The 60 × 20-km Samosir resurgent dome within the 74-ka Toba Caldera features several clusters of rhyolitic lava domes. Because the previously known Tuk-Tuk and Samosir Fault lava domes occur near the base of a major resurgent dome fault, they appear associated with resurgent uplift, and dating them could provide constraints on the timing of resurgence. Towards that goal, we mapped and sampled the Tuk-Tuk and Samosir Fault lava domes, discovered two additional lava dome clusters in the uplifted interior of Samosir Island, then determined modal mineralogy, major and trace element geochemistry, and 40 Ar/ 39 Ar sanidine ages on several samples from each cluster. These quartz-bearing rhyolite lava domes have SiO 2 contents ranging from ~ 70-76 wt%, crystallinities of 28-54%, and 40 Ar/ 39 Ar ages (~ 74-76 ka) that overlap with those of the Youngest Toba Tuff (YTT), ~ 74-75 ka. Our field observations and the remarkable similarity in mineralogy, geochemistry, and ages among the dome clusters and YTT support the interpretation that these domes represent remnant YTT magma that erupted shortly after the climactic YTT eruption. Later, during resurgence, these pre-resurgent lava domes were uplifted to their present locations, some near current lake level, others up to 440 m above lake level.

中文翻译：

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印度尼西亚苏门答腊多巴火山口沙摩西岛熔岩穹顶的神秘起源和位置

位于 74 ka Toba Caldera 内的 60 × 20 公里的 Samosir 复活圆顶具有几个流纹岩熔岩圆顶群。由于先前已知的 Tuk-Tuk 和 Samosir 断层熔岩穹顶发生在主要复活穹顶断层的底部附近，它们似乎与复活隆起有关，并且确定它们的年代可能会限制复活的时间。为实现这一目标，我们对 Tuk-Tuk 和 Samosir 断层熔岩穹顶进行了测绘和采样，在 Samosir 岛隆起的内部发现了另外两个熔岩穹顶簇，然后确定了模态矿物学、主要和微量元素地球化学以及 40 Ar/ 39 Ar sanidine来自每个集群的几个样本的年龄。这些含石英的流纹岩熔岩圆顶的 SiO 2 含量范围为 ~ 70-76 wt%，结晶度为 28-54%，和 40 Ar/ 39 Ar 年龄 (~ 74-76 ka) 与最年轻的 Toba Tuff (YTT) 重叠，~ 74-75 ka。我们的实地观察以及圆顶群和 YTT 在矿物学、地球化学和年龄方面的显着相似性支持了这些圆顶代表 YTT 高潮喷发后不久喷发的残余 YTT 岩浆的解释。后来，在回潮期间，这些回潮前的熔岩穹顶被抬升到现在的位置，有的接近现在的湖面，有的高达湖面以上 440 m。