Radiometric dating of Ochoan (Permian) evaporites, WIPP (Waste Isolation Pilot Plant) site, Delaware Basin, New Mexico, USA
We have attempted radiometric dating of halide-sulfate salts and clay minerals from the Delaware Basin, New Mexico, USA, as part of geochemical study of the stability of the evaporite sequence at the WIPP (Waste Isolation Pilot Plant - a US DOE facilty) site. We undertook this dating to determine: (1) primary age of evaporite genesis or time(s) of recrystallization; (2) if previously undated evaporite minerals (leonite, polyhalite, kieserite) give useful data; and (3) if the detrital clay minerals have been radiometrically reset at any time following their incorporation into the evaporite medium. We have shown earlier that polyhalites can indeed be successfully dated by the K-Ar method, and once corrections are applied for admixed halide minerals, dates of 210-230 Ma for the Delaware Basin are obtained. Rb-Sr isochrons from early stage sylvites-polyhalites- anhydrites yield 220 +- 10 Ma, even when some sylvites yield lower K-Ar dates due to loss of *40-Ar. K-Ar dates on leonites and kieserities are also low due to *40-Ar loss, but their Rb-Sr dates are higher. Detrital clay minerals from the Delaware Basin collectively yield a highly scattered isochron (390 +- 77 Ma), but samples from a local area, such as the WIPP Site, give a much better age of 428 +- 7 Ma. These dates show that the interaction between the clay minerals and the evaporitic brines was insufficient to reset the clay minerals Rb-Sr systematics. In a related study, we note that a dike emplaced into the evaporite at 34 Ma had only very limited effect on the intruded rocks; contact phenomena were all within 2 m of the dike. All of our geochemical (radio-metric and trace element) studies of the WIPP site argue for preservation of the isotopic and chemical integrity of the major minerals for the past 200 Ma.
- Research Organization:
- New Mexico Univ., Albuquerque (USA). Dept. of Geology; Sandia National Labs., Albuquerque, NM (USA)
- DOE Contract Number:
- AC04-76DP00789
- OSTI ID:
- 7039408
- Report Number(s):
- SAND-86-2192C; CONF-861207-16; ON: DE87002484
- Country of Publication:
- United States
- Language:
- English
Similar Records
Potassium-argon and neutron activation analysis studies of polyhalites near the WIPP site
Occurrence of clays and their bearing of evaporite mineralogy in the Salado Formation, Delaware Basin (New Mexico)
Related Subjects
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
58 GEOSCIENCES
580100 -- Geology & Hydrology-- (-1989)
AGE ESTIMATION
ALKALI METAL COMPOUNDS
ALKALINE EARTH METAL COMPOUNDS
CALCIUM COMPOUNDS
CALCIUM SULFATES
CHEMISTRY
CLAYS
EVAPORITES
FEDERAL REGION VI
FUNCTIONAL MODELS
GEOCHEMISTRY
GEOLOGIC AGES
ISOTOPE DATING
MAGNESIUM COMPOUNDS
MAGNESIUM SULFATES
MINERALS
NATIONAL ORGANIZATIONS
NEW MEXICO
NORTH AMERICA
NUCLEAR FACILITIES
OXYGEN COMPOUNDS
PALEOZOIC ERA
PERMIAN PERIOD
PILOT PLANTS
POLYHALITE
POTASSIUM COMPOUNDS
POTASSIUM SULFATES
RADIOACTIVE WASTE FACILITIES
ROCKS
SEDIMENTARY ROCKS
SULFATE MINERALS
SULFATES
SULFUR COMPOUNDS
UNDERGROUND FACILITIES
US DOE
US ORGANIZATIONS
USA
WIPP