Towards the definition of AMS facies in the deposits of pyroclastic density currents
The Use of Palaeomagnetism and Rock Magnetism to Understand Volcanic Processes
By: M.H. Ort, T.T. Newkirk, J.F. Vilas, and J.A. Vazquez
Edited by: M.H. Ort, Massimiliano Porreca, and J. W. Geissman
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Abstract
Anisotropy of magnetic susceptibility (AMS) provides a statistically robust technique to characterize the fabrics of deposits of pyroclastic density currents (PDCs). AMS fabrics in two types of pyroclastic deposits (small-volume phreatomagmatic currents in the Hopi Buttes volcanic field, Arizona, USA, and large-volume caldera-forming currents, Caviahue Caldera, Neuquén, Argentina) show similar patterns. Near the vent and in areas of high topographical roughness, AMS depositional fabrics are poorly grouped, with weak lineations and foliations. In a densely welded proximal ignimbrite, this fabric is overprinted by a foliation formed as the rock compacted and deformed. Medial deposits have moderate–strong AMS lineations and foliations. The most distal deposits have strong foliations but weak lineations. Based on these facies and existing models for pyroclastic density currents, deposition in the medial areas occurs from the strongly sheared, high-particle-concentration base of a density-stratified current. In proximal areas and where topography mixes this denser base upwards into the current, deposition occurs rapidly from a current with little uniformity to the shear, in which particles fall and collide in a chaotic fashion. Distal deposits are emplaced by a slowing or stalled current so that the dominant particle motion is vertical, leading to weak lineation and strong foliation.
Suggested Citation
Ort, M., Newkirk, T., Vilas, J., Vazquez, J., 2014, Towards the definition of AMS facies in the deposits of pyroclastic density currents: The Use of Palaeomagnetism and Rock Magnetism to Understand Volcanic Processes, v. 396, 22 p., https://doi.org/10.1144/SP396.8.
Study Area
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Towards the definition of AMS facies in the deposits of pyroclastic density currents |
| Series title | The Use of Palaeomagnetism and Rock Magnetism to Understand Volcanic Processes |
| DOI | 10.1144/SP396.8 |
| Volume | 396 |
| Publication Date | January 23, 2014 |
| Year Published | 2014 |
| Language | English |
| Publisher | Geological Society of London |
| Contributing office(s) | Volcano Science Center |
| Description | 22 p. |
| Larger Work Type | Article |
| Larger Work Subtype | Journal Article |
| Larger Work Title | The Use of Palaeomagnetism and Rock Magnetism to Understand Volcanic Processes |
| Country | Argentina;United States |
| State | Arizona;Neuqu�n |
| Other Geospatial | Caviahue Caldera;Hopi Buttes Volcanic Field |