Reaction textures in cordierite-bearing gneisses from the Ruby Range, southwestern Montana: Petrogenetic implications
Conference
·
· Geological Society of America, Abstracts with Programs; (United States)
OSTI ID:5019364
- Kent State Univ., OH (United States). Dept. of Geology
The Ruby Range is an Archean terrane dominated by granitic gneisses conformably overlain by metasedimentary rocks of continental shelf affinity, which experienced high-grade metamorphism during the Beartooth Orogeny (ca. 2750 Ma). Cordierite occurs in pelitic, hypersthene, and gedrite gneisses at several horizons within this terrane. Assemblages, reaction textures, and possible protolith(s) for these rocks are highly similar to those described for the Ammonoosuc Volcanics (New Hampshire) by Robinson and Jaffe and Schumacher. Rim compositions of garnet and coronal cordierite in 18 gar-crd-sil-qtz-bearing rocks yield P-T estimates of 4.8[+-]1.0 kbar and 560[+-]30 C, consistent with unloading associated with a Proterozoic thermal overprint observed in these and other lithologies. A gedrite gneiss horizon near Stone Creek contains the sole occurrence of staurolite in the Ruby Range. Aluminous enclaves in this rock contain optically continuous remnants of staurolite pseudomorphously replaced by sillimanite-hercynite symplectite, which itself is partially to completely replaced by anorthite. The above phases are invariably separated from the foliated gedr-gar-bio matrix by coronas of undeformed cordierite. The Ca source for reaction (3) was probably an adjacent dolomitic marble unit, with a well-exposed contact, 15 cm from the sample location. The above textural relationships and reactions indicate post-tectonic development of the enclaves, which probably occurred during the unroofing recorded by the gar-crd rim compositions.
- OSTI ID:
- 5019364
- 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
Similar Records
Cordierite reaction textures in semipelitic rocks from metamorphic zone IV in central Massachusetts: Their interpretation and possible p-t significance
Metamorphic signature of the Gneiss Canyon Shear Zone, Lower Granite Gorge, Grand Canyon, Arizona
Metamorphism of San Antonio Terrane metapelites, San Gabriel Mountains, California
Conference
·
Sun Feb 28 23:00:00 EST 1993
· Geological Society of America, Abstracts with Programs; (United States)
·
OSTI ID:5587942
Metamorphic signature of the Gneiss Canyon Shear Zone, Lower Granite Gorge, Grand Canyon, Arizona
Conference
·
Tue Dec 31 23:00:00 EST 1991
· Geological Society of America, Abstracts with Programs; (United States)
·
OSTI ID:5806134
Metamorphism of San Antonio Terrane metapelites, San Gabriel Mountains, California
Conference
·
Wed Mar 31 23:00:00 EST 1993
· Geological Society of America, Abstracts with Programs; (United States)
·
OSTI ID:5423320