Basic Study for a Catalogue of Upper Mantle Xenoliths in the Japan Island Arcs

日本岛弧上地幔包体目录的基础研究

基本信息

批准号：
02640626
负责人：
ARAI Shoji
金额：
$ 1.41万
依托单位：
Kanazawa University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1990
资助国家：
日本
起止时间：
1990 至 1991
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-02640626/
关键词：
Upper Mantle Lower Crust Japan Island Arcs Peridotites Xenoliths 上部マントルかんらん岩

项目摘要

Petrological characteristics of the upper mantle-lower crust beneath the Japan arcs can be deduced from xenoliths as follows. (1) Rocks constituting the upper mantle-lower crust beneath the Japan arcs are very heterogeneous in terms of thickness of cumulus mantle (Group I ultramafic rocks), degree of refractoriness of mantle peridotites, degree of accretion of young Fe, Al-rich rocks (Group II), and degree of hydration. (2) Deep-seated rocks can be selectively incorporated into host magmas. Uprising magmas may tend to selectively pass through young dikelets and may not catch wall rocks of the dikelets. (3) The heterogeneity of degree of refractoriness of mantle peridotites may be controlled by abundance of associated cumulative ultramafic rocks, especially of dunites. Mantle peridotite xenoliths which are associated with large amounts of dunite xenoliths are usually harzburgite or refractory lherzolite with high-Cr spinel. Formation of dunites within the mantle peridotites makes depletion aureoles around the dunites, enhancing the heteorgeneity of the mantle peridotites. (4) The deep part of the Japan arcs is composed of, in an an ascending order, mantle peridotites (harzburgite and/or Iherzolite), dunite-websterites, olivine gabbros (oe thier metamorphosed equivalents, spinel websterites), and pyroxene-gabbros (mafic granulites). Part of them have been later hydrated to be hornblendebearing peridotites, harnblende websterites and hornblende gabbros (or amphibolites).

日本弧下上地幔-下地壳的岩石学特征可以从捕虏体中推断如下。 (1)日本弧下上地幔-下地壳岩石的积云地幔(I族超镁铁质岩石)厚度、地幔橄榄岩的难熔程度、年轻富铁、富铝岩石的增生程度等方面存在很大的不均匀性（第二组）和水合程度。 (2)深部岩石可以选择性地融入宿主岩浆中。上升的岩浆可能倾向于选择性地穿过年轻的小堤，并且可能不会捕获小堤的围岩。 (3) 地幔橄榄岩耐火度的不均一性可能受伴生超镁铁质岩石，特别是纯橄榄岩丰度的控制。与大量纯橄榄岩捕虏体伴生的地幔橄榄岩捕虏体通常为方辉橄榄岩或含高铬尖晶石的难熔二辉橄榄岩。地幔橄榄岩内沙丘的形成使得沙丘周围出现贫化光环，增强了地幔橄榄岩的异质性。 (4) 日本弧深部按升序由地幔橄榄岩（方辉橄榄岩和/或二辉橄榄岩）、纯橄榄岩、韦氏辉长岩、橄榄辉长岩（其变质对应物，尖晶石韦氏辉长岩）和辉石-辉长岩组成（镁铁质粒岩）。其中一部分后来被水化成为含角闪石橄榄岩、角闪石网辉长岩和角闪石辉长岩（或角闪岩）。