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通过对北太行紫荆关晚中生代基性岩体的岩石学和地球化学特征研究,讨论其岩浆源区特征及成因.结果表明,紫荆关岩体主要由橄榄二辉石岩、角闪辉长岩和闪长岩等岩石组成.橄榄二辉石岩具有明显的堆晶结构,可能是堆晶成因,而角闪辉长岩和闪长岩可能是堆晶形成之后的残余岩浆的结晶.闪长岩中的斜长石显示复杂的结构和成分环带,相对富钠的核部见富钙斜长石叠加,后者又向富钠斜长石演化.闪长岩中的单斜辉石也显示复杂的成分环带,主要是最边部的MgO含量比紧邻的内侧辉石更高.这表明在闪长岩形成过程中有新的幔源高温富镁的岩浆注入.以上各岩石类型具有类似的地球化学性质,包括较强的稀土分异((La/Yb)N比值为5.76～23.13),高Sr/Y比值(50.95～146.13),富集K、Sr、Ba等大离子亲石元素和LREE,亏损Nb、Zr、Ti等高场强元素和HREE,Eu异常不明显.都显示富集的Sr-Nd同位素特征,ISr=0.7058～0.7066,εNd(t)=-13.8～-18.2.这些特征表明紫荆关基性岩体的母岩浆来源于EM1型富集地幔的部分熔融.橄榄辉石岩和角闪辉长岩具有类似的Nd同位素成分(主要为εNd(t)=-15.0～-16.6),但形成较晚的闪长岩的εNd(t)值却比较高(-13.8～-14.6),也支持新的幔源岩浆在晚期的注入.
Based on the study of the petrological and geochemical characteristics of the Mesozoic basic rock mass of Bauhiniawan Pass in the Northern Taihang Mountains, the characteristics and genesis of the magmatic source area are discussed. The results show that the Bauhinia rock mass is mainly composed of olivine pyroxene rock, And diorite.The olivine-pyroxeneite has obvious heap structure, which may be the genesis of heap, whereas the hornblende gneiss and diorite may be the crystallization of the residual magma after the formation of the heap.Flame length The plagioclase in the rocks shows a complex structure and composition of the annular zone, and the relatively sodium-rich nuclei see the calcareous plagioclase overgrowth and the latter to the sodium-rich plagioclase. The clinopyroxene Showing a complex zoning of the constituents, mainly with the higher MgO content at the margins being higher than the adjacent gneisses, suggesting a new mantle-derived magnesia-rich magmatic intrusion during the diorite formation.The above types of rocks have Similar geochemical properties include strong RE (5.76-23.13 for La / Yb) N ratio and high Sr / Y ratio (50.95-146.13), enrichment for large ionophilic rocks such as K, Sr and Ba Element and LREE, loss of high field strength elements such as Nb, Zr, Ti and HREE, Eu anomalies are not obvious, have shown that the enrichment of Sr-Nd These features indicate that the parent magma of the Zijinguan mafic mass originates from the partial melting of the enriched mantle of the EM1 type. Olivine pyroxene and horn flash The gabbro has a similar Nd isotopic composition (mainly εNd (t) = -15.0 ~ -16.6), but the εD (t) values of the late-formed diorites are relatively high (-13.8 ~ -14.6) Support new late mantle-derived magma injections.