K-Ar ages, major and minor element compositions and Sr, Nd isotope ratios of volcanic rocks from the western part of south Sakhalin, USSR.

概要

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Cenozoic volcanic rocks are widely distributed in the south of Uglegorsk in the western part of South Sakhalin. In the north of the town, large numbers of dolerite sheets and dykes, which are represented by the Morotsu dolerite sheet, intrude the Miocene formations. K-Ar ages of two basalts, a dolerite and an andesite are 11.3, 11.8, 9.2 and 4.7 Ma respectively and these are consistent with the stratigraphical succession. However, one basalt dated at 18.0 Ma is older than the others. Based on major element compositions, the basalts belong to the high alkali tholeiite series and the andesite to the calc-alkali rock series. On the MORB-normalized spidergram patterns of minor element compositions including REE, the volcanic rocks are divided into two groups. Those of the first group are similar to those of E-MORB and BABB and are different from that of high alkali tholeiite of the Japan arc because of enrichment of Nb. On the εNd-87Sr/86Sr diagram, two basalts and an andesite lie on the mantle array and are considered to have been derived from enriched source material which is different from that of the Quaternary volcanic rocks of NE Japan. The basalt and dolerite having higher εNd and 87Sr/86Sr may have been affected by interaction with sea water or post-magmatic alteration.
日本鉱物科学会の論文