Trace element characteristics of clinozoisite pseudomorphs after lawsonite in talc-garnet-chloritoid schists from the Makbal UHP Complex, northern Kyrgyz Tian-Shan Rustam Orozbaev a,b, ⁎, Takao Hirajima a , Apas Bakirov b , Akira Takasu c , Kenshi Maki a , Kenta Yoshida a , Kadyrbek Sakiev b , Azamat Bakirov b , Takafumi Hirata a , Michio Tagiri d , Asel Togonbaeva b a Department of Geology and Mineralogy, Kyoto University, Kitashirakawa Oiwake-cho, 606-8502 Kyoto, Japan b Institute of Geology, Kyrgyz National Academy of Sciences, 30 Erkindik Avenue, 720481 Bishkek, Kyrgyzstan c Department of Geosciences, Shimane University, 1060 Nishikawatsu, 690-8504 Matsue, Japan d Hitachi City Museum, 5-2-22 Miyatacho, 317-0055 Hitachi, Japan abstract article info Article history: Received 2 April 2014 Accepted 15 October 2014 Available online 25 October 2014 Keywords: Pseudomorphs after lawsonite Trace elements Makbal UHP complex Cold subduction Kyrgyzstan Tian-Shan Polyphase mineral aggregates (PMAs) composed of clinozoisite + kyanite + quartz ± chlorite ± paragonite ± phengite have been found within garnet and in the matrix of talc-garnet-chloritoid schists from the Makbal ultrahigh-pressure complex in the northern Kyrgyz Tian-Shan. These mineral textures are interpreted as pseudo- morphs after lawsonite, and we reconstructed the compositions of PMAs of clinozoisite + kyanite + quartz, con- sistent with lawsonite. Petrological study demonstrated that lawsonite was stable during the prograde to the UHP peak stage (P = 28–33 kbar and T = 530–580 °C) and decomposed to the PMAs during isothermal decom- pression around P = 16–20 kbar and T = 510–580 °C. Trace element characteristics of the clinozoisite grains in the PMAs (former lawsonite) show a flat rare earth element (REE) chondrite-normalized pattern, comparable with the typical reported REE pattern of lawsonite, although the abundance of REE varied from sample to sample. Thus, the REE content of clinozoisite in the PMAs included in garnet was likely inherited from the former lawsonite as the decomposition reaction took place isolated from the matrix. Discrete clinozoisite grains in the matrix have high light REE enrichment over heavy REE in the chondrite-normalized pattern, consistent with the typical epidote pattern. Our results indicate that the talc-garnet-chloritoid schists in the Makbal complex were buried to great depth (N 100 km) with a low geothermal gradient (b 6 °C/km) during the Early Paleozoic (480–509 Ma). Lawsonite decomposition and clinozoisite-forming reactions accompany fluid release during the isothermal decompression stage, implying that the fluids can be generated not only during subduction, but also during exhumation of ultrahigh-pressure rocks in cold subduction settings. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Lawsonite [CaAl 2 Si 2 O 7 (OH) 2 ·H 2 O] is a critical hydrous mineral (~12 wt% H 2 O) that forms at high-P/T metamorphic conditions (Nitsch, 1968). Generally, occurrence of lawsonite in metamorphic rocks indicates that the rocks were formed in cold subduction zones along a low geothermal gradient (b 8 °C/km) (Tsujimori et al., 2006; Zack et al., 2004; Zhang et al., 2007). Lawsonite can be stable up to ultrahigh-pressure (UHP) conditions (b 300 km depth) as suggested by experimental data (Okamoto and Maruyama, 1999; Pawley, 1994; Schmidt, 1995) and petrogenetic grid calculations for the Na 2 O–CaO– K 2 O–FeO–MgO–Al 2 O 3 –SiO 2 –H 2 O (NCKFMASH) system (Wei and Powell, 2006; Yang and Powell, 2006). Thus, because of its high water content and wide pressure-temperature (P–T) stability, formation and breakdown of lawsonite may play important roles in deep fluid activity, intermediate–deep earthquakes, and partial melting of mantle wedges (Jung et al., 2004; Pawley, 1994; Schmidt and Poli, 1998). Most lawsonite has been reported from blueschist facies metamor- phic rocks, but limited occurrences have been described in high- pressure and ultrahigh-pressure (HP–UHP)“eclogite-facies” rocks (Tsujimori et al., 2006) (Fig. S1: supplementary data and references). Among these, occurrence of lawsonite under UHP conditions has been reported only from the eclogite xenolith in the ultramafic microbreccia diatreme of Garnet Ridge, Colorado Plateau (Usui et al., 2006). During subduction-exhumation processes, if lawsonite-bearing metamorphic rocks reach their peak temperature conditions outside lawsonite stability field, lawsonite can be decomposed to clinozoisite/ epidote and associated phases. Under such circumstances, petrologists identify the former presence of lawsonite (hereafter “pseudomorphs after lawsonite”) by prismatic shaped polyphase mineral aggregates Lithos 226 (2015) 98–115 ⁎ Corresponding author at: Department of Geology and Mineralogy, Kyoto University, Kitashirakawa Oiwake-cho, 606–8502 Kyoto, Japan. E-mail address: r.t.orozbaev@gmail.com (R. Orozbaev). http://dx.doi.org/10.1016/j.lithos.2014.10.008 0024-4937/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Lithos journal homepage: www.elsevier.com/locate/lithos