Experimental early crystallization of K-feldspar in granitic systems. Implications on the origin of magmatic fabrics in granitic rocks


  • J. DÍAZ-ALVARADO Departamento de Geología. Universidad de Atacama Copayapu 485, Copiapó, Chile.




K-feldspar megacrysts, Experimental petrology, Granodiorites, Magmatic fabrics, Spanish Central System batholith.


One of the most outstanding characteristics of some granodioritic to granitic rocks is the presence of K-feldspar megacrysts. For instance, granodiorites and monzogranites of the Spanish Central System batholith present variable amounts of large (up to 10cm in length) euhedral K-feldspar crystals. The porphyritic textures, the euhedral shape, the alignment of plagioclase and biotite inclusions and the magmatic fabrics point to a magmatic origin for these megacrysts.

This work presents a phase equilibria study in a high-K2O granodioritic system. A series of experiments were conducted with a granodioritic composition (GEMbiot) to study the crystallization sequence at the emplacement conditions in the Gredos massif, i.e. 4 H2O wt.% and 0.4GPa. Experimental results show that orthopiroxene is the liquidus phase at 1010ºC, which reacts with the H2O-rich melt to stabilize biotite between 980 and 940ºC. Plagioclase crystallizes at around 910ºC, and K-feldspar crystallizes in the matrix between 750 and 700ºC when the crystal fraction is around 0.5. However, at 850 ºC, a pelite-doped experiment shows euhedral K-feldspar (≈5vol%) in both the reactive xenolith domain together with cordierite and the granodioritic domain, where the K2O wt.% rise from 4.5 in the normal experiment to 5.9 in the doped experiment. These results suggest that the bulk-assimilation process promotes the bulk and heterogeneous K2O enrichment in a huge granodioritic magma volume, which triggers an early crystallization of K-feldspar megacrysts. Because of this early crystallization of the megacrysts, the magmatic foliations defined by K-feldspar megacrysts are formed during and after the emplacement processes and are highly influenced by tectonic kinematics.


Boettcher, A.L., Wyllie, P.J., 1969. Phase relationships in the system NaAlSiO4-SiO2-H2O to 35 kilobars pressure. American Journal of Science, 267, 875-909.

Bogaerts, M., Scaillet, B., Vander Auwera, J., 2006. Phase equilibria of the Lyngdal Granodiorite (Norway): Implications for the origin of meta-aluminous ferroan granitoids. Journal of Petrology, 47(12), 2405-2431.

Burnham, C.W., 1979. The importance of volatile constituents. In: Yoder, H.S.J. (ed.). The Evolution of the Igneous Rocks.

Princeton, New Jersey, Princeton University Press, 602pp.

Burnham, C.W., Wayne, C., Jahns, R.H., 1962. A method for determining the solubility of water in silicate melts. American Journal of Science, 260, 721-745.

Capdevila, R., Corretgé, L.G., Floor, P., 1973. Les granitoides varisques de la Mesete Iberique. Bulletin de la Société Géologique de France, 7-15, 209-228.

Castro, A., 2001. Plagioclase morphologies in assimilation experiments. Implications for disequilibrium melting in the generation of granodiorite rocks. Mineralogy and Petrology, 71, 31-49.

Castro, A., 2013. Tonalite-granodiorite suites as cotectic systems: a review of experimental studies with applications to granitoid petrogenesis. Earth Science Reviews, 124, 68-95.

Castro, A., Patiño Douce, A., Corretgé, L.G., de la Rosa, J.D., El-Biad, M., El-Hmidi, H., 1999. Origin of peraluminous granites and granodiorites, Iberian Massif, Spain: an experimental test of granite petrogenesis. Contributions to Mineralogy and Petrology, 135, 255-276.

Castro, A., Corretgé, L.G., de la Rosa, J., Enrique, P., Martínez, F.J., Pascual, E., Lago, M., Arranz, E., Galé, C., Fernández, C., Donaire, T., López, S., 2002. Paleozoic magmatism. In: Gibbons, W., Moreno, M.T. (eds.). The Geology of Spain. Geological Society, London, 117-153.

Castro, A., García Casco, A., Fernández, C., Corretgé, L.G., Moreno-Ventas, I., Gerya, T., Löw, I., 2009. Ordovician ferrosilicic magmas: experimental evidence for ultrahigh temperatures affecting a metagreywacke source. Gondwana Research, 16, 622-632.

