Close spatial relationship between plutons and shear zones

This paper explores the relationship between granitic plutons and transcurrent shear zones using examples from the Borborema province, northeastern Brazil. Syntectonic plutons of this province generally have en cornue shapes and were emplaced preferentially within or at the margins of wide, regional-scale transcurrent shear zones, particularly where shear zones intersect major lithological boundaries. It is argued that the plutons' shapes and their closeness to shear zones are indicative of a causal relationship between granite plutons and shear zones. With the support of numerical models, it is further argued that pluton emplacement in transcurrent terranes is controlled by low-mean-pressure magma traps at the shoulders of shear zones, resulting from strain incompatibility caused by regional variations in rheological properties.