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Peter Tropper - One of the best experts on this subject based on the ideXlab platform.
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Phase‐equilibrium constraints on Titanite and rutile activities in mafic epidote amphibolites and geobarometry using Titanite–rutile equilibria
Journal of Metamorphic Geology, 2009Co-Authors: Paul Kapp, Craig E. Manning, Peter TropperAbstract:Activities of Titanite (Ttn, CaTiSiO5) and ⁄ or rutile (Rt, TiO2) phase components were calculated for 45 well-characterized natural Titanite- or rutile-undersaturated epidote-amphibolites by using the equilib- ria: (i) 3 anorthite + 2 zoisite ⁄ clinozoisite + rutile + quartz = 3 anorthite + Titanite + water (referred to as TZARS) and (ii) anorthite + 2 Titanite = grossular + 2 rutile + quartz (referred to as GRATiS). In Titanite-bearing and rutile-absent samples aRt is 0.75 ± 0.26. In Titanite-absent, rutile- bearing samples aTtn is 0.89 ± 0.16. Mean values derived for aRt ⁄ aTtn are 0.92 ± 0.12 for rutile + Titanite-bearing samples and 0.42 ± 0.27 for samples lacking both Titanite and rutile. Use of these values with TZARS yields pressure estimates for epidote-amphibolites that differ on average by
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The current status of Titanite-rutile thermobarometry in ultrahigh-pressure metamorphic rocks : The influence of Titanite activity models on phase equilibrium calculations
Chemical Geology, 2008Co-Authors: Peter Tropper, Craig E. ManningAbstract:Abstract Titanite, an important accessory mineral in ultrahigh-pressure (UHP) rocks, commonly deviates significantly from its ideal composition (CaTiSiO 4 O) by the substitution of Al and (F, OH) for Ti for O. This compositional variability of Titanite could be used in phase equilibrium calculations, if the activity–composition relations in (Al + F)-bearing Titanites were sufficiently known. Experimental investigations by Troitzsch and Ellis ([Troitzsch, U. and Ellis, D.J. (2002) Thermodynamic properties and stability of AlF-bearing Titanite CaTiOSiO 4 –CaAlFSiO 4 . Contributions to Mineralogy and Petrology, 142, 543–563]) and Tropper et al. ([Tropper, P., Manning, C., Essene, E.J. 2002. The substitution of Al and F in Titanite at high pressure and temperature: experimental constraints on phase relations and solid solution properties. Journal of Petrology 43, 1787–1814.) derived non-ideal-mixing models for solid solutions along the join CaTiSiO 4 O–CaAlSiO 4 F. Tropper et al. [Troitzsch, U. and Ellis, D.J. (2002) Thermodynamic properties and stability of AlF-bearing Titanite CaTiOSiO 4 –CaAlFSiO 4 . Contributions to Mineralogy and Petrology, 142, 543–563] derived a preliminary regular model in the T range 900–1100 °C, in which the T -dependent interaction parameter, W G , was negative. In contrast, Troitzsch and Ellis ([Troitzsch, U. and Ellis, D.J. (2002) Thermodynamic properties and stability of AlF-bearing Titanite CaTiOSiO 4 –CaAlFSiO 4 . Contributions to Mineralogy and Petrology, 142, 543–563]) favored a regular activity model with positive W G . The different signs of the interaction parameter strongly influence calculated non-ideal Titanite activities. Comparing available simple ideal ionic (coupled-ionic, non-coupled-ionic) activity models with the non-ideal models shows that a CaTiSiO 4 O , calculated with the ideal ionic models is substantially lower at almost all T . Calculation of two suitable Titanite–rutile-involving equilibria for thermobarometry applied to literature data from rocks from four UHP terranes shows that ideal ionic models yield the best convergence with independently established P estimates. Although the literature data have to be treated with caution (e.g. retrogression, compositional disequilibrium etc.), the calculations nonetheless indicate that in terms of T estimates, high-Al ( X Al > 0.5) Titanites yield a large variation of up to 300 °C in T and low-Al ( X Al T estimates. This study shows that P and T estimates derived from ideal models and experimentally constrained non-ideal models for Titanite activity may show large deviations at UHP conditions, ranging from 0.05 to 3.0 GPa and up to 300 °C. Therefore the current status of Titanite–rutile-involving thermobarometry allows it only to be applied to Al-rich ( X Al > 0.2) Titanites from UHP rocks if independent, more robust P–T estimates are available. Until better activity constraints are available, it is recommended that the user employ either the ideal coupled-ionic model for Titanite solid solutions involving mixing on the Ti and the O1-site and compare the results to an experimentally derived activity model, or adopt a range of different activity models (ionic and regular) to obtain a range of P–T conditions.
