Late-stage volcano geomorphic evolution of the Pleistocene San Francisco Mountain, Arizona (USA), based on high-resolution DEM analysis and 40Ar/39Ar chronology

Dávid Karátson, Tamás Telbisz, Brad S. Singer

Research output: Contribution to journalArticle

12 Citations (Scopus)

Abstract

The cone-building volcanic activity and subsequent erosion of San Francisco Mountain, AZ, USA, were studied by using high-resolution digital elevation model (DEM) analysis and new 40Ar/39Ar dating. By defining remnants or planèzes of the volcano flanks in DEM-derived images, the original edifice can be reconstructed. We propose a two-cone model with adjacent summit vents which were active in different times. The reconstructed cones were 4,460 and 4,350 m high a.s.l., corresponding to ~2,160 and 2,050 m relative height, respectively. New 40Ar/39Ar data allow us to decipher the chronological details of the cone-building activity. We dated the Older and Younger Andesites of the volcano that, according to previous mapping, built the stage 2 and stage 3 stratocones, respectively. The new 40Ar/39Ar plateau ages yielded 589-556 ka for the Older and 514-505 ka for the Younger Andesites, supporting their distinct nature with a possible dormant period between. The obtained ages imply an intense final (≤100 ka long) cone-building activity, terminating ~100 ka earlier than indicated by previous K-Ar ages. Moreover, 40Ar/39Ar dating constrains the formation of the Inner Basin, an elliptical depression in the center of the volcano initially created by flank collapse. A 530 ka age (with a ±58.4 ka 2σ error) for a post-depression dacite suggests that the collapse event is geochronologically indistinguishable from the termination of the andesitic cone-building activity. According to our DEM analysis, the original cone of San Francisco Mountain had a volume of about 80 km3. Of this volume, ~7.5 km3 was removed by the flank collapse and subsequent glacial erosion, creating the present-day enlarged Inner Basin, and ~2 km3 was removed from the outer valleys by erosion. Based on volumetric analysis and previous and new radiometric ages, the average long-term eruption rate of San Francisco Mountain was ~0.2 km3/ka, which is a medium rate for long-lived stratovolcanoes. However, according to the new 40Ar/39Ar dates for the last ≤100 ka period, the final stratovolcanic activity was characterized by a greater ~0.3 km3/ka rate.

Original languageEnglish
Pages (from-to)833-846
Number of pages14
JournalBulletin of Volcanology
Volume72
Issue number7
DOIs
Publication statusPublished - Apr 30 2010

Keywords

  • Ar/Ar geochronology
  • Colorado Plateau
  • DEM analysis
  • Erosion
  • San Francisco Mountain
  • Stratovolcanic activity
  • Volcanic geomorphology

ASJC Scopus subject areas

  • Geochemistry and Petrology

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