Genesis of felsic and mafic HP granulites from the Moldanubian Zone, Lower Austria

2020 ◽  
Author(s):  
Christoph Hauzenberger ◽  
Philip Schantl ◽  
Elena Sizova ◽  
Harald Fritz ◽  
Fritz Finger ◽  
...  
Keyword(s):  
High Pressures ◽  
Melt Inclusions ◽  
Garnet Growth ◽  
Uniform Temperature ◽  
Metamorphic Overprint ◽  
Moldanubian Zone ◽  
Second Stage ◽  
Tectonic Processes ◽  
Pt Path ◽  
Zr In Rutile

<p><span><span>The granulite occurrences from the Moldanubian zone were extensively studied in the last three decades and their metamorphic overprint at high pressures and at UHT conditions are well constrained. However, there are still some discrepancies regarding the prograde PT-path evolution, the genesis of the granulites and the tectonic processes required to produce the proposed PT-paths. Here we present a comprehensive petrological study where we have investigated more than 300 granulite samples from one of the largest occurrences, the Poechlarn-Wieselburg area - Dunkelsteinerwald. C</span><span>onventional geothermobarometry, garnet zoning pattern, thermodynamic modelling and Zr-in-rutile thermometry on rutile grains enclosed in garnets in felsic and mafic granulites allowed to constrain the prograde as well as the retrograde segments of the PT path. Polycrystalline melt inclusions and high-Ti biotite relics as well as a uniform temperature of approximately 800°C obtained from rutile inclusions (Zr-in-rutile thermometry) in garnet cores disagree with a continuous prograde garnet growth but favour a metastable overstepping of the garnet-in reaction and growth by the peritectic biotite breakdown reaction to garnet and melt within a very narrow PT interval. Subsequent heating to T>1000°C initiated a second stage of garnet growth with a very distinct chemical composition. The preservation of the zoning pattern at these metamorphic conditions clearly document a very short lived process. Diffusion models predict a time span of <5 Ma and cooling rates of 50-60°C/my.</span><span> Zircon U-Pb ages usually cluster around 340 Ma representing the metamorphic peak. However, in mafic granulites zircon ages from approximately 410 Ma to 340 Ma are obtained indicating either an older formation age for the precursor rock of the mafic granulites or just documenting the occurrence of xenocrysts. We applied a series of coupled petrological–thermomechanical tectono-magmatic numerical model to reproduce our deduced PTt-path that evolved from exhumation of subducted lower crust followed by intense heating at the crust-mantle boundary.</span></span></p>

scholarly journals New evidence for the prograde and retrograde PT-path of high-pressure granulites, Moldanubian Zone, Lower Austria, by Zr-in-rutile thermometry and garnet diffusion modelling

Lithos ◽  
2019 ◽  
Vol 342-343 ◽  
pp. 420-439 ◽  
Author(s):  
Philip Schantl ◽  
Christoph Hauzenberger ◽  
Friedrich Finger ◽  
Thomas Müller ◽  
Manfred Linner
Keyword(s):  
High Pressure ◽  
Moldanubian Zone ◽  
Diffusion Modelling ◽  
Pt Path ◽  
New Evidence ◽  
Garnet Diffusion ◽  
Zr In Rutile

Determining the speed of intracontinental subduction – preliminary results of zoned garnet geochronology in micaschists from the Schneeberg and Radenthein Complexes, Eastern Alps

2021 ◽  
Author(s):  
Kathrin Fassmer ◽  
Peter Tropper ◽  
Hannah Pomella ◽  
Thomas Angerer ◽  
Gerald Degenhart ◽  
...  
Keyword(s):  
High Pressure ◽  
Carbonaceous Material ◽  
Eastern Alps ◽  
Garnet Growth ◽  
Published Data ◽  
Prograde Metamorphism ◽  
Preliminary Results ◽  
Pt Path ◽  
Zr In Rutile ◽  
Different Parts