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formation of magmatic Titanite and Titanite ilmenite phase relations during granite alteration in the tribec mountains western carpathians slovakia
Lithos, 2007Co-Authors: Igor Broska, Peter Tropper, Daniel E. Harlov, Pavol SimanAbstract:Abstract In this study, formation of Titanite, in Carboniferous I-type granites/granitoids from the Tribec Mountains (Slovakia), and its subsequent alteration products are described. Titanite occurs in early magmatic differentiates of I-type granites/granitoids. Calculation of model mineral equilibria in the system K 2 O–CaO–FeO–Al 2 O 3 –TiO 2 –SiO 2 –H 2 O–O 2 (KCFATSHO) indicates that Titanite forms in granites/granitoids as a consequence of a reaction between titanomagnetite, biotite, and anorthite in a fluid-rich environment under relatively oxidizing conditions, during the later stages of magma crystallisation. Evidence for this reaction can be found in low temperature inclusions of Ti-rich magnetite and biotite inclusions in the Titanite, as well as in the formation of Titanite not only interstitially, but also locally in quartz. The Titanite alteration process has lead to the complete replacement of Titanite by ilmenite, quartz, REE-bearing epidote, and allanite while preserving the characteristic euhedral, diamond shape of the former Titanite. Completely altered Titanite grains become optically opaque due to the presence of ilmenite. The formation of REE-bearing epidote and allanite is probably due to the release of REE from the Titanite during alteration. This can be explained by model hydration reactions such as Titanite + anorthite + annite + H 2 O = ilmenite + clinozoisite + muscovite + quartz. Calculation of mineral equilibria involving magmatic precursor minerals, such as plagioclase and biotite, indicate that the formation of ilmenite from Titanite requires an influx of H 2 O and/or an increase in f O 2 . Titanite with the highest degree of ilmenite replacement occurs in a strongly mylonitized granite, in which the rock-forming minerals have been replaced by sericite, epidote, and chlorite. This breakdown of Titanite to ilmenite is a common phenomenon in some granites from the southwest area of the Tribec Mountains, indicating widespread late-stage fluid activity, associated with high f O 2 during the subsolidus cooling.
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Formation of magmatic Titanite and Titanite–ilmenite phase relations during granite alteration in the Tribeč Mountains, Western Carpathians, Slovakia
Lithos, 2006Co-Authors: Igor Broska, Peter Tropper, Daniel E. Harlov, Pavol SimanAbstract:Abstract In this study, formation of Titanite, in Carboniferous I-type granites/granitoids from the Tribec Mountains (Slovakia), and its subsequent alteration products are described. Titanite occurs in early magmatic differentiates of I-type granites/granitoids. Calculation of model mineral equilibria in the system K 2 O–CaO–FeO–Al 2 O 3 –TiO 2 –SiO 2 –H 2 O–O 2 (KCFATSHO) indicates that Titanite forms in granites/granitoids as a consequence of a reaction between titanomagnetite, biotite, and anorthite in a fluid-rich environment under relatively oxidizing conditions, during the later stages of magma crystallisation. Evidence for this reaction can be found in low temperature inclusions of Ti-rich magnetite and biotite inclusions in the Titanite, as well as in the formation of Titanite not only interstitially, but also locally in quartz. The Titanite alteration process has lead to the complete replacement of Titanite by ilmenite, quartz, REE-bearing epidote, and allanite while preserving the characteristic euhedral, diamond shape of the former Titanite. Completely altered Titanite grains become optically opaque due to the presence of ilmenite. The formation of REE-bearing epidote and allanite is probably due to the release of REE from the Titanite during alteration. This can be explained by model hydration reactions such as Titanite + anorthite + annite + H 2 O = ilmenite + clinozoisite + muscovite + quartz. Calculation of mineral equilibria involving magmatic precursor minerals, such as plagioclase and biotite, indicate that the formation of ilmenite from Titanite requires an influx of H 2 O and/or an increase in f O 2 . Titanite with the highest degree of ilmenite replacement occurs in a strongly mylonitized granite, in which the rock-forming minerals have been replaced by sericite, epidote, and chlorite. This breakdown of Titanite to ilmenite is a common phenomenon in some granites from the southwest area of the Tribec Mountains, indicating widespread late-stage fluid activity, associated with high f O 2 during the subsolidus cooling.