Castro, A., Gerya, T., García-Casco, A., Fernández, C., DíazAlvarado, J., Moreno-Ventas, I., Löw, I., 2010. Melting relations of MORB-sediment mélanges in underplated mantle wedge plumes; implications for the origin of Cordilleran-type batholiths. Journal of Petrology, 51, 1267-1295.

Díaz Alvarado, J., Castro, A., Fernández, C., Moreno-Ventas, I., 2011. Assessing bulk assimilation in cordierite-bearing granitoids from the central system batholith, Spain; experimental, geochemical and geochronological constraints. Journal of Petrology, 52, 223-256.

Díaz Alvarado, J., Fernández, C., Díaz Azpiroz, M., Castro, A., Moreno-Ventas, I., 2012. Fabric evidence for granodiorite emplacement with extensional shear zones in the Variscan Gredos massif (Spanish Central System). Journal of Structural Geology, 42, 74-90.

Díaz-Alvarado, J., Castro, A., Fernández, C., Moreno-Ventas, I., 2013. SHRIMP U-Pb zircon geochronology and thermal modeling of multilayer granitoid intrusions. Implications for the building and thermal evolution of the central system batholith, Iberian Massif, Spain. Lithos, 175-176, 104-123.

Díaz-Alvarado, J., Fernández, C., Chichorro, M., Castro, A., Pereira, M.F., 2016. Tracing the Cambro-Ordovician ferrosilicic to calc-alkaline magmatic association in Iberia by in situ U-Pb SHRIMP zircon geochronology (Gredos massif, Spanish Central System batholith). Tectonophysics, 681, 95-110.

Farina, F., Dini, A., Innocenti, F., Rocchi, S., Westerman, D.S., 2010. Rapid incremental assembly of the Monte Capanne pluton (Elba Island, Tuscany) by downward stacking of magma sheets. Geological Society of America Bulletin, 122, 1463-1479.

Farina, F., Stevens, G., Villaros, A., 2012. Multi-batch, incremental assembly of a dynamic magma chamber: the case of the Peninsula pluton granite (Cape Granite Suite, South Africa). Mineralogy and Petrology, 106(3), 193-216.

Fernández, C., Becchio, R., Castro, A., Viramonte, J.M., MorenoVentas, I., Corretgé, L.G., 2008. Massive generation of atypical ferrosilicic magmas along the Gondwana active margin: implications for cold plumes and back-arc magma generation. Gondwana Research, 14, 451-473.

Frost, B.R., Barnes, C.G., Collins, W.J., Arculus, R.J., Ellis, D.J., Frost, C.D., 2001. A geochemical classification for granitic rocks. Journal of Petrology, 42, 2033-2048.

García-Arias, M., Stevens, G., 2017. Phase equilibrium modelling of granite magma petrogenesis: B. An evaluation of the magma compositions that result from fractional crystallization. Lithos, 277, 109-130.

Glazner, A.F., Johnson, B.R., 2013. Late crystallization of K-feldspar and the paradox of megacrystic granites. Contributions to Mineralogy and Petrology, 166, 777-799.

Holtz, F., Becker, A., Freise, M., Johannes, W., 2001. The water-undersaturated and dry Qz-Ab-Or system revisited. Experimental results at very low water activities and geological implications. Contributions to Mineralogy and Petrology, 141, 347-357.

James, R.S., Hamilton, D.L., 1969. Phase relations in the system NaAlSi3O8 - KAlSi3O8 - CaAlSi2O8-SiO2 at 1kbar water

pressure. Contributions to Mineralogy and Petrology, 21, 111-141.

Johannes, W., Holtz, F., 1996. Petrogenesis and Experimental Petrology of Granitic Rocks. Springer, Berlin Heidelberg, 335pp.

Johannes W., Chipman, D.W., F, H.J., Bell, P.M., Mao, H.K., Newton, R.C., Boettcher, A.L., Seifert, F., 1971. An interlaboratory comparison of piston-cylinder pressure calibration using the albite-breakdown reaction. Contributions to Mineralogy and Petrology, 32, 24-38

Johnson, M.C., Rutherford, M.J., 1989. Experimentally determined conditions in the Fish Canyon Tuff, Colorado, magma chamber. Journal of Petrology, 30, 711-737.

Johnson, B.R., Glazner, A.F., 2010. Formation of K-feldspar megacrysts in granodioritic plutons by thermal cycling and late-stage textural coarsening. Contributions to Mineralogy and Petrology, 159, 599-619.

