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1
Degeling, H., S. Eggins, and D. J. Ellis. "Zr budgets for metamorphic reactions, and the formation of zircon from garnet breakdown." Mineralogical Magazine 65, no. 6 (December 2001): 749–58. http://dx.doi.org/10.1180/0026461016560006.
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AbstractThe construction of zirconium (Zr) budgets for metamorphic reactions in high-grade rocks provides new insight into zircon growth during metamorphism. In this study we target reactions involving garnet, as they enable zircon growth to be related to known pressure and temperature conditions. Two reactions involving the breakdown of Zr-bearing garnet from Rogaland, SW Norway have been investigated in detail, showing contrasting behaviour of Zr, with zircon formation being subject to the solubility of Zr in product phases. In the decompression reaction garnet + sillimanite + quartz → cordierite, Zr released during garnet breakdown cannot be incorporated into the cordierite structure, resulting in zircon nucleation and growth. In contrast, for the reaction garnet + biotite + sillimanite + quartz → osumilite + orthopyroxene + spinel + magnetite, no new zircon growth takes place, despite the garnet involved containing more than double the Zr concentration of the former reaction. In the latter case, all the Zr released by garnet breakdown can be detected in the product phases osumilite and orthopyroxene, thereby preventing growth of new metamorphic zircon. This study highlights the potential for high resolution geochronology in metamorphic rocks by relating zircon growth to specific metamorphic reactions.
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Ridley, John. "Modelling of the relations between reaction enthalpy and the buffering of reaction progress in metamorphism." Mineralogical Magazine 50, no. 357 (September 1986): 375–84. http://dx.doi.org/10.1180/minmag.1986.050.357.03.
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AbstractA proportion of the heat added to a body of rock during prograde metamorphism will be absorbed in the chemical work of metamorphic recrystallization. When and where heat is so absorbed will affect the exact thermal histories of the rocks, and hence the metamorphic textures. This paper reports the results of modelling of the inter-relations between reaction progress and thermal histories in a rock column. The results suggest that volumes of rock undergoing reaction at any moment act as heat sinks and absorb heat from the surrounding rock, that reaction generally takes place close to the temperature at which nucleation took place, and that steady heating of a rock pile can give rise to a reaction history in which spurts of reaction are separated by ‘quiet’, non-reactive intervals.
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Urueña, Cindy L., Charlotte Möller, and Anders Plan. "Metamorphic titanite–zircon pseudomorphs after igneous zirconolite." European Journal of Mineralogy 35, no. 5 (September 19, 2023): 773–88. http://dx.doi.org/10.5194/ejm-35-773-2023.
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Abstract. The formation of metamorphic zircon after baddeleyite is a well-known reaction that can be used to date the metamorphism of igneous silica-undersaturated rocks. By contrast, metamorphic minerals formed after igneous zirconolite have rarely been reported. In this paper, we document metamorphic titanite + zircon pseudomorphs formed from the metamorphic breakdown of igneous zirconolite in syenodiorite and syenite, in the southeastern Sveconorwegian Province, Sweden. Water-rich fluid influx during tectonometamorphism in epidote–amphibolite-facies metamorphic conditions caused the release of silica during a metamorphic reaction involving igneous feldspar and pyroxene and the simultaneous breakdown of igneous Zr-bearing phases. Typical titanite + zircon intergrowths are elongated or platy titanite crystals speckled with tiny inclusions of zircon. Most intergrowths are smaller than 15 µm; some are subrounded in shape. Locally, bead-like grains of titanite and zircon are intergrown with silicate minerals. The precursor igneous zirconolite was found preserved only in a sample of near-pristine igneous syenodiorite, as remnant grains of mainly < 2 µm in size. Two somewhat larger crystals, 8 and 12 µm, allowed semiquantitative confirmation using microprobe analysis. Analogous with zircon pseudomorphs after baddeleyite, titanite + zircon pseudomorphs after zirconolite potentially offer dating of the metamorphic reaction, although the small size of the crystals makes dating with today's techniques challenging. The scarcity of reports of zirconolite and pseudomorphs reflects that they are either rare or possibly overlooked.
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Tettelaar, Tanya, and Aphrodite Indares. "Granulite-facies regional and contact metamorphism of the Tasiuyak paragneiss, northern Labrador: textural evolution and interpretation." Canadian Journal of Earth Sciences 44, no. 10 (October 1, 2007): 1413–37. http://dx.doi.org/10.1139/e07-029.
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The Tasiuyak paragneiss at the western margin of the Nain Plutonic Suite has been subjected to two granulite-facies metamorphic events: (i) regional metamorphism during the Paleoproterozoic Torngat orogeny, and (ii) contact metamorphism due to emplacement of the Mesoproterozoic Nain Plutonic Suite. Regional metamorphism led to partial melting of pelitic rocks and the development of a locally well-preserved sequence of prograde and retrograde textures. These textures are partly controlled by bulk composition and formed in the pressure–temperature (P–T) field of the continuous reaction: biotite + sillimanite + plagioclase + quartz = garnet + K-feldspar + melt, along a hairpin P–T path with peak conditions of ~8–10 kbar (0.8–1.0 GPa) and up to 870 °C in the NaKFMASH (Na2O–K2O–FeO–MgO–Al2O3–SiO2–H2O) system. These textures controlled the development of the contact metamorphic assemblages. Contact metamorphism of the pelitic rocks between the Tessiarsuyungoakh intrusion and the Makhavinekh Lake pluton led to growth of orthopyroxene-cordierite symplectite after garnet–biotite, and cordierite–spinel symplectite after garnet–sillimanite. These phase associations attest to reactions in specific microtextural settings, some of which produced a second generation of partial melt. Maximum temperatures were above ~750 °C and pressures were lower than those of the regional metamorphism. The aureole around the Makhavinekh Lake pluton is ~4 km wide and shows a progressive development of the contact metamorphic assemblages toward the pluton. In contrast, the contact metamorphic overprint is incipient around the Tessiarsuyungoakh intrusion, which developed a ~20 m wide contact aureole and is most prominent in screens of paragneiss within that intrusion.
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Xiao, Ling-Ling, and Min-Hua Chen. "Metamorphic Age Comparison and Its Implications between the Zuoquan and Zanhuang Complexes in the Central North China Craton, Based on LA-ICP-MS Zircon U–Pb Dating." Minerals 9, no. 12 (December 13, 2019): 780. http://dx.doi.org/10.3390/min9120780.
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The Trans-North China Orogen (TNCO) is well-known as an early Precambrian orogenic belt in the North China Craton (NCC). Three meaningful groups of metamorphic ages have been reported in the metamorphic complexes throughout the TNCO, including c. 1.85 Ga, c. 1.95 Ga, and c. 2.5 Ga. The spatial distributions and relationships of these ages provide notable insight into the formation timing and tectonic evolution of the NCC basement. The Zuoquan and Zanhuang complexes are exposed in the south–central TNCO and are adjacent to the Eastern Block. In order to place new constraints on the timing of two phases of metamorphism that occurred in the complexes, combined U–Pb and rare earth element analyses were performed on zircons from different types of metamorphic rocks. Uranium–Pb zircon dating in this study shows that two groups of metamorphic ages of 1.88–1.85 Ga and 2.48–2.46 Ga were commonly recorded by metamorphic rocks in the Zanhuang and Zuoquan complexes, respectively. Our previous geochronological studies showed that metamorphic ages of c. 2.51 Ga and c. 1.90 Ga were locally recorded in the Zanhuang and Zuoquan complexes, respectively. These data indicate that metamorphic rocks in the two complexes underwent at least two phases of metamorphism, i.e., 2.51–2.46 Ga (Phase I) and 1.90–1.85 Ga (Phase II). In combination with previous studies regarding reaction microstructures, metamorphic pressure–temperature paths, and geochronology, the Phase II metamorphic ages are interpreted to be linked to the collision between the Western and Eastern Blocks along the TNCO between 1.97 Ga and 1.80 Ga, whereas the Phase I metamorphic ages, as a result of an earlier and extensive tectono-thermal event that occurred in the Eastern and Western Blocks of the NCC, were related to underplating of mantle-derived magma. It is inferred that the rocks with c. 2.51–2.46 Ga metamorphic ages in the two complexes formed in the Eastern Block and underwent regional metamorphism during that period, and then were tectonically involved in the TNCO and experienced c. 1.90–1.85 Ga metamorphism. Metamorphic peaks occurred at different crustal levels in the orogen, resulting in distinct metamorphic ages and peak conditions preserved by metamorphic rocks in the two complexes.
