CONSTRAINTS ON THE AGE OF EXTENSIVE FLUVIAL FACIES OF THE UPPER SANTA FE GROUP, ALBUQUERQUE AND SOCORRO BASINS, CENTRAL NEW MEXICO
CONNELL, S.D., New Mexico Bureau of Mines and Mineral Resources, New Mexico Institute of Mining and Technology, 2808 Central Ave SE, Albuquerque, NM 87106
CHAMBERLIN, R.M., CATHER, S.M., MCINTOSH, W.C., DUNBAR, N., New Mexico Bureau of Mines and Mineral Resources, New Mexico Institute of Mining & Technology, 801 Leroy Place, Socorro, NM 87801
SMITH, G.A., Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131
LUCAS, S.G., New Mexico Museum of Natural History, 1801 Mountain Rd NW, Albuquerque, NM 87104
Many 40Ar/39Ar ages and geochemical correlations determined from primary
and fluvially recycled tephra and volcanic flows in the upper Santa Fe
Group (SFG) of the Albuquerque and Socorro basins constrain the timing
of development of external drainage in these basins and provide a basis
for correlation in the Rio Grande rift. The hallmark of the upper SFG,
the onset of major regional fluvial deposition (ancestral Rio Grande,
ARG) and major tributaries, began in the northern basin before deposition
of a 6.9-Ma Peralta Tuff tephra. Major fluvial fans, not clearly tied
to the northern ARG, developed between 7.0 and 9 Ma. In the Socorro area
to the south playa-lake facies of the Popotosa Fm were deposited from
15.2 to 6.9 Ma. A trachyandesite flow at San Acacia (4.87±0.04
Ma) overlies an eastern piedmont facies that may have graded westward
into ARG deposits. The basalt of Socorro Canyon (3.73±0.1 Ma) flowed
eastward onto ARG deposits. These relationships and ages suggest that
the establishment of fluvial deposition became younger from north to south.
The youngest fluvial SFG is constrained by the 1.22-Ma ash from the Tshirege
Mbr (Bandelier Tuff) near the top of ARG sections near Tonque Arroyo,
Tijeras Arroyo, Hell Canyon Wash, and Socorro basin, and by a 1.05-Ma
ash of Valles Dome rhyolite in Hell Canyon. An ARG gravel inset below
the top of the SFG along the western margin of the Rio Grande Valley contains
tephra correlated to the 0.66 Ma Lava Creek B ash. Thus, SFG deposition
ceased between 1.0-0.7 Ma south of Santo Domingo. This constraint on the
initial incision of the Rio Grande Valley and cessation of extensive ARG
deposition is similar to events in southern New Mexico dated between 0.7-0.8
Ma. This widespread, relatively contemporaneous, and rapid incision suggests
that the development of the Rio Grande Valley from Santo Domingto to Las
Cruces, NM, was strongly influenced by climate.
Love, D.W., Connell, S.D., Chamberlin, R.M., Cather, S.M., McIntosh, W.C., Dunbar, N., Smith, G.A., Lucas, S.G., 2001, Constraints on the age of extensive fluvial facies of the upper Santa Fe Group, Albuquerque and Socorro basins, central New Mexico: Geological Society of America, Abstracts with Programs, v. 33, n. 5, p. A-48.
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