Cooling and inferred uplift/erosion history of the Grenville Orogen, Ontario: Constraints from sup 40 Ar/ sup 39 Ar thermochronology

Miscellaneous · Sun Jan 01 00:00:00 EST 1989

OSTI ID:6602831

Cosca, M A

Thermochronological ({sup 40}Ar/{sup 39}Ar) data are presented from 76 mineral separates of hornblende, muscovite, biotite, phlogopite, and K-feldspar. Samples were selected from regionally metamorphosed gneiss, amphibolite, metasediment, marble, metagabbro and pegmatite across the two major metamorphic belts of the Grenville Province, the Central Metasedimentary Belt (CMB) and the Central Gneiss Belt (CGB). When combined with published temperature estimates for closure to argon diffusion in the phases analyzed, cooling rates from {approximately}500 C to {approximately}120 C of 1-4 C/MA are calculated across the entire Grenville Province of Ontario. Regional uplift/erosion rates for the Grenville Orogen of Ontario have been estimated from the {sup 40}Ar/{sup 39}Ar data, a retrograde P-T path for rocks of the CGB, and an upper time constraint provided by flat, overlying Cambro-Ordovician sediments. Twenty-two of the hornblendes used for thermochronology have been quantitatively analyzed for major elements by microprobe, Fe{sup 2+}/Fe{sup 3+} by wet chemistry, and for H{sub 2}O by manometric measurement. Water activities calculated from hornblende equilibria are typically low (<0.01) because of the exponential dilutions in hornblende (tremolite) activity required by present activity-composition models. An oxyamphibole component of 25% further reduces any amphibole component and the H{sub 2}O activity by as much as 50% below that calculated with simplifying assumption. These findings indicate that different amphibole normalization schemes have a marked effect on the activity calculated for a specific amphibole or H{sub 2}O, and should be carefully evaluated.

• Research Organization: Michigan Univ., Ann Arbor, MI (USA)
• OSTI ID: 6602831
• Resource Relation: Other Information: Thesis (Ph. D.)
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
GEOLOGIC DEPOSITS
OROGENESIS
TECTONICS
ONTARIO
ARGON 39
ARGON 40
BIOTITE
COOLING
ELECTRON MICROPROBE ANALYSIS
EQUATIONS
EROSION
FELDSPARS
GEOLOGIC AGES
GEOLOGIC HISTORY
GROUND UPLIFT
HORNBLENDE
ISOTOPE DATING
ISOTOPE RATIO
MOISTURE
MOUNTAINS
MULTI-ELEMENT ANALYSIS
MUSCOVITE
AGE ESTIMATION
AMPHIBOLE
ARGON ISOTOPES
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CANADA
CHEMICAL ANALYSIS
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
ISOTOPES
LIGHT NUCLEI
MICA
MICROANALYSIS
MINERALS
NORTH AMERICA
NUCLEI
RADIOISOTOPES
SILICATE MINERALS
STABLE ISOTOPES
YEARS LIVING RADIOISOTOPES
580000* - Geosciences