Cretaceous complexes of the frontal zone of the Moneron-Samarga island arc: geochemical evidence of basalts from the deep hole on Moneron Island (Sea of Japan)
Variations of petrogenic oxides and microelements determined by the ICP-MS method have been studied in the Cretaceous rocks outstripped by a deep hole on Moneron Island in the depth interval 1253-4011 m. The volcanogenic section holds two complexes: Early Cretaceous and Late Cretaceous. The rocks of the Early Cretaceous complex occur below 1500 m. Chemically, they belong to low-potassium island arc tholeiites, and microelement distribution suggests their formation in a suprasubduction mantle wedge under the influence of water fluids, which arrived first from the subducting sediments and oceanic plate during dehydration of the subducted sedimentary rocks and oceanic basalts; and at the final stages, mainly from basalts of the oceanic plate. The Early Cretaceous basalts from the hole belong to the frontal part of the Moneron-Samarga island-arc system. The volcanic rocks of the Late Cretaceous complex occur above 1500 m. They are also a subsubduction geodynamic type in the structure of the East Sikhote-Alin marginal-continental volcanic belt that formed after accretion of the Moneron-Samarga island-arc system to the Asian continent. The island-arc section of the Moneron hole holds dikes of andesite basalts, which geochemically are comparable with the Early-Middle Miocene volcanic rocks of SW Sakhalin.