Slab kinematics and strain localization in NE China: Polyphase deformation of the Hulin Complex during Late Mesozoic subduction

Crustal shear zones in Northeast China preserve a critical record of Paleo-Pacific subduction, yet distinguishing the superimposed tectonic fabrics remains a challenge. We resolved this by reconstructing the structural and thermal history of the Hulin Complex, linking local deformation directly to specific slab dynamics. During the Late Jurassic to Early Cretaceous (D₁: ca. 160–130 Ma), a moderate oblique subduction angle (∼30–40°) drove NE–SW sinistral transpression. This phase produced distributed general shear (Flinn's k = 0.73–0.91; W_k = 0.64–0.67) under mid-crustal conditions (∼350–500 °C), accommodated by quartz rhomb <a> and prism <a> slip at differential stresses of 15–18 MPa. In the Cretaceous (D₂: ca. 130–85 Ma), accelerated SE-directed slab rollback stretched the lithosphere, triggering regional extension (Flinn's k = 0.85–1.01; W_k = 0.57–0.62). Strain localized into weak, mica-rich zones (>15 vol%) as differential stresses dropped to 13–14 MPa and temperatures cooled to 300–400 °C. This extension facilitated synchronous magmatism. By the Late Cretaceous (D₃: ca. 85–68 Ma), a shift to W–NW subduction created a lower obliquity angle (∼20–30°). This renewed dextral transpression reactivated older structures in the mid-to-lower crust (≤300–400 °C) but at significantly higher stresses (21–34 MPa). Quartz fabrics shifted to basal <a> slip, reflecting strain repartitioning (Flinn's k = 0.63–0.76; W_k = 0.67–0.71). Our findings demonstrate that shear zone evolution is governed by specific subduction parameters: (1) shallower slab dips enhance coupling to localize strain; (2) rapid rollback weakens the lithosphere to drive extension; and (3) high convergence obliquity (angles <30°) amplifies the simple shear component. Thus, the Hulin Complex acts as a sensitive rheological recorder, capturing the changing tempo and geometry of the subducting slab.