Abstract

The Bunger Hills, East Antarctica occupies an area of about 300 km² and is underlain by large Neoarchean tonalite–granite orthogneiss bodies in the southern part and a Paleoproterozoic volcanosedimentary sequence, buckled into isoclinal folds and metamorphosed to the granulite facies, in the northern. The sequence is intruded by large syncollisional charnockite plutons and consists predominantly of strongly migmatized garnet–sillimanite–cordierite paragneisses (metapelitic granulites). A characteristic feature of the mineral composition of these rocks is the paragenesis of Zn-poor spinel and quartz. The P–T conditions for the equilibrium of these two minerals are 6–7 kbar and 970–1030°C as estimated with the method of isochemical phase diagrams and 985–1005°C, as calculated with the aid of Ti-in-quartz thermobarometry (Huang and Audétat, 2012). Quartz contains needle-shaped microinclusions less than 1 μm in thickness aligned along the [0001] direction and evenly distributed throughout the quartz grains. According to data of electron-probe analysis, they are heterogeneous and consist of rutile and spinel (hercynite) intergrowths. The available data suggest that the genesis of the microinclusions is related to the exsolution process and the diffusion of structural impurities in quartz (Al, Fe, and Ti) in the direction of parallel translation-slip zones (10\(\bar {1}\)10), along which the high-temperature plastic deformations of quartz took place during the postpeak stage. The appearance of spinel in the microparagenesis of the oxides of the Al–Fe–Mg–Ti system is interpreted as a result of the processes synchronous with the intracrystal diffusion: the open-system diffusion of Mg atoms along the weakness zones of the quartz lattice or the infiltration of Mg-rich fluids along the microscopic cleavage planes formed as a result of hydrofracturing.

中文翻译：

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南极洲东部邦格山变泥质麻粒岩石英中 Al-Fe-Mg-Ti 氧化物的定向微包裹体

摘要

东南极洲邦格山面积约 300 km ²，南部为大型新太古代英闪长岩-花岗岩正片麻岩体，北部为古元古代火山沉积序列，弯曲成等斜褶皱并变质为麻粒岩相。该层序被大型同碰撞角锥岩体侵入，主要由强烈混合化的石榴子石-硅线石-堇青石副片麻岩（变泥质麻粒岩）组成。这些岩石矿物成分的一个特征是贫锌尖晶石和石英的共生。这两种矿物平衡的P-T条件为 6-7 kbar 和 970-1030°C（根据等化相图方法估算）和 985-1005°C（根据石英中钛计算）温压测定法（Huang 和 Audétat，2012）。石英含有厚度小于 1 μm 的针状微包裹体，这些微包裹体沿 [0001] 方向排列，均匀分布在整个石英颗粒中。根据电子探针分析数据，它们是异质的，由金红石和尖晶石（铁尖晶石）共生体组成。现有数据表明，微夹杂物的成因与石英中结构杂质（Al、Fe 和 Ti）沿平行平移滑移带方向（10 \(\bar {1} \) 10)，石英的高温塑性变形发生在峰后阶段。 Al-Fe-Mg-Ti 体系氧化物微共生中尖晶石的出现被解释为与晶内扩散同步的过程的结果：Mg 原子沿着石英晶格的薄弱区域进行开放体系扩散或富镁流体沿着水力压裂形成的微观解理面渗透。