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Dutta, Upama, Ayan Kumar Sarkar, Sadhana M. Chatterjee, Anirban Manna, Alip Roy, and Subhrajyoti Das. "Petrological implications of element redistribution during metamorphism: insights from meta-granite of the South Delhi Fold Belt, Rajasthan, India." Geological Magazine 159, no. 5 (February 23, 2022): 735–60. http://dx.doi.org/10.1017/s0016756821001345.
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AbstractMeta-granites of the South Delhi Fold Belt, northwestern India, contain spectacular reaction textures formed during the metamorphic replacement of primary minerals. Textural relationships imply that amphibole was replaced sequentially in two stages. Epidote + titanite + quartz symplectite formed syn-tectonically on amphibole grain boundaries/fractures, followed by post-deformational growth of euhedral garnet overprinting amphibole grains. Besides occurring as symplectite grown during deformation, titanite in this rock also developed as a post-tectonic corona around magnetite. Parent magnetite contains exsolutions of ilmenite and/or ultrafine lamellae of Ti-rich oxide (Ti-oxd). Textures involving coronal titanite suggest their formation through a magnetite + ilmenite(/Ti-oxd) + plagioclase → titanite reaction. Compositional attributes and the calculation of the gain versus loss of components during the reaction suggest that the Mn2+ for garnet (XSpss = 0.23–0.29) that grew replacing amphibole was supplied by ilmenite (Mn2+ is 0.118–0.128 apfu) as it disintegrated to form coronal titanite. The redistribution of components between the metamorphic reaction sites connects the texturally unrelated domains and suggests that these zones were in chemical equilibrium during metamorphism. We estimated the P–T conditions of metamorphism for these post-tectonic assemblages as ∼650–700 °C from pseudosection modelling and conventional thermometry. Zircon data from this study suggest that the granitic rock crystallized at 988.8 ± 8.8 Ma. We propose that the metamorphic phases replaced the primary minerals during the mid Neoproterozoic tectonic activity reported from this terrane. The syn-tectonic symplectitic assemblage formed as the temperature increased during prograde metamorphism, and the post-tectonic minerals developed at peak conditions following the cessation of deformation.
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McElhinney, Tara R., Tim J. Dempster, and Peter Chung. "The influence of microscale lithological layering and fluid availability on the metamorphic development of garnet and zircon: insights into dissolution–reprecipitation processes." Mineralogical Magazine 86, no. 1 (December 13, 2021): 9–26. http://dx.doi.org/10.1180/mgm.2021.97.
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AbstractThe response of garnet and zircon to prograde amphibolite-facies metamorphism in late Proterozoic mica schists from the Scottish Highlands has been investigated. Spatial analysis of zircon populations using scanning electron microscopy was undertaken in Dalradian Schists that have undergone a sequence of prograde garnet growth and localised breakdown reactions involving coupled dissolution–reprecipitation. Fluid availability and matrix permeability strongly control this metamorphic response and different generations of garnet contain radically different populations of metamorphic micro-zircon and associated changes in the detrital zircon population. Micro-zircon abundance increases during garnet growth, whereas that of detrital zircon decreases. The mineralogy of the matrix influences zircon abundance in porphyroblast phases, where garnet overgrows a micaceous matrix zircon-rich garnet forms and where it overgrows a quartzofeldspathic matrix the result is zircon-poor garnet. Following garnet growth, micro-zircon abundance decreases at each stage of the prograde reaction history, with sillimanite-zone schists containing the lowest abundance, suggesting micro-zircons are texturally less stable at staurolite- and sillimanite-grade metamorphism. Micro-zircons are distributed evenly across host minerals in the matrix, with the exception of retrograde chlorite where micro-zircons are absent due to fluids removing Zr before new zircon can precipitate. There is an overall decrease in the mode of zircon at each stage of the reaction history, indicating that zircon is a highly reactive phase during amphibolite-facies metamorphism and is very sensitive to individual prograde and retrograde reactions.
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Lazzarotto, Manuele, David R. M. Pattison, Simon Gagné, and Paul G. Starr. "Metamorphic and structural evolution of the Flin Flon – Athapapuskow Lake area, west-central Manitoba." Canadian Journal of Earth Sciences 57, no. 11 (November 2020): 1269–88. http://dx.doi.org/10.1139/cjes-2019-0136.
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The Flin Flon – Athapapuskow Lake area, situated in the Flin Flon Greenstone Belt, Manitoba, consists of ocean-floor and island-arc assemblages, deformed and metamorphosed during the Trans-Hudson Orogeny (∼1.86–1.69 Ga). A new map of metamorphic mineral assemblages and isograds has been compiled that reveals a largely coherent regional metamorphic sequence increasing in metamorphic grade from prehnite–pumpellyite to amphibolite facies. Regional metamorphism postdates most of the deformation within the area, with the exception of the reactivation of major block-bounding faults. The regional prograde sequence has been subdivided into 10 metamorphic zones, separated by 9 isograds, that describe the transition from prehnite–pumpellyite to greenschist to amphibolite facies. The formation of contact metamorphic aureoles, pre-dating regional metamorphism, record conditions up to amphibolite facies. Equilibrium phase diagrams for the island-arc (low-Mg) and ocean-floor (high-Mg) assemblages were calculated and allow for the evaluation of the modelling techniques and determination of pressure–temperature conditions. Discrepancies between the modelling predictions and natural observations occur due to (1) limitations in the thermodynamic models for some of the complex minerals (e.g., amphibole); and (2) metastable persistence of some minerals to higher grade due to sluggish reaction kinetics. Notwithstanding these discrepancies, the modelling suggests that metamorphosed mafic rocks in the Flin Flon – Athapapuskow Lake area reached about 430–480 °C and 3.0–4.5 kbar. Peak metamorphic conditions within contact aureoles that preceded regional metamorphism did not exceed 500 °C (at a pressure between 2.7 and 4.4 kbar). The metamorphic field gradient records a transition from 250–300 °C/1.5–2.3 kbar to 430–480 °C/3–4.5 kbar (100–150 °C/kbar), defining a geothermal gradient of approximately 25–31 °C/km.
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Mitchell, J. N. "A Scanning Electron Microscopic study of hematite inclusions in cordierite porphyroblasts." Proceedings, annual meeting, Electron Microscopy Society of America 44 (August 1986): 680–981. http://dx.doi.org/10.1017/s0424820100144796.
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Porphyroblasts are monocrystalline to polycrystalline mineral grains in metamorphic rocks that are distinctly larger than the matrix grain surrounding them. Their presence reflects the metamorphic release and rapid diffusion of their chemical components, with subsequent crystallization at limited nucleation sites. Small inclusions of other minerals are often present in porphyroblasts, especially in members of the garnet group, staurolite, and cordierite. Various hypotheses may be suggested to explain such inclusions: (1) they are relics of earlier grains, either of the protolith or of a stage of metamorphism prior to porphyroblast growth; (2) they are reaction residues of the mineral grains that decomposed to form the porphyroblasts; or (3) they are decomposition products produced from the porphyroblasts by secondary or retrograde metamorphism.
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Powell, W. G., D. M. Carmichael, and C. J. Hodgson. "Conditions and timing of metamorphism in the southern Abitibi greenstone belt, Quebec." Canadian Journal of Earth Sciences 32, no. 6 (June 1, 1995): 787–805. http://dx.doi.org/10.1139/e95-067.
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Regional metamorphism, ranging in grade from the subgreenschist-facies to the greenschist–amphibolite-facies transition, affects all Archean supracrustal rocks (>2677 Ma) in the Rouyn–Noranda area. Contact metamorphic minerals associated with the posttectonic Preissac–Lacorne batholith (2643 Ma) show no evidence of a regional retrograde event. Accordingly, the age of regional metamorphism can be bracketed between 2677 and 2643 Ma. Three reaction isograds were mapped in subgreenschist-facies metabasites, dividing the low-grade rocks into three metamorphic zones: the pumpellyite–actinolite zone, the prehnite–pumpellyite zone, and the prehnite–epidote zone. In addition, the pumpellyite–actinolite–epidote–quartz bathograd, corresponding to a pressure of approximately 200 MPa, occurs on both sides of the Porcupine–Destor fault. Low-pressure regional metamorphism is also indicated both by the occurrence of an actinolite–oligoclase zone, and the persistence of pre-regional-metamorphic andalusite. The coincidence of andalusite and the actinolite-oligoclase zone indicates that pressure was <330 MPa at the greenschist-amphibolite transition. The geothermal gradient during metamorphism was approximately 30 °C/km. Regionally, isograds dip shallowly to the north and trend subparallel to lithological and structural trends. Metamorphic minerals in metabasites define tectonic fabrics only near major fault zones and in zones of CO2 metasomatism. In biotite zone metasedimentary rocks the schistosity is defined by mica and amphibole. These textures indicate that metamorphism and fabric development were coeval. However, the actinolite–epidote isograd cuts the Porcupine–Destor fault, indicating that regional metamorphism postdates movement along this fault. The strong fabrics associated with the Porcupine–Destor and Larder Lake–Cadillac faults must have developed through a process dominated by flattening strain.
