Cenozoic magmatism in the western Ross Embayment: Role of mantle plume versus plate dynamics in the development of the West Antarctic Rift System
Cenozoic magmatism in the western Ross Embayment: Role of mantle plume versus plate dynamics in the development of the West Antarctic Rift System
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DOI：
10.1029/2001jb000515
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发表时间：
2002-09
影响因子：
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通讯作者：
S. Rocchi;P. Armienti;M. D’Orazio;S. Tonarini;J. Wijbrans;G. Vincenzo
中科院分区：
文献类型：
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作者：
S. Rocchi;P. Armienti;M. D’Orazio;S. Tonarini;J. Wijbrans;G. Vincenzo
[1]利用北方维多利亚地（南极洲）新生代岩体和岩脉的地球化学和年代学数据，提出了西南极裂谷系（WARS）这一部分的构造-岩浆模型。七个主要的岩体是成分双峰，辉长岩和正长岩部分。在研究的180个岩脉中，大多数岩脉厚度为1 m，成分为碱性玄武岩-碧玄岩-软玉，沿着有少量的中间岩。粗面流纹岩脉（厚达50米）远不常见。岩脉的40 Ar-39 Ar数据表明始新世中期至渐新世早期的年龄，这是迄今为止发现的整个WARS地区最古老的火成岩活动。地质年代学构造框架提供了证据，同期侵位的两个主要的NW-SE和N-S走向的趋势，而在不同的时间发生在相邻的地壳部门的深成次火山活动的堤坝。基性岩脉显示的主要和微量元素分布的典型的大洋岛屿玄武岩，如高比例的Nb和Ta的大离子亲石和重稀土元素，再加上突出的负K和Pb异常的原始地幔标准化的多元素图。初始同位素组成为0.70299-0.70372（87 Sr/86 Sr）和4.2-6.3（eNd）。这些特征是年轻的新近纪熔岩所共有的。基性岩脉和熔岩的地球化学模拟表明，富集的岩浆源，其特征在于残留钾质含水相，从而指出地幔源几乎均匀整个50百万年。WARS的其他新生代火山区和整个南极板块的岩浆源具有可比的地球化学特征。裂谷早期火成岩的新数据证明了岩浆演化、区域构造和板块动力学之间的年代-结构联系，这表明WARS岩浆活动的模型可以替代目前的羽流假说。我们建议，岩浆成因和侵位有关的重新激活的预先存在的translithospheric故障，促进本地减压熔融的富集地幔，以前脉在减压插曲与无岩浆晚白垩世伸展裂谷阶段。
[1] Geochemical and chronological data for Cenozoic plutons and dikes from northern Victoria Land (Antarctica), were used to propose a tectonic-magmatic model for this portion of the West Antarctic Rift System (WARS). The seven major plutons are compositionally bimodal, with gabbroic and syenitic portions. Among the 180 studied dikes, most are 1 m thick and have alkali basalt-basanite-tephrite compositions, along with minor intermediate rocks. Trachytic-rhyolitic dikes (up to 50 m thick) are by far less common. The 40Ar-39Ar data for dikes indicate middle Eocene to early Oligocene ages, the oldest found to date for igneous activity throughout the WARS. The geochronological-structural framework provides evidence for coeval emplacement of dikes on two main NW-SE and N-S striking trends, whereas plutonic-subvolcanic activity occurred in adjacent crustal sectors at different times. Mafic dikes display major and trace element distribution typical of basalts from oceanic islands, such as high ratios of Nb and Ta to large ion lithophile and heavy rare earth elements, coupled with prominent negative K and Pb anomalies in the primitive mantle-normalized multielement diagrams. Initial isotopic compositions are within the ranges of 0.70299–0.70372 for 87Sr/86Sr and 4.2–6.3 for eNd. These features are shared by younger Neogene lavas. Geochemical modeling for both mafic dikes and lavas indicates an enriched magma source characterized by a residual potassic hydrous phase, thus pointing out a mantle source nearly uniform throughout 50 m.y. Comparable geochemical signature are reported for the magma source of the other Cenozoic volcanic provinces of the WARS and the whole Antarctic Plate. The new data for the early igneous rocks of the rift put in evidence a chronologic-structural link between magmatic evolution, regional tectonics and plate dynamics which suggests a model for WARS magmatism that is alternative to current plume hypotheses. We propose that magma genesis and emplacement are related to reactivation of preexisting translithospheric faults, which promoted local decompression melting of an enriched mantle that was previously veined during the decompression episode associated with the amagmatic late Cretaceous extensional rift phase.