Neogene rhyolites of the northern Jemez volcanic field, New Mexico

Journal Article · Fri Jun 10 04:00:00 EDT 1988 · J. Geophys. Res.; (United States)

DOI:https://doi.org/10.1029/JB093iB06p06157· OSTI ID:6991110

Loeffler, B M; Vaniman, D T; Baldridge, W S; Shafiqullah, M

Volcanic centers previously mapped as the 20 Ma El Rechuelos Rhyolite in the northern Jemez volcanic field, New Mexico, include three distinct episodes of rhyolitic volcanism. An early (7.5 Ma) extrusive dome of flow-banded biotite rhyolite and an intermediate (5.8 Ma) rhyolite, possibly a volcanic neck, correspond in age to rhyolites of the Keres Group in the southern Jemez volcanic field. Three other extrusive domes of aphyric, pumiceous rhyolite and obsidian comprise a late volcanic episode, dated at 2.0 Ma. We retain the name El Rechuelos Rhyolite only for these late centers. Another center, farther north than the others but previously mapped with the El Rechuelos Rhyolite, is a dacite pumice ring whose age (5.2 Ma), petrography, major- and trace-element chemistry, and Sr initial ratio all suggest it should be included with rocks of the Tschicoma Formation. Nd and Sr isotopic ratios of the Neogene rhyolites of the northern Jemez volcanic field suggest that these rhyolites were not produced by partial melting of either upper or lower crust. Rather, they may have been generated from a mantle-derived mafic magma, such as the nearby Lobato Basalt, by fractional crystallization with concomitant assimilation of small amounts (<6%) of lower crust. If the El Rechuelos is derived from a lower crust magma chamber, as seems likely, then it is not related to the bandelier magma system, even though it is part of a continuum of rhyolite volcanism ranging from 3.6 Ma to 130,000 years ago that includes the Bandelier and precursor rhyolitic units. copyright American Geophysical Union 1988

• Research Organization: Department of Geology, Colorado College, Colorado Springs
• OSTI ID: 6991110
• Journal Information: J. Geophys. Res.; (United States), Journal Name: J. Geophys. Res.; (United States) Vol. 93:B6; ISSN JGREA
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580202* -- Geophysics-- Volcanology-- (1980-1989)
ACTIVATION ANALYSIS
AGE ESTIMATION
ALKALINE EARTH METALS
CALDERAS
CHEMICAL ANALYSIS
CHEMISTRY
ELEMENTS
FEDERAL REGION VI
GEOCHEMISTRY
GEOTHERMAL SYSTEMS
IGNEOUS ROCKS
ISOTOPE DATING
JEMEZ MOUNTAINS
MAGMA SYSTEMS
METALS
MOUNTAINS
NEODYMIUM
NEUTRON LOGGING
NEW MEXICO
NORTH AMERICA
PETROGRAPHY
RADIOACTIVITY LOGGING
RARE EARTHS
RHYOLITES
ROCKS
STRONTIUM
USA
VOLCANIC ROCKS
VOLCANISM
WELL LOGGING