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Lasaga, Antonio C. "Metamorphic reaction rate laws and development of isograds." Mineralogical Magazine 50, no. 357 (September 1986): 359–73. http://dx.doi.org/10.1180/minmag.1986.050.357.02.
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AbstractNew data on the kinetics of dehydration of muscovite + quartz suggest the necessity for a careful treatment of both surface kinetics and diffusion processes in metamorphic reactions. A new model is proposed that illustrates the relative role of diffusion and surface reactions in the overall metamorphic process. The rate law for the reaction at mineral surfaces derived from the experimental data is shown to be probably non-linear and similar to rate laws derived from Monte Carlo calculations. The experimental rate data is then used in a heat flow calculation to model the evolution of the muscovite isograd in the field. The position of the isograd, the temperature oversteps above equilibrium, and the width of ‘reaction zones’ are then analysed as a function of intrusion size and kinetic parameters.
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Maruyama, S., J. G. Liou, and Y. Sasakura. "Low-temperature recrystallization of Franciscan greywackes from Pacheco Pass, California." Mineralogical Magazine 49, no. 352 (June 1985): 345–55. http://dx.doi.org/10.1180/minmag.1985.049.352.05.
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AbstractLow-temperature metamorphism of the Franciscan complex at Pacheco Pass occurs at P-T conditions near the so-called jadeite isograd. Along Highway 152 in the Diablo Range, from west to east, four distinct prograde metamorphic zones are defined: (I) albite-quartz zone, (II) albite-rich, albite-quartz-clinopyroxene assemblage, (III) clinopyroxene-rich, albite-quartz-clinopyroxene assemblage, and (IV) clinopyroxene zone. Metamorphic pyroxenes are restricted to zones II, III, and IV in metagreywackes, but metabasites contain augite-rich pyroxenes even in zone I. With increasing grade, the compositions of pyroxene in metagreywackes change in XJd from nearly 100 in zone II to about 60 in zone III. The diopside component has little effect on the XJd of pyroxene. The apparent change of XJd reflects differences in pressure and temperature rather than in bulk rock composition. In metagreywackes, at the onset of zone II, albite breaks down to form Jd100 according to the reaction Ab = Jd+Qz. With increasing grade, this reaction leads to less jadeitic pyroxene. From zones II to III, a continuous reaction is delineated: Qz+2 pyroxenes (Jd80Ac15Aug5)=pyroxene (Jd60Ac30Aug10) + Ab.The metamorphic temperatures are estimated to be about 170°C in zones I and II, and about 230°C in zones II and III. The temperature variation recorded in a single rock is probably less than 30°C The pressure estimate depends on the choice of experimental data for the jadeite-albite-quartz curve; it ranges from 4.5 to 8 kbar. A gently folded thermal structure of the Cretaceous subduction zone metamorphism is postulated for this area.
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Kovaleva, Elizaveta, Håkon O. Austrheim, and Urs S. Klötzli. "Interpretation of zircon coronae textures from metapelitic granulites of the Ivrea–Verbano Zone, northern Italy: two-stage decomposition of Fe–Ti oxides." Solid Earth 8, no. 4 (July 25, 2017): 789–804. http://dx.doi.org/10.5194/se-8-789-2017.
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Abstract. In this study, we report the occurrence of zircon coronae textures in metapelitic granulites of the Ivrea–Verbano Zone. Unusual zircon textures are spatially associated with Fe–Ti oxides and occur as (1) vermicular-shaped aggregates 50–200 µm long and 5–20 µm thick and as (2) zircon coronae and fine-grained chains, hundreds of micrometers long and ≤ 1 µm thick, spatially associated with the larger zircon grains. Formation of such textures is a result of zircon precipitation during cooling after peak metamorphic conditions, which involved: (1) decomposition of Zr-rich ilmenite to Zr-bearing rutile, and formation of the vermicular-shaped zircon during retrograde metamorphism and hydration; and (2) recrystallization of Zr-bearing rutile to Zr-depleted rutile intergrown with quartz, and precipitation of the submicron-thick zircon coronae during further exhumation and cooling. We also observed hat-shaped grains that are composed of preexisting zircon overgrown by zircon coronae during stage (2). Formation of vermicular zircon (1) preceded ductile and brittle deformation of the host rock, as vermicular zircon is found both plastically and cataclastically deformed. Formation of thin zircon coronae (2) was coeval with, or immediately after, brittle deformation as coronae are found to fill fractures in the host rock. The latter is evidence of local, fluid-aided mobility of Zr. This study demonstrates that metamorphic zircon can nucleate and grow as a result of hydration reactions and mineral breakdown during cooling after granulite-facies metamorphism. Zircon coronae textures indicate metamorphic reactions in the host rock and establish the direction of the reaction front.
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Friend, C. R. L., A. S. Janardhan, and N. Shadakshara Swamy. "A retrogressive sapphirine-cordierite-talc paragenesis in a spinel-orthopyroxenite from southern Karnataka, India." Mineralogical Magazine 57, no. 387 (June 1993): 273–88. http://dx.doi.org/10.1180/minmag.1993.057.387.10.
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AbstractWithin amphibolite facies Peninsular gneisses in the south of the Dharwar craton, units of Sargur supracrustal rocks contain ultrabasic enclaves. One of these enclaves is an orthopyroxenite which comprises bronzite, spinel and minor phlogopite preserving coarse-grained, relic textures of probable igneous origin. After incorporation into the gneisses the enclave evolved through several distinct stages, elucidation of which allow an assessment of its metamorphic history.Firstly, deformation during closed system, anhydrous recrystallisation caused the coarse-grained textures to be partially overprinted by similar mineral assemblages but with a granoblastic texture. Secondly, open system hydration caused retrogression of the bronzite to alumino-gedrite at the margins of the enclave. Subsequently, the penetration of these fluids along grain boundaries caused reactions between spinel and bronzite to produce reaction pockets carrying assemblages of peraluminous sapphirine associated with cordierite and talc. The differences in the mineral assemblages in each pocket coupled with slight variations in their chemistry, suggest that equilibrium did not develop over the outcrop. Because sapphirine + magnesite is present in some pockets, it is evident that CO2 was also a component of the fluid.Phase relations from the MASH portion of the FMASH system, to which the chemistry of the reaction pockets approximates, suggest that the hydrous metamorphism causing the changes depended upon the assemblage enstatite + spinel + vapour which exists at PT conditions above the position of I16, ∼760°C at 3 kbar and below I21 at ∼765°C at 5.6 kbar (Seifert, 1974, 1975), where sapphirine is replaced by kornerupine. The suggested path of reaction occurred between I18 and I21. Subsequent reactions related to I20 cause the formation of cordierite. Talc formation has to be modelled in a different reaction grid.The metamorphism recorded by these reactions is thus at a maximum of amphibolite facies and is interpreted to have formed during the uplift and cooling history of the gneiss complex when hydrous fluids were free to migrate. Given the complex high-grade metamorphic history of this part of the Dharwar craton this event is likely to be late Archaean or Palaeoproterozoic in age.
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Spiess, Richard, and Tim H. Bell. "Microstructural controls on sites of metamorphic reaction: a case study of the inter-relationship between deformation and metamorphism." European Journal of Mineralogy 8, no. 1 (February 22, 1996): 165–86. http://dx.doi.org/10.1127/ejm/8/1/0165.
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Baxter, Ethan F. "Natural constraints on metamorphic reaction rates." Geological Society, London, Special Publications 220, no. 1 (2003): 183–202. http://dx.doi.org/10.1144/gsl.sp.2003.220.01.11.
