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Postcumulus processes in layered intrusions

Published online by Cambridge University Press:  01 May 2009

R. S. J. Sparks ,
H. E. Huppert ,
R. C. Kerr ,
D. P. McKenzie  and
S. R. Tait
R. S. J. Sparks
Affiliation:
Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, U.K.
H. E. Huppert
Affiliation:
Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge CB3 9EW, U.K.
R. C. Kerr
Affiliation:
Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge CB3 9EW, U.K.
D. P. McKenzie
Affiliation:
Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, U.K.
S. R. Tait
Affiliation:
Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, U.K.
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Abstract

During the postcumulus stage of solidification in layered intrusions, fluid dynamic phenomena play an important role in developing the textural and chemical characteristics of the cumulate rocks. One mechanism of adcumulus growth involves crystallization at the top of the cumulate pile where crystals are in direct contact with the magma reservoir. Convection in the chamber can enable adcumulus growth to occur to form a completely solid contact between cumulate and magma. Another important process may involve compositional convection in which light differentiated melt released by intercumulus crystallization is continually replaced by denser melt from the overlying magma reservoir. This process favours adcumulus growth and can allow adcumulus growth within the pore space of the cumulate pile. Calculations indicate that this process could reduce residual porosities to a few percent in large layered intrusions, but could not form pure monomineralic rocks. Intercumulus melt may also be replaced by more primitive melt during episodes of magma chamber replenishment. Dense magma, emplaced over a cumulate pile containing lower density differentiated melt may sink several metres into the underlying pile in the form of fingers. Reactions between melt and matrix may lead to changes in mineral compositions, mineral textures and whole rock isotope compositions. Another important mechanism for forming adcumulate rocks is compaction, in which the imbalance of the hydrostatic and lithostatic pressures in the cumulate pile causes the crystalline matrix to deform and intercumulus melt to be expelled. For cumulate layers from 10 to 1000 metres in thickness, compaction can reduce porosities to very low values (< 1%) and form monomineralic rocks. The characteristic time-scale for such compaction is theoretically short compared to the time required to solidify a large layered intrusion. During compaction changes of mineral compositions and texture may occur as moving melts interact with the surrounding matrix. Both compaction and compositional convection can be interrupted by solidification in the pore spaces. Compositional convection will only occur if the Rayleigh number is larger than 40, if the residual melt becomes lower in density, and the convective velocity exceeds the solidification velocity (measured by the rate of crystal accumulation in the chamber). Orthocumulates are thus more likely to form in rapidly cooled intrusions where residual melt is frozen into the pore spaces before it can be expelled by compaction or replaced by convection.

Type
Articles
Information
Geological Magazine , Volume 122 , Issue 5 , September 1985 , pp. 555 - 568
Copyright
Copyright © Cambridge University Press 1985

