Origin of Baotoudong syenites in North China Craton: Petrological, mineralogical and geochemical evidence
Origin of Baotoudong syenites in North China Craton: Petrological, mineralogical and geochemical evidence
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华北克拉通包头洞正长岩的成因：岩石学、矿物学和地球化学证据
DOI：
10.1007/s11430-015-5216-1
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发表时间：
2015
期刊：
影响因子：
--
通讯作者：
Mingchun Yang
中科院分区：
文献类型：
--
作者：
Jingsui Yang;Fei Liu;Yongyu Zhang;Mingchun Yang
包头东正长岩体位于内蒙古包头市东部，华北陆缘北方沿着三叠纪碱性岩浆带的最西端。本文通过对该岩体的锆石U-Pb年龄、岩石学、矿物学和地球化学等资料的研究，对该岩体的成因和幔源特征进行了初步的探讨。岩体由霞石-单斜辉石正长岩和碱长正长岩组成，锆石U-Pb年龄为214.7± 1.1Ma。主要矿物为透辉石（核）-霓辉石（边）、黑云母、正长石和霞石。包头洞正长岩稀土元素含量高，以富集轻稀土元素和大离子亲石元素为特征，Rb、Ba、Sr），重稀土元素（HREE）和高场强元素（HFSE）亏损。它们具有富集的Sr-Nd同位素组成，初始87 Sr/86 Sr为0.7061 ~ 0.7067，εNd（t）值为-9.0 ~-11.2。矿物学、岩石学和地球化学研究表明，该正长岩的母岩浆为SiO2-欠饱和钾质-超钾质岩浆，具有高CaO、Fe 2 O3、K2 O、Na 2 O和流体成分（H2O），高温高氧逸度的特征。这些正长岩来自石榴子石稳定区（>80 km）富含金云母的富集岩石圈地幔源区。包头洞正长岩和其它许多类似年龄的超钾碱性杂岩在晚三叠世出现在华北克拉通北方边缘，表明华北克拉通北方边缘岩石圈地幔曾被俯冲蚀变的古蒙古洋壳熔体/流体交代，晚三叠世克拉通北方边缘进入大规模伸展状态，成为一个破坏性的大陆边缘。
Baotoudong syenite pluton is located to the east of Baotou City, Inner Mongolia, the westernmost part of the Triassic alkaline magmatic belt along the northern margin of the North China Craton (NCC). Zircon U-Pb age, petrological, mineralogical and geochemical data of the pluton were obtained in this paper, to constrain its origin and mantle source characteristics. The pluton is composed of nepheline-clinopyroxene syenite and alkali-feldspar syenite, with zircon U-Pb age of 214.7±1.1 Ma. Diopside (cores)-aegirine-augite (rims), biotite, orthoclase and nepheline are the major minerals. The Baotoudong syenites have high contents of rare earth elements (REE), and are characterized by enrichment in light rare earth elements (LREE) and large ion lithophile elements (LILE; e.g., Rb, Ba, Sr), depletion in heavy rare earth elements (HREE) and high field strength elements (HFSE). They show enriched Sr-Nd isotopic compositions with initial87Sr/86Sr ranging from 0.7061 to 0.7067 and εNd(t) values from–9.0 to–11.2. Mineralogy, petrology and geochemical studies show that the parental magma of the syenites is SiO2-undersaturated potassic-ultrapotassic, and is characterized by high contents of CaO, Fe2O3, K2O, Na2O and fluid compositions (H2O), and by high temperature and high oxygen fugacity. The syenites were originated from a phlogopite-rich, enriched lithospheric mantle source in garnet-stable area (>80 km). The occurrence of the Baotoudong syenites, together with many other ultrapotassic, alkaline complexes of similar ages on the northern margin of the NCC in Late Triassic implies that the lithospheric mantle beneath the northern margin of the NCC was previously metasomatized by melts/fluids from the subducted, altered paleo-Mongolian oceanic crust, and the northern margin of the craton has entered into an extensively extensional regime as a destructive continental margin in Late Triassic.
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DOI：
10.1130/2007.2418(09
发表时间：
2007
期刊：
--
影响因子：
--
作者：
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通讯作者：
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