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Sturm, Robert. "Microscopy and Microanalysis of Corona Textures in Eclogitic Greenschists from the Eastern Alps, Austria." Microscopy Today 16, no. 2 (March 2008): 26–31. http://dx.doi.org/10.1017/s1551929500055899.
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Metamorphic rocks formed under conditions of high temperature (>600°C) and high lithological pressure (>1 GPa) and being subject to a subsequent tectonic uplift commonly include a remarkable number of fascinating mineral textures. One type of these well known and extensively described high-grade metamorphic textures are the so-called corona structures or reaction rims which, by definition, are primarily based on metamorphic reactions that cause the formation of concentric layers of new mineral phases separating an older and unstable mineral core from a newer and equally unstable mineral matrix. In other words, corona structures in metamorphic rocks preserve evidence of changes in the environmental conditions (temperature, pressure, fugacity of H2O) experienced by the rock during its tectonometamorphic history.
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Rathossi, C., P. Tsolis-Katagas, and C. Katagas. "Thermal behaviour of ‘metamorphic vermiculite’ in Ca-rich ancient ceramic sherds and experimental ceramics." Mineralogical Magazine 74, no. 4 (August 2010): 747–71. http://dx.doi.org/10.1180/minmag.2010.074.4.747.
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AbstractA ‘metamorphic vermiculite’-like phase was identified in Ca-rich ancient ceramic sherds from excavations in NW Peloponnese, Greece. Archaeometric investigations have shown that the raw materials used in the production of ancient ceramics were derived from local Plio-Pleistocene sediments. Analysis by X-ray diffraction and scanning electron microscopy-energy dispersive spectroscopy showed that ‘metamorphic vermiculite’ is a common constituent phase of these sediments occurring in three texturally different types: as interstratified white mica-chlorite and chlorite-vermiculite, and white mica-(white mica-chlorite) stacks. In an attempt to elucidate the thermal transformation of ‘metamorphic vermiculite’ present in the calcareous raw materials, we produced experimental ceramics made from these local raw materials and fired them at 700, 750, 850, 950 and 1050°C in a static air furnace. The mixed-layered chlorite-vermiculite was transformed completely at ∼800°C contributing to the formation of new high-Tminerals. The two other types of ‘metamorphic vermiculite’ retain their original lath-like shape up to 1050°C and only a few crystals show that they have undergone complete transformation at this temperature. In the latter crystals, numerous nanocrystals were formed sub-parallel to the former cleavages of ‘metamorphic vermiculite’ pseudomorphs, suggesting their contribution to the nucleation of high-Tminerals (i.e. ferrian aluminian diopside, spinel, Fe oxides) by reactions with the available CaO. It is suggested that the firing conditions (i.e. maximum reaction temperature of 1050°C, reaction time of 1 h, oxygen atmosphere) which promote disequilibrium reactions, and the greater contribution of the white mica constituent against chlorite in some of the initial structures of ‘metamorphic vermiculite’ may be responsible for the delay of its thermal decomposition at 1050°C.
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PRAKASH, DIVYA, DEEPAK, PRAVEEN CHANDRA SINGH, CHANDRA KANT SINGH, SUPARNA TEWARI, MAKOTO ARIMA, and HARTWIG E. FRIMMEL. "Reaction textures and metamorphic evolution of sapphirine–spinel-bearing and associated granulites from Diguva Sonaba, Eastern Ghats Mobile Belt, India." Geological Magazine 152, no. 2 (August 14, 2014): 316–40. http://dx.doi.org/10.1017/s0016756814000399.
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AbstractThe Diguva Sonaba area (Vishakhapatnam district, Andhra Pradesh, South India) represents part of the granulite-facies terrain of the Eastern Ghats Mobile Belt. The Precambrian metamorphic rocks of the area predominantly consist of mafic granulite (±garnet), khondalite, leptynite (±garnet, biotite), charnockite, enderbite, calc-granulite, migmatic gneisses and sapphirine–spinel-bearing granulite. The latter rock type occurs as lenticular bodies in khondalite, leptynite and calc-granulite. Textural relations, such as corroded inclusions of biotite within garnet and orthopyroxene, resorbed hornblende within pyroxenes, and coarse-grained laths of sillimanite, presumably pseudomorphs after kyanite, provide evidence of either an earlier episode of upper-amphibolite-facies metamorphism or they represent relics of the prograde path that led to granulite-facies metamorphism. In the sapphirine–spinel-bearing granulite, osumilite was stable in addition to sapphirine, spinel and quartz during the thermal peak of granulite-facies metamorphism but the assemblage was later replaced by Crd–Opx–Qtz–Kfs-symplectite and a variety of reaction coronas during retrograde overprint. Variable amounts of biotite or biotite+quartz symplectite replaced orthopyroxene, cordierite and Opx–Crd–Kfs–Qtz-symplectite at an even later retrograde stage. Peak metamorphic conditions of c. 1000°C and c. 12 kbar were computed by isopleths of XMg in garnet and XAl in orthopyroxene. The sequence of reactions as deduced from the corona and symplectite assemblages, together with petrogenetic grid and pseudosection modelling, records a clockwise P–T evolution. The P–T path is characteristically T-convex suggesting an isothermal decompression path and reflects rapid uplift followed by cooling of a tectonically thickened crust.
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Nielsen, Peter A. "Metamorphism of the Arseno Lake area, N.W.T., Canada: an Abukuma facies series of Aphebian age." Canadian Journal of Earth Sciences 23, no. 5 (May 1, 1986): 646–69. http://dx.doi.org/10.1139/e86-066.
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Progressive mineralogical and mineral–chemical changes are described for metapelitic rocks from an Abukuma-type metamorphic series ranging from greenschist to upper amphibolite – granulite facies in the Bear Structural Province, Northwest Territories, Canada.The first appearance of the following minerals defines six isograds: biotite; andalusite; cordierite (muscovite + chlorite out); sillimanite (andalusite out); sillimanite + K-feldspar (muscovite + quartz out); and almandine + K-feldspar ± cordierite (biotite + sillimanite + quartz out).Electron microprobe analyses of the Fe–Mg silicates, biotite, cordierite, and garnet, display two distinct trends of mineral chemistry with increasing metamorphic grade. In the almandine + K-feldspar ± cordierite zone, where garnet is present, Fe/(Fe + Mg) decreases in all of the Fe–Mg silicates observed. However, in the cordierite zone and in the higher grade rocks where garnet is absent, Fe/(Fe + Mg) increases in both biotite and cordierite. Ilmenite and rutile are involved in all continuous reactions and lead to increasing Fe/Mg with grade unless garnet is a product of reaction. There is also a displacement towards lower Fe content at the sillimanite + K-feldspar isograd.The scale of equilibration decreases to 1–2 mm in the almandine + K-feldspar ± cordierite zone, which is most probably a function of the decrease of [Formula: see text] and therefore [Formula: see text]in the metamorphic fluid with increasing metamorphic grade.The physical conditions of metamorphism in the Arseno Lake area range from [Formula: see text] at 2–2.5 kbar with[Formula: see text] in the chlorite zone to ≥650 °C at 3.5–4.0 kbar where [Formula: see text] in the almandine + K-feldspar ± cordierite zone.
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Schumacher, Renate. "Zincian staurolite in Glen Doll, Scotland." Mineralogical Magazine 49, no. 353 (September 1985): 561–71. http://dx.doi.org/10.1180/minmag.1985.049.353.10.
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AbstractTextures and relict mineralogy in the Dalradian gneisses from the southern contact aureole of the Glen Doll diorite trace the development of three stages of metamorphism through regional and contact metamorphic phases. Regional metamorphic stage I is characterized by the stability of sillimanite+muscovite; recognition of a subsequent regional metamorphic stage II of lower grade is based on textural criteria, the stability of kyanite and staurolite + quartz, and geothermometry/geobarometry. The breakdown of zincian staurolite occurred under the conditions of contact metamorphism (stage III). Textural evidence from the outer part of the contact aureole suggests that zincian staurolite broke down by the following oxidation reaction:zincian staurolite + muscovite + quartz + O2 → andalusite + Zn-rich spinel + magnetite + biotite + H2O.Various stages of completion of this reaction have been observed in different parts of a sample. Predominance of magnetite over Zn-rich spinel (⩽ 14 wt. % ZnO) as a breakdown product can be explained by the initial breakdown of Fe-staurolite component + muscovite + quartz+O2 to form andalusite+biotite+magnetite. These product phases were joined by the Zn-rich spinel when sufficient Zn-staurolite component had concentrated in the unreacted staurolite. Rare local examples where Zn-rich spinel is dominant over magnetite may reflect lower O2 fugacity and/or higher initial Zn contents of the staurolite.
