Lawsonite Composition and Zoning As an Archive of Metamorphic Processes in Subduction Zones

Research Paper THEMED ISSUE: Subduction Top to Bottom 2

GEOSPHERE Lawsonite composition and zoning as an archive of metamorphic processes in subduction zones

GEOSPHERE; v. 15, no. 1 Katherine F. Fornash, Donna L. Whitney, and Nicholas C.A. Seaton Department of Earth Sciences, University of Minnesota, Minneapolis, Minnesota 55455, USA

https://doi.org/10.1130/GES01455.1 ABSTRACT fluid-rock interaction, their compositions and microstructures may provide a 13 figures; 2 tables; 1 set of supplemental materials record of fluid compositions and sources as well as fluid transport pathways in

The hydrous, high-pressure mineral lawsonite is important in volatile and the subducted slab. Of these phases, lawsonite [CaAl2Si2O7(OH)2·H2O] is of par- CORRESPONDENCE: forna011@umn.edu element cycling between the crust and mantle in subduction zones and may ticular importance to fluid processes and element cycling in subduction zones also influence the rheology and deformation behavior of the subducted crust because it is abundant over a wide range of depths (and may be the main CITATION: Fornash, K.F., Whitney, D.L., and Seaton, and associated sediments. However, despite its potential geochemical and hydrous phase at pressures [P ] >2.5 GPa) (e.g., Pawley, 1994; Schmidt and N.C.A., 2019, Lawsonite composition and zoning as an archive of metamorphic processes in subduction geodynamic significance, little is known about the trace element affinity and Poli, 1994), has a high water content (11.5 wt%), and is a significant reservoir for zones: Geosphere, v. 15, no. 1, p. 24–46, https:// the types and origins of zoning patterns in lawsonite. To evaluate the signif- trace elements in high-pressure assemblages, particularly rare earth elements doi.org/10.1130/GES01455.1. icance of trace element variations and zoning in lawsonite, we conducted a (REEs), Sr, Pb, Th, and U (Tribuzio et al., 1996; Ueno, 1999; Spandler et al., geochemical and microstructural study of lawsonite in a suite of different rock 2003; Martin et al., 2014; Vitale Brovarone et al., 2014). It can also be used to Science Editor: Shanaka de Silva types from the Sivrihisar Massif, Turkey, one of the few places in the world date subduction metamorphism (Mulcahy et al., 2009, 2014; Vitale Brovarone Guest Associate Editor: Gray Bebout where pristine lawsonite has survived in eclogite during exhumation from and Herwartz, 2013), to document the deformation behavior of subducted oce-

Received 7 November 2016 depths of ~75–80 km. Lawsonite in metamafic, metasedimentary (impure anic crust and associated sedimentary rocks (Teyssier et al., 2010; Kim et al., Revision received 17 June 2018 quartzite and quartz-rich schists), and metasomatic chlorite-rich rocks con- 2013, 2015; Cao et al., 2014; Cao and Jung, 2016; Whitney et al., 2014), and to Accepted 23 October 2018 tains Fe, Ti, and/or Cr as major constituents (substituting for Al) and com- interpret seismic properties of subducted slabs (e.g., Abers and Sarker, 1996; Published online 10 January 2018 monly displays zoning in these elements. Intragrain variations (up to two or- Hacker, 1996; Connolly and Kerrick, 2002; Hacker et al., 2003; Fujimoto et al., ders of magnitude) in rare earth elements and other trace elements are also 2010; Chantel et al., 2012; Mookherjee and Bezacier, 2012; Reynard and Bass, common and in some cases correlate with transition-metal zoning. For some 2014). Lawsonite dehydration has also been proposed as a driving force for elements (e.g., Ti), uptake was crystallographically controlled, whereas for some intermediate-depth earthquakes in subduction zones (e.g., Kita et al., others, compositional variations may reflect changes in the local metamor- 2006; Abers et al., 2013). It is therefore important to understand the chemical phic environment, such as the growth or breakdown of other mineral phases and physical properties and behavior of lawsonite. that compete for trace elements (garnet, titanite, epidote-group minerals, In comparison to other hydrous phases in subduction systems, relatively apatite) or shifts in the bulk-rock composition during subduction. Deforma- little is known about compositional variations and zoning of lawsonite because tion may have assisted the mobilization of some elements during and after it has been proposed to exhibit little compositional variation (e.g., Pawley, crystal growth, including relatively immobile elements such as Ti. Intersample 1994) and because it is rarely preserved in subduction-related rocks exhumed variations in lawsonite composition likely reflect variations inherited from the to the Earth’s surface (Zack et al., 2004; Whitney and Davis, 2006). Furthermore, protolith. Lawsonite from Sivrihisar metamafic rocks has high Sr/Pb, whereas many lawsonite-bearing localities preserve lawsonite only in texturally and/or OLD G lawsonite from quartz-rich metasediments yielded lower Sr/Pb, with a few spatially restricted sites, such as inclusions in garnet (Zhang and Meng, 2006; exceptions that may indicate interactions between oceanic crust and sedi- Tsujimori et al., 2006) or in a xenolith (Usui et al., 2006) (Fig. 1). In some cases, ments during metamorphism. This study shows that lawsonite composition, the (former) presence of lawsonite can only be inferred from rectangular or zoning, and microstructure can be used to track processes during subduction prismatic-shaped aggregates of epidote + paragonite + quartz ± albite ± talc OPEN ACCESS metamorphism and deformation and can potentially be used to document (at lower pressures; e.g., Ballèvre et al., 2003) or epidote + kyanite + quartz/ fluid-rock interaction within and between different lithologic layers. coesite ± garnet ± omphacite (at higher pressures), from phase equilibria modeling, or from mass-balance calculations (e.g., Guo et al., 2013) (Fig. 1). The INTRODUCTION scarcity of well-preserved lawsonite, particularly in eclogite, has prevented a comprehensive understanding of the compositions, substitution mechanisms, Water is transported into the deep parts of subduction systems via hydrous trace element affinity, and types and origins of zoning patterns in lawsonite. This paper is published under the terms of the phases such as lawsonite, phengite, amphibole, epidote-group minerals, talc, One of the few places in the world with fresh, unaltered lawsonite in CC‑BY-NC license. chlorite, and serpentine. Because these hydrous phases form as a result of eclogite- and blueschist-facies rocks is the Sivrihisar Massif of the Tavşanlı

120°W 0° 120°E

Spitsbergen

60°N Kyrgyzstan 60°N Tianshan Sivrihisar North Qilian British Columbia Monviso Central Pontides Corsica Franciscan Dominican Eastern Shikoku Republic Figure 1. Distribution of lawsonite eclogite Colorado Plateau localities in the world, classified by the xenolith Western Dabie Guatemala textural position of the lawsonite (Lws) (matrix, inclusion in garnet [grt], pseudo- 0° 0° morph).

Sulawesi New Caledonia Port Macquarie

Lawsonite Eclogite Localities 60°S 60°S Lws in matrix Lws inclusions in grt ( ± Lws pseudomorphs) Lws pseudomorph 120°E

Zone, Turkey (Davis and Whitney, 2006, 2008) (Fig. 1), which contains a coher- OVERVIEW OF THE TAVŞANLI ZONE ent sequence of metamafic and metasedimentary rocks that were metamorphosed and deformed at or near the top of a subducting slab (Teyssier et al., The Tavşanlı Zone of western Turkey is a Late Cretaceous paleosubduction 2010; Whitney et al., 2014). Lawsonite is abundant in the Sivrihisar Massif and zone (Okay and Kelley, 1994; Okay, 1998; Sherlock et al., 1999; Seaton et al., occurs in blueschist- and eclogite-facies metamafic, metasedimentary (calc- 2009, 2014; Mulcahy et al., 2014; Fornash et al., 2016) formed during the closure schist, quartzite), and metasomatic rocks, as well as in lawsonite-rich veins and of the Neo-Tethys Ocean (Okay, 1980a, 1984, 1986) and is exposed as a 50-km- layers developed at mafic pod margins (Figs. 2, 3). Petrographic and textural wide and 350-km-long, east-west–trending, high-pressure–low-temperature evidence suggests that lawsonite was stable along the prograde metamorphic (HP-LT) metamorphic belt. It consists of a coherent continental blueschist- path (inclusions in garnet), at the peak (matrix grains), and along the retro- facies sequence overlain by an accretionary complex and large ophiolite slabs grade path. The preservation of lawsonite in a variety of rock types, coupled (Okay, 1998; Okay and Whitney, 2010). Undeformed Eocene granitoids (ca. with its stability over a significant portion of the subduction and exhumation 48–53 Ma; Harris et al., 1994; Okay, 1998; Sherlock et al., 1999) locally intruded cycle in the Sivrihisar Massif, provides an opportunity to document in a sys- the HP-LT sequence and the overlying ophiolite. tematic way the composition and zoning of lawsonite and to interpret these Blueschist-facies rocks from the western part of the belt record pres- features in the context of subduction metamorphism and deformation. sure-temperature (P-T ) conditions of up to 2.4 GPa and 430 °C (Okay and Kel- In this study, we integrate results of major and trace element compositional ley, 1994; Okay, 2002) to 470–550 °C (Plunder et al., 2013), whereas blueschists analyses of lawsonite by electron microprobe (EMP) and laser ablation–induc- from a more southeastern portion of the belt record lower P (0.9–1.1 GPa) and tively coupled mass spectrometry (LA-ICPMS) with microstructural analysis of T (375–450 °C) (Droop et al., 2005). Preserved lawsonite eclogite occurs only in lawsonite by electron backscatter diffraction (EBSD) to characterize different types the Sivrihisar Massif, located where the Tavşanlı Zone changes from an east- of zoning and to document compositional variations in lawsonite from different west to a NE-SW trend, and records maximum P-T conditions of 2.4–2.5 GPa rock types. This data set is used to evaluate the controlling factors in lawsonite and 550 °C, corresponding to depths of ~75–80 km (Davis and Whitney, 2006, composition and zoning at eclogite- and blueschist-facies conditions and to in- 2008; Whitney and Davis, 2006). The Sivrihisar Massif thus represents one of vestigate the utility of lawsonite as a monitor of metamorphic, fluid, and defor the deepest-formed known occurrences of fresh lawsonite eclogite exhumed mation processes over a range of depths during subduction and exhumation. from an oceanic subduction zone (Whitney et al., 2014).

