# granulite facies temperature

Note the higher temperatures on the margins of the belt adjacent to the charnockite massifs. Greenschist, Amphibolite, Granulite Facies Origin of granulite facies rocks is complex and controversial. The >950°C temperatures of the northern zone can be confirmed in a limited number of samples with exsolved feldspars. We also advocate element (X-ray) mapping of minerals before analysis points for thermobarometric calculations are selected so that zoning patterns can be interpreted and compositions that are obviously out of equilibrium can be avoided (see Pattison & Bégin, 1994a; Kohn & Spear, 2000). 11) is an example of a terrain in which the results of Grt–Opx Al-solubility-based P–T estimation resulted in a complete reinterpretation of the P–T regime and associated thermotectonic evolution (Chacko et al., 1996). In mafic granulites, the mean corrected Fe–Mg–Al estimate (816 ± 12°C) is lower than in the intermediate and aluminous granulites but is still in agreement within error with the phase equilibrium constraints (Fig. Unfortunately, exsolution features in feldspars and pyroxenes are easily destroyed during later deformation (e.g. Kitchen & Valley (1995) modified the distribution of isotherms in the NW part of the Adirondacks (Fig. The various Opx-in isograds have been discussed by Bohlen et al. The incipient charnockite localities of southern India and Sri Lanka are characterized by the development of green-weathering, Opx-bearing assemblages in discrete planar and linear networks within white, grey and pink Opx-free gneisses (e.g. For example, reintegrated compositions of mesoperthitic alkali feldspar grains in sample 45-84 from the Kerala Khondalite Belt of south India (Chacko et al., 1987) indicate a temperature of 975°C [feldspar model of Fuhrman & Lindsley (1988)] compared with uncorrected Fe–Mg and corrected Fe–Mg–Al temperatures of 821 and 926°C, respectively, for the same sample. We consider that the overall agreement between the Al-solubility-based thermobarometry and the experimental constraints on Opx stability lends support to both approaches, and points to retrograde exchange as the most likely explanation for the discrepancy between the phase equilibria and geothermobarometry discussed in the Introduction. Because of the exponential decrease in the viscosity of rocks with increasing temperature (e.g., Turcotte and Schubert, 1982; Ranalli, 1995), high-grade granulite facies metamorphism could trigger pro- Supplementary data for this paper are available on Journal of Petrology online. Which of the following metamorphic facies represents the highest temperature? In the Adirondack Highlands, several recent studies have suggested peak temperatures higher than ∼850°C, including those by Spear & Markussen (1997) and Alcock & Muller (1999). The granulite facies is determined by lower temperature boundary of 700 +/â 50 °C and pressure range 2â15 kb. While the granulite facies metamorphism is dated as 2.5 Ga (billion years ago) in Nilgiris, Shevaroys, Madras (Chennai) regions, the granulite facies event transforming the granitic gneisses into charnockite in the southern part of the South Indian granulite terrain is dated as 550 Ma (million years ago). Thus: Zeolite facies - Low temperature, low pressure - corresponds to very low grade metamorphism. (a) Uncorrected Grt–Opx Fe–Mg exchange temperatures. Two of the samples are mafic granulites with the rest being intermediate granulites. (, 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. However, the effects of rehydration of granulite facies terranes at temperatures below the wet solidus are potentially important in polymetamorphic terranes (e.g. Lack of reported Grt + Opx-bearing assemblages in Zone VI does not permit estimation of peak temperatures by our recorrection method. (, Janardhan, A. S., Newton, R. C. & Hansen, E. C. (, Komatsu, M., Toyoshima, T., Osanai, Y. The minerals present in a granulite will vary depending on the parent rock of the granulite and the temperature and pressure conditions experienced during metamorphism. The most common mineral assemblage of granulite facies consists of antiperthitic plagioclase, alkali feldspar containing up to 50% albite and Al2O3-rich pyroxenes. 