摘要:
位于东天山黄山岩带最东端的四顶黑山镁铁质-超镁铁质层状杂岩体规模较大,呈北东向展布,可分为南、北2个岩体.主要岩石类型有单辉橄榄岩、橄榄辉石岩、橄榄苏长辉长岩、橄榄辉长岩、辉石角闪岩、辉长岩和角闪辉长岩,超镁铁岩相常与辉长岩相呈韵律互层.主量元素化学组成主要属拉斑玄武岩系列.岩石稀土元素配分曲线呈平坦型以及Eu的正异常,普遍富集大离子亲石元素(Rb、Ba、U),显示明显的Sr正异常以及Nb、Ta的亏损.通过橄榄石最高的Fo值(79.6)估算出母岩浆中MgO和FeO含量分别为6.23%和6.60%.岩浆在演化过程中发生了橄榄石、斜方辉石、单斜辉石、斜长石的分离结晶/堆晶作用以及较弱的上地壳同化混染作用.岩石高的(La/Yb)N值1.550和1.744值表明岩浆源区的深度可能大于90km;Th/U值特征以及Th/Yb-Nb/Yb和La/Ba-La/Nb图解表明,四顶黑山岩体的岩浆源区可能为受俯冲作用改造的岩石圈地幔.
Abstract:
The Sidingheishan layered intrusion is located in the eastern of the Huangshan mafic-ultramafic rocks belt,East Tianshan,large-scale,northeast trending,can be divided into north and south intrusion,composes of clinopyroxene peridotite,olivine pyroxenite,olivine norite-gabbro,olivine gabbro,pyroxene amphibolite,gabbro,hornblende gabbro,diorite,and the ultramafic rock phase and gabbro phase often showed a rhythm with interbedded.The petrochemical compositions belong to the tholeiitic series.The chondrite-normalized REE patterns are flat type and positive Eu anomalies,generally enriched in LILE (i.e.,Rb,Ba,U),significant positive anomalies of Sr and Nb,Ta loss.Estimate the MgO and FeO content of the parental magma is 6.23% and 6.60% by the highest Fo values (79.6) of olivine,respectively.The magma experiences olivine,orthopyroxene,clinopyroxene,plagioclase fractionation / cumulate and weakly upper crustal contamination in the parental magma.The high (La/Yb)N ratio (1.550) and (Gd/Yb)N ratio (1.744) indicates that the depth of the magma source may be greater than 90Km; The Th/U ratio characteristic and Th/Yb versus Nb/Yb and La/Ba versus La/Nb diagrams show that the magma source of the Sidingheishan intrusion may be the modified lithosphere mantle by subduction.
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