GEOSPHERE | Volume 15 | Number 1 Fornash et al. | Lawsonite composition and zoning as an archive of metamorphic processes in subduction zones Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/15/1/24/4619067/24.pdf 25 by guest on 03 October 2021 on 03 October 2021 by guest Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/15/1/24/4619067/24.pdf Research Paper Cpx—clinopyroxene, Ep—epidote, Gln—glaucophane, Grt—garnet, Lws—lawsonite, Omp—omphacite, Ph—phengite, Qz—quartz. A silver pen is provided for scale in panel K. indicatedveins by (K; vein star) and as a matrix phase (L; XPL). Lawsonite in impure quartzite is commonly tabular and elongate (M; PPL). Amp—amphibole, Chl—chlorite, from the same sample display oscillatory zoning features in XPL (J). Lawsonite epidote–rich from pod margin the chlorite + is coarse grained and occurs as monomineralic Sparse grains of lawsonite in lawsonite blueschist sample SV13-01 occur at an angle to the dominant foliation and are wrapped by the foliation (I; PPL). Some lawsonite grains on millimeter scales (F; PPL). In garnet-bearing lawsonite blueschists, lawsonite can contain inclusions of garnet (G; XPL) or occur as an inclusion within the garnet (H; PPL). plane-polarized light [PPL]) and as inclusions in garnet (E; PPL). In some lawsonite from lawsonite blueschists, variations in lawsonite grain size and modal abundance occurs from the pod margin is coarse-grained and inclusion-poor (C; XPL). Lawsonite in the retrogressed eclogite sample occurs as a matrix phase in the chlorite-rich matrix (D; dral grains (A; cross-polarized light [XPL]; dotted line is used to delineate the lawsonite grain boundaries) and large, polycrystalline aggregates (B; XPL), whereas lawsonite microstructures, textural positions, and inclusion assemblages. Lawsonite from the core of the fresh lawsonite eclogite pod is inclusion-rich and occurs both as small, euhe - Figure 2. Representative photomicrographs and photos of metamafic (A–L) and metasedimentary (M) rock samples from the Sivrihisar Massif, Turkey, highlighting the different M J D G A 0.5 mm 0.5 mm 1.0 mm 1 mm Ch Qz Lw l s Gr t Gr Lw Ph t s Am Lw Ph p s SV12-13E 0.5 mm SV13-06 SV13-01 SV08-4A SV10-06 Lw s Cp x B Gl H E K 0.5 mm n Gr t Lw Om s Lw p s Lw Lw Gr Lw s s t s SV12-24B Am Gr Ch p t SV12-13E l 0.25 mm 0.5 mm SV08-4A SV12-59 SV12-24 C F L I 1.0 mm 1.0 mm 1.0 mm Gl 1 mm n Lw Lw s Lw s s Lw Ph s Chl + Ep Cp o SV03-103A Fe xides SV12-24 SV13-01 SV13-15 -T Gl i n x

GEOSPHERE | Volume 15 | Number 1 Fornash et al. | Lawsonite composition and zoning as an archive of metamorphic processes in subduction zones 26 Research Paper

A SV12-21D B TZ10-2.2c C TZ10-2.2c

Lws

Lws+Chl Chl rocks

serpentinite Lws

Chl 3 mm

D SV12-21D E SV13-17A F SV03-103 B Lws C

Lws Grt

Chl A Chl 3 mm 3 mm

Figure 3. Representative photos and photomicrographs of lawsonite + chlorite–rich rocks (A–E) and lawsonite-rich layers (F) from the Sivrihisar Massif, Turkey. (A) Photograph from the Halilbağı region showing the field relationships between serpentinite lenses and the lawsonite + chlorite–rich rocks from which sample SV12-21D was collected (indicated with a star). (B) Photograph of the lawsonite + chlorite–rich boulder from which sample TZ10-2.2c was collected. Coin (~26 mm in diameter) provided for scale. (C–E) Photomicrographs showing the coarse-grained lawsonite in samples TZ10-2.2c (C; cross-polarized light [XPL]), SV12-21D (D; XPL), and SV13-17A (E; plane-polarized light). (F) Thin-section scan of the pod margin (samples SV03-103A, SV03-103B, and SV03-103C) showing the millimeter- to centimeter-scale lithologic layering (A—eclogite; B—glaucophane-rich layer; C—Lws + Grt + Ph–rich layer). The thin section is 46 mm in length. Chl—chlorite, Grt—garnet, Lws—lawsonite, Ph—phengite.

In the Sivrihisar Massif, lawsonite-bearing rocks are well exposed near the PETROLOGY OF LAWSONITE-BEARING ROCKS villages of Halilbağı and İkipınar, where they occur as meter- to kilometer-scale metasedimentary (calc-schist, quartzite) and metamafic layers (blueschist). Ten samples of metamafic rocks (four eclogite, five blueschist, one Metasedimentary rocks contain HP minerals such as lawsonite, sodic pyrox- chlorite + epidote–rich pod margin) and three samples of quartz-rich meta ene, sodic amphibole, and phengitic white mica, and quartzite also contains sedimentary rocks collected near the villages of Halilbağı and İkipınar were piemontite (Mn-rich epidote) and spessartine-rich garnets. Hundreds of mafic selected for detailed major and trace element composition and/or micro- pods, including lawsonite eclogite pods, occur throughout the field area, where structural analysis (Table 1; Fig. 2). Sample locations and a summary of the they are hosted within blueschist, calc-silicate, and quartzite (Davis and Whit- analytical methods used are provided in Table S1 [footnote 1] for all sam- ney, 2006). Some pods have chlorite + epidote–rich margins that contain coarse- ples for which compositional (± microstructural) data are presented. We note grained patches of lawsonite and crosscutting, monomineralic lawsonite veins. that the names “blueschist” and “eclogite” are used to describe metamafic This sequence of HP-LT rocks is in fault contact with a low-grade meta- samples consisting of glaucophane-rich and garnet + omphacite–rich assem- morphosed ultramafic and mafic complex to the north. A mylonite zone that blages, respectively, and do not necessarily reflect the metamorphic facies extends ~150 m south from the fault developed under HP-LT conditions (Teys- in which the rock equilibrated; i.e., some garnet + glaucophane–rich assem- sier et al., 2010; Whitney et al., 2014). Meter-scale antigorite serpentinite lenses blages (blueschist) and garnet + omphacite–rich assemblages (eclogite) may occur within several hundred meters of this contact and are bordered by law- be cofacial, with differences in mineral assemblage reflecting differences sonite + chlorite ± garnet assemblages (Zack, 2013; Whitney et al., 2014). in bulk composition. In addition to metamafic and metasedimentary rocks,

TABLE 1. SAPLE LOCATIONS AND INERAL ASSEBLAGES, TASANLI ONE, TRKEY T coordinates Easting Northing Sample m m GrtCp Na‑AmphPhLws Ep Chltz Cal Accessory phases etamafic samples Eclogite samples S12‑13E 351574 4384265 , Inc Rt rimmed by Ttn, Ap, rn S03‑103A 351574 4384265 Rt rimmed by Ttn S03‑305 351574 4384265 Rt rimmed by Ttn S08‑4A 350046 4385062 , Inc Rt rimmed by Ttn, Aln Blueschist samples S12‑59 344596 4386992 , IncFe‑oides, Ttn, rn S03‑103B 351574 4384265 Rt S13‑15 350572 4385194 Ttn, rn S13‑06 350615 4385109 Rt rimmed by Ttn, Fe‑oides, rn, Aln S13‑01 350295 4384946 Ttn, Aln, Ap Chlorite + epidote pod S12‑24 344581 4386678 Fe‑Ti oides etasedimentary samples S08‑281C 350194 4385116 Ttn S10‑06 350066 4385206 Fe‑Ti oides Lawsonite chlorite rocks T10‑2.2c 741000 4400780 Ttn S13‑17A 349839 4384940 , Inc Ttn, Fe‑oides S12‑21D 350042 4384924 Ttn Lawsonite‑rich layers and veins S03‑103C 351574 4384265 Rt, rn S12‑24B 344581 4386678 Note: matri phase; Incinclusion in garnet. ineral abbreviations follow the recommendations of Whitney and Evans 2010. ineral abbreviations used: Grtgarnet, Cpclinopyroene, Na‑Amphsodium amphibole, Phphengite, Lwslawsonite, Epepidote, Chlchlorite, tzuartz, Calcalcite, Rtrutile, Ttntitanite,Apapatite, rnzircon,AlnAllanite. Coordinates are reported using the European Datum 1950 niversal Transverse ercator, T zone 36 reference system. Ep refers to epidote‑group minerals, including allanite.

lawsonite-rich veins and layers (Davis and Whitney 2008) and lawsonite + phosphate), and/or zircon (Figs. 2A–2C). Minor, texturally late glaucophane is chlorite–rich rocks associated with serpentinite lenses were also collected to common. Lawsonite occurs as subhedral to euhedral rhombs (Fig. 2A) or as investigate the composition of lawsonite associated with metasomatic fea- polycrystalline aggregates (Fig. 2B). Retrogressed eclogite largely consists of tures (Fig. 3). lawsonite and chlorite (Fig. 2D) with minor epidote (with allanitic cores) and accessory rutile (rimmed by titanite) and zircon. Relict omphacite, zoned amphi- Metamafic Rocks bole, and highly fractured garnet partly replaced by chlorite are also present (Fig. 2E). Lawsonite occurs as inclusions in garnet and as a matrix phase (Figs. Lawsonite composes ~10%–50% of the mode in Tavşanlı metamafic rocks 2D, 2E). Lawsonite blueschist consists of glaucophane + lawsonite + phengite ± (Okay, 1980a; Davis and Whitney, 2006, 2008), although modal abundances garnet ± omphacite ± quartz ± chlorite, with minor amounts of epidote-group vary over millimeter to centimeter scales in some samples with compositional minerals (commonly with allanitic cores or rims) and calcite (Figs. 2F–2J). The banding. Fresh lawsonite eclogite typically consists of omphacite + garnet + dominant accessory phases include titanite, apatite, Fe-oxides, and/or zircon. lawsonite + phengite, minor amounts of epidote-group minerals, and acces- Chlorite + epidote–rich assemblages along pod margins, interpreted as retro- sory rutile (rimmed by titanite), apatite, florencite (an aluminous REE-rich gressed eclogite (Davis and Whitney, 2006, 2008), consist of coarse-grained

lawsonite in a fine-grained matrix of epidote, chlorite, and clinopyroxene with To determine whether some lawsonite zoning types are crystallographically accessory Fe-Ti oxides, apatite, and titanite (Figs. 2K, 2L). A centimeter-scale, controlled and whether deformation affects trace element distribution in law- cross-cutting, monomineralic lawsonite vein (sample SV12-24B) was also sam- sonite, the crystallographic orientations of lawsonite crystals displaying core-to- pled from the margin of this pod (Fig. 2K). rim, sector, and oscillatory zoning from ten samples representing different rock types (six metamafic rocks, one quartz-rich metasediment, two lawsonite + chlo- Metasedimentary Rocks rite–rich rocks, and one lawsonite-rich layer) were measured using EBSD. Grain- scale EBSD maps and orientation contrast images were also obtained for individ- Lawsonite-bearing quartz-rich metasedimentary rocks consist of quartz + ual lawsonite crystals to evaluate whether there was any relationship between phengite + lawsonite (3%–5% modal abundance) ± garnet ± clinopyroxene ± microstructural features (subgrains, grain boundaries, twinning) and zoning pat- sodic amphibole ± calcite, with minor amounts of epidote-group minerals, terns. All compositional and microstructural analyses were conducted in situ on including piemontite, and accessory Fe-Ti oxides (Fig. 2M). In calcite-bearing polished thin sections cut parallel to the lineation and perpendicular to foliation. samples, titanite is also present as an accessory phase and is spatially associated with calcite-rich domains. Electron Microprobe (EMP) Analysis (Major Elements)

