THE CENOZOIC BASALTIC ROCKS OF EASTERN CHINA - PETROLOGY AND CHEMICAL-COMPOSITION
THE CENOZOIC BASALTIC ROCKS OF EASTERN CHINA - PETROLOGY AND CHEMICAL-COMPOSITION
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DOI：
10.1093/petrology/32.4.765
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发表时间：
1991-08-01
影响因子：
3.9
通讯作者：
HOOPER, PR
中科院分区：
文献类型：
--
作者：
FAN, QC;HOOPER, PR
中国东部新生代火山活动完全是玄武岩质的，在空间和时间上广泛分布，与地堑盆地及其区域边界断层密切相关。 本文研究了中国东部30多个地点的157个样品。 它们主要是碱性玄武岩，但在成分上从橄榄石霞石岩和白榴岩到石英拉斑玄武岩变化。 大多数为无斑晶，但也有一些含有橄榄石和单斜辉石斑晶。 全岩分析（X射线荧光）的所有样品的主要和13种微量元素，是所有主要矿物相的组成，由电子显微probe.它认为，最原始的碧玄岩，碱性橄榄玄武岩，橄榄拉斑玄武岩代表原生或近原生岩浆形成的不同程度的部分熔融的上地幔在不同的深度。 橄榄石拉斑玄武岩代表深度< 66 km的尖晶石橄榄岩的较大程度的部分熔融（8-9%）。 碱性玄武岩携带尖晶石和石榴石橄榄岩捕虏体，似乎是由深度> 79 km的石榴石二辉橄榄岩（50%ol，25%opx，15%cpx，10%石榴石）的1-7%部分熔融形成的。 橄榄石霞石可能是由更小程度的部分熔融形成的。大多数流不是原生的;其成分的变化与矿物学上不均匀的源的不同程度的部分熔融所产生的原生母岩光谱的分离结晶相一致。 拉斑玄武岩中的单斜辉石和部分橄榄石被分离，碱性玄武岩中的单斜辉石被分离，橄榄石的比例较小。 Sr的不相容行为意味着斜长石不存在于任何分馏组合中，再加上辉石斑晶的高Al含量，表明大部分分馏作用发生在地幔深度和压力下。中国东部新生代岩浆作用被视为与大陆伸展有关的火山作用的典型例子。 也就是说，小体积的主要是碱性玄武岩和橄榄拉斑玄武岩爆发了很长一段时间，并与伸展盆地及其边界断层。 因此，该省不同于大陆洪水玄武岩省。
The Cenozoic volcanicity of eastern China is entirely basaltic and occurred as relatively small eruptions widely dispersed in space and time, closely associated with graben basins and their regional bounding faults. Samples (157) from over 30 sites in eastern China have been studied. They are predominantly alkaline basalts, but vary in composition from olivine nephelinites and leucitites to quartz tholeiites. The majority are aphyric but some contain olivine and clinopyroxene phenocrysts. Whole-rock analyses (X-ray fluorescence) of all samples for the major and 13 trace elements are used, as are the compositions of all the major mineral phases determined by electron microprobe.It is argued that the most primitive basanites, alkali olivine basalts, and olivine tholeiites represent primary or near-primary magmas which were formed by different degrees of partial melting of the upper mantle at different depths. The olivine tholeiites represent larger degrees of partial melting (8-9%) of a spinel peridotite at depths of < 66 km. The alkalic basalts carry xenoliths of spinel and garnet peridotite and appear to have been derived by 1-7% partial melting of a garnet lherzolite (50% ol, 25% opx, 15% cpx, 10% garnet) at depths > 79 km. The olivine nephelinite may have formed by even smaller degrees of partial melting.Most flows are not primary; the variations in their compositions are consistent with fractional crystallization from the spectrum of primary parents created by varying degrees of partial melting of a mineralogically heterogeneous source. The tholeiites have fractionated by the removal of clinopyroxene and some olivine; the alkali basalts by the removal of clinopyroxene with a smaller proportion of olivine. The incompatible behavior of Sr implies the absence of plagioclase from any of the fractionating assemblages and, together with the high Al content of the pyroxene phenocrysts, suggests that much of the fractionation occurred at mantle depths and pressures.The Cenozoic magmatism of eastern China is seen as a typical example of volcanism associated with continental extension. That is, small volumes of predominantly alkalic basalts and olivine tholeiites erupted over a prolonged period and associated with extensional basins and their bounding faults. As such, the province is distinct from continental flood basalt provinces.