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Rutter, E. H., and K. H. Brodie. "Experimental approaches to the study of deformation/metamorphism relationships." Mineralogical Magazine 52, no. 364 (March 1988): 35–42. http://dx.doi.org/10.1180/minmag.1988.052.364.03.
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AbstractRock deformation and metamorphism can interact at the mechanistic level in the following ways: (a) facilitation of cataclasis through the release of high-pressure fluid during dehydration and decarbonation reactions; (b) facilitation of intracrystalline plasticity through the stresses induced during solid-state volume changes; (c) enhanced deformability through the transient existence of fine-grained reaction products; (d) modification of chemical potential gradients driving diffusion if a reaction can occur along the diffusion path; (f) changes in the resistance to intracrystalline plasticity through the effect of reaction-induced changes, pore fluid pressure and chemistry on point defect chemistry of the solid phases.Examples of experimental studies of each of these types of interaction are described. Special experimental problems arise through: (i) the effects of solid phase and pore space volume changes, and their effects on pore fluid pressure and measured strain; (ii) the effects of such microstructural changes on the determination of flow law parameters; and (iii) in many instances the need for very long duration deformation experiments if reaction kinetics are sluggish.There is an outstanding need for experimental studies of the effects of non-hydrostatic stress on the conditions for the onset of metamorphic reactions and phase transformations, as a basis for understanding some classes of deformation/metamorphism interaction. However, it is emphasized that the threefold classification of rock deformation mechanisms into cataclastic, crystal-plastic, and diffusive mass transfer processes, established from the study of deformation of monomineralic rocks, forms an essential framework for the understanding of deformation/metamorphism inter-relationships.
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Watkins, James M., and Michael A. Antonelli. "Beyond Equilibrium: Kinetic Isotope Fractionation in High-Temperature Environments." Elements 17, no. 6 (December 1, 2021): 383–88. http://dx.doi.org/10.2138/gselements.17.6.383.
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Igneous and metamorphic rocks exhibit greater isotopic heterogeneity than expected from equilibrium. Large nonequilibrium isotope effects can arise from diffusion and chemical reactions, such as crystal growth and dissolution. The effects are time-dependent and can, therefore, be used to probe timescales of igneous and metamorphic processes that are inaccessible to direct observation. New discoveries of isotopic variability in nature, informed by diffusion and reaction modeling, can provide unique insights into the formation of rocks in the interiors of planetary bodies.
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Ashworth, J. R., V. V. Reverdatto, V. YU kolobov, V. V. Lepetyukha, V. S. Sheplev, and N. A. Bryxina. "Textures of diffusion-controlled reaction in contact-metamorphosed Mg-rich granulite, Kokchetav area, Kazakhstan." Mineralogical Magazine 62, no. 2 (April 1998): 213–24. http://dx.doi.org/10.1180/002646198547585.
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AbstrsctIn a granulite from the Kokchetav massif, a complex mineral assemblage and intricate textures have resulted from a combination of unusual rock composition and two–stage metamorphic history. The second, contact metamorphism produced mainly cordierite and anthophyllite, reflecting a bulk composition attributed to pre–metamorphic alteration of basic igneous rock. From the first, highpressure metamorphism, garnet relics persist while another mineral has been completely pseudomorphed. The garnet is partly replaced by a symplectite of three minerals: orthopyroxene vermicules in a coarser intergrowth of cordierite and calcic plagioclase. Despite variable proportions of cordierite and plagioclase, the Al:Si ratio of the symplectite is almost constant, because the proportion of orthopyroxene is smaller where the dominant aluminous mineral is cordierite (Al:Si ≈ 0.8) than where the even more aluminous plagioclase (Al:Si ≈ 0.89) is prominent. The bulk Al:Si ratio of this symplectite, approximately 0.69, is very close to that of reactant garnet (0.66), indicating that Al and Si have been retained almost completely during the local reaction, while other elements were more mobile. In the pseudomorphs, aluminous cores (with Al:Si ratios 1.61–1.93) indicate that the mineral which has been completely replaced was probably kyanite. These cores comprise plagioclase, zoisite, corundum and spinel, and are surrounded by layers of plagioclase and cordierite. Fe, Mg, and Ca have diffused to the core, through layers with low bulk concentrations of these elements, probably by grainboundary diffusion in the solid state.
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Abad, I., F. Nieto, D. R. Peacor, and N. Velilla. "Prograde and retrograde diagenetic and metamorphic evolution in metapelitic rocks of Sierra Espuña (Spain)." Clay Minerals 38, no. 1 (March 2003): 1–23. http://dx.doi.org/10.1180/0009855033810074.
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AbstractAn unusually complete sequence of pelitic rocks ranging from diagenetic to greenschist-facies metamorphic grades occurs in southern Sierra Espun˜a, Spain. Prograde and retrograde reactions have been studied by X-ray diffraction and electron microscopy (SEM, TEM and AEM). The prograde reaction series, with reactions facilitated by tectonic stress, includes: (1) R4 interstratified illite-smectite in the diagenetic Malaguide Complex that preserves the variable orientation of original smectite packets, and has 1Md polytypism; (2) chemically heterogeneous illite and Na-K dioctahedral white micas that progressively evolve toward chemical and textural equilibrium in the anchizonal Intermediate Units; and (3) thick, defect-free packets of phengite, paragonite and clinochlore which have a typical metamorphic texture, in the Alpujarride Complex. Two superimposed retrograde episodes produced: (a) sudoite at near-peak metamorphic conditions and (b) dioctahedral smectite during low-temperature retrograde diagenesis.
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Waldron, K. A., G. T. R. Droop, and P. E. Champness. "Kinetic controls on the formation of metastable phases during the experimentally induced breakdown of chlorite." Mineralogical Magazine 57, no. 386 (March 1993): 141–56. http://dx.doi.org/10.1180/minmag.1993.057.386.14.
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AbstractThe kinetics and reaction mechanisms of chlorite breakdown have been studied in a series of experiments at conditions similar to those achieved during contact metamorphism (T = 600-725°C P = 1 kbar). Cores of chlorite schist were used as starting material in order to simulate natural metamorphic systems and preserve reaction textures. Reaction products were analysed by electron microprobe, scanning- and transmission-electron microscopy (SEM, TEM). Although the texture of the original chlorite was preserved in experiments run below 680°C talc had replaced chlorite. Olivine and spinel formed along grain boundaries, indicating long-range diffusion of aluminium. Above 680°C the chlorite was replaced by patches of disordered, aluminous pyroxene. Olivine and spinel grew both within the pyroxene and along what are believed to be former chlorite grain-boundaries. Reactions relevant to the observed textures and assemblages are:Thermodynamic calculations show that both of these reactions are metastable in the FeO-MgO-Al2O3-SiO2-H2O system in the P-T range of our experiments. In addition, previous experimental studies and our calculations indicate that the stable reaction is:The absence of cordierite in the run products, and the formation of talc and orthopyroxene while thermodynamically metastable, show that the ease of nucleation of these phases controlled the reaction mechanisms in the early stages.
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Rao, Rameshwar, and Hakim Rai. "Mineral chemistry of eclogites to investigate the evolutionary metamorphic history of UHP rocks from Tso-Morari region, Ladakh, India." Journal of Nepal Geological Society 40 (December 1, 2010): 13–20. http://dx.doi.org/10.3126/jngs.v40i0.23592.
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Micro textures of metabasics from the Tso-Morari region, Ladakh were studied in order to understand the evolutionary metamorphic history of eclogites. The mineral chemistry, paragenesis of mineral inclusions in garnet, and zoning in omphacite, garnet and amphibole suggest three main metamorphic stages: (i) an eclogite stage with late blueschist facies metamorphism, (ii) a medium-pressure amphibolite facies stage, and (iii) a low-pressure amphibolite to greenschist facies stage. The high Si content in phengite, presence of rutile besides almandine-rich garnet and omphacite in eclogites indicate the attainment of high pressures. Also, the textural features and composition of amphiboles indicate that blueschist facies conditions represented by growth of glaucophane at high pressure and low temperature were followed by a lower-pressure stage of metamorphism represented by partial and in some cases complete reaction of glaucophane to calcic green amphibole such as magnesio-hornblende. The relationships define a clock-wise P-T path with the involvement of an isothermal uplift path for the eclogites and associated garnet-amphibolites of Tso-Morari region.
