Noble gas study of the Reunion hotspot: evidence for distinct less-degassed mantle sources
Noble gas study of the Reunion hotspot: evidence for distinct less-degassed mantle sources
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留尼旺热点的稀有气体研究：明显的少脱气地幔源的证据
DOI：
10.1016/s0012-821x(01)00489-7
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发表时间：
2001
影响因子：
5.3
通讯作者：
K. Uto
中科院分区：
文献类型：
--
作者：
T. Hanyu;T. Dunai;G. Davies;I. Kaneoka;S. Nohda;K. Uto
我们提出了一个广泛的He，Ne和Ar同位素数据集，从留尼汪热点，证明了一个均匀的羽源，具有独特的同位素特征的存在。3 He/4 He比的两个火山留尼汪岛（Piton de la Fournaise，<0.53 Ma; Piton des Neiges，2-0.44 Ma）是统一的12-13.5 Ra，无论4 He浓度和样品年龄。毛里求斯的屏蔽建造老系列（5-8 Ma）具有恒定的3 He/4 He比，约为11.5 Ra。它们之间的3 He/4 He和Sr-Nd同位素比值的相似性表明，这些火山在800万年的时间里具有与地幔柱活动有关的共同的均质源。这些火山的20 Ne/22 Ne和21 Ne/22 Ne在Ne三同位素图上定义了一个线性趋势，在Loihi和MORB相关线之间具有一个斜率。~（20）Ne/~（22）Ne与~（40）Ar/~（36）Ar有明显的相关性。毛里求斯和罗德里格斯的中系列（2-3 Ma）和年轻系列（<1 Ma）（1.5Ma）的3 He/4 He比值与MORB相似，Sr和Nd同位素比值比留尼汪和毛里求斯的老系列更接近MORB。因此，这些中期和年轻系列熔岩记录了毛里求斯下的晚期热再生，其来源与地幔柱无关。留尼汪岩浆源区的同位素特征为：3 He/4 He（13 Ra）较低，Ne三同位素图呈中等斜率，Sr同位素比值相对放射成因。这些源区特征不能用地壳混染或MORB源区与Loihi型原始地幔混合来解释。因此，He-Ne-Ar-Sr-Nd同位素表明，这个地幔柱的来源与其他大的地幔柱（洛伊希和冰岛）的来源不同，清楚地表明地幔包含几个相对较少脱气的储层，而不是一个单一的原始来源。留尼汪和夏威夷两个热点的同位素特征不同可能有两种解释：（1）留尼汪源区比洛伊希源区含有更多的再循环物质;（2）在地幔演化早期，留尼汪源区比洛伊希源区经历了更强的脱气/分异作用。在这两种情况下，在地幔中的对流模式是必要的，隔离和保存几个较少脱气水库对流搅拌下地幔。
We present an extensive He, Ne and Ar isotope data set from the Reunion hotspot that demonstrates the presence of a homogeneous plume source that has unique isotopic characteristics.3He/4He ratios of the two volcanoes on Reunion (Piton de la Fournaise, <0.53 Ma; Piton des Neiges, 2–0.44 Ma) are uniform 12–13.5 Ra regardless of4He concentration and sample age. The shield-building Older Series of Mauritius (5–8 Ma) has a constant3He/4He ratio around 11.5 Ra. The similarity of3He/4He and Sr–Nd isotope ratios among them demonstrate that the volcanoes have had a common homogeneous source related to the mantle plume activity over a period of 8 Myr.20Ne/22Ne and21Ne/22Ne of these volcanoes define a linear trend on a Ne three-isotope diagram with a slope between the Loihi and MORB correlation lines. There is a clear correlation between20Ne/22Ne and40Ar/36Ar. In contrast, Intermediate (2–3 Ma) and Younger Series (<1 Ma) of Mauritius and Rodrigues (1.5 Ma) have3He/4He ratios similar to MORB and Sr and Nd isotope ratios closer to MORB than lavas from Reunion and Older Series of Mauritius. These Intermediate and Younger Series lavas therefore record a late stage thermal rejuvenation beneath Mauritius derived from a source that is unrelated to the mantle plume. The isotopic characteristics of the source of the Reunion magmatism are relatively low3He/4He (13 Ra), an intermediate slope in a Ne three-isotope diagram and relatively radiogenic Sr isotope ratios. These source characteristics cannot be explained by either crustal contamination or MORB source mixing with Loihi-type primitive mantle. Thus He–Ne–Ar–Sr–Nd isotopes demonstrate that this plume source is distinct from the source of other large plumes (Loihi and Iceland), clearly showing that the mantle contains several relatively less-degassed reservoirs and not a single primitive source. Two possible models can account for the different isotopic signature of Reunion and Hawaii hotspots; (1) the Reunion source contains more recycled material than Loihi source and (2) the Reunion source experienced stronger degassing/differentiation than the Loihi source in the early stage of mantle evolution. In both cases a convection mode in the mantle is required that isolates and preserves several less-degassed reservoirs in the convectively stirred lower mantle.