Reference 1621

Abstract

The Eocene Big Smoky Creek Stock is one of many shallow graniticplutons located along the eastern margin of the Idaho Batholith insouth-central Idaho. The Big Smoky Creek Stock is a homogeneous bodyof medium grained, hornblende-biotite granite. The granite suite isuniform mineralogically and texturally. The granite is closely relatedtemporally and spatially with a dacite-granodiorite suite which formsa hypabyssal-plutonic complex surrounding the Big Smoky Creek Stock.The dacite-granodiorite suite is a quartz monzodiorite to granite andcomprises numerous gradational dikes and plutons. Previous work andfield relations have shown the dacite-granodiorite to be older andthat the two suites have different parent magmas. The BSCS wasaffected by hydrothermal activity after crystallization, based onoxygen isotopes. This activity did not affect Sr since Rb-Sr datingreturns ages of approximately 50 Ma, similar to previous ages in thearea. The suites have an anorogenic origin with partial meltingcompletely within the middle to lower continental crust facilitated byan extensional regime prior to and during the emplacement of the twosuites. Major, trace and REE suggest different sources for the twosuites non-co-magmatic. Radiogenic isotopes suggest the sourceregion was the lower crust with the dacite-granodiorite sourceslightly deeper than the granite source, although mixing ofdacite-granodiorite sources can not be ruled out. Oxygen isotopic datasuggest minor, if any, upper crustal contamination. The source rocksare possibly granulite rocks of Proterozoic age. Thesegranulite-facies rocks appear to have limited to absent garnet in theresidue. REE suggest limited plagioclase in the dacite-granodiorite'ssource residue and larger amounts of plagioclase in the granite'ssource residue. A mafic amphibolite facies source is suggested for thedacite-granodiorite and a more felsic source for the granite. Pb andNd model ages determined sources of Proterozoic age. Successful REEmodelling from a greywacke source suggests Proterozoic metasedimentaryrocks Belt Supergroup as a possible source component for the granitesuite.

44 samples from this reference