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References

Brown, G. M. 1956. The layered ultrabasic rocks of Rhum, Inner Hebrides. Philosophical Transactions of the Royal Society of London B240, 1–53.Google Scholar
Butcher, A. R. 1985. Channelled metasomatism in Rhum layered cumulates – evidence from late-stage veins. Geological Magazine 122, 503–18.CrossRefGoogle Scholar
Butcher, A. R., Young, I. M. & Faithfull, J. W. 1985. Finger structures in the Rhum Complex. Geological Magazine 122, 491–502.CrossRefGoogle Scholar
Campbell, I. H. 1978. Some problems with the cumulus theory. Lithos 11, 311–23.CrossRefGoogle Scholar
Chen, C. F. & Turner, J. S. 1980. Crystallization in double-diffusive system. Journal of Geophysical Research 85, 2573–93.CrossRefGoogle Scholar
Hess, H. H. 1939. Extreme fractional crystallization of a basaltic magma: the Stillwater igneous complex. Transactions of the American Geophysical Union 3, 431–2.Google Scholar
Hess, H. H. 1960. Stillwater Igneous Complex, Montana, a Quantitative Mineralogical Study. Geological Society of America Memoir no. 80.Google Scholar
Hess, G. B. 1972. Heat and mass transfer – Stillwater Complex. Geological Society of America Bulletin (Harry Hess Volume), Memoir 132, 503–20.CrossRefGoogle Scholar
Huppert, H. E. & Sparks, R. S. J. 1980. The fluid dynamics of a basaltic magma chamber, replenished by an influx of hot, dense ultrabasic magma. Contributions to Mineralogy and Petrology 75, 279–89.CrossRefGoogle Scholar
Huppert, H. E. & Sparks, R. S. J. 1984, Double-diffusive convection due to crystallization in magmas. Annual Reviews of Earth and Planetary Sciences 12, 11–37.CrossRefGoogle Scholar
Huppert, H. E. & Worster, M. G. 1985. Dynamic solidification of a binary melt. Nature 314, 703–6.CrossRefGoogle Scholar
Irvine, T. N. 1970. Heat transfer during the solidification of layered intrusions. I. Sheets and sills. Canadian Journal of Earth Sciences 7, 1031–61.CrossRefGoogle Scholar
Irvine, T. N. 1980. Magmatic infiltration metasomatism, double-diffusive fractional crystallization, and adcumulus growth in the Muskox and other layered intrusions. In Physics of Magmatic Processes (ed. Hargraves, R. B.), pp. 325–83. Princeton University Press.CrossRefGoogle Scholar
Irvine, T. N. 1982. Terminology for layered intrusions. Journal of Petrology 23, 127–62.CrossRefGoogle Scholar
Irvine, T. N., Keith, D. W. & Todd, S. G. 1983. The J–M Platinum–Palladium Reef of the Stillwater Complex, Montana. I. Origin by double-diffusive convective magma mixing and implications for the Bushveld Complex. Economic Geology 78, 1287–1334.CrossRefGoogle Scholar
Jackson, E. D. 1961. Primary textures and mineral associations in the ultramafic zone of the Stillwater Complex, Montana. U.S. Geological Survey Professional Paper no. 358, p. 106.Google Scholar
Kerr, R. C. & Tait, S. R. (1985 a). Crystallization and compositional convection in a porous medium cooled from below with application to layered igneous intrusions. Journal of Geophysical Research (sub judice).Google Scholar
Kerr, R. C. & Tait, S. R. (1985 b). Convective exchange between pore fluid and an overlying reservoir of dense fluid: applications to replenished magma chambers. Earth and Planetary Science Letters (in press).CrossRefGoogle Scholar
Kerr, R. C. & Turner, J. S. 1982. Layered convection and crystal layers in multicomponent systems. Nature 298, 731–3.CrossRefGoogle Scholar
Lapwood, E. R. 1948. Convection of a fluid in a porous medium. Proceedings of the Cambridge Philosophical Society 44, 508–27.CrossRefGoogle Scholar
McBirney, A. R. 1980. Mixing and unmixing of magmas. Journal of Volcanology and Geothermal Research 7, 357–71.CrossRefGoogle Scholar
McBirney, A. R. & Noyes, R. M. 1979. Crystallization and layering of the Skaergaard intrusion. Journal of Petrology 20, 487–554.CrossRefGoogle Scholar
McKenzie, D. P. 1984. The generation and compaction of partially molten rock. Journal of Petrology 25, 713–65.CrossRefGoogle Scholar
McKenzie, D. P. 1985. The extraction of magma from the crust and mantle. Earth and Planetary Science Letters (in press).CrossRefGoogle Scholar
Morse, S. A. 1969. Geology of the Kiglapait Layered Intrusion, Labrador. Geological Society of America Memoir no. 112.Google Scholar
Morse, S. A. 1979. Kiglapait Geochemistry. II. Petrography. Journal of Petrology 20, 591–624.CrossRefGoogle Scholar
Morse, S. A. 1982. Adcumulus growth of anorthosite at the base of the Lunar Crust. Journal of Geophysical Research, Supplement to Volumes 87 and 88: Proceedings of the 13th Lunar and Planetary Science Conference, p. 29.Google Scholar
Palacz, Z. A. & Tait, S. R. 1985. Isotopic and geochemical investigation of unit 10 from the Eastern Layered Series of the Rhum Intrusion, Northwest Scotland. Geological Magazine 122, 485–90.CrossRefGoogle Scholar
Richter, F. M. & McKenzie, D. P. 1984. Dynamical models for melt segregation from a deformable matrix. Journal of Geology 92, 729–40.CrossRefGoogle Scholar
Scott, D. R. Stevenson, D. J. 1984. Magma solitons. Geophysical Research Letters 11, 1161–4.CrossRefGoogle Scholar
Sparks, R. S. J. & Huppert, H. E. 1984. Density changes during the fractional crystallization of basaltic magmas: implications for the evolution of layered intrusions. Contributions to Mineralogy and Petrology 85, 300–9.CrossRefGoogle Scholar
Tait, S. R. 1985. Fluid dynamic and geochemical evolution of cyclic unit 10, Rhum, Eastern Layered Series. Geological Magazine 122, 469–84.CrossRefGoogle Scholar
Tait, S. R., Huppert, H. E. & Sparks, R. S. J. 1984. The role of compositional convection in the formation of adcumulate rocks. Lithos 17, 139–46.CrossRefGoogle Scholar
Wadsworth, W. J. 1985. Terminology of postcumulus processes and products in the Rhum layered intrusion. Geological Magazine 122, 549–54.CrossRefGoogle Scholar
Wager, L. R. & Brown, G. M. 1968. Layered Igneous Rocks. Edinburgh and London: Oliver & Boyd.Google Scholar
Wager, L. R., Brown, G. M. & Wadsworth, W. J. 1960. Types of igneous cumulates. Journal of Petrology 1, 73–85.CrossRefGoogle Scholar
Wager, L. R. & Deer, W. A. 1939. Geological investigations in East Greenland. Part III. The petrology of the Skaergaard intrusion, Kangerlwgssauk. Meddelelser om Gronland 105, (4), 1–352.Google Scholar
Wilson, A. H. 1982. The Geology of the Great Dyke of Zimbabwe; The ultramafic rocks. Journal of Petrology 23, 240–92.CrossRefGoogle Scholar
Wilson, J. R. & Larsen, S. B. 1985. Two-dimensional study of a layered intrusion – the Hyllingen Series, Norway. Geological Magazine 122, 97–124.CrossRefGoogle Scholar
Young, I. M. 1984. Mixing of supernatant and interstial fluids in the Rhum layered intrusion. Mineralogical Magazine 48, 345–50.CrossRefGoogle Scholar
Young, I. M. & Donaldson, C. H. 1985. Formation of granular-textured layers and laminae within the Rhum crystal pile. Geological Magazine 122, 519–28.CrossRefGoogle Scholar