Lawsonite + Chlorite–Rich Rocks Major element compositions and element maps were obtained with a JEOL JXA-8900 electron microprobe at the Department of Earth Sciences, University Lawsonite + chlorite–rich rocks occur throughout the Tavşanlı Zone (Zack, of Minnesota (Minneapolis, Minnesota, USA). Major element analyses were 2013; Plunder et al., 2013; Whitney et al., 2014) and are typically associated performed with a 15 kV accelerating voltage, 15 nA beam current, and defo- with serpentinite lenses (Fig. 3A). They are largely composed of lawsonite cused 5–10 μm beam diameter to minimize beam damage to minerals. Natural in a chlorite-rich matrix with accessory titanite, although some samples also mineral standards were used in calibrations. Oxygen and OH were calculated contain epidote-group minerals, clinopyroxene, and garnet. Lawsonite is typi- by cation stoichiometry and included in the matrix corrections. Lawsonite min- cally coarse-grained (>0.5 mm; Figs. 3B–3E) and slightly pink in hand sample, eral formulas were calculated on an eight-oxygen basis. X-ray element maps reflecting the presence of Cr (Fig. 3B). Three lawsonite + chlorite–rich rocks were acquired using a 15 kV accelerating voltage, 100 nA beam current, fo- were sampled: two from the Halilbağı region of the Sivrihisar Massif (samples cused beam, dwell time of 50 ms, and stage-rastering step sizes ranging from SV12-21D, SV13-17A) and one from farther west in the Tavşanlı Zone (sample 1 to 6 μm depending on lawsonite grain size. TZ10-2.2c; for location, see stop 2.2 in Okay and Whitney [2010]) (Table 1). Laser Ablation–Inductively Coupled Mass Spectrometry Lawsonite-Rich Veins and Layers (LA‑ICPMS) (Trace Elements)

Two lawsonite-rich veins and layers were sampled from the margins of Laser ablation–inductively coupled mass spectrometry (LA-ICPMS) trace metamafic pods: lawsonite + garnet + phengite layer sample SV03-103C is from element analyses of lawsonite were acquired at the Research School of Earth the margin of the lawsonite eclogite pod studied by Davis and Whitney (2008) Sciences, Australian National University (Acton ACT). Trace elements were and from which fresh lawsonite eclogite samples SV12-13E (core) and SV03- measured on an argon fluoride excimer laser coupled to a quadrupole ICPMS 103A and SV03-305 (margin) were collected; and monomineralic lawsonite vein Agilent 7700, using the setup described by Eggins et al. (1998). The laser was sample SV12-24B was collected from the epidote + chlorite–rich pod margin tuned to a frequency of 5 Hz and energy of 50 mJ, and spot sizes ranged from from which sample SV12-24 was obtained (Fig. 2K). Trace element analyses of 28 μm to 47 μm depending on the size of the grain and compositional zoning lawsonite in sample SV03-103C were previously presented by Martin et al. (2014). features. Counting times were 20 s for the background and 50 s for sample analysis. The internal isotope used to quantify the analyses was 29Si. The U.S. ANALYTICAL METHODS National Institute of Standards and Technology (NIST) 612 glass was used as a primary standard (Jochum and Stoll, 2008; GeoReM 2902), and the Columbia To evaluate the major and trace element affinities of lawsonite in different River Basalt BCR-2G glass was used as a secondary standard. The effects of bulk compositions and assemblages, the composition of lawsonite in different small inclusions of rutile, zircon, and allanite on the analyses were removed rock types and in different textural sites within each sample was determined manually by examining the time-resolved spectra for each analysis prior to using EMP analysis (major elements) and LA-ICPMS (trace elements). X-ray data reduction. The data were reduced with the freeware Iolite (Paton et al., element maps were also obtained to examine zoning patterns and trends in re- 2011) and its data reduction scheme for trace elements (Woodhead et al., 2007). lation to mineral assemblages and textures, as this could provide information Accuracy and reproducibility of the secondary standard were generally within about reaction history and mechanisms. 10% of the reference value.

Electron Backscatter Diffraction (EBSD) Lawsonite Trace Element Composition

TABLE S1. SAMPLE LOCATIONS AND SUMMARY OF METHODS USED UTM Coordinates* Methods EastingNorthing Element MapMajor Elements Trace Elements EBSD MapBulk Rock Analysis (m)(m) (EMP)(EMP) (LA-ICPMS) Metamafic samples The crystallographic orientation and microstructures of lawsonite were ana Results from LA-ICPMS analysis of lawsonite from the Tavşanlı Zone shows SV12-13E (core) 351574 4384265 XX XX X SV03-103A (margin) 351574 4384265 XX XX SV03-103B (margin) 351574 4384265 XX X SV03-305 (margin) 351574 4384265 XX lyzed with a JEOL 6500 field-emission gun scanning electron microscope and that lawsonite can incorporate a variety of trace elements, including REEs (light SV08-4A 350046 4385062 XX SV12-24 344581 4386678 XX XX SV08-76 347773 4381019 XX SV12-59 344596 4386992 XXX SV13-15 350572 4385194 XXX the Oxford Instruments HKL Channel 5 software in the Characterization Facility REEs [LREEs], middle REEs [MREEs], and heavy REEs [HREEs]), some transi- SV13-06 350615 4385109 XX SV13-07 350711 4384917 X SV01-75 350347 4385060 X SV13-01 350295 4384946 XX XX of the College of Science and Engineering, University of Minnesota. Scanning tion metals (Sc, V, Mn, Ni), and high-field strength elements (HFSEs; Th, U), as

Metasedimentary samples SV08-281D 350194 4385116 XX SV10-06 350066 4385206 X electron microscope conditions were 70° tilt, 20 kV accelerating voltage, and well as Sr, Pb, Y, and P (Table 2; Table S2 [footnote 1]). The concentrations of SV10-03B 349975 4384913 X SV13-12 350674 4384682 X Lawsonite + chlorite rocks ~15 nA beam current. The phase details and solution models used to index large-ion lithophile elements (LILEs; Rb, Ba, Cs) and other HFSEs (Zr, Hf, Ta) in TZ10-2.2c† 741000 4400780 XX X SV13-17A 349839 4384940 XX XX SV12-21D 350042 4384924 XX XX the lawsonite and the sample and acquisition reference frame are provided in lawsonite were at or below detection level in all rock types analyzed (Table S2). Lawsonite-rich layers and veins SV03-103C 351574 4384265 XX XX SV12-24B 344581 4386678 X Figure S1 in the Supplemental Materials1. Rare earth element concentrations vary at both the sample and the grain *Coordinates are reported using the European Datum 1950 (Universal Transverse Mercator, UTM) reference system, zone 36 †Coordinates reported are from Okay and Whitney (2010) scale. Lawsonite from metabasaltic rocks typically contains REE concentra- 1Supplemental Materials. Locations of all studied tions of 1×–1000× chondrite (Figs. 5A–5C). In general, lawsonite in blueschist samples (Table S1), representative major and trace RESULTS and retrogressed eclogite contains higher concentrations of REE (~10×–1000× element analyses of lawsonite (Table S2), the solution models and acquisition reference frame for EBSD chondrite) than lawsonite in fresh eclogite and shows REE patterns that

analyses (Figure S1), and a backscattered electron The results of the major and trace element zoning and composition analy are enriched in the LREEs relative to the MREEs and/or HREEs ([La/Dy]N > 1 image of a lawsonite grain (Figure S2). Please visit ses are summarized in Table 2 and presented in Table S2 (footnote 1), orga- [N indicates a chondrite-normalized concentration]; Fig. 5A). Lawsonite from https://doi .org /10 .1130/GES01455 .S1 or access the full-text article on www.gsapubs.org to view the Sup- nized by rock type. For lawsonite in which Fe, Ti, and/or Cr oxide content is metasedimentary rocks contains the highest concentration of REEs, and dis- plemental Materials. >0.5 wt%, composition data from microprobe analyses are reported; for law- plays chondrite-normalized REE patterns that are enriched in LREEs relative

sonite in which Fe, Ti, and/or Cr oxide content is <0.5 wt%, composition data to HREEs ([La/Yb]N > 1; Figs. 5A, 5C) and exhibit a negative Eu anomaly. Law- from LA-ICPMS analyses are reported. Rare earth element concentrations and sonite from the lawsonite-rich layers and veins displays similar REE patterns as trace element ratios were normalized to the chondritic and primitive mantle lawsonite from metasedimentary samples (enrichment in LREEs over HREEs, compositions of Sun and McDonough (1989). negative Eu anomaly), but has lower overall REE concentrations (~100× chondrite; Fig. 5A). Lawsonite in the metasomatic lawsonite + chlorite–rich rocks displays the lowest overall REE concentrations (~1×–100× chondrite) and the Lawsonite Major Element Composition greatest diversity of REE patterns (flat, MREE-enriched, and/or HREE-enriched; Figs. 5A–5C). At the grain scale, lawsonite REE concentrations typically vary Lawsonite from all studied samples contains FeO* (asterisk indicates that by one to two orders of magnitude. In some cases, these intragrain variations

all iron is reported as FeO) and, more rarely, TiO2 and/or Cr2O3 as impurities are correlated with major or minor element (Fe, Ti, Cr) zoning or the textural at the weight percent level, and displays zoning in these elements (Table 2; position of the analysis (i.e., core versus rim), whereas in others, there is no Fig. 4). The most common zoning types are core-to-rim (Fe, Ti), sector (Fe, Ti), obvious correlation between variations in REE concentrations and the spatial and oscillatory (Fe, Cr) (Figs. 4A–4L). In zoned lawsonite, Fe, Ti, and Cr typically position of the analysis. covary with Al. The types of zoning observed within some samples is hetero- Transition metals, including V (32–1551 ppm), Sc (1–50 ppm), and Mn (6– geneous at millimeter to centimeter scales: some individual lawsonite grains 365 ppm), are also incorporated into the lawsonite structure at trace levels in display different types of zoning patterns, and within some grains, different some grains. As with Fe, Ti, and Cr, there are few correlations between tran- elements display different zoning types. For example, some lawsonite grains sition metal content in lawsonite and rock type. In general, lawsonite in the in blueschist sample SV13-01 display oscillatory zoning in Fe and Cr, whereas quartz-rich metasediments has the lowest overall V concentrations (Table 2). others display Fe and Ti sector zoning and variations in Cr concentrations that Similar V concentrations are observed in lawsonite from lawsonite-rich veins mimic the inclusion pattern (Table 2). In the lawsonite-rich layer sample (SV03- and layers and the chlorite + epidote–rich pod margin (Table 2). Manganese 103C), a single lawsonite grain displays core-to-rim zoning in Fe, sector zoning concentrations are highest in lawsonite in impure quartzite sample SV10-06 in Ti, and oscillatory zoning in Cr (Table 2). (73–365 ppm) and show a negative correlation with Fe. With few exceptions Intersample variations in the overall range of Fe, Ti, and Cr concentrations (samples TZ10-2.2c, SV13-17A, SV13-01), Sc concentrations are generally low in lawsonite also occur. In general, lawsonite in the Halilbağı metasomatic law- in lawsonite (<10 ppm) and show small intrasample variations (standard devi-

sonite + chlorite–rich rocks contains the highest TiO2 concentrations (maxi- ations are generally <3 ppm). Although Ni concentrations are generally at or

mum of 1 wt%) measured in this study (Table 2). Similar TiO2 contents were below detection levels in most samples, in blueschist sample SV13-01, Cr-rich documented in lawsonite from lawsonite metasomatites in Corsica (Vitale Bro- lawsonite tends to be Ni rich (16–53 ppm; Table S2 [footnote 1]).Yttrium con-

varone et al., 2014). No rigorous correlation between FeO* or Cr2O3 content in centrations range from 3 to 537 ppm and generally mirror the trends observed lawsonite and rock type is observed. in Mn contents, with the highest concentrations in lawsonite from impure

