Contributions to Mineralogy and Petrology

, Volume 81, Issue 3, pp 230–239 | Cite as

Crystallization processes in the Rocky Hill granodiorite Pluton, California: An interpretation based on compositional zoning of plagioclase

  • Timothy P. Loomis
  • Paul W. Welber


The Rocky Hill Pluton was chosen for study of plagioclase zoning because it has an apparently simple geometry and one-stage emplacement history, documented by Putman and Alfors (1969). The pluton is divided texturally into a hypidiomorphic granular rim fades and porphyritic core facies, both comprising zoned plagioclase phenocrysts averaging 2–4 mm in diameter. Major features of compositional zoning profiles of plagioclase were found to be consistent within a sample, showing resorbed core regions followed by a sharp drop of ca. 10% An to a plateau region, and ending with normal zoning. The width of the plateau region is narrow in samples near the pluton rim but increases systematically toward the pluton core, and the outer part of the plateau develops reverse zoning in the core facies. A review of the effects of pressure, water content of the melt, and temperature on equilibrium and disequilibrium crystallization processes concludes that only variations of temperature and water content during disequilibrium crystallization of plagioclase phenocrysts can produce the observed zoning patterns. Experimental data suggest that the trend toward finer grain size toward the interior of the pluton may be due to increasing water content rather than due to increasing cooling rate.

The compositional zoning of plagioclase and textural variations in the pluton can be explained by a model in which the pluton crystallized by migration of a partly crystalline “mush zone” inward from the edge of the plutonic chamber while convection within the residual magma: (1) redistributed water excluded from the mush zone and (2) slowed the cooling rate of the mush zone. The reverse zoning of plagioclase growing in the convecting magma changed to normal zoning after capture in the mush zone because the cooling rate increased and water was removed.

Comparison of the results from our study of Rocky Hill with published descriptions of plutons and experimental and theoretical studies of crystallization processes leads to the conclusions that: (1) convection is an active process during the crystallization of many plutons, causing redistribution of mainly water and heat in silicic ones but differentiating other components in intermediate ones; (2) most of the crystallization of granitic rocks may occur in a “mush zone” or static boundary layer between the solid boundary and convecting inner magma body; (3) water content may be an important factor controlling grain size; (4) reverse zoning of plagioclase may be more typical of plagioclase grown under slowly-cooled conditions than “normal” zoning; and (5) variations of plagioclase zoning in plutons can provide useful information on crystallization processes.


