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Comparison of gabbroic inclusions derived from lower crust beneath the northeast Japan Arc, their ragiogenic ages and petrological significances.

日本东北弧下下地壳辉长岩包裹体的比较、其成因年龄和岩石学意义。

基本信息

批准号：
09640540
负责人：
FUJIBAYASHI Norie
金额：
$ 2.05万
依托单位：
NIIGATA UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 2000
项目状态：
已结题

项目摘要

Ultramafic and mafic inclusions from the Northeast Japan Arc, Izu-Ogasawara Arc and Fossa Magna Region were studied. Based on their mineral chemistries, most of them are interpreted to be cumulates from arc tholeiite, formed in magma chambers at the depth near the crust-mantle boundary. Some amphibole-poor ultramafic and mafic xenoliths from the lchinomegata maar ejecta and the Miocene Ogi basalt, however, are the cumulates formed by crystallization of oceanic tholeiite. Clinopyroxenites from the lchinomegata maar and olivine gabbro from the Miocene Atsumi dolerite are crystallized from alkali basalt magmas. Gabbronorites from the Fuji volcano and the Yatsugatake volcano are cumulates from dacitic magmas mixed with basaltic magmas. Sr isotope ratios of the inclusions from the Pliocene volcanics in Sanogawa area are low (0.7031-33), and able to be characterized as the products of back-arc magmatism in the Ancient Izu-Shichitou Arc. Some gabbroic inclusions from the Yatsugatake volcano have low Sr isotopic ratios (<0.7040) significant of the Izu=ogasawara arc volcanoes, and the others show high ivalues (>0.7040) significant of frontal volcanos in the Northeast Japan Arc. Sr isotope ratios of the most gabbroic inclusions from the Atsumi dolerite show low values (0.7032-33), but some olivine gabbros show high values (0.7038-39). Useful isochron ages are only determined for inclusions from the Atsumi area by Sm-Nd method. The ages are from 28 to 32 Ma for the olivine gabbros and 54 to 66 Ma for gabbros.

研究了日本东北弧、伊豆小笠原弧和大窝地区的超镁铁性和基性包裹体。根据它们的矿物化学性质，它们大多被解释为弧拉斑岩的堆积，形成于地壳-地幔边界附近深处的岩浆房中。而来自lchinomegata maar喷出物和中新世Ogi玄武岩的一些缺乏角闪石的超镁铁质和基性捕虏体则是海洋拉斑岩结晶形成的堆积物。lchinomegata maar中的斜辉石岩和中新世Atsumi白云岩中的橄榄辉长岩是由碱性玄武岩岩浆结晶而成的。富士火山和矢竹火山的辉长岩是英英质岩浆与玄武质岩浆混合形成的。三野川地区上新世火山岩包裹体Sr同位素比值较低（0.7031-33），为古伊豆-七头弧弧后岩浆活动的产物。Yatsugatake火山辉长岩包裹体的Sr同位素比值较低（<0.7040），具有伊豆-小笠原弧火山的特征，而其他辉长岩包裹体的Sr同位素比值较高（>0.7040），具有日本东北弧锋面火山的特征。多数辉长岩包裹体Sr同位素值较低（0.7032 ~ 33），部分橄榄辉长岩包裹体Sr同位素值较高（0.7038 ~ 39）。有用的等时线年龄只能用Sm-Nd法测定来自Atsumi地区的包裹体。橄榄辉长岩年龄为28 ~ 32 Ma，辉长岩年龄为54 ~ 66 Ma。