Trachytic Melt Inclusions Hosted in Clinopyroxene Offer a Glimpse Into Samoan EM2-Endmember Melts
Trachytic Melt Inclusions Hosted in Clinopyroxene Offer a Glimpse Into Samoan EM2-Endmember Melts
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DOI：
10.1029/2020gc009212
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发表时间：
2021-03-01
影响因子：
3.5
通讯作者：
Jackson, M. G.
中科院分区：
文献类型：
--
作者：
Adams, J., V;Spera, F. J.;Jackson, M. G.
我们提出的主要和微量元素数据单斜辉石托管，玻璃质熔体包裹体（MI）从萨摩亚热点高度富集（高Sr-87/Sr-86 = 0.71856）熔岩（ALIA-D115-18）。经过包埋后结晶校正，MI为粗面状（62.6- 65.4wt%SiO2，1.5- 3.0wt%MgO，和7.2- 10.6wt%总碱（Na 2 O + K2 O））在西萨摩亚萨瓦伊岛海底侧翼挖掘出的ALIA-D115熔岩先前被认为表现出镁铁质，低Sr-87/Sr-86岩浆和演化的高Sr-87/Sr-86岩浆（富集地幔2端元; EM 2）。在主量和微量元素空间，这些ALIA-D115熔岩形成更原始的萨摩亚盾熔岩和本研究的MI之间的混合趋势，这表明MI可以代表EM 2衍生的混合端员。最近限制EM 2混合端元组成的努力显示出与MI组成的显着重叠，支持了它们可以代表ALIA-D115熔岩的Sr-87/Sr-86混合端元并且源自EM 2端元的论点。此外，一个熔体包裹体含有Fo（73）橄榄石不与粗面质熔体平衡，表明熔体与镁铁质岩浆相互作用，然后才被包裹在寄主单斜辉石中。在Sr-87/Sr-86与SiO2和K2 O空间中预测ALIA-D115混合趋势表明，该趋势在Sr-87/Sr-86值类似于0.725处与平均MI组成相交，从而提供了一个窗口，进入与EM 2端元相关的更极端的组成。
We present major and trace element data on clinopyroxene-hosted, glassy melt inclusions (MIs) from a highly enriched (high Sr-87/Sr-86 = 0.71856) lava (ALIA-D115-18) from the Samoan hot spot. Following correction for post-entrapment crystallization, the MIs are trachytic (62.6-65.4 wt% SiO2, 1.5-3.0 wt% MgO, and 7.2-10.6 wt% total alkalis (Na2O + K2O)) ALIA-D115 lavas dredged off the submarine flanks of Savai'i Island, western Samoa have previously been suggested to exhibit binary endmember magma mixing between a mafic, low Sr-87/Sr-86 magma and an evolved, high Sr-87/Sr-86 magma (the Enriched Mantle 2 endmember; EM2). In major and trace element space, these ALIA-D115 lavas form a mixing trend between more primitive Samoan shield lavas and the MIs of this study, suggesting the MIs could represent the EM2-derived mixing endmember. Recent efforts to constrain the EM2 mixing endmember composition shows remarkable overlap with the MI compositions, supporting the argument they could represent the Sr-87/Sr-86 mixing endmember to the ALIA-D115 lavas and are derived from the EM2 endmember. Additionally, one melt inclusion contains Fo(73) olivines not in equilibrium with the trachytic melt, suggesting the melt interacted with a mafic magma prior to entrapment within host clinopyroxene. Projecting the ALIA-D115 mixing trend in Sr-87/Sr-86 versus SiO2 and K2O space shows that the trend intersects an average MI composition at Sr-87/Sr-86 values of similar to 0.725, thereby offering a window into more extreme compositions associated with the EM2 endmember.