Syncollisional magmatism plays an impor­tant but underappreciated role in continental crust growth and maturation. However, the origin of syncollisional intermediate magmas in continental subduction zones is controver­sial, with some models suggesting they form by arc-related processes, and others indicat­ing they form by later slab breakoff–induced melting. Diorite porphyry dikes intruding granitic gneiss in the Paleo-Tethyan Sulu ultrahigh-pressure (UHP) continental col­lisional orogen have inherited zircon grains with 206Pb/238U ages of ca. 749–238 Ma, and magmatic zircons with weighted mean ages of 216–215 Ma, falling within the well-con­strained time range (ca. 235–208 Ma) track­ing exhumation of the Sulu UHP rocks from UHP peak conditions to amphibolite facies; they are thus syncollisional. The dikes have high Cr (330–402 ppm), Ni (84.5–103 ppm), and Mg# (64–66) values, showing a mantle origin. The porphyries have relatively high Sm/Yb, Nb/Y, La/Yb, and Gd/Yb ratios, rep­resenting a classic signature of slab breakoff magmatism. Together with the arc-like trace-element patterns and enriched Sr-Nd isotope compositions, ages, and εHf(t) values (−19.5 to −17.0) of magmatic zircons and their tectonic setting, we propose a syncollisional slab breakoff model in which the melts were initially generated from asthenospheric up­welling in the gap created when the oceanic slab attached to the Yangtze craton detached underneath the North China craton during Late Triassic collision following Paleo-Tethys Ocean closure. The diorite porphyry dikes have consistent Sr-Nd isotope composi­tions and spatiotemporal relationships with the nearby Shidao gabbro-syenite-granite complex, for which the tectonic affinity is controversial. Thus, we argue that the diorite porphyries and Shidao complex were sourced from two cratons, including the enriched sub­continental lithospheric mantle of the North China craton, which interacted with abun­dant felsic melts derived from the sinking slab breaking away from the subducted crust of the Yangtze continental-ocean transitional margin. This study sheds new light on crustal recycling versus continental growth in col­lisional orogens and implies that consider­able syncollisional intermediate magmas can be generated by slab breakoff in continental subduction zones, representing hybrid addi­tions to continental growth that are different and more evolved than arc magmas and have a composition similar to that of the bulk con­tinental crust.