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首页> 外文期刊>Journal of geodynamics >Late Cretaceous to early Paleogene forearc magmatism and subduction initiation in the Paleo-Kuril arc-trench system, eastern Hokkaido, Japan
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Late Cretaceous to early Paleogene forearc magmatism and subduction initiation in the Paleo-Kuril arc-trench system, eastern Hokkaido, Japan

机译：北海道东部古-古里尔弧-槽系统中的白垩纪晚期至古近纪早期前岩浆作用和俯冲作用

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摘要

New major and trace elemental data presented here imply a temporal and spatial change in the magmatic evolution and mode of subduction initiation in the Paleo-Kuril arc-trench system, eastern Hokkaido, Japan. Late Cretaceous to early Paleogene igneous rocks from the Nemuro Group (Nokkamappu, Hamanaka, and Kiritappu Formations) in the forearc basin of the Paleo-Kuril arc consist of the tholeiitic, alkaline and calc-alkaline rock series, based on petrographic and major-element (K2O, total alkalies [K2O + Na2O], and SiO2 contents) data. Immobile-element features on the Zr/TiO2 vs. Nb/Y diagram indicate that a majority of the alkaline rocks are classified as non-alkaline rock. The low TiO2 ( 1%), high V/Ti, and low Nb/Yb ratios of the igneous rocks show that the original mantle compositions of alkaline and non-alkaline rocks were highly refractory in nature. The magmas were produced with a 10-20% partial melting of the depleted mantle, which is common in arc-related non-alkaline magma. The high Th/Yb, Ba/La, Rb/La, and Ba/Th ratios and low La/Sm ratios of the alkaline and tholeiitic rocks from the Nokkamappu and Hamanaka Formations strongly reflect the imprint of substantial fluid components from the subducting slab. The enriched K and Rb in the alkaline magma source are indicative of fluid derived from mica breakdown. Cs fractionation in the slab-derived fluids is indicated by variations in Y/Cs and Nb/Cs, and the fluids are controlled by fluid derived from the breakdown of mica such as phengite. Tholeiitic and calc-alkaline rocks from the Kiritappu Formation show less aqueous fluids. Late Cretaceous magmatism, with decompression melting and formation of the forearc basin, resulted from rollback during subducting initiation, which was associated with a rift system created by the upwelling of depleted mantle following the onset of the sinking of the slab into the mantle. Subsequently, the rollback of the subducting slab slowed down and stabilized, and consequently, normal tholeiitic and calc-alkaline magmas were produced in the early Paleogene.
机译：这里介绍的新的主要和微量元素数据暗示了日本北海道东部古柯里尔弧-沟系统岩浆演化和俯冲起始模式的时空变化。古库里尔弧前陆盆地内穆罗群的晚白垩纪至古近纪火成岩（Nokkamappu，Hamanaka和Kiritappu地层）由基于岩石学和主要元素的生硬，碱性和钙碱性岩石系列组成（K2O，总碱度[K2O + Na2O]和SiO2含量）数据。 Zr / TiO2与Nb / Y图上的固定元素特征表明，大多数碱性岩石被归类为非碱性岩石。火成岩的低TiO2（<1％），高的V / Ti和低的Nb / Yb比表明，碱性和非碱性岩石的原始地幔成分在本质上是高度难熔的。岩浆产生时，耗尽的地幔部分熔化了10-20％，这在与弧有关的非碱性岩浆中很常见。来自Nokkamappu和Hamanaka地层的碱性和生硬岩的高Th / Yb，Ba / La，Rb / La和Ba / Th比以及低La / Sm比强烈反映了俯冲板块中大量流体组分的印记。碱性岩浆源中富集的K和Rb表示云母分解产生的流体。 Y / Cs和Nb / Cs的变化表示板坯衍生流体中的Cs分馏，而流体则受源自云母分解的流体（如陨石）的控制。 Kiritappu组的生硬质和钙碱性岩石显示出较少的含水流体。白垩纪晚期岩浆活动，减压融化并形成前陆盆地，是由于俯冲作用开始时的回滚所致，这与裂陷系统有关，该裂陷系统是由板块下沉开始后枯竭的地幔上升形成的。随后，俯冲板块的回滚速度减慢并稳定下来，因此，在古近纪早期就产生了正常的高渗岩浆和钙碱性岩浆。

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