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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).

从捕虏体中可以推断出日本弧下上地幔-下地壳的岩石学特征如下。(1)构成日本弧下的上地幔-下地壳的岩石在积云地幔厚度（第I组超镁铁岩）、地幔橄榄岩的耐火度、年轻富铁、富铝岩石（第II组）的增积程度和水化程度方面是非常不均匀的。(2)深层岩石可以有选择地与寄主岩浆结合。上升的岩浆可能倾向于选择性地穿过年轻的岩基岩，而不会捕获岩基岩的围岩。(3)地幔橄榄岩耐火度的不均匀性可能受伴生超基性岩，特别是纯橄榄岩的丰度控制。与大量纯橄榄岩包体共生的地幔橄榄岩包体通常为方辉橄榄岩或含高铬尖晶石的难熔二辉橄榄岩。地幔橄榄岩中纯橄榄岩的形成，使纯橄榄岩周围形成亏损晕，增强了地幔橄榄岩的流变性。(4)日本岛弧深部由地幔橄榄岩（方辉橄榄岩和/或二辉橄榄岩）、纯橄榄-二辉橄榄岩、橄榄辉长岩（或其变质等价物，尖晶石二辉橄榄岩）和辉石-辉长岩（镁铁质麻粒岩）组成，其组成顺序由上而下。其中一部分后来水化形成角闪石橄榄岩、角闪石辉长岩和角闪石辉长岩（或角闪岩）。