A Complex Interplay Between Pluton Emplacement, Tectonic Deformation, and Plate Kinematics in the Cretaceous Sierra Nevada Magmatic Arc, California

The relation of plate kinematics to the structural record of arc plutons and their host rocks is complex and still not fully understood. We address this issue through a combination of field mapping, structural analysis, anisotropy of magnetic susceptibility analysis, and fabric modeling in the Late Cretaceous Tuolumne Intrusive Complex, Sierra Nevada, California. A pattern of anti-clockwise rotation from similar to NNW-SSE to WNW-ESE steep foliations and change in fabric ellipsoid shape from oblate to prolate was revealed in successively emplaced Kuna Crest (similar to 95-92 Ma), Half Dome (similar to 92-89 Ma), and Cathedral Peak (similar to 89-84 Ma) granodiorites. The numerical model indicates that the Kuna Crest was emplaced in a transpressional setting with an angle of convergence alpha = 60-40 degrees, whereas the Half Dome and Cathedral Peak required simultaneous vertical constriction overprinted by transpression with alpha = 35-15 degrees. This transition, which occurred at similar to 92 Ma, is accompanied by a shallowing of the lineation plunge observed also in other similar to 88-84 Ma central Sierra Nevada plutons. Provided that the Cretaceous Sierra Nevada arc was constructed during overall dextral transpression, these transitions reflect significant changes in kinematics, where similar to 107-92 Ma plutons were emplaced during pure shear-dominated transpression, which was followed by a transition to wrench-dominated transpression recorded in similar to 92-84 Ma plutons. Such a transition in kinematics is explained as a result of progressively increasing obliquity of the relative convergence of the Farallon plate subducting beneath the North American continental margin, in agreement with most paleogeographic reconstructions. Field mapping, structural analysis, magnetic anisotropy, and fabric modeling were carried out in the Tuolumne Intrusive Complex Changes in foliation strike, fabric symmetry, and lineation plunge imply a change in the angle of convergence The transition from pure shear to wrench-dominated transpression reflects increasing convergence obliquity of the Farallon plate