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formation of al rich Titanite catisio4o caalsio4oh reaction rims on ilmenite in metamorphic rocks as a function of fh2o and fo2
Lithos, 2006Co-Authors: Daniel E. Harlov, Peter Tropper, Wolfgang Seifert, T.g. Nijland, Hans-jürgen FörsterAbstract:Abstract Reaction rims of Titanite on ilmenite are described in samples from four terranes of amphibolite-facies metapelites and amphibolites namely the Tamil Nadu area, southern India; the Val Strona area of the Ivrea-Verbano Zone, northern Italy, the Bamble Sector, southern Norway, and the northwestern Austroalpine Otztal Complex. The Titanite rims, and hence the stability of Titanite (CaTiSiO4O) and Al–OH Titanite, i.e. vuaganatite (hypothetical end-member CaAlSiO4OH), are discussed in the light of fH2O- and fO2-buffered equilibria involving clinopyroxene, amphibole, biotite, ilmenite, magnetite, and quartz in the systems CaO–FeO/Fe2O3–TiO2–SiO2–H2O–O2 (CFTSH) and CaO–FeO/Fe2O3–Al2O3–SiO2–H2O–O2 (CFASH) present in each of the examples. Textural evidence suggests that Titanite reaction rims on ilmenite in rocks from Tamil Nadu, Val Strona, and the Bamble Sector originated most likely due to hydration reactions such as clinopyroxene + ilmenite + quartz + H2O = amphibole + Titanite and oxidation reactions such as amphibole + ilmenite + O2 = Titanite + magnetite + quartz + H2O during amphibolite-facies metamorphism, or, as in the case of the Otztal Complex, during a subsequent greenschist-facies overprint. Overstepping of these reactions requires fH2O and fO2 to be high for Titanite formation, which is also in accordance with equilibria involving Al–OH Titanite. This study shows that, in addition to P, T, bulk–rock composition and composition of the coexisting fluid, fO2 and fH2O also play an important role in the formation of Al-bearing Titanite during amphibolite- and greenschist-facies metamorphism.
Daniel E. Harlov - One of the best experts on this subject based on the ideXlab platform.
