当前位置: X-MOL 学术Precambrian. Res. › 论文详情
Our official English website, www.x-mol.net, welcomes your feedback! (Note: you will need to create a separate account there.)
The Neoproterozoic alkaline rocks from Fangcheng area, East Qinling (China) and their implications for regional Nb mineralization and tectonic evolution
Precambrian Research ( IF 3.8 ) Pub Date : 2020-11-01 , DOI: 10.1016/j.precamres.2020.105852
Yu-Xiang Zhu , Lian-Xun Wang , Chang-Qian Ma , Michael Wiedenbeck , Wei Wang

Abstract An integrated study was carried out on samples from the Fangcheng alkaline complex so as to establish the origin and evolution of the Nb-rich alkaline felsic magmas. The Fangcheng complex is composed of nepheline syenites, biotite syenites, alkali-feldspar syenites, quartz syenites and syenogranites. Titanite and zircon U-Pb dating reveals that these rocks were simultaneously emplaced between 867 and 833 Ma. They are strongly enriched in HFSEs (e.g., Nb and Zr) and LREEs, with obvious depletions of Ba, Sr and Eu. Notably, all Fangcheng alkaline rocks are enriched in Nb, and this is particularly true for the nepheline syenites (Nb = 161–461 ppm). The nepheline syenites and biotite syenites yield relatively high eNd(t) values (−0.7 to −1.5) and initial 208Pb/204Pb ratios (36.12–37.61) as compared to the quartz syenites and syenogranites (−4.5 to −4.9 and 23.40–36.72, respectively). Likewise, lower zircon eHf(t) values (−4.2 to −6.9) are recorded by the quartz syenites and syenogranites. Based on our results, we suggest that the Fangcheng alkaline rocks were generated via low degrees of partial melting of an enriched mantle during which the fractionation of an alkali basaltic melt generated a nepheline syenite magma. An ongoing segregation of sodic minerals caused the parent melt to evolve towards a potassium-rich composition, leading to the generation of the biotite syenites and alkali-feldspar syenites. Ultimately, the quartz syenites and syenogranites represent the end products of a highly evolved alkaline magma containing a significant degree of contamination by siliceous-rich crustal materials. The enrichment of Nb in all lithologies was controlled by both magmatic and hydrothermal processes. In an initial F- and HFSE-rich magmatic system, prolonged fractionation of Nb-poor minerals led to the concentration of both F and Nb in the residual melts, as is recorded by the Nb-rich titanite. Hydrothermal metasomatism by Na- and F-rich fluids induced further remobilization and subsequent precipitation of Nb to form secondary titanite, pyrochlore, euxenite and rutile in a post-magmatic stage. We infer that the Neoproterozoic Fangcheng alkaline rocks were emplaced in a post-collisional extensional regime, implying that the assembly of the Rodinia supercontinent might have been completed prior to ca. 833 Ma.

中文翻译:

东秦岭防城地区新元古代碱性岩及其对区域Nb成矿和构造演化的意义

摘要 对防城碱性杂岩体样品进行综合研究,确定富Nb碱性长英质岩浆的成因和演化。防城杂岩由霞石正长岩、黑云母正长岩、碱长石正长岩、石英正长岩和正长花岗岩组成。钛铁矿和锆石 U-Pb 测年表明,这些岩石同时发生在 867 至 833 Ma 之间。它们富含HFSE(例如Nb 和Zr)和LREE,Ba、Sr 和Eu 明显减少。值得注意的是,所有防城碱性岩都富含 Nb,尤其是霞石正长岩(Nb = 161–461 ppm)。与石英正长岩和正长花岗岩 (-4.) 相比,霞石正长岩和黑云母正长岩产生相对较高的 eNd(t) 值(-0.7 至 -1.5)和初始 208Pb/204Pb 比率(36.12-37.61)。5 到 -4.9 和 23.40–36.72)。同样,石英正长岩和正长花岗岩记录到较低的锆石 eHf(t) 值(-4.2 至 -6.9)。根据我们的研究结果,我们认为防城碱性岩是通过富集地幔的低度部分熔融形成的,在此期间碱性玄武岩熔体的分馏产生了霞石正长岩浆。钠矿物的持续分离导致母熔体向富含钾的成分演化,导致黑云母正长岩和碱长石正长岩的产生。最终,石英正长岩和正长花岗岩代表了高度演化的碱性岩浆的最终产物,其中含有大量富含硅质地壳物质的污染。所有岩性中 Nb 的富集均受岩浆和热液过程控制。在最初的富含 F 和 HFSE 的岩浆系统中,贫 Nb 矿物的长期分馏导致残余熔体中 F 和 Nb 都集中,如富含 Nb 的钛铁矿所记录的那样。富钠和富氟流体的热液交代作用引起了 Nb 的进一步再迁移和随后的沉淀,在岩浆后阶段形成了次生钛铁矿、烧绿石、渗锌矿和金红石。我们推断新元古代防城碱性岩位于碰撞后的伸展体制中,这意味着罗迪尼亚超大陆的组装可能在大约 10 年前完成。833 马。贫铌矿物的长时间分馏导致残余熔体中 F 和 Nb 的浓度升高,如富含 Nb 的钛铁矿所记录的那样。富钠和富氟流体的热液交代作用引起了 Nb 的进一步再迁移和随后的沉淀,在岩浆后阶段形成了次生钛铁矿、烧绿石、渗锌矿和金红石。我们推断新元古代防城碱性岩位于碰撞后的伸展体制中,这意味着罗迪尼亚超大陆的组装可能在大约 10 年前完成。833 马。贫铌矿物的长时间分馏导致残余熔体中 F 和 Nb 的浓度升高,如富含 Nb 的钛铁矿所记录的那样。富钠和富氟流体的热液交代作用引起了 Nb 的进一步再迁移和随后的沉淀,在岩浆后阶段形成了次生钛铁矿、烧绿石、渗锌矿和金红石。我们推断新元古代防城碱性岩位于碰撞后的伸展体制中,这意味着罗迪尼亚超大陆的组装可能在大约 10 年前完成。833 马。我们推断新元古代防城碱性岩位于碰撞后的伸展体制中,这意味着罗迪尼亚超大陆的组装可能在大约 10 年前完成。833 马。我们推断新元古代防城碱性岩位于碰撞后的伸展体制中,这意味着罗迪尼亚超大陆的组装可能在大约 10 年前完成。833 马。
更新日期:2020-11-01
down
wechat
bug