Genetic relation of charnockite to fluids derived from high-grade rocks in the Limpopo Belt

菱镁矿与林波波带高品位岩石流体的成因关系

• 批准号: 03453055
• 负责人: MIYANO Takashi
• 金额: $ 5.06万
• 依托单位: The University of Tsukuba
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for General Scientific Research (B)
• 财政年份: 1991
• 资助国家: 日本
• 起止时间: 1991 至 1993
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-03453055/
• 关键词: Limpopo Belt; charnockite; fluid composition; high-grade rocks; iron formation; fluid inclusion; isotope; Archean; 流体; ジンバブエ; 変成作用; グリーンストーンベルト; 先カンブリア; チヤノッカイト; 変成流体; Rb; Sr,Sm; Nd同位体比; UーPbジルコン年代; 剪断帯

On the basis of mineralogic, petrologic and chemical features of various high-grade metamorphic rocks in the Limpopo Belt, southern Africa, it is concluded that charnockite formation took place at P_<solid> (=P_s) < P_<total fluid> (=P_f) interacting with fluids derived from mainly sheered quartzofeldspathic gneisses in the process of crustal uplift or during retrograde metamorphism. Accordingly, in the case of charnockitization, source of CO_2 not necessarily originate in either mantle or underlain greenstone belt to cause decomposition of biotite into orthopyroxene. This report also thermodynamically examined how the oxygen fugacity and X (CO_2) vary in this process in terms of dehydration reactions observed in the rocks. In addition to this results, microthermometric data (homonization temperature, freezing temperature, and final melting temperature) of fluid inclusions in both charnockite and quartzofeldspathic gneiss represent that most of them are H_2O-rich in composition. On the … More other hand, in order to examine behavior of the fluids in the fracture zones, thermodynamic treatments for phase analysis and petrogenesis were summarized under conditions of P_s>P_f. The equilibria at P_s>P_f were applied to charnockitization of quartzofeldspathic gneisses and formation of the orthoamphibole isograd in the Limpopo belt. The fluids responsible for both charnockitization and formation of the orthoamphibole isograd are considered to have a wide range of composition and rather H_2O-rich at P_f<P_s, although they are CO_2-rich (X (H_2O) <0.2) at P_s=P_f. The calculation results at P_f<P_s may account various compositions of fluid inclusions in quartz in the charnockites. In the fracture system created during the crustal uplift, it is proposed that the "fluid path" with repetitive cycles of decreasing and increasing P_f has playd an important role for stabilization of orthopyroxenc. Generally migration (infiltration or influx) of fluids in the fracture zones gives rise to not only important dehydration and hydration reactions, but also may be related to formation of progressive, regionally metamorphosed rocks in the orogenic belt. Less

根据南部非洲林波波带各种高级变质岩的矿物学、岩石学和化学特征，认为紫苏花岗岩的形成是<solid><total fluid>在地壳隆升或退变质过程中，与以剪切石英长石质片麻岩为主的流体相互作用的结果，形成于P_（=P_s）&lt; P_（=P_f）。因此，在紫苏岩化作用中，CO_2源不一定来自地幔或下伏绿岩带，也不一定导致黑云母分解成斜方辉石。本文还根据岩石中观察到的脱水反应，对氧逸度和X（CO_2）在这一过程中的变化进行了分析。除此之外，紫苏花岗岩和石英长石质片麻岩中流体包裹体的显微测温数据（均一化温度、冻结温度和最终熔融温度）表明，它们大多富含H_2O。上 ...更多信息 另一方面，为了考察断裂带中流体的行为，总结了P_s&gt;P_f条件下相分析和岩石成因的热力学处理方法。P_s&gt;P_f的平衡被应用于林波波带长英质片麻岩的紫苏花岗岩化和正角闪石等梯度的形成。在P_s=P_f时，流体为富CO_2（X（H_2O）&lt;0.2），而在P_f&lt;P_s时，流体为富H_2O。P_f&lt;P_s的计算结果可以解释紫苏辉石岩中石英流体包裹体成分的变化。在地壳隆升过程中形成的断裂系统中，具有P_f减小和增大的反复循环的“流体通道”对正辉岩的稳定起着重要作用。一般而言，流体在断裂带中的迁移（渗透或涌入）不仅引起重要的脱水和水化反应，而且可能与造山带中渐进的区域变质岩石的形成有关。少

项目成果

8)Tsunogae, T.: "Oxygen barometry of quarzfeldspathic granulites from the Northern Marginal Zone of the Limpopo Belt,Zimbabwe." Blenkinsop,T.and Rollinson,H.(eds.)North Limpopo Field Workshop.Dept.Geol.Univ.of Zimbabwe. 1. 47-47 (1992)

8) Tsunogae, T.：“津巴布韦林波波带北缘带石英长石麻粒岩的氧气压测定。”

10)Tsunogae, T.: "Oxygen barometry of Archean quartzofeldspathic granulites in the Northern Marginal Zone of the Limpopo Belt,Zimbabwe." Jour.Mineral.Petrol.Econ.Geol(in Japanese with English abstarct).88. 34-40 (1993)

10) Tsunogae, T.：“津巴布韦林波波带北缘带太古代石英长石麻粒岩的氧气压测量。”

13)Miyano, S.: "Synthetic ferri-annite at low-temperature hydrothermal conditions." Sci.Rept.,Inst.Geosci.,(Section B),Univ.of Tsukuba. 15. 9-14 (1994)

13)Miyano, S.：“低温水热条件下的合成亚铁锰矿。”

14)Tsunogae, T.: "Compositional zoning of garnet in pelitic schist from Kelin Letaba Mine,Sutherland Greenstone Belt,South Africa." Sci.Rept.Dept Earth Sci.,Fac.Edu.,Simane Univ.27. 27-36 (1994)

14) Tsunogae, T.：“南非萨瑟兰绿岩带 Kelin Letaba 矿泥质片岩中石榴石的成分分区。”

Arakawa, Y., Miyano, T.and D.D.van Reenen: "Rb-Sr ages of metamorphic rocks in the Rhenosterkoppies Greenstone belt, Kaapvaal craton, South Africa." Ann.Rept., Inst.Geosci., Univ.Tsukuba. no.18. 80-84 (1992)

Arakawa, Y.、Miyano, T. 和 D.D.van Reenen：“南非卡普瓦尔克拉通 Rhenosterkoppies 绿岩带变质岩的 Rb-Sr 年龄。”