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Ings, S. J., and J. V. Owen. "‘Decompressional’ reaction textures formed by isobaric heating: an example from the thermal aureole of the Taylor Brook Gabbro Complex, western Newfoundland." Mineralogical Magazine 66, no. 6 (December 2002): 941–51. http://dx.doi.org/10.1180/0026461026660069.
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Abstract Reaction textures including corona structures in granulites from the Proterozoic Long Range Inlier of western Newfoundland are spatially associated with a Silurian (0.34 Ga) mafic intrusion, the Taylor Brook Gabbro Complex. They comprise, in metabasites and tonalitic gneiss, coronal orthopyroxene and plagioclase on garnet and, in metapelites, cordierite and spinel formed at the expense of sillimanite, garnet and quartz. Although generally interpreted to indicate near-isothermal decompression (ITD) following regional metamorphism, which in the inlier occurred at ˜1.10–1.03 Ga, these features appear to be absent elsewhere. Therefore they are interpreted to be products of contact metamorphism (near-isobaric heating – IBH) within the thermal aureole of the gabbro. Thus, there is a ˜0.7 Ga difference (i.e. mid-Proterozoic vs. mid-Silurian) between the age of the regional metamorphic mineral assemblages and the contact aureole assemblages. The observation that classic ITD features occur in this aureole environment underscores the fact that P-sensitive reactions can progress during IBH as well as by pressure release.
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Zaccarini, Federica, Giorgio Garuti, George L. Luvizotto, Yuri de Melo Portella, and Athokpam K. Singh. "Testing Trace-Element Distribution and the Zr-Based Thermometry of Accessory Rutile from Chromitite." Minerals 11, no. 7 (June 22, 2021): 661. http://dx.doi.org/10.3390/min11070661.
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Trace element distribution and Zr-in-rutile temperature have been investigated in accessory rutile from stratiform (UG2, Merensky Reef, Jacurici), podiform (Loma Peguera), and metamorphic chromitites in cratonic shields (Cedrolina, Nuasahi). Rutile from chromitite has typical finger-print of Cr-V-Nb-W-Zr, whose relative abundance distinguishes magmatic from metamorphic chromitite. In magmatic deposits, rutile precipitates as an intercumulus phase, or forms by exsolution from chromite, between 870 °C and 540 °C. The Cr-V in rutile reflects the composition of chromite, both Nb and Zr are moderately enriched, and W is depleted, except for in Jacurici, where moderate W excess was a result of crustal contamination of the mafic magma. In metamorphic deposits, rutile forms by removal of Ti-Cr-V from chromite during metamorphism between 650 °C and 400 °C, consistent with greenschist-amphibolite facies, and displays variable Cr-Nb, low V-Zr, and anomalous enrichment in W caused by reaction with felsic fluids emanating from granitoid intrusions. All deposits, except Cedrolina, contain Rutile+PGM composite grains (<10 µm) locked in chromite, possibly representing relics of orthomagmatic assemblages. The high Cr-V content and the distinctive W-Nb-Zr signature that typifies accessory rutile in chromitite provide a new pathfinder to trace the provenance of detrital rutile in placer deposits.
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BELL, T. H., and N. HAYWARD. "Episodic metamorphic reactions during orogenesis: the control of deformation partitioning on reaction sites and reaction duration." Journal of Metamorphic Geology 9, no. 5 (September 1991): 619–40. http://dx.doi.org/10.1111/j.1525-1314.1991.tb00552.x.
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PATTISON, D. R. M., C. DE CAPITANI, and F. GAIDIES. "Petrological consequences of variations in metamorphic reaction affinity." Journal of Metamorphic Geology 29, no. 9 (July 18, 2011): 953–77. http://dx.doi.org/10.1111/j.1525-1314.2011.00950.x.
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Liu, Fulai, Qihan Shen, Yuansheng Eng, Xuechun Xu, and Rui Ma. "Genetic relationship of metamorphic reaction and dehydration-melting." Science in China Series D: Earth Sciences 41, no. 1 (April 1998): 49–56. http://dx.doi.org/10.1007/bf02932420.
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Lamont, Thomas N., Michael P. Searle, David J. Waters, Nick M. W. Roberts, Richard M. Palin, Andrew Smye, Brendan Dyck, Phillip Gopon, Owen M. Weller, and Marc R. St-Onge. "Compressional origin of the Naxos metamorphic core complex, Greece: Structure, petrography, and thermobarometry." GSA Bulletin 132, no. 1-2 (June 4, 2019): 149–97. http://dx.doi.org/10.1130/b31978.1.
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Abstract The island of Naxos, Greece, has been previously considered to represent a Cordilleran-style metamorphic core complex that formed during Cenozoic extension of the Aegean Sea. Although lithospheric extension has undoubtedly occurred in the region since 10 Ma, the geodynamic history of older, regional-scale, kyanite- and sillimanite-grade metamorphic rocks exposed within the core of the Naxos dome is controversial. Specifically, little is known about the pre-extensional prograde evolution and the relative timing of peak metamorphism in relation to the onset of extension. In this work, new structural mapping is presented and integrated with petrographic analyses and phase equilibrium modeling of blueschists, kyanite gneisses, and anatectic sillimanite migmatites. The kyanite-sillimanite–grade rocks within the core complex record a complex history of burial and compression and did not form under crustal extension. Deformation and metamorphism were diachronous and advanced down the structural section, resulting in the juxtaposition of several distinct tectono-stratigraphic nappes that experienced contrasting metamorphic histories. The Cycladic Blueschists attained ∼14.5 kbar and 470 °C during attempted northeast-directed subduction of the continental margin. These were subsequently thrusted onto the more proximal continental margin, resulting in crustal thickening and regional metamorphism associated with kyanite-grade conditions of ∼10 kbar and 600–670 °C. With continued shortening, the deepest structural levels underwent kyanite-grade hydrous melting at ∼8–10 kbar and 680–750 °C, followed by isothermal decompression through the muscovite dehydration melting reaction to sillimanite-grade conditions of ∼5–6 kbar and 730 °C. This decompression process was associated with top-to-the-NNE shearing along passive-roof faults that formed because of SW-directed extrusion. These shear zones predated crustal extension, because they are folded around the migmatite dome and are crosscut by leucogranites and low-angle normal faults. The migmatite dome formed at lower-pressure conditions under horizontal constriction that caused vertical boudinage and upright isoclinal folds. The switch from compression to extension occurred immediately following doming and was associated with NNE-SSW horizontal boudinage and top-to-the-NNE brittle-ductile normal faults that truncate the internal shear zones and earlier collisional features. The Naxos metamorphic core complex is interpreted to have formed via crustal thickening, regional metamorphism, and partial melting in a compressional setting, here termed the Aegean orogeny, and it was exhumed from the midcrust due to the switch from compression to extension at ca. 15 Ma.
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Moazzen, Mohssen, Intizor Silmonov, and Sangin Elnazarov. "Metamorphic dolomitic marble-hosted talc from the Mulvoj area in the Western Pamir Mountains, Tajikistan." Mineralogia 54, no. 1 (January 1, 2023): 30–41. http://dx.doi.org/10.2478/mipo-2023-0004.
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Abstract Talc is crystallized in the metamorphic dolomitic rocks of the southwest Pamir mountains in the Mulvoj area, Tajikistan. Field studies show that talc is restricted to metamorphic dolomitic marble layers in the garnet-mica schist and gneiss. The layers are parallel to the original sedimentary bedding and schistosity of the metamorphic rocks. Petrography and whole rock geochemistry reveal calcite, tremolite, quartz and dolomite as the main mineral phases in the talc-bearing metamorphosed dolomitic rocks, while calcite is absent in the samples without talc. XRD studies show that talc samples are almost pure, and geochemistry indicates very low Fe and Cr and very high Mg contents. Geochemical features along with field observations clearly shows that Mulvoj talc is not originated from peridotite. Based on phase relations studies in the CaO-MgO-SiO2-H2O-CO2 system, the reaction between dolomite, quartz, and water at pressure greater than 2 kbar and temperature up to ~460°C and XCO2 up to 0.6 was the main talc forming reaction. Talc and calcite consuming reaction produced tremolite, dolomite and binary (CO2-H2O) fluid.