TABLE 2. SARY OF AJOR AND TRACE ELEENT COPOSITIONS AND ONING PATTERNS IN LAWSONITE FOR SELECTED SAPLES, TASANLI ONE, TRKEY Fe Ti Cr ppm ppm oning patterns wt ppm Sr/Pb La/DyN Dy/LuN La/YbN Sample Fe Ti Cr in. a. in. a. in.a.Average Std. dev. average average average average etamafic samples Eclogite samples S12‑13E Irregular Irregular, N.D. 1.27 1.47 375 4030211 404319 69 38 2.58 39.1911.97 Sector S03‑103A Irregular Irregular N.D. 1.00 1.59 347 423031296 25328431.2312.16 4.57 S03‑305 Irregular Irregular N.D. N.. N.. N.. N.. N.. N.. N.. N.. N.. N.. N.. N.. S08‑4A N.. N.. N.. 1.29 1.98 160 3132181047635 83 41 7.17 19 44.57 Blueschist samples S12‑59 Core to rim Irregular N.D. 1.05 1.81 403 111832426 54149181 2.76.1 18.36 S03‑103B Oscillatory Irregular Oscillatory 0.79 1.27 319 264285648 28831383.168.5813.46 S13‑15 Core to rim Irregular N.D. N.. N.. 239 30304125562 73 29 12.922.6932.87 S13‑06 N.. N.. N.. N.. N.. 395 2840233 852412 20 29 2.82 34.4327.41 S13‑01 Cr-poor lws Sector Sector Irregular 1.3 1.86 125 24100.27 wt 1.12 wt 557265 42 5.28 1.19 8.76 Cr-rich lws Oscillatory Irregular Oscillatory 1.68 2.12 231 13371.73 wt 5.81 wt 516106 22 6.33 1.83 7.49 Chlorite + epidote pod S12‑24 Irregular Irregular N.D. 1.69 2.98 220 2508112 1083 2041687.07 1.31 10.01 etasedimentary samples S08‑281C N.. N.. N.. 1.21 1.86 306 120023.9258 22814115.481.6118.83 S10‑06 N.. N.. N.. N.. N.. 233 596 20.9 224171 64 56.4634.07 106.12 S10‑03B Irregular N.D. N.D. 1.72 1.98 N.. N.. N.. N.. N.. N.. N.. N.. N.. N.. Lawsonite chlorite rocks T10‑2.2c Irregular Irregular N.D. 0.66 1.63 172 139150138 1240 213450.831.721.5 S13‑17A Core to rim, Sector Oscillatory 1.04 2.08 249 0.87 5651452723 142250.152.090.29 oscillatory wt S12‑21D Irregular Irregular N.D. 1.12 2.15 246 1.05 118629 24717290.640.832.85 wt Lawsonite‑rich layers and veins S03‑103C Layer margin Core to rimSector Oscillatory 0.51 1.45 535 2349320 1051 18941422.2257.88 24.24 Layer center Core to rim, Sector N.D. 0.65 1.24 200 3060468 78 54 41 3.29 14.8715.84 oscillatory S12‑24B N.. N.. N.. 2.69 0.13 wt 20189 N.A. 13 6.32 2.21 13.35 Note: in.minimum; a.maimum; Std. dev.standard deviation; lwslawsonite; N..not measured; N.D.not detected in the analyzed grains; N.A.not applicable. Where core‑to‑rim zoning in Fe is reported, minimum values correspond to Fe‑poor core and maimum values correspond to Fe‑rich rim. Ti is reported in ppm, ecept where noted with wt. Where sector zoning in Ti is reported, minimum values correspond to Ti‑poor sectors and maimum values correspond to Ti‑rich sectors. Cr is reported in ppm, ecept where noted with wt. Ratios are normalized to the chondritic values of Sun and cDonough 1989. aor and trace element data obtained from a bulk‑rock analysis of vein material.

quartzite sample SV10-06 (113–537 ppm). Concentrations of Th and U in law- rocks (Table 2). Lawsonite from the monomineralic lawsonite vein (sample sonite are highly variable at both the sample and grain scale, and range from SV12-24B) and its host chlorite + epidote–rich pod has Sr/Pb similar to those below detection level to 127 ppm and 13 ppm, respectively. In contrast to most observed in metasedimentary rocks, whereas lawsonite from lawsonite-rich trace elements, Sr and Pb contents are correlated with rock type, such that layer sample SV03-103C and metasomatic lawsonite + chlorite–rich rocks has lawsonite in metasediments has lower Sr/Pb than lawsonite from metamafic Sr/Pb similar to that in metamafic rocks (Table 2).

A SV13-15 B SV13-07 C SV13-07 D SV13-07 Gln Ph Grt

Lws Gln Ttn

truncated zoning Lws Figure 4. Iron (Fe), Ti, and Cr zoning pat- Gln terns in lawsonite. Core-to-rim zoning in Fe is commonly symmetric with respect 100 m 100 m 100 m 50 m to grain boundaries, but zoning in some Fe Fe Ti Fe samples is truncated at grain boundaries SV13-13 SV13-13 SV01-75A (A). In some cases, an individual lawsonite E SV13-07 F G H grain displays the same type of zoning in Fe and Ti (i.e., core-to-rim zoning; B, C), whereas in others, the lawsonite grain Grt displays contrasting zoning features in Fe Gln and Ti (e.g., core to rim in Fe [F]; and sec- Lws tor zoning in Ti [G]). Some lawsonite inclu- Ph sions in garnet (D, E) also display zoning features that contrast with those in lawsonite in the matrix (B, C). Chromium-rich lawsonite typically displays oscillatory zoning (H). In addition to sector zoning in Fe-rich core Fe-rich core Ti (G, L), some lawsonite grains also dis- regions regions play sector zoning in Fe (J, K). The habit Ti 50 m Fe 200 m Ti 200 m Cr 100 m of the lawsonite can also affect Ti zoning: euhedral lawsonite crystals in eclogite I SV13-01 J SV13-01 K SV01-75A L SV12-13E sample SV12-13E display sector zoning (L), whereas polycrystalline aggregates of lawsonite in the same sample display irregular Ti concentrations (M). Lawsonite in quartzite sample SV10-03B displays heterogeneous distributions of Fe (N) and Al (O). Gln—glaucophane, Grt—garnet, Lws—lawsonite, Ph—phengite, Ttn—titanite. The white dotted lines are used to delineate the lawsonite grain boundary. Lws Dark blue and purple colors indicate low concentrations of the analyzed element, whereas brighter purple and pink colors Cr 100 m Fe 150 m Fe 150 m Ti 150 m indicate higher concentrations. In grayscale images (N, O), dark gray colors correspond SV12-13E SV10-03B SV10-03B to low concentrations of the analyzed ele- M N O ment, and lighter gray colors correspond to higher concentrations.

Lws Fe-rich Lws region 0.25 mm Fe 0.25 mm Al

Ti 200 m

100 1000 A B

10 100 N N u) y) 1 10 y/L Metama c Rocks (D (La/D SV12-13E Metasedimentary Rocks SV03-103A SV08-281C SV08-4A 0.1 SV10-06 SV03-103B 1 SV12-59 Lws + Chl Rocks SV13-01 SV13-17A SV13-15 Lws Layers SV12-21D SV13-06 SV03-103C TZ10-2.2c SV12-24 0.01 0.1 110100 1000 10,000 110100 1000

(Dy)N (La)N

1000 C 100

N 10 Figure 5. Chondrite-normalized rare earth element concentrations and ratios in lawsonite in samples from the Sivrihisar Massif. Lws—lawsonite; Chl—chlorite. (La/Yb ) 1

0.1

0.01 110100 1000 10,000

(La)N

DISCUSSION also vary markedly, displaying patterns that range from flat to LREE-, MREE-, and/or HREE-enriched (Fig. 5). Lawsonite from all rock types displays large variations in the concentra- To understand the processes giving rise to these compositional variations, tions of transition metals (Fe, Ti, Cr) and other trace elements (REEs, Sr, Pb) we first review Fe, Ti, and Cr substitution in lawsonite. We then examine the and commonly displays zoning in these elements. Within a sample, and even types of zoning patterns and their relationship (if any) to microstructural fea- within a single lawsonite grain, chondrite-normalized REE concentrations vary tures to consider processes acting at the grain scale. Finally, we consider pro- by one to two orders of magnitude, consistent with the results of trace and REE cesses that may have operated at a larger scale to affect the major and trace analyses conducted on lawsonite from other HP-LT terranes (e.g., Spandler element systematics of lawsonite, such as rock composition (protolith), meta et al., 2003; Martin et al., 2011, 2014; Vitale Brovarone et al., 2014). REE trends morphic assemblage, and fluid-rock interaction among different rock types.

