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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Volcanic stratigraphy and geochemistry of the Soufriere Volcanic Centre, Saint Lucia with implications for volcanic hazards
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Volcanic stratigraphy and geochemistry of the Soufriere Volcanic Centre, Saint Lucia with implications for volcanic hazards

机译：圣卢西亚Soufriere火山中心的火山地层和地球化学对火山灾害的影响

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The Soufriere Volcanic Complex (SVC), Saint Lucia, represents one of the largest silicic centres in the Lesser Antilles arc. It comprises extensive pumiceous pyroclastic flow deposits, lava flows as well as Pelean-style domes and dome collapse block-and-ash-flow deposits. These deposits occur within and around the Qualibou Depression, a ~10-km diameter wide sector collapse structure. To date, vent locations for SVC pyroclastic deposits and their relationship to the sector collapse have been unclear because of limited stratigraphic correlation and few radiometric ages. In this study we reconstruct the geologic history of the SVC in light of new and recently published (U-Th)/He, U-Th and U-Pb zircon chronostratigraphic data, aided by mineralogical and geochemical correlation. Compositionally, SVC deposits are monotonous medium-K, calc-alkaline rocks with 61.6 to 67.7 wt.% SiO_2 and display similar trace element abundances. Combined U-Th and (U-Th)/He zircon dating together with ()C ages and mineral fingerprinting reveals significant explosive eruptions at 640, 515, 265, 104, 60 and 40 ka (producing deposits previously grouped together as the "Choiseul" unit) and at 20 ka (Belfond unit). The mineralogically and geochemically distinct Belfond unit is a large, valley-filling pumiceous pyroclastic flow deposit distributed to the north, northeast, south and southeast of the Qualibou Depression that was probably deposited during a single plinian eruption. The unit previously referred to as 'Choiseul tuff is much less well defined. The typical Choiseul unit comprises a series of yellowish-white, crystal-poor, non-welded pumiceous pyroclastic deposits cropping out to the north and southeast of the Qualibou depression; however its age is poorly constrained. A number of other units previously mapped as Choiseul can be distinguished based on age, and in some cases mineral and whole rock chemistry. Pyroclastic deposits at Micoud (640 ± 19 ka), Bellevue (264 ± 8 ka), Anse John (104 ± 4 ka) and La Pointe (59.8 ± 2.1 ka), Anse Noir and Piaye were all previously grouped with or associated with the Choiseul tuff (all uncertainties la). We suggest that these units represent individual periods of activity spanning a range of ages, whereas Choiseul pumice at the type locality has yielded a (U-Th)/He zircon age of 515 ± 19 ka. Their overall geochemical and mineralogical similarities with the Choiseul at the type locality suggest that they might have all originated from the same centre. Morne Tabac (532 ± 21 ka) is a dome truncated by the depression escarpment, whereas Morne Bonin (273 ±15 ka), Gros Piton and Petit Piton (71 ± 3 ka and 109 ± 4 ka, resp.), Belfond (13.6 ± 0.4 ka) and Terre Blanche (15.3 ± 0.4 ka) are domes within the Qualibou Depression. Belfond