Geochemical variations during Kilauea's Pu'u 'O'o Eruption reveal a fine-scale mixture of mantle heterogeneities within the Hawaiian Plume
Geochemical variations during Kilauea's Pu'u 'O'o Eruption reveal a fine-scale mixture of mantle heterogeneities within the Hawaiian Plume
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基拉韦厄 Puu Oo 喷发期间的地球化学变化揭示了夏威夷地幔柱内地幔异质性的精细混合
DOI：
10.1093/petrology/egn025
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发表时间：
2008
影响因子：
3.9
通讯作者：
M. Norman
中科院分区：
文献类型：
--
作者：
J. Marske;Michael O. Garcia;A. Pietruszka;J. Rhodes;M. Norman
对持续25年的puu ' (cid:1) O ' (cid:1) O喷发的熔岩进行长期地球化学监测，使我们能够以无与伦比的细节探测K (cid:1) |lauea火山下的地壳和地幔岩浆过程。本文报道了1998 ~ 2005年喷发的Pu ' u ' (cid:1) O ' （cid:1）火山的Pb、Sr和Nd同位素比值、主微量元素丰度、橄榄石组成和岩石学资料。橄榄石分馏和聚集是火山喷发的重要地壳过程，在最近的熔岩中观察到少量斜辉石分馏。87 Sr/ 86 Sr和不相容的微量元素比值的小而系统的变化，以及镁归一化的主元素丰度证明了传递给普乌（cid:1） O (cid:1) O的母岩浆组成的快速变化。最近（1998 ~ 2003）的熔岩显示了一个系统的时间演化，朝向历史K (cid:1) |熔岩和莫纳罗亚熔岩组成场之间的中间区域。至少需要三种不同的地幔源成分来解释普乌（cid:1） O (cid:1) O熔岩的整体同位素和化学变化。在1998年以前的Pu ' u ' (cid:1) O ' (cid:1) O熔岩中观测到的两种来源成分具有相似的Pb、Sr和Nd同位素比率，尽管其中一种经历了最近（5.8 ka）的小程度熔融事件，并失去了不相容的微量元素。这种最近枯竭的成分是1985年至1998年间熔岩喷发的一个日益重要的来源。第三个组成部分是一种混合成分，由几乎相等比例的K (cid:1) |lauea和类似莫纳罗亚的地幔源组成。从1998年到2003年，它的开采量逐渐增加，随后减少。如果熔融通道从K (cid:1) |lauea的典型熔融区域（对1985 ~ 1998年熔岩很重要）内的区域向莫纳罗亚迁移，则混合源的重要性日益增加，在莫纳罗亚，可能存在相似比例的K (cid:1) |lauea和类似莫纳罗亚的地幔成分。Pu ' u ' (cid:1) O ' (cid:1) O资料表明Kea和Loa地幔成分在夏威夷地幔柱中有精细的分布，两者都存在于K (cid:1) |lauea火山之下。根据puu ' (cid:1) O ' （cid:1）喷发期间的地球化学和同位素变化，估计K (cid:1) |火山和冒纳罗亚火山的成分非均质性体积为5 10^35 km 3。Pb Nd Sr al以下分析细节Pb同位素用于仪器质量分馏同位素比值Tl与Thirlwall的平均Tl校正值Pb n¼Pb Pb同位素为NBS981
Long-term geochemical monitoring of lavas from the continuing 25-year-old Pu‘u ‘ (cid:1) O‘ (cid:1) o eruption allows us to probe the crustal and mantle magmatic processes beneath K (cid:1) |lauea volcano in unparalleled detail. Here we present new Pb, Sr, and Nd isotope ratios, major and trace element abundances, olivine compositions, and petrographic data for Pu‘u ‘ (cid:1) O‘ (cid:1) olavas erupted from 1998 to 2005. Olivine fractionation and accumulation are important crustal processes for the eruption, with minor clinopyroxene fractionation observed in the most recent lavas. Small, yet systematic variations in 87 Sr/ 86 Sr and incompatible trace element ratios, and MgO-normalized major element abundances document rapid changes in the parental magma composition delivered to Pu‘u ‘ (cid:1) O‘ (cid:1) o. Recent (1998^2003) lavas display a systematic temporal evolution towards an intermediate area between the compositional fields of historical K (cid:1) |lauea and Mauna Loa lavas. At least three distinct mantle source components are required to explain the overall isotopic and chemical variability of Pu‘u ‘ (cid:1) O‘ (cid:1) o lavas. Two of these source components observed in pre-1998 Pu‘u ‘ (cid:1) O‘ (cid:1) o lavas have similar Pb, Sr, and Nd isotope ratios, although one underwent a recent ( 5 8 ka) small-degree melting event and became depleted in incompatible trace elements.This recently depleted component was an increasingly important source for lavas erupted between 1985 and 1998. The third component is a hybrid mixture of nearly equal portions of K (cid:1) |lauea- and Mauna Loa-like mantle source compositions. It was progressively tapped in greater amounts from 1998 to 2003 and then subsequently decreased. The increasing importance of the hybrid source can be explained if melt pathways migrated from an area within K (cid:1) |lauea’s typical melting region (important for the 1985^1998 lavas) towards Mauna Loa, where a similar proportion of K (cid:1) |lauea- and Mauna Loa-like mantle components might exist. The Pu‘u ‘ (cid:1) O‘ (cid:1) o data suggest that Kea and Loa mantle components are distributed on a fine-scale within the Hawaiian plume, and both are present beneath K (cid:1) |lauea volcano. Based on the geochemical and isotopic variations during the Pu‘u ‘ (cid:1) O‘ (cid:1) oeruption, the estimated volume for K (cid:1) |lauea and Mauna Loa compositional heterogeneities is 5 10^35 km 3 . Pb Nd Sr al following analytical details Pb isotope for instrumental mass fractionation the isotope ratio Tl the with Thirlwall The average Tl-corrected value for Pb n ¼ Pb Pb isotopic are NBS981