Accepted Manuscript Initiation of plate tectonics in the Hadean: Eclogitization triggered by the ABEL Bombardment S. Maruyama, M. Santosh, S. Azuma PII: S1674-9871(16)30207-9 DOI: 10.1016/j.gsf.2016.11.009 Reference: GSF 514 To appear in: Geoscience Frontiers Received Date: 9 May 2016 Revised Date: 13 November 2016 Accepted Date: 25 November 2016 Please cite this article as: Maruyama, S., Santosh, M., Azuma, S., Initiation of plate tectonics in the Hadean: Eclogitization triggered by the ABEL Bombardment, Geoscience Frontiers (2017), doi: 10.1016/ j.gsf.2016.11.009. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. ACCEPTED MANUSCRIPT MANUSCRIPT ACCEPTED P a g e ‐|‐1111‐‐‐‐ ACCEPTED MANUSCRIPT ‐ 1‐ Initiation of plate tectonics in the Hadean: 2‐ Eclogitization triggered by the ABEL 3‐ Bombardment 4‐ 5‐ S. Maruyama a,b,*, M. Santosh c,d,e , S. Azuma a 6‐ a Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1, 7‐ Ookayama-Meguro-ku, Tokyo 152-8550, Japan 8‐ b Institute for Study of the Earth’s Interior, Okayama University, 827 Yamada, 9‐ Misasa, Tottori 682-0193, Japan 10‐ c Centre for Tectonics, Resources and Exploration, Department of Earth 11‐ Sciences, University of Adelaide, SA 5005, Australia 12‐ d School of Earth Sciences and Resources, China University of Geosciences 13‐ Beijing, 29 Xueyuan Road, Beijing 100083, China 14‐ e Faculty of Science, Kochi University, KochiMANUSCRIPT 780-8520, Japan 15‐ *Corresponding author. E-mail address: [email protected] 16‐ 17‐ Abstract 18‐ When plate tectonics began on the Earth has been long debated and 19‐ here we argue this topic based on the records of Earth-Moon geology and 20‐ asteroid beltACCEPTED to conclude that the onset of plate tectonics was during the middle 21‐ Hadean (between 4.37–4.20 Ga). The trigger of the initiation of plate tectonics is 22‐ the ABEL Bombardment, which delivered oceanic and atmospheric components 23‐ on a completely dry reductive Earth, originally comprised of enstatite 1‐ ‐ P a g e ‐|‐2222‐‐‐‐ ACCEPTED MANUSCRIPT ‐ 24‐ chondrite-like materials. Through the accretion of volatiles, shock metamorphism 25‐ processed with vaporization of both CI chondrite and supracrustal rocks at the 26‐ bombarded location, and significant recrystallization went through under wet 27‐ conditions, caused considerable eclogitization in the primordial continents 28‐ composed of felsic upper crust of 21 km thick anorthosite, and 50 km or even 29‐ thicker KREEP lower crust. Eclogitization must have yielded a powerful slab-pull 30‐ force to initiate plate tectonics in the middle Hadean. Another important factor is 31‐ the size of the bombardment. By creating Pacific Ocean class crater by 1000 km 32‐ across impactor, rigid plate operating stagnant lid tectonics since the early 33‐ Hadean was severely destroyed, and oceanicMANUSCRIPT lithosphere was generated to 34‐ have bi-modal lithosphere on the Earth to enable the operation of plate tectonics. 35‐ Considering the importance of the ABEL Bombardment event which initiated 36‐ plate tectonics including the appearance of ocean and atmosphere, we propose 37‐ that the Hadean Eon can be subdivided into three periods: (1) early Hadean 38‐ (4.57–4.37 Ga), (2) middle Hadean (4.37–4.20 Ga), and (3) late Hadean ACCEPTED 39‐ (4.20–4.00 Ga). 40‐ 2‐ ‐ P a g e ‐|‐3333‐‐‐‐ ACCEPTED MANUSCRIPT ‐ 41‐ Keywords: Initiation of plate tectonics; ABEL Bombardment; Eclogitization; 42‐ Stagnant lid tectonics; Primordial continents 43‐ 44‐ 1. Introduction 45‐ The Earth is the only example among all planets in our solar system with 46‐ active plate tectonics (Fig. 1), and also life-bearing since Hadean (e.g. Turner et 47‐ al., 2014; Ebisuzaki and Maruyama, 2016). This rocky planet is characterized by 48‐ both H 2O ocean and wide-spread granitic continents covering its surface. The 49‐ appearance of ocean triggered the operation of plate tectonics, which promoted 50‐ subduction of oceanic plate at the MANUSCRIPTtrench and generation of TTG 51‐ (tonalite-trondhjemite-granodiorite) magmas at the continental region. As a 52‐ result, important nutrients are being continuously supplied for the survival for life, 53‐ together with CO 2, N 2, and H 2O as components of the building blocks of life. 54‐ Thus, the Habitable Trinity environment is sustained which is one of the basic 55‐ conditions for life. Plate tectonics, life, H 2O ocean, and granitic continents must ACCEPTED 56‐ genetically relate with each other (e.g. Dohm and Maruyama, 2015). 57‐ “When plate tectonics began on this planet” is one of the most heated 58‐ debates in Earth Sciences ever since the new paradigm of plate tectonics was 3‐ ‐ P a g e ‐|‐4444‐‐‐‐ ACCEPTED MANUSCRIPT ‐ 59‐ established in 1968 (e.g., Le Pichon, 1968; Morgan, 1968; McKenzie, 1969). 