Architecture of the Sulu crustal suture between the North China Craton and Yangtze Craton: Constraints from Mesozoic granitoids

Abstract

The Yangtze Craton (YC) and the North China Craton (NCC) collided in the Triassic, producing the prominent NNE-trending Sulu high-ultrahigh pressure metamorphic belt and associated crustal thickening. Late Jurassic–Early Cretaceous granitic plutons in the Sulu orogenic belt and the Jiaobei terrane to the west were used to investigate the crustal architecture across the suture. Our new data show that the granitoids from these two regions have similar chemical and isotope compositions. They are all characterized by very high Sr and low Y–Yb contents, high Sr/Y and (La/Yb)N ratios, similar ƐNd(t) values from −18.2 to −21.4, and similar initial 87Sr/86Sr ratios from 0.7076 to 0.7119. The calculated Nd two-stage model ages (TDM2) based on whole rock data vary from 2415 to 2662Ma. Co-magmatic zircon crystals from the granitoids have variably negative ƐHf(t) values from −26.8 to −12.8, with the calculated Hf TDM2 from 2008 to 2892Ma. The inherited zircon crystals from these rocks are dominated by Neoproterozoic (800–600Ma) and Triassic–Early Jurassic (~220Ma and ~180Ma) ages. The ƐHf(t) values of the inherited zircon crystals with U–Pb ages between 180Ma and 800Ma from Sulu and Jiaobei range from −21.6 to 4.2 and from −23 to −1.9, respectively. They all plot within the field of crustal evolution between 1385 and 2583Ma. The similar whole rock geochemical signatures and similar inherited zircon data indicate a similar source for the granitoids in these two regions. We propose that the source regions across the suture all belong to the YC. The occurrence of the YC crust beneath the NCC at this location is thought to have resulted from the westward subduction of the YC beneath the NCC and subsequent continental collision in the Triassic. In this model, the abundant 800 to 230Ma inherited zircon crystals in the granitoids are interpreted to have been derived from the source region whereas the rare older inherited zircon crystals are thought to have been derived from the overlying NCC during magma ascent.