Abstract
Chrome-spinels from the layered Peridotilte Series of the unmetamorphosed, anorogenic 60 Ma Cuillin Igneous Complex, Isle of Skye, display a wide variety of compositions. Cumulus (within seams) chrome-spinels from the lowest exposed portion of the Peridotite Series exhibit features indicative of textural equilibrium, are rich in Al and Mg, and have low values of the ratio Cr/(Cr+Al). Cumulus chrome-spinels from higher up in the series are different from these: particularly, textural disequilibrium is evident, intercumulus plagioclase and olivine are present, and the chrome-spinels are rich in Cr, Fe and Ti, with high values of the ratio Cr/(Cr+Al). Intercumulus (dispersed) chrome-spinels tend towards anhedral forms and define enrichment trends towards Fe (both Fe2+ and Fe3+) with decreasing Mg, Cr and Al, and towards Al, with decreasing Fe2+ and Cr (and increasing Mg). Individual crystals are completely homogeneous and are devoid of reaction rims. The observed textural characteristics and compositional data of the chrome-spinels documented here suggest that the semi-quantitative peritectic reaction: aluminous chrome-spinel + melt→plagioclase + olivine + chromian chrome-spinel, is responsible for the observed parageneses, and that both the environment of crystallization (eumulus or intercumulus) and the role of plagioclase ±olivine crystallization are critical parameters for this geochemical trend in spinels within upper crustal magmatic systems. The effects of pyroxene crystallization on the development of this geochemical trend are also considered. This investigation highlights the need to consider the role of post-cumulus mineral-melt reactions and their influences upon the final compositions of major oxide and silicate phases within layered intrusions.
Article PDF
Similar content being viewed by others
Avoid common mistakes on your manuscript.
References
Agata T (1988) Chrome spinels from the Oura layered igneous complex, Central Japan. Lithos 21:97–108
Bell BR, Harris JW (1986) An excursion guide to the geology of the Isle of Skye. Geol Soc Glasgow
Bevan JC (1982) Reaction rims of orthopyroxene and plagioclase around chrome spinels in olivine from Skye and Rhum (NW Scotland). Contrib Mineral Petrol 79:124–129
Brooks CK (1980) Episodic volcanism epeirogenesis and the formation of the North Atlantic Ocean. Palaeogeogr Palaeoclimatol Palaeoecol 30:229–242
Brown GM (1956) The layered ultrabasic rocks of Rhum, Inner Hebrides. Phil Trans R Soc Lond B 240:1–53
Cameron EN (1969) Postcumulus changes in the eastern Bushveld Complex. Am Mineral 54:754–779
Cameron EN (1975) Postcumulus and subsolidus equilibration of chromite and coexisting silicates in the eastern Bushveld Complex. Geochim Cosmochim Acta 39:1021–1033
Claydon RV, Bell BR (1992) The structure and petrology of ultrabasic rocks in the southern part of the Cuillin Igneous Complex, Isle of Skye. Trans R Soc Edinb: Earth Sci (in press)
Deer WA, Howie RA, Zussman J (1966) An introduction to rockforming minerals. Longman, London
Dick HJB, Bullen T (1984) Chromian spinel as a petrogenetic indicator in abyssal and alpine-type peridotites and spatially associated lavas. Contrib Mineral Petrol 86:54–76
Donaldson CH, Drever HI, Johnston R (1973) Crystallization of poikilo-macrospherulitic feldspar in a Rhum peridotite. Nature (Phys Sci) 243:69–70
Dunham AC, Wadsworth WJ (1978) Cryptic variation in the Rhum layered intrusion. Mineral Mag 42:347–356
Dunham AC, Wilkinson FCF (1985) Sulphide droplets and the unit 11/12 chromite band, Rhum: a mineralogical study. Geol Mag 122:539–548