Kim, K.T., Burley, B.J., 1971. Phase Equilibria in the System NaAlSi3O8-NaAlSiO4-H2O with Special Emphasis on the Stability of Analcite. Canadian Journal of Earth Sciences, 8, 311-337.

Kratinová, Z., Schulmann, K., Edel, J.B., Jezek, J., Schaltegger, U., 2007. Model of successive granite sheet emplacement in transtensional setting: integrated microstructural and anisotropy of magnetic susceptibility study. Tectonics, 26, TC6003. DOI: 10.1029/2006TC002035.

Lambert, I.B., Robertson, J.K., Wyllie, P.J., 1969. Melting reactions in the system KAlSi3O8-SiO2-H2O to 18.5 kilobars. American Journal of Science, 267, 609-626.

Lindsley, D.H., 1967. P-T projection for part of the system kalsitesilica. Carnegie Institution Washington Yearbook, 65, 244-247.

London, D., 2009. The origin of primary textures in granitic pegmatites. The Canadian Mineralogist, 47, 697-724.

Luth, R.W., 1969. The systems NaAlSi3O8-SiO2 and KAlSi3O8-SiO2 to 20kb and the relationship between H2O content, PH2O, and Ptotal in granitic magmas. American Journal of Science, 267-A, 325-341.

Luth, R.W., 1976. Granitic Rocks. In: Balley, D.K., Mac Donald, R., (eds.). The Evolution of the Crystalline Rocks, Academic

Press, London, 335-417.

Luth, R.W., Jahns, R.H., Tuttle, O.F., 1964. The granite system at pressures of 4 to 10 kilobars. Journal of Geophysical Research, 69, 759-773.

Maaløe, S., Wyllie, P.J., 1975. Water content of a granite magma deduced from the sequence of crystallization determined

experimentally with water-undersaturated conditions. Contributions to Mineralogy and Petrology, 52, 175-191.

Merril, R.B., Robertson, J.K., Wyllie, P.J., 1970. Melting reactions in the system NaAlSi3O8-KAlSi3O8-SiO2-H2O to 20 kilobars compared with results for other feldspar-quartz-H2O and rock-H2O systems. Journal of Geology, 78, 558-569.

Moore, J.G., Sisson, T.W., 2008. Igneous phenocrystic origin of K-feldspar megacrysts in granitic rocks from the Sierra Nevada batholith. Geosphere, 4, 387-400.

Moreno-Ventas, I., 1991. Petrología de los Granitoides y Rocas Básicas asociadas de la Sierra de Gredos, Sistema Central

Español. PhD Thesis, Huelva, Universidad de Sevilla, 431pp.

Moreno-Ventas, I., Rogers, G., Castro, A., 1995. The role of hybridization in the genesis of Hercynian granitoids in the Gredos massif, Spain: inferences from Sr-Nd isotopes. Contributions to Mineralogy and Petrology, 120, 137-149.

Mulchrone, K.F., Grogan, S., De, P., 2005. The relationship between magmatic tiling, fluid flow and crystal fraction. Journal of Structural Geology, 27, 179-197.

Naney, M.T., 1983. Phase equilibria of rock-forming ferromagnesian silicates in granitic systems. American Journal of Science, 283, 993-1033.

Parga-Pondal, I., Matte, P., Capdevila, R., 1964. Introduction à la géologie de l’Ollo de Sapo, formation porphyroide anté-silurienne du Nord-Ouest de l’Espagne. Notas y Comunicaciones del Instituto Geológico y Minero de España, 76, 119-153.

Paterson, S.R., Fowler, T.K., Schmidt, K.G., Yoshinobu, A.S., Yuan, E.S., Miller, R.B., 1998. Interpreting magmatic fabric patterns in plutons. Lithos, 44, 53-82.

Patiño Douce, A.E., 1996. Effects of pressure and H2O content on the compositions of primary crustal melts. Transactions of the Royal Society of Edinburgh, Earth Science, 87, 11-21.

Patiño Douce, A.E., Beard, J.S., 1996. Effects of P, f(O2) and Mg/Fe ratio on dehydration-melting of model metagreywackes.

Journal of Petrology, 37, 999-1024.

Pereira, M.F., Castro, A., Fernández, C., 2015. The inception of a Paleotethyan magmatic arc in Iberia. Geoscience Frontiers,

, 297-306.

Peters, T., Luth, R.W., Tuttle, O.F., 1966. The melting of analcite solid solutions in the system NaAlSiO4-NaAlSi3O8-H2O.