<p>In collisional orogens continental crust is subducted to (ultra-)high-pressure (HP/UHP) conditions as constrained by petrologic, tectonic and geophysical observations. Despite a wealth of studies on the subduction and exhumation of UHP rocks, the duration of prograde metamorphism during subduction is still not well constrained.</p><p>We plan to apply Lu-Hf and Sm-Nd geochronology on metamorphic rock samples to date the duration of garnet growth, which represents a major part of prograde metamorphism from the greenschist-facies onward. Micaschist samples from the Schneeberg and Radenthein Units in the Eoalpine high-pressure belt (Eastern Alps) will be used for dating as they contain cm- to dm-sized garnet blasts, which experienced only one subduction-exhumation cycle. With dating different parts of big garnet grains, we test whether (1) it is possible to resolve the duration of garnet growth within single crystals, and (2) Lu-Hf and Sm-Nd systems date the same events in the PT-path or yield complementary information. Additionally, we will perform U-Pb geochronology on titanite in order to obtain the age of the first stages of exhumation; in addition, dating of rutile inclusions as well as matrix rutiles will be used to test Eoalpine prograde age. We will also apply U-Th-Pb monazite dating (EPMA and LA-ICPMS) to some of the samples. Collectively, these data will allow us to compare the duration of subduction and the timing of initial exhumation in a single sample. We then will constrain the PT-path of the dated samples by pseudosection modeling combined with Zr-in-rutile, quartz-in-garnet, and carbonaceous material geothermo(baro)metry. We already have preliminary results for Zr-in-rutile thermometry of rutile inclusions in garnets and matrix rutiles for samples from both locations. We measured Zr content with an EPMA and used the calibrations of Tomkins et al. (2007) and Kohn (2020). The calibration of Kohn (2020) gives overall slightly lower temperatures, but all obtained temperatures lay in a range of c. 500-600 °C in accordance with previously published data. In addition, EPMA, µ-XRF, LA-ICPMS, and µCT will be used to control if garnets preserved major and trace elemental growth zoning and to provide spatial 3D information on inclusion patterns. µCT analyses were already successfully used to obtain the chemical centre of the garnet grains in order to be able to cut them directly through there center. This is important for all in-situ chemical analyses. With dating different parts of single garnet crystals separately with Lu-Hf and Sm-Nd geochronology, we will add tight time constraints to the PT-path and constrain the duration of garnet growth.</p><p>With this contribution we formulate the working hypothesis that prograde subduction together with exhumation is a fast process. The basis for testing the idea of fast prograde metamorphism is that many geochronological studies propose a prograde duration of < 10 Ma and studies using geospeedometry sometimes propose an even shorter duration, which is the impetus for this investigation.</p><p>References:</p><p>Kohn, M.J. (2020). A refined zirconium-in-rutile thermometer. American Mineralogist(105), 963-971.</p><p>Tomkins, H.S., Powell, R. & Ellis, D.J. (2007). The pressure dependence of the zirconium-in-rutile thermometer. Journal of Metamorphic Geology(25), 703-713.</p>

scholarly journals A method of designing equipment for heat processing of polymer workpieces

2021 ◽  
Vol 2094 (2) ◽  
pp. 022016
Author(s):  
A O Glebov ◽  
S V Karpushkin
Keyword(s):  
Temperature Field ◽  
Parametric Optimization ◽  
Heat Processing ◽  
Uniform Temperature ◽  
Heating Equipment ◽  
Uniform Heating ◽  
Rubber Mixture ◽  
Second Stage ◽  
Sequential Solution ◽  
Uniform Temperature Field

Abstract The paper describes a method of designing heating equipment that maintains a predetermined temperature field. The method consists in sequential solution of two problems. At the first stage, the heat generation field was calculated using the stationary heat conduction equation. At the second stage, parametric optimization of the temperature field was performed with reference to the power and configuration limits of the heaters. To test this method, the problem of maintaining a predetermined non-uniform temperature field was solved. A practical example of the application of the method for designing a uniform heating plate used in vulcanizing presses was given. To assess the efficiency of the plate, the results of modeling the heat processing of a workpiece from a rubber mixture were presented.