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formation of magmatic Titanite and Titanite ilmenite phase relations during granite alteration in the tribec mountains western carpathians slovakia
Lithos, 2007Co-Authors: Igor Broska, Peter Tropper, Daniel E. Harlov, Pavol SimanAbstract:Abstract In this study, formation of Titanite, in Carboniferous I-type granites/granitoids from the Tribec Mountains (Slovakia), and its subsequent alteration products are described. Titanite occurs in early magmatic differentiates of I-type granites/granitoids. Calculation of model mineral equilibria in the system K 2 O–CaO–FeO–Al 2 O 3 –TiO 2 –SiO 2 –H 2 O–O 2 (KCFATSHO) indicates that Titanite forms in granites/granitoids as a consequence of a reaction between titanomagnetite, biotite, and anorthite in a fluid-rich environment under relatively oxidizing conditions, during the later stages of magma crystallisation. Evidence for this reaction can be found in low temperature inclusions of Ti-rich magnetite and biotite inclusions in the Titanite, as well as in the formation of Titanite not only interstitially, but also locally in quartz. The Titanite alteration process has lead to the complete replacement of Titanite by ilmenite, quartz, REE-bearing epidote, and allanite while preserving the characteristic euhedral, diamond shape of the former Titanite. Completely altered Titanite grains become optically opaque due to the presence of ilmenite. The formation of REE-bearing epidote and allanite is probably due to the release of REE from the Titanite during alteration. This can be explained by model hydration reactions such as Titanite + anorthite + annite + H 2 O = ilmenite + clinozoisite + muscovite + quartz. Calculation of mineral equilibria involving magmatic precursor minerals, such as plagioclase and biotite, indicate that the formation of ilmenite from Titanite requires an influx of H 2 O and/or an increase in f O 2 . Titanite with the highest degree of ilmenite replacement occurs in a strongly mylonitized granite, in which the rock-forming minerals have been replaced by sericite, epidote, and chlorite. This breakdown of Titanite to ilmenite is a common phenomenon in some granites from the southwest area of the Tribec Mountains, indicating widespread late-stage fluid activity, associated with high f O 2 during the subsolidus cooling.
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Formation of magmatic Titanite and Titanite–ilmenite phase relations during granite alteration in the Tribeč Mountains, Western Carpathians, Slovakia
Lithos, 2006Co-Authors: Igor Broska, Peter Tropper, Daniel E. Harlov, Pavol SimanAbstract:Abstract In this study, formation of Titanite, in Carboniferous I-type granites/granitoids from the Tribec Mountains (Slovakia), and its subsequent alteration products are described. Titanite occurs in early magmatic differentiates of I-type granites/granitoids. Calculation of model mineral equilibria in the system K 2 O–CaO–FeO–Al 2 O 3 –TiO 2 –SiO 2 –H 2 O–O 2 (KCFATSHO) indicates that Titanite forms in granites/granitoids as a consequence of a reaction between titanomagnetite, biotite, and anorthite in a fluid-rich environment under relatively oxidizing conditions, during the later stages of magma crystallisation. Evidence for this reaction can be found in low temperature inclusions of Ti-rich magnetite and biotite inclusions in the Titanite, as well as in the formation of Titanite not only interstitially, but also locally in quartz. The Titanite alteration process has lead to the complete replacement of Titanite by ilmenite, quartz, REE-bearing epidote, and allanite while preserving the characteristic euhedral, diamond shape of the former Titanite. Completely altered Titanite grains become optically opaque due to the presence of ilmenite. The formation of REE-bearing epidote and allanite is probably due to the release of REE from the Titanite during alteration. This can be explained by model hydration reactions such as Titanite + anorthite + annite + H 2 O = ilmenite + clinozoisite + muscovite + quartz. Calculation of mineral equilibria involving magmatic precursor minerals, such as plagioclase and biotite, indicate that the formation of ilmenite from Titanite requires an influx of H 2 O and/or an increase in f O 2 . Titanite with the highest degree of ilmenite replacement occurs in a strongly mylonitized granite, in which the rock-forming minerals have been replaced by sericite, epidote, and chlorite. This breakdown of Titanite to ilmenite is a common phenomenon in some granites from the southwest area of the Tribec Mountains, indicating widespread late-stage fluid activity, associated with high f O 2 during the subsolidus cooling.
