Advertisement

Contributions to Mineralogy and Petrology

, Volume 121, Issue 2, pp 115–125 | Cite as

A clinopyroxene geobarometer for basaltic systems based on crystal-structure modeling

  • Paolo Nimis
Article

Abstract

The crystal chemical response of basalt clinopyroxene to increasing pressure was investigated by means of crystal-structure simulation (a procedure that enables modeling of the structural parameters of a clinopyroxene of known chemistry without requiring direct X-ray diffraction analysis) using available experimental chemical data. Pressure proved the main physical variable governing clinopyroxene behavior in a magmatic environment. The general internal consistency of the simulation data permitted construction of an empirical geobarometer based on the relationship of cell volume (Vc) vs M1-site volume (VM1). The straightforward geobarometric formulation in the absence of direct X-ray analysis is: P(kbar) = 698.443 + 4.985-AlT - 26.826-Fe M1 2+ - 3.764-Fe3+ + 53.989-AlM1 + 3.948-Ti + 14.651.Cr - 700.431.Ca - 666.629.Na - 682. 848-MgM2 - 691.138-Fe M2 2+ - 688.384-Mn - 6.267-(MgM2)2 -4.144-(Fe M2 2+ ) where: (Fe M1 2+ -MgM2)/(Fe M2 2+ -MgM1) = e**(0.238-R3+ + 0.289.CNM - 2.315), CNM = Ca + Na + Mn, and R3+ = A1M1 + Fe3+ + Ti + Cr, with cations in atoms per formula unit. The geobarometer reproduces experimental pressures within α 2 kbar (= 1 σ max. dev. ≤ 5 kbar; N = 29) in the range 0-24 kbar and is applicable to near-liquidus C2/c clinopyroxenes crystallized from basaltic melts in the absence of garnet (excepting high-Al2O3 basalts). It is therefore suitable for many natural clinopyroxenes occurring as mega- or phenocrysts or forming well-preserved cumulate pyroxenites. If the above restrictions are not wholly satisfied, the Vc vs VM1 plot can also be used qualitatively to deduce the relative pressure conditions of clinopyroxenes forming from similar batches of magma. The structural simulation of experimental data also provided insight into the influence of minor chemical changes of the parental magma on the crystal chemistry of clinopyroxene at high pressure. Within the considered compositional space at given P-T, αCaO and αSi02 in the melt have opposite effects on M2- and T-site cation populations. As a result, under similar physical conditions, clinopyroxenes from high-er-CaO or more undersaturated basalts have higher VM2, VT and Vc and lower VM1. For basalts with normal contents of A12O3 (< 18 wt%), variations of major elements in the melt do not reduce the accuracy of the geobarometer.

Keywords

Contrib Mineral Petrol Alkaline Basalt Basaltic System Similar Physical Condition Relative Pressure Condition 
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.

