The Skaergaard trough layering: sedimentation in a convecting magma chamber
The Skaergaard trough layering: sedimentation in a convecting magma chamber
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斯卡尔加德槽分层：对流岩浆室中的沉积
DOI：
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发表时间：
2018
影响因子：
3.5
通讯作者：
J. Andersen
中科院分区：
文献类型：
--
作者：
Z. Vukmanovic;M. Holness;K. Monks;J. Andersen
东格陵兰岛Skaergaard侵入体的底部堆积层的上部含有丰富的槽特征。这些槽是平缓倾伏的同形结构，由新月形模态渐变层堆叠而成，具有明显的基性岩基底，向上渐变为富含斜长石的物质。槽和分层的起源是有争议的，归因于不同的沉积矿物颗粒的岩浆流从附近的墙壁下降，或在原位发展的局部重结晶重力驱动的压实。它们的特点是露头规模的功能，如平行于槽轴的矿物线理，侵蚀和层截断与槽轴的迁移相关的证据，并通过同岩浆滑塌分层中断。一个详细的微观结构研究的模式槽层，使用电子背散射衍射与地球化学制图，表明这些岩石没有记录的证据变形的位错蠕变或溶解-再沉淀。相反，槽的特点是自形斜长石晶体与未修改的主要火成岩成分分区的对齐。我们认为，线理和叶理，因此，在岩浆流动的晶粒排列的后果。积累后放大的模式分层发生的结果，不混溶的间隙液的差异迁移，向上迁移的富硅共轭到斜长石丰富的上部的层，而富铁的不混溶共轭留在基性岩基地。现场和微观结构的证据支持的起源槽的重复沉积从附近的腔室壁下降的晶体丰富的电流的网站。
The upper parts of the floor cumulates of the Skaergaard Intrusion, East Greenland, contain abundant features known as troughs. The troughs are gently plunging synformal structures comprising stacks of crescentic modally graded layers with a sharply defined mafic base that grades upward into plagioclase-rich material. The origin of the troughs and layering is contentious, attributed variously to deposition of mineral grains by magmatic currents descending from the nearby walls, or to in situ development by localised recrystallisation during gravitationally-driven compaction. They are characterised by outcrop-scale features such as mineral lineations parallel to the trough axis, evidence of erosion and layer truncation associated with migration of the trough axis, and disruption of layering by syn-magmatic slumping. A detailed microstructural study of the modal trough layers, using electron backscatter diffraction together with geochemical mapping, demonstrates that these rocks do not record evidence for deformation by either dislocation creep or dissolution–reprecipitation. Instead, the troughs are characterised by the alignment of euhedral plagioclase crystals with unmodified primary igneous compositional zoning. We argue that the lineations and foliations are, therefore, a consequence of grain alignment during magmatic flow. Post-accumulation amplification of the modal layering occurred as a result of differential migration of an unmixed immiscible interstitial liquid, with upwards migration of the Si-rich conjugate into the plagioclase-rich upper part of the layers, whereas the Fe-rich immiscible conjugate remained in the mafic base. Both field and microstructure evidence support the origin of the troughs as the sites of repeated deposition from crystal-rich currents descending from the nearby chamber walls.