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The distribution of hydroxyl in garnets from the subcontinental mantle of southern Africa

Abstract

166 garnets of dominantly mantle origin were analyzed for OH content by infrared (IR) spectroscopy. IR spectra in the 3400–3700 cm-1 region display consistent absorption patterns attributable to OH structurally bound within the garnet crystal, occasionally contaminated by low intensity OH absorptions from microscopic inclusions. The principal structural OH absorption occurs near 3570 cm-1, with the appearance of additional absorptions near 3512 cm-1 and 3650 cm-1 dependent on garnet composition or paragenesis. Samples derive from a wide variety of rock types occurring as xenoliths in kimberlites of southern Africa. OH abundances, using the best currently available calibration, range from less than 1 up to 135 ppm H2O, and increase in the general order as follows: on-craton eclogites<coarse-granular peridotites<Ti-rich deformed peridotites<some off-craton eclogites<Cr-poor megacrysts. OH abundances in garnet are closely linked to host rock paragenesis and cannot be explained purely by any crystal chemical factors which we have investigated. Cr-poor garnet megacryst nodules display striking inverse correlations between OH contents and Mg/(Mg+Fe) ratios, which we interpret to reflect the progressively increasing water content of the differentiating parental megacryst magmas. OH abundances in garnet megacrysts decrease in the host rock order Group 2 (micaceous) kimberlite>Group 1 (basaltic) kimberlite>alnöite>alkali basalt. The OH contents of common lithospheric granets from coarse peridotites, including several phlogopite-bearing samples are typically less than 20 ppm H2O, for tectonic settings of kimberlites both on and off the Archaean Kaapvaal craton. Ti-rich garnets from deformed peridotites are richer in OH, supporting previous suggestions of association of these xenoliths with putative megacryst magmas. Subcalcic Cr-rich xenocrysts, diamond inclusion garnets and garnets from diamondiferous eclogites have very low OH contents, similar to eclogites and depleted peridotites without macroscopic diamonds. The OH content of southern African peridotite and eclogite garnets are significantly lower on average than those previously examined from the Colorado Plateau diatremes. While details of emplacement-related H mobility in garnets remain to be established, our results suggest that garnets record useful information on the role of water or other hydrous volatile species in petrological processes at their source regions in the mantle. Although garnets do not appear to constitute a large reservoir of mantle hydrogen, the large stability range of OH-bearing garnet in the crust and mantle implies wide applicability as a qualitative hydrobarometer.

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References

  • Ackermann L, Cemic L, Langer K (1983) Hydrogarnet substitution in pyrope: A possible location for “water” in the mantle. Earth Planet Sci Lett 62:208–214

    Google Scholar 

  • Aines RD, Rossman GR (1984a) The hydrous component in garnets: pyralspites. Am Mineral 69:1116–1126

    Google Scholar 

  • Aines RD, Rossman GR (1984b) Water content of mantle garnets. Geology 12:720–723

    Google Scholar 

  • Aoki K (1975) Origin of phlogopite and potassic richterite bearing peridotite xenoliths from South Africa. Contrib Mineral Petrol 53:145–156

    Google Scholar 

  • Armstrong JT (1984) Quantitative analysis of silicate and oxide minerals: A re-evaluation of ZAF corrections and proposal for new Bence-Albee coefficients. In: Romig AD Jr, Goldstein JI (eds) Microbeam analysis. San Francisco Press, pp 208–212

  • Basu AR, Ongley JS, MacGregor ID (1986) Eclogites, pyroxene geotherm and layered mantle convection. Science 233:1303–1305

    Google Scholar 

  • Bell DR, Rossman GR (1992) Water in Earth's mantle: the role of nominally anhydrous minerals. Science 255:1391–1397

    Google Scholar 

  • Birkett TC, Trzcienski WE Jr (1984) Hydrogarnet: multi-site hydrogen occupancy in the garnet structure. Canad Mineral 22:675–680

    Google Scholar 

  • Carswell DA (1975) Primary and secondary phlogopites in garnet lherzolite xenoliths. Phys Chem Earth 9:417–430

    Google Scholar 

  • Chapman NA (1976) Inclusions and megacrysts from undersaturated tuffs and basanites, East Fife, Scotland. J Petrol 17:472–498

    Google Scholar 

  • Danchin RV (1979) Mineral and bulk chemistry of garnet lherzolite and garnet harzburgite xenoliths from the Premier Mine, South Africa. In: Boyd FR, Meyer HOA (eds) The mantle sample: inclusions in kimberlites and other volcanics. AGU, Washington, pp 104–126

