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乌兰敖包基性-超基性岩位于阿拉善北缘兴蒙造山带,由方辉橄榄岩、辉绿岩、辉长岩组成。地球化学分析表明:蛇纹石化橄榄岩为地幔橄榄岩,辉绿岩和辉长岩为拉斑玄武岩系列岩石,均具有与N-MORB相似的微量元素特征,但区别于N-MORB,3种岩石共同组成了蛇绿混杂岩。矿物学分析表明蛇纹石化橄榄岩中橄榄石为地幔橄榄岩中镁橄榄石(Fo=91.10~91.81),铬铁矿为铬尖晶石,具有高的Cr~#和Mg~#值分别为61.04~64.44、50.40~56.37)。单斜辉石出现在方辉橄榄岩、辉长岩及辉绿岩中,而斜方辉石只出现在方辉橄榄岩中,其中方辉橄榄岩中单斜辉石为顽透辉石,辉长岩中为普通辉石,而辉长岩中为次透辉石、贫钙普通辉石、普通辉石,斜方辉石均为斜顽辉石。辉长岩U-Pb年龄为344.5±1.5 Ma,表明该蛇绿混杂岩形成于早石炭世。地球化学及矿物学特征表明乌兰敖包蛇绿岩形成于俯冲早期的弧前环境中,属于SSZ型蛇绿岩。蛇绿混杂岩成因提供铬铁矿形成的有利条件,因此应围绕铬铁矿进行找矿工作。
The Ulan-Obo-basic-ultrabasic rocks are located in the Xingmeng orogenic belt on the northern margin of the Alxa Mountains and consist of hacerite, diabase and gabbro. Geochemical analysis shows that the serpentinized peridotites are mantle-peridotites, diabase and gabbro are tholeiite series rocks with trace element characteristics similar to N-MORB, but different from N-MORB and 3 The rocks together form a ophiolite melange. Mineralogical analysis shows that the olivine in the serpentinized peridotite is forsterite in the mantle peridotite (Fo = 91.10-91.81), the chromite is chromospine, and high Cr ~ # and Mg ~ # values are 61.04 ~ 64.44, 50.40 ~ 56.37). The clinopyroxene appears in the harzburgites, gabbro and diabase, while orthopyroxene only appears in the harzburgites, in which the clinopyroxenes in the harzburgites are hematite, The gabbro is an ordinary pyroxene, while the gabbro is a diopside, a poor-calcareted pyroxene, an ordinary pyroxene, and an orthopyroxene are all oblique enstatites. The gabbro U-Pb age is 344.5 ± 1.5 Ma, indicating that the ophiolite melange formed in the Early Carboniferous. Geochemical and mineralogical characteristics indicate that the Ulan-Aobao ophiolite was formed in the pre-arc pre-subduction environment and belonged to the SSZ ophiolite. The origin of ophiolite melange provides favorable conditions for the formation of chromite and should therefore be investigated for chromite.