Mantle plume injection during the spreading of the back-arc basin-Evidences from the volcanic fields in north Hokkaido, Japan-

弧后盆地扩张过程中的地幔柱注入——来自日本北海道北部火山田的证据——

基本信息

批准号：
09640541
负责人：
SHUTO Kenji
金额：
$ 2.3万
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 1999
项目状态：
已结题

项目摘要

The results obtained from this research project are summarized as follows.1. The late Miocene Engaru volcanic field in northeastern Hokkaido contains basalts (Tomeoka basalt (TM) and Chiyoda-Kakurezawa basalt (CK)) and rhyolite (Wakamatsu rhyolite (WK)) with subordinate amounts of andesite (Sakaeno andesite (SK)) that erupted during 7-9 Ma. Both the TM and CK basalts have geochemical characteristics similar to those of back-arc basin basalt (BABB). Based on differences in major and trace element abundances and the initial values of Sr and Nd isotopic ratios (SrI and NdI), the CK basalt, SK andesite and WK rhyolite can be divided into two types (I and II), respectively. The SK type I andesite and WK type I rhyolite are of calc-alkaline series, whereas the SK type II andesite (including icelandite-like andesite) and WK type II rhyolite are of tholeiitic series. The WK type I rhyolite has remarkably high SrI and low NdI values compared with other volcanic rocks from the study area. The si … More milarity in SrI and NdI of the rhyolite to S-type granitoids and pelitic-psammitic rocks of the Hidaka belt suggests the lower crustal origin of the rhyolite. The SK type I andesite is plotted on or near mixing lines between the CK type I basalt and WK type I rhyolite in major and trace element variation diagrams and SrI vs. NdI diagram, implying its mixing origin. On the other hand, major- and trace- element and Sr- and Nd- isotopic characteristics indicate that the SK type II andesite and WK type II rhyolite were generated from the CK type II basaltic magma by fractional crystallization accompanied by a minor degree of assimilation of crustal materials. The genetic relationship of these coeval basalts, andesite and rhyolite can be attributed to spreading of the Kurile basin. BABB magma which is a partial melt in a hot asthenosphere uprising below the island arc during the basin spreading, could have heated the lower crust to generate calc-alkaline rhyolitic magma. Andesitic rocks were derived both by mixing of BABB magma with the lower crust-derived rhyolitic magma and by fractional ctystallization of BABB magma.2. Basalts and andesites from the Iwao Formation, occurring in the Hamamasu area along the Japan Sea coast in northwest Hokkaido, were derived from a volcano which has been erupted during a relatively short period of 3.7 to 3.8 Ma. Similar disequilibrium phenocryst assemblages (Mg-rich olivine + Mg-rich clinopyroxene + Mg-poor orthopyroxene + hornblende + An-rich plagioclase + An-poor plagioclase + quartz + Fe-Ti oxide) are commonly found in the basalts and andesites. Detailed microprobe analyses as well as petrographic observations of coexisting phenocrysts reveal that the disequilibrium phenocryst assemblages in these volcanic rocks may be attributable to mixing of a basaltic magma in which olivine, clinopyroxene and An-rich plagioclase were crystallizing, and a dacitic magma in which orthopyroxene, hornblende, An-poor plagioclase, quartz and Fe-Ti oxide were crystallizing. Not only chemical variation but also petographic variation from basalts to andesites of the Iwao Formation are accounted for by the difference in mixing ratios of basaltic and dacitic magmas. Less

从该研究项目获得的结果总结如下1。东北北海道的中新世恩加鲁火山场晚期包含玄武岩（TMOKA玄武岩（TM）和Chiyoda-kakurezawa玄武岩（CK））和Rhyolite（Wkamatsu Rihyolite（WK）），并在7-Sakaeeno（Sakaeeno）（Sakaeeno）（sakaeeno）（Skakaeeno）（Skakaeeno）（Skakaeeno）（Skakaeeno）（Skakaeno）（Skakaeno）（Skakaeno）（Skakaeno）。 TM和CK玄武岩的地球化学特征都与后弧盆地玄武岩（BABB）相似。基于主要和微量元素丰度的差异以及SR和ND同位素比的初始值（SRI和NDI），CK底层，SK和SK和SK和SOSTITE和WK ryolite可以分别分为两种类型（I和II）。 SK型I型和WK I型流纹岩是钙碱性系列的，而SK II型和现场（包括类似冰岛的类和现场）和WK II型流纹岩是Tholeitic系列的。与研究区域的其他火山岩相比，WK I型流纹岩具有非常高的SRI和低NDI值。 Si…在Sri和Rhyolite的NDI中更多的牛奶与hideka腰带的S型花岗岩和毛发性岩石岩石表明，这表明流纹岩的下层甲壳起源。 SK型I和现场在主要和痕量元素变化图中的CK I型玄武岩和I型流纹岩之间的混合线上绘制或附近的混合线，以及SRI与NDI图，这意味着其混合起源。另一方面，主要和痕量元素以及SR-和ND同位素特征表明，SK II型和现场和WK型II型流纹岩是由CK II型玄武岩岩浆通过少量同化的CK II型玄武岩结晶而产生的。这些共层玄武岩的遗传关系，现场和流纹岩的遗传关系归因于库里尔盆地的扩散。 Babb岩浆是在盆地扩散期间在岛弧下方的热量运动圈起义中的部分熔体，可能会加热下地壳以产生钙碱性流纹岩岩浆。通过将Babb岩浆与下皮衍生的流纹状岩浆和Babb Magma.2的分数CTyStallation混合而得出的安第斯山岩岩石。来自IWAO地层的玄武岩和矿物质发生在西北北海道的日本海岸的Hamamasu地区，源自一座火山，该火山在相对较短的3.7至3.8 MA时爆发。相似的二动作表晶组合（富含Mg的橄榄石 +富含mg的clinopyroxene + mg贫困的牙本质异耐 +角闪烯 +角闪闪脉 +富含的斜长石 +良好的斜长石 +贫民窟的斜肌 + Quartz + Quartz + Quartz + fe-ti氧化物）通常在玄武岩和盆地和底座中发现。详细的微型探针分析以及对共存的表晶的观察结果表明，这些火山岩中的二十一个二含量的表晶组合可能归因于碱性岩浆的混合，在该基底岩浆中，绿色，clinerroxen和and-rich plagiocipience of Crystally and or crystally of Crystally of Crystally of Crystally of Crystally of Crystalle and of cypo ign cysally of cypo po cypo cypo y magmma cypo y miglox cypo y migrox to cypo。斜长石，石英和Fe-Ti氧化物结晶。不仅化学变化，而且还通过玄武岩和dacitic岩浆的混合比的差异来解释从玄武岩到岩层形成的岩石学变化。较少的