Element variations in rhyolitic magma resulting from gas transport
Element variations in rhyolitic magma resulting from gas transport
复制标题
DOI：
10.1016/j.gca.2013.07.032
复制
发表时间：
2013-11-15
影响因子：
5
通讯作者：
Geraki, K.
中科院分区：
文献类型：
--
作者：
Berlo, K.;Tuffen, H.;Geraki, K.
凝灰岩脉是岩浆在管道内脱气过程中碎裂而形成的玻璃填充裂隙。这些矿脉形成了短暂的通道，通过这些通道，出溶气体可以从岩浆中逸出。本研究的目的是确定在何种程度上的化学不均匀性熔体内的气体运输的结果，并评估如何可以用来研究岩浆脱气。对冰岛Torfajokull和智利Chaiten两处流纹岩喷发形成的凝灰岩脉进行了详细研究。来自托尔法冰盖的凝灰岩脉来自一个浅的解剖管道（类似于70 ka），该管道供给了脱气的熔岩流，而来自柴滕的样品是2008年5月普林尼活动减弱阶段喷出的炸弹。详细的现场化学分析结果（同步加速器XRF，FTIR，LA-ICP-MS）表明，在两种静脉中，较大的囊泡碎片富含挥发性元素（Torfajokull：H，Li，Cl; Chaiten：Li、Cl、Cu、Zn、As、Sn、Sb），而周围较小的颗粒在Torfajokull矿脉中被贫化（Li，Cl，Zn，Br，Rb，Pb），但在柴田脉中富集（K，Cu，Zn，As，Mo，Sb，Pb）。这两个矿脉的寿命以及通过它们的气体和粒子通量可以使用扩散剖面和富集因子来估计。Torfajokull静脉有较长的寿命（类似于一天）和较低的粒子速度（类似于cm/s），而Chaiten静脉的寿命较短（
Tuffisite veins are glass-filled fractures formed when magma fragments during degassing within the conduit. These veins form transient channels through which exsolved gases can escape from magma. The purpose of this study is to determine the extent to which chemical heterogeneity within the melt results from gas transport, and assess how this can be used to study magma degassing. Two tuffisite veins from contrasting rhyolitic eruptions at Torfajokull (Iceland) and Chaiten (Chile) were studied in detail. The tuffisite vein from Torfajokull is from a shallow dissected conduit (similar to 70 ka) that fed a degassed lava flow, while the sample from Chaiten was a bomb ejected during the waning phases of Plinian activity in May 2008. The results of detailed in situ chemical analyses (synchrotron XRF, FTIR, LA-ICP-MS) show that in both veins larger vesiculated fragments are enriched in volatile elements (Torfajokull: H, Li, Cl; Chaiten: Li, Cl, Cu, Zn, As, Sn, Sb) compared to the host, while the surrounding smaller particles are depleted in the Torfajokull vein (Li, Cl, Zn, Br, Rb, Pb), but enriched in the Chaiten vein (K, Cu, Zn, As, Mo, Sb, Pb). The lifespans of both veins and the fluxes of gas and particles through them can be estimated using diffusion profiles and enrichment factors. The Torfajokull vein had a longer lifespan (similar to a day) and low particle velocities (similar to cm/s), while the Chaiten vein was shorter lived (