U-Pb ages of mafic intrusions from the southeast margin of the Wyoming province: Implications for timing of rifting and deformation

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

OSTI ID:5421279

Cox, D M; Chamberlain, K R ^[1]; Heaman, L M ^[2]; Snyder, G L ^[3]

---

1. Univ. of Wyoming, Laramie, WY (United States). Dept. of Geology and Geophysics
2. Royal Ontario Museum, Toronto, ON (Canada). Dept. of Geology
3. Geological Survey, Denver, CO (United States). Federal Center

The southeast margin of the Wyoming Province exposed in the Laramie Mountains is dominated by Archean granitic gneiss that has been intruded by mafic dike swarms. The metamorphic grade of these mafic bodies ranges from lower amphibolite to garnet amphibolite facies. Three distinct compositional groups are recognized: (1) plagioclase porphyry; (2) diabase; and (3) peridotite. The diabase intrudes the plagioclase porphyry and locally contains relict igneous textures. The peridotite intrudes both and contain relict olivine and orthopyroxene. Both the granitic gneiss and the mafic intrusions have been deformed into map scale folds with a northwest trending axis, and subsequently refolded about a northeast trending axis. The northeast structures are subparallel to the trend of the Cheyenne belt. In one locality, diabase dikes intrude a 2.05 Ga. granodiorite (K.R. Ludwig in Snyder, et al. 1992). Field relations provide relative ages, and samples were collected of each dike type to determine absolute age by U-Pb geochronological analysis. Preliminary baddeleyite U-Pb data from a folded diabase yields a minimum crystallization age of 2.05 Ga. The mafic intrusions may be related to rifting of the Archean margin, which has been constrained from other ranges in southeast Wyoming to 2.0--2.3 Ga. In addition, the baddeleyite age establishes that much of the deformation of the Archean craton postdates 2.05 Ga. and may be related to suturing along the Cheyenne belt ca. 1.75 Ga.

• OSTI ID: 5421279
• 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
ACTINIDE ISOTOPES
AGE ESTIMATION
AMPHIBOLITES
DEVELOPED COUNTRIES
DIKES
GEOLOGIC DEPOSITS
GEOLOGIC STRUCTURES
GEOLOGY
GNEISSES
IGNEOUS ROCKS
ISOTOPE DATING
ISOTOPES
LEAD ISOTOPES
METAMORPHIC ROCKS
MOUNTAINS
NORTH AMERICA
OROGENESIS
PERIDOTITES
PETROGENESIS
PETROLOGY
PLUTONIC ROCKS
RIFT ZONES
ROCKS
ROCKY MOUNTAINS
TECTONICS
URANIUM ISOTOPES
USA
WYOMING