new constraints on the p t path of ht uht metapelites from the highland complex of sri lanka

Accepted Manuscript New constraints on the P–T path of HT/UHT metapelites from the Highland Complex of Sri Lanka P.L Dharmapriya, Sanjeewa P.K Malaviarachchi, L.M Kriegsman, Andrea Galli, K Sajeev, Chengli Zhang PII: S1674-9871(17)30027-0 DOI: 10.1016/j.gsf.2016.12.005 Reference: GSF 534 To appear in: Geoscience Frontiers Received Date: September 2016 Revised Date: December 2016 Accepted Date: 18 December 2016 Please cite this article as: Dharmapriya, P.L., Malaviarachchi, S.P.K., Kriegsman, L.M., Galli, A., Sajeev, K., Zhang, C., New constraints on the P–T path of HT/UHT metapelites from the Highland Complex of Sri Lanka, Geoscience Frontiers (2017), doi: 10.1016/j.gsf.2016.12.005 This is a PDF file of an unedited manuscript that has been accepted for publication As a service to our customers we are providing this early version of the manuscript The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain AC C EP TE D M AN U SC RI PT ACCEPTED MANUSCRIPT ACCEPTED MANUSCRIPT New constraints on the P–T path of HT/UHT metapelites from the Highland Complex of Sri Lanka P L Dharmapriyaa,b,c, Sanjeewa P K Malaviarachchia,b*, L M Kriegsmanc,d, Andrea Gallie, K Sajeevf, Chengli Zhangg RI PT a Postgraduate Institute of Science, University of Peradeniya, 20400, Sri Lanka b Department of Geology, Faculty of Science, University of Peradeniya, 20400, Sri Lanka c Naturalis Biodiversity Center, Darwinweg 2, NL-2333 CR Leiden, The Netherlands d Department of Earth Sciences, Utrecht University, Budapestlaan 4, NL-3584 CD Utrecht, The Netherlands SC e Department of Earth Sciences, ETH Zurich, Sonnegstrasse 5, CH-8092 Zurich, Switzerland 11 f Centre for Earth Sciences, Indian Institute of Science, Bangalore 560012, India 12 g Key Laboratory of Continental Dynamics of Northwest University, Department of Geology, 13 Northwest University, Xi'an 710069, China M AN U 10 14 16 17 TE D 15 * Corresponding Authors: Sanjeewa, P.K Malaviarachchi* 19 E-mail addresses : malavi@pdn.ac.lk, 20 Postal Addresses : *Department of Geology, Faculty of Science, University of Peradeniya, 20400, Sri Lanka 21 23 Phone No : +94 81 2394215* AC C 22 EP 18 ACCEPTED MANUSCRIPT 24 ABSTRACT We report here rare evidence for the early prograde P–T evolution of garnet– 26 sillimanite–graphite gneiss (khondalite) from the central Highland Complex, Sri Lanka Four 27 types of garnet porphyroblasts (Grt1, Grt2, Grt3 and Grt4) are observed in the rock with 28 specific types of inclusion features Only Grt3 shows evidence for non-coaxial strain 29 Combining the information shows a sequence of main inclusion phases, from old to young: 30 oriented quartz inclusions at core, staurolite and prismatic sillimanite at mantle, kyanite and 31 kyanite pseudomorph, and biotite at rim in Grt1; fibrolitic sillimanite pseudomorphing kyanite 32 ± corundum, kyanite, and spinel+sillimanite after garnet+corundum in Grt2; biotite, 33 sillimanite, quartz ± spinel in Grt3 and: ilmenite, rulite, quartz and sillimanite in Grt4 SC RI PT 25 The pre-melting, original rock composition was calculated through stepwise re- 35 integration of melt into the residual, XRF based composition, allowing the early prograde 36 metamorphic evolution to be deduced from petrographical observations and pseudosections 37 The earliest recognizable stage occurred in the sillimanite field at around 575 °C at 4.5 kbar 38 Subsequent collision associated with Gondwana amalgamation led to crustal thickening along 39 a P–T trajectory with an average dP/dTof ~30 bar/0C in the kyanite field, up to ~660 °C at 6.5 40 kbar, before crossing the wet-solidus at around 675 °C at 7.5 kbar The highest pressure 41 occurred at P> 10 kbar and T around 780 °C before prograde decompression associated with 42 further heating At 825 °C and 10.5 kbar, the rock re-entered into the sillimanite