Eales HV, Reynolds IM (1986) Cryptic variations within chromitites of the upper critical zone, northwestern Bushveld Complex. Econ Geol 81:1056–1066
Evans BW, Moore JG (1968) Mineralogy as a function of depth in the pre-historic Makaopuhi tholeiitic lava lake, Hawaii. Contrib Mineral Petrol 17:85–115
Eabries J (1979) Spinel-olivine geothermometry in peridotites from ultramafic complexes. Contrib Mineral Petrol 69:329–336
Finger LW (1972) The uncertainty in the calculated ferric iron content of a microprobe analysis. Carnegie Inst Washington Yearb 71:600–603
Fisk MR, Bence AE (1980) Experimental crystallization of chrome spinel in FAMOUS basalt 527-1-1. Earth Planet Sci Lett 48:111–123
Haggerty SE (1976) Opaque mineral oxides in terrestrial igneous rocks. In: Rumble D (ed) Oxide minerals. Res Mineral, Mineral Soc Am, vol 3
Hamlyn PR, Keays RR (1979) Origin of chromite compositional variation in the Panton Sill, western Australia. Contrib Mineral Petrol 69:75–82
Harker A (1904) The Tertiary igneous rocks of Skye. Memoir, Brit Geol Sury
Henderson P (1975) Reaction trends shown by chrome-spinels of the Rhum layered intrusion. Geochim Cosmochim Acta 39:1035–1044
Henderson P, Suddaby P (1971) The nature and origin of the chrome-spinel of the Rhum layered intrusion. Contrib Mineral Petrol 33:21–31
Henderson P, Wood RJ (1981) Reaction relationships of chromespinels in igneous rocks-further evidence from the layered intrusions of Rhum and Mull, Inner Hebrides. Contrib Mineral Petrol 78:225–229
Hunter RH (1987) Textural equilibration in layered igneous rocks. In: Parsons I (ed) Origins of igneous layering. Reidel, Dordrecht, pp 473–503
Irvine TN (1965) Chromian spinel as a petrographic indicator. Pt 1 Theory. Can J Earth Sci 2:648–672
Irvine TN (1967) Chromian spinel as a petrographic indicator. Pt 2 Petrologic applications. Can J Earth Sci 4:71–103
Irvine TN (1982) Terminology for layered intrusions. J Petrol 23:127–162
Irvine TN (1987) Processes involved in the formation and development of layered igneous rocks. In: Parsons I (ed) Origins of igneous layering. Reidel, Dordrecht, pp 649–656
Irvine TN, Smith CH (1969) Primary oxide minerals in the layered series of the Muskox intrusion. In: Wilson HDB (ed) Magmatic ore deposits — a symposium. Monogr Econ Geol 4:76–94
Jackson ED (1963) Stratigraphic and lateral variation of chromite composition in the Stillwater Complex. Mineral Soc Am Sp Pap 1:46–54
Jan MQ, Windley BF (1990) Cr-spinel-silicate chemistry in ultramafic rocks of the Jijal Complex, NW Pakistan. J Petrol 31:667–715
Ozawa K (1983) Evaluation of olivine-spinel geothermometry as an indicator of thermal history for peridotites. Contrib Mineral Petrol 82:52–65
Parsons I (1987) Origins of igneous layering. Reidel, Dordrecht
Ridley WI (1977) The crystallization trends of spinels in Tertiary basalts from Rhum and Muck and their petrogenetic significance. Contrib Mineral Petrol 64:243–255
Roeder PL, Campbell IH, Jamieson HE (1979) A re-evaluation of the olivine-spinel geothermometer. Contrib Mineral Petrol 68:325–334
Thayer TP (1946) Preliminary chemical correlation of chromite with the containing rocks. Econ Geol 41:202–217
Wager LR, Brown GM (1968) Layered igneous rocks. Oliver and Boyd, Edinburgh
Weedon DS (1965) The layered ultrabasic rocks of Sgurr Dubh, Isle of Skye. Scot J Geol 1:41–68
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Bell, B.R., Claydon, R.V. The cumulus and post-cumulus evolution of chrome-spinels in ultrabasic layered intrusions: evidence from the Cuillin Igneous Complex, Isle of Skye, Scotland. Contr. Mineral. and Petrol. 112, 242–253 (1992). https://doi.org/10.1007/BF00310458
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00310458