Transtension in the Coso-China Lake Region, westernmost Basin and Range, southeastern California

The Coso-China Lake (CCL) region borders the southeastern Sierra Nevada Mountains in the transtensional corridor bounding the eastern margin of the Sierra Nevada microplate known as the Eastern California shear zone/Walker Lane. The focus of this work is on how rocks of the brittle upper crust accommodate non-plane strain transtensional deformation from plate boundary to outcrop scale. The dynamic nature of Coso makes it an ideal natural laboratory for studying active processes.Chapter 1 deals with the constrictional nature of transtension, which generates rotation about vertical and horizontal axes and the internal deformation of rotating blocks. Constriction is achieved by simultaneous arrays of rotating normal and wrench faults, partitioned spatially and temporally. Coso illustrates the complex synchroneity and polyphase superposition of rotating fault arrays in a constrictional strain field in the brittle regime.The focus of Chapter 2 is the description of non-plane strain brittle transtension through field observations and theoretical applications. Fundamental geometric relationships in transtensional zones and tectonic reconstruction allow practical applications of theory, using zone parameters from Coso, and expand our ability to describe triaxial strain in three dimensions. Multi-scale partitioning of strain and rotation, influenced by preexisting and reactivated structures, characterizes transtensional deformation at Coso, and is well described by kinematic analysis of structural field observations and regional theoretical applications and analyses.Chapter 3 presents an expanded application of transtensional theory to structural provinces of the Eastern California shear zone-Walker Lane. The local geometry of the transtensional zone boundary and the microplate transport direction determine orientations of the instantaneous strain axes for each province. Fault orientations predicted with respect to these axes are consistent with those observed in each structural province.Chapter 4 uses extensive field structural mapping and kinematic data analyses to comprehensively characterize the structural geology of the Coso region at the outcrop scale. The degree of partitioning of transtensional structures decreases with the scale of observation. Structural patterns at Coso have been strongly influenced by a preexisting fabric in the Sierra Nevada basement, now reactivated by transtensional faulting.