field The 43 temperature peaked at 900 °C at ca 9–9.5 kbar Subsequent near-isobaric cooling led to the 44 growth of Grt4 and rutile at T ~880 °C Local pyrophyllite rims around sillimanite suggest a 45 late stage of rehydration at T< 400 °C, which probably occurred after uplift to upper crustal 46 levels U–Pb dating of zircons by LA–ICPMS of the khondalite yielded two concordant 47 206 48 and 514 ± Ma (MSWD = 0.50, Th/U = 0.01–0.05) interpreted as peak metamorphism of the 49 khondalite and subsequent melt crystallization during cooling TE D EP Pb/238U age groups with mean values of 542 ± Ma (MSWD = 0.24, Th/U = 0.01–0.03) AC C 50 M AN U 34 51 Keywords – Prograde evolution, melt re-integration, Highland Complex, Sri Lanka, UHT 52 granulites 53 54 Introduction 55 Granulites give information on the petrological evolution of the Earth’s middle to 56 lower crust (e.g Ouzegane et al., 2003) Petrologists have shown great interest in aluminous 57 pelitic granulites, as these rock types may preserve peak mineral assemblages and a vast ACCEPTED MANUSCRIPT range of reaction textures useful to reconstruct the near peak P–T evolution (e.g Waters, 59 1986; Hensen, 1987; Droop, 1989) Nevertheless, in numerous high-grade terrains, most 60 evidence on the prograde evolution is obliterated due to strong ductile deformation at high 61 temperatures (Whitney and Dilek, 1997; Mathavan et al., 1999) or by peak metamorphic 62 equilibration Thus, the preservation of prograde metamorphic stages is generally uncommon 63 (e.g., Hiroi et al., 1994; Raase and Schenk, 1994; Ouzegane et al., 2003) Exceptionally, 64 crucial information for the reconstruction of early stages of a pressure–temperature–time (P– 65 T–t) path for a specific tectonic domain may be preserved as relict reaction textures and/or 66 microstructures trapped as single or composite inclusions within mineral porphyroblasts, 67 commonly garnet, during the prograde metamorphic history SC RI PT 58 In this study, we report inclusion microtextures associated with garnet evidencing 69 early prograde metamorphismof corundum–spinel–kyanite–staurolite bearing garnet– 70 sillimanite–graphite gneiss (khondalite) from the Highland Complex of Sri Lanka Coupling 71 textural observations (textures associate with in garnet and in the matrix) and thermodynamic 72 modeling we reconstruct the prograde to retrograde P–T path followed by the khondalite 73 Also we present related U–Pb zircon geochronology data of studied rock After summarizing 74 results of this study and most recently published petrological and U–Pb zircon 75 geochonological data of HT/UHT metasediments of the Highland Complex, we attempted 76 reconstruction of P–T–t path followed by the Highland Complex metasediments TE D M AN U 68 77 78 General geology of Sri Lanka Sri Lanka represents a small but important crustal fragment of eastern Gondwana On 80 the basis of Nd model ages and zircon U–Pb dating (Milisenda et al., 1988, 1994; Kröner et 81 al., 1991; Liew et al., 1991), the Proterozoic basement of Sri Lanka has been subdivided into 82 four litho-tectonic units (Cooray, 1994; Fig 1a), namely from west to east the Wanni 83 Complex (WC), Kadugannawa Complex (KC), Highland Complex (HC) and Vijayan 84 Complex (VC) 86 AC C 85 EP 79 2.1 Overview of geology, petrology and geochronology of Sri Lankan basement 87 88 2.1.1.The Highland Complex (HC) 89 The HC contains granulite facies metasedimentary and metaigneous rocks including 90 quartzites, marbles, calcsilicates, pelitic gneisses, charnockites and orthogneisses (Cooray, 91 1962, 1984, 1994; Mathavan and Fernando, 2001) In the central and northern part of the HC, ACCEPTED MANUSCRIPT 92 hundreds of meters' thick marble and quartzite units are traceable for more than 40 km In 93 contrast, in the southwestern part of the HC, marble and quartzite are scarce (Mathavan et al., 94 1999) and cordierite-bearing metapelitic