmarek et al 2016, Ge et al 2018) and a non-subduction (non-plate tectonic?) process (e.g., Robin and Bailey, 2009, Smithies et al 2009, Thébaud and Ray, 2013, Zhang et al 2013Hawkesworth et al 2016, Rozel et al, 2017Wiemer et al, 2018).…”