The Initiation and Growth of Transpressional Shear Zones Through Continental Arc Lithosphere, Southwest New Zealand

Structural analyses combined with new U-Pb zircon and titanite geochronology show how two Early Cretaceous transpressional shear zones initiated grew through a nearly complete section of continental arc crust during oblique convergence. Both reactivated Carboniferous faults that penetrated the upper mantle below Zealandia's Median Batholith but opposite growth patterns dissimilar relationships respect to magmatism. The Grebe-Indecision Creek zone was magma-starved first at ?136 Ma as an oblique-reverse fault, along which outboard batholith partially subducted beneath Gondwana. This system nucleated or above ?20 km depth propagated downward 2–3 mm yr?1, accumulating least 35–45 horizontal (arc-normal) shortening by ?124 Ma. In contrast, magma-rich George Sound in lower (?55 depth) upward ?3 reaching ?110 this latter system, magmatism influenced architecture drove its while subduction convergence ended. As magma entered roots began solidify, deformation driven out into middle where widened factor three when fold-thrust belts formed on either side steep, central zone. study illustrates reactivation structural weaknesses localizes all depths lithosphere shows magma-deformation feedbacks influence connectivity built from bottom up.