Pyroclastic chronology of the Sancy stratovolcano (Mont-Dore, French Massif Central): New high-precision 40Ar/39Ar constraints
Pyroclastic chronology of the Sancy stratovolcano (Mont-Dore, French Massif Central): New high-precision 40Ar/39Ar constraints
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DOI：
10.1016/j.jvolgeores.2012.02.006
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发表时间：
2012-05-01
影响因子：
2.9
通讯作者：
Nehlig, Pierre
中科院分区：
文献类型：
--
作者：
Nomade, Sebastien;Scaillet, Stephane;Nehlig, Pierre
桑西山(16公里)是构成法国中部山丘的两座层状火山中最年轻的一座。目前，高精度放射性同位素年龄的有限数量限制了我们对这座建筑的火山碎屑年代学的了解，该建筑是在东南欧中更新世层序中发现的许多Tephra层的来源。为了提高我们对这座层状火山建造阶段的了解，我们收集了13个火山碎屑单位，覆盖了整个最近的记录。我们介绍了40Ar/39Ar单颗粒激光测年技术，该测年技术是在法国伊维特河畔吉夫苏尔所建立的实验室中进行的。40Ar/39Ar年龄范围为1101+/-11ka~392+/-7ka(其外部)。确定了4个平均持续100ka的火山碎屑旋回(C.I~C.IV)。C.i对应于1101ka至1000ka之间的早期爆炸阶段，并比先前认为的早100ka开始。第二次火山碎屑旋回(C.II)是主要的火山碎屑幕，时间跨度为818~685ka。这个旋回至少由8次主要火山碎屑喷发组成，其中包括一次重大事件，相当于719+/-10ka(外部1西格玛)的一次大型普里尼安喷发，记录为桑西火山东南60公里处1.4米厚的层。然而，这种大规模喷发和火山口形成之间的联系仍然是假设的。第三次火山碎屑旋回(C.III)发现于桑西山(蒙多尔谷)东北部，时间跨度为642~537 ka。最年轻的火山碎屑旋回(C.IV)始于392ka，可能在280ka左右结束。每个火山碎屑旋回的年龄-地理位置指示了火山碎屑事件的导流和/或火山建筑物坍塌的三个优先方向：西北向西(C.L)，东南(C.II)，最后北向东北(C.III和IV)。新的高精度40Ar/39Ar年龄(642+/-9ka)与CoCherie等人获得的U/Pb年龄基本一致。(2009)[Geochimica et Cosmochica Acta，73,1095-1108]，并表明岩浆在一个浅的、短暂的、小的岩浆室中停留的时间很短。最后，在Pianico Sellere Varive层序(意大利北部)中发现的t21d Tephra层的来源不是Brauer等人提出的Rivaux浮岩流。(2007)[第四纪科学期刊22，85-96]，而且都不是Roulleau等人建议的C.II火山碎屑单位。(2009)[第四纪国际204，31-43]。因此，t21d层的来源尚未在Sancy或其他地方找到。(C)2012爱思唯尔B.V.保留所有权利。
The Sancy (16 km(2)) 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/39Ar 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 (his external). 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 (1 sigma 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. l), southeast (C. II) and finally north to northeast (C. III and IV). The new high precision 40Ar/39Ar 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. (C) 2012 Elsevier B.V. All rights reserved.