Phase-equilibrium constraints on titanite and rutile activities in mafic epidote amphibolites and geobarometry using titanite-rutile equilibria (original) (raw)
Related papers
2008
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 .
Contributions to Mineralogy and Petrology, 2018
A Fe-Ti-rich garnet, clinopyroxene, and quartz eclogite sample from the 1.0 Ga Sveconorwegian orogen, SW Sweden, contains abundant quartz, rutile, and zircon in distinct micro-textural sites: garnet core, garnet rim, and matrix, constituting an ideal case for investigation of the behavior of Zr-in-rutile and Ti-in-quartz at high-pressure and temperature. A P-T path, peaking at 16.5-19 kbar and 850-900 °C, has been constrained independently for the same rock by pseudosection modelling; input pressures from this model were used for trace element geothermometry of each garnet micro-textural domain. Trace element thermo(baro)metry, based on in situ Secondary Ion Mass Spectrometry analyses of Ti contents in quartz and Zr contents in rutile, yields P-T estimates of progressive crystallization of quartz and rutile along the prograde metamorphic path. For inclusions in the garnet cores, Zr-in-rutile geothermometry yields 700-715 °C and Ti-in-quartz 620-640 °C at 7 kbar. For inclusions in the garnet rims, temperature estimates are 760-790 °C (Zr-in-rutile) and 740-920 °C (Ti-in-quartz) at 12-18 kbar. Finally, matrix rutile records 775-800 °C and locally ~ 900 °C, and quartz records temperatures up to 900 °C at 18 kbar. Ti-in-quartz estimates for the metamorphic peak (inclusions in the garnet rims and matrix) conform to the pseudosection, but appear too low for the early prograde stage (garnet cores), possibly due to lack of equilibrium at T < 700 °C. The pseudosection shows that rutile was produced by continuous ilmenite breakdown during the early stages of prograde metamorphism, a reaction that was completed at ~ 730 °C. Rutile grains in the garnet rims and the matrix grew subsequently larger by recrystallization of previously produced rutile. However, recrystallized rutile does not predominantly record peak temperatures, but instead yield 745-840 °C between 12 and 18 kbar. In the pseudosection, this temperature range broadly coincides with a stage during which (Ti-bearing) hornblende was consumed and clinopyroxene produced (i.e., dehydration); the Zr contents thus appear to reflect the last stage of efficient rutile recrystallization, catalysed by fluids released by the dehydration of hornblende preceding the metamorphic peak. Concurrently, combination of the isopleths for Ti content in quartz and Zr content in rutile (i.e. independent from pseudosection modelling) yields pressure and temperature conditions in almost perfect agreement with the P-T path as deduced from the pseudosection. The variation in Ti concentration in quartz is small regardless of crystal size, and the Ti-in-quartz geothermometer provides both precise and accurate peak temperatures of 875-920 °C, without a significant diffusional reequilibration. The lack of significant Ti diffusion in quartz is consistent with an inferred short residence time at high temperature. This study illustrates that Zr-in-rutile and Ti-in-quartz geothermobarometry can robustly constrain prograde P-T conditions and yield further insights into recrystallization processes at high temperature. The combination of these methods and integration of the results with pseudosection modelling is a versatile tool for investigating the petrologic history of high-grade rocks.
Titanium in phengite: a geobarometer for high temperature eclogites
Contributions to Mineralogy and Petrology, 2010
Phengite chemistry has been investigated in experiments on a natural SiO 2 -TiO 2 -saturated greywacke and a natural SiO 2 -TiO 2 -Al 2 SiO 5 -saturated pelite, at 1.5-8.0 GPa and 800-1,050°C. High Ti-contents (0.3-3.7 wt %), Ti-enrichment with temperature, and a strong inverse correlation of Ti-content with pressure are the important features of both experimental series. The changes in composition with pressure result from the Tschermak substitution (Si ? R 2? = Al IV ? Al VI ) coupled with the substitution: Al VI ? Si = Ti ? Al IV . The latter exchange is best described using the end-member Ti-phengite (KMgTi[Si 3 Al]O 10 (OH) 2 , TiP). In the rutile-quartz/coesite saturated experiments, the aluminoceladonite component increases with pressure while the muscovite, paragonite and Ti-phengite components decrease. A thermodynamic model combining data obtained in this and previous experimental studies are derived to use the equilibrium MgCel ? Rt = TiP ? Cs/Qz as a thermobarometer in felsic and basic rocks. Phengite, rutile and quartz/coesite are common phases in HT-(U)HP metamorphic rocks, and are often preserved from regression by entrapment in zircon or garnet, thus providing an opportunity to determine the T-P conditions of crystallization of these rocks. Two applications on natural examples (Sulu belt and Kokchetav massif) are presented and discussed. This study demonstrates that Ti is a significant constituent of phengites that could have significant effects on phase relationships and melting rates with decreasing P or increasing T in the continental crust.