gneisses, orthogneisses and thin bands of 95 wollastonite- and scapolite-bearing calcsilicates are the prominent rock types (Perera, 1984; 96 Prame, 1991) Using conventional thermobarometric calculations and petrogenetic grids, the HC has 98 been classically interpreted as a tilted crustal section with a peak metamorphic gradient 99 increasing from 4.5–6 kbar and 700–750 °C in the southwest up to 8–9 kbar and 800-–900 °C 100 in the east and southeast (Faulhaber and Raith, 1991; Raase and Schenk, 1994; Schumacher 101 and Faulhaber, 1994; Kriegsman, 1996; Mathavan et al., 1999; Kriegsman and Schumacher, 102 1999; Braun and Kriegsman, 2003) In addition, rare UHT granulites that formed at extreme 103 crustal conditions of 925–1150 °C and 9–12.5 kbar have been reported from a few localities 104 (Fig 1) in the central and southwestern HC (e.g Osanai, 1989; Kriegsman and Schumacher, 105 1999; Bolder-Schrijver et al., 2000; Osanai et al., 2000; Sajeev and Osanai, 2004a, b; Osanai 106 et al., 2006; Sajeev et al., 2007; Dharmapriya et al., 2015a) These UHT granulite conditions 107 were suggested using conventional thermobarometric calculations and petrogenetic grids 108 (Osanai, 1989; Osanai et al., 2000, Sajeev and Osanai, 2004a, 2004b; Osanai et al., 2006, 109 2016a, b) and pseudosection modeling (e.g Sajeev et al., 2007; Dharmapriya et al., 2015a) TE D M AN U SC RI PT 97 The HC yields Nd-model ages of 3400–2000 Ma (Milisenda et al., 1988, 1994) 111 Detrital zircons separated from the HC granulite facies metasediments suggest provenance U- 112 Pb ages between 3200 Ma and 2000 Ma (Kröner et al., 1987; Hölzl et al., 1991, 1994), and a 113 peak metamorphic age around 610–550 Ma (e.g Baur et al., 1991; Hölzl et al., 1991, 1994; 114 Kröner et al.,1994) Discordant zircons from the HC orthogneisses yields 2000–1850 Ma and 115 670 Ma as upper intercept ages, which have been interpreted as the timing of pluton 116 emplacement, and 610–530 Ma as lower intercept ages, which have been interpreted as 117 metamorphic ages (e.g., Baur et al., 1991; Hölzl et al., 1991, 1994; Kröner and Williams, 118 1993) Similar metamorphic zircon ages of c 570 Ma have been reported by Sajeev et al 119 (2007) from HP/UHT mafic granulites AC C EP 110 120 In contrast, Sajeev et al (2010) reported U–Pb zircon and monazite ages from the HC 121 UHT metapelits in the HC clustering around 2300 Ma, 1700 Ma and 1400-830 Ma, some of 122 those having metamorphic overgrowths at c 570 Ma Using CHIME dating for monazite in 123 metasediments, Malaviarachchi and Takasu (2011) reported a wide range of metamorphic 124 ages from 728 to 460 Ma Most recently, Dharmapriya et al (2015b, 2016) reporteddetrital 125 zircon U–Pb ages from ca 2800 Ma to 720 Ma from UHT metapelites indicating that the ACCEPTED MANUSCRIPT metasediments of the HC have been derived from Neoarchean to Neoproterozoic multiple 127 provenances during Neoproterozoic ear (after 700 Ma).Takamura et al (2016) also have 128 provided evidence for Neoproterozoic sedimentation of the HC and authors have reported 129 detrital zircon age spectrum from ca 3500 to < 700 Ma Dharmapriya et al (2016) reported 130 that evidence for multiple metamorphic events from ca 665 Ma to 530 Ma with peak UHT 131 metamorphism around 580 Ma – 530 Ma In addition, Santosh et al (2014), He et al (2015) 132 and Takamura et al.