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Bulletin of Volcanology

, 68:37 | Cite as

Gravitational spreading causes en-echelon diking along a rift zone of Madeira Archipelago: an experimental approach and implications for magma transport

  • Andreas Klügel
  • Thomas R. Walter
  • Stefanie Schwarz
  • Jörg Geldmacher
Research Article

Abstract

Many volcanic rift zones show dikes that are oriented oblique rather than parallel to the morphological ridge axis. We have evidence that gravitational spreading of volcanoes may adjust the orientation of ascending dikes within the crust and segment them into en-echelon arrays. This is exemplified by the Desertas Islands which are the surface expression of a 60 km long submarine ridge in southeastern Madeira Archipelago. The azimuth of the main dike swarm (average = 145°) deviates significantly from that of the morphological ridge (163°) defining an en-echelon type arrangement. We propose that this deviation results from the gravitational stress field of the overlapping volcanic edifices, reinforced by volcano spreading on weak substratum. We tested our thesis experimentally by mounting analogue sand piles onto a sand and viscous PDMS substratum. Gravitational spreading of this setup produced en-echelon fractures that clearly mimic the dike orientations observed, with a deviation of 10°–32° between the model’s ridge axis and that of the main fracture swarm. Using simple numerical models of segmented dike intrusion we found systematic changes of displacement vectors with depth and also with distance to the rift zone resulting in a complex displacement field. We propose that at depth beneath the Desertas Islands, magmas ascended along the ridge to produce the overall present-day morphology. Above the oceanic basement, gravitational stress and volcano spreading adjusted the principal stress axes’ orientations causing counterclockwise dike rotation of up to 40°. This effect limits the possible extent of lateral dike propagation at shallow levels and may have strong control on rift evolution and flank stability. The results highlight the importance of gravitational stress as a major, if not dominant factor in the evolution of volcanic rift zones.

Keywords

Rift zone Volcanic spreading En-echelon Volcano-tectonics Dikes Oceanic island Madeira Archipelago 

Notes

Acknowledgements

We are grateful to Directors H. Costa-Neves and S. Fontinha and the staff from the Parque Natural da Madeira for their kind permission and excellent support during our field studies on Ilhas Desertas. Without the professional help on the islands and the zodiac rides provided by the park rangers, this study would not have been possible. K. Schmidt and S. Tille helped us carry out the experiments. A. Gudmundsson and A. Borgia are thanked for their constructive reviews and critical suggestions that improved the manuscript. The research was supported by the Deutsche Forschungsgemeinschaft (DFG grant KL1313/2-1 and KL1313/4-2)

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Copyright information

© Springer-Verlag 2005

Authors and Affiliations

  • Andreas Klügel
    • 1
  • Thomas R. Walter
    • 2
  • Stefanie Schwarz
    • 1
  • Jörg Geldmacher
    • 3
  1. 1.Universität Bremen, Fachbereich GeowissenschaftenBremenGermany
  2. 2.Marine Geology and Geophysics, RSMASUniversity of MiamiMiamiUSA
  3. 3.IFM-GEOMAR, Leibniz-Institute for Marine SciencesKielGermany

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