Geologic cross section – Hazard Creek Complex, Little Goose Creek Complex, and Payette River Complex: Supplement 2 from 'Geology and geochemistry of the oceanic arc-continent boundary in the western Idaho batholith near McCall' (Thesis)

NOTE: Text or symbols not renderable in plain ASCII are indicated by [.]. Abstract is included in .pdf document. A major lithospheric boundary is preserved within the western Idaho Batholith. The juxtaposition of two suites of supracrustal rocks, exposed as sheets within intrusive rocks, is the expression of this boundary at the level of exposure. The western suite of mafic layered gneisses are inferred to be metamorphosed oceanic arc rocks; the eastern suite of biotite schist, quartzite and calc-silicate gneiss are inferred to be metamorphosed continental sedimentary rocks. Three broadly Cretaceous, plutonic and meta-plutonic complexes record the presence of the boundary at greater depth. The Hazard Creek complex, west of the supracrustal boundary, is comprised of epidote-bearing intrusives. The Little Goose Creek complex is comprised primarily of the porphyritic orthogneiss that intruded the supracrustal boundary. The Payette River complex, east of the supracrustal boundary, is comprised of large bodies of tonalite and granite. Each complex has a distinct geochemical character. The Hazard Creek complex is dominantly a tonalite-trondhjemite suite characterized by [.] less than .7045, [.] less than 8.4, high Sr, Na2O and Al2O3 concentrations and low MgO, Rb and K2O concentrations. Porphyritic orthogneiss in the Little Goose Creek complex has a remarkable range in [.] and [.] (.7042-.7097,8.0-10.7). The porphyritic orthogneiss is interpreted as dominated by two components: one similar in composition to the Hazard Creek complex and a second, modeled as Precambrian sedimentary material, with high [.], [.] and K2O concentrations and lower Sr concentration. The Payette River complex has generally high [.] (.7076-.7100) and variable [.](7.2-10.4). The geochemical changes indicate that the supracrustal boundary is the surface expression of a steeply-dipping structure which juxtaposes oceanic-arc lithosphere against continental lithosphere. An abrupt geochemical discontinuity preserved within the porphyritic ...