Petrogenesis of the Early Jurassic–Early Cretaceous Adakite-like Rocks in the Erguna Block, NE China: Implications for the Tectonic Evolution of the Mongol–Okhotsk Ocean

The petrogenesis and geodynamic setting of the Mesozoic magmatic rocks in the Erguna Block, NE China remains controversial, especially the relationship between magmatism and the subduction history of the Mongol–Okhotsk oceanic plate. Here we present data for the Early Jurassic–Early Cretaceous adakite-like magmatic rocks from Chaoman Farm in the northeastern part of the Erguna Block. Zircon U-Pb dating reveals that the syenogranites crystallized at around 190–180 Ma, while the monzonites, quartz diorite porphyries, and quartz monzonite porphyries were emplaced at around 147–143 Ma. The syenogranites, monzonites, quartz diorite porphyries, and quartz monzonite porphyries are adakite-like rocks. The syenogranites and quartz monzonite porphyries were produced by the partial melting of a thickened ancient mafic lower continental crust and a thickened juvenile lower crust, respectively. Meanwhile, the monzonites and quartz diorite porphyries were formed as a result of partial melting of the oceanic crust. In conclusion, the occurrence of these Early Jurassic magmatic rocks was closely linked to the process of southward subduction of the Mongol–Okhotsk oceanic plate. On the contrary, the Late Jurassic to early Early Cretaceous magmatism (147–143 Ma) occurred in an extensional environment, and was probably triggered by upwelling of the asthenosphere.