[sup 40]Ar/[sup 39]Ar dating of the McKinley Pluton, Denali National Park, Alaska

Conference · Thu Apr 01 04:00:00 EST 1993 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5099451

West, A W; Layer, P W ^[1]

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1. Univ. of Alaska, Fairbanks, AK (United States). Geophysical Inst.

The McKinley pluton is one of the northern-most plutons of the Alaska-Aleutian Range batholith. This biotite granite intrusion makes up most of the 6,194 meter high Mt. McKinley massif. Previous K-Ar and apatite fission-track studies suggest that the pluton has had a protracted cooling/uplift history since its emplacement at approximately 55 Ma. The great relief available for sampling makes the McKinley pluton an ideal intrusion for a thermochronometric study through [sup 40]Ar/[sup 39]Ar dating of micas and K-feldspars. Thus far the authors have dated samples ranging in elevation from 3,500 meters to 6,000 meters. Four biotites and one primary white mica have relatively flat age spectra with plateau ages between 55.4 Ma and 55.8 Ma. The consistent mica ages most likely reflect uniform cooling of the pluton. The K-feldspars exhibit saddle-shaped age spectra that vary significantly from each other. The youngest age fraction of each sample shows a pattern of the highest sample being oldest (46 Ma) and the lower samples being progressively younger (42 Ma to 36 Ma). This suggests slow cooling or prolonged uplift. The plateau ages vary greatly (54.0 Ma to 48.1 Ma) but do not correlate with sample elevation. Analysis of argon release in the step heating experiments indicates that the feldspars may contain multiple diffusion domains. The authors are using detailed step heating experiments and computer modeling to determine the distribution of these domains, and to constrain the thermal and uplift history of the McKinley pluton between 36 and 54 Ma. In addition, they will examine differences in K-feldspar composition and texture and possible relationships to variations in the age spectra.

• OSTI ID: 5099451
• Report Number(s): CONF-9305259--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 25:5
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
AGE ESTIMATION
ALASKA
ALKALI METAL COMPOUNDS
ALUMINIUM COMPOUNDS
ALUMINIUM SILICATES
ARGON 39
ARGON 40
ARGON ISOTOPES
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CHEMICAL COMPOSITION
DEVELOPED COUNTRIES
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
FELDSPARS
GEOLOGIC DEPOSITS
GEOLOGIC HISTORY
GEOLOGY
GRANITES
IGNEOUS ROCKS
ISOTOPE DATING
ISOTOPES
LIGHT NUCLEI
MICA
MINERALS
MOUNTAINS
NORTH AMERICA
NUCLEI
ORTHOCLASE
OXYGEN COMPOUNDS
PETROGENESIS
PETROLOGY
PLUTONIC ROCKS
POTASSIUM COMPOUNDS
POTASSIUM SILICATES
RADIOISOTOPES
ROCKS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
STABLE ISOTOPES
USA
YEARS LIVING RADIOISOTOPES