(2015) reported multiple late Neoproterozoic to early Cambrian U–Pb 133 spectra of zircons from metaigneous rocks in the HC Santosh et al (2014) reported Hf 134 crustal model ages of zircon from mafic and intermediate granulites and charnockites in the 135 range of 2800–1500 Ma SC 136 RI PT 126 The WC, VC and KC rocks (see Santosh et al., 2014; Dhatmapriya et al., 2015a, b; He et al., 2015, 2016 for further details) have yielded Nd-model ages of 2000–1000 Ma, 1800–1100 Ma and 138 2000–1000 Ma (Milisenda et al., 1988; 1994) respectively and were metamorphosed under upper 139 amphibolite to granulite facies conditions (e.g Cooray, 1994; Kehelpannala, 1997; Mathavan et al., 140 1999; Kröner et al., 2013; He et al., 2015, 2016) M AN U 137 141 142 2.2 Overview of the deformation history of the Sri Lankan basement TE D 143 144 Tthe Sri Lankan basement underwent a polyphase deformational evolution (e.g., 145 Berger and Jayasinghe 1976; Kriegsman, 1991, 1994, 1995; Kleinschrodt, 1994; 146 Kehelpannala, 1997) Berger and Jayasinghe (1976) suggested that the 147 subjected to at least three deformation phases in which D1 and D2 formed the major lineation 148 and a composite foliation (L–S fabric), whereas D3 resulted in the formation of large-scale 149 upright folds The same authors, as well as Kriegsman (1991, 1994) and Kehelpannala (1997) 150 suggested that D2 was coeval with the peak of metamorphism during Gondwana assembly 151 (e.g., Kroner et al., 2003; Kehelpannala, 2004) Evidence for D1 is preserved only within 152 garnet porphyroblasts as aligned mineral inclusions defining a well-developed crenulation S1 153 (Kehelpannala, 1991; Kriegsman, 1991) oblique to the main matrix foliation S2 (Kriegsman, 154 1991, 1994; Kehelpannala, 1997) AC C EP basement was 155 A slightly different interpretation is given by Kehelpannala (1997), who suggested 156 that the HC underwent six phases of ductile deformation, where D1 to D3 are similar to those 157 described by earlier workers However, the author argued that D4 produced large, gentle, ACCEPTED MANUSCRIPT 158 nearly E-W trending, upright folds, whereas D5 was responsible for the large-scale upright 159 folds and D6 caused local refolding of the D5 structures 160 161 2.3 Suggested P-T trajectories for Sri Lankan basement rocks 162 As illustrated by Fig 2, the reconstruction of the P–T path for the HC granulites is 164 still a matter of debate and no general consensus exists on the P–T trajectory followed by the 165 HC According to many studies, which reported sillimanite both as inclusion and as matrix 166 mineral in garnet-bearing metapelites, the equilibration at peak T occurred in the sillimanite 167 field (e.g., Perera, 1987, 1994; Hiroi et al., 1994; Raase and Schenk, 1994, Fig 2a–f) Since 168 relict kyanite and staurolite have been observed as inclusions in porphyroblastic garnet in 169 sillimanite-bearing metapelites (Hiroi et al., 1994; Raase and Schenk, 1994), most of the 170 workers suggested a clockwise P–T trajectory for the HC granulites M AN U SC RI PT 163 Kriegsman (1993, Fig 2c) and Raase and Schenk (1994, Fig 2d) inferred a strong 172 pressure increase at amphibolite facies conditions from the sillimanite field to the kyanite 173 field, probably due to crustal thickening during prograde metamorphism Kriegsman (1993) 174 inferred that P increased up to peak T, while Raase and Schenk (1994) suggested that peak P 175 was followed by near isobaric heating from the kyanite to the sillimanite field up to peak T 176 (Fig 2d) Alternatively, several workers (e.g., Ogo et al., 1992; Hiroi et al., 1994; Osanai et 177 al., 2006; Dharmapriya et al., 2015a,b) argued that peak P was followed by prograde 178 decompression up to peak T from different peak P conditions TE D 171 After peak T (in the sillimanite field), many studies suggested a period of near 180 isobaric cooling (IBC), followed by rapid near isothermal decompression (ITD) within the 181 sillimanite field (Perera, 1987, 1994; Schumacher et al., 1990; Faulhaber and Raith, 1991, 182 Prame, 1991; Raase and Schenk, 1994; Mathavan and Fernando, 2001; Osanai et al., 2006) 183 In contrast, other works suggested an ITD stage directly after peak T (Ogo et al., 1992; 184 Kriegsman, 1993; Hiroi et al., 1994; Takamura et al., 2015) AC C EP 179 Hiroi et al (1994) and Raase and Schenk (1994) showed evidence for local growth of 185 186 andalusite indicating that the latest metamorphic stage of the HC occurred in the andalusite 187 