The nature and evolution of mantle upwelling at Ross Island, Antarctica, with implications for the source of HIMU lavas
The nature and evolution of mantle upwelling at Ross Island, Antarctica, with implications for the source of HIMU lavas
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DOI：
10.1016/j.epsl.2018.05.049
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发表时间：
2018-09
影响因子：
5.3
通讯作者：
E. Phillips;K. Sims;J. Blichert‐Toft;R. Aster;G. Gaetani;P. Kyle;P. Wallace;D. Rasmussen
中科院分区：
文献类型：
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作者：
E. Phillips;K. Sims;J. Blichert‐Toft;R. Aster;G. Gaetani;P. Kyle;P. Wallace;D. Rasmussen
南极洲罗斯岛的多个、近端的、年轻的和/或活跃的火山中心为研究碱性岩浆成因的深、浅过程和地幔不均匀性的长度尺度提供了一个独特的机会。南极洲罗斯岛是四个硅不饱和碱性火山中心的集合体，其中包括活跃的响岩质埃里伯斯火山（1.2至0 Ma）。山特雷尔山Bird和Hut Point半岛围绕罗斯岛外围的埃里伯斯，大多年代较老（约0.3 ~ 4 Ma），成分主要为玄武质。虽然埃里伯斯熔岩的地球化学成分和HIMU同位素特征很好地表征了周围火山中心的地球化学，直到这项研究，知之甚少。为了进一步研究罗斯岛下地幔源区和岩浆作用的性质，我们测量了埃里伯斯火山周边三座火山的57个样品的主元素、微量元素和Sr、Nd、Hf、Pb同位素组成，并将结果与后者以前的地球化学和同位素研究结果进行了比较。山特雷尔山Bird和Hut Point半岛的87 Sr/86 Sr范围为0.702907至0.703147，ε Nd范围为+ 4.3至+ 6.3，ε Hf范围为+ 5.6至+ 8.6，206 Pb/204 Pb范围为19.282至20.241。所有四个火山（埃里伯斯，恐怖，鸟，小屋点半岛）的Sr，Nd，Hf和Pb同位素组成落在HIMU和DMM地幔端员之间的混合线，与EM组件的微小贡献。四座火山的同位素组成存在微小但明显的差异，最明显的是Mt. Bird，意味着罗斯岛下地幔源的不均匀性，其长度尺度相当于或小于火山间距离（即小于50公里）。罗斯岛火山岩样品的主要和微量元素系统学和同位素特征与西兰迪亚样品和代表新生代碱性岩浆区岩浆的较老南极样品不同。罗斯岛熔岩和火山岩的化学和同位素组成的最好的解释是一个古老的软流层源含有残余石榴石的小程度熔融。此外，最近的全球层析成像建模表明，罗斯岛下方1200公里深处存在低剪切波速度异常。这表明一个深层次的上升流柱冲击浅交代地幔已逐渐被侵蚀，不再是罗斯岛岩浆活动的潜在来源。相反，罗斯岛熔岩的来源是古老的（太古代至早元古代）物质从深部地幔上涌，而不是古生代俯冲交代的陆下岩石圈地幔熔融。虽然我们的研究结果在了解罗斯岛火山作用方面具有本地意义，并为中生代周围地区火山作用的演化提供了新的视角，但它们也对测量HIMU地幔源的性质，年龄和演化具有重要的全球影响。
The multiple, proximal, young and/or active volcanic centers of Ross Island, Antarctica, provide a unique opportunity to investigate both deep and shallow processes of alkaline magma genesis and the length scales of mantle heterogeneity. Ross Island, Antarctica is an assembly of four silica-undersaturated alkaline volcanic centers, including the active phonolitic Erebus volcano (1.2 to 0 Ma). Mt. Terror, Mt. Bird, and Hut Point Peninsula surround Erebus on the periphery of Ross Island and are mostly older (∼ 0.3 to 4 Ma) and mainly basanitic in composition. While the geochemical compositions and HIMU isotopic signature of Erebus lavas are well characterized, the geochemistry of the peripheral volcanic centers was, until this study, poorly known. To further investigate the nature of mantle sources and magmatic processes beneath Ross Island, we therefore measured major and trace element and Sr, Nd, Hf, and Pb isotope compositions on fifty-seven samples from the three volcanoes peripheral to Erebus volcano and compared the results to previous geochemical and isotopic studies of the latter. Mt. Terror, Mt. Bird, and Hut Point Peninsula have 87 Sr/86 Sr ranging from 0.702907 to 0.703147, ε Nd ranging from+ 4.3 to+ 6.3, ε Hf ranging from+ 5.6 to+ 8.6, and 206 Pb/204 Pb ranging from 19.282 to 20.241. The Sr, Nd, Hf, and Pb isotope compositions of all four volcanoes (Erebus, Terror, Bird, and Hut Point Peninsula) fall on a mixing line between the HIMU and DMM mantle end-members, with a minor contribution from an EM component. Small, but distinct differences in the isotopic compositions of the four volcanoes, most notably Mt. Bird, imply mantle source heterogeneity beneath Ross Island on a length scale comparable to or smaller than inter-volcano distances (ie, less than 50 km). The major and trace element systematics and isotopic signatures of the Ross Island volcanic samples are distinct from those for samples from Zealandia and older Antarctic samples that typify magmas from the Cenozoic alkaline magmatic province. The chemical and isotopic compositions of the Ross Island lavas and tephras are best explained by small-degree melting of an ancient asthenospheric source containing residual garnet. Additionally, recent global tomographic modeling indicates low shear wave velocity anomalies with depths down to∼ 1200 km beneath Ross Island. This suggests a deep-seated upwelling plume impinging on shallower metasomatized mantle which has been gradually eroded away and is no longer a potential source of Ross Island magmatism. Rather, the source of Ross Island lavas is old (Archean to early Proterozoic) material upwelling from the deep mantle as opposed to melting of subcontinental lithospheric mantle metasomatized by Paleozoic subduction. While our findings have local significance in terms of understanding Ross Island volcanism and providing a new perspective on the evolution of volcanism in the surrounding region during the Phanerozoic, they also have important global implications for gauging the nature, age, and evolution of the HIMU mantle source.