Evidence for different eruptive conditions for two simultaneous, late Miocene, rhyolitic phreatomagmatic eruptions: Jemez Mountains, New Mexico
- Univ. of New Mexico, Albuquerque, NM (United States). Dept. of Earth and Planetary Sciences
The Peralta Tuff Member of the Bearhead Rhyolite records episodic, rhyolitic volcanism during the late Miocene. It is composed of primary and reworked pyroclastic-flow (PF), tephra-fall (TF), and pyroclastic-surge (PS) deposits intercalated with braided-stream deposits. Two eruptive units have been informally named the Tuffs of West Mesa (TWM) and the Tuffs of Lower Peralta Canyon (TLPC). The TWM consist of 20 m of PF and minor PS deposits erupted from a vent in the Bearhead Park dome complex. In most places the TLPC consist of 50 m of PF, PS, and TF and were erupted from a vent located 7 km SE of Bearhead Peak. The absence of inter-eruptive sediments, erosional surfaces, or paleosols, along with the intercalated nature of the two units, indicates that the two eruptions were simultaneous. Granulometric, vesiculation, petrographic, and stratigraphic data indicate that the TWM eruption began with a phreatomagmatic (PM) component, resulting in the formation of a tuff ring at least 70 m thick, and ended with [ge]20 m of drier PF that traveled at least 6 km from the vent. The TLPC eruption began with several PM eruptive cycles of wet, ash-rich, low-angle x-bedded PS to drier, pumiceous, lapilli-rich PS. Abundant fragments of underlying rift-fill sediments decrease upward in the cycles. The cyclic deposits were followed by 20 m of pumice-rich, x-bedded PS, containing only rare sedimentary fragments. The TLPC eruption concluded with a 2 m TF. The greater phreatomagmatic component to the TLPC eruption, despite its proximity to the simultaneously active TWM vent, is apparently related to the mixing of magma with basin-fill sediments at a topographically lower ([ge]300 m) position and at a site that probably has less subjacent, relatively dry, older volcanic rocks.
- OSTI ID:
- 5099737
- Report Number(s):
- CONF-9305259-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 25:5; Conference: 89. annual meeting of the Cordilleran Section and the 46th annual meeting of the Rocky Mountain Section of the Geological Society of America (GSA), Reno, NV (United States), 19-21 May 1993; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
Similar Records
Volcanism and sedimentation along the western margin of the Rio Grande rift between caldera-forming eruptions of the Jemez Mountains volcanic field, north-central New Mexico, USA
Intracaldera volcanic activity, Toledo caldera and embayment, Jemez Mountains, New Mexico
Related Subjects
GEOLOGIC DEPOSITS
PETROGENESIS
PETROGRAPHY
NEW MEXICO
RHYOLITES
TUFF
ERUPTION
GEOLOGIC HISTORY
MAGMATISM
MIOCENE EPOCH
PALEOMAGNETISM
STRATIGRAPHY
VOLCANISM
VOLCANOES
CENOZOIC ERA
DEVELOPED COUNTRIES
GEOLOGIC AGES
GEOLOGY
IGNEOUS ROCKS
MAGNETISM
NORTH AMERICA
PETROLOGY
ROCKS
TERTIARY PERIOD
USA
VOLCANIC ROCKS
580000* - Geosciences