Lithospheric magma dynamics beneath the El Hierro Volcano, Canary Islands: insights from fluid inclusions
Lithospheric magma dynamics beneath the El Hierro Volcano, Canary Islands: insights from fluid inclusions
复制标题
加那利群岛埃尔耶罗火山下方的岩石圈岩浆动力学：来自流体包裹体的见解
作者：
E. Oglialoro;M. Frezzotti;S. Ferrando;C. Tiraboschi;C. Principe;G. Groppelli;I. Villa
在活火山中，岩石学研究已被证明是确定岩浆在地幔和地壳中运移和储存的深度条件的可靠方法。基于地幔捕虏体中的流体包裹体和矿物地质温压学，我们提出了一个埃尔埃罗岛（加那利群岛）岩浆管道系统的模型。这里研究的橄榄岩被夹带在暴露在埃尔玉兰谷的熔岩流。这些熔岩是发生在耶罗岛上的裂谷火山作用的一部分，大约在40-30 ka。橄榄岩是尖晶石二辉橄榄岩、方辉橄榄岩和纯橄榄岩，它们在压力为1.5至2 GPa、温度为800至950 °C（低温橄榄岩; LT）以及900至1100 °C（高温橄榄岩; HT）的较高平衡温度下在浅地幔中平衡。流体包裹体的显微测温和拉曼分析揭示了两种不同的流体相的捕获：早期I型交代CO2-N2流体（XN ~ 2 = 0.01-0.18;流体密度（d）= 1.19 g/cm ~ 3），与硅酸盐-碳酸盐熔体共存于LT橄榄岩中，在LT（d = 1.11-1.00和0.75-0.65 g/cm ~ 3）和HT（d = 1.04-1.11和0.75-0.65 g/cm ~ 3）橄榄岩中均存在晚期II型纯CO_2流体。虽然I型流体在岩浆活动开始之前，在大洋岩石圈深部（在60-65公里的深度）的交代阶段，II型CO2流体证明两个流体捕获事件的捕虏体在其主机镁铁质岩浆上升。通过对II型CO2流体包裹体和矿物地质温压法的解释，岩浆聚集带的识别表明，在22至36公里（或0.67至1 GPa）的深度之间的浅岩石圈地幔中存在一个相互连接的小岩浆储层的垂直堆叠系统。这一岩浆聚集区提供了位于下洋壳10-12 km（或0.26-0.34 GPa）深度的短期岩浆储存区。根据我们的模型，耶罗岛40-30 ka的火山活动与这个基于地幔的岩浆系统有关，我们建议这个系统为最近的2011-2012年喷发提供了支持。
At active volcanoes, petrological studies have been proven to be a reliable approach in defining the depth conditions of magma transport and storage in both the mantle and the crust. Based on fluid inclusion and mineral geothermobarometry in mantle xenoliths, we propose a model for the magma plumbing system of the Island of El Hierro (Canary Islands). The peridotites studied here were entrained in a lava flow exposed in the El Yulan Valley. These lavas are part of the rift volcanism that occurred on El Hierro at approximately 40–30 ka. The peridotites are spinel lherzolites, harzburgites, and dunites which equilibrated in the shallow mantle at pressures between 1.5 and 2 GPa and at temperatures between 800 and 950 °C (low-temperature peridotites; LT), as well as at higher equilibration temperatures of 900 to 1100 °C (high-temperature peridotites; HT). Microthermometry and Raman analyses of fluid inclusions reveal trapping of two distinct fluid phases: early type I metasomatic CO2-N2 fluids (XN2 = 0.01–0.18; fluid density (d) = 1.19 g/cm3), coexisting with silicate-carbonate melts in LT peridotites, and late type II pure CO2 fluids in both LT (d = 1.11–1.00 and 0.75–0.65 g/cm3) and HT (d = 1.04–1.11 and 0.75–0.65 g/cm3) peridotites. While type I fluids represent metasomatic phases in the deep oceanic lithosphere (at depths of 60–65 km) before the onset of magmatic activity, type II CO2 fluids testify to two fluid trapping episodes during the ascent of xenoliths in their host mafic magmas. Identification of magma accumulation zones through interpretation of type II CO2 fluid inclusions and mineral geothermobarometry indicate the presence of a vertically stacked system of interconnected small magma reservoirs in the shallow lithospheric mantle between a depth of 22 and 36 km (or 0.67 to 1 GPa). This magma accumulation region fed a short-lived magma storage region located in the lower oceanic crust at a depth of 10–12 km (or 0.26–0.34 GPa). Following our model, the 40–30-ka-old volcanic activity of El Hierro is related to this mantle-based magma system, a system that we propose fed the recent 2011–2012 eruption.
影响因子：
5.8
作者：
Longpre, Marc-Antoine;Kluegel, Andreas;Stix, John
通讯作者：
Stix, John