Fe, Ti, and Cr Substitution in Lawsonite There are few studies of Fe, Ti, and Cr systematics in lawsonite. In Corsi- can metasomatic rocks, Ti-rich lawsonite occurs in low-grade and highly al- Although the major element composition of lawsonite has been reported tered rocks, whereas Fe- and Cr-rich lawsonite occurs in higher-grade rocks as near end-member (Pawley, 1994; Okay and Kelley, 1994), the lawsonite crys- (Vitale Brovarone et al., 2014). A positive correlation between Fe content tal structure can accommodate a variety of different elements as both major in lawsonite and metamorphic grade was also documented by Maruyama and trace elements (Martin et al., 2014). The most common impurities at the and Liou (1988) in Franciscan metabasites. In the Sivrihisar rocks, there is weight percent level are Fe (maximum reported ~8 wt%; Maekawa et al., 1992), no difference in the Fe (or Cr) content of lawsonite in blueschist- versus Ti (maximum reported ~1 wt%; Vitale Brovarone et al., 2014; this study), and Cr eclogite-facies rocks (Fig. 7), although this may reflect the fact that some (maximum reported ~8 wt%; Mevel and Kienast, 1980; Vitale Brovarone et al., eclogite and blueschist may be cofacial (Davis and Whitney, 2006). In law- 2014). Some lawsonite also contains LREEs at weight percent levels (Ueno, sonite from the western part of the Tavşanlı Zone, Plunder et al. (2015) ob- 1999). These elements are likely incorporated into the lawsonite crystallo- served a correlation between lawsonite Fe content and oxide assemblage, graphic structure via substitution on the octahedral Ca2+ site, the octahedral such that lawsonite in metabasalt containing titanite had lower FeO* con- Al3+ site, and/or the tetrahedral Si4+ site. On the basis of similarities in charge tents (0–1.5 wt%) than lawsonite from impure quartzite (inferred metachert) and/or ionic radii, previous studies have suggested that Sr2+, Pb2+, and REE3+ containing hematite (1–2.2 wt% FeO*). Therefore, another possibility is that reside on the octahedral Ca site (Ueno, 1999; Martin et al. 2011), whereas Ti4+ intersample variations in Fe content reflect variations in the oxidation state (Ueno, 1999) and Cr3+ reside on the octahedral Al site (Sherlock and Okay, 1999). of the protolith. In Sivrihisar lawsonite, the most common impurity is Fe (0.5–3 wt% FeO*; Lawsonite containing high concentrations of Cr is not common; nearly all Table 2), which covaries with Al, suggesting that Fe substitutes for Al3+ and is major element analyses of lawsonite from the Sivrihisar Massif and in the therefore likely ferric iron. Plots of the sum of Fe, Ti, and Cr versus Al atoms published literature show higher concentrations of Fe and Ti than Cr (Fig. 7). per formula unit in lawsonite show a negative correlation, which is consistent with previous results indicating that these elements substitute for Al (Fig. 6). Cr (p.f.u.)

Metama c Rocks Metasedimentary Rocks 0.40 SV12-13E SV08-281C Metama c Rocks Metasedimentary Rocks SV03-103A SV10-03B SV12-13E SV08-281C SV08-4A SV03-103A SV03-103B Lws + Chl Rocks SV10-03B SV13-17A 0.35 SV08-4A Lws + Chl Rocks SV12-59 SV03-103B SV13-01 SV12-21D SV13-17A TZ10-2.2c SV12-59 SV12-21D SV12-24 SV13-01 TZ10-2.2c Lws Layers 0.30 SV12-24 SV03-103C Lws Layers Literature Data SV03-103C Ma c (blueschist) Ma c (eclogite) 0.25 Metasedimentary .u.) Lws vein .f

0.20 + Cr (p Ti

+ 0.15 Fe

0.10

0.05 Ti (p.f.u.x 4) Fe (p.f.u.)

Figure 7. Ternary diagram showing the major element variations in Fe, Ti, and Cr in lawsonite 0.00 (in atoms per formula unit, p.f.u.) from a variety of different rock types in the Sivrihisar Massif 1.60 1.65 1.70 1.75 1.80 1.85 1.90 1.95 2.00 (this study; Martin et al., 2014), the Franciscan Complex (California, western USA; Martin et al., Al (p.f.u.) 2014), the Dominican Republic (Zack et al., 2004), the North Qilian belt (China; Xiao et al., 2013), the Colorado Plateau (western USA; Usui et al., 2006), Port Macquarie (Australia; Och Figure 6. Plot of the sum of the Fe, Ti, and Cr versus the Al atoms per formula unit (p.f.u.) in et al., 2003), and the Central Pontides (Turkey; Altherr et al., 2004). Lws—lawsonite; Chl— lawsonite from different rock types in the Sivrihisar Massif. Lws—lawsonite; Chl—chlorite. chlorite.

Chromium-rich lawsonite from the Sivrihisar Massif and elsewhere (Sherlock These features suggest that Fe zoning may be related to changes in re- and Okay, 1999; Vitale Brovarone et al., 2014) commonly displays oscillatory action history. Results of phase equilibria modeling and the presence of epi- zoning, possibly suggesting growth in a fluid-rich environment. dote inclusions in garnet, omphacite, and lawsonite indicate that prograde P-T paths passed through the epidote stability field or close to the epidote-law- Lawsonite Zoning Patterns sonite stability boundary (Davis and Whitney, 2006). Therefore, one possibility to explain the observed core-to-rim increase in Fe in lawsonite would be the The most common types of major and minor element zoning in lawsonite breakdown of coexisting Fe3+-bearing epidote. Lawsonite that grew concur- are oscillatory (Sherlock and Okay, 1999; Vitale Brovarone et al., 2014; this rently with epidote along the prograde path would be poor in Fe3+ relative to study), core-to-rim (this study), and sector (Ueno, 1999; Tsujimori and Ernst, epidote. Upon breakdown of epidote, lawsonite would take up the Fe, resulting 2014; Vitale Brovarone et al., 2014; this study). Similar zoning has also been ob- in an increase in Fe3+ toward the lawsonite rim. It is also possible that some 3+ served for trace elements (Y, Sr, Th, REEs) (Ueno, 1999; Martin et al., 2011, 2014; intragrain variations in Fe reflect changes in oxygen fugacity f( O2) during Tsujimori and Ernst, 2014; Vitale Brovarone et al., 2014; this study). Under metamorphism. Okay (1980b) suggested that hydrous phases may be more 2+ 3+ standing the types and mechanisms of zoning in lawsonite, particularly in Fe, sensitive to fluctuations inf O2, and that core-to-rim variations in the Fe /Fe Ti, Cr, and REEs, is important because these elements have been used to track ratio of sodic amphiboles from the western part of the Tavşanlı Zone were

changes in mineral parageneses (Martin et al., 2011), monitor metamorphic recording changes in fO2. Sodic amphiboles from the Sivrihisar region have grade (Maruyama and Liou, 1988; Vitale Brovarone et al., 2014), and date sub- similar zoning patterns to those documented in that study (Davis and Whitney, duction zone metamorphism (Mulcahy et al., 2009, 2014; Vitale Brovarone and 2006), and in the studied samples, Fe zoning in coexisting lawsonite and sodic Herwartz, 2013). amphibole is similar (i.e., both record rimward increases in Fe3+). Some individual lawsonite grains display similar zoning patterns in differ- Some lawsonite grains from both metamafic and metasedimentary rocks ent elements (e.g., core-to-rim zoning in Fe, Ti, and Cr), or display different zon- exhibit core-to-rim variation in REEs. In quartzite sample SV10-06 and retro- ing patterns in different elements (e.g., core-to-rim zoning in Fe, sector zoning gressed eclogite sample SV08-4A, lawsonite records a core-to-rim decrease in Ti, oscillatory zoning in Cr), demonstrating that the uptake and distribution in REE concentrations with no change in the overall shape of the REE pattern of different elements may be controlled by different mechanisms. In the fol- (Figs. 9A, 9B). In the latter sample, lawsonite inclusions in garnet have REE lowing sections, we discuss each zoning type and consider crystallographic concentrations similar to those in the core regions of matrix lawsonite (100×– and local environmental factors that may have resulted in such zoning. 1000× chondrite; Fig. 9B). In these samples, the rimward depletion in REEs may be related to the depletion of these elements from the rock matrix during Core-to-Rim Zoning progressive crystallization of lawsonite. In other samples, however, lawsonite records a core-to-rim variation in the shape of the REE pattern and/or an in- Lawsonite from nearly every rock type studied displays core-to-rim zoning crease in REE concentrations (Figs. 9C, 9D, 9E). These zoning trends cannot in Fe, with Fe-poor cores and Fe-rich rims (Table 2; Figs. 4A, 4B, 4F). The abso- be explained by the continued fractionation of REEs from the matrix during lute variation in Fe content varies between samples and between grains within lawsonite growth, and instead likely reflect the growth or breakdown of other a sample, although the latter may to some extent reflect sectioning effects. In phases that compete for REEs in the rock. Besides lawsonite, the other primary contrast to core-to-rim zoning in other minerals such as garnet (in which zon- REE hosts in blueschist- and eclogite-facies metamafic and metasedimentary ing is commonly continuous), the change in Fe content in lawsonite is typically rocks are epidote-group minerals (LREEs), titanite (MREEs), garnet (HREEs), abrupt, showing either a well-defined core and rim region (Figs. 8A, 8B) or and apatite (LREEs to MREEs) (Tribuzio et al. 1996; Hermann, 2002; Zack et al., an Fe-poor core that transitions to a rim with oscillatory variations (Fig. 8C). 2002a; Spandler et al., 2003; John et al., 2008; El Korh et al., 2009; Beinlich Core-to-rim zoning is commonly concentric and centered (i.e., symmetric with et al., 2010; Guo et al., 2012, 2013), of which epidote, titanite, and garnet are the respect to grain boundaries), but zoning in some samples is truncated at grain most common in the studied samples. boundaries (Fig. 4A), indicating that lawsonite has been modified by post-crys- In lawsonite from garnet blueschist sample SV13-06, the shape of the tallization processes such as dissolution. REE pattern changes from core to rim such that the Fe-rich rim is enriched In some cases, core-to-rim zoning is accompanied by a change in inclusion in MREEs (Fig. 9C), likely as a result of the breakdown of an MREE-rich phase assemblage. For example, lawsonite from blueschist sample SV13-07 has an such as titanite or apatite. In several samples, lawsonite records a core-to-rim Fe-poor, Ti-rich core with abundant glaucophane and titanite inclusions and an increase in REEs, particularly LREEs, that correlates with the core-to-rim in- inclusion-poor Fe-rich, Ti-poor rim (Figs. 4B, 4C). In this sample, lawsonite increase in Fe (Figs. 9D, 9E). This trend is consistent with the interpretation that clusions in garnet display different zoning patterns than matrix lawsonite; law- Fe zoning in some lawsonite may be related to epidote stability, as epidote sonite inclusions have Ti-rich and titanite-bearing margins (Fig. 4E), whereas breakdown releases not only Fe3+ but also LREEs, Sr, Pb, Th, and U, which can matrix lawsonite displays Ti-rich and titanite-bearing cores (Fig. 4C). be incorporated into newly formed lawsonite (e.g., Hermann, 2002; Spandler

A A′ 2.5 A Ep A Fe-rich rim

2.0

1.5 eO* (wt%) F Chl A′ 1.0 Fe-poor core

150 m SV13-17A Pro le across grain shown in A 0.5

A A 1.6 ′ B Gln SV03-103C Figure 8. Iron (Fe) X-ray element maps 1.4 Fe-rich rim and corresponding compositional profiles A′ (A–A′) showing core-to-rim zoning in law- 1.2 sonite from the Sivrihisar Massif. Although the boundary between the Fe-poor core 1.0 and Fe-rich rim is always sharp, Fe concentrations in the rim can be relatively constant or show oscillatory variations. 0.8

eO* (wt%) Chl—chlorite, Ep—epidote, Gln—glauco- A F phane, Ph—phengite. Dark blue and pur- Ph 0.6 ple colors indicate low concentrations of Fe-poor core Fe, whereas lighter blue and purple colors 0.4 200 m indicate higher concentrations. Pro le across grain shown in B 0.2

