Mesozoic magmatism and deformation in the northern Owyhee Mountains, Idaho: Implications for along-zone variations for the western Idaho shear zone

Abstract

The northern Owyhee Mountains of southwestern Idaho contain granitoid rocks that are the same age as the Cretaceous western border zone of the Idaho batholith to the north of the Snake River Plain. They contain a well-developed and consistently oriented 020° foliation, zircon yielding U-Pb dates of ca. 160-48 Ma, and initial 87 Sr/ 86 Sr isotopic compositions that show a steep west-to-east transition in values from 0.704 to 0.708 over a distance of ~30 km. The rocks of the northern Owyhee Mountains are interpreted to be the southward continuation (Owyhee segment) of the western Idaho shear zone. Similar to a well-studied section of the western Idaho shear zone by McCall (McCall segment), the Owyhee segment displays steep foliation and lineation orientations, deformation of 98-90 Ma plutons, steep Sr isotopic gradients, and syntectonic tonalite intrusions. However, the Owyhee segment has three major differences from the McCall segment: (1) signifi cantly less well-developed solid-state strain fabric foliations; (2) trend of 020° rather than 000°; and (3) a wider transition zone in initial Sr ratios from 0.704 to 0.708. We present a simple tectonic model to explain these differences, assuming a 20° along-zone difference in the initial orientation of the western margin of the Laurentia, a rigid-body collision, homogeneous material behavior, and transpressional kinematics. For the Owyhee segment, the model predicts a lower oblique-convergence angle, less convergent displacement, more dextral transcurrent displacement, and an overall lower fi nite strain relative to the McCall segment.

Isotopic compositions of intrusive rocks from the Wallowa and Olds Ferry arc terranes of northeastern Oregon and western Idaho: Implications for Cordilleran evolution, lithospheric structure, and Miocene magmatism

“…The work of Armstrong et al (1977) spurred numerous studies that have helped to characterized the lithologic, structural, and geo chemical nature, and tectonic significance of this fundamental lithospheric boundary (cf. Isotopic compositions of intrusive rocks, Wallowa and Olds Ferry arc terranes | THEMED ISSUE and Criss, 1985;Criss and Fleck, 1987;Lund and Snee, 1988;Strayer et al, 1989;Leeman et al, 1992;Manduca et al, 1992Manduca et al, , 1993McClel land et al, 2000;Giorgis et al, 2005Giorgis et al, , 2008Gray and Oldow, 2005;King et al, 2007;McClelland and Oldow, 2007;Benford et al, 2010). Rocks that spatially coincide with this tran sitional boundary record multiple episodes of deformation; the orientations of major structural features related to these events are also gener ally concordant with respect to the inferred sub vertical geometry of the boundary.…”

Temporal and geochemical signatures in granitoids of northwestern Nevada: Evidence for the continuity of the Mesozoic magmatic arc through the western Great Basin

“…105-92 Ma SRR-BRH intrusions are temporally coincident with the following regional magmatic pulses: (1) (2) the suture zone suite of the Salmon River suture zone (ca. 125-90 Ma, Giorgis et al, 2008;Gaschnig et al, 2010); (3) Benford et al, 2010). Broad geochemical similarities between the SRR-BRH intrusions and the neighboring batholith systems suggest that the SRR-BRH intrusions were formed in a similar continental magmatic arc setting.…”

“…Although widespread Cenozoic volcanism and faulting within the present-day Basin and Range Province obscures much of the earlier Mesozoic relationships, several studies have argued that the Cretaceous magmatic arc was continuous throughout northwestern Nevada and southwestern Idaho (e.g., Smith et al, 1971;Barton et al, 1988. Van Buer et al, 2009Van Buer and Miller, 2010;Benford et al, 2010). Based on petrography, bulk elemental analyses, and K/Ar ages, Smith et al (1971) (Benford et al, 2010).…”

“…Van Buer et al, 2009Van Buer and Miller, 2010;Benford et al, 2010). Based on petrography, bulk elemental analyses, and K/Ar ages, Smith et al (1971) (Benford et al, 2010).…”

“…A paleogeologic map reconstruction of northwestern Nevada also demonstrated that the Sierra Nevada batholith was continuous to the northeast across the Basin and Range(Van Buer et al, 2009). Additionally,Benford et al (2010) examined several isolated intrusions within the Owyhee Mountains of southwestern Idaho. Geochronologic, structural, and isotopic analyses of these intrusions reveal similar ages, deformation histories, and initial 87 Sr/ 86 Sr isotope gradients comparable to the western Idaho shear zone (WISZ) of the Idaho batholith.…”