Abstract

Mineral zoning in fenites around miaskite intrusions of the Vishnevye Mountains complex can be interpreted as a magmatic-replacement zonal metasomatic aureole (in D.S. Korzhinskii’s understanding): the metasomatic transformations of the fenitized gneisses under the effect of deep alkaline fluid eventually resulted in the derivation of nepheline syenite eutectic melt. Based on the P–T–fO₂ parameters calculated from the composition of minerals coexisting in the successive zones, isobaric–isothermal fO₂–aSiO₂ and µNa₂O–µAl₂O₃ sections were constructed with the Perplex program package to model how the fenites interacted with H₂O–CO₂ fluid (in the Na–K–Al–Si–Ca–Ti–Fe–Mg–O–H–C system). The results indicate that the fluid–rock interaction mechanisms are different in the outer (fenite) and inner (migmatite) parts of the zonal aureole. Its outer portion was dominated by desilication of rocks, which led, first, to quartz disappearance from these rocks and then to an increase in the Al# of the coexisting minerals (biotite and clinopyroxene). In the inner part of the aureole, fenite transformations into biotite–feldspathic metasomatic rocks and nepheline migmatite were triggered by an increase in the Na and Al activities in the system alkaline H₂O–CO₂ fluid–rock. As a consequence, the metasomatites were progressively enriched in Al₂O₃ and alkalis, and these transformations led to the development of biotite in equilibrium with K–Na feldspar and calcite at the sacrifice of pyroxene. The further introduction of alkalis led to the melting of the biotite–feldspathic metasomatites and the origin of nepheline migmatites. The simulated model sequence of metasomatic zones that developed when the gneiss was fenitized and geochemical features of the successive zones (differences in the LILE and REE concentrations in the rocks and minerals of the fenitization aureole and the Sm–Nd isotope systematics of the rocks of the alkaline complex) indicate that the source of the fluid responsible for the origin of zonal fenite–miaskite complexes may have been carbonatite, a derivative of mantle magmas, whereas the miaskites were produced by metasomatic transformations of gneisses and subsequent melting under the effect of fluid derived from carbonatite magmas.

中文翻译：

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俄罗斯南部乌拉尔山脉维斯涅维山脉的辉绿岩-碳白云母复合体的火山岩：过程的交代区划和热力学模拟

摘要

Vishnevye山综合体的辉石岩侵入体周围的菲尼特石中的矿物区带可以解释为岩浆置换带状交代变质的金黄色（根据DS Korzhinskii的理解）：片状片麻岩在深碱性流体作用下的交代转换最终导致了霞石正长岩共晶熔体。基于该P - Ť - ˚F ö ₂从矿物中连续的区域共存，等压等温的组成计算参数˚F ö ₂ -一个的SiO ₂和μNa ₂ -O-μAl ₂ ö ₃用Perplex程序包构造截面，以模拟网状体如何与H ₂ O–CO ₂流体（在Na–K–Al–Si–Ca–Ti–Fe–Mg–O–H–C系统中）相互作用。结果表明，在纬向金黄色带的外部（菲尼特）和内部（蒙脱石）的流体-岩石相互作用机制是不同的。它的外部主要是岩石的干燥，这首先导致石英从这些岩石中消失，然后导致共存矿物质（黑云母和斜辉石）中Al＃的增加。在金针内部，由于碱性H ₂ O–CO ₂系统中Na和Al活性的增加，触发了从菲涅特向黑云母-长石交代岩石和霞石辉石的转变。流体岩石。结果，交代岩逐渐富集了Al ₂ O _3。和碱，这些转变导致黑云母在牺牲辉石的情况下与K–Na长石和方解石处于平衡状态。碱的进一步引入导致黑云母-长石交代矿物的融化和霞石蒙脱石的起源。片麻岩化后形成的交代带的模拟模型序列和连续带的地球化学特征（特征性金针和岩石的Sm-Nd同位素系统中岩石和矿物的LILE和REE浓度差异）碱性络合物）表明负责地带性fenite-miaskite络合物起源的流体来源可能是碳酸盐岩，这是地幔岩浆的衍生物，