A A′ C Ph SV03-103C 1.4

1.2 oscillatory A′ Fe-rich rim

1.0

eO* (wt%) 0.8 F A 0.6 Fe-poor core 250 m Pro le across grain shown in C 0.4

et al., 2003; El Korh et al., 2009; Guo et al., 2013). Therefore, the Fe- and LREE- reflecting the presence of sector or oscillatory zoning in these elements or poor lawsonite cores may represent lawsonite that crystallized in equilibrium variations in these elements at scales smaller than the spot size used for LA- with epidote, and the Fe- and LREE-rich lawsonite rims may represent law- ICPMS analysis (28–48 μm). sonite that crystallized during epidote destabilization or dissolution. Although In sample SV03-103C, one lawsonite grain records a core-to-rim reversal some lawsonite with rimward increases in Fe also record increases in Sr in the sign of the Eu anomaly, with the core recording a weak positive Eu and/or Pb content, this relationship is not observed in all samples, perhaps anomaly and the rim recording a negative anomaly. In some Corsican meta

SV10-06 Quartzite SV13-06 Lawsonite garnet blueschist 10,000 1000 SV08-4A Retrogressed lawsonite eclogite 10,000 A B C

e 1000 e 1000 100 e

100 100 10 10

10 1 Lawsonite / chondrit Lawsonite / chondrit Lawsonite / chondrit 1 inclusion in garnet Fe-poor core core core rim rim Fe-rich rim 1 0.1 0.1 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

SV03-103B Lawsonite garnet blueschist 1000 1000 SV03-103C Lawsonite-rich layer D E e e 100 100 Figure 9. Chondrite-normalized rare earth element (REE) patterns for lawsonite. In some samples, lawsonite records a core-to-rim decrease in REE concentrations (A, B), 10 10 whereas in others, lawsonite records a core-to-rim increase in REE concentrations and/or a change in the shape of the REE pattern (C, D, E).

1 1 Lawsonite / chondrit Lawsonite / chondrit

Fe-poor core Fe-poor core Fe-rich rim Fe-rich rim 0.1 0.1 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

somatic rocks, lawsonite also records a core-to-rim change in the sign of the Oscillatory Zoning Eu anomaly, but the trend is opposite to that of Sivrihisar lawsonite: in the Corsican samples, the core records a negative Eu anomaly and the rim has a Oscillatory zoning in lawsonite was first documented by Sherlock and positive Eu anomaly. Martin et al. (2011) attributed the change in the sign of Okay (1999) in blueschist-facies metamafic rocks from the Tavşanlı Zone. In

the Eu anomaly to lawsonite-core growth during prograde blueschist-facies that study, oscillatory variations in Cr (ranging from 3 to 6 wt% Cr2O3) were (plagioclase-stable) metamorphism and lawsonite-rim growth during eclogite- attributed to the breakdown of inferred precursor Cr-rich phases such as chro- facies (plagioclase-absent) metamorphism, suggesting that lawsonite zoning mite (which is not observed in the rocks) and concomitant fluid-rock interac- can be used to track changes in P-T conditions. Although there is some tex- tion during subduction metamorphism. Oscillatory Cr zoning in lawsonite was tural evidence for retrograde transformation of eclogite to blueschist in the further documented in eclogite-facies veins from Corsica (Vitale Brovarone

Sivrihisar rocks (Davis and Whitney, 2006, 2008; Whitney et al., 2014), there is et al., 2014), where high Cr2O3 contents (up to 8 wt%) were interpreted as re- no plagioclase present in our sample or adjacent blueschist, so it is unlikely sulting from interactions with fluids derived from the adjacent serpentinite. that the core-to-rim change in the sign of the Eu anomaly is related to a transi- Oscillatory Cr zoning in Sivrihisar lawsonite occurs in alternating law- tion from plagioclase-absent (eclogite-facies) to plagioclase-stable (blueschist- sonite-rich and glaucophane-rich layers at eclogite pod margins, as well as in facies) conditions. In this case, the shift in Eu anomaly could be (1) related to metamafic rocks and in some metasomatic lawsonite + chlorite–rich rocks ad

a change in oxidation state, as the switch in Eu anomaly also correlates with jacent to serpentinite (Figs. 4H, 10A–10C). However, Cr-rich (>1 wt% Cr2O3) law core-to-rim zoning in Fe3+; (2) due to a change in bulk-rock Eu as a result of sonite has only been observed in blueschist (sample SV13‑01) and chlorite + external fluid flux (Vitale Brovarone et al., 2014); or (3) inherited from epidote talc–rich pod rinds sampled in the HP shear zone near the fault contact of the that formed by prograde reaction of plagioclase. unit (Teyssier et al., 2010; Whitney et al., 2014). Chromium-rich lawsonite in

A A 7.00 ′ 2.20 A Cr 6.00 FeO 2.00

5.00 A 1.80 4.00

(wt%) 1.60 3 Cr2O3

A′ O 3.00 2 eO* (wt%) F Cr 1.40 2.00

1.00 1.20 50 m SV13-01 Pro le across grain shown in A 0.00 1.00

A A′ 0.25 1.60 B Fe Pro le across grain shown in B 1.40 0.20 FeO 1.20 Figure 10. Chromium (Cr) (A) and Fe (B, C) X-ray element maps and corresponding A 1.00 compositional profiles (A–A′) showing 0.15 oscillatory zoning in lawsonite from the Sivrihisar Massif. Gln—glaucophane. Dark (wt%) 0.80 3 blue and purple colors indicate low concen- O

2 0.10 trations of the analyzed element, whereas A′ 0.60 eO* (wt%) F Cr brighter blue and purple colors indicate higher concentrations. Gln 0.40 0.05 0.20 Cr O 200 m SV03-103B 2 3 0.00 0.00

A A′ 0.45 2.50

C Fe 0.40

0.35 FeO 2.00 A A′ 0.30 1.50 0.25 (wt%) 3

O 0.20 SV13-17A 2 1.00

150 m eO* (wt%) Cr 0.15 F

0.10 0.50 Cr2O3 0.05 Pro le across grain shown in C 0.00 0.00

SV13-01 contains overall higher concentrations of LREEs, Ni, Sr, Y, and Pb than et al., 2014). In Sivrihisar lawsonite, Ti sector zoning is most common, although Cr-poor lawsonite (Table 2; Table S2 [footnote 1]) and also tends to lack the other elements, such as Fe and Sr, can also display sector zoning (Figs. 4G, 4J, Fe and Ti sector zoning observed in Cr-poor lawsonite, suggesting that it rep- 4K, 4L, 11). The shape of the sectors can vary: boundaries between adjacent resents a distinct population of lawsonite. In metamorphic minerals, oscilla- sectors are straight (Figs. 11B, 11D, 11E) or curved (Figs. 4J, 4K), or transition tory zoning is commonly interpreted as resulting from repeated fluctuations from a curved boundary in the core to a straight boundary in the rim (Fig. in pressure, temperature, fluid supply or composition, and/or rates of thrust- 11A). As the boundary between two adjoining sectors represents the inter- ing (Jamtveit, 1991; Yardley et al., 1991; Kohn, 2004). Because the Sivrihisar section of two growth planes, its geometry will depend on the growth rates, Massif records only a single subduction-exhumation cycle, and compositional and thus growth mechanisms, of the two planes. Straight boundaries develop oscillations are not observed in coexisting minerals, the most plausible expla- when the growth rates of adjoining faces remain constant, whereas curved nation for the presence of Cr oscillatory zoning is the involvement of a Cr-rich boundaries develop if the growth rates change at different rates during crys- fluid. Although Cr is commonly assumed to be immobile, Cr-rich minerals and tal growth. Although the boundaries between Ti-rich and Ti-poor sectors are mineral domains have been documented in HP metasomatic features and en- either curved or straight, the boundaries between Fe-rich and Fe-poor sectors vironments, including eclogite-facies veins, serpentinite mélanges, and shear are always curved (Figs. 4J, 4K), implying that particular growth conditions zones (Tsujimori and Liou, 2004; Spandler et al., 2011; Angiboust et al., 2014; may be needed for the development of Fe sector zoning. Vitale Brovarone et al., 2014), indicating that Cr may be mobilized by fluids in Ueno (1999) studied the compositional differences between sectors in subduction zones. lawsonite in the Sanbagawa pelitic schists and proposed that the {100} sector In the eclogite-facies veins from Monviso (Western Alps, northwestern Italy), shows enrichment in REEs, the {001} sector shows enrichment in Ti, and the Cr-rich domains in garnet, clinopyroxene, and rutile are also enriched in Ni, B, {010} sector records a near-ideal lawsonite composition (following the nomen Sb, As, and/or LREEs (relative to MREEs) (Spandler et al., 2011). Because ser- clature adopted by Ueno [1999], in which sectors are denoted as {100}, {010}, pentinites commonly have high concentrations of these elements (Tenthorey and {001} according to the axis along which they grew). In that study, crystal- and Hermann, 2004; Deschamps et al., 2011, 2013), this elemental association lographic directions were inferred from petrographic observation. Although has been used to infer the presence of fluids derived from ultramafic sources. lawsonite commonly forms euhedral rhombs, it can be difficult to identify One possible source for Cr-rich fluids in the blueschist mylonite zone in the crystallographic axes from petrographic observation alone, in part because Sivrihisar Massif could therefore be the nearby (i.e., within ~3 m) antigorite the two-dimensional cross-sectional geometry of lawsonite can vary and/or serpentinite bodies. It is unknown if the Cr- and Ni-rich lawsonite contains ele be modified by post-crystallization processes. We therefore conducted EBSD vated concentrations of B and Sb, as these elements were not measured in analyses of lawsonite displaying sector zoning to determine crystallographic this study. However, As concentrations in lawsonite were below detection level orientation. Results show that sector zoning is typically observed in lawsonite for all analyzed lawsonite, indicating either that lawsonite is not a host for this crystals cut perpendicular to the crystallographic a- and b-axes (Fig. 11). element or that the fluids were derived from other Cr- and Ni-rich rocks, such as Titanium-rich sectors tend to grow in the direction of the a-axis (observed if metagabbro, that would not be expected to contain appreciable amounts of As. the crystal is intersected perpendicular to the b-axis) or in the direction of the Oscillatory zoning in other elements, such as Fe, is also observed in Sivri- b-axis (observed if the crystal is intersected perpendicular to the a-axis) (Fig. hisar lawsonite (Fig. 10). In the case of oscillatory Fe zoning, variations in Fe 11), whereas Ti-poor sectors tend to grow in the direction of the c-axis. When occur either across the entire grain (Fig. 10) or only in the Fe-rich rim (Fig. 8C). both Ti and Fe or Sr sector zoning is present in lawsonite, the Fe- and/or Sr-rich In some samples that display both Fe and Cr oscillatory zoning, Fe and Cr con- sectors tend to occur in the Ti-poor sectors. centrations are correlated such that high concentrations of Fe3+ coincide with A notable feature of Ti sector zoning in Sivrihisar lawsonite is the irregularity high concentrations of Cr3+ (Figs. 10A, 10C). This observation is consistent with of Ti concentrations within Ti-rich sectors, which generally vary from ~1000

the hypothesis that fluctuations in thef O2 of the fluid might play a role in the to 4000 ppm regardless of rock type (Table 2; Figs. 4, 11). Irregular Ti con- generation of oscillatory zoning in lawsonite, with oxidizing fluids facilitating centrations have been documented in sector-zoned metamorphic tourmaline the Cr3+-Al3+ substitution in lawsonite (Sherlock and Okay, 1999). (van Hinsberg et al., 2006) and garnet (Carlson, 2002), in which variations in Ti were interpreted as reflecting a preexisting heterogeneity overgrown by the Sector Zoning mineral. This interpretation is consistent with observations from sector-zoned lawsonite from blueschists that show low Ti concentrations in Fe-rich regions Sector zoning develops when elements are preferentially incorporated onto which may represent preexisting minerals that were overgrown by lawsonite specific growth surfaces and these differences are preserved in the crystal as a (Figs. 4F, 4G). Preservation of these heterogeneities implies slow diffusion rates result of rapid growth and/or slow intracrystalline diffusion rates (Watson and for Ti in lawsonite. In some Sivrihisar lawsonite, Ti variation within a sector Liang, 1995). Calcium, Ti, Sr, and REE sector zoning has previously been de- appears to be oscillatory, suggesting that intrasector variations in Ti may be scribed in lawsonite (Ueno, 1999; Tsujimori and Ernst, 2014; Vitale Brovarone related to variations in Ti availability. The major sources of Ti in the Sivrihisar

