Geochemical Characteristics of Basic Dikes from Jiling Area in Longshoushan and Its Geological Significance
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摘要: 以甘肃省龙首山芨岭地区基性岩脉为研究对象，在研究基性岩脉地球化学特征基础上，探讨其岩浆源区特征及演化过程。该区基性岩脉SiO2为47.09%~51.13%；具有高Al（Al2O3为14.56%~15.97%）、富Na（Na2O为3.35%~3.69%）、低K（K2O为0.347%~1.23%）的特征。稀土总量较低（105.7×10-6~186.97×10-6），稀土配分模式为右倾轻稀土富集型（（La/Yb）N=4.50~9.63）。富集元素Ba、U、Pb、P、Ti，亏损元素Rb、Th、K，属拉斑玄武岩系列。基性岩脉形成于板内拉张环境，经历了以橄榄石、单斜辉石、Ti-Fe氧化物为主的分离结晶作用；岩浆上升过程中基本未受到地壳物质的混染。其原岩岩浆是地幔岩部分熔融后，经地幔交代作用形成的熔体。基性岩脉岩浆产生于过渡型地幔源区，源区为尖晶石+石榴子石二辉橄榄岩地幔。Abstract: The mafic dikes from Jiling area in Longshoushan has selected been as the study object, and the magmatic source characteristics and evolutionary processhas been discussed in this paper. SiO2 content of mafic dikes in Jiling area is 47.09%~51.13%. They are characterized by high aluminum (Al2O3=14.56%~15.97%),rich sodium (Na2O=3.35%~3.69%) and low potassium (K2O=0.347%~1.23%). The ∑ REE(105.7×10-6~186.97×10-6)is relative low with the right type of LREE distribution patterns((La/Yb)N=4.50~9.63). These mafic dikes have a characteristic of rich Ba, U, Pb, P and Ti and depleted Rb, Th and K, belonging to the tholeiite series. They were formed in extensional intraplateenvironment and experienced fractional crystallization of olivine, clinopyroxene and Ti-Fe oxides.The magma hadn't been contaminated by crustal materials during its ascent process. Its original magma was derived from the melt of the pyrolite which was formed by the mantle metasomatism after the partial melting. Thus, the magma of mafic dikes was derived from transitional mantle source region,with the source of spinel + garnet lherzolite mantle.
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Keywords:
- Jiling /
- mafic dikes /
- geochemical characteristics /
- source region
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