Reference 1783

Abstract

The Papoose Peak Quadrangle, located in central Idaho on the northeastside of the Atlanta lobe of the Late Cretaceous Idaho batholith, ismostly made up of a shallow Eocene intrusion. The Eocene intrusivesuite contains Precambrian metasedimentary roof pendants and intrudesthe Idaho batholith on the northeast corner of the quadrangle. Eoceneintrusive rocks have been divided into two suites: pink granite andquartz monzodiorite (Bennett and Knowles, 1985; Lewis and Kiilsgaard,1991). Previous geochemical evidence for Eocene suites throughoutcentral Idaho suggests they are not related by crystal fractionationof a single magma type. Although the intrusive suite studied hereshows textural characteristics of both the pink granite and the quartzmonzodiorite suites, modal compositions plot in the granite field ofthe I.U.G.S. classification scheme (Strekeisen, 1976). Silica contentof the intrusive suite ranges from 62% to 73% and are calc-alkaline.Geochemical affinities do not clearly classify the intrusive suite ashaving an I-, S-, or A-type source, but possibly a combination ofthese sources. Field relations and linear trends observed throughoutHarker plots suggest the intrusive suite is related through crystalfractionation. Two different crystal fractionation models, one usingratios of trace-elements from different samples and the other amass-balance modeling program using major-element data, suggest theintrusive suite may be related through crystal fractionation. Theintrusive suite of the study area has mineralogical and geochemicalcharacteristics of both the pink granite and quartz monzodioritesuites defined by Bennett and Knowles (1985), and crystalfractionation models support the idea that the intrusive suiteoriginated from one source, with both mantle- and crustal-derivedcomponents. Isotopic data are needed to further test this hypothesis.

12 samples from this reference