A SV08-76 D SV13-17A a

b a b c

c 100 m 150 m

B SV13-01 E c a

SV13-17A a 150 m c

100 m

Figure 11. Titanium (Ti) X-ray element maps of lawsonite C SV03-103C from a variety of rock types showing the presence of sector zoning. The crystallographic orientation for each lawsonite grain (determined by electron backscatter diffraction analy- a sis) is shown to the right of each map. In all cases, growth of the Ti-rich sectors occurs in the direction of the crystal- b lographic a- and b-axes, but not the c-axis. Dark blue and purple colors indicate low concentrations of Ti, whereas brighter purple and pink colors indicate higher concentrations. Dashed line is used to delineate lawsonite grain boundaries, and solid lines are used to highlight the boundaries of compositional sectors. c 250 m

rocks are rutile, titanite, and Fe-Ti oxides, so the periodic availability of Ti could Other Zoning Types be related to the destabilization of these phases. A similar mechanism was proposed by Vitale Brovarone et al. (2014) to explain high Ti concentrations Some lawsonite grains display irregular compositional variation, includ- (~1 wt%) in lawsonite from metasomatic rocks in Corsica. In that lawsonite, ing in elements such as Ti that in other cases display geometrically orga- Ti concentrations were positively correlated with Nb, which also resides in nized zoning (core-to-rim, oscillatory, sector). Results from EBSD and EMP Ti-bearing phases (e.g., Zack et al., 2002b), lending support to the interpreta- analyses show that, in some cases, there is a correlation between zoning tion that rutile was the source of Ti. However, no correlation between Ti and and the presence of subgrain (defined here as a misorientation <10°) and Nb concentrations or any other HFSE element has been observed thus far in grain (defined here as a misorientation >10°) boundaries. In layered eclogite Sivrihisar lawsonite. Samples displaying sector zoning in Fe do not appear to and blueschist sample SV08-76, for example, the shape of a Ti-rich sector display similar intrasectoral compositional heterogeneities (Figs. 4J, 4K). is distorted in the region where a subgrain is present (Figs. 12A, 12B). The

boundary between the Fe-poor core and Fe-rich rim is also irregular adjacent In most cases, however, lawsonite grains with little to no misorientation to the subgrain (Fig. 12C), perhaps indicating deformation-assisted mobili- display distinct and irregular zoning features that require other explanations. zation of Fe and Ti in lawsonite. Further study is needed to understand the Lawsonite from quartz-rich rock sample SV10-03B displays Fe-rich and Al-poor influence of deformation on compositional zoning and element mobility in regions that are typically located in or near the geometric center of the grain lawsonite. but that in some cases are located near the rim; some lawsonite crystals con- In eclogite pod margin sample SV03-305 (Davis and Whitney, 2008), col- tain more than one Fe-rich region, and these regions may be irregularly shaped, lected from the same pod as eclogite samples SV12-13E and SV03-103A, Ti tabular, or rounded (Figs. 4N, 4O). One hypothesis to account for these obser- (but not Fe or Cr) is concentrated along lawsonite grain boundaries (Figs. 12D, vations is that lawsonite formed as a pseudomorph after a precursor Fe-rich 12E, 12F). This may indicate that Ti was mobilized in fluids and concentrated phase (such as an epidote-group mineral) and that subsequent lower-Fe law- along grain boundaries that served as pathways for Ti-bearing fluids. The fact sonite grew around this initial crystal. Similar zoning features were observed in that Fe and Cr are not similarly concentrated suggests that the Ti was released blueschists (Figs. 4A, 4F) and a lawsonite grain from a lawsonite + phengite + by the breakdown of a Ti-rich and Fe- and Cr-poor mineral phase. Alterna- garnet + omphacite layer from the western part of the Tavşanlı Zone (Fig. S2 tively, the composition and/or nature of the metamorphic fluids could have [footnote 1]). In some lawsonite from blueschist sample SV13-01, Cr variations in preferentially mobilized Ti relative to Fe and Cr, as experimental results and the interior of the grain appear to mimic the inclusion pattern (Fig. 4I), indicating empirical observations from exhumed high-pressure rocks have shown that that the Cr variations may be inherited from the distribution of Cr in the fabric Ti, commonly assumed to be fluid immobile, can be soluble in the presence that the lawsonite overgrew. Yang and Rivers (2001) and Martin (2009) proposed Cl- or F-rich brines or dissolved albite components (Gao et al., 2007; Antignano a similar mechanism to explain the heterogeneous distribution of Cr in meta- and Manning, 2008; Rapp et al., 2010). morphic garnets from pelitic schists.

A Orientation Contrast Image B Ti C Fe

polysynthetic twinning Figure 12. (A) Orientation contrast image showing the presence of polysynthetic twinning and subgrains in a lawsonite from a layered blueschist and eclogite subgrain subgrain (sample SV08-76). (B, C) Ti (B) and Fe subgrain (C) X-ray element maps of the same lawsonite grain shown in A show distortion of the sector and core-to-rim zoning in the region of the subgrain. (D) Euler map 100 m SV08-76 100 m 100 m obtained from electron backscatter diffraction analysis of sample SV03-305, with Euler Map Ti Fe grain boundaries (~26° of misorientation) D E F indicated by dashed lines. (E, F) X-ray element maps of Ti (E) and Fe (F) of the area shown in D show that Ti is preferentially concentrated along lawsonite grain boundaries but Fe is not. Dark blue and purple colors indicate low concentrations of the analyzed element, whereas brighter grain purple and pink colors indicate higher con- boundaries centrations.

500 m SV03-305 400 m 400 m

Controls on Lawsonite Composition and Compositional Variation Lawsonite in Corsican lawsonite + chlorite–rich rocks contains high concentrations of REEs (up to 1000×–10,000× chondrite), Th, and U (Martin et al., The few published studies of lawsonite geochemistry to date document 2011; Vitale Brovarone et al., 2014). Lawsonite in Tavşanlı lawsonite + chlorite– that lawsonite is a major reservoir for trace elements in all rock types in which rich rocks typically contains much lower trace element concentrations, particu- it occurs (eclogite, blueschist, quartz-rich metasediment, metasomatic lawso- larly for LREEs (~10×–100× chondrite; Table 2; Fig. 5). One explanation for this nitite) (e.g., Spandler et al., 2003; Martin et al., 2011, 2014; Vitale Brovarone difference is that Corsican lawsonite + chlorite–rich rocks formed as a result of et al., 2014). In this paper, we extend the trace element data set for lawsonite interactions between serpentinite and adjacent REE-enriched metasedimen- in eclogite- and blueschist-facies metamafic and metasedimentary (impure tary rocks (Martin et al., 2011; Vitale Brovarone et al., 2014), whereas field rela- quartzite) rocks and lawsonite-rich veins, layers, and metasomatic (lawsonite + tions in the Sivrihisar Massif suggest that the lawsonite + chlorite–rich rocks chlorite–rich) rocks. formed as a result of metasomatic interactions between serpentinite and meta basalt, the latter of which has lawsonite REE concentrations similar to those of Rare Earth Element Composition lawsonite from the lawsonite + chlorite–rich rocks (Fig. 5). Within the Tavşanlı Zone, however, there are large variations in the trace Trace element analysis of lawsonite from metamafic rocks in the Sivrihisar element content of lawsonite from lawsonite + chlorite–rich rocks. For exam- Massif shows that chondrite-normalized REE concentrations are typically ple, lawsonite from the sample (TZ10-2.2c) from the western part of the belt ~10×–1000× chondrite (Figs. 5, 9B–9D). These concentrations are similar to contains the highest V concentrations (>1000 ppm) of any sample analyzed in those documented in lawsonite in metamafic rocks from other oceanic and this study, whereas a sample (SV12-21D) from the Sivrihisar region contains continental subduction complexes, such as the Franciscan Complex (Califor- some of the lowest V concentrations measured (<300 ppm) (Table 2). Rare nia, western USA; Mulcahy et al., 2009), New Caledonia (Spandler et al., 2003), earth element patterns also vary markedly, with lawsonite from the western the Ligurian Alps (northwestern Italy; Tribuzio et al., 1996), and the North Qilian Tavşanlı sample yielding flat patterns, in contrast to Sivrihisar lawsonite that belt (China; Xiao et al., 2013). Although lawsonite from metamafic rocks from displays patterns that range from flat to MREE- and/or HREE-enriched (Figs. these areas all have similar concentrations of REEs, the shape of the chon- 5B, 5C). In Sivrihisar sample SV12-21D, the shift from HREE-enriched to flat drite-normalized REE pattern varies. For example, in Franciscan metabasalt, REE patterns correlates with Fe and Ti zoning: Fe- and Ti-poor regions are lawsonite displays high MREE to HREE concentrations relative to LREE, enriched in HREEs, and Fe- and Ti-rich regions have flat REE patterns. These whereas lawsonite from Sivrihisar metamafic rocks displays more LREE- variations may stem from heterogeneities in the source rocks and/or from vari- enriched patterns (Figs. 5A, 5C). This difference may reflect variations in reac- ation in the extent of fluid-rock interaction. tion history, as the Franciscan blueschist formed on the retrograde path after garnet breakdown (Mulcahy et al., 2009) and therefore lawsonite likely incor- Sr and Pb porated HREEs liberated by garnet. In contrast, Sivrihisar lawsonite likely grew either concurrently with garnet or after significant garnet growth, resulting in A possible monitor of lawsonite compositional variation as a function of a relative depletion in HREEs. rock type are the Sr and Pb concentrations of lawsonite. A global review of law- Compared to lawsonite from metamafic rocks, lawsonite from Sivrihisar sonite composition shows that lawsonite may contain the majority of Sr and Pb metasedimentary rocks typically yields higher LREE contents (100×–10,000× in HP-LT mafic rocks: up to ~60% of Pb and up to ~100% of Sr (Martin et al., 2014). chondrite; Table 2; Figs. 5A, 5C), similar to results obtained for lawsonite in Concentrations of Sr and Pb in metabasalt are typically distinct from those in metasedimentary rocks in other HP-LT terranes (Ueno, 1999; Spandler et al., metasedimentary rocks (Martin et al., 2014): lawsonite in blueschist and eclogite 2003; Martin et al., 2014). One explanation for this enrichment is that there are tends to yield higher Sr/Pb ratios than lawsonite in metasedimentary rocks. In fewer phases competing with lawsonite for available trace elements (Martin Sivrihisar rocks, Sr/Pb generally defines two linear arrays, one corresponding et al., 2014). Another factor may be that the modal abundance of lawsonite in to metamafic rocks and the other to quartz-rich metasedimentary rocks (Fig. metasedimentary rocks is lower than in metamafic rocks (~3%–5% in Sivrihisar 13A). Bulk-rock Sr/Pb appears to closely match lawsonite Sr/Pb and plot along quartz-rich metasedimentary rocks versus ≥20% in metamafic rocks), so avail- the array defined by lawsonite in each sample (Fig. 13A). able trace elements are distributed over fewer grains. In zoned lawsonite from Corsican metasomatic rocks, lawsonite cores Lawsonite + chlorite–rich rocks interpreted to represent metasomatic re- yielded Sr/Pb ratios similar to those of metasedimentary rocks (their inferred action between serpentinite and metamafic or metapelitic rocks occur in the protolith) and rims yielded Sr/Pb similar to those of metamafic rocks (Martin Tavşanlı Zone (Plunder et al., 2013), including the Sivrihisar Massif (Zack, 2013, et al., 2014). The lawsonite cores were interpreted as forming prior to meta Whitney et al., 2014), and in Corsica (Martin et al., 2011; Vitale Brovarone et al., somatic interaction with mafic and ultramafic rocks, and the rims as forming 2014). Possible pseudomorphic equivalents have also been described in the during the metasomatic event (Martin et al., 2011). Therefore, intragrain shifts Southern Ural Mountains, Russia (Beane and Liou, 2005). in lawsonite Sr/Pb may be an indicator of changes in the bulk-rock composition