60‐ The major argument to demonstrate the operation of plate tectonics was based 61‐ on the presence or absence of ophiolites remaining as a thin and narrow belt 62‐ within orogenic belts as an index of the tectonic movement of the oceanic plates 63‐ which have already disappeared by collision of continents (e.g. Komiya et al., 64‐ 1999). However, definition of ophiolite depends on the rock assemblages 65‐ (Maruyama et al., 1989), and therefore when, where, and how plate tectonics 66‐ began to operate remains unsolved. To tackle these questions, we start from 67‐ clarifying what plate tectonics is from its most essential characters such as 68‐ rigidity, plate boundary processes, role ofMANUSCRIPT water as a driving force, mantle 69‐ potential temperature, and evaluate the multi-disciplinary aspects of the theory. 70‐ Finally, we propose a trigger to initiate plate tectonics on Hadean Earth. 71‐ 72‐ 2. What is plate tectonics? 73‐ ACCEPTED 74‐ 2.1. Definition of plate tectonics and three-dimensional structure of 75‐ lithosphere 4‐ ‐ P a g e ‐|‐5555‐‐‐‐ ACCEPTED MANUSCRIPT ‐ 76‐ Plate tectonics is basically defined as follows; The Earth’s surface is 77‐ covered by more than a dozen rigid lithospheres called plate. The movement of 78‐ these plates is rotational motion on the spherical body of the Earth. Hence both 79‐ the rotational pole and angular velocity of the rotation are given to all plates on 80‐ the globe. Thus, the motion at any point on the globe is determined, if both 81‐ direction of plate motion and speed are given on the globe. This is the core of the 82‐ theory of plate tectonics. 83‐ Another important factor of plate tectonics is the rigidity of the plate. The 84‐ Earth is characterized by rigid lithospheric plates, and the rigidity accompanies 85‐ brittle deformation. However, the deformationMANUSCRIPT mechanism of rocks changes with 86‐ increase in temperature from brittle to ductile, as seen in rock types from basalts, 87‐ gabbros and mantle peridotites which can be highly ductile above 800 °C (Arzi, 88‐ 1978; Kohlstedt et al.,1995). If volatiles such as H 2O and CO 2 are present, rocks 89‐ start melting at around this temperature. The presence of volatiles and melts are 90‐ imaged through velocity drop in geophysical studies (e.g. Nehlig, 1993). ACCEPTED 91‐ Furthermore, the ductility acts as a catalyzer to promote slippage at the bottom 92‐ of the lithosphere. 5‐ ‐ P a g e ‐|‐6666‐‐‐‐ ACCEPTED MANUSCRIPT ‐ 93‐ One of the major features of plate tectonics is the three-dimensional 94‐ subduction of lithosphere in the shape of plate. In the upper mantle, the platy 95‐ structure of lithosphere is preserved during the subduction process. However, 96‐ the lithosphere cannot keep the platy form in the lower mantle. Platy or 97‐ curtain-like structure of lithosphere seen above 410 km changes to blob-shaped 98‐ structure in the lower mantle through the mantle transition zone at 410–660 km 99‐ depth with the phase changes from olivine to wadsleyite at 410 km, wadsleyite to 100‐ ringwoodite at 520 km, and finally into perovskite and wüstite at 660 km depth. 101‐ The recent observations, particularly derived from seismic tomographic data, 102‐ have revealed the architecture of subductingMANUSCRIPT plates at depth (Fukao, 1992; 103‐ Maruyama, 1994; Maruyama et al., 2007) including the total amount of 104‐ accumulated slabs. 105‐ Recent multidisciplinary research of the deep Earth including deep 106‐ mantle and even core have brought new insights into the dynamics of the Earth 107‐ combined with geologic history of the Earth, particularly back to 200 Ma, with ACCEPTED 108‐ information on the location of slab graveyards that have been well documented 109‐ in seismic tomographic images. A ca. 300 m topographic bulge over 3000 km 110‐ above the Pacific superplume has been identified where 5 independent hot 6‐ ‐ P a g e ‐|‐7777‐‐‐‐ ACCEPTED MANUSCRIPT ‐ 111‐ spots are concentrated beneath the southern Pacific region (e.g. Zhao, 2007). 112‐ These observations have led to the concept of a coupled tectonic system where 113‐ upper mantle is dominated by horizontal plate movement with curtain-like 114‐ upwelling beneath the mid-oceanic ridge down to the 400 km depth (Zhao, 2004, 115‐ 2009; Zhao et al., 2007). Curtain-like upwelling makes the platy lithosphere at 116‐ mid-oceanic ridge which then moves to the trench and subducts to a depth of 117‐ 660 km. At the mantle transition zone from 410 to 660 km, the platy structure 118‐ becomes unclear with stagnation. From this depth to the bottom of the 119‐ core-mantle boundary (CMB), the plates do not show a simple curtain-like 120‐ structure.