铙钹寨岩体是蛇绿岩吗？——评“也谈铙钹寨超镁铁岩体的成因和构造类型的归属问题”

王希斌等根据铙钹寨岩体恢复的原岩由亏损强烈的方辉橄榄岩、纯橄岩和弱亏损的二辉橄榄岩组成以及有豆荚状铬铁矿存在,认为铙钹寨岩体属于大洋岩石圈地幔,是蛇绿岩的成员;并且还根据岩体存在两种地幔橄榄岩组合进一步推断铙钹寨岩体"可能经历了洋内扩张(形成 MOR 型的地幔残余)和洋内俯冲两个阶段的演化过程"。我们认为,铙钹寨岩体是交代的地幔橄榄岩,它不大可能是蛇绿岩;铙钹寨岩体的特征比较接近大陆岩石圈地慢而非大洋岩石圈地幔;铬铁矿不是判别蛇绿岩的标志;不能根据岩体存在强烈亏损和弱亏损的两种橄榄岩而推断其形成于两种环境。

Does the Raobazhai intrusion an ophiolite? —Comments on "Origin and structural nature of Raobozhai ultamafic rock: A discussion"

Wang et al.argued that the Raobazhai intrusion belongs to oceanic lithosphere mantle and part of an ophiolite in terms of its strongly depleted harzbugite,dunite and slightly depleted lherzolite as well as podiform chromitite.They assumed that the Raobaozhai intrusion has undergone a process from intraplate spreading to subduction on the basis of two types of the peridotites in the intrusion.However,the Raobazhai intrusion is composed of metasomatized peridotite,and is thus unlikely ophiolite.The petrographic features indicate that the Raobazhai intrusion is more like a subcontinental lithosphere mantle rather than an oceanic lithosphere mantle. Podiform chromitite should not be used as a criteria for ophiolite.It may be not suitable to discriminate out two tectonic settings of the Raobazhai intrusion only because of the occurrence of two types of peridotite,i.e.,high-depleted and low-depleted peridoite.