1400 400 Metama c Rocks Metasedimentary Rocks Alpine Corsica A SV12-13E / BR SV08-281C B Lws + Chl rocks SV03-103A SV10-06 New Caledonia SV08-4A SV13-12 BR 350 Blueschist (ma c) 1200 SV03-103B Lws + Chl Rocks Blueschist (pelite) SV12-59 / BR SV13-17A SV13-01 Lws inclusion in grt SV12-21D Metasediments SV13-15 / BR 300 s + Chl rocks Franciscan Complex TZ10-2.2c SV13-06 Lws vein Reference Values Lw 1000 SV12-24 North Qilian Belt Lws Layers and Veins GLOSS II BR NMORB BR 250 Blueschist (ma c) SV03-103C EMORB BR Tianshan SV12-24B BR OIB BR Lws inclusion in pyr

800 N 200

N e Pb Pb Eclogit 150 600 Blueschist

100

400 s layers

Lw 50 200 0 020406080100 120140 region shown in B 0 SrN 0 20 40 60 80 100 120 140 160 180

SrN

Figure 13. Plots of primitive mantle–normalized Sr versus Pb contents in lawsonite from the Tavşanlı Zone (A) and from worldwide lawsonite-bearing localities (B). BR indicates a bulk rock analysis. Strontium and Pb lawsonite data for B were compiled from the following sources: Alpine Corsica (Vitale Brovarone et al., 2014), Franciscan Complex (California, western USA; Martin et al., 2014), New Caledonia (Spandler et al., 2003; Martin et al., 2014), North Qilian belt (China; Xiao et al., 2013), and Tianshan (China; Li et al., 2013). Colored fields (derived from the data points in panel A) show the range of Sr and Pb contents observed in lawsonite from different rock types in the Sivrihisar Massif, Turkey. The Sr and Pb values used for GLOSS (global subducting sediment) II were obtained were from Plank (2014), and the Sr and Pb values for normal mid-ocean-ridge basalt (NMORB), enriched mid-ocean-ridge basalt (EMORB), and oceanic island basalt (OIB) were obtained from Sun and McDonough (1989). Chl—chlorite, Grt—garnet, Lws—lawsonite, Pyr—pyrite.

resulting from pervasive fluid-rock interactions or mechanical mixing between has Sr/Pb similar to that of metasedimentary rocks (Table 2; Fig. 13A), suggest- different rock types during subduction and exhumation (Martin et al., 2014). ing that this pod may have experienced interactions with fluids derived from In the Sivrihisar samples, no lawsonite recorded significant intragrain adjacent metasedimentary rocks prior to or during lawsonite growth. shifts in Sr/Pb, indicating either that these rocks did not experience extensive A comparison of Sr and Pb concentrations in lawsonite from the Tavşanlı fluid-rock interactions with externally derived fluids or that such interactions Zone (including Sivrihisar samples) with published data for lawsonite from occurred early in the subduction history, prior to lawsonite growth. Although other HP-LT and ultrahigh-pressure terranes (Fig. 13B) shows that although Sr no intragrain variations in Sr/Pb were observed, lawsonite from one sample— and Pb contents are correlated for lawsonite in most samples, the association the chlorite + epidote–rich pod margin (sample SV12-24)—records lawsonite of Sr/Pb and rock type observed in Tavşanlı samples is not generally applica- Sr/Pb that is apparently inconsistent with its rock type. Lawsonite from this ble. Lawsonite from mafic rocks in other subduction complexes typically de- sample plots along the Sr/Pb array for metasedimentary rocks (Fig. 13A) and fines a flat or much shallower Sr/Pb slope, similar to lawsonite from blueschist also contains REE concentrations similar to those of metasedimentary rocks sample SV12-59. The only lawsonite that follows the “metamafic” trend that (~100×–1000× chondrite; Table 2). Bulk-rock analysis of the monomineralic characterizes the majority of Sivrihisar lawsonite is from Corsican meta lawsonite vein from this chlorite + epidote–rich pod (sample SV12-24B) also somatic rocks that had metapelitic protoliths (Vitale Brovarone et al., 2014). As

stated earlier, one possible explanation for this observation is that the analyzed Abers, G.A., Nakajima, J., van Keken, P.E., Kita, S., and Hacker, B.R., 2013, Thermal-petrological Sivrihisar rocks (with the exception of SV12-59) experienced interactions with controls on the location of earthquakes within subducting plates: Earth and Planetary Sci- ence Letters, v. 369, p. 178–187, https://doi.org/10.1016/j.epsl.2013.03.022. metasedimentary rocks prior to lawsonite growth, resulting in Sr/Pb ratios Altherr, R., Topuz, G., Marschall, H., Zack, T., and Ludwig, T., 2004, Evolution of a tourma- between those of metasedimentary rocks and those of (unaltered) metamafic line-bearing lawsonite-eclogite from the Elekdağ area (Central Pontides, N Turkey): Evidence rocks. Additional information about the history of fluid-rock interaction in the for infiltration of slab-derived B-rich fluids during exhumation: Contributions to Mineralogy and Petrology, v. 148, p. 409–425, https://doi.org/10.1007/s00410-004-0611-1. Tavşanlı Zone and studies of lawsonite from other HP-LT terranes are needed Angiboust, S., Pettke, T., De Hoog, J.C.M., Caron, B., and Oncken, O., 2014, Channelized fluid flow to understand the Sr/Pb systematics of lawsonite and its utility as an indicator and eclogite-facies metasomatism along the subduction shear zone: Journal of Petrology, of metasomatic events, especially in terranes with abundant carbonate-rich v. 55, p. 883–916, https://doi.org/10.1093/petrology/egu010. Antignano, A., and Manning, C.E., 2008, Rutile solubility in H2O, H2O-SiO2, and H2O-NaAlSi3O8 rocks or sulfides that could serve as additional reservoirs for Sr and/or Pb. fluids at 0.7 GPa and 700–1000 °C: Implications for mobility of nominally insoluble elements: Chemical Geology, v. 255, p. 283–293. CONCLUSIONS Ballèvre, M., Pitra, P., and Bohn, M., 2003, Lawsonite growth in epidote blueschists from the Ile de Groix (Armorican Massif, France): A potential geobarometer: Journal of Metamorphic Geology, v. 21, p. 723–735, https://doi.org/10.1046/j.1525-1314.2003.00474.x. This study of the composition and zoning of lawsonite from different rock Beane, R.J., and Liou, J.G., 2005, Metasomatism in serpentinite mélange rocks from the types and bulk compositions (metamafic and metasedimentary rocks, law- high-pressure Maksyutov Complex, southern Ural Mountains, Russia: International Geology sonite + chlorite–rich rocks, lawsonite-rich layers and veins) from the Sivrihisar Review, v. 47, p. 24–40, https://doi.org/10.2747/0020-6814.47.1.24. Beinlich, A., Klemd, R., John, T., and Gao, J., 2010, Trace-element mobilization during Ca-metaso- Massif, Turkey, shows that lawsonite can display a diversity of zoning patterns matism along a major fluid conduit: Eclogitization of blueschist as a consequence of fluid- in both major and trace elements, including core-to-rim zoning in Fe, which rock interaction: Geochimica et Cosmochimica Acta, v. 74, p. 1892–1922, https://doi .org/10 is described for the first time here. Within a single grain, different elements .1016/j.gca.2009.12.011. Cao, Y., and Jung, H., 2016, Seismic properties of subducting oceanic crust: Constraints from can display contrasting zoning types, suggesting that the incorporation and natural lawsonite-bearing blueschist and eclogite in Sivrihisar Massif, Turkey: Physics of distribution of different elements in lawsonite is controlled by different mech- the Earth and Planetary Interiors, v. 250, p. 12–30, https://doi.org/10.1016/j.pepi.2015.10.003. anisms. 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Whit- Deschamps, F., Godard, M., Guillot, M., and Hattori, K., 2013, Geochemistry of subduction zone ney acknowledges funding from the College of Science and Engineering at the University of Min- serpentinites: A review: Lithos, v. 178, p. 96–127, https://doi.org/10.1016/j.lithos.2013.05.019. nesota. Parts of this work were carried out in the Characterization Facility, University of Minnesota, Droop, G.T.R., Karakaya, M.C., Eren, Y., and Karakaya, N., 2005, Metamorphic evolution of which receives partial support from the NSF through the Materials Research Science and Engi- blueschists of the Altınekin Complex, Konya area, south central Turkey: Geological Journal, neering Center program. The authors thank S.C. Kruckenberg for EBSD analysis of lawsonite to v. 40, p. 127–153, https://doi.org/10.1002/gj.1000. help with inter-lab verification of lawsonite indexing, S. Penniston-Dorland and C. 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