Abstract
Vapor-undersaturated fractional crystallization experiments with Macusani glass (macusanite), a peraluminous rhyolite obsidian, at 200 MPa yield mineralogical fabrics and zonation, and melt fractionation trends that closely resemble those found in zoned granitic pegmatites and other granitoids of comparable composition (typically peraluminous, Li-Be-Ta-rich deposits). The zonation from the edge of charges inward is characterized by: (1) fine-grained sodic feldspar-quartz border zones; (2) a fringe of very coarse-grained graphic quartz-feldspar intergrowths that flair radially toward melt and terminate with nearly monophase K-feldspar; (3) cores of very coarse-grained, nearly monominerallic quartz or virgilite (LiAlSi5O12)±mica; and (4) late-stage, fine-grained albite+mica intergrowths that are deposited from alkaline, Na-rich interstitial melt at vapor saturation. Similar experimental products have been observed in compositionally simpler, less evolved systems. Liquid lines of descent from initially H2O-undersaturated runs are marked by a decrease in SiO2, and increases in Na/K, B, P, F, H2O, and a variety of trace lithophile cations. These trends are believed to be governed by three factors: (1) disequilibrium growth of feldspars (±quartz) via metastable supersaturation; (2) fractionation of melt toward SiO2-depleted, Na-rich compositions due to increases in B, P, and F; and (3) changes in nucleation and growth rates, mostly as a function of the H2O content of melt (X mw ). In contrast, experiments that are cooled below the liquidus from the field of melt+aqueous vapor (London et al. 1988) fail to replicate pegmatitic characteristics in most respects. On the basis of these and other experiments, we suggest that the formation of pegmatite fabrics stems primarily from fractional crystallization in volatile-rich melts, and that enrichments in normally trace lithophile elements result from melt differentiation trends toward increasingly alkaline, silica-depleted compositions. Although vapor saturation at near-solidus and subsolidus conditions may promote extensive recrystallization, an aqueous vapor phase does not appear to be necessary for the generation of most of the salient characteristics of pegmatites.
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Barnes VE, Edwards G, McLaughlin WA, Friedman I, Joensuu O (1970) Macusanite occurrence, age, and composition, Macusani, Peru. Geol Soc Am Bull 81:1539–1546
Benard F, Moutou P, Pichavant M (1985) Phase relations of tourmaline leucogranites and the significance of tourmaline in silicic magmas. J Geol 93:271–291
Brookins DG, Fairbain HW, Hurley PM, Pinson WH (1969) A Rb-Sr geochronological study of the pegmatites of the Middletown area, Connecticut. Contrib Mineral Petrol 42:157–168
Burnham CW (1979) Magmas and hydrothermal fluids. In: Barnes HL (ed) Geochemistry of hydrothermal ore deposits, 2nd ed. Wiley, New York, pp 71–136
Burnham CW, Davis NF (1971) The role of H2O in silicate melts: I. P-V-T relations in the system NaAlSi3O8-H2O to 10 kilobars and 1000° C. Am J sci 270:54–79
Burnham CW, Davis NF (1974) The role of H2O in silicate melts: II. Thermodynamic and phase relations in the system NaAlSi3O8-H2O to 10 kilobars and 700–1100° C. Am J Sci 274:902–940
Burnham CW, Jahns RH (1962) A method for determining the solubility of water in silicate melts. Am J sci 260:721–745
Burnham CW, Nekvasil H (1986) Equilibrium properties of granite pegmatite melts. Am Mineral, Jahns Mem 71:239–263
Carron JP, Lagache M (1980) Etude expérimentale du fractionement des éléments Rb, Cs, Sr, et Ba entre feldspaths alcalins, solutions hydrothermales, et liquides silicates dans le systeme Q Ab Or H2O à 2 kbar entre 700° et 800° C. Bull Mineral 103:571–578
Černý P (1982a) Anatomy and classification of granitic pegmatites. In: P Černý (ed) Short course in granitic pegmatites in science and industry. Mineral Assoc Can Short Course Hanbook 8:1–40
Černý P (1982b) Petrogenesis of granitic pegmatites. In: P Černý (ed) Short course in granitic pegmatites in science and industry. Mineral Assoc Can Short Course Hand 8:405–462
Černý P, Meintzer RE, Anderson AJ (1985) Extreme fractionation in rare-element granite pegmatites: selected examples of data and mechanisms. Can Mineral 23:381–421
Chappell BW, White AJR (1974) Two contrasting granite types. Pacific Geol 8:173–174
Dingwell DB, Harris DM, Scarfe CM (1984) The solubility of H2O in the system SiO2-A12O3-Na2O-K2O at 1 and 2 kbar. J Geol 92:387–395