Multispecies Diffusion of Yttrium, Rare Earth Elements and Hafnium in Garnet

2020 ◽  
Vol 61 (7) ◽  
Author(s):  
E M Bloch ◽  
M C Jollands ◽  
A Devoir ◽  
A -S Bouvier ◽  
M Ibañez-Mejia ◽  
...  
Keyword(s):  
High Pressures ◽  
Diffusion Mechanism ◽  
Significant Degree ◽  
Reaction Model ◽  
Diffusion Reaction ◽  
Garnet Growth ◽  
Fast Diffusion ◽  
Silica Activity ◽  
Low Concentrations ◽  
Diffusion Mechanisms

Abstract We report experimental data for Y, La, Lu and Hf diffusion in garnet, in which diffusant concentrations and silica activity have been systematically varied. Experiments were conducted at 950 and 1050 °C, at 1 atm pressure and oxygen fugacity corresponding to the quartz–fayalite–magnetite buffer. At Y and REE concentrations below several hundred ppm we observe both slow and fast diffusion mechanisms, which operate simultaneously and correspond to relatively high and low concentrations, respectively. Diffusivity of Y and REE is independent of silica activity over the studied range. General formulae for REE diffusion in garnet, incorporating data from this and previous studies, are  logDREE(f)(m2 s−1)=−10·24(±0·21)−221057(±4284)2·303RT(K) for the ‘fast’ REE diffusion mechanism at 1 atm pressure, and  logDREE(s)(m2 s−1)=−9·28(±0·65)−265200(±38540)+10800(±2600)×P(GPa)2·303RT(K) for the ‘slow’ REE diffusion mechanism. These slow and fast diffusion mechanisms are in agreement with previous, apparently conflicting, datasets for REE diffusion in garnet. Comparison with high-pressure experiments suggests that at high pressures (>∼1 GPa minimum) the fast diffusion mechanism no longer operates to a significant degree. When Y and/or REE surface concentrations are greater than several hundred ppm, complex concentration profiles develop. These profiles are consistent with a multi-site diffusion–reaction model, whereby Y and REE cations diffuse through, and exchange between, different crystallographic sites. Diffusion profiles of Hf do not exhibit any of the complexities observed for Y and REE profiles, and can be modeled using a standard (i.e. single mechanism) solution to the diffusion equation. Hafnium diffusion in garnet shows a negative dependence on silica activity, and is described by  logDHf(m2 s−1)=−8·85(±0·38)−299344(±15136)+12500(±900)×P(GPa)2·303RT(K)−0·52(±0·09)×log⁡10aSiO2. In many natural garnets, diffusion of both Lu and Hf would be sufficiently slow that the Lu–Hf system can be reliably used to date garnet growth. In cases in which significant Lu diffusion does occur, preferential retention of 176Hf/177Hf relative to 176Lu/177Hf will skew isochron relationships such that their apparent ages may not correspond to anything meaningful (e.g. garnet growth, peak temperature or the closure temperature of Lu or Hf). Late-stage reheating events are capable of causing larger degrees of preferential retention of 176Hf/177Hf relative to 176Lu/177Hf and partial to full resetting of the Sm–Nd system within garnet, thus increasing the separation between garnet Lu–Hf and Sm–Nd isochron dates, owing to the fact that these systems are more significantly disturbed through diffusion as more radiogenic 176Hf and 143Nd have accumulated.

scholarly journals Using the elastic properties of zircon-garnet host-inclusion pairs for thermobarometry of the ultrahigh-pressure Dora-Maira whiteschists: problems and perspectives

