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Geochemical and paleomagnetic variations in basalts from the Wendell Regional Aquifer Systems Analysis (RASA) drill core; evidence for magma recharge and assimilation-fractional crystallization from the central Snake River plain, Idaho

Marlon M. Jean, John W. Shervais, Duane E. Champion and Scott K. Vetter
Geochemical and paleomagnetic variations in basalts from the Wendell Regional Aquifer Systems Analysis (RASA) drill core; evidence for magma recharge and assimilation-fractional crystallization from the central Snake River plain, Idaho
Geosphere (Boulder, CO) (September 2013) 9 (5): 1319-1335

Abstract

The temporal and magmatic evolution of central Snake River Plain (SRP; Idaho, USA) olivine tholeiites erupted within the past 4 m.y. is evaluated here. This investigation correlates and merges both geochemical and paleomagnetic measurements to constrain the volcanic history recovered from the 340 m Regional Aquifer Systems Analysis (RASA) test well located near Wendell, Idaho. Only a handful of studies have accomplished this task of shedding light on the chemical stratigraphy of the SRP and the petrogenesis of basalts with depth, and therefore through time.Paleomagnetic relationships suggest that time breaks between individual lava flows represent a few years to decades, time breaks between flow groups represent at least a couple of hundred years or possibly much longer, while significant hiatuses in volcanism, revealed by thick sediment packages or polarity reversals (both are evidenced in this well), are inferred to last thousands to tens of thousands of years. Major element geochemistry from 52 basaltic lava flows demonstrates near primitive compositions (i.e., approximately 10 wt% MgO) and tholeiitic iron enrichment trends, similar to lavas from the eastern SRP. Trace element concentrations are similar to those of ocean island basalts, with enriched Ba and Pb, and light rare earth element (REE)/heavy REE ratios similar to those of many Neogene volcanics of the western Cordillera. When combined, we identify a total of 11 flow groups, which we also classify as fractionation or recharge on the basis of decreasing or increasing MgO weight percent with depth.Taking into consideration these trends, we review the potential recharge, fractionation, and assimilation processes that characterize much of SRP olivine tholeiite, and conclude that assimilation, in combination with fractional crystallization, is the dominant petrogenesis for the basalts in the central SRP. Although fractionation of Wendell parent magmas was accompanied by assimilation of crustal material, this could not have been assimilation of ancient cratonic crust. The geochemical cycles observed in this well are inferred to represent fractionation and recharge of basaltic magma from a series of sill-like layered mafic intrusions located in the middle crust, similar to what has been proposed for the processes that control the eruptive history of basalts in the eastern SRP.


EISSN: 1553-040X
Serial Title: Geosphere (Boulder, CO)
Serial Volume: 9
Serial Issue: 5
Title: Geochemical and paleomagnetic variations in basalts from the Wendell Regional Aquifer Systems Analysis (RASA) drill core; evidence for magma recharge and assimilation-fractional crystallization from the central Snake River plain, Idaho
Affiliation: Northern Illinois University, Department of Geology, DeKalb, IL, United States
Pages: 1319-1335
Published: 20130913
Text Language: English
Publisher: Geological Society of America, Boulder, CO, United States
Number of pages: 17
References: 61
Accession Number: 2013-080195
Categories: Igneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. strat. col., 3 tables, sketch map
N42°46'60" - N42°46'60", W114°42'00" - W114°42'00"
Secondary Affiliation: Utah State University, USA, United StatesU. S. Geological Survey, USA, United StatesCentenary College, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201347
Program Name: USGSOPNon-USGS publications with USGS authors
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