Na-metasomatic augite and aegirine-augite episyenites are hosted by subalkaline amphibole granites in the 1.644 Ga Suomenniemi rapakivi granite complex, southeastern Finland. In an examined drill core, episyenites are bordered by up to 50-cm-wide zones of Na-enriched augite-bearing granite in which alkali feldspar forms rims on plagioclase, and aggregates of augite and magnetite have formed by fluid-induced dehydration of hastingsite and biotite. In the episyenites, quartz has been partially removed, alkali feldspar (An<1Ab50Or50) and plagioclase have been partially recrystallized to granoblastic polygonal aggregates, and clinopyroxene (augite or aegirine-augite) has coarsened and been enriched in the aegirine component. Mass balance modeling implies addition of mainly Na, depletion of Si, F, Rb, Ba, Sr and 10–20% volume loss (by quartz dissolution) in the episyenitized zones in the drill core. Quartz-depletion and recrystallization may have been caused by several superimposed stages of alteration, probably related to voluminous dike- and A-type granite magmatism in the Suomenniemi area 10–15 m.y. after the emplacement of the Suomenniemi complex. Because of the coarse recrystallization textures and near-solidus recrystallization temperatures, distinguishing these fenite-like metasomatic rocks from igneous syenites is not trivial. In epizonal A-type granite complexes, high-temperature episyenites may be more common than currently thought.

中文翻译：

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芬兰东南部元古界 rapakivi 花岗岩中的单斜辉石背斜长岩——再结晶结构、传质和对 A 型花岗岩复合体岩石学的影响

Na-交代辉石和 aegirine-augite 附正长岩位于芬兰东南部 1.644 Ga Suomenniemi rapakivi 花岗岩复合体中的亚碱性角闪石花岗岩中。在检查的钻芯中，副正长岩与高达 50 厘米宽的含钠辉石花岗岩区域接壤，其中碱长石在斜长石上形成边缘，并且辉石和磁铁矿的聚集体是由流体诱导的黑斯廷石脱水形成的和黑云母。表正长岩中石英被部分去除，碱性长石（An<1Ab50Or50）和斜长石部分重结晶为粒晶多边形聚集体，单斜辉石（辉石或辉辉石-辉石）粗化并富集辉石成分。质量平衡建模意味着主要添加 Na，消耗 Si、F、Rb、Ba、Sr 和 10-20% 的体积损失（通过石英溶解）在钻芯中的副斜层带中。石英耗竭和再结晶可能是由几个叠加的蚀变阶段引起的，可能与芬兰堡杂岩就位后 10-15 年的芬兰堡地区大量的岩脉和 A 型花岗岩岩浆作用有关。由于粗糙的再结晶结构和接近固相线的再结晶温度，将这些类铁质交代岩与火成岩正长岩区分开来并非易事。在表带 A 型花岗岩复合体中，高温表正长岩可能比目前认为的更常见。可能与芬兰堡杂岩就位后 10-15 年芬兰堡地区大量岩脉和 A 型花岗岩岩浆作用有关。由于粗糙的再结晶结构和接近固相线的再结晶温度，将这些类铁质交代岩与火成岩正长岩区分开来并非易事。在表带 A 型花岗岩复合体中，高温表正长岩可能比目前认为的更常见。可能与芬兰堡杂岩就位后 10-15 年芬兰堡地区大量岩脉和 A 型花岗岩岩浆作用有关。由于粗糙的再结晶结构和接近固相线的再结晶温度，将这些类铁质交代岩与火成岩正长岩区分开来并非易事。在表带 A 型花岗岩复合体中，高温表正长岩可能比目前认为的更常见。