Research paper
The effect of explosive eruption processes on geochemical patterns within pyroclastic deposits

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Abstract

The effects of magma fragmentation and atmospheric transport of pyroclasts in modifying tephra chemistry are quantitatively examined in order to assist in devising geochemical sampling strategies for young pyroclastic deposits, with particular regard to air-fall tephra. Magma fragmentation during explosive eruption results in crystal fractionation, the extent of which increases with decreasing tephra particle size. Among the products of a single sustained plinian eruption, variable atmospheric flight times of pyroclasts may cause simultaneous deposition of earlier-erupted and later-erupted material. Both of these processes will affect the degree and nature of chemical variations found in individual pyroclastic deposits. Their effects may be largely overcome by sampling coarse tephra within a narrow grain-size range.

References (35)

  • R.L. Hay

    Formation of the crystal-rich glowing avalanche deposits of St. Vincent

    B.W.I. J. Geol.

    (1959)
  • W. Hildreth

    The Bishop Tuff: evidence for the origin of compositional zonation in silicic magma chambers

    Geol. Soc. Am., Spec. Pap.

    (1979)
  • P.W. Lipman

    Chemical comparison of glassy and crystalline volcanic rocks

    U.S. Geol. Surv. Bull.

    (1965)
  • P.W. Lipman

    Mineral and chemical variations within an ash-flow sheet from Aso Caldera, Southwestern Japan

    Contrib. Mineral. Petrol.

    (1967)
  • P.W. Lipman et al.

    Retention of alkalies by calc-alkaline rhyolites during recrystallisation and hydration

    Am. Mineral.

    (1969)
  • D.C. Noble

    Sodium, potassium and ferrous iron contents of some secondarily hydrated natural silicic glasses

    Am. Mineral.

    (1967)
  • R.J. Parker

    Factors affecting the quality of major element rock analysis by X-ray fluorescence combined with flux-fusion sample preparation

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    Present address: Geology Department, University of Texas at Arlington, UTA Box No. 19049, Arlington, TX 76019, U.S.A.

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