Data from: Influence of magmatism on the architecture of transpressional faults and shear zones in the deep crust of the Late Cretaceous Southern California batholith

Structural analyses combined with U‐Pb zircon petrochronology show the
influence of arc magmatism on the evolution of two transpressional shear
zones in the deep root of the Late Cretaceous Southern California
batholith.  The mid-crustal Black Belt and lower-crustal
Cucamonga shear zones (eastern San Gabriel Mountains) formed at ~84 Ma
shortly after a large mass of tonalite and granodiorite intruded the lower
crust.  Both shear zones were active until at least ~74 Ma and
probably until 72-70 Ma.  In the mid-crustal shear zone,
rheological contrasts between mingling magmas localized deformation at
dike margins.  The deformation began as hypersolidus flow in
partially crystallized dikes and then transitioned to deformation below
the solidus when alternations between viscous creep and brittle faulting
produced interlayered pseudotachylyte, cataclasite, and mylonite. As the
dikes solidified, strain hardening drove shear zone growth and created
thin (10-30 m) high-strain zones and faults that are widely spaced across
~1 km. In contrast, the lower-crustal Cucamonga shear zone was
magma-starved, lacks the variety of shear zone fabrics exhibited by its
mid-crustal counterpart, and formed by the reactivation of a pre-existing
fabric that records pure reverse displacements at 124-93 Ma.  The
two shear zones created a partitioned style of intra-arc transpression
where sinistral-reverse (mostly arc-parallel with some arc-oblique)
displacements were accommodated on moderately dipping faults and shear
zones and arc-normal shortening was accommodated by coeval
folds.  This study shows how a magmatic surge influenced the
architecture and style of Late Cretaceous transpression in the Southern
California batholith, including the evolution of high-strain zones that
record alternating episodes of brittle, ductile, and hypersolidus
deformation.  The results illustrate how magmatism localizes
strain on deep-crustal faults during orogenesis and oblique convergence.