A characteristic mineral for this facies and the pyroxene- hornblende facies is orthopyroxene. (1990) presented a pattern of isotherms based on a variety of geothermobarometers that they considered to represent peak or near-peak P–T conditions. (1990a, fig. The most common mineral assemblage of granulite facies consists of antiperthitic plagioclase, alkali feldspar containing up to 50% albite and Al2O3-rich pyroxenes. Greenschist, Amphibolite, Granulite Facies Origin of granulite facies rocks is complex and controversial. @article{osti_6596880, title = {Pressure-temperature conditions in granulite facies rocks of the northern Canadian Shield, Arctic Canada}, author = {Frisch, T}, abstractNote = {The northernmost part of the Churchill Structural Province of the Canadian Shield, underlying 60,000 km/sup 2/ of southeastern Ellesmere Island, Coburg Island and eastern Devon Island, consists of granulite facies â¦ Unfortunately, exsolution features in feldspars and pyroxenes are easily destroyed during later deformation (e.g. (1993) and references therein] and reintegrated Fe–Ti-oxide–olivine–pyroxene thermometry (Frost & Lindsley, 1992; Lindsley & Frost, 1992). Even with X-ray maps, non-central sectioning of Opx grains is an important factor to consider, given the generally small core–rim variation in Al content of individual Opx grains (typically ∼1–2 wt %) and the strong temperature dependence on these small changes. Read More on This Topic metamorphic rock: Granulite facies Thus mineralization at Griffinâs Find must have been introduced prior to granulite facies metamorphism. (, Riciputi, L. R., Valley, J. W. & McGregor, V. R. (, Santosh, M., Harris, N. B. W., Jackson, D. H. & Mattey, D. P. (, Schumacher, J. C., Hollocher, K. T., Robinson, P. & Tracy, R. J. Granulite facies. (1992) dataset (see Appendix). In this paper we describe late-M 2 channelled retrogression of Mg-rich marbles, calc-silicate rocks and metapsammites from a granulite-facies portion of the Upper Calcsilicate Unit (Figs 1 and 2a), where peak-M 2 temperatures were probably â¼750°C (Dirks et â¦ (1996) and are listed in the Appendix and Electronic Appendix B. The results obtained with our Grt–Opx Al-solubility method are comparable with those obtained with other thermobarometry methods based on refractory cation systems, such as reintegrated feldspar thermometry [Kroll et al. Granulite facies Granulite facies (Fig.1) was introduced by Eskola (1939) to define the highest grade of regional metamorphic rocks that contain pyroxene in place of normal hydrous ferromagnesian minerals. Spr, Opx + Sil, Spl + Qtz). According to TURNER and VERHOOGEN, the granulite facies comprises temperatures â¦ e. Eclogite Facies: Updates? & Wall, V. J. (c) Corrected Grt–Opx Fe–Mg–Al temperatures taking account of stoichiometrically calculated Fe3+ in Opx. (a) $$X_{\mathrm{Ca}}^{\mathrm{Grt}}$$ vs $$X_{\mathrm{Al}}^{\mathrm{opx}}$$ ⁠. Terrains in which a significant proportion of the sample suite consists of mafic granulites tend to show the lowest P–T estimates [e.g. The zeolite facies is the metamorphic facies with the lowest metamorphic grade. D.R.M.P. ○, uncorrected Fe–Mg estimates. Temperatures of 650â1,100 Â°C (1,200â2,000 Â°F) and pressures of 3 to 10 kilobars (1 kilobar equals about 15,000 pounds per square inch) may be reached. There is general agreement, however, on two points 1) Granulites represent unusually hot conditions â¢ Temperatures > 700 o C (geothermometry has yielded some very high temperatures, even in excess of 1000 o C) Geochronology and phase equilibria modelling of ultra-high temperature sapphirine + quartz-bearing granulite at Usilampatti, Madurai Block, Southern India. They do correspond to different plate tectonic settings. The gneisses did not undergo fluid-absent melting until temperatures in excess of 900°C (at P ≥ 6 kbar) were reached. The positions of the Kfs + Sil-in, Grt + Crd-in and Opx-in isograds, discussed by Bohlen et al. (, Xishan, L., Wei, J., Shuxun, L. & Xuechun, X. Figure 10c shows the range of P–T conditions along transect A–B in Fig. As metamorphic rocks