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Bulletin of Volcanology

, Volume 49, Issue 6, pp 765–776 | Cite as

Variation in peperite textures associated with differing host-sediment properties

  • Cathy J. Busby-Spera
  • James D. L. White
Article

Abstract

Peperites formed by mixing of magma and wet sediment are well exposed along Punta China, Baja California, Mexico, where two sills intrude a section of lava flows, limestones, and volcaniclastic rocks. Irregular lobes and dikes extend from the sills several meters into host sediments, including highly comminuted flow top breccias (lithic lapilli tuff breccias) and shelly micrites, whereas intrusive contacts with lava flows are sharp and planar. Where one sill intruded both coarse-grained volcaniclastic rock and fine-grained limestone, textural differences between the hosts produced strikingly different styles of peperite. Blocky masses of the basaltic intrusions up to 1 m in size were dispersed for distances up to 3 m into host lithic lapilli tuff breccias; the blocks consequently underwent in situ fragmentation as they were rapidly quenched. The high degree of dispersion resulted from steam explosions as the magma enveloped pockets of water in the coarse-grained permeable host. Elutriation of fine-grained material from vertical pipes in tuff breccia above the lower sill provides evidence for meter-scale fluidization of the host. The contact zone between the basaltic magma and the shelly micrite host resembles a mixture of two viscous, immiscible fluids (fluidal peperite). Intrusion occurred behind a stable vapor film which entrained lime mud particles and carried them off “grain by grain” as magma advanced into the host. Thin-section-scale elutriation pipes formed. Microglobular peperite represents a “frozen” example of a fuel-coolant interaction (FCI) between basaltic magma and fluidized micrite host. The intimate intermixing of magma and host at the submillimeter level is attributed to fluid instabilities developed along the magma-vapor-host interface. Such intimate intermixing of magma and water-bearing fragmental debris is commonly a precursory step toward explosive hydrovolcanism.

Keywords

Breccia Lava Flow Micrite Basaltic Magma Steam Explosion 
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.

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Copyright information

© Springer-Verlag 1987

Authors and Affiliations

  • Cathy J. Busby-Spera
    • 1
  • James D. L. White
    • 1
  1. 1.University of CaliforniaDepartment of Geological SciencesSanta BarbaraUSA

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