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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Impact of volcanism on the evolution of Lake Van II: Temporal evolution of explosive volcanism of Nemrut Volcano (eastern Anatolia) during the past ca. 0.4 Ma
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Impact of volcanism on the evolution of Lake Van II: Temporal evolution of explosive volcanism of Nemrut Volcano (eastern Anatolia) during the past ca. 0.4 Ma

机译：火山活动对范II号湖演变的影响：内姆鲁特火山（安纳托利亚东部）爆发性火山活动的时间演变。 0.4毫安

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Thirty-two new single crystal ages document 400 000 years of widespread explosive volcanism of historically active Nemrut Volcano towering over huge alkaline Lake Van (Eastern Anatolia). The dated deposits were selected to monitor the volcanic and compositional evolution of Nemrut Volcano through time and thus to provide a rigorous temporal framework for the tephra record of the PaleoVan Drilling Project. Tephra samples were taken from large-volume deposits or those that occur in medial to distal localities, well-exposed strati-graphic sections or from the initial phase of an eruptive sequence. Mainly fallout deposits were chosen because most ignimbrites show more complex and corroded feldspar populations owing to compositional zoning and magma mixing. Moreover, fallout deposits held the promise to be more clearly identifiable with-and correlat-able to→ 300 tephra layers in the PaleoVan drill cores, even though commonly in amounts marginal or insufficient in thickness to allow well-supported single crystal dating. The crystals dated are dominantly anorthodase, the main phenocryst phase in the trachytic to rhyolitic, slightly to strongly peralkaline Nemrut magmas. Ages obtained so far range from ca. 400 ka to ca. 30 ka for Nemrut Volcano. The causes of significant changes in the frequency, volume and composition of tephra layers per unit time are discussed in terms of external (erosion, climate changes, geodynamic factors) and internal forcing (changes in magma supply and composition and incubation periods preceding large volume rhyolitic eruptions). For example, the low frequency of tephra layers deposited prior to ca. 200 ka may be due to low explosive activity, severe erosion between MIS 9 and MIS 11, or both. Nevertheless, the overall frequency of explosive eruptions appears to have increased during the past ca. 200 ka. We also recognize a slight peak in explosive eruptions during warm periods (e.g. MIS 5 and MIS 7) and speculate on lithospheric unloading triggering increased partial melting or magma reservoir unloading following massive glacier melting. The ages of 5 dated ignimbrites span ca. 250 000 years suggesting that Nemrut Volcano went through a polycyclic evolution with multiple caldera collapses and major pyrodastic flow eruptions, the oldest dated so far as 265 ka. The widely held view of the impressive Nemrut Caldera now dated to have formed at ca. 30 ka, as the main paroxysmal event during the evolution of the volcano is no longer tenable. Distinct and coherent compositional characteristics, especially in trace element concentrations, characterize several groups of trachytic tephras. We speculate that the growth of Nemrut Volcano caused the isolation of the Lake Van basin. On account of their mineralogical (anorthodase, hedenbergite, fayalite, aenigmatite) and alkalic chemical compositions and large volume, dated Nemrut fallout tephras are likely to represent excellent markers in lakes and other sites of paleodimatological or archeological interest in neighboring countries to the northeast of Lake Van as far as the Caspian Sea in what may be called the East Anatolian Tephra Province.
机译：二十二个新的单晶时代记录了40万年历史悠久的活跃内姆鲁特火山爆炸性火山爆发，这些火山耸立在巨大的碱性凡克湖（东安纳托利亚）上。选择了过时的矿床来监测内姆鲁特火山随时间的火山和成分演化，从而为PaleoVan钻井项目的特非拉记录提供严格的时间框架。 Tephra样品取自大量沉积物，或发生在中部至远端的地层，暴露的地层剖面或喷发序列的初始阶段。之所以选择沉降矿床是因为大多数火成岩由于成分分区和岩浆混合而显示出更复杂且腐蚀的长石种群。此外，余尘沉积物有望与PaleoVan钻芯中的300颗特弗拉岩层更加清晰地识别和关联，尽管通常数量很少或厚度不足以支持良好支撑的单晶测年。过时的晶体占主导地位的是正钙钛矿酶，即从短曲状到流纹岩状的，主要到显碱性的Nemrut岩浆的主要隐晶相。迄今获得的年龄范围大约为。 400 ka至约内姆鲁特火山30 ka。从外部（侵蚀，气候变化，地球动力因素）和内部强迫（岩浆供应和成分的变化以及大容量流纹岩形成之前的潜伏期）方面讨论了每单位时间的特菲拉层的频率，体积和组成发生重大变化的原因。爆发）。例如，大约在大约20分钟之前沉积的特菲拉层的低频。 200 ka可能是由于炸药活动低，MIS 9和MIS 11之间的侵蚀严重或两者兼有。然而，在过去约20年间，爆炸爆发的总频率似乎有所增加。 200 ka。我们还认识到在温暖时期（例如MIS 5和MIS 7）爆发性喷发的轻微高峰，推测岩石圈的卸荷在大规模冰川融化后触发了部分融化或岩浆储集层卸荷的增加。 5个带日期的火成岩的年龄大约为。 25万年表明内姆鲁特火山经历了多循环演化，火山口多次塌陷，并且主要的火山爆发流爆发，最古老的日期可追溯到265 ka。令人印象深刻的内姆鲁特火山口（Nemrut Caldera）的广为流传的观点现在可以追溯到约30 ka，作为火山演变过程中的主要阵发事件，不再成立。不同和连贯的成分特征，尤其是痕量元素的浓度，表征了几组短链的特弗拉斯。我们推测内姆鲁特火山的增长导致了范湖盆地的孤立。由于其矿物学（过氧化钙钛矿，方铁矿，方铁矿，钙镁铝石）和碱性化学成分以及体积大，过时的内姆鲁特沉积特弗拉斯很可能是湖泊以及东北湖周边国家其他古生物学或考古学热点的极佳标志物。范（Van）到达里海（Caspian Sea），可能被称为东安纳托利亚提弗拉省（East Anatolian Tephra Province）。

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