change under heat and pressure, their ingredients recombine into new minerals that are suited to the conditions. (, Grover, T. W., Pattison, D. R. M., MacNicol, V. J. Figures 6 and 8a and b show that these results correspond to the generally low $$X_{\mathrm{Al}}^{\mathrm{opx}}$$ in the more Ca-rich mafic samples. The granulite facies is determined by the lower temperature boundary of 700 +/â 50 °C and the pressure range of 2â15 kb. Granulite facies The granulites facies is determined by the lower temperature boundary of 700 +/â 50 °C and the pressure range of 2â15 kb. In their summary papers on the granulite-facies metamorphism of the Adirondacks, Bohlen et al. Where our method of thermobarometry may be most useful is for bulk compositions that maintain the same mineral assemblage over large ranges of elevated P and T, such as in the 800–1000°C range for intermediate and mafic bulk compositions (e.g. A. schist - shale B. quartzite - granite C. greenstone - basalt D. marble - limestone. 16, with values above the gap largely restricted to mafic mineral assemblages containing either or both of the calcic mafic phases Hbl and Cpx, and values below the gap restricted to intermediate and aluminous mineral assemblages lacking these phases. This research was supported by NSERC Discovery Grants 0037233 to D.R.M.P. Even though low-aH2O fluid infiltration appears to have triggered the production of Opx in these localities, the amount by which aH2O in the fluid was lower than ambient values in the host gneisses might have been rather modest if the host gneisses were close to a temperature where they would produce Opx by closed-system dehydration melting. 10b). This scatter is difficult to attribute to any single factor, arising from some combination of: differences in peak P–T conditions of the samples; varying degrees of retrograde Fe–Mg exchange; retrograde net-transfer reactions; mineral compositions that may not have been in equilibrium before late Fe–Mg exchange; analytical issues relating to the relatively small concentrations of Al in Opx; and possible deficiencies in the thermodynamic modelling of Al in Opx, especially at low concentrations (see section below on mafic granulites). (, Sills, J. D., Ackermand, D., Herd, R. K., & Windley, B. F. (, Spear, F. S., Kohn, M. J. 7g–i). It is charcterized by the following mineral assemblages: In metabasites: orthopyroxene + clinopyroxene + plagioclase ± olivine or quartz In â¦ & Ellis, D. J. Adirondack Highlands), we have plotted the corrected Fe–Mg–Al P–T estimates to maintain consistency, even though we favour the higher estimates. Schumacher et al. 1. Geological Journal, Vol. (1985), are shown on the map in Fig. Recalculation of the same samples using RCLC reveals a sharp contrast between a lower P–T (∼800–850°C, 6 kbar) central zone with numerous incipient charnockite localities, a northern marginal zone where extreme P–T conditions (>950°C, 9–10 kbar) are found, and a southern marginal zone where less extreme but still elevated temperatures of 850–950°C are found (Fig. We see no reason why retrograde net-transfer reactions should be more prevalent in mafic granulites than in aluminous and intermediate granulites. of some Precambrian granulite terrains in hot continental crust characterized by extremely low dP/dT gradients. (1985). & Sheraton, J. W. (, Harris, N. W. B., Holt, R. W. & Drury, S. A. (a, d, g) Uncorrected Fe–Al temperatures – uncorrected Fe–Mg temperatures. (, Oxford University Press is a department of the University of Oxford. The scatter of P–T results using our method calls into question the reliability of any individual P–T estimate, and suggests that to be confident of a P–T estimate for a given area, many samples need to be analyzed. *Srikantappa et al. Reactions are numbered as in the text and Fig. 7 show considerable scatter. Mineral assemblages and thermobarometry indicate granulite assemblages equilibrate over a broad range of temperatures generally from about 650 to 900°C but to as much as 1050°C and pressures of generally 5 kbar to as much as 12 kbar, or depths of 20-45 km (Harley, 1989, 1998). (1990) dataset (see Appendix). High grade metamorphic rocks of the Granulite Facies form at temperatures >700 o C and pressures ranging from 4-10 kb. Transition between amphibolite and granulite facies â¦ About 10% of the aluminous and intermediate samples have uncorrected Fe–Mg temperatures that are higher than the uncorrected Fe–Al temperatures. As in all metamorphic rocks, the composition of the parent rock exerts a strong control on the particular mineralogy that is observed. The various Opx-in isograds have been discussed by Bohlen et al. Assuming that Fe–Mg always closes at lower temperature than Al, the most likely explanations are: (1) Fe–Mg diffusion is slower in Ca-rich garnets than in Ca-poor garnets, resulting in a smaller temperature gap between closure of Fe–Mg and Al; (2) the rocks experienced retrograde net-transfer reactions (Spear & Florence, 1992), leading to spuriously high Fe–Mg temperatures; (3) the parts of the Grt and Opx analyzed were not in equilibrium before late Fe–Mg exchange; (4) some of the analytical data for the generally low Al concentrations in Opx in these rocks are in error (too low); (5) the thermodynamic model for Al solubility in Opx loses accuracy at low $$\mathit{X}_{\mathrm{Al}}^{\mathrm{opx}}$$ ⁠. An independent indication of higher peak temperatures in the Adirondack Lowlands in the vicinity of the isograds comes from a recalculated Fe–Mg–Al solubility temperature of 820°C for the one Grt + Opx-bearing sample (RS-34) reported by Edwards & Essene (1988). (1990) against widespread fluid infiltration and therefore favour an explanation involving P–T underestimation as a result of either retrograde exchange from peak conditions or the effects of a cryptic, lower-grade overprint. Mean corrected Fe–Mg–Al temperatures from the Enderby Land granulites (∼950°C; see above) are similar to temperatures calculated from reintegrated mesoperthitic feldspars [950–1050°C, using the analyses of Ellis et al. 3) is 45 ± 9 and 34 ± 4°C for aluminous and intermediate granulites, respectively (see Table 1). and 0046751 to T.C. (1992)], and may be unreliable for the reasons discussed above. As discussed above, we consider the uncorrected Fe–Al P–T estimates to be more reliable for these samples. Corrected Fe–Mg–Al: point C in Fig. 9). If, however, mid-crustal granulites typically form at temperatures of ∼850°C and above (Fig. †Raith et al. Supplementary data for this paper are available on Journal of Petrology online. (, Valley, J. W., Bohlen, S. R., Essene, E. J. In contrast, the mean uncorrected Fe–Mg exchange estimate (793 ± 13°C) is considerably higher than in the intermediate and aluminous granulites. 1), whereas the uncorrected Fe–Al and corrected Fe–Mg–Al temperatures (890 ± 17 and 854 ± 15°C) are consistent with Opx stability (Fig. Textures in mineralized microcline-rich gneiss imply original mineralization temperatures within the greenschist facies, similar to the conditions of formation for other orogenic gold deposits. (, Janardhan, A. S., Newton, R. C. & Hansen, E. C. (, Komatsu, M., Toyoshima, T., Osanai, Y. McFarlane et al., 2003). Thus mineralization at Griffinâs Find must have been introduced prior to granulite facies metamorphism. 9b is to show that the corrected Fe–Mg–Al P–T estimates largely fall in or close to the granulite-facies stability field, in contrast to the uncorrected Fe–Mg P–T estimates which typically fall well below the granulite-facies stability field. & Worley, B. The temperature and pressure differences are strongly correlated because of the dependence of the pressure estimate on the temperature. Opx-In isograds have been introduced prior to granulite facies metamorphism points C and 5 to 11 kilobars pressure the of. & Frost, Simon Harley and Frank Spear for their reviews of samples with exsolved feldspars of metamorphism! Pressure range of 2â15 kb annual subscription or purchase an annual subscription to revise the article net-transfer should. Range of 2â15 kb 50 % albite and Al2O3-rich pyroxenes is determined the! 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