Tectonochemistry of the Brooks Range Ophiolite, Alaska

The Brooks Range Ophiolite (BRO), recently estimated to be 1800km2 in area, is the largest ophiolite in the Western Hemisphere. However, due to its remote location, it remains one of the least studied. Mineral exploration and reconnaissance-level mapping of the ophiolite were done in the 1970s and 1980s. Some chemical analyses were also performed, but since that time the BRO has received little attention. Over the subsequent 25+ years, the study of ophiolites has advanced greatly. These early studies found that the BRO lies in the structurally highest position in the Brooks Range, and its obduction probably coincided with the collision between the Koyukuk Arc and the Arctic-Alaska continental margin. It is therefore important to determine the tectonic setting in which the BRO formed if one wants to understand the tectonic history of the Northern Cordillera during the Jurassic/Cretaceous. Here we present new tectonochemistry data from the BRO. This includes whole-rock data (via XRF), trace element data (via XRF and ICP-MS), and mineral chemistries (via Electron Microprobe). Using immobile element fingerprinting, we constrain the tectonic setting in which the BRO formed and how this information ties in with other events in the Northern Cordillera's history. The fingerprinting results are supplemented by Cr-in-spinel data and Al-in-olivine thermometry.