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. Baerlocher C, Hepp A, Meier WM (1977) DLS-76. A program for the simulation of crystal structures by geometric refinement. Institute of Crystallography and Petrography, ETH Zürich, SwitzerlandGoogle Scholar
  2. Bartels KS, Kinzler RJ, Grove TL (1991) High pressure phase relations of primitive high-alumina basalts from Medicine Lake volcano, northern California. Contrib Mineral Petrol 108: 253–270CrossRefGoogle Scholar
  3. Bender JF, Hodges FN, Bence AE (1978) Petrogenesis of basalts from the project FAMOUS area: experimental study from 0 to 15 kbars. Earth Planet Sci Lett 41: 277–302CrossRefGoogle Scholar
  4. Bertolo S, Nimis P, Dal Negro A (1994) Low-Ca augite from experimental alkali basalt at 18 kbar: structural variation towards the miscibility gap. Am Mineral 79: 668–674Google Scholar
  5. Brey GP, Köhler T (1990) Geothermobarometry in four-phase lherzolites II. New thermobarometers, and practical assessment of existing thermobarometers. J Petrol 31: 1353–1378Google Scholar
  6. Burnham CW, Clark JR, Papike JJ Prewitt CT (1967) A proposed crystallographic nomenclature for clinopyroxene structures. Z Krist 125: 109–119CrossRefGoogle Scholar
  7. Dal Negro A, Carbonin S, Molin GM, Cundari A, Piccirillo EM (1982) Intracrystalline cation distribution in natural clinopyroxenes of tholeiitic, transitional, and alkaline basaltic rocks. In: Saxena SK (ed) Advances in physical geochemistry (vol 2). Springer, New York Berlin, pp 117–150Google Scholar
  8. Dal Negro A, Molin GM, Salviulo G, Secco L, Cundari A, Piccirillo EM (1989a) Crystal chemistry of clinopyroxene and its petrogenetic significance: a new approach. In: Boriani A, Bonafede M, Piccardo GB, Vai GB (eds) The lithosphere in Italy: advances in earth science research (Italian National Committee for the International Lithosphere Program). Acc Naz Lincei, Atti Convegni Lincei 80: 271–295Google Scholar
  9. Dal Negro A, Manoli S, Secco L, Piccirillo EM (1989b) Megacrystic clinopyroxenes from Victoria (Australia): crystal chemical comparisons of pyroxenes from high and low pressure regimes. Eur J Mineral 1: 105–121Google Scholar
  10. Draper DS, Johnston AD (1992) Anhydrous PT phase relations of an Aleutian high-MgO basalt: an investigation of the role of olivine-liquid reaction in the generation of arc-alumina basalts. Contrib Mineral Petrol 112: 501–519CrossRefGoogle Scholar
  11. Dunn T(1987) Partitioning of Hf, Lu, Ti, and Mn between olivine, clinopyroxene and basaltic liquid. Contrib Mineral Petrol 96: 476–494CrossRefGoogle Scholar
  12. Green DH, Hibberson W (1970) Experimental duplication of conditions of precipitation of high-pressure phenocrysts in a basaltic magma. Phys Earth Planet Inter 3: 247–254CrossRefGoogle Scholar
  13. Green DH, Ringwood AE (1967) The genesis of basaltic magmas. Contrib Mineral Petrol 15: 103–190CrossRefGoogle Scholar
  14. Johnston AD (1986) Anhydrous P-T phase relations of near-primary high-alumina basalt from the South Sandwich Islands. Implications for the origin of island arcs and tonalite-trondhjemite series rocks. Contrib Mineral Petrol 92: 368–382CrossRefGoogle Scholar
  15. Knutson J, Green DH (1975) Experimental duplication of a high-pressure megacryst/cumulate assemblage in a near-saturated hawaiite. Contrib Mineral Petrol 52: 121–132CrossRefGoogle Scholar
  16. Kuno H (1960) High-alumina basalt. J Petrol 1: 121–145Google Scholar
  17. Mahood GA, Baker DR (1986) Experimental constraints on depths of fractionation of mildly alkalic basalts and associated felsic rocks: Pantelleria, Strait of Sicily. Contrib Mineral Petrol 93: 251–264CrossRefGoogle Scholar
  18. Malgarotto C, Molin GM, Zanazzi PF(1993) Crystal chemistry of clinopyroxenes from Filicudi and Salina (Aeolian Islands, Italy). Geothermometry and barometry. Eur J Mineral 5: 915–923Google Scholar
  19. Manoli S, Molin GM (1988) Crystallographic procedures in the study of experimental rocks: X-ray single-crystal structure refinement of C2/c clinopyroxene from lunar 74275 high-pressure experimental basalt. Mineral Petrol 39: 187–200CrossRefGoogle Scholar
  20. Mellini M, Carbonin S, Dal Negro A, Piccirillo EM (1988) Tholeiitic hypabyssal dykes: how many clinopyroxenes? Lithos 22: 127–134CrossRefGoogle Scholar
  21. Molin G, Zanazzi PF (1991) Intracrystalline Fe2+-Mg ordering in augite: experimental study and geothermometric applications. Eur J Mineral 3: 863–875Google Scholar
  22. Nimis P (1994) Cristallochimica di clinopirosseni e spinelli di noduli ultrafemici (Iblei, Sicilia) ed applicazioni geotermobarometriche. PhD thesis, Univ. degli Studi di PadovaGoogle Scholar
  23. Nimis P, Vannucci R (1995) An ion microprobe study of clinopyroxenes in websteritic and megacrystic xenoliths from Hyblean Plateau (SE Sicily, Italy): constraints on HFSE/REE/Sr fractionation at mantle depth. Chem Geol (in press)Google Scholar
  24. Ottonello G, Delia Giusta A, Dal Negro A, Baccarin F (1992) A structure energy model for C2/c pyroxenes in the system Na-Mg-Ca-Mn-Fe-Al-Cr-Ti-Si-O. In: Saxena SK (ed) Advances in Physical Geochemistry, Thermodynamic Data. Springer, New York Berlin pp 194–238Google Scholar
  25. Papike JJ, Cameron K, Baldwin K (1974) Amphiboles and pyroxenes; characterization of other than quadrilateral components and estimates of ferric iron from microprobe data. Geol Soc Am Abstr Prog 6: 1053–1054Google Scholar
  26. Sack RO, Carmichael ISE, Rivers M, Ghiorso MS (1980) Ferricferrous equilibria in natural silicate liquids at 1 bar. Contrib Mineral Petrol 75: 369–376CrossRefGoogle Scholar
  27. Takeda H (1972) Crystallographic studies of coexisting aluminan orthopyroxene and augite of high-pressure origin. J Geophys Res 77: 5798–5811CrossRefGoogle Scholar
  28. Thompson RN (1974) Some high-pressure pyroxenes. Mineral Mag 39: 768–787CrossRefGoogle Scholar
  29. Thy P (1991) High and low pressure phase equilibria of a mildly alakalic lava from the 1965 Surtsey eruption: experimental results. Lithos 26: 223–243CrossRefGoogle Scholar
  30. Tormey DR, Grove TL, Bryan WB (1987) Experimental petrology of normal MORB near the Kane Fracture Zone: 22°-25° N, mid-Atlantic ridge. Contrib Mineral Petrol 96: 121–139CrossRefGoogle Scholar

Copyright information

© Springer-Verlag 1995

Authors and Affiliations

  • Paolo Nimis
    • 1
  1. 1.Dipartimento di Mineralogia e PetrologiaUniversità degli Studi di PadovaPadovaItaly

Personalised recommendations