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formation of al rich Titanite catisio4o caalsio4oh reaction rims on ilmenite in metamorphic rocks as a function of fh2o and fo2
Lithos, 2006Co-Authors: Daniel E. Harlov, Peter Tropper, Wolfgang Seifert, T.g. Nijland, Hans-jürgen FörsterAbstract:Abstract Reaction rims of Titanite on ilmenite are described in samples from four terranes of amphibolite-facies metapelites and amphibolites namely the Tamil Nadu area, southern India; the Val Strona area of the Ivrea-Verbano Zone, northern Italy, the Bamble Sector, southern Norway, and the northwestern Austroalpine Otztal Complex. The Titanite rims, and hence the stability of Titanite (CaTiSiO4O) and Al–OH Titanite, i.e. vuaganatite (hypothetical end-member CaAlSiO4OH), are discussed in the light of fH2O- and fO2-buffered equilibria involving clinopyroxene, amphibole, biotite, ilmenite, magnetite, and quartz in the systems CaO–FeO/Fe2O3–TiO2–SiO2–H2O–O2 (CFTSH) and CaO–FeO/Fe2O3–Al2O3–SiO2–H2O–O2 (CFASH) present in each of the examples. Textural evidence suggests that Titanite reaction rims on ilmenite in rocks from Tamil Nadu, Val Strona, and the Bamble Sector originated most likely due to hydration reactions such as clinopyroxene + ilmenite + quartz + H2O = amphibole + Titanite and oxidation reactions such as amphibole + ilmenite + O2 = Titanite + magnetite + quartz + H2O during amphibolite-facies metamorphism, or, as in the case of the Otztal Complex, during a subsequent greenschist-facies overprint. Overstepping of these reactions requires fH2O and fO2 to be high for Titanite formation, which is also in accordance with equilibria involving Al–OH Titanite. This study shows that, in addition to P, T, bulk–rock composition and composition of the coexisting fluid, fO2 and fH2O also play an important role in the formation of Al-bearing Titanite during amphibolite- and greenschist-facies metamorphism.
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Formation of Al-rich Titanite (CaTiSiO4O–CaAlSiO4OH) reaction rims on ilmenite in metamorphic rocks as a function of fH2O and fO2
Lithos, 2005Co-Authors: Daniel E. Harlov, Peter Tropper, Wolfgang Seifert, T.g. Nijland, Hans-jürgen FörsterAbstract:Abstract Reaction rims of Titanite on ilmenite are described in samples from four terranes of amphibolite-facies metapelites and amphibolites namely the Tamil Nadu area, southern India; the Val Strona area of the Ivrea-Verbano Zone, northern Italy, the Bamble Sector, southern Norway, and the northwestern Austroalpine Otztal Complex. The Titanite rims, and hence the stability of Titanite (CaTiSiO4O) and Al–OH Titanite, i.e. vuaganatite (hypothetical end-member CaAlSiO4OH), are discussed in the light of fH2O- and fO2-buffered equilibria involving clinopyroxene, amphibole, biotite, ilmenite, magnetite, and quartz in the systems CaO–FeO/Fe2O3–TiO2–SiO2–H2O–O2 (CFTSH) and CaO–FeO/Fe2O3–Al2O3–SiO2–H2O–O2 (CFASH) present in each of the examples. Textural evidence suggests that Titanite reaction rims on ilmenite in rocks from Tamil Nadu, Val Strona, and the Bamble Sector originated most likely due to hydration reactions such as clinopyroxene + ilmenite + quartz + H2O = amphibole + Titanite and oxidation reactions such as amphibole + ilmenite + O2 = Titanite + magnetite + quartz + H2O during amphibolite-facies metamorphism, or, as in the case of the Otztal Complex, during a subsequent greenschist-facies overprint. Overstepping of these reactions requires fH2O and fO2 to be high for Titanite formation, which is also in accordance with equilibria involving Al–OH Titanite. This study shows that, in addition to P, T, bulk–rock composition and composition of the coexisting fluid, fO2 and fH2O also play an important role in the formation of Al-bearing Titanite during amphibolite- and greenschist-facies metamorphism.
Milan Novák - One of the best experts on this subject based on the ideXlab platform.