field 188 189 Field relations and sample descriptions 190 Highly aluminous garnet–sillimanite–graphite gneisses (khondalite) were collected 191 from a road exposure south of Gampola (Fig 1a and b) This area mainly consists of ACCEPTED MANUSCRIPT khondalites, quartzites, charnockitic and granitic gneisses, and marbles (Fig 1b) The 193 investigated khondalite occurs as slightly weathered rocks within the road cut The sampling 194 point is located close to the inferred ductile shear zone separating the HC from the KC 195 (Kröneret al., 1991; Voll and Kleinschrodt, 1991; Cooray, 1994) Rocks of this area exhibit 196 strong ductile deformation features such as ribbon quartz, recrystallized elongate feldspars 197 and a well demarcated sillimanite lineation RI PT 192 The khondalite, which is overlain by a ~30 cm thick quartzite layer, is characterized 199 by coarse-grained, euhedral to subhedral garnet porphyroblasts, with diameters ranging from 200 0.25 to cm (Fig 3a–c) The rock displays a well-developed foliation defined by stretched 201 quartz (up to cm long) and coarse prismatic sillimanite needles (up to 1.3 cm long) 202 Sillimanite is present within the main foliation between elongated quartz grains or wrapping 203 around porphyroblastic garnet Elongate feldspars and fine- to medium-grained graphite 204 flakes can also be identified The strike and dip of the foliation of the exposure is N300E and 205 250NW 206 207 Petrography 208 4.1 Textures of garnet porphyroblasts TE D 209 M AN U SC 198 Four types of garnet (Grt1, Grt2, Grt3 and Grt4) can be distinguished on the basis of 211 specific inclusion features, from the collected samples from the road exposure Rarely, three 212 types of garnet (Grt1, Grt3 and Grt4) can be identified in approximately 10 cm × 10 cm sized 213 rock specimens Grt2 are relatively less abundance and occurred only some domains where 214 matrix quartz are relatively less abundance compare to rest of the portions of the rock EP 210 Garnet type (Grt1): these porphyroblasts display euhedral to subhedral crystal 216 shapes and are to 1.5 cm in diameter The core is mainly inclusion-free while the mantle 217 contains numerous oriented quartz inclusions with minor ilmenite, which define a 218 discontinuous internal foliation (Si) oblique to the matrix foliation (Fig 4a and b) Towards 219 the mantle area, there is prismatic, up to 0.5 mm long sillimanite, isolated or in contact with 220 quartz (Fig 4a–d), and isolated staurolite grains (Fig 4a) The orientation of staurolite (close 221 to the top-right edge of the garnet in Fig.4a) is parallel to Si Staurolite (Fig 4d and e), 222 isolated biotite flakes (Fig 4a and e), up to 0.4 cm long kyanite and minor ilmenite inclusions 223 are present within the rim (Fig 4f) Rarely, euhedral kyanite inclusions are partially 224 pseudomorposed by a second generation of sillimanite In this texture (Fig 4f), the kyanite 225 core, with typical low order interference colours and oblique extinction, is still preserved, AC C 215 ACCEPTED MANUSCRIPT 226 while the rim has been converted into pseudomorphic sillimanite with higher order 227 interference colours and parallel extinction Garnet type (Grt2): 228 the core and mantle area of these euhedral to subhedral porphyroblasts (up to cm in diameter) contain numerous isolated inclusions of anhedral, 230 medium- to fine-grained corundum (0.5 – mm in size) coexisting with clusters of 231 sillimanite (Fig 5a and b) The subhedral and monoclinic (Fig 5a) shape of these clusters 232 suggests that sillimanite may have grown as pseudomorphs after kyanite Medium- to coarse- 233 grained prismatic sillimanite (up to mm long) and medium-grained spinel also occur 234 associated with corundum grains (Fig 5d) Occasionally, prismatic sillimanite has numerous 235 of spinel inclusions (Fig 5e–g) and rare corundum inclusions (Fig 5e–g) Isolated anhedral 236 staurolite (up to 0.3 mm) is