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.

研究了来自日本东北部，Izu-Ogasawara Arc和Fossa Magna地区的超镁铁质和镁铁质夹杂物。根据它们的矿物化学成分，其中大多数被解释为累积的弧形，在岩浆腔室中形成，在地壳甲壳虫边界附近的深度处形成。然而，一些来自Lchinomegata maar ejecta和中新世的Ogi玄武岩的闪石贫困的超镁质和镁铁质异形体是由海洋Tholeiite结晶形成的累积物。来自中新世Atsumi dolerite的Lchinomegata Maar和Olivine Gabbro的Clinopyroxenites从碱玄武岩岩浆中结晶。来自富士火山和Yatsugatake火山的Gabbronorites是来自Dacitic Magmas和玄武岩岩浆的累积。来自Sanogawa地区上新世火山的夹杂物的SR同位素比率很低（0.7031-33），并且能够被描述为古代Izu-Shichitou Arc中的后弧岩浆产物。来自Yatsugatake火山的一些gabbroic夹杂物的同位素比（<0.7040）较低，Izu = Ogasawara Arc火山，而其他人则在日本Arc的额叶火山中显示出较高的eiallues（> 0.7040）。来自Atsumi Dolerite的最gabbroic夹杂物的SR同位素比值低（0.7032-33），但一些橄榄石GABBROS显示出较高的值（0.7038-39）。仅通过SM-ND方法从Atsumi区域确定有用的等速线年龄。对于橄榄石Gabbros的年龄为28至32 Ma，Gabbros的年龄为54至66 MA。