Reconstructing the Western Idaho Shear Zone: A Geochronology Framework

Patzke, Mollie; Johnson, Jah Isaac; Tremain, Thomas; Surpless, Kathleen D.; Tikoff, Basil; Wang, Da; Vervoort, Jeff D.

doi:10.1130/abs/2017cd-292786

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“…Western Idaho plutons can account for the 120-100 Ma detrital zircon in the Ochoco basin, including the greater variability in detrital-zircon ε Hf values. The western Idaho shear zone marks the continental boundary (Lund and Snee, 1988;Manduca et al, 1993;McClelland et al, 2000), and ε Hf values for 120-109 Ma plutons intruded across this boundary range from +10 to +4.7 (Patzke et al, 2017), with more positive ε Hf associated with 87 Sr/ 86 Sr values < 0.7045 to the west and more negative ε Hf associated with 87 Sr/ 86 Sr values > 0.7070 to the east across the shear zone ( 87 Sr/ 86 Sr values from Fleck and Criss, 1985). Giorgis et al (2005) suggested that restoring 105-90 Ma transpressional deformation along the western Idaho shear zone results in a 110-100 Ma magmatic arc that may have been comparable in width to the Cretaceous Sierra Nevada batholith.…”

Section: Ochoco Basin Provenancementioning

confidence: 99%

Provenance analysis of the Ochoco basin, central Oregon: A window into the Late Cretaceous paleogeography of the northern U.S. Cordillera

Surpless¹,

Gulliver²

2018

Tectonics, Sedimentary Basins, and Provenance: A Celebration of the Career of William R. Dickinson

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Cretaceous forearc strata of the Ochoco basin in central Oregon may preserve a record of regional transpression, magmatism, and mountain building within the Late Cretaceous Cordillera. Given the volume of material that must have been eroded from the Sierra Nevada and Idaho batholith to result in modern exposures of midand deep-crustal rocks, Cretaceous forearc basins have the potential to preserve a record of arc magmatism no longer preserved within the arc, if forearc sediment can be confi dently linked to sources. Paleogeographic models for mid-Cretaceous time indicate that the Blue Mountains and the Ochoco sedimentary overlap succession experienced postdepositional, coast-parallel, dextral translation of less than 400 km or as much as 1700 km. Our detailed provenance study of the Ochoco basin and comparison of Ochoco basin provenance with that of the Hornbrook Formation, Great Valley Group, and Methow basin test paleogeographic models and the potential extent of Cretaceous forearc deposition. Deposition of Ochoco strata was largely Late Cretaceous, from Albian through at least Santonian time (ca. 113-86 Ma and younger), rather than Albian-Cenomanian (ca. 113-94 Ma). Provenance characteristics of the Ochoco basin are consistent with northern U.S. Cordilleran sources, and Ochoco strata may represent the destination of much of the mid-to Late Cretaceous Idaho arc that was intruded and eroded during and following rapid transpression along the western Idaho shear zone. Our provenance results suggest that the Hornbrook Formation and Ochoco basin formed two sides of the same depositional system, which may have been linked to the Great Valley Group to the south by Coniacian time, but was not connected to the Methow basin. These results limit northward displacement of the Ochoco basin to less than 400 km relative to the North American craton, and

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