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complexly zoned niobian Titanite from hedenbergite skarn at pisek czech republic constrained by substitutions al nb ta ti 2 al f oh tio 1 and snti 1
Mineralogical Magazine, 2008Co-Authors: Jan Cempírek, Stanislav Houzar, Milan NovákAbstract:Euhedral crystals of complexly zoned niobian Titanite (up to 0.3 mm) are enclosed in hedenbergite (Hd53-81Di15-43Jh3-5) and quartz from a hedenbergite vein skarn at Kamenne doly near Pisek, Czech Republic. They are associated with minor clinozoisite-epidote (Ps3-22), calcite, plagioclase (An95), scapolite (Me80-82), scheelite, pyrrhotite, fluorapatite, arsenopyrite, native bismuth and Bi,Te-minerals. The following textural and compositional subtypes were recognized: (I) Nb-rich Titanite, (II) Nb-moderate Titanite in the central zone, (III) Nb-poor, Sn-enriched Titanite and (IV) Nb-poor, Al,F-rich Titanite in the outer zone. The substitution Al(Nb,Ta)Ti-2 is dominant in subtypes I and II, the Titanite subtype I being characterized by elevated contents of Al ≤0.257 atoms per formula unit (a.p.f.u.), Nb (≤0.161 a.p.f.u.) and Ta (≤0.037 a.p.f.u.). Amounts of Al, Nb and Ta in subtype II are smaller and more variable. The minor substitution SnTi-1 occurs chiefly in Titanite subtype III with a content of Sn ≤0.039 a.p.f.u.. The substitution Al(F,OH)(TiO)-1 is typical for Titanite subtype IV exhibiting elevated contents of Al (≤0.221 a.p.f.u.), F (≤0.196 a.p.f.u.) and Fe (≤0.039 a.p.f.u.). The negative relationship of substitutions Al(F,OH)(TiO)-1 vs . SnTi-1 and Al(Nb,Ta)Ti-2 is constrained chiefly by crystal structure rather than by the composition of parent medium alone. Textural relations suggest that the Nb-moderate Titanite in the core zone and entire outer zone are products of fluids-induced dissolution-reprecipitation processes. The studied niobian Titanite represents a new F-enriched type from a medium-grade, calc-silicate rock.
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Complexly zoned niobian Titanite from hedenbergite skarn at Písek, Czech Republic, constrained by substitutions Al(Nb,Ta)Ti-2, Al(F,OH)(TiO)-1 and SnTi-1
Mineralogical Magazine, 2008Co-Authors: Jan Cempírek, Stanislav Houzar, Milan NovákAbstract:Euhedral crystals of complexly zoned niobian Titanite (up to 0.3 mm) are enclosed in hedenbergite (Hd53-81Di15-43Jh3-5) and quartz from a hedenbergite vein skarn at Kamenne doly near Pisek, Czech Republic. They are associated with minor clinozoisite-epidote (Ps3-22), calcite, plagioclase (An95), scapolite (Me80-82), scheelite, pyrrhotite, fluorapatite, arsenopyrite, native bismuth and Bi,Te-minerals. The following textural and compositional subtypes were recognized: (I) Nb-rich Titanite, (II) Nb-moderate Titanite in the central zone, (III) Nb-poor, Sn-enriched Titanite and (IV) Nb-poor, Al,F-rich Titanite in the outer zone. The substitution Al(Nb,Ta)Ti-2 is dominant in subtypes I and II, the Titanite subtype I being characterized by elevated contents of Al ≤0.257 atoms per formula unit (a.p.f.u.), Nb (≤0.161 a.p.f.u.) and Ta (≤0.037 a.p.f.u.). Amounts of Al, Nb and Ta in subtype II are smaller and more variable. The minor substitution SnTi-1 occurs chiefly in Titanite subtype III with a content of Sn ≤0.039 a.p.f.u.. The substitution Al(F,OH)(TiO)-1 is typical for Titanite subtype IV exhibiting elevated contents of Al (≤0.221 a.p.f.u.), F (≤0.196 a.p.f.u.) and Fe (≤0.039 a.p.f.u.). The negative relationship of substitutions Al(F,OH)(TiO)-1 vs . SnTi-1 and Al(Nb,Ta)Ti-2 is constrained chiefly by crystal structure rather than by the composition of parent medium alone. Textural relations suggest that the Nb-moderate Titanite in the core zone and entire outer zone are products of fluids-induced dissolution-reprecipitation processes. The studied niobian Titanite represents a new F-enriched type from a medium-grade, calc-silicate rock.
Pavol Siman - One of the best experts on this subject based on the ideXlab platform.