also present in the core and mantle (Fig 5e) Towards the mantle 237 to rim contact, garnet encloses isolated quartz grains, medium- to fine-grained clusters of 238 alkali-feldspar (Fig 5h) and patches of pyrophyllite, which often contain tiny, partially 239 consumed sillimanite needles (Fig 5i) Additionally, the core to rim area of garnet contains 240 oriented rutile needles and minor apatite rods with ilmenite (Fig 5j and k) Some ilmenite 241 needles show orientations at an angle of approximately 45°– 60° (Fig 5k) Similar to Ague 242 and Eckert (2012), we interpret these as exsolution features M AN U SC RI PT 229 Garnet type (Grt3): the presence of medium- to fine-grained, elongated and locally 244 curved quartz grains together with minor alkali-feldspar, rutile and ilmenite inclusions at the 245 core and inner mantle areas of these coarse-grained (up to 2.5 cm in diameter), rounded 246 porphyroblasts (Fig 6a and b).Curved quartz inclusion could indicate that this particular area 247 of Grt3 formed under strong non-coaxial stress The outer mantle and rim areas lack evidence 248 for rotation and contain fewer inclusions than core and inner mantle Thus, the outer mantle 249 probably formed under the absence of a strong non-coaxial stresses The outer mantle to the 250 rim parts of Grt3 contain relict biotite flakes, coexisting with sillimanite and fine-grained 251 spinel (Fig 6c) Relatively coarse-grained alkali-feldspars (~3 mm) are found throughout the 252 garnet Locally, in the mantle to rim areas, sillimanite is found rimmed by pyrophyllite (Fig 253 6d) AC C EP TE D 243 254 Garnet type (Grt4): is fine-grained (up to 0.25 – 0.60 cm in diameter), anhedral and 255 encloses oriented sillimanite needles and minor quartz, alkali-feldspar, zircon and rutile (Fig 256 6e–g) Oriented sillimanite inclusions display the same orientations as sillimanite grains in 257 the rock matrix (Fig 6e) Theses garnets occur close to coarse-grained sillimanite, ilmenite, 258 quartz (Fig 6f–i) and alkali-feldspars in the matrix, which is described in the following 259 section In addition to these inclusions, euhedral rutile is present in the matrix close to Grt4 AC C EP TE D M AN U SC RI PT ACCEPTED MANUSCRIPT AC C EP TE D M AN U SC RI PT ACCEPTED MANUSCRIPT AC C EP TE D M AN U SC RI PT ACCEPTED MANUSCRIPT AC C EP TE D M AN U SC RI PT ACCEPTED MANUSCRIPT AC C EP TE D M AN U SC RI PT ACCEPTED MANUSCRIPT AC C EP TE D M AN U SC RI PT ACCEPTED MANUSCRIPT AC C EP TE D M AN U SC RI PT ACCEPTED MANUSCRIPT AC C EP TE D M AN U SC RI PT ACCEPTED MANUSCRIPT AC C EP TE D M AN U SC RI PT ACCEPTED MANUSCRIPT AC C EP TE D M AN U SC RI PT ACCEPTED MANUSCRIPT AC C EP TE D M AN U SC RI PT ACCEPTED MANUSCRIPT AC C EP TE D M AN U SC RI PT ACCEPTED MANUSCRIPT AC C EP TE D M AN U SC RI PT ACCEPTED MANUSCRIPT AC C EP TE D M AN U SC RI PT ACCEPTED MANUSCRIPT ACCEPTED MANUSCRIPT Highlights Preservation of textural evidence for early prograde to late retrograde P-T path has been RI PT presented First attempt of P-T calculation using thermodyanamic modeling of early prograde P-T SC trajectory followed by the Highland Complex metasediments M AN U Peak metamorphic P-T-t conditions are around ~9 kbar, 900 0C and 540 Ma respectively AC C EP TE D Implications of P-T-t evolution of metasediments in the Highland Complex of Sri Lanka ... C EP TE D M AN U SC RI PT ACCEPTED MANUSCRIPT ACCEPTED MANUSCRIPT New constraints on the P? ? ?T path of HT/ UHT metapelites from the Highland Complex of Sri Lanka P L Dharmapriyaa,b,c, Sanjeewa P. .. a possible PT path for the HC and put the studied rock in the context 649 of the Srilankan tectono-metamorphic evolution TE D 646 651 EP 650 9.2.1 Prograde evolution Prograde compression: the. .. reactions) of UHT granulites in the HC These crenulation lineation is oblique to 702 the major matrix lineation of the UHT granulites indicating the rotation of garnet during their 703 growth