Petrological and geochemical characteristics of lithospheric mantle and magmatism related to its evolution at the Southwest Japan arc

来自日本西南部Kurose的超镁铁质捕虏体代表了活跃的日本西南部火山-构造弧后弧下的岩石圈地幔碎片。我们将黑罗斯橄榄岩包体分为三种类型，根据13个超基性捕虏体中斜辉石质Sr-Nd同位素和微量元素组成，(1)日本海玄武岩型，表现为不相容元素的缺失，Sr-Nd同位素组成变化与日本海玄武岩相似；(2)EM I型，具有与九州新生代玄武岩相似的Sr-Nd同位素组成范围；(3)EM II型，Sr-Nd同位素组成和不相容元素富集。这些捕虏体可能经历了以下事件；(1)大陆岩石圈的开放体系部分熔融，在弧后盆地和日本海开口期间涌入了一个类似morb同位素组成的软流圈熔体；(2)与九州玄武岩有关的软流圈熔体的交代作用。

Ultramafic xenoliths from Kurose, Southwest Japan represent fragments of the lithospheric mantle beneath the back-arc of the active Southwest Japan volcano-tectonic arc. We divided the Kurose peridotite xenoliths into three types, on the basis of the Sr-Nd isotopic and trace element compositions of the clinopyroxenes in the 13 ultramafic xenoliths,(1) Japan-Sea basalt type which shows depletion of incompatible elements and similar variation of Sr-Nd isotopic compositions of Japan-Sea basalts,(2) EM I type which has similar Sr-Nd isotopic compositional range of Cenozoic balasts of Kyushu and(3) EM II type with enriched Sr-Nd isotopic composition and incompathible elements. These xenoliths would have experienced the following events ;(1) open-system partial melting of the continental lithosphere with influx of an asthenospheric melt with MORB-like isotopic composition during the back arc basin the Japan Sea opening,(2) metasomatism with the asthenospheric melt related to the Kyushu basalts.