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formation of magmatic Titanite and Titanite ilmenite phase relations during granite alteration in the tribec mountains western carpathians slovakia
Lithos, 2007Co-Authors: Igor Broska, Peter Tropper, Daniel E. Harlov, Pavol SimanAbstract:Abstract In this study, formation of Titanite, in Carboniferous I-type granites/granitoids from the Tribec Mountains (Slovakia), and its subsequent alteration products are described. Titanite occurs in early magmatic differentiates of I-type granites/granitoids. Calculation of model mineral equilibria in the system K 2 O–CaO–FeO–Al 2 O 3 –TiO 2 –SiO 2 –H 2 O–O 2 (KCFATSHO) indicates that Titanite forms in granites/granitoids as a consequence of a reaction between titanomagnetite, biotite, and anorthite in a fluid-rich environment under relatively oxidizing conditions, during the later stages of magma crystallisation. Evidence for this reaction can be found in low temperature inclusions of Ti-rich magnetite and biotite inclusions in the Titanite, as well as in the formation of Titanite not only interstitially, but also locally in quartz. The Titanite alteration process has lead to the complete replacement of Titanite by ilmenite, quartz, REE-bearing epidote, and allanite while preserving the characteristic euhedral, diamond shape of the former Titanite. Completely altered Titanite grains become optically opaque due to the presence of ilmenite. The formation of REE-bearing epidote and allanite is probably due to the release of REE from the Titanite during alteration. This can be explained by model hydration reactions such as Titanite + anorthite + annite + H 2 O = ilmenite + clinozoisite + muscovite + quartz. Calculation of mineral equilibria involving magmatic precursor minerals, such as plagioclase and biotite, indicate that the formation of ilmenite from Titanite requires an influx of H 2 O and/or an increase in f O 2 . Titanite with the highest degree of ilmenite replacement occurs in a strongly mylonitized granite, in which the rock-forming minerals have been replaced by sericite, epidote, and chlorite. This breakdown of Titanite to ilmenite is a common phenomenon in some granites from the southwest area of the Tribec Mountains, indicating widespread late-stage fluid activity, associated with high f O 2 during the subsolidus cooling.
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Formation of magmatic Titanite and Titanite–ilmenite phase relations during granite alteration in the Tribeč Mountains, Western Carpathians, Slovakia
Lithos, 2006Co-Authors: Igor Broska, Peter Tropper, Daniel E. Harlov, Pavol SimanAbstract:Abstract In this study, formation of Titanite, in Carboniferous I-type granites/granitoids from the Tribec Mountains (Slovakia), and its subsequent alteration products are described. Titanite occurs in early magmatic differentiates of I-type granites/granitoids. Calculation of model mineral equilibria in the system K 2 O–CaO–FeO–Al 2 O 3 –TiO 2 –SiO 2 –H 2 O–O 2 (KCFATSHO) indicates that Titanite forms in granites/granitoids as a consequence of a reaction between titanomagnetite, biotite, and anorthite in a fluid-rich environment under relatively oxidizing conditions, during the later stages of magma crystallisation. Evidence for this reaction can be found in low temperature inclusions of Ti-rich magnetite and biotite inclusions in the Titanite, as well as in the formation of Titanite not only interstitially, but also locally in quartz. The Titanite alteration process has lead to the complete replacement of Titanite by ilmenite, quartz, REE-bearing epidote, and allanite while preserving the characteristic euhedral, diamond shape of the former Titanite. Completely altered Titanite grains become optically opaque due to the presence of ilmenite. The formation of REE-bearing epidote and allanite is probably due to the release of REE from the Titanite during alteration. This can be explained by model hydration reactions such as Titanite + anorthite + annite + H 2 O = ilmenite + clinozoisite + muscovite + quartz. Calculation of mineral equilibria involving magmatic precursor minerals, such as plagioclase and biotite, indicate that the formation of ilmenite from Titanite requires an influx of H 2 O and/or an increase in f O 2 . Titanite with the highest degree of ilmenite replacement occurs in a strongly mylonitized granite, in which the rock-forming minerals have been replaced by sericite, epidote, and chlorite. This breakdown of Titanite to ilmenite is a common phenomenon in some granites from the southwest area of the Tribec Mountains, indicating widespread late-stage fluid activity, associated with high f O 2 during the subsolidus cooling.