American Mineralogist, 51, 736-753.

Piwinskii, A.J., 1968. Studies of batholithic feldspars: Sierra Nevada, California. Contributions to Mineralogy and Petrology, 17, 204-223.

Piwinskii, A.J., Wyllie, P.J., 1968. Experimental studies of igneous rock series: A zoned pluton in the Wallowa batholith, Oregon. Journal of Geology, 76, 205-234.

Piwinskii, A.J., Wyllie, P.J., 1970. Experimental studies of igneous rock series: Felsic body suite from Needle Point pluton, Wallowa batholith, Oregon. Journal of Geology, 78, 52-76.

Rodríguez, C., Castro, A., 2017. Silicic magma differentiation in ascent conduits. Experimental constraints. Lithos, 272-273, 261-277.

Rodríguez, C., Geyer, A., Castro, A., Villaseñor, A., 2015. Natural equivalents of thermal gradient experiments. Journal of

Volcanology and Geothermal Research, 298, 47-58.

Rodríguez Alonso, M.D., Díez Balda, M.A., Perejón, A., Pieren, A., Liñán, E., López Díaz, F., Moreno, F., Gámez Vintaned, J.A.,

González Lodeiro, F., Martínez Poyatos, D., Vegas, R., 2004. Dominio del Complejo Esquisto-grauváquico. Estratigrafía.

La secuencia litoestratigráfica del Neoproterozoico-Cámbrico Inferior. In: Vera, J.A., (ed.). Geología de España. Sociedad

Geológica Española (SGE)-Instituto Geológico y Minero de España (IGME), Madrid, 78-81.

Scarfe, C.M., Luth, R.W., Tuttle, O.F., 1966. An experimental study bearing on the absence of leucite in plutonic rocks. American Mineralogist, 51, 726-735.

Schmidt, M.W., 1996. Experimental constraints on recycling of potassium from subducted oceanic crust. Science, 272, 1927-

Steiner, J.C., 1970. An experimental study of the assemblage alkali feldspar + liquid + quartz in the system NaAlSi3O8-KAlSi3O8-SiO2-H2O at 4000bars. PhD Thesis, Stanford University, 98pp.

Steiner, J.C., Jahns, R.H., Luth, R.W., 1975. Crystallization of alkali feldspar and quartz in the haplogranite system NaAlSi3O8-KAlSi3O8-SiO2-H2O at 4kbar. Geological Society of America Bulletin, 86, 83-97.

Thomas, R., 2000. Estimation of water contents of granite melt inclusions by confocal laser Raman microprobe spectroscopy. American Mineralogist, 85, 868-872.

Tuttle, O.F., Bowen, N.L., 1958. Origin of granite in the light of experimental studies in the system NaAlSi3O8-KAlSi3O8-

SiO2-H2O. The Geological Society of America Memoir, 74, 1-146.

Ugidos, J.M., Stephens, W.E., Carnicero, A., Ellam, R.M., 2008. A reactive assimilation model for regional-scale cordieritebearing granitoids: geochemical evidence from the Late Variscan granites of the Central Iberian Zone, Spain. Earth and Environmental Science Transactions of the Royal Society of Edinburgh, 99, 225-250.

Vernon, R.H., Paterson, S.R., 2008. How late are K-feldspar megacrysts in granites? Lithos, 104, 327-336.

Vigneresse, J.L., 2014. Textures and melt-crystal-gas interactions in granites. Geoscience Frontiers, 6, 635-663.

Weinberg, R.F., Sial, A.N., Pessoa, R.R., 2001. Magma flow within the Tavares pluton, northeastern Brazil: compositional and thermal convection. Bulletin of the Geological Society of America, 113, 508-520.

Whitney, J.A., 1975. The effects of pressure, temperature, and XH2O on phase assemblage in four synthetic rock compositions. Journal of Geology, 83, 1-31.

Whitney, J.A., 1988. The origin of granite; the role and source of wáter in the evolution of granitic magmas. Geological Society of America Bulletin, 100, 1886-1897.

Wyllie, P.J., 1979. Magmas and volatile components. American Journal of Science, 64, 469-500.

Zák, J., Paterson, S.R., Memeti, V., 2007. Four magmatic fabrics in the Tuolumne batholith, central Sierra Nevada, California

(USA): implications for interpreting fabric patterns in plutons and evolution of magma chambers in the upper crust. Geological Society of America Bulletin, 119, 184-201.






Granites and Related Rocks. A tribute to Guillermo Corretgé