Corundum + quartz and Mg-staurolite bearing granulite from the Limpopo Belt, southern Africa: Implications for a P–T path
Corundum + quartz and Mg-staurolite bearing granulite from the Limpopo Belt, southern Africa: Implications for a P–T path
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DOI：
10.1016/j.lithos.2006.03.052
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发表时间：
2006-12
期刊：
影响因子：
3.5
通讯作者：
T. Tsunogae;D. D. Reenen-D.
中科院分区：
文献类型：
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作者：
T. Tsunogae;D. D. Reenen-D.
在津巴布韦新太古代林波波带中央带的一种辉石-石榴石岩石中，发现了一种新的稀有刚玉+石英组合和镁质十字石。样品中含有大量刚玉+石英±硅线石、镁刚玉+蓝宝石±斜方辉石、蓝宝石+硅线石组合包裹体和单相包裹体。刚玉通常含有亚面体到圆形的石英，在石榴石中以亚面体到正面体包裹体的形式出现。石英和刚玉以直接颗粒接触的形式出现，没有反应结构的证据。柱石包裹体和寄主石榴石的结构和Fe-Mg比表明，St→Grt+CrN+QTZ+H2O是一种进行性脱水反应，形成刚玉+石英组合。斜方辉石+蓝宝石和石榴石+十字石组合在9-10 Kbar时的峰温为890-930℃。峰期为4-6kbar，逆行温度为500-570°C。异常镁球石(Mg/[Fe+Mg]=0.47-0.53)和刚玉+石榴石组合的存在为中央带早期高压变质作用提供了证据，可能接近榴辉岩相。进行性高压事件以及随后的高温-超高温变质作用和林波波带的快速抬升可能是新太古代碰撞造山作用的结果，涉及津巴布韦和卡帕瓦尔克拉通。
A new occurrence of the rare corundum+quartz assemblage and magnesian staurolite has been found in a gedrite–garnet rock from the Central Zone of the Neoarchean Limpopo Belt in Zimbabwe. Poikiloblastic garnet in the sample contains numerous inclusions of corundum+quartz±sillimanite, magnesian staurolite+sapphirine±orthopyroxene, and sapphirine+sillimanite assemblages, as well as monophase inclusions. Corundum, often containing subhedral to rounded quartz, occurs as subhedral to euhedral inclusions in the garnet. Quartz and corundum occur in direct grain contact with no evidence of a reaction texture. The textures and Fe–Mg ratios of staurolite inclusions and the host garnet suggest a prograde dehydration reaction of St→Grt+Crn+Qtz+H2O to give the corundum+quartz assemblage. Peak conditions of 890–930 °C at 9–10 kbar are obtained from orthopyroxene+sapphirine and garnet+staurolite assemblages. A clockwise P–T path is inferred, with peak conditions being followed by retrograde conditions of 4–6 kbar and 500–570 °C. The presence of unusually magnesian staurolite (Mg/[Fe+Mg]=0.47–0.53) and corundum+garnet assemblages provides evidence for early high-pressure metamorphism in the Central Zone, possibly close to eclogite facies. The prograde high-pressure event followed by high- to ultrahigh-temperature metamorphism and rapid uplifting of the Limpopo Belt could have occurred as a result of Neoarchean collisional orogeny involving the Zimbabwe and Kaapvaal Cratons.