Crystallization Crystallization Process Plateau Region Increase Water Content Plagioclase Phenocryst 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. Bateman PC, Nokleberg WJ (1978) Solidification of the Mount Givens granodiorite, Sierra Nevada, California. J Geol 86:563–579Google Scholar
  2. Bateman PC, Chappell BW (1979) Crystallization, fractionation, and solidification of the Tuolumne Intrusive Series, Yosemite National Park, California. Geol Soc Am Bull Pt 1 90:465–482Google Scholar
  3. Bottinga Y, Kudo A, Weill D (1966) Some observations on ocillatory zoning and crystallization of magmatic plagioclase. Am Mineral 51:792–806Google Scholar
  4. Burnham CW (1979) The importance of volatile constitutents. In: Yoder HS (ed) A fiftieth anniversary appraisal of Bowen's evolution of the igneous rocks. Princeton University, Princeton, NJ, pp 439–482Google Scholar
  5. Burri C, Parker RL, Wenke E (1967) Die optische Orientierung der Plagioklaseunterlagen und Diagramme zur Plagioklasebestimmung nach der Drehtischmethode. Birkhäuser Verlag, Basel Stuttgart, p 334Google Scholar
  6. Eggler DH (1972) Water-saturated and undersaturated melting relations in a Paricutin andesite and an estimate of water content in the natural magma. Contrib Mineral Petrol 34:262–271Google Scholar
  7. Eggler DH, Burnham CW (1973) Crystallization and fractionation trends in the system andesite -H2O-CO2-O2 at pressures to 10 Kb. Geol Soc Am Bull 2517–2532Google Scholar
  8. Fenn PM (1977) Nucleation and growth of alkali feldspar from hydrous melts. Can Mineral 15:135–161Google Scholar
  9. Greenwood HJ, McTaggart KC (1957) Correlation of zones in plagioclase. Am J Sci 255:656–666Google Scholar
  10. Harloff C (1927) Zonal structure in plagioclase. Leids Geol Meded 2:99–114Google Scholar
  11. Karner FR (1968) Compositional variation in the Tunk Lake granite pluton, southeastern Maine. Geol Soc Am Bull 79:192–222Google Scholar
  12. Lofgren G (1974) An experimental study of plagioclase crystal morphology: Isothermal crystallization. Am J Sci 274:243–274Google Scholar
  13. Loomis TP (1979) An empirical model for plagioclase equilibrium in hydrous melts. Geochim Cosmochim Acta 43:1753–1759Google Scholar
  14. Loomis TP (1982) Numerical simulations of crystallization processes of plagioclase in complex melts: The origin of irregular and oscillatory zoning in plagioclase. Contrib Mineral Petrol 81:219–229Google Scholar
  15. Maaloe S (1978) The zoned plagioclase of the Skaergaard intrusion, east Greenland. J Petrol 17:398–419Google Scholar
  16. Marsh BD (1978) On the cooling of ascending andesitic magma. Philos Trans R Soc Lond Ser A 288:611–625Google Scholar
  17. McBirney AR, Noyes RM (1979) Crystallization and layering of the Skaergaard intrusion. J Petrol 20:487–554Google Scholar
  18. McDowell SD (1978) Little Chief granite porphyry: Feldspar crystallization history. Geol Soc Am Bull 89:33–49Google Scholar
  19. Piwinskii AJ, Wyllie PJ (1968) Experimental studies of igneous rock series: A zoned pluton in the Wallowa batholith, Oregon. J Geol 76:205–234Google Scholar
  20. Pringle GJ, Trembath LT, Pajari GE Jr (1974) Crystallization history of a zoned plagioclase. Mineral Mag 39:867–877Google Scholar
  21. Putman GW, Alfors JT (1969) Geochemistry and petrology of the Rocky Hill Stock, Tulare County, California. Geol Soc Am Spec Pap 120, 109pGoogle Scholar
  22. Ragland PC, Butler JR (1972) Crystallization of the West Farrington pluton, North Carolina, USA. J Petrol 13, 381–404Google Scholar
  23. Ribbe PH, Smith JV (1966) X-ray emission microanalysis of rock forming minerals. IV. Plagioclase feldspars. J Geol 74:217–233Google Scholar
  24. Rodriguez-Gil F (1960) First degree 3 point smoothing routine. In: Collected Algorithms from CACM. The Assoc. for Computing Machinery, Inc., Algorithm 188Google Scholar
  25. Shaw HR (1974) Diffusion of H2O in granitic liquids. In: Hofmann AW, Giletti BJ, Yoder HS Jr, Yund RA (eds) Geochemical transport and kinetics. Carnegie Inst Wash Pub 634:139–170Google Scholar
  26. Sibley DF, Vogel TA, Walker BW, Byerly G (1976) The origin of oscillatory zoning in plagioclase: A diffusion and growth controlled model. Am J Sci 276:275–284Google Scholar
  27. Swanson SE (1977) Relation of nucleation and crystal-growth rate to the development of granitic textures. Am Mineral 62:966–978Google Scholar
  28. Swanson SE (1978) Petrology of the Rocklin pluton and associated rocks, western Sierra Nevada, California. Geol Soc Am Bull 89:679–686Google Scholar
  29. Taubeneck (1957) Geology of the Elkhorn Mountains, Northeastern Oregon: Bald Mountain Batholith. Geol Soc Am Bull 68:181–238Google Scholar
  30. Vance JA (1962) Zoning in igneous plagioclase: Normal and oscillatory zoning. Am J Sci 260:746–760Google Scholar
  31. Vance JA (1965) Zoning in igneous plagioclase: Patchy zoning. J Geol 73:636–651Google Scholar
  32. Whitney JA (1975) The effects of pressure, temperature, and \(X_{H_2 O}\) on phase assemblage in four synthetic rock compositions. J Geol 83:1–31Google Scholar
  33. Wiebe RA (1968) Plagioclase stratigraphy: A record of magmatic conditions and events in a granite stock. Am J Sci 266:670–703Google Scholar
  34. Winkler HGF (1947) Kristallgröße und Abkühlung. Heidelb Beitr Mineral Petrogr 1:86–104Google Scholar

Copyright information

© Springer-Verlag 1982

Authors and Affiliations

  • Timothy P. Loomis
    • 1
  • Paul W. Welber
    • 1
  1. 1.Department of GeosciencesUniversity of ArizonaTucsonUSA

Personalised recommendations