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首页> 外文期刊>The island arc >Petrological variation of large-volume felsic magmas from Hakkoda-Towada caldera cluster: Implications for the origin of high-K felsic magmas in the Northeast Japan Arc
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Petrological variation of large-volume felsic magmas from Hakkoda-Towada caldera cluster: Implications for the origin of high-K felsic magmas in the Northeast Japan Arc

机译：八甲田-十和田破火山口大体积长英质岩浆的岩石学变化：对东北弧高钾长质岩浆岩成因的启示

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The Hakkoda-Towada caldera cluster (HTCC) is a typical Late Cenozoic caldera cluster located in the northern part of the Northeast Japan Arc. The HTCC consists of five caldera volcanoes, active between 3.5 Ma and present time. The felsic magmas can be classified into high-K (HK-) type and medium- to low-K (MLK-) type based on their whole-rock chemistry. The HK-type magmas are characterized by higher K2O and Rb contents and higher Sr-87/Sr-86 ratios than MLK-type magmas. Both magmas cannot be derived from fractional crystallization of any basaltic magma in the HTCC. Assimilation-fractional crystallization model calculations show that crustal assimilation is necessary for producing the felsic magmas, and HK-type magmas are produced by higher degree of crustal assimilation with fractional crystallization than MLK-type magmas. Although MLK-type magmas were erupted throughout HTCC activity, HK-type magmas were erupted only during the initial stage. The temporal variations of magma types suggest the large contribution of crustal components in the initial stage. A major volcanic hiatus of 3 my before the HTCC activity suggests a relatively cold crust in the initial stage. The cold crust probably promoted crustal assimilation and fractional crystallization, and caused the initial generation of HK-type magmas. Subsequently, the repeated supply of mantle-derived magmas raised temperature in the crust and formed relatively stable magma pathways. Such a later system produced MLK-type magmas with lesser crustal components. The MLK-type magmas are common and HK-type magmas are exceptional during the Pliocene-Quaternary volcanism in the Northeast Japan Arc. This fact suggests that exceptional conditions are necessary for the production of HK-type magmas. A relatively cold crust caused by a long volcanic hiatus (several million years) is considered as one of the probable conditions. Intensive crustal assimilation and fractional crystallization promoted by the cold crust may be necessary for the generation of highly evolved HK-type felsic magmas.
机译：八甲田-十和田破火山口群（HTCC）是典型的晚新生代破火山口群，位于日本东北弧的北部。 HTCC由五个火山口火山组成，活跃在3.5 Ma和当前时间之间。根据它们的整体岩石化学性质，将长英质岩浆分为高K（HK-）型和中低K（MLK-）型。与MLK型岩浆相比，HK型岩浆的特征在于具有更高的K2O和Rb含量以及更高的Sr-87 / Sr-86比。这两个岩浆不能从HTCC中任何玄武岩浆的分级结晶中获得。同化-分形结晶模型计算表明，地壳同化是生产长英质岩浆所必需的，而HK型岩浆是通过分步结晶的地壳同化程度高于MLK型岩浆而产生的。尽管在整个HTCC活动中喷发了MLK型岩浆，但HK型岩浆仅在初始阶段喷发。岩浆类型的时间变化表明，在初始阶段地壳成分的贡献很大。在HTCC活动之前，主要的火山裂隙为3 my，表明初始阶段地壳较冷。冷壳可能促进了地壳同化和部分结晶，并导致了HK型岩浆的初始生成。随后，地幔源岩浆的反复供应提高了地壳的温度，并形成了相对稳定的岩浆通道。这种后来的系统产生了具有较少地壳成分的MLK型岩浆。在东北弧上新世-第四纪火山活动期间，MLK型岩浆很常见，而HK型岩浆则例外。这一事实表明，生产HK型岩浆需要特殊的条件。由长时间的火山裂隙（几百万年）引起的相对较冷的地壳被认为是可能的条件之一。冷壳促进的强烈地壳同化和部分结晶可能是产生高度演化的HK型长英质岩浆的必要条件。

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