2021 ◽  
Vol 176 (5) ◽  
Author(s):  
Nicola Campomenosi ◽  
Marco Scambelluri ◽  
Ross J. Angel ◽  
Joerg Hermann ◽  
Mattia L. Mazzucchelli ◽  
...  
Keyword(s):  
Phase Equilibria ◽  
Western Alps ◽  
Thermodynamic Modelling ◽  
The Other ◽  
Ultrahigh Pressure ◽  
Garnet Growth ◽  
Threshold Temperature ◽  
Other Hand ◽  
Chemical Equilibration ◽  
Zr In Rutile

AbstractThe ultrahigh-pressure (UHP) whiteschists of the Brossasco-Isasca unit (Dora-Maira Massif, Western Alps) provide a natural laboratory in which to compare results from classical pressure (P)–temperature (T) determinations through thermodynamic modelling with the emerging field of elastic thermobarometry. Phase equilibria and chemical composition of three garnet megablasts coupled with Zr-in-rutile thermometry of inclusions constrain garnet growth within a narrow P–T range at 3–3.5 GPa and 675–720 °C. On the other hand, the zircon-in-garnet host-inclusion system combined with Zr-in-rutile thermometry would suggest inclusion entrapment conditions below 1.5 GPa and 650 °C that are inconsistent with the thermodynamic modelling and the occurrence of coesite as inclusion in the garnet rims. The observed distribution of inclusion pressures cannot be explained by either zircon metamictization, or by the presence of fluids in the inclusions. Comparison of the measured inclusion strains with numerical simulations shows that post-entrapment plastic relaxation of garnet from metamorphic peak conditions down to 0.5 GPa and 600–650 °C, on the retrograde path, best explains the measured inclusion pressures and their disagreement with the results of phase equilibria modelling. This study suggests that the zircon-garnet couple is more reliable at relatively low temperatures (< 600 °C), where entrapment conditions are well preserved but chemical equilibration might be sluggish. On the other hand, thermodynamic modelling appears to be better suited for higher temperatures where rock-scale equilibrium can be achieved more easily but the local plasticity of the host-inclusion system might prevent the preservation of the signal of peak metamorphic conditions in the stress state of inclusions. Currently, we cannot define a precise threshold temperature for resetting of inclusion pressures. However, the application of both chemical and elastic thermobarometry allows a more detailed interpretation of metamorphic P–T paths.

scholarly journals Insights from elastic thermobarometry into exhumation of high-pressure metamorphic rocks from Syros, Greece

2020 ◽  
Author(s):  
Miguel Cisneros ◽  
Jaime D. Barnes ◽  
Whitney M. Behr ◽  
Alissa J. Kotowski ◽  
Daniel F. Stockli ◽  
...  
Keyword(s):  
High Pressure ◽  
Oxygen Isotope ◽  
Garnet Growth ◽  
Metamorphic Rocks ◽  
Core Complex ◽  
Subduction Channel ◽  
Pressure Groups ◽  
Second Stage ◽  
Mineral Growth ◽  
Metamorphic Terranes

Abstract. We combine elastic thermobarometry with oxygen isotope thermometry to quantify the pressure-temperature (P-T) evolution of retrograde metamorphic rocks of the Cycladic Blueschist Unit (CBU), an exhumed subduction complex exposed on Syros, Greece. We employ quartz-in-garnet and quartz-in-epidote barometry to constrain pressures of garnet and epidote growth near peak subduction conditions and during exhumation, respectively. Oxygen isotope thermometry of quartz and calcite within boudin necks was used to estimate temperatures during exhumation and to refine pressure estimates. Three distinct pressure groups are related to different metamorphic events and fabrics: high-pressure garnet growth at ~1.4–1.7 GPa between 500–1550 °C, retrograde epidote growth at ~1.3–1.5 GPa between 400–500 °C, and a second stage of retrograde epidote growth at ~1.0 GPa and 400 °C. These results are consistent with different stages of deformation inferred from field and microstructural observations, recording prograde subduction to blueschist-eclogite facies and subsequent retrogression under blueschist-greenschist facies conditions. Our new results indicate that the CBU experienced cooling during decompression after reaching maximum high-pressure/low-temperature conditions. These P-T conditions and structural observations are consistent with exhumation and cooling within the subduction channel in proximity to the refrigerating subducting plate, prior to Miocene core-complex formation. This study also illustrates the potential of using elastic thermobarometry in combination with structural and microstructural constraints, to better understand the P-T-deformation conditions of retrograde mineral growth in HP/LT metamorphic terranes.

