Application of uranium-thorium systematics to rocks from the Lassen Dome Field, California

Technical Report · Sat Dec 31 23:00:00 EST 1983

OSTI ID:5118150

Trimble, D A; Clynne, M A; Robinson, S W

/sup 238/U-/sup 230/Th disequilibrium systematics were applied to a suite of fifteen dacites, rhyodacites, and mafic inclusions from the Lassen dome field, Lassen Volcanic National Park, California. Chemical procedures were established and are reported for separation and purification of uranium and thorium from whole-rock samples and mineral separates. Activities of /sup 230/Th, /sup 232/Th, /sup 234/U, and /sup 238/U were determined by alpha spectrometry. Age determinations were made for five of the rhyodacite units using /sup 230/Th-/sup 238/U isochrons. The determined ages range from 3600 to 57,000 years, and are in agreement with volcanic and glacial stratigraphy and with preliminary radiocarbon and K-Ar ages. The data support a origin for the intermediate and silicic rocks of the Lassen Volcanic Center by fractional crystallization of mantle derived mafic magmas in an open system. 24 figs., 8 tabs.

• Research Organization: Geological Survey, Menlo Park, CA (USA)
• OSTI ID: 5118150
• Report Number(s): USGS-OFR-84-371; ON: TI86900052
• Country of Publication: United States
• Language: English

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ACTINIDE ISOTOPES
ACTINIDE NUCLEI
AGE ESTIMATION
ALPHA DECAY RADIOISOTOPES
CALIFORNIA
EQUILIBRIUM
EVEN-EVEN NUCLEI
FEDERAL REGION IX
FRACTIONATION
HEAVY NUCLEI
IGNEOUS ROCKS
ISOTOPE DATING
ISOTOPES
MAGMA
NORTH AMERICA
NUCLEI
PETROGENESIS
RADIOISOTOPES
ROCKS
SEPARATION PROCESSES
THORIUM 230
THORIUM ISOTOPES
URANIUM 238
URANIUM ISOTOPES
USA
VOLCANIC ROCKS
VOLCANOES
YEARS LIVING RADIOISOTOPES