Rare earth element patterns as correlation tools and tectonic indicators for the Paleogene Dillon Volcanics, southwestern Montana
Abstract
The Dillon Volcanics of the Paleogene Renova Formation consist of epiclastic, pyroclastic, and volcanic rocks. The latter are composed of alkaline and transitional basalts and rhyolites. Major and trace element variation diagrams indicate that both rock types had a similar parent magma source, and that the rhyolites were mainly derived from a basaltic parent magma. This is confirmed by very similar rare earth element (REE) patterns. The REE patterns are typical of continental rift zone volcanics, and indicate that bimodal rift zone volcanism occurred in a back-arc setting 30 m.y. before basin-and-range extension. Subsequent normal faulting, combined with Neogene erosion, has separated the dillon Volcanics into isolated outcrops that cannot be accurately correlated in the field. Major and trace element compositional trends are not good correlation tools, but chondrite-normalized REE patterns are almost parallel for the rhyolites and can be used to correlate now-isolated outcrops. REE patterns for the basalts do not show the same degree of similarity, but their patterns do indicate a common magmatic source. REE patterns for continental rift settings typically show enrichment in light REE's, reflecting derivation from a light REE-enriched mantle source such as sub-continental lithosphere. As eruption of the Dillon volcanics was partly contemporaneousmore »
- Authors:
-
- Georgia State Univ., Atlanta, GA (United States). Dept. of Geology
- Publication Date:
- OSTI Identifier:
- 5098625
- Report Number(s):
- CONF-9305259-
Journal ID: ISSN 0016-7592; CODEN: GAAPBC
- Resource Type:
- Conference
- Journal Name:
- Geological Society of America, Abstracts with Programs; (United States)
- Additional Journal Information:
- Journal Volume: 25:5; Conference: 89. annual meeting of the Cordilleran Section and the 46th annual meeting of the Rocky Mountain Section of the Geological Society of America (GSA), Reno, NV (United States), 19-21 May 1993; Journal ID: ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
- Subject:
- 58 GEOSCIENCES; GEOLOGIC FORMATIONS; GEOCHEMISTRY; PETROGENESIS; MONTANA; VOLCANIC ROCKS; MAGMATISM; RARE EARTHS; SUBDUCTION ZONES; TERTIARY PERIOD; VOLCANISM; CENOZOIC ERA; CHEMISTRY; DEVELOPED COUNTRIES; ELEMENTS; GEOLOGIC AGES; GEOLOGY; IGNEOUS ROCKS; METALS; NORTH AMERICA; PETROLOGY; ROCKS; USA; 580000* - Geosciences
Citation Formats
McDowell, R J, Fritz, W J, and Ghazi, A M. Rare earth element patterns as correlation tools and tectonic indicators for the Paleogene Dillon Volcanics, southwestern Montana. United States: N. p., 1993.
Web.
McDowell, R J, Fritz, W J, & Ghazi, A M. Rare earth element patterns as correlation tools and tectonic indicators for the Paleogene Dillon Volcanics, southwestern Montana. United States.
McDowell, R J, Fritz, W J, and Ghazi, A M. 1993.
"Rare earth element patterns as correlation tools and tectonic indicators for the Paleogene Dillon Volcanics, southwestern Montana". United States.
@article{osti_5098625,
title = {Rare earth element patterns as correlation tools and tectonic indicators for the Paleogene Dillon Volcanics, southwestern Montana},
author = {McDowell, R J and Fritz, W J and Ghazi, A M},
abstractNote = {The Dillon Volcanics of the Paleogene Renova Formation consist of epiclastic, pyroclastic, and volcanic rocks. The latter are composed of alkaline and transitional basalts and rhyolites. Major and trace element variation diagrams indicate that both rock types had a similar parent magma source, and that the rhyolites were mainly derived from a basaltic parent magma. This is confirmed by very similar rare earth element (REE) patterns. The REE patterns are typical of continental rift zone volcanics, and indicate that bimodal rift zone volcanism occurred in a back-arc setting 30 m.y. before basin-and-range extension. Subsequent normal faulting, combined with Neogene erosion, has separated the dillon Volcanics into isolated outcrops that cannot be accurately correlated in the field. Major and trace element compositional trends are not good correlation tools, but chondrite-normalized REE patterns are almost parallel for the rhyolites and can be used to correlate now-isolated outcrops. REE patterns for the basalts do not show the same degree of similarity, but their patterns do indicate a common magmatic source. REE patterns for continental rift settings typically show enrichment in light REE's, reflecting derivation from a light REE-enriched mantle source such as sub-continental lithosphere. As eruption of the Dillon volcanics was partly contemporaneous with arc volcanism related to the Laramide orogeny, the sub-continental lithosphere may have been enriched in light REE's bu subduction zone fluids derived from the down-going Farallon plate. However, it might not be possible to distinguish continental rift zone volcanics from continental back-arc basin volcanics. The authors favor the latter model because of the chronologic and geographic relationship of the dillon Volcanics with nearby continental arc volcanic fields.},
doi = {},
url = {https://www.osti.gov/biblio/5098625},
journal = {Geological Society of America, Abstracts with Programs; (United States)},
issn = {0016-7592},
number = ,
volume = 25:5,
place = {United States},
year = {Thu Apr 01 00:00:00 EST 1993},
month = {Thu Apr 01 00:00:00 EST 1993}
}