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

从捕虏体可以推断出日本弧下上地幔-下地壳的岩石学特征如下。(1)构成日本弧下上地幔-下地壳的岩石在积云地幔厚度（I类超镁质岩）、地幔橄榄岩的耐火度、富铁富铝年轻岩石（II类）的吸积程度和水化程度等方面均呈非均匀性。(2)深部岩石可选择性地与寄主岩浆结合。上升的岩浆可能倾向于选择性地穿过年轻的散粒，而不可能捕获散粒的壁岩。(3)地幔橄榄岩耐火度的非均质性可能受伴生超镁质岩石的丰度控制，其中尤以砾质为主。地幔橄榄岩包体与大量的灰岩包体伴生的通常是含高铬尖晶石的辉钼矿或难熔辉钼矿。在地幔橄榄岩内部形成的泥质岩使泥质岩周围形成损耗光圈，增强了地幔橄榄岩的非均质性。(4)日本弧深部由地幔橄榄岩（辉长岩和/或辉长岩）、暗辉长岩、橄榄辉长岩（或其变质物尖晶石辉长岩）和辉长岩（镁质麻粒岩）组成。其中部分后来被水化为含角闪石橄榄岩、角闪石韦氏岩和角闪石辉长岩（或角闪岩）。

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).