Jemez Mountains & Valles Caldera

Location: Valles Caldera, 35 degrees, 30 minutes to 36 degrees, 15 minutes N latitude, 105 degrees, 15 minutes to 106 degrees, 45 minutes W longitude Type: Basalt-Rhyolite Volcanism and Resurgent Caldera Age: Early Pliocene to late Pleistocene Significance: The type area for resurgent ash flow calderas; one of the largest young calderas in the world.

The Valles Caldera lies within the Jemez Volcanic Field, a large complex of basaltic through rhyolitic volcanism accumulated over the last 13 million years, culminating in ash flow eruptions and caldera collapse. The Valles Caldera is the type area for resurgent ash flow calderas. This type of caldera is characterized by post-collapse upward buldging, or resurgence, of the caldera floor and eruptions of late silicic domes along the interior ring fracture.

basaltic through rhyolitic volcanic rocks erupted >13 to 0.04 Ma overlies western margin of the Rio Grande rift intersection of rift with Jemez lineament Tertiary basin fill of Española and Santo Domingo basins underlie east side Paleozoic, Mesozoic, Precambrian rocks underlie the west side Click on the image at right to view a larger version.

• Ignimbrite plateaus around field a result of one and possibly two (?) separate caldera-forming eruptions
• Formation of Toledo caldera during eruption of the Otowi member at 1.45 Ma remians a question
• Recent study suggest that Otowi member was not erupted from Toledo, but ring fracture
• Collapse resulting from eruption from upper part of magma chamber
• Roof of magma chamber at 5 to 6 km depth
• Eruption temperatures from 700°C to 850°C
• Structure of caldera complex controlled by NE-trending structures/Jemez fault zone
• After collapse volcanic acvtivity continued with eruption of rhyolite domes
• Domes erupted along caldera ring fracture until about 0.04 Ma
• Youngest eruption is The 30 to 70 m thick Banco Bonito obsidian flow on SW ring fracture
• Battleship Rock ignimbrite resulted from explosive precursor to Banco
• Many faults re-acted during caldera formation and resurgent doming to form Redondo Peak
• Resurgent doming of the caldera floor occurred during 100,000 years after Valles collapse
• Due to buoyant rise of the magma chamber after unloading of upper part onto surface
• Caldera fill deposits now exposed on summit of Redondo Peak, 1000 m above caldera moat

• 13 to 10 Ma eruptions of basalt and rhyolite along Cañada de Cochiti fault zone
• Interbedded with basin-fill conglomerate and laharic breccias of Cochiti Formation
• Between 10 and 7 Ma basalt and rhyolite erupted 1/2 the volume of the volcanic field
• 7 to 6 Ma eruptions of mixd magmas and sharp reduction in volcanic activity
• 7 to 4 Ma lull in volcanic activity and Cañada de Cochiti fault zone became inactive
• 5 to 4 Ma tectonic activity shifted to the Parajito fault zone and continued to Quaternary
• Renewed basaltic activity from 4 Ma to 2 Ma around margins and to east (Cerros del Rio)
• Movement on faults of the Parajito and and Jemez fault zones continued to Quaternary