Computers & Geosciences, 1995
for IBM-compatible personal computers with minimum hardware requirements, that can be used in thermometric and barometric calculations by petrologists concerned with the determination of P-T paths in mafic and ultramafic rocks. The program creates ASCII files of normalized chemical analyses of amphiboles, garnet, epidote, ilmenite, muscovite, pyroxenes (ortho-and clinopyroxene), olivine, plagioclase, and spinel. The program carries out a wide range of stoichiometric and thermodynamic calculations on these minerals, such as cation site-allocations at the different structural positions, the molar fractions and mole percent of the end-member terms, and the application of different thermodynamic models for calculation of activity coefficients and activities.
Contributions to Mineralogy and Petrology, 1992
Enthalpy of formation and third law entropy for andradite (Ca3Fe2Si3012) and hedenbergite (CaFeSi206) at standard state have been retrieved from experimental P-T-f (O 2) data on the stability relations of these phases. The data for hedenbergite were combined with the thermodynamic data for related phases (Berman 1988) to formulate the geobarometers based on the reactions CaFeSi206 + 2CaA12Si208 + 2FeTiO3 = Ca3A12Si3012 + Fe3A12Si3012 + 2TIO2 (CPG-IR), 3CaFeSizO6 + 3CaA12Si208 + 3FeTiO3 = Ca3A12Si3012 + 2Fe3AI2Si3012+3CaTiSiO5 (CPG-IS) and 3CaFeSi206 + 3CaA12Si2Os = 2CaaA12Si3012 + Fe3A12Si3012 + 3SIO2 (CPG-O). The geobarometers involving rutile and sphene are proposed for the first time. In several granulite terranes, pressures have been estimated from the three geobarometers for basic granulites and charnockitic suite of rocks containing the above assemblages. In clinopyroxene-garnet-plagioclase-quartz-ilmenite-rutile assemblages, pressures obtained from CPG-IR are within + 500 bars of pressures calculated from the CPG-Q barometer. However, if rutile is absent, the pressures computed from the CPG-IR barometer are 300 to 1200 bars higher than those calculated from the CPG-Q barometer. For maximum differences in pressures obtained from the two equilibria, TiO2 activity [a(TiO2)] in the rocks is calculated to be 0.8. The sphene-bearing geobarometer (CPG-IS) also registers pressures comparable (< + 500 bars) to those obtained from the CPG-Q barometer. The close agreement in pressure values obtained from the CPG-IR and the CPG-IS equilibria with those registered by the CPG-Q geobarometer in assemblages containing quartz implies that the rutile-and sphene-bearing geobarometers which do not involve quartz, can also be applied to estimate pressures from quartz-absent assemblages-assemblages which are not amenable to quantitative geobarometry using existing formulations.
… et Cosmochimica Acta, 2001
Measurements of oxygen isotope fractionations between coexisting igneous titanite (Ttn) and zircon (Zrc) have been used to formulate a self-consistent, empirical calibration of equilibrium oxygen isotope partitioning: 1000 ln␣(Zrc Ϫ Ttn) ϭ 1.02 ϫ 10 6 /(T 2 ) This calibration is based on the average measured ⌬(Zrc-Igneous Ttn) ϭ 1.2 Ϯ 0.3‰ (n ϭ 27 rocks) and a closure temperature of titanite to oxygen diffusion of approximately 650°C. The average measured fractionation between zircon and metamorphic titanite is 2.1 Ϯ 0.4‰ (n ϭ 5 rocks). These results show that ⌬(Zrc-Ttn) can be used to distinguish igneous vs. metamorphic (or hydrothermal) titanite.
The Ti Record of Quartz in Anatectic Aluminous Granulites
Journal of Petrology, 2018
The distribution and concentration of Ti in quartz was assessed in five rutile-bearing anatectic aluminous granulites from the Grenville Province, Canada, each with previously constrained P-T conditions of metamorphism. Characterisation of quartz in these samples with the aid of cathodoluminescence (CL) mapping revealed two distinct types in each sample, resorbed quartz partly consumed by melting reactions during the prograde portion of metamorphism and quartz grown from crystallisation of partial melt during retrogression. In two of the samples, pseudomorphs after former melt in the form of quartz overgrowths on existing quartz were discovered using CL which are not visible by other methods. The P-T conditions recorded by each type based on Ti-in-quartz thermobarometry are in poor agreement with microstructures and P-T results inferred from phase equilibria modelling. The negative correlation between Ti incorporation into quartz and P suggests that prograde quartz, which is expected to record near-peak P-T, should be Ti-poor relative to retrograde quartz, which crystallised at conditions several kbar lower than peak P. The opposite trend was found; retrograde quartz is typically relatively Ti-poor and quartz overgrowths may be nearly Ti-free. Additionally, prograde quartz has variable Ti contents and fails to systematically record near peak P-T. Despite the presence of rutile in the samples, which is generally considered to ensure a Ti-saturated system, these results are strong evidence for Ti-undersaturation of quartz caused by disequilibrium between quartz and rutile. In addition, Zr-in-rutile thermometry generally gives lower temperatures than expected for these rocks, which can be explained by retrograde resetting of Zr in rutile and potentially by disequilibrium between rutile and zircon. Based on these results, the degree of Ti (or Zr) saturation achieved at any stage of metamorphism should be assessed with caution, as coexistence of quartz and rutile (or rutile and zircon) within a thin section or sample may not be a sufficient criterion for equilibrium.
