ADOPTING AN ORPHANED TERRANE: USING WHOLE ROCK GEOCHEMICAL ANALYSIS TO DETERMINE A PARENT TO THE OUTER CONDREY MOUNTAIN SCHIST IN THE KLAMATH MOUNTAINS, CA AND OR

The outer Condrey Mountain schist (CMSo) is a metavolcanic–metasedimentary subunit within the Klamath Mountains Province (KMP), exposed along the outer margins of a structural window centered on Condrey Mountain, CA. A dearth of zircon within the CMSo has precluded temporal correlation with other KMP terranes, but U-Pb zircon ages on an intrusive body place deposition of the host CMSo as Middle Jurassic or earlier (≥170 Ma). Potentially correlative KMP protolith units are the Middle Jurassic western Hayfork terrane and coherent cover sequences of the Late Triassic to Early Jurassic Rattlesnake Creek terrane (RCT). Previous workers also correlated the CMSo with the Galice Formation, the Late Jurassic cover sequence to the Josephine ophiolite. However, despite petrographic similarities and similarities in relative structural position, the Galice Formation is too young to be correlative (ca. 155 Ma). Other potential protolith units include metavolcanics of the Late Jurassic Rogue-Chetco forearc complex and amphibolite sequences of the RCT. In addition, a potential correlative of CMSo exposed west of the dome (Fort Goff schist) was also analyzed.

New whole rock major and trace element data, combined with published and unpublished data, were plotted on various discrimination diagrams. Datasets were grouped according to broad lithology, and subunit. The data indicate that CMSo metavolcanic rocks are tholeiitic with flat chondrite-normalized REE patterns indicative of E-MORB affinities. Similar flat patterns are evident in some RCT cover sequence samples (Bolan Lake and Salt Creek), some RCT amphibolites (Gold Flat), and a sample from the Ft Goff schist. Previous workers have mapped the CMSo/Fort Goff schist as structurally above the Galice Formation and below the RCT in an eastward dipping duplex west of the dome. The tectonistratigraphic position of the CMSo between these two KMP terranes and similarities to units noted above indicate that the protolith of the CMSo is likely also a KMP terrane. Analyses of additional samples as well as a comparison of the crosscutting intrusive body in the CMSo with potential plutonic correlatives will aid in determining a parent for the orphaned terrane of the CMSo.