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Huang, Wenqing, Pei Ni, Jungui Zhou, Ting Shui, Junying Ding, Renzhi Zhu, Yitao Cai, and Mingsen Fan. "Discovery of Disulfane (H2S2) in Fluid Inclusions in Rubies from Yuanjiang, China, and Its Implications." Crystals 11, no. 11 (October 27, 2021): 1305. http://dx.doi.org/10.3390/cryst11111305.
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Raman spectra of fluid inclusions in gem rubies from Yuanjiang deposit (China) within the Ailao Shan-Red River (ASRR) metamorphic belt showed the presence of compounds such as CO2, COS, CH4, H2S, and elemental sulfur (S8), accompanied by two bands at approximately 2499 and 2570 cm−1. These two frequencies could be assigned to the vibrations of disulfane (H2S2). This is the second case of the sulfane-bearing fluid inclusions in geological samples reported, followed by the first in quartzite from Bastar Craton of India. The H2S2 was likely in situ enclosed by the host rubies rather than a reaction product that formed during the cooling of H2S and S8, suggesting sulfanes are stable at elevated temperatures (e.g., >600 °C). By comparing the lithologies and metamorphic conditions of these two sulfane-bearing cases (Bastar and Yuanjiang), it is suggested that amphibolite facies metamorphism of sedimentary sequence that deposited in a continental platform setting might favor the generation of sulfanes. Sulfanes may play an important role in the mobilization of Cr that is essential for ruby crystallization.
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Moore, J. M., and A. M. Reid. "A Pan-African zincian staurolite imprint on Namaqua quartz–gahnite–sillimanite assemblages." Mineralogical Magazine 53, no. 369 (March 1989): 63–70. http://dx.doi.org/10.1180/minmag.1989.053.369.06.
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AbstractQuartz-gahnite-sillimanite asssemblages are described from a supracrustal enclave at Kraaifontein, 45 km south-west of Springbok in the Namaqualand Metamorphic Complex, South Africa. The assemblage formed by prograde reaction in the granulite facies zone during the 1100 Ma Namaqua event, possibly as the result of desulphidation of sphalerite. Subsequent lower-amphibolite-facies retrogression occurred in close proximity to shear zones during an early Pan-African metamorphic event at 700 Ma. Zincian staurolite formed as overgrowths on gahnite in a hydration reaction involving the consumption of gahnite, quartz, and sillimanite. Compositional zoning to more zinc-rich rims in gahnite at Kraaifontein is unrelated to the retrograde reaction, but is interpreted as a result of changing conditions during the prograde Namaqua event.
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Merriman, R. J., and B. Roberts. "Low-grade metamorphism in the Scottish Southern Uplands terrane: deciphering the patterns of accretionary burial, shearing and cryptic aureoles." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 91, no. 3-4 (2000): 521–37. http://dx.doi.org/10.1017/s0263593300008373.
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ABSTRACTSystematic studies of metapelitic grade linked with the geological re-survey of the Southern Uplands have been used to generate a contoured metamorphic map currently covering nearly two-thirds of the terrane. These studies, based on approximately one pelite sample per 2·5 km2, have used XRD measurements of clay mineral reaction progress, particularly illite crystallinity, to delineate zones of diagenesis and low-grade metamorphism in the imbricated Ordovician and Silurian strata. The regional pattern revealed by metapelitic zonal sequences does not agree with earlier observations that grade increases across the strike, from SE to NW. Instead, the map shows considerable variations in metamorphic trends, including patterns of grade increasing from older into younger strata, indicative of accretionary burial. Other patterns identified include those generated by high strain rates in the Moniaive Shear Zone (MSZ), and by extensive low-temperature cryptic aureoles associated with late granitic intrusions. The present pattern is the result of uplift that generated normal movement on reactivated thrust faults and differential block movement on NW-trending faults.Regional metamorphic patterns were generated by burial and underplating in an accretionary thrust stack. Subduction was initiated in the early Caradoc and probably ceased in the early Wenlock. Metapelitic patterns suggest that two levels of accretion are exposed in the terrane. Strata accreted to the toe of the prism and stacked above the décollement zone are typically at late diagenetic grade. Underplated strata below the décollement are typically at anchizonal grades with moderate to well-developed slaty cleavage. Coherent thrust-bounded tracts of strata at both levels were rotated and buried to produce a syntectonic depth-controlled pattern of meta-morphism. Shear zone metamorphism at depths of 12 km or more was probably confined to the underplated lower level of the thrust stack, and Devonian granitic intrusions were also emplaced mainly within the underplated strata.
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Lasaga, A. C., and D. M. Rye. "Fluid flow and chemical reaction kinetics in metamorphic systems." American Journal of Science 293, no. 5 (May 1, 1993): 361–404. http://dx.doi.org/10.2475/ajs.293.5.361.
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Balashov, V. N., and B. W. D. Yardley. "Modeling metamorphic fluid flow with reaction-compaction-permeability feedbacks." American Journal of Science 298, no. 6 (June 1, 1998): 441–70. http://dx.doi.org/10.2475/ajs.298.6.441.
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Lasaga, Antonio C. "Fluid flow and chemical reaction kinetic in metamorphic systems." Chemical Geology 70, no. 1-2 (August 1988): 80. http://dx.doi.org/10.1016/0009-2541(88)90426-3.
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Stewart, E. M., Jay J. Ague, John M. Ferry, Craig M. Schiffries, Ren-Biao Tao, Terry T. Isson, and Noah J. Planavsky. "Carbonation and decarbonation reactions: Implications for planetary habitability." American Mineralogist 104, no. 10 (October 1, 2019): 1369–80. http://dx.doi.org/10.2138/am-2019-6884.
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Abstract The geologic carbon cycle plays a fundamental role in controlling Earth's climate and habitability. For billions of years, stabilizing feedbacks inherent in the cycle have maintained a surface environment that could sustain life. Carbonation/decarbonation reactions are the primary mechanisms for transferring carbon between the solid Earth and the ocean–atmosphere system. These processes can be broadly represented by the reaction: CaSiO3 (wollastonite) + CO2 (gas) ↔ CaCO3 (calcite) + SiO2 (quartz). This class of reactions is therefore critical to Earth's past and future habitability. Here, we summarize their significance as part of the Deep Carbon Obsevatory's “Earth in Five Reactions” project. In the forward direction, carbonation reactions like the one above describe silicate weathering and carbonate formation on Earth's surface. Recent work aims to resolve the balance between silicate weathering in terrestrial and marine settings both in the modern Earth system and through Earth's history. Rocks may also undergo carbonation reactions at high temperatures in the ultramafic mantle wedge of a subduction zone or during retrograde regional metamorphism. In the reverse direction, the reaction above represents various prograde metamorphic decarbonation processes that can occur in continental collisions, rift zones, subduction zones, and in aureoles around magmatic systems. We summarize the fluxes and uncertainties of major carbonation/decarbonation reactions and review the key feedback mechanisms that are likely to have stabilized atmospheric CO2 levels. Future work on planetary habitability and Earth's past and future climate will rely on an enhanced understanding of the long-term carbon cycle.
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Neuhoff, P. S., and D. K. Bird. "Partial dehydration of laumontite: thermodynamic constraints and petrogenetic implications." Mineralogical Magazine 65, no. 1 (February 2001): 59–70. http://dx.doi.org/10.1180/002646101550127.
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AbstractLaumontite is a common zeolite mineral indicative of low-grade metamorphism of lavas and volcaniclastic sediments. Stoichiometric laumontite (CaAl2Si4O12·4.5H2O) dehydrates in air at 298.15 K, 1 bar to leonhardite (CaAl2Si4O12·3.5H2O) via loss of water from the W1 crystallographic site. Consideration of reported X-ray diffraction and calorimetric data indicates that the standard molal volume and entropy for dehydration of laumontite to leonhardite + liquid water are ∼13 cc/mol and ∼8 cal/molK, respectively, at 298.15 K, 1 bar. Equilibrium between laumontite and leonhardite occurs at 70 to 80% relative humidity at 298.15 K, 1 bar, corresponding to a standard molal Gibbs energy and enthalpy of reaction of ∼170±40 and ∼2630±100 cal/mol, respectively. Calculated univariant equilibrium for this reaction is nearly linear from 46±3°C at 1 bar to 235±3°C at 5000 bar. Comparison of geological observations with these results suggests that laumontite forms as ‘leonhardite’ during metamorphism and diagenesis. Consideration of ‘leonhardite’, instead of laumontite, in low-grade metamorphic phase relations facilitates prediction of the relative stabilities of zeolites in natural and geologic systems, where calculated entropies of reaction incorrectly predict that assemblages bearing fully hydrated laumontite are stable at lower temperatures than the zeolites heulandite and stilbite.