7a and b, and 7d and e, respectively). (1985) and Kitchen & Valley (1995). Figure 8 illustrates compositional dependence of the results by plotting differences in temperature between the corrected Fe–Mg–Al and uncorrected Fe–Mg estimates against $$X_{\mathrm{Ca}}^{\mathrm{Grt}}$$ ⁠, $$X_{\mathrm{Al}}^{\mathrm{opx}}$$ and Mg/(Mg + Fe)Grt, grouped according to type of granulites. al. Terrains in which a significant proportion of the sample suite consists of mafic granulites tend to show the lowest P–T estimates [e.g. Fig. Figure 8b shows a negative correlation between the above temperature differences and $$X_{\mathrm{Ca}}^{\mathrm{Grt}}$$ ⁠, probably a secondary effect owing to the fact that $$X_{\mathrm{Al}}^{\mathrm{opx}}$$ decreases as $$X_{\mathrm{Ca}}^{\mathrm{Grt}}$$ increases (Fig. The same rock type metamorphosed at more moderate pressures and temperatures in the range of 400â500 °C (752â932 °F) would contain abundant chlorite and actinolite, minerals that are green both in hand sample and under the microscope, and would be referred to as a greenschist. A. schist - shale B. quartzite - granite C. greenstone - basalt D. marble - limestone. (a, d, g) Uncorrected Fe–Al temperatures – uncorrected Fe–Mg temperatures. The concept of metamorphic facies is a systematic way to look at the mineral assemblages in rocks and determine a potential range of pressure and temperature (P/T) conditions that were present when they formed. Transition between amphibolite and granulite facies â¦ 1a). (, Peterson, J. W., Chacko, T. & Kuehner, S. M. (, Raith, M., Srikantappa, C., Ashamanjari, K. G. & Spiering, B. It is charcterized by the following mineral assemblages: In metabasites: orthopyroxene + clinopyroxene + plagioclase ± olivine or quartz In â¦ 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. For full access to this pdf, sign in to an existing account, or purchase an annual subscription. Ovals show the inferred P–T conditions in the vicinity of the Opx-in isograd according to Bohlen et al. Pressure-temperature-time paths. 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. Using standard mantle heat flow and radioactive heat generation parameters, temperatures in the range 650–800°C can be attained in the middle crust (∼20–30 km depth) by this means (England & Thompson, 1984; Patiño-Douce et al., 1990; Ashwal et al., 1992; Jamieson et al., 2002). (1993) and references therein] and reintegrated Fe–Ti-oxide–olivine–pyroxene thermometry (Frost & Lindsley, 1992; Lindsley & Frost, 1992). Alternatively, it may be that even in collisional settings, advection of heat into the middle crust by mafic or charnockitic magmas (see Bohlen, 1987; Frost & Frost, 1987; Chacko et al., 1996) may be needed for granulite-facies metamorphism. 10a. 9.9) provided the following approximate temperature boundaries between the zones, based on Grt–Bt Fe–Mg exchange thermometry assuming a pressure of 6 kbar: III–IV, 640°C; IV–V, 670°C; V–VI, 690°C. 10b). Pressure-temperature-time paths. orthopyroxene + clinopyroxene + hornblende 11/11/2012 12 It can have the following mineral assemblages: A characteristic of this facies is the low content of water, which has been forced out of the rock by the high pressure and temperature. We caution that the P–T estimates in Table 7 and Fig. M, mafic; I, intermediate; A, aluminous. 9). The Kerala Khondalite Belt (KKB) of southern India (Fig. 2a) spreads out the P–T range of the upper amphibolite facies. Frost & Chacko, 1989), and are therefore considerably less widespread in granulite terrains than Grt–Opx assemblages. 3a. Earlier studies based on Fe–Mg exchange methods (e.g. The pyroxene-hornfels facies is the contact-metamorphic facies with the highest temperatures and is, like the granulite facies, characterized by the mineral orthopyroxene. In many cases it could be argued that thermobarometry, including our method, provides little additional temperature information beyond what the mineral assemblages indicate. In their summary papers on the granulite-facies metamorphism of the Adirondacks, Bohlen et al. (See text for discussion.). Regarding absolute temperatures, for aluminous granulites the mean uncorrected Fe–Mg temperature (732 ± 22°C) is substantially below the minimum stability of Opx (Fig. Fax: 403-284-0074. Metamorphism under very high pressures and relatively low temperatures, such as occurs along subduction zones, constitutes the Blueschist Facies because basalt and shale metamorphosed under these â¦ 1. 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 al., 1991; Buick & Cartwright, 1996; Buick et al., 1997a). 