Ellison AJ, Hess PC (1986) Solution behavior of +4 cations in high silica melts: Petrologic and geochemical implications. Contrib Mineral Petrol 94:343–351
Exley CS, Stone M (1964) The granitic rocks of southwest England. In: KHG Hosking, GJ Shrimpton (eds) Present views of some aspects of the geology of Cornwall and Devon. Trans R Geol Soc Cornwall 150th Anniv Vol, pp 131–184
Exley CS, Stone M (1982) The Hercynian granites. In: DS Sutherland (ed) Igneous rocks of the British Isles, Wiley, Chichester, pp 287–320
Fenn PM (1977) The nucleation and growth of alkali feldspars from hydrous melts. Can Mineral 15:135–161
Fenn PM (1979) On the origin of graphic intergrowths. (abstr) Geol Soc Am Abstr Prog 11:424
Fenn PM (1986) On the origin of graphic granite. Am Mineral 71:325–330
Goad BE, Černý P (1981) Peraluminous pegmatitic granites and their pegmatite aureoles in the Winnipeg River district, southeastern Manitoba. Can Mineral 19:177–194
Heinrich KFJ (1981) Electron beam microanalysis. Van Nostrand Reinhold Company, New York, pp 578
Hess PC (1988) The role of high field strength cations in silicate melts. in: I Kushiro, I Perchuk (eds) Advances in physical geochemistry. Springer, New York Berlin Heidelberg Tokyo (in press)
Isuk EE, Carmen JH (1981) The system Na2Si2O5-K2Si2O5MoS2-H2O with implications for molybdenum transport in silicate melts. Econ Geol 76:2222–2235
Jahns RH (1953) The genesis of pegmatites. I. Occurrence and origin of giant crystals. Am Mineral 38:563–598
Jahns RH (1982) Internal evolution of pegmatite bodies. In: P Černý (ed) Granitic pegmatites in science and industry. Mineral Assoc Can Short Course Handb 8:293–327
Jahns RH, Burnham CW (1969) Experimental studies of pegmatite genesis: I. A model for the derivation and crystallization of granitic pegmatites. Econ Geol 64:843–864
Jolliff BL, Papike JJ, Shearer CK, Laul JC (1986) Tourmaline as a recorder of pegmatite evolution: Bob Ingersoll pegmatite, Black Hills, South Dakota. Am Mineral 71:472–500
Kirkpatrick RJ (1981) Kinetics of crystallization of igneous rocks. In: AC Lasaga, RJ Kirkpatrick (eds) Kinetics of geochemical processes. Mineral Soc Am Rev Mineral 8:321–398
Kovalenko VI, Kovalenko NI (1984) Problems of the origin, orebearing and evolution of rare-metal granitoids. Phys Earth Planet Int 35:51–62
Kovalenko VI, Kuz'Min MI, Antipin VS, Petrov LL (1971) Topazbearing quartz keratophyre (ongonite), a new variety of subvolcanic igneous vein rock. Dokl Acad Sci USSR Earth Sci Sect 199:132–135
Loebel R (1969) Heat of fusion of some inorganic compounds. In: RC Weast (ed) Handbook of chemistry and physics, 50th ed. Chemical Rubber Company, Cleveland, B260-B264
Lofgren GE (1973) Experimental crystallization of plagioclase at prescribed cooling rates. (abstr) EOS 54:482
Lofgren GE, Donaldson CH (1975) Curved branching crystals and differentiation in comb-layered rocks. Contrib Mineral Petrol 49:309–319
London D (1979) Occurrence and alteration of lithium minerals, White Picacho pegmatites, Arizona. MS thesis Arizona State University, pp 131
London D (1984) Experimental phase equilibria in the system LiAlSiO4-SiO2-H2O: A petrogenetic grid for lithium-rich pegmatites. Am Mineral 69:995–1004
London D (1986a) Magmatic-hydrothermal transition in the Tanco rare-element pegmatite: Evidence from fluid inclusions and phase equilibrium experiments. Am Mineral 71:376–395
London D (1986b) Formation of tourmaline-rich gem pockets in miarolitic pegmatites. Am Mineral 71:396–405
London D (1986c) Holmquistite as a guide to pegmatitic rare-metal deposits. Econ Geol 81:704–712
London D (1987) Internal differentiation of rare element pegmatites: effects of boron, phosphorus, and fluorine. Geochim Cosmochim Acta 51:403–420
London D (1989) Internal differentiation of rare-element pegmatites: A synthesis of recent research. Geol Soc Am Spec Pap (in press)
London D, Burt DM (1982) Chemical models for lithium alumino-silicate stabilities in pegmatites and granites. Am Mineral 67:494–509
London D, Hervig RH, Morgan GB VI (1988) Melt-vapor solubilities and elemental partitioning in peraluminous granite-pegmatite systems: experimental results with Macusani glass at 200 MPa. Contrib Mineral Petrol 99:360–373
Luth RW (1988) Effects of F on phase equilibria and liquid structure in the system NaAlSiO4-CaMgSi2O6-SiO2. Am Mineral 73:306–312
Manning DAC (1981) The effect of fluorine on liquidus phase relationships in the system Qz-Ab-Or with excess water at 1 kb. Contrib Mineral Petrol 76:206–215