scholarly journals Significance of Zr-in-Rutile Thermometry for Deducing the Decompression P–T Path of a Garnet–Clinopyroxene Granulite in the Moldanubian Zone of the Bohemian Massif

2017 ◽  
Vol 58 (6) ◽  
pp. 1173-1198 ◽  
Author(s):  
Tadashi Usuki ◽  
Yoshiyuki Iizuka ◽  
Takao Hirajima ◽  
Martin Svojtka ◽  
Hao-Yang Lee ◽  
...  
Keyword(s):  
Bohemian Massif ◽  
Moldanubian Zone ◽  
T Path ◽  
Zr In Rutile

Tectonic implications of the metamorphic field gradient in the Austrian Drosendorf and Gföhl units, Moldanubian Zone

2020 ◽  
Author(s):  
Dominik Sorger ◽  
Christoph A. Hauzenberger ◽  
Manfred Linner ◽  
Fritz Finger ◽  
Harald Fritz
Keyword(s):  
Variscan Orogeny ◽  
Duplex Structure ◽  
The South ◽  
Mafic Rocks ◽  
Moldanubian Zone ◽  
Second Stage ◽  
The North ◽  
Tectonic Position ◽  
Lower Crustal ◽  
Comprehensive Study

&lt;p&gt;The Moldanubian Zone in Austria is traditionally subdivided into several tectonostratigraphic subunits, which were juxtaposed to their nowadays position during the Variscan orogeny. The Gf&amp;#246;hl unit at the highest tectonic position exposes the Moldanubian granulites at the top, underlain by the granitic Gf&amp;#246;hl orthogneiss. At its base lies the Raabs unit, a sequence of mafic rocks (amphibolites and sepentinites) accompanied by metasediments. The Drosendorf unit represents a sedimentary sequence mainly consisting of paragneisses, amphibolites and marbles. At the lowest position the Ostrong unit is dominated by low-P paragneisses with local appearances of eclogites.&lt;br&gt;A comprehensive study along four W&amp;#8211;E profiles from the Danube valley (P1) in the south, to the Thaya valley (P4) in the north, revealed a disparate distribution of metamorphic conditions within the Drosendorf and the Gf&amp;#246;hl units (Raabs unit and Gf&amp;#246;hl orthogneiss). Along P1 several lithologies of the investigated units show similar P&amp;#8211;T conditions of 0.8&amp;#8211;1.2 GPa and 750&amp;#8211;800 &amp;#176;C, followed by a decompression stage to 0.6&amp;#8211;0.8 GPa and ~750 &amp;#176;C. Towards the north the temperature within the Drosendorf unit is continuously decreasing to 650&amp;#8211;700 &amp;#176;C, at pressure conditions of 0.4&amp;#8211;0.8 GPa. P&amp;#8211;T conditions for Raabs unit and Gf&amp;#246;hl orthogneiss are decreasing as well but are increasing again at P4. At the western end of P4 they reach similar conditions as in P1 (0.6&amp;#8211;1.0 GPa and 725&amp;#8211;800), but a decrease towards the east can be observed. A slight W&amp;#8211;E decreasing trend is also observable in P2 and P3. Th&amp;#8211;U&amp;#8211;Pb microprobe dating of several metasedimentary and orthogneiss samples resulted in a Carboniferous age (~340 Ma) for metamorphism. At one locality in the south an older monazite generation indicates an incipient collisional metamorphism in the Devonian (~370 Ma).&lt;br&gt;The observed N&amp;#8211;S gradient indicates that the southern parts represent formerly deeper buried lower crustal parts, whereas towards the north middle crustal levels are exposed, which were exhumed in a first stage. In a second stage of exhumation in the northernmost area, the oblique thrusting of lower crustal segment including the Gf&amp;#246;hl unit onto the already exhumed lower-middle crustal parts caused the formation of a duplex structure, which is responsible for the present appearance of the area around the Drosendorf window.&lt;/p&gt;

Determining the speed of intracontinental subduction – preliminary results of zoned garnet geochronology in micaschists from the Schneeberg Complex, Eastern Alps.

