SHRIMP Dating of Adakites in the Tulingkai Ophiolite, Inner Mongolia: Evidence for the Early Paleozoic Subduction

Abstract

The newly recognized adakites in the Tulingkai ophiolite, Inner Mongolia, lithologically including quartz diorite, trondhjemite, anorthosite and dacite, are magmatic markers of the Early Paleozoic Ondor Sum-Tulingkai subduction zone. The rocks are precisely dated using SHRIMP. The quartz diorite intruded at 467± 13 Ma, implying that the oceanic subduction started at this time or earlier. Shortly afterwards, at about 451± 18 Ma, the high-grade metamorphism and/or partial melting took place. The dacite erupted at 459 ± 8 Ma, the trondhjemite intruded at 451 ± 7 Ma, and finally, the anorthosite dike was formed at 429 ± 7 Ma. It is therefore suggested that the time interval of the Early Paleozoic subduction of the Ondor Sum-Tulingkai oceanic crust is over 38 Ma.