Manning DAC, Martin JS, Pichavant ML, Henderson CMB (1984) The effect of F, B, and Li on melt structures in the granite system: different mechanisms? In: CMB Henderson (ed) Progress in experimental petrology. Nat Env Res Council Publ Ser D25:36-41
Morgan GB VI (1988) Igneous and metamorphic geochemistry of boron. Ph D dissertation, University of Oklahoma, pp 394
Morgan GB VI, London D (1987a) Alteration of amphibolitic wallrocks around the Tanco rare element pegmatite, Bernic Lake, Manitoba. Am Mineral 72:1097–1121
Morgan GB VI, London D (1987b) Behavior of boron and tourmaline stability in granitic systems. (abstr) Geol Soc Am Abstr Prog 19:777–778
Mysen BO, Ryerson F, Virgo D (1981) The structural role of phosphorus in silicate melts. Am Mineral 66:107–117
Mysen BO, Virgo D (1986a) Volatiles in silicate melts at high temperature and pressure 1. Interaction between OH groups and Si4+, Al3+, Ca2+, Na+, and H+. Chem Geol 57:303–331
Mysen BO, Virgo D (1986b) Volatiles in silicate melts at high temperature and pressure 2. Water in melts along the join NaAlO4-SiO2 and a comparison of the solubility mechanisms of water and fluorine. Chem Geol 57:333–358
Naski GC, Hess PC (1985) SnO2 solubility: Experimental results in peraluminous and peralkaline high silica glasses. (abstr) EOS 66:412
Oxtoby S, Hamilton DL (1978) The discrete association of water with Na2O and SiO2 in NaAl silicate melts. Contrib Mineral Petrol 66:185–188
Pan JJY (1988) The geochemistry and mode of occurrence of phosphorus in pegmatite feldspars. Sr Thesis, University of Manitoba, Winnipeg
Petersen JS, Lofgren GE (1986) Lamellar and patchy intergrowths in feldspars: Experimental crystallization of eutectic silicates. Am Mineral 71:343–355
Pichavant M (1981) An experimental study of the effect of boron on a water saturated haplogranite at 1 kbar vapour pressure. Contrib Mineral Petrol 76:430–439
Pichavant M (1983) Melt-fluid interaction deduced from studies of silicate-B2O-H2O systems at 1 kbar. Bull Mineral 106:201–211
Pichavant M (1987) Effects of B and H2O on liquidus phase relations in the haplogranite system at 1 kbar. Am Mineral 72:1056–1070
Pichavant M Verrera JV, Boulmer S, Brique L, Joron J-L, Juteau M, Marin L, Michard A, Sheppard SMF, Treuil M, Vernet M (1987) The Macusani glasses, SE Peru: evidence of chemical fractionation in peraluminous magmas. In: Mysen BO (ed) Magmatic processes: physicochemical principles. Geochem Soc Spec Publ 1:359–373
Pouchou JL, Pichoir F (1985) “PAP” (phi-rho-Z) procedure for improved quantitative microanalysis. In: JT Armstrong (ed) Microbeam analysis. San Francisco Press, San Francisco, pp 104–106
Remelle R, Stanton T, McMillan P, Holloway JR (1986) Raman spectra of hydrous glasses along the quartz-albite join. (abstr) EOS 67:1274
Ryerson FJ (1985) Oxide solution mechanisms in silicate melts: Systematic variation in the activity coefficient of SiO2. Geochim Cosmochim Acta 49:637–649
Simpson DR (1977) Aluminum phosphate variants of feldspar. Am Mineral 62:351–355
Swanson SE (1977) Relation of nucleation and crystal growth rate to the development of granite textures. Am Mineral 62:966–978
Swanson SE, Fenn PM (1986) Quartz crystallization in igneous rocks. Am Mineral 71:331–342
Taylor BE, Freidrichsen H (1983) Light stable isotope systematics of granitic pegmatites from North America and Norway. Isotope Geosci 1:127–167
Taylor BE, Foord EE, Friedrichsen H (1979) Stable isotope and fluid inclusion studies of gem-bearing granitic pegmatite-aplite dikes, San Diego County, California. Contrib Mineral Petrol 68:187–205
Vlasov KA (1961) Principles of classifying granite pegmatites and their textural-paragenetic types. Izvestiya Acad Sci USSR Geol Ser 1:5–20
Walker RJ (1985) The origin of the Tin Mountain pegmatite, Black Hills, South Dakota. Ph D dissertation, State University of New York, Stony Brook
Watson EB (1979) Zircon saturation in felsic liquids: Experimental results and applications to trace element geochemistry. Contrib Mineral Petrol 70:407–419
Watson EB, Harrison TM (1983) Zircon saturation revisisted: temperature and composition effects in a variety of crustal magma types. Earth Planet Sci Lett 64:295–304
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London, D., Morgan, G.B. & Hervig, R.L. Vapor-undersaturated experiments with Macusani glass+H2O at 200 MPa, and the internal differentiation of granitic pegmatites. Contr. Mineral. and Petrol. 102, 1–17 (1989). https://doi.org/10.1007/BF01160186
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DOI: https://doi.org/10.1007/BF01160186