Paleo-Pacific subduction in Southeast Vietnam: Evidence from Late Cretaceous intrusive rocks in the Dalat zone

The Dalat zone in Southeast Vietnam forms a key component of the Paleo-Pacific subduction system, which stretches from the Coastal South China to West Borneo. Petrology, zircon U-Pb geochronology and in-situ Lu-Hf isotopes, and whole-rock geochemical analyses for gabbros and granitoids in this zone might define details of its role in the Pacific subduction. The gabbros in this region yield an age of ca. 93 Ma, and are enriched in large-ion lithophile elements (LILEs) and depleted in high field strength elements (HFSEs) with remarkable negative anomalies in Nb-Ta and Ti, similar to the Cretaceous mafic rocks in the Coastal South China. Their initial 87Sr/86Sr ratios range from 0.70531 to 0.70615, & epsilon;Nd(t) values range from -0.8 to +1.4, (206Pb/204Pb)i ratios range from 18.58 to 18.67 and zircon in-situ & epsilon;Hf(t) values range from +0.4 to +9.7. These characteristics suggest that the gabbros originated from a mantle wedge that had modified by sediment-derived melts. The granitoids found in the Deoca, Dinhquan, Ankroet (Cana) suits of the Dalat zone formed at 103-93 Ma. They exhibit significant variations in major oxide content (SiO2 = 58.84-78.61 wt%; MgO = 0.04-2.66 wt%), classifying them as high-K calc-alkaline I-type granites. In comparison with coeval gabbros, the granitoids show similar whole-rock Sr-Nd-Pb and zircon in-situ Lu-Hf isotopic compositions, arguing for a juvenile crust with arc-like geochemical affinities. The Cretaceous igneous rocks in the Dalat zone of Southeast Vietnam give collectively two age-clusters of ca. 122-112 Ma and ca. 108-75 Ma, resembling those in the Coastal South China and West Borneo. Consequently, these rocks are considered the part of the Cretaceous Paleo-Pacific subduction system, providing a connection between South China in the north and West Borneo in the south.

Automated summary

The Dalat zone in Southeast Vietnam plays a significant role in the Paleo-Pacific subduction system, and the petrology and geochemical characteristics of the gabbros and granitoids in this zone provide insights into its subduction history. The gabbros in this region have an age of approximately 93 Ma and show characteristics similar to the Cretaceous mafic rocks in the Coastal South China. The granitoids in the Dalat zone formed at 103-93 Ma and exhibit affinities to juvenile crust with arc-like geochemical characteristics.