A doubly vergent fan structure in the Peninsular Ranges batholith: Transpression or local complex flow around a continental margin buttress?

摘要: [1] The Jura-Cretaceous Peninsular Ranges batholith (PRB) of southern and Baja California contains a remarkable example crustal transition between juxtaposed oceanic continental floored arcs. deformation in the PRB is focused along this lithospheric discontinuity defines zone contractional that stretches at least 800 km batholith. The western edge associated with dramatic eastward increase maximum recorded metamorphic pressures (from 2 to 6 kbar) temperatures 650°C). Elsewhere North American Cordillera, similar boundaries are thought accommodate various amounts orogen-parallel displacements outboard tectonic fragments. To test proposal PRB, we examined an unusually well-preserved part Sierra San Pedro Martir (SSPM). Here spectacular ∼20 wide, doubly vergent fan structure, which developed over period >40 m.y. during both Jurassic Cretaceous magmatism, occurs zone. This structure consists moderately inward dipping, outward vergent, fold thrust belts widespread mylonitic fabrics steepen toward center where magmatic occur syntectonic, vertically sheeted plutons. Mineral lineations change from steeply pitching on sides center. A number constraints possible displacements, rotation units, duration fabric formation limit amount displacement few kilometers across SSPM. Instead, propose local feature results combination wedging caused by cusp rigid, pre-Mesozoic margin crust location vise tectonics arose strong lateral rheological gradients resulting extensive heating tonalite complex, discontinuity, subsequent strain softening. We suggest these mechanical controls orthogonal convergence may be common other orogens structures have been attributed transpression, emphasizing need for caution interpreting such features as zones significant, displacement.