    Google Scholar 

  • Delaney JS, Smith JV, Carswell DA, Dawson JB (1980) Chemistry of micas from kimberlites and xenoliths-II. Primary- and secondary-textured micas from peridotite xenoliths. Geochim Cosmochim Acta 44:857–872

    Google Scholar 

  • Drury MR, Van Roermund HLM (1989) Fluid assisted recrystallization in upper mantle peridotites from kimberlites. J Petrol 30:133–152

    Google Scholar 

  • Eggler DH, McCallum ME, Smith CB (1979) Megacryst assemblages in kimberlite from northern Colorado and southern Wyoming: petrology, geothermometry-barometry and areal distribution. In: Boyd FR, Meyer HOA (eds) The mantle sample: inclusions in kimberlites and other volcanics. AGU, Washington, pp 213–226

    Google Scholar 

  • Erlank AJ, Waters FG, Hawkesworth CJ, Haggerty SE, Allsopp HL, Rickard RS, Menzies MA (1987) Evidence for mantle metasomatism in peridotite nodules from the Kimberley pipes, South Africa. In: Menzies MA (ed) Mantle metasomatism. Academic Press, London, pp 221–311

    Google Scholar 

  • Finger LW, Prewitt CT (1989) Predicted compositions for high-density hydrous magnesium silicates. Geophys Res Lett 16:1395–1397

    Google Scholar 

  • Fyfe WS (1970) Lattice energies, phase transformations and volatiles in the mantle. Phys Earth Planet Int 3:196–200

    Google Scholar 

  • Garlick GD, MacGregor ID, Vogel DE (1971) Oxygen isotope ratios in eclogites from kimberlites. Science 172:1025–1027

    Google Scholar 

  • Griffin WL, Carswell DA, Nixon PH (1979) Lower crustal granulites and eclogites from Lesotho, southern Africa. In: Boyd FR, Meyer HOA (eds) The mantle sample: inclusions in kimberlites and other volcanics. AGU, Washington, pp 59–86

    Google Scholar 

  • Griffin WL, Smith D, Boyd FR, Cousens DR, Ryan CG, Sie SH, Suter GF (1989) Trace element zoning in garnets from sheared mantle xenoliths. Geochim Cosmochim Acta 53:561–567

    Google Scholar 

  • Gurney JJ (1984) A correlation between garnets and diamonds in kimberlites. In: Glover JE, Harris PG (eds) Kimberlite occurrence and origin: a basis for conceptual models in exploration. Geology Department and University Extension, University of Western Australia. Spec Publ 8:143–16

  • Gurney JJ, Harte B (1980) Chemical variations in upper mantle nodules from southern African kimberlites. Phil Trans Royal Soc London A297:273–293

    Google Scholar 

  • Gurney JJ, Jakob WRO, Dawson JB (1979) Megacrysts from the Monastery kimberlite pipe, South Africa. In: Boyd FR, Meyer HOA (eds) The mantle sample: inclusions in kimberlites and other volcanics. AGU, Washington, pp 227–243

    Google Scholar 

  • Gurney JJ, Mathias M, Siebert C, Moseley G (1971) Kyanite eclogites from the Rietfontein kimberlite pipe, Mier Coloured Reserve, Gordonia, Cape Province, South Africa. Contrib Mineral Petrol 30:46–52

    Google Scholar 

  • Harte B (1983) Mantle peridotites and processes — the kimberlite sample. In: Hawkesworth CJ, Norry MJ (eds) Continental basalts and mantle xenoliths. Shiva, Cheshire, pp 46–91

    Google Scholar 

  • Harte B, Gurney JJ (1975) Evolution of clinopyroxene and garnet in an eclogite nodule from the Roberts Victor kimberlite pipe, South Africa. Phys Chem Earth 9:367–388

    Google Scholar 

  • Harte B, Gurney JJ (1981) The mode of formation of chromiumpoor megacryst suites from kimberlites. J Geol 89:749–753

    Google Scholar 

  • Hartnady CJ, Joubert P, Stowe CW (1985) Proterozoic crustal evolution in southwestern Africa. Episodes 8:236–244

    Google Scholar 

  • Hatton CJ (1978) The geochemistry and origin of xenoliths from the Roberts Victor Mine. Unpubl PhD thesis, University of Cape Town