2020 ◽  
Author(s):  
Kathrin Fassmer ◽  
Peter Tropper ◽  
Hannah Pomella ◽  
Thomas Angerer ◽  
Gerald Degenhard ◽  
...  
Keyword(s):  
High Pressure ◽  
Carbonaceous Material ◽  
Eastern Alps ◽  
Garnet Growth ◽  
Prograde Metamorphism ◽  
Fast Process ◽  
Pt Path ◽  
3D Information ◽  
Growth Zoning ◽  
Different Parts

&lt;p&gt;In collisional orogens continental crust is subducted to (ultra-)high-pressure (HP/UHP) conditions as constrained by petrologic, tectonic and geophysical observations. These (U)HP rocks are exhumed by an extremely fast process (few Ma) as numerous rocks still preserve their high-pressure metamorphic assemblages, which would not be the case if they had time to re-equilibrate at lower pressure conditions. Despite a wealth of studies on the subduction and exhumation of UHP rocks, the duration of prograde metamorphism during subduction is still not well constrained.&lt;/p&gt;&lt;p&gt;We plan to do Lu-Hf and Sm-Nd geochronology on metamorphic rock samples to date the duration of garnet growth, which represents a major part of prograde metamorphism from the greenschist-facies on. Micaschist samples from the Schneeberg and Radenthein Units in the Eoalpine high-pressure belt (Eastern Alps) will be used for dating as they contain cm- to dm-sized garnets, which experienced only one subduction-exhumation cycle with P-T conditions reaching 600 &amp;#176;C and up to 1 GPa. With dating different parts of big garnet grains we test (1) if it is possible to resolve the duration of garnet growth within single crystals, (2) if both systems, Lu-Hf and Sm-Nd, are needed for better age-constraints, and (3) whether both systems date the same events in the PT-path or give differing information. Additionally we will perform U-Pb geochronology on titanite in order to obtain the age of the first stages of exhumation and on rutile inclusions as well as matrix rutiles to confirm the Eoalpine prograde age with this additional method. Therefore, we will be able to compare the duration of subduction and the timing of initial exhumation in a single sample. We then will constrain the PT-path of the samples that will be dated by pseudosection modeling combined with Zr-in-rutile geothermometer, quartz-in-garnet geobarometer, and carbonaceous material geothermometer. In addition EPMA, &amp;#181;-XRF, LA-ICPMS, and &amp;#181;CT will be used to control if garnets preserved major and trace elemental growth zoning and to provide spatial 3D information on inclusion patterns. With dating different parts of single garnet crystals separately with Lu-Hf and Sm-Nd geochronology, we will add tight time constraints to the PT-path and constrain the duration of garnet growth.&lt;/p&gt;&lt;p&gt;With this contribution we formulate the working hypothesis that prograde subduction together with&amp;#160; exhumation is a fast process. The basis for testing the idea of fast prograde metamorphism is that many geochronological studies propose a prograde duration of &lt; 10 Ma and studies using geospeedometry sometimes propose an even shorter duration, which is the impetus for this investigation.&lt;/p&gt;

Rutile petrochronology of Eo-Archaean metasediments from the southern Inukjuak domain, Québec (Canada) and Akila island (SW Greenland)

2020 ◽  
Author(s):  
Peter Tropper ◽  
Axel Schmitt ◽  
Stephen Mojzsis ◽  
Craig Manning
Keyword(s):  
Phase Equilibrium ◽  
Mineral Assemblage ◽  
Secondary Ion Mass Spectrometry ◽  
High Sensitivity ◽  
Amphibolite Facies ◽  
Metamorphic Overprint ◽  
Supracrustal Belt ◽  
A Minor ◽  
Equilibrium Calculations ◽  
Zr In Rutile

