KINEMATIC PARTITIONING IN THE ECHO LAKE DEFORMATION ZONE, SEIAD ULTRAMAFIC COMPLEX, KLAMATH MOUNTAINS, CA

The Echo Lake deformation zone (ELDZ) is a >60 m-thick lithologically diverse shear zone. The ELDZ is situated between two amphibolite- to granulite-facies peridotite bodies in the Seiad ultramafic complex in the Rattlesnake Creek Terrane, which is an oceanic crust and mantle mélange located in the Klamath Mountains Province, northwestern California and southwestern Oregon. Tectonites in the ELDZ include metasedimentary rocks (marble, quartzite, and quartz-rich schist) and peridotites (dunite, harzburgite, and lherzolite) which share a planar fabric that crosscuts adjacent rocks in the complex. Mineral stretching lineations are well-developed across the ELDZ and exhibit a preferred NW-plunging orientation, compatible with previous kinematic investigations that inferred either top-to-NW or top-to-SE shear sense. Conversely, the directions of kinematic indicators and local vorticity axes vary across the zone and within units. Vorticity axis patterns in the metasedimentary rocks include foliation-parallel girdles, lineation-parallel maxima, and lineation-perpendicular maxima, whereas vorticity axes in the peridotites define an elongated-maxima pattern (partially girdled). Compared to vorticity axes measured in deformation experiments with different geometries (simple shear, compression, tension, and transpression), patterns observed in ELDZ tectonites suggest mesoscopic kinematic partitioning and reveal a larger-scale transpressional kinematic regime related to Middle Jurassic regional contraction and juxtaposition of the Rattlesnake Creek and Western Hayfork terranes.