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(一)上地幔中为啥是二辉橄榄岩? 前人资料中指出:二辉橄榄岩代表了上地幔超镁铁质岩石的总成分。笔者认为言之有理,因为二辉橄榄岩在超镁铁质岩石中属于中间类型,它既有多量的辉石(5—90％或25—70％),又有多量的橄榄石(95—10％或75—30％),而且辉石中既有斜方辉石又有单斜辉石。它的形成环境为高温、高压、极低的应变速率。而且主要为比较均匀的静压环境。它的形成历史漫长,先为岩浆熔融体,后来逐渐变为固态或塑性体。这样的岩石在超镁铁岩的初期分异最差,矿物的分布也比较均匀,就其矿物的含量比例而言,相当于二辉橄榄岩类型,所以上地幔中超镁铁质岩石的总成分可以由二辉橄榄岩作为它的代表。
(A) why the upper mantle is the lherzolite? Predecessary data pointed out: lherzolite on behalf of the upper mantle ultramafic rocks of the total composition. I consider it reasonable, because lherzolites belong to an intermediate type in the ultramafic rocks and contain both large amounts of pyroxene (5-90% or 25-70%) and a large amount of olivine (95- 10% or 75-30%), and pyroxene has both orthopyroxenes and clinopyroxene. Its formation environment is high temperature, high pressure, very low strain rate. And mainly for more uniform static pressure environment. Its formation of a long history, first magma melt, and later gradually become solid or plastic body. Such rocks have the poorest differentiation in the early stages of the ultramafic rocks and the even distribution of minerals, which is equivalent to the lherzolite type in terms of their mineral content. Therefore, the total composition of the ultramafic rocks in the upper mantle It can be made of lherzolite as its representative.