&lt;p&gt;The world&amp;#8217;s oldest rocks of demonstrable volcano-sedimentary origin comprise the Archean &amp;#8220;supracrustal belts&amp;#8221;, in which they occur as variably deformed enclaves within ancient metamorphosed granite-granitoid gneiss terranes. The Inukjuak Domain in northern Qu&amp;#233;bec is part of the Archean Minto Block in the northwestern Superior Province of Canada. Eoarchean (ca. 3800-3780 Ma) rocks of the Nuvvuagittuq supracrustal belt (NSB) and the Ukaliq supracrustal belt (USB) are the best known of numerous supracrustal enclaves within this domain. Sample IN14032 represents a quartzite, interpreted as a quartz-pebble metaconglomerate from the USB. The main mineral assemblage is anthophyllite + muscovite + quartz + rutile + zircon. Owing to the pervasive greenschist-facies retrogression of the sample it was not possible to constrain P-T conditions using phase equilibrium calculations; however, the Zr-in-rutile geothermometer provides a tight constraint on T. A total of 41 rutile analyses were done by electron microprobe at the University of Innsbruck. Zr contents of rutile range from 407 ppm to 914 ppm and yielded T of 660-730&amp;#176;C at an assumed pressure of 0.6 GPa and the calculated mean T is 670&amp;#176;C &amp;#177; 40&amp;#176;C (2s). U-Pb dating of rutile from this sample using the ion microprobe at Heidelberg University following Schmitt &amp; Zack (2012) yielded ages of 2500-2600 Ma, which correlate well with the youngest zircon ages from this sample, consistent with the lower closure T for Zr diffusion in rutile (&lt;600&amp;#176;C).&lt;/p&gt;&lt;p&gt;Similarly, supracrustal rocks from the Nuuk region of West Greenland preserve a record of surficial processes in the early Archean (&gt;3600 Ma). Within the lithologies of the enclave a minor anthophyllite-garnet rock (sample GR114) with chemical characteristics suggesting a sedimentary protolith was identified. The main mineral assemblage of this sample is garnet + anthophyllite + hornblende + biotite + plagioclase + K-feldspar + quartz. Evidence for a later metamorphic overprint is given by the growth of a second generation of biotite and plagioclase as well as diffusive modification of the garnet composition along fractures. Phase equilibrium calculations of the main matrix assemblage yielded average P-T conditions of 580 &amp;#177; 40&amp;#176;C and 0.6 &amp;#177; 0.1 GPa. Zr-in-rutile geothermometry of rutile inclusions in garnet yielded increasing T from 610 &amp;#177; 30&amp;#176;C in the core to 670 &amp;#177; 30&amp;#176;C in the rims. U-Pb dating of rutile from this sample yielded discordant ages of 2400-1400 Ma. The upper intercept yields an age of ca. 2500 Ma, which again correlates again well with previous U-Pb zircon ages around 2700 Ma whereas the lower intercept at ca. 1000 Ma is indicative of a Grenville-age overprint.&lt;/p&gt;&lt;p&gt;The rutile U-Pb ages combined with Zr-in-rutile geothermometry show that Neoarchean metamorphism reached upper amphibolite-facies conditions (580-670&amp;#176;C) in both supracrustal localities in accordance with previous P-T estimates and U-Pb zircon ages. In addition, the sample from Akilia island yields hitherto unknown evidence of a later-stage Grenville metamorphic (high-greenschist-lower amphibolite-facies) overprint.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Schmitt, A. K., &amp; Zack, T. (2012). High-sensitivity U&amp;#8211;Pb rutile dating by secondary ion mass spectrometry (SIMS) with an O&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt; primary beam. Chemical Geology, 332, 65-73.&lt;/p&gt;

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