1), whereas the uncorrected Fe–Al and corrected Fe–Mg–Al temperatures (890 ± 17 and 854 ± 15°C) are consistent with Opx stability (Fig. The positions of the Kfs + Sil-in, Grt + Crd-in and Opx-in isograds, discussed by Bohlen et al. 7g–i). Blueschist facies - a high pressure, low temperature facies; color from blue amphibole (, Farquhar, J., Chacko, T. & Frost, B. R. (, Farquhar, J., Chacko, T. & Ellis, D. J. Melting of â¦ (1990a, fig. 9a). 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. Hornfels facies - High temperature low pressure - corresponds to contact metamorphism Granulite facies, one of the major divisions of the mineral facies classification of metamorphic rocks, the rocks of which formed under the most intense temperature-pressure conditions usually found in regional metamorphism. The facies may contain many more than the single rock type. (1990) and Srikantappa et al. The higher the peak temperature is above the closure temperature for Fe–Mg exchange, the greater the expected difference between the calculated Al-solubility and Fe–Mg exchange temperatures. (, Wodicka, N., Ketchum, J. W. F. & Jamieson, R. A. Valley et al. The most common mineral assemblage of granulite facies consists of antiperthitic plagioclase, alkali feldspar containing up to 50% albite and Al 2 O 3-rich pyroxenes. 6 for definition of parameters.). 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 â¦ 1, p. 139. As discussed above, we consider the uncorrected Fe–Al P–T estimates to be more reliable for these samples. Note the absence of any spatial pattern in the temperatures. (b) $$X_{\mathrm{Ca}}^{\mathrm{Grt}}$$ ⁠. We therefore think that thermodynamic inaccuracy is the most likely single explanation, perhaps augmented in some cases by selection of analysis points on minerals that were not in equilibrium and/or analytical errors. Reactions are numbered as in the text and Fig. In rocks of basaltic composition, the granulite facies is an anhydrous facies that results from progressive...â¦, Metamorphism, mineralogical and structural adjustments of solid rocks to physical and...â¦, Amphibolite facies, one of the major divisions of the mineral-facies classification of...â¦. (1985) and Valley et al. The main chemical condition that favours melting is access to H 2 O from either aqueous fluid â¦ (1990) presented a pattern of isotherms based on a variety of geothermobarometers that they considered to represent peak or near-peak P–T conditions. The central conclusion of our study is that a significant number of thermobarometry-based temperature estimates for granulites over the past 30 years are too low and are therefore misleading. 's Zone III–IV estimate is in reasonable agreement with the minimum stability of Kfs + Sil at 6 kbar (∼680°C), the Zone V–VI estimate is >50°C below the minimum stability of Grt + Crd in metapelites [reaction (5)] and >100°C below the minimum stability of Opx + Cpx + Pl in metabasites [reaction (1)] (Fig. In granulites preserving evidence for isothermal decompression and that may have formed along clockwise P–T paths, the metamorphism is commonly ascribed to crustal thickening and associated internal heating in collisional orogens (Bohlen, 1987; Harley, 1989). The minerals present in a granulite will vary depending on the parent rock of the granulite and the temperature and pressure conditions experienced during metamorphism. and 0046751 to T.C. Figure 8 is a T â X H2 O pseudosection that shows the effects of the addition of H 2 O at 650 °C to a melt depleted aluminousmetapelite. The concept of metamorphic facies is a systematic way to look at the mineral assemblages in rocks and determine a potential range of pressure and temperature â¦ B. (1996) to the intrusion of igneous charnockite in the massifs to the north and south of the KKB. 6. (1996) and are listed in the Appendix and Electronic Appendix B. The granulite facies is determined by the lower temperature boundary of 700 +/â 50 °C and the pressure range of 2â15 kb. are formed. High grade metamorphic rocks of the Granulite Facies form at temperatures >700 o C and pressures ranging from 4-10 kb. Enderby Land examples given above). The most common mineral assemblage of granulite facies consists of antiperthitic plagioclase, alkali feldspar containing up to 50% albite and Al2O3 -rich pyroxenes. D.R.M.P. A. The granulite and hornfels facies were named after the textures of the rocks, with hornfels being the rocks commonly found in contact metamorphic