GEOLEX

Summary of Citation: Amalia

Publication:
McKinlay, P.F., 1956, Geology of the Costilla and Latir Peak
   quadrangles, Taos County, New Mexico: New Mexico Bureau of
   Mines and Mineral Resources Bulletin, no. 42, 32 p.

Usage in Publication:
Amalia formation

Modifications:	Geologic Province:	Dominant Lithology:
Named	San Luis basin	Basalt Tuff

Summary:
Named for Amalia Post Office, which lies on west side of Costilla Valley, 5 mi southeast of town of Costilla, about T32N, R14E, Latir Peak quad, Taos Co., NM in the San Luis basin. The best exposures are east of Rio Costilla, 4-5 mi south of Costilla and on north side of canyon formed by Rito de Los Cedros. Does not extend south of Box Canyon of the Rio Costilla. Includes arkosic sedimentary rocks, basalt flows (olivine basalt, in places amygdaloidal at new base of formation), and rhyolite tuffs approximately 2,000 ft thick. Thought to be middle or late Tertiary age. Interfingers with underlying andesite and andesite tuffs, and with contemporaneous Latir Peak latite, and with an unnamed rhyolite.

Summary of Citation: Amalia

Publication:
Lipman, P.W., 1983, The Miocene Questa Caldera, northern New
   Mexico; relation to batholith emplacement and associated
   molybdenum mineralization, IN Babcock, J.W., chairperson,
   The genesis of Rocky Mountain ore deposits; changes with time
   and tectonics: Society of Exploration Geologists, Denver
   Region, Symposium Proceedings, November 4-5, 1982, p.
   133-148

Usage in Publication:
Amalia Tuff*

Modifications:	Geologic Province:	Dominant Lithology:
Redescribed Principal reference	San Luis basin	Tuff

Summary:
Amalia Formation (McKinlay, 1956) adopted and renamed Amalia Tuff, as it is restricted in this report to the ash-flow sheet from the Questa caldera in northern part of Latir volcanic field, San Luis basin. Is a distinctive high-silica alkali rhyolite characterized by phenocrysts of smoky quartz and chatoyant microperthitic sodic sanidine, 2-3 km thick. Extends beyond margins of the caldera as discontinuous erosional remnants several tens of meters thick. Other units included in Amalia now recognized as early Tertiary sedimentary rocks, precaldera andesitic sequence, Latir Peak Quartz Latite, and postcaldera sedimentary rocks of the Santa Fe Group. Principal reference locality set up along State Hwy 196, 0.5 km west of Amalia. Reference section designated south of pass between upper Costilla Valley and Underwood Lakes. Densely welded parts of Amalia recognized 25 km northeast of caldera in Underwood Lakes area and 45 km to southwest near Petaca, Tusas Mountains. Is of early Miocene or latest Oligocene, or about 23 m.y. K-Ar and fission-track ages.

Summary of Citation: Amalia

Publication:
Lipman, P.W. and Reed, J.C., Jr., 1989, Geologic map of the
   Latir volcanic field and adjacent areas, northern New Mexico:
   U.S. Geological Survey Miscellaneous Investigations Series
   Map, I-1907, 2 sheets, scale 1:48,000

Usage in Publication:
Amalia Tuff*

Modifications:	Geologic Province:	Dominant Lithology:
Age modified	San Luis basin

Summary:
Age changed from latest Oligocene or early Miocene, about 23 m.y. to Oligocene only. Radiometric ages vary from 23-26; only the older dates are considered reliable. A main unit and lithic-rich lower facies. Map area is south of the town of Costilla, east of the towns of Questa and Arroyo Hondo, north of 36 deg 30 min, and west of 105 deg in Taos Co, NM in the San Juan basin.