Very-low-temperature record of the subduction process: A review of worldwide lawsonite eclogites Tatsuki Tsujimori a, ⁎ , Virginia B. Sisson b , Juhn G. Liou a , George E. Harlow b , Sorena S. Sorensen c a Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305-2115, USA b Department of Earth and Planetary Sciences, American Museum of Natural History, Central Park West at 79th Street, New York, New York 10024-5192, USA c Department of Mineral Sciences, NHB-119, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560-0119, USA Received 29 May 2005; accepted 30 March 2006 Available online 19 June 2006 Abstract Lawsonite eclogites preserve a record of very-low-temperature conditions in subduction zones. All occur at active margin settings, typically characterized by accretionary complexes lithologies and as tectonic blocks within serpentinite-matrix mélange. Peak lawsonite-eclogite facies mineral assemblages (garnet + omphacite + lawsonite + rutile) typically occur in prograde-zoned garnet porphyroblasts. Their matrix is commonly overprinted by higher-temperature epidote-bearing assemblages; greenschist- or amphibolite-facies conditions erase former lawsonite-eclogite relics. Various pseudomorphs after lawsonite occur, particularly in some blueschist/eclogite transitional facies rocks. Coesite-bearing lawsonite-eclogite xenoliths in kimberlitic pipes and lawsonite pseudomorphs in some relatively low-temperature ultrahigh-pressure eclogites are known. Using inclusion assemblages in garnet, lawsonite eclogites can be classified into two types: L-type, such as those from Guatemala and British Columbia, contain garnet porphyroblasts that grew only within the lawsonite stability field and E-type, such as from the Dominican Republic, record maximum temperature in the epidote-stability field. Formation and preservation of lawsonite eclogites requires cold subduction to mantle depths and rapid exhumation. The earliest occurrences of lawsonite-eclogite facies mineral assemblages are Early Paleozoic in Spitsbergen and the New England fold belt of Australia; this suggests that since the Phanerozoic, secular cooling of Earth and subduction-zone thermal structures evolved the necessary high pressure/temperature conditions. Buoyancy of serpentinite and oblique convergence with a major strike-slip component may facilitate the exhumation of lawsonite eclogites from mantle depths. © 2006 Elsevier B.V. All rights reserved. Keywords: Cold subduction; HP-UHP metamorphism; Lawsonite; Eclogite; P–T trajectory 1. Introduction The discovery of supracrustal rocks metamorphosed at ultrahigh-pressure (UHP) and/or ultrahigh-tempera- ture (UHT) conditions is a revolution in our under- standing of crustal-scale processes in the lithosphere (e.g., Liou et al., 1994; Coleman and Wang, 1995; Maruyama et al., 1996; Liou et al., 1997; Hacker and Liou, 1998; Harley, 1998; Pattison et al., 2003; Carswell and Compagnoni, 2003; Rumble et al., 2003; Liou et al., 2004). These extreme high-P or high-T metamorphic processes have played a crucial role in the evolution of Lithos 92 (2006) 609 – 624 www.elsevier.com/locate/lithos ⁎ Corresponding author. Present address: Venture Business Labora- tory, Kanazawa University, Kanazawa, Ishikawa 920-1192, Japan. E-mail address: tatsukix@mac.com (T. Tsujimori). 0024-4937/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.lithos.2006.03.054