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Brodie, K. H., and E. H. Rutter. "The role of transiently fine-grained reaction products in syntectonic metamorphism: natural and experimental examples." Canadian Journal of Earth Sciences 24, no. 3 (March 1, 1987): 556–64. http://dx.doi.org/10.1139/e87-054.
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It is proposed that one of the most important mechanisms of interrelationship between deformation and metamorphism is the facilitation of one of several grain-size-sensitive deformation mechanisms resulting from the formation of fine-grained products of a metamorphic reaction. During prograde metamorphism, such effects are likely to be transient, because grain coarsening and textural equilibration are likely in response to rising temperature conditions. Thus deformation mechanisms are often difficult to infer from such naturally deformed rocks.In localized shear zones exhibiting retrogressive metamorphism, evidence of enhanced deformability by such mechanisms is most likely to be preserved, because cooling conditions inhibit grain growth and both deformed and undeformed rocks are likely to be preserved.An experimental study has been made of the effects of deformation on serpentinite under conditions of progressive dehydration but with controlled pore pressure. A marked weakening (near-linear viscous rheology) at low strain rates was observed in association with the onset of dehydration to olivine. The enhancement of deformability is interpreted as due to the formation of thin, planar zones of ultrafine-grained but equiaxed (0.25 μm) olivine, which deform by diffusion-accommodated grain-boundary sliding. The experimental data therefore support the idea that a great deal of natural deformation during prograde metamorphism may occur in association with the transient existence of fine-grained reaction products, followed by grain growth and textural equilibration under essentially static conditions of relaxed stress.
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Mposkos, E., and M. Perraki. "Metamorphic record in metalherzolite pockets within the Virsini metaharzburgite from the Kechros HP metamorphic complex in Eastern Rhodope, Greece." Bulletin of the Geological Society of Greece 47, no. 1 (September 5, 2013): 397. http://dx.doi.org/10.12681/bgsg.11015.
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The Virsini antigorite serpentinite from the Kechros HP metamorphic complex in eastern Rhodope is a serpentinized harzburgite with pockets of lherzolitic composition. In the metalherzolites the mantle assemblage is Ol-1+Opx+Cpx-1+Cr-Spl. The metamorphic assemblage is Atg+Ol-2+Cpx-2+Ol-3+Chl+Tr+Cr-Mag. Antigorite and Cr-magnetite formed in an early stage of the metamorphic event. With increase in metamorphic grade olivine (Ol-2) was formed at the expense of antigorite and with further increase tremolite, olivine (Ol-3) and chlorite were formed at the expense of clinopyroxene and antigorite. P-T conditions of ≈1.7 GPa/≈570 oC are recorded in neighbouring eclogites. For the temperature of 570 oC the reaction Di+Atg→Ol+Tr+H2O occurs at pressure of ~1.2 GPa suggesting that the stability field of the mineral assemblage Atg+Ol+Tr in the metalherzolite is crossed during decompression.
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Kozhoukharova, Evgenia. "Metasomatic gabbroids – markers in the tectono-metamorphic evolution of the Eastern Rhodopes." Geologica Balcanica 29, no. 1-2 (June 30, 1999): 89–109. http://dx.doi.org/10.52321/geolbalc.29.1-2.89.
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Metasomatic gabbroids – markers in the tectonometamorphic evolution of the Eastern Rhodopes. Pegmatite-aplitic veins cut the serpentinites of Precambrian ophiolite association in Byala Rcka anticline. As a result, bimetasomalic reactions took place and dyke-like bodies of metasomatic rocks, similar to gabbros appear. The bodies are concordant with the schistosity of the serpentinites. The rocks have coarse-grained, spotted or slightly schistose structure. Their mineral composition is dominated by zoisite, epidote, and plagioclase ranging between albite-oligoclase and anorthite. Thc other common minerals are diopside, quartz, talc, chlorite, amphibole (actinolite and hastingsite), grossular, K-feldspar, titanite, dolomite. The texture is commonly pseudomorphos, corrosional, simplectitic, diablastic. The varying chemical composition of the metasomatites distincts them from the petrochemical group of the basic magmatic rocks. On the other hand, they differ in structure, texture, character of the deformation, and chemical and mineral composition from the earlier metamorphosed basic magmatic rocks which are components of the ophiolitic association. The metasomatic gabbroids are synmetamorphic, postdeformation reaction products related to the differentiates of later deep level migmatization of the Prarhodopian Supergroup. They were formed during the second metamorphic event of the second metamorphic cycle. Probably, the metasomatic gabbroids were synchronous to the gneiss-granites from the Orlov vruh peak. Temporally they follow the stage of syndeformation metamorphic recrystallisation and mark the beginning of the ultrabasic rock assimilation. The metasomatic gabbro ids are important markers in the evolution of the metamorphic basement of the Rhodope massif.
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Manby, G. M. "Mid-Palaeozoic metamorphism and polyphase deformation of the Forland Complex, Svalbard." Geological Magazine 123, no. 6 (November 1986): 651–63. http://dx.doi.org/10.1017/s001675680002416x.
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AbstractThe Forland Complex of Prins Karls Forland has been subjected to mid-Palaeozoic greenschist facies metamorphism and polyphase deformation. Metamorphism was initiated prior to D1 deformation and gave rise to a parallelism of stratigraphic and metamorphic reaction surfaces. D1 gave rise to imbricately thrust, southwest-directed fold nappes which have not noticeably disturbed the isograd surfaces. D2, interpreted as belonging to the mid-Cenozoic West Spitsbergen Orogeny (WSO) which was coaxial but not coplanar with D1, produced crenulation folds and pressure solution cleavages and some thrusting. D3 structures are related to the formation of the Prins Karls Forland–Forlandsundet–Oscar II horst and graben system which is a late expression of the WSO. The rejuvenation of the Prins Karls Forland horst along NNW–SSE faults, the large scale E–W flexures and ENE–WSW faults in the Forland Complex and Tertiary graben deposits are assigned to D3.
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Thomas, Harel, and Lalu P. Paudel. "Geothermobarometer based on coexisting garnet-orthopyroxene-plagioclase-quartz equilibria." Journal of Nepal Geological Society 51 (December 31, 2016): 1–9. http://dx.doi.org/10.3126/jngs.v51i0.24083.
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The garnet-orthopyroxene-plagolcase-quartz pairs are commonly found in the assemblages of basic granulites/charnockite and hence are suitable for estimating equilibrium temperature and pressure of most metamorphic rocks. The temperature based on garnet-orthopyroxene Fe-Mg exchange reaction and pressure based on net transfer reaction of garnet-orthopyroxeneplagioclase- quartz equilibria, mainly based on reactions, using the equation given by different workers. i. 1/2 Ferrosilite + 1/3 Pyrope = 1/2 Enstatite + 1/3 Almandine. ii. Ferrosilite + Anorthite = 2/3 Almandine + 1/3 Grossularite + Quartz iii. Enstatite + Anorthite = 2/3 Pyrope + 1/3 Grossularite + Quartz. The author developed software in visual basic with the executable code MPET3.EXE
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Lasaga, A. C., and D. M. Rye. "Erratum; Fluid flow and chemical reaction kinetics in metamorphic systems." American Journal of Science 293, no. 8 (October 1, 1993): 867–0. http://dx.doi.org/10.2475/ajs.293.8.867.
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Chapman, Timothy, Geoffrey L. Clarke, Sandra Piazolo, Victoria A. Robbins, and Patrick W. Trimby. "Grain‐scale dependency of metamorphic reaction on crystal plastic strain." Journal of Metamorphic Geology 37, no. 7 (March 19, 2019): 1021–36. http://dx.doi.org/10.1111/jmg.12473.
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Proyer, Alexander, Franco Rolfo, Daniele Castelli, and Roberto Compagnoni. "Diffusion-controlled metamorphic reaction textures in an ultrahigh-pressure impure calcite marble from Dabie Shan, China." European Journal of Mineralogy 26, no. 1 (March 31, 2014): 25–40. http://dx.doi.org/10.1127/0935-1221/2013/0025-2349.
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