Crustal-scale, en echelon "P-shear' tensional bridges: a possible solution to the batholithic room problem

The apparent paradox of voluminous granitoid emplacement in an overall compressional magmatic arc has been somewhat alleviated by the idea of pluton emplacement in tension cracks and dilational jogs within arc-parallel, strike-slip fault systems. As an alternative hypothesis, we propose that an en echelon P-shear array provides a continuous, batholith-scale zone of dilation along the trend of active magmatism and that it is favored by transpressional tectonics. In the Sierra Nevada, California, the late Cretaceous granitoids of the Cathedral Range intrusive epoch are consistent with emplacement into bridges between P shears because (1) they are elongated oblique to the magmatic trend, consistent with P-shear orientation within a dextral system; (2) they were all emplaced within 5-10 m.y. along a 300 km trend, resulting in a displacement rate of ~1 cm/yr across the arc; and (3) syn- to late-magmatic, dextral shear zones bound and crosscut the plutons, as in a P-shear tensional bridge. -Authors