Pressures and temperatures are estimated for the high grade portion (Region D) of the Bamble granulite facies terrane using barometers based on the assemblages almandine-grossular-ferrosilite-anorthite-quartz and pyrope-grossular-enstatite-anorthite-quartz and a garnet-orthopyroxene Fe 2-Mg K D exchange thermometer based on the experimental data of Lee and Ganguly (1988). Both barometers utilize the same thermochemical data base (Berman, 1988, 1990) and the same garnet (Berman, 1990) and orthopyroxene mixing models (Wood and Banno, 1973; Sack and Ghiorso, 1989) which are internally consistent both with each other and the Berman (1988, 1990) data base. Thus any disagreement between the two barometers is dependent only on the mixing models chosen. When Fe 2-Mg mixing in orthopyroxene and garnet is taken to be ideal, pressures from the two barometers are found to be in poor agreement with P Alm-Fs (P avg 9.2/À1.0 kb (1')) consistently greater than P Pyr-En (P avg 7.5/À1.2 kb (1')) by 1.4 to 2.4 kb per sample. If the non-ideal orthopyroxene mixing model of Sack and Ghiorso (1989) is used and their internally consistent value for mixing on the Fe 2-Mg join in garnet is incorporated in the Berman (1990) garnet mixing model, P Alm-Fs and P Pyr-En are now in good agreement with the mean pressures for P Alm-Fs and P Pyr-En at 7.1/À0.9 kb (1') and 7.0/À1.1 kb (1') respectively. Individual pressures per sample are generally within /À1 kb of each other which is within the error range of either barometer. The mean temperature is found to be 793/À58 C (1') which is in good agreement with a mean temperature of 795 C obtained from titaniferous magnetite-ilmenite thermometry (Harlov, 1992) as well as the stability ®elds of sillimanite and Mg-rich cordierite.
Temperature dependence of Zr in rutile: empirical calibration of a rutile thermometer
Contributions to Mineralogy and Petrology, 2004
Rutile is an important carrier of high field strength elements (HFSE; Zr, Nb, Mo, Sn, Sb, Hf, Ta, W). Its Zr content is buffered in systems with quartz and zircon as coexisting phases. The effects of temperature (T) and pressure (P) on the Zr content in rutile have been empirically calibrated in this study by analysing rutile-quartz-zircon assemblages of 31 metamorphic rocks spanning a T range from 430 to 1,100°C. Electron microprobe measurements show that Zr concentrations in rutile vary from 30 to 8,400 ppm across this temperature interval, correlating closely with metamorphic grade. The following thermometer has been formulated based on the maximum Zr contents of rutile included in garnet and pyroxene:
Journal of Metamorphic Geology, 2010
The stability of pumpellyite + actinolite or riebeckite + epidote + hematite (with chlorite, albite, titanite, quartz and H 2 O in excess) mineral assemblages in LTMP metabasite rocks is strongly dependent on bulk composition. By using a thermodynamic approach (THERMOCALC), the importance of CaO and Fe 2 O 3 bulk contents on the stability of these phases is illustrated using P-T and P-X phase diagrams. This approach allowed P-T conditions of 4.0 kbar and 260°C to be calculated for the growth of pumpellyite + actinolite or riebeckite + epidote + hematite assemblages in rocks containing variable bulk CaO and Fe 2 O 3 contents. These rocks form part of an accretionary wedge that developed along the east Australian margin during the Carboniferous-Triassic New England Orogen. P-T and P-X diagrams show that sodic amphibole, epidote and hematite will grow at these conditions in Fe 2 O 3 -saturated (6.16 wt%) metabasic rocks, whereas actinolite and pumpellyite will be stable in CaO-rich (10.30 wt%) rocks. With intermediate Fe 2 O 3 (3.50 wt%) and CaO (8.30 wt%) contents, sodic amphibole, actinolite and epidote can coexist at these P-T conditions. For Fe 2 O 3 -saturated rocks, compositional isopleths for sodic amphibole (Al 3+ and Fe 3+ on the M2 site), epidote (Fe 3+ ⁄ -Fe 3+ + Al 3+ ) and chlorite (Fe 2+ ⁄ Fe 2+ + Mg) were calculated to evaluate the efficiency of these cation exchanges as thermobarometers in LTMP metabasic rocks. Based on these calculations, it is shown that Al 3+ in sodic amphibole and epidote is an excellent barometer in chlorite, albite, hematite, quartz and titanite buffered assemblages. The effectiveness of these barometers decreases with the breakdown of albite. In higher-P stability fields where albite is absent, Fe 2+ -Mg ratios in chlorite may be dependent on pressure. The Fe 3+ ⁄ Al and Fe 2+ ⁄ Mg ratios in epidote and chlorite are reliable thermometers in actinolite, epidote, chlorite, albite, quartz, hematite and titanite buffered assemblages.