Mingguo Zhai - One of the best experts on this subject based on the ideXlab platform.
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metamorphic evolution mineral chemistry and thermobarometry of schists and orthogneisses hosting ultra high pressure eclogites in the dabieshan of central china
Lithos, 2000Co-Authors: D. A. Carswell, R. N. Wilson, Mingguo ZhaiAbstract:As is typical of ultra-high pressure (UHP) terrains, the regional extent of the UHP terrain in the Dabieshan of central China is highly speculative, since the volume of eclogites and paragneisses preserving unequivocal evidence of coesite and/or diamond stability is very small. By contrast, the common garnet (XMn=0.18–0.45)–phengite (Si=3.2–3.35)–zoned epidote (Ps38–97)–biotite–Titanite–two feldspars–quartz assemblages in the more extensive orthogneisses have been previously thought to have formed under low P–T conditions of ca. 400±50°C at 4 kbar. However, certain orthogneiss samples preserve garnets with XCa up to 0.50, rutile inclusions within Titanite or epidote and relict phengite inclusions within epidote with Si contents p.f.u. of up to 3.49 — overlapping with the highest values (3.49–3.62) recorded for phengites in samples of undoubted UHP schists. These and other mineral composition features (such as A-site deficiencies in the highest Si phengites, Na in garnets linked to Y+Yb substitution and Al F Ti−1 O−1 substitution in Titanites) are taken to be pointers towards the orthogneisses having experienced a similar metamorphic evolution to the associated UHP schists and eclogites. Re-evaluated garnet–phengite and garnet–biotite Fe/Mg exchange thermometry and calculated 5 rutile+3 grossular+2SiO2+H2O=5 Titanite+2 zoisite equilibria indicate that the orthogneisses may indeed have followed a common subduction-related clockwise P–T path with the UHP paragneisses and eclogites through conditions of Pmax at ca. 690°C–715°C and 36 kbar to Tmax at ca. 710°C–755°C and 18 kbar, prior to extensive re-crystallisation and re-equilibration of these ductile orthogneisses at ca. 400°C–450°C and 6 kbar. The consequential conclusion, that it is no longer necessary to resort to models of tectonic juxtapositioning to explain the spatial association of these Dabieshan orthogneisses with undoubted UHP lithologies, has far-reaching implications for the interpretation of controversial gneiss–eclogite relationships in other UHP metamorphic terrains.
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Ultra-high pressure aluminous Titanites in carbonate-bearing eclogites at Shuanghe in Dabieshan, central China
Mineralogical Magazine, 1996Co-Authors: D. A. Carswell, R. N. Wilson, Mingguo ZhaiAbstract:Petrographic features and compositions of Titanites in eclogites within the ultra-high pressure metamorphic terrane in central Dabieshan are documented and phase equilibria and thermobarometric implications discussed. Carbonate-bearing eclogite pods in marble at Shuanghe contain primary metamorphic aluminous Titanites, with up to 39 mol.% Ca(Al,Fe3+)FSiO4 component. These Titanites formed as part of a coesite-bearing eclogite assemblage and thus provide the first direct petrographic evidence that AlFTi−1O−1 substitution extends the stability of Titanite, relative to rutile plus carbonate, to pressures within the coesite stability field. However, it is emphasised that A1 and F contents of such Titanites do not provide a simple thermobarometric index of P—T conditions but are constrained by the activity of fluorine, relative to CO2, in metamorphic fluids — as signalled by observations of zoning features in these Titanites. These ultra-high pressure Titanites show unusual breakdown features developed under more H2O-rich amphibolite-facies conditions during exhumation of these rocks. In some samples aluminous Titanites have been replaced by ilmenite plus amphibole symplectites, in others by symplectitic intergrowths of secondary, lower Al and F, Titanite plus plagioclase. Most other coesite-bearing eclogite samples in the central Dabieshan terrane contain peak assemblage rutile often partly replaced by grain clusters of secondary Titanites with customary low Al and F contents.
