Petrogenesis of the Ultrapotassic Fanshan Intrusion in the North China Craton: Implications for Lithospheric Mantle Metasomatism and the Origin of Apatite Ores
Petrogenesis of the Ultrapotassic Fanshan Intrusion in the North China Craton: Implications for Lithospheric Mantle Metasomatism and the Origin of Apatite Ores
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DOI：
10.1093/petrology/egv021
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发表时间：
2015-05
影响因子：
3.9
通讯作者：
T. Hou;Zhaochong Zhang;J. Keiding;I. Veksler
中科院分区：
文献类型：
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作者：
T. Hou;Zhaochong Zhang;J. Keiding;I. Veksler
中国克拉通北部的梵山岩体以正长岩为核心(单元1)，周围为超镁铁质岩石(单斜辉石岩和黑云单斜辉石岩；单元2)，外缘为富石榴石的单斜辉石岩和斜长石单斜辉石岩和正长岩(单元3)。侵入岩由不同数量的富钙辉石、黑云母、斜长石、黑铁矿、石榴石、磁铁矿和磷灰石组成，并有少量的原生方解石。单矿物磷灰石、钠铝石和闪锌矿仅产于单元2中。在地球化学特征上，反山岩高度富含轻稀土元素(LREE)和大离子亲石元素(LILE)，中等亏损高场强元素(HFSE)，其锶-钕-氧同位素组成范围有限。三个单元相似的矿物学、矿物组成和微量元素特征表明，所有岩石都是同岩浆。母岩浆是超钾质的，类似于卡马辉石。交代岩石圈地幔的极低程度部分熔融最好地解释了梵山侵入体母岩浆的地球化学和岩石成因。我们认为，地幔源区可能是由含水碳酸盐熔体交代作用的结果，熔体具有富集锶-钕同位素特征和不相容元素的富集性，具有明显的Nb-Ta-Zr-Hf-Ti负异常和轻稀土元素富集性。地幔源富集可能与石炭纪和二叠纪古亚洲大洋板块向南俯冲过程中海洋沉积物的再循环有关。我们认为，结晶沉淀和机械分选以及原始岩浆的反复补充和与先前分离岩浆的混合是磷灰石矿石形成的主要过程。
The Fanshan intrusion in the North China Craton (NCC) is concentrically zoned with syenite in the core (Unit 1), surrounded by ultramafic rocks (clinopyroxenite and biotite clinopyroxenite; Unit 2), and an outer rim of garnet-rich clinopyroxenite and orthoclase clinopyroxenite and syenite (Unit 3). The intrusive rocks are composed of variable amounts of Ca-rich augite, biotite, orthoclase, melanite, garnet, magnetite and apatite, with minor primary calcite. Monomineralic apatite rocks, nelsonite and glimmerite exclusively occur in Unit 2. Geochemically, the Fanshan rocks are highly enriched in light rare earth elements (LREE) and large ion lithophile elements (LILE), moderately depleted in high field strength elements (HFSE), and have a limited range of Sr‐Nd‐O isotopic compositions. The similar mineralogy, mineral compositions, and trace element characteristics of the three units suggest that all the rocks are co-magmatic. The parental magma is ultrapotassic and is akin to kamafugite. Very low-degree partial melting of metasomatized lithospheric mantle best explains the geochemistry and petrogenesis of the parental magmas of the Fanshan intrusion. We propose that the mantle source may have been metasomatized by a hydrous carbonate-bearing melt, which has imprinted the enriched Sr‐Nd isotopic signature and incompatible element enrichment with conspicuous negative Nb‐Ta‐Zr‐Hf‐Ti anomalies and LREE enrichments. The mantle source enrichment may be correlated with oceanic sediment recycling during southward subduction of the Paleo-Asian oceanic plate during the Carboniferous and Permian. We propose that crystal settling and mechanical sorting combined with repeated primitive magma replenishment and mixing with previously fractionated magma is the predominant process responsible for the formation of the apatite ores.