Petrology of arc type volcanic rocks from Moneron Island, constructed Cretaceous volcanic zone of Rebun-Kabato zone, south Sakhalin, Far East Asia

Abstract

Cretaceous–early Cenozoic tectonic and slab–mantle processes in Far East Asia have been investigated mainly using granitic rocks. However, most granitic magmas are generated by assimilation and/or partial melting of crust. Therefore, it is important to use mafic igneous rock chemistry for investigating such processes in this period, because these rocks are less crustally contaminated than granitic rocks. A core of >4000 m in length was obtained from Moneron Island, southwest of Sakhalin Island, Far East Asia. The core consists mainly of Lower and Upper Cretaceous volcanic rocks, with basaltic–andesitic compositions. Whole-rock K–Ar ages of 101.9 ± 2.3 and 98.2 ± 2.2 Ma were obtained for the Lower Cretaceous rocks. Based on the location and eruption age, the Cretaceous volcanic rocks from Moneron Island belong to the Rebun–Kabato zone in Hokkaido. We also determined the mineral chemistry, and whole-rock major and trace element and Sr–Nd–Hf isotopic compositions of these rocks. The Moneron volcanic rocks have subduction-related compositional features with similar HFSE contents as N-MORB. Furthermore, these rocks exhibit a decreasing trend of Th/Yb and La/Nb, which are signatures of a slab-derived component, in the shallow part of the core. The Nd–Hf isotopic compositions also suggest a decreasing flux of slab-derived sediment from the subducting Izanagi Plate. In the western Pacific, recent studies have proposed that subduction of the Farallon–Izanagi Ridge occurred at ca. 127 Ma, a volcanic hiatus occurred at 56–46 Ma due to subduction of the Izanagi–Pacific Ridge, and depletion of the mantle occurred after 46 Ma, based mainly on zircons from granitic rocks. However, our results imply that the Cretaceous mantle wedge beneath the study area was already depleted at ca. 100 Ma.