  • Helmstaedt HH, Schulze DJ (1988) Eclogite facies ultramafic xenoliths from Colorado Plateau diatreme breccias: comparison with eclogites in crustal environments, evaluation of the subduction hypothesis, and implications for eclogite xenoliths from diamondiferous kimberlites. In: Smith DC (ed) Eclogites and eclogite-facies rocks. Elsevier, Amsterdam, pp 387–450

    Google Scholar 

  • Holmes A (1936) A contribution to the petrology of kimberlite and its inclusions. Trans geol Soc S Afr 39:379–427

    Google Scholar 

  • Hops JJ, Gurney JJ, Harte B, Winterburn P (1989) megacrysts and high temperature nodules from the jagersfontein kimberlite pipe. In: Kimberlites and related rocks. Vol 2. Their mantle/crust setting, diamonds and diamond exploration. Geol Soc Australia spec Publ 14:759–770

  • Jagoutz E, Dawson JB, Hoernes S, Spettel B, Wanke H (1984) Anorthositic oceanic crust in the Archean Earth (abstr) Lunar and Planetary Science Conference XV abstracts:395–396

  • Jones RA (1987) Strontium and neodymium isotopic and rare-earth element evidence for the genesis of megacrysts in kimberlites of southern Africa. In: Nixon PH (ed) Mantle xenoliths. Wiley, Chichester, pp 711–724

    Google Scholar 

  • Lager G, Armbruster T, Rotella FJ, Rossman GR (1989) OH substitution in garnets: X-ray and neutron-diffraction, infrared, and geometric-modeling studies. Am Mineral 74:840–851

    Google Scholar 

  • Lappin MA, Dawson JB (1975) Two Roberts Victor cumulate eclogites and their re-equilibration. Phys Chem Earth 9:351–366

    Google Scholar 

  • Liu L (1987) Effects of H2O on the phase behavior of the forsterite-enstatite system at high pressures and temperatures and implications for the earth. Phys Earth Planet Int 49:142–167

    Google Scholar 

  • Luth RW, Virgo D, Boyd FR, Wood BJ (1990) Ferric iron in mantle-derived garnets; implications for thermobarometry and for the oxidation state of the mantle. Contrib Mineral Petrol 104:56–72

    Google Scholar 

  • MacGregor ID (1975) Petrologic and thermal structure of the upper mantle beneath South Africa in the Cretaceous. Phys Chem Earth 9:455–466

    Google Scholar 

  • Mackwell SJ, Kohlstedt DL (1990) Diffusion of hydrogen in olivine: implications for water in the mantle. J Geophys Res 95:5079–5088

    Google Scholar 

  • Martin RF, Donnay G (1972) Hydroxyl in the mantle. Am Mineral 57:554–570

    Google Scholar 

  • Mitchell RH (1984) Garnet lherzolites from the Hanaus-I and Louwrensia kimberlites of Namibia. Contrib Mineral Petrol 86:178–188

    Google Scholar 

  • Mitchell RH (1986) Kimberlites: mineralogy, geochemistry and petrology, Plenum, New York, 442 pp

    Google Scholar 

  • Mitchell RH (1987) Megcrysts in kimberlites from the Gibeon field, Namibia. Neues Jahrb Mineralogie Abh 157:267–283

    Google Scholar 

  • Moore RO (1986) A study of the kimberlites, diamonds and associated rocks and minerals from the Monastery Mine, South Africa. Unpubl PhD Thesis, University of Cape Town

  • Navon O, Hutcheon ID, Rossman GR, Wasserburg GJ (1988) Mantle-derived fluids in diamond micro-inclusions. Nature 335:784–789

    Google Scholar 

  • Neal CR, Davidson JP (1989) An unmetasomatized source for the Malaitan alnoite (Solomon Islands): petrogenesis involving zone refining, megacryst fractionation, and assimilation of oceanic lithosphere. Geochim Cosmochim Acta 53:1975–1990

    Google Scholar 

  • Nixon PH, Boyd FR (1973a) Petrogenesis of the granular and sheared ultrabasic nodule suite in kimberlite. In: Nixon PH (ed) Lesotho Kimberlites. Lesotho National Development Corporation, Maseru, pp 48–56

    Google Scholar 

  • Nixon PH, Boyd FR (1973b) The discrete nodule (megacryst) association in kimberlites from northern Lesotho. In: Nixon PH (ed) Lesotho Kimberlites. Lesotho National Development Corporation, Maseru, pp 67–75

    Google Scholar 

  • Paterson MS (1982) The determination of hydroxyl by infrared absorption in quartz, silicate glasses and similar materials. Bull Mineral 105:20–29

