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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Pyroclastic chronology of the Sancy stratovolcano (Mont-Dore, French Massif Central): New high-precision ~40Ar/~39 Ar constraints
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Pyroclastic chronology of the Sancy stratovolcano (Mont-Dore, French Massif Central): New high-precision ~40Ar/~39 Ar constraints

机译：Sancy层状火山的火山碎屑年代学（Mont-Dore，法国地块中部）：高精度〜40Ar /〜39Ar新限制

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摘要

The Sancy (16 km2) is the youngest of the two stratovolcanoes that constitute the Mont-Dore Massif (Massif Central, France). The restricted number of high precision radio-isotopic ages currently limits our knowledge of the pyroclastic chronology of this edifice which is the source of many tephra layers detected in middle Pleistocene sequences in southeast Europe. To improve our knowledge of the building phases of this stratovolcano, we collected thirteen pyroclastic units covering the entire proximal record. We present ~40Ar/~39 Ar single grain laser dating performed in the facility hosted at the LSCE (Gif-sur-Yvette, France). The ~40Ar/~39Ar ages range from 1101 ±11 ka to 392±7 ka (laextemal). Four pyroclastic cycles lasting on average 100 ka were identified (C. I to C. IV). C. I corresponds to the earlier explosive phase between 1101 ka and 1000 ka and starts about 100 ka earlier than previously thought. The second pyroclastic cycle (C. II) is the main pyroclastic episode spanning from 818 to 685 ka. This cycle is constituted of a minimum of 8 major pyroclastic eruptions and includes a major event that corresponds to a large plinian eruption at 719 ± 10 ka (la external) and recorded as a 1.4 m thick layer 60 km south-east of the Sancy volcano. The link between this large eruption and formation of a caldera stays however, hypothetical. The third pyroclastic cycle (C. Ⅲ) found in the northeastern part of the Sancy (Mont-Dore valley) spanned from 642 to 537 ka. Finally, the youngest pyroclastic cycle (C. IV) starts at 392 ka and probably ends around 280 ka. The age versus geographic location of each pyroclastic cycle indicates three preferential directions of channeling of the pyroclastic events and/or collapse of the volcanic edifice: northwest to west (C. I), southeast (C. II) and finally north to northeast (C. Ⅲ and IV). The new high precision ~40 Ar/~39 Ar age for the Queureuilh bas pyroclastic unit (642 ± 9 ka) is identical within error with the U/Pb age obtained by Cocherie et al. (2009) [Geochimica et Cosmochimica Acta, 73, 1095-1108] and suggests a short residence time of the magma in a shallow, short-lived, small magmatic chamber. Finally, the source of the t21d tephra layer found in the Pianico Sellere varved sequence (Northern Italy) is not the Rivaux pumice flow as proposed by Brauer et al. (2007) [journal of Quaternary Science 22, 85-96] and neither one of the C. II pyroclastic units as suggested by Roulleau et al. (2009) [Quaternary International 204, 31-43], Accordingly, the source for the t21d layer has yet to be found at Sancy or elsewhere.
机译：Sancy（16 km2）是构成Mont-Dore Massif（法国Massif Central）的两个平流火山中最年轻的一个。目前，受限制的高精度放射性同位素年龄数限制了我们对这座大厦的火山碎屑年代学的了解，而这座大厦是东南欧中更新世序列中发现的许多特菲拉层的来源。为了提高对这一平流层火山建造阶段的了解，我们收集了涵盖整个近端记录的13个火山碎屑单元。我们介绍了在LSCE（法国伊夫特河畔吉夫）托管的设施中进行的〜40Ar /〜39 Ar单晶激光测年。 〜40Ar /〜39Ar年龄范围从1101±11 ka到392±7 ka（拉米特）。确定了四个平均持续100 ka的火山碎屑循环（C. I至C. IV）。 C. I对应于1101 ka和1000 ka之间的较早爆炸阶段，并且比先前认为的要早约100 ka开始。第二个火山碎屑循环（C. II）是主要的火山碎屑事件，范围从818到685 ka。该周期至少由8次主要火山碎屑喷发构成，包括一次重大事件，对应于719±10 ka（拉外部）的一次大的普林尼埃火山喷发，记录为桑西火山东南60公里处的1.4 m厚层。 。但是，这种大喷发与破火山口形成之间的联系仍然存在。在桑奇东北部（蒙特多尔谷地）发现的第三次火山碎屑循环（C.Ⅲ）跨度为642至537 ka。最后，最年轻的火山碎屑循环（C. IV）始于392 ka，可能终止于280 ka左右。每个火山碎屑循环的年龄对地理位置的指示指示了火山碎屑事件的引导和/或火山大厦倒塌的三个优先方向：西北至西（C. I），东南（C. II）以及最终北至东北（C Ⅲ和Ⅳ） Queureuilh bas火山碎屑单元的新高精度〜40 Ar /〜39 Ar年龄（642±9 ka）在误差范围内与Cocherie等人获得的U / Pb年龄相同。 （2009）[Geochimica et Cosmochimica Acta，73，1095-1108]，并提出岩浆在浅层，短寿命的小型岩浆室内的停留时间短。最后，在Pianico Sellere瓦尔韦德序列（意大利北部）中发现的t21d特非拉层的来源不是Brauer等人提出的Rivaux浮石流。 （2007）[第四纪研究杂志，第85-96页]，并且Roulleau等人建议的C. II火山碎屑单元均不存在。 （2009）[Quaternary International 204，31-43]，因此，尚未在Sancy或其他地方找到t21d层的来源。

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