Abstract
The southern Madison Range of southwestern Montana contains two distinct Precambrian lithologic assemblages: 1) a complex of tonalitic to granitic gneisess that has been thrust over (2) a medium-grade metasupracrustal sequence dominated by pelitic schist. Crystallization ages for the protolith of a granodioritic gneiss that intruded the metasupracrustal sequence (~2.6 Ga) along with an intercalated meta-andesite (~2.7 Ga) confirm the sequence as Archean. Chemical and geochronologic data for selected components of the gneiss complex indicate two groups of gneisses: an older, tonalitic to trondhjemitic group (~3.3 Ga) and a younger, mostly granitic group (~2.7 Ga). Both groups of gneisses exhibit the radiogenic Pb and nonradiogenic Nd isotopic signature characteristic of Middle and Late Archean rocks from throughout the Wyoming province. -from Authors
Original language | English (US) |
---|---|
Pages (from-to) | 437-446 |
Number of pages | 10 |
Journal | Geological Society of America Bulletin |
Volume | 105 |
Issue number | 4 |
DOIs | |
State | Published - 1993 |
Externally published | Yes |
ASJC Scopus subject areas
- Geology