Emergent Low-Angle Detachments in 3D Transtension: Influence of Crustal Inheritance and Strike-Slip Partitioning

Low-angle normal faults (LANFs) and extensional detachments commonly nucleate and evolve within complex three-dimensional strain fields, especially where strike-slip motion interacts with extension in post-orogenic settings. In many orogens (Norway, the Aegean, Turkey, Variscan Europe), field evidence shows that transtensional transfer zones exert a first-order control on the geometry of metamorphic core complexes and on the activation of low-angle shear zones. Despite this, the mechanics allowing LANFs to initiate, rotate, and exhume deep crustal rocks in oblique strike-slip systems remain poorly constrained, and existing numerical studies rarely allow detachment localisation to emerge without kinematic prescription.

We present new three-dimensional thermo-mechanical models that track the spontaneous development of LANFs and metamorphic core complexes in transtensional right-lateral systems. Boundary conditions impose only far-field oblique motion; the location and orientation of strike-slip faults and low-angle detachments are not prescribed but arise from crustal rheology and stress evolution. We test three end-member crustal architectures capturing different forms of tectonic inheritance: a homogeneous reference column (REF), a vertically heterogeneous but continuous Buckling column, and a Nappe Stack column containing a weak décollement inherited from crustal-scale nappe stacking.

The models reveal that tectonic inheritance exerts the primary control on LANF initiation and MCC geometry in 3D transtension. Nappe Stack configurations produce large low-angle detachments and a-type metamorphic domes with significant exhumation, whereas Buckling configurations generate oblique wide rifts with incomplete exhumation, and REF architectures form non-detached spreading domes. These results show that the evolution of LANFs and detachment systems in transtensional environments strongly depends on inherited crustal layering, the 3D strain field, and the degree of strike-slip partitioning.