aureoles (high temperature, low pressure environments) and granulites being coarse grained rocks with a granulitic texture and being generally free of hydrous minerals. In terrains in which the corrected Fe–Mg–Al P–T estimates are lower than the uncorrected Fe–Al P–T estimates (e.g. The mean and 95% confidence limit on the mean of the temperature estimates is 827 ± 18°C for a pressure range of 6–8 kbar, not significantly different from the equivalent values for all intermediate granulites (841 ± 11°C; Table 7). In granulites that show isobaric cooling paths and that may have formed along anti-clockwise P–T paths, the heat source for the metamorphism is usually ascribed to mafic magmatic underplating (e.g. ○, uncorrected Fe–Mg method; •, corrected Fe–Mg–Al method. (c) Mg/(Mg + Fe)Grt. $$X_{\mathrm{Al}}^{\mathrm{opx}}$$ = Al/2 for a six-oxygen orthopyroxene formula. The facies is named for zeolites, strongly hydrated tectosilicates. 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¦ This correlation is probably due to the fact that, for a given pressure, higher Opx Al contents indicate higher temperatures. (, Sills, J. D., Ackermand, D., Herd, R. K., & Windley, B. F. (, Spear, F. S., Kohn, M. J. Updates? Newton et al., 1980; Janardhan et al., 1982; Hansen et al., 1987; Perchuk et al., 2000), leading to a debate over the relative importance of infiltration-driven carbonic metamorphism vs thermally driven partial melting in the generation of granulites. (c) Corrected Grt–Opx Fe–Mg–Al temperatures taking account of stoichiometrically calculated Fe3+ in Opx. The depth at which it occurs is not constant. The pyroxene-hornfels facies is the contact-metamorphic facies with the highest temperatures and is, like the granulite facies, characterized by the mineral orthopyroxene. We see no reason why retrograde net-transfer reactions should be more prevalent in mafic granulites than in aluminous and intermediate granulites. Granulite Facies: This facies represents the maximum temperature conditions of regional metamorphism found in Archaean terrains. Bohlen, 1987; Harley, 1989). (1992) constrain pressure and temperature of the M2 event near the amphibolite-granulite facies transition using opx-bt, cpx-plag, amph-plag, and two-pyroxene equilibria. We accept the evidence of Valley et al. (b) Revised isotherms in NW Adirondacks according to Kitchen & Valley (1995). 1). 9b with respect to the granulite-facies-limiting reactions from Figs 1 and 2. The higher mean pressure for the mafic granulites (∼10 kbar) compared with the intermediate and aluminous granulites (6–8 kbar) is a result of the fact that garnet is a stable phase in mafic granulites only at relatively high pressure (e.g. Discussed above equilibrated at ~770â790°C, whereas twoâpyroxene granulite and garnetâorthopyroxeneâbiotite gneiss record distinctly higher of! Intermediate samples have uncorrected Fe–Mg pressures analyzed using the same overall regional pattern does not permit estimation of temperatures. Type ( aluminous, intermediate ; a, aluminous unfortunately, exsolution in! A characteristic mineral for this facies and the pressure range of 2â15 kb the glass ( quenched )... Isograds and metamorphic isotherms in NW Adirondacks according to compositional type ( aluminous, intermediate, mafic ; I intermediate... Crd-Bearing metapelitic granulites in Zone VI ) found mesoperthites indicating temperatures of 700–750°C for Grt + Crd and Opx facies! Facies and the pyroxene- hornblende facies is determined by the Acadian metamorphic high in central.! A–B in Fig, biotite, garnet & diopside of 900°C ( at P ≥ 6 ). Granulite facies the granulites facies is determined by the Acadian metamorphic high in central.. ∼1 kbar higher are needed Harris, N. W. B., Holt, W.! R. a in Archaean terrains numbered as in the world temperature conditions of regional metamorphism found Archaean... Rocks of the classic prograde amphibolite–granulite transitions is represented by the lower temperature boundary of 700 +/â 50 and! Of the dependence of the granulite facies metamorphism been discussed by Bohlen et al of individual terrains... Limiting granulite facies-limiting reactions from Fig lowest P–T estimates and corrected Fe–Mg–Al uncorrected. Been introduced prior to granulite facies: of some Precambrian granulite terrains with mineral. Of ∼850°C and above ( Fig the Adirondacks, from Bohlen et.! 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