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Rocky Mountain (66th Annual) and Cordilleran (110th Annual) Joint Meeting (19–21 May 2014)

Paper No. 3
Presentation Time: 1:50 PM

GEOCHEMICAL AND GEOCHRONOLOGICAL CHARACTERIZATION OF MULTIPLE GENERATIONS OF MAFIC MAGMATISM IN THE BELT-PURCELL AND WYOMING BASINS, FOCUSING ON THE MOYIE-PURCELL CA. 1460 MA INTRAPLATE MAGMATIC EVENT


ROGERS, Chris1, MACKINDER, Alana J.1, ERNST, Richard E.2 and COUSENS, Brian3, (1)Department of Earth Sciences, Carleton University, 1125 Colonel By Drive, Ottawa, ON K1S 5B6, Canada, (2)Dept. of Earth Sciences, Carleton University, 1125 Colonel By Drive, Ottawa, ON K1S 5B6, Canada, (3)Ottawa-Carleton Geoscience Centre, Department of Earth Sciences, Carleton University, 1125 Colonel By Drive, Ottawa, ON K1S 5B6, Canada, chris.rogers@carleton.ca

Mesoproterozoic and Neoproterozoic intraplate magmatism that is exposed along the western side of the Laurentian margin between Kimberley BC and north of Yellowstone National Park in Wyoming can be divided into at least two Large Igneous Provinces: 1) The ca. 1460 Ma Moyie-Purcell event consists of i) the Purcell lavas and other dykes and sills in the USA, ii) the gabbroic Moyie sills of the Belt-Purcell basin and associated dykes. This magmatism is composed of tholeiitic basalts and basaltic andesites. 2) The ca. 780 Ma Gunbarrel LIP consists of dykes, sills and volcanic rocks and is also comprised of tholeiitic basalts and basaltic-andesites.

Until this research the Moyie-Purcell event has not been geochemically characterized. We are integrating our new geochemistry with that of previous studies to model and characterize the Moyie-Purcell event in terms of mantle source, interactions with lithosphere (mantle and crust) and fractionation. These results will be contrasted with those of a parallel study on the Gunbarrel event (see Mackinder, et al. this session).

The Moyie-Purcell and Gunbarrel magmatic events each have distinct geochemical fingerprints. For instance there is a difference in rare-earth slopes between the two events (i.e. the Moyie-Purcell event consistently plots with a shallower slope). Some units of both events exhibit a negative Nb-Ta anomaly thought to reflect interaction with subduction modified lithospheric mantle. Trace element geochemistry is consistent with petrography that indicates at most minor alteration of primary igneous petrology. From our geochemical modelling we aim to assess the origin of the magmatism: that may include one or more the following: a) plume(s), b) subduction-back arc, and/or c) decompressing associated with rifting.

Session No. 22

T4. Precambrian II: Meso- and Neoproterozoic Evolution of Western Laurentia I: In Honor of Don Winston
Tuesday, 20 May 2014: 1:00 PM-5:00 PM
Gaines Hall 101 (Montana State University)
Geological Society of America Abstracts with Programs. Vol. 46, No. 5, p.70
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