    Google Scholar 

  • Richardson SH, Erlank AJ, Hart SR (1985) Kimberlite-borne garnet peridotite xenoliths from old enriched subcontinental lithosphere. Earth Planet Sci Lett 75:116–128

    Google Scholar 

  • Ringwood AE (1975) The composition and petrology of the earth's mantle. McGraw-Hill, New York, 668 pp

    Google Scholar 

  • Robey JV (1981) Kimberlites of the Central Province, South Africa, Unpubl PhD Thesis, University of Cape Town

  • Rossman GR, Aines RD (1991) The hydrous components in garnets: grossular-hydrogrossular. Am Mineral 76:1153–1164

    Google Scholar 

  • Rossman GR, Rauch F, Livi R, Tombrello TA, Shi CR, Zhou ZY (1988) Nuclear reaction analysis of hydrogen in almandine, pyrope and spessartite garnets. Neues Jahrb Mineral Monatsh 1988 (4):172–178

    Google Scholar 

  • Sautter V, Harte B (1988) Diffusion gradients in an eclogite xenolith from the Roberts Victor kimberlite pipe: I. Mechanism and evolution of garnet exsolution in Al2O3-rich clinopyroxene. J Petrol 29:1325–1352

    Google Scholar 

  • Schulze DJ (1984) Cr-poor megacrysts from the Hamilton Branch kimberlite, Elliott County, Kentucky. In: Kornprobst J (ed) Developments in petrology, Vol 11 B, Kimberlites II. The mantle and crust-mantle relationships. Elsevier, Amsterdam, pp 97–108

    Google Scholar 

  • Schulze DJ (1987) Megacrysts from alkalic volcanic rocks. In: Nixon PH (ed) Mantle xenoliths. Wiley, Chichester, pp 433–451

    Google Scholar 

  • Schulze DJ (1989) Green garnets from South African kimberlites and their relationship to wehrlites and crustal uvarovites. In: Kimberlites and related rocks. Vol 2. Their mantle/crust seeting, diamonds and diamond exploration. Geol Soc Australia Spec Publ 14:820–826

  • Skogby HS, Rossman GR (1991) The intensity of amphibole OH bands in the infrared absorption spectrum. Phys Chem Minerals 18:64–68

    Google Scholar 

  • Skogby H, Bell DR, Rossman GR (1990) Hydroxide in pyroxenes; variations in the natural environment. Am Mineral 7:764–774

    Google Scholar 

  • Smith D, Boyd FR (1987) Compositional heterogeneities in a high temperature lherzolite nodule and implications for mantle processes. In: Nixon PH (ed) Mantle xenoliths. Wiley, Chichester, pp 551–561

    Google Scholar 

  • Smyth JR, Bell DR, Rossman GR (1991) Hydroxyl in upper mantle clinopyroxenes. Nature 35:732–735

    Google Scholar 

  • Smyth JR, Caporuscio FA, McCormick TC (1989) Mantle eclogite: evidence of igneous fractionation in the mantle. Earth Planet Sci Lett 93:133–141

    Google Scholar 

  • Van Calsteren PWC, Harris NBW, Hawkesworth CJ, Menzies MA, Rogers NW (1986) Xenoliths from southern Africa: perspectives on the lower crust. In: Dawson JB, Carswell DA, Hall J, Wedepohl KH (eds) The nature of the lower continental crust. Geol Soc Spec Publ 24:351–362

  • Waters FG (1987) A geochemical study of metasomatized peridotite and MARID nodules from the Kimberley pipes, South Africa. Unpubl PhD Thesis, University of Cape Town

  • Wilkins RWT, Sabine W (1973) Water content of some nominally anhydrous silicates. Am Mineral 58:508–516

    Google Scholar 

  • Winterburn PA, Harte B, Gurney JJ (1990) Peridotite xenoliths from the Jagersfontein kimberlite pipe: I. Primary and primary-metasomatic mineralogy. Geochim Cosmochim Acta 54:329–341

    Google Scholar 

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Revised manuscript submitted to Contributions to Mineralogy and Petrology November 13, 1991

Contribution number 4938

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Bell, D.R., Rossman, G.R. The distribution of hydroxyl in garnets from the subcontinental mantle of southern Africa. Contrib Mineral Petrol 111, 161–178 (1992). https://doi.org/10.1007/BF00348949

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Keywords

  • Alkali Basalt
  • Colorado Plateau
  • Garnet Crystal
  • Kaapvaal Craton
  • Garnet Composition