Origin of felsic magmas produced during the spreading of the back-arc basin

弧后盆地扩张过程中产生的长英质岩浆的起源

基本信息

批准号：
12440134
负责人：
SHUTO Kenji
金额：
$ 8.77万
依托单位：
NIIGATA UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2002
项目状态：
已结题

项目摘要

The results obtained from this research project are summarized as follows.1) Miocene volcanic rocks from the Okkope area along the Okhotsk Sea coast, north Hokkaido can be divided into three groups based on their petrographical and geochemical characteristics ; 1) andesitic to dacitic rocks in the Toyono Formation, 2) Mitsuiyama lavas and dike rocks of type I, and 3) dike rocks of type II. The first rocks with much higher Sr/Y ratios compared to the ordinary island arc type andesitic rocks are defined as adakitic andesite and dacite, whereas the second and third rocks chracterized by high SiO_2 and high MgO contents correspond to high-Mg andesites. The adakitic intermediate rocks may result from a modification of the subducting oceanic crust derived felsic magma due to interaction with the overlying mantle peridotite during its rise to the surface. It is likely that the second rocks may be derived by mixing between the primary high-Mg andesitic magma and more felsic magma.2) Most of mi … More ddle Miocene to Quaternary basaltic rocks younger than around12 Ma from north Hokkaido show initial ^<87>Sr/^<86>Sr (SrI) and initial ^<143>Nd/^<144>Nd (NdI) in narrow ranges slightly undepleted, compared to MORB ; 0.70296-0.70393 in SrI and 0.51288-0.51307 in NdI, respectively, but no temporal variation in SrI and NdI, whereas the exceptional basalts from one location (Ohmu area) exhibit more undepleted Sr and Nd isotopic signature than other north Hokkaido basaltic rocks (the NH basaltic rocks). The generation of the NH basaltic rocks seems to be deeply related to the mantle evolution delineated as the asthenospheric injection into continental lithosphere beneath north Hokkaido, accompanying with the spreading of the Kurile back-arc basin ; the magma source for the Ohmu area basalts may correspond to the subcontinental lithospheric mantle material thinned by the injection of asthenospheric mantle material from which most of the NH basaltic magmas have been derived. These asthenospheric mantle materials are slightly different from MORB source with respect to major and trace element characteristics such as TiO2/K2O and Zr/Y ratios as well as Sr and Nd isotopes Less

从该研究项目中获得的结果总结如下。1）北北北北北北北北北北沿海的奥克科普地区的中新世火山岩可以根据其岩石学和地球化学特征分为三组； 1）Toyono地层中的安第斯山脉到达奇特岩石，2）三山熔岩和I型的堤防岩石，以及3）II型堤防岩石。与普通的岛弧类型的安西特岩相比，SR/Y比的第一批岩石被定义为Adakitic Andesitic和Dacite，而第二和第三岩石则被高SIO_2和高MGO含量和高MGO内容物所对应，对应于高Mg Andesiites。 Adakitic中间岩石可能是由于与上覆的地幔橄榄岩相互作用在其上升到表面的情况下的相互作用而导致的俯冲岩层衍生的长英质岩浆。第二块岩石可能是通过在主要高毫克的安第斯山岩岩浆和更多的长英质岩浆之间进行的。与MORB相比，范围略有尚未复制； 0.70296-0.70393 in SrI and 0.51288-0.51307 in NdI, respectively, but no temporary variation in SrI and NdI, whereas the exceptional basalts from one location (Ohmu area) exposed more undupleted Sr and Nd isotopic signature than other north Hokkaido basaltic rocks (the NH basaltic rocks). NH盆地岩石的产生似乎与在北北北北北部的连续岩石圈中注射到近北北岩的连续岩石圈时所描绘的地幔进化密切相关，随着库里里尔后背 - 弧盆地的扩散。欧姆区域玄武岩的岩浆源可能对应于通过注射软层地幔材料所稀薄的岩石圈地幔材料，大多数NH底层岩浆已得出。对于主要和痕量元素特征，例如TiO2/K2O和ZR/Y比以及SR和ND同位素，这些动态层地幔材料与MORB源略有不同