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小张家口超基性岩体是华北板块北缘超基性岩带的一个典型岩体，岩相分带明显，由透辉岩、闪辉岩、二辉岩和纯橄岩组成，主要矿物组成包括透辉石、贵橄榄石、角闪石等。化学成分上富ＦｅＯ、ＣａＯ而贫ＭｇＯ，ｍ／ｆ平均２．２１，属铁质或富铁质超基性岩。稀土分布形式为轻稀土富集型，具不显著的负铕异常，微量元素以富含不相容元素Ｒｂ、Ｔｉ、Ｓｒ、Ｖ等而贫Ｃｒ、Ｃｏ、Ｎｉ等相容元素为特征。Ｓｍ－Ｎｄ等时年龄１８３７Ｍａ，Ｎｄ（ｔ）为十１０．７２。该岩体由亏损型地幔部分熔融所产生的岩浆经结晶分异作用而形成。
The Xiaozijiakou ultrabasic rock mass is a typical rock mass of the ultrabasic rock belt in the northern margin of the North China Plate. The lithofacies zoning is obvious and consists of diopside, dianghuiyan, dacite and dunite. The major mineral components Including diopside, peridot, hornblend and so on. The chemical composition of rich FeO, CaO and poor MgO, m / f an average of 2.21, is iron or iron-rich ultrabasic rocks. The distribution pattern of REE is light rare earth enrichment with no obvious negative Eu anomaly. The trace elements are characterized by the incompatible elements Rb, Ti, Sr, V and depleted Cr, Co, Ni and other compatible elements. The Sm-Nd isochron age is 1837Ma and Nd (t) is 10.72. The rock body is formed by the crystallization differentiation of the magma produced by partial melting of the depleted mantle.