and Terre Blanche have whole rock geochemistry and mineral assemblages similar to the Belfond pyroclastic flow deposit, thus possibly representing late-erupted degassed portions of the magma that produced the Belfond pyroclastics. The geochemical characteristics and similar zircon age distributions of the silicic lava domes and pyroclastics of the SVC suggest that these share a common magma source beneath the Qualibou depression. The distribution of the pyroclastic flows and the wide range in their eruption ages makes it unlikely that these were erupted during caldera-forming activity, and we instead invoke a series of smaller-volume explosive eruptions from the area of the current depression, the earliest of which occurred from a large proto-Qualibou edifice that subsequently underwent sector collapse. Activity from this proto-Qualibou centre may have ceased sometime between 38 and 59 ka ago, it therefore seems unlikely given our present understanding that there will be another eruption from the southern central highland region. However, the young dome-forming activity in the Qualibou depression may have occurred in or close to the Holocene, and there have been dome collapse events and explosion craters formed since then. A new dome eruption or renewed activity at a dome within the depression, growing in the style of the ongoing Soufriere Hills lava dome on the nearby island of Montserrat, is possible; as is a future plinian eruption from this area. Such an eruption would not only have a devastating impact on Saint Lucia, but would also have significant regional and global impacts.
机译：圣卢西亚的Soufriere火山综合体（SVC）代表了小安的列斯群岛最大的硅质中心之一。它包括大量的火山灰质碎屑流沉积物，熔岩流以及佩利恩式穹顶和穹顶塌陷块状灰烬流沉积物。这些沉积物发生在Qualibou凹陷内和周围，该凹陷是直径约10公里的宽扇形塌陷结构。迄今为止，由于地层相关性有限且辐射年龄很少，尚不清楚SVC火山碎屑沉积的出气位置及其与扇形塌陷的关系。在这项研究中，我们借助矿物学和地球化学相关性，根据新近和最近发表的（U-Th）/ He，U-Th和U-Pb锆石年代地层数据重建了SVC的地质历史。从成分上讲，SVC沉积物是单调的中等K钙碱性岩石，具有61.6至67.7 wt。％的SiO_2，并显示出相似的痕量元素丰度。 U-Th和（U-Th）/ He锆石相结合，加上（）C年龄和矿物指纹，发现在640、515、265、104、60和40 ka处有明显的爆发喷发（产生的矿床以前被归类为“ Choiseul” ”）和20 ka（Belfond单位）。在矿物学和地球化学上独特的Belfond单元是分布在Qualibou凹陷的北部，东北部，南部和东南部的，充满山谷的大型火山碎屑流沉积物，可能是在一次普利山喷发期间沉积的。以前称为“ Choiseul凝灰岩”的单位定义不清。典型的Choiseul单元包括一系列黄白色，晶体贫乏，无焊接的火山灰热碎屑沉积物，这些沉积物生长在Qualibou凹陷的北部和东南部。但是，它的年龄限制很有限。可以根据年龄（在某些情况下还包括矿物和整个岩石的化学性质）来区分以前映射为Choiseul的许多其他单位。 Micoud（640±19 ka），Bellevue（264±8 ka），Anse John（104±4 ka）和La Pointe（59.8±2.1 ka），Anse Noir和Piaye的火山碎屑沉积物以前均与Choiseul凝灰岩（所有不确定性la）。我们建议这些单位代表跨越一定年龄范围的各个活动时期，而在特定类型的Choiseul浮石产生的（U-Th）/ He锆石年龄为515±19 ka。它们在类型上与Choiseul的总体地球化学和矿物学相似之处表明，它们可能都起源于同一中心。莫恩·塔巴克（Morne Tabac）（532±21 ka）是被悬崖峭壁截断的圆顶，而莫恩·波宁（Morne Bonin（273±15 ka），格罗斯·皮顿和珀蒂·皮顿（71±3 ka和109±4 ka，分别），贝尔方（13.6） ±0.4 ka）和Terre Blanche（15.3±0.4 ka）是Qualibou凹陷内的穹顶。 Belfond和Terre Blanche具有类似于Belfond火山碎屑流沉积物的整个岩石地球化学和矿物组合，因此可能代表了产生Belfond火山碎屑岩的岩浆的晚期喷发脱气部分。 SVC的硅质熔岩穹顶和火山碎屑岩的地球化学特征和相似的锆石年龄分布表明，这些在Qualibou凹陷之下共享着一个共同的岩浆源。火山碎屑流的分布和喷发年龄的广泛范围使得它们不太可能在形成破火山口的活动中喷发，我们改为从当前的凹陷地区（最早的火山喷发区）调用一系列较小数量的爆发性喷发。这是由于大型的Qualibou原始建筑物产生的，随后该建筑物崩溃了。这个原始Qualibou中心的活动可能在38到59 ka之前的某个时间停止了，因此，鉴于我们目前的理解，南部中部高地地区还将再次爆发，因此似乎不太可能。但是，Qualibou凹陷中年轻的穹顶形成活动可能发生在全新世或其附近，并且此后发生了穹顶坍塌事件和爆炸坑。有可能在附近的蒙特塞拉特岛（Montserrat）上进行中的Soufriere Hills熔岩穹顶的形式，在凹陷内的穹顶上进行新的穹顶喷发或新的活动；以及该地区未来的普林尼亚喷发。这种喷发不仅会对圣卢西亚造成毁灭性影响，而且还将对区域和全球产生重大影响。

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