Evidence for an age progression along the Tristan-Gough volcanic track from new 40Ar/39Ar ages on phenocryst phases
Evidence for an age progression along the Tristan-Gough volcanic track from new 40Ar/39Ar ages on phenocryst phases
复制标题
斑晶阶段新 40Ar/39Ar 年龄沿 Tristan-Gough 火山轨迹的年龄进展证据
DOI：
10.1016/j.tecto.2012.08.026
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发表时间：
2013
期刊：
影响因子：
2.9
通讯作者：
R. Werner
中科院分区：
文献类型：
--
作者：
Joana Rohde;P. Bogaard;K. Hoernle;F. Hauff;R. Werner
通常认为，年龄递进热点链是岩石圈在地幔柱上运动时减压熔融形成的。南大西洋的特里斯坦-高夫火山轨迹由沃尔维斯海岭和相关的盖奥特省组成，从纳米比亚的埃滕代卡大陆溢流玄武岩延伸到火山活跃的特里斯坦-达库尼亚库尼亚和高夫岛。本文对取自特里斯坦-高夫火山岩迹和格兰德河海隆的矿物样品进行了新的激光步热~（40）Ar/~（39）Ar年龄测定。40 Ar/39 Ar年龄主要测定长石晶体，但也测定黑云母晶体（一个样品）和整个岩石碎片（一个样品）。我们的数据表明，从Etendeka CFB到特里斯坦-达库尼亚和高夫的年龄增长。年龄范围从东北端的114 Ma到位于沃尔维斯海岭西南端的DSDP 525 A和528站点的58-72 Ma，到Guyot省的27-49 Ma和格兰德河海隆的80-87 Ma，该海隆被认为是南美洲板块上沃尔维斯海岭的对应物。我们还发现了非常年轻的（晚期）火山活动的沃尔维斯海岭（~ 55马）和格兰德河上升（~ 46马），其中，像其他热点轨道的晚期火山活动，代表更多的二氧化硅不饱和的组成比主要的“盾阶段”拉斑玄武岩火山活动。将我们的新年龄与已公布的Etendeka CFB的年龄相结合，假设非洲板块的速度恒定，则Tristan-Gough轨迹的一般火山迁移速率为~ 30 mm/a。我们的新的地质年代学的年龄进展的限制提供了进一步的支持Tristan-Gough轨道的地幔柱起源。最后，我们的新年龄数据意味着这个热点轨道的火山迁移速度比以前公布的速度更快，这需要考虑到板块构造重建模型。
Age progressive hotspot chains are commonly believed to form by decompression melting as the lithosphere moves over a mantle plume. The Tristan-Gough volcanic track in the South Atlantic, composed of the Walvis aseismic ridge and the associated Guyot Province, extends from the Etendeka continental flood basalts (CFBs) in Namibia to the volcanically active islands of Tristan da Cunha and Gough. Here we present new laser step-heating40Ar/39Ar ages of mineral separates from samples from the Tristan-Gough volcanic track and the Rio Grande Rise. The40Ar/39Ar ages have primarily been determined on feldspar crystals, but also on biotite crystals (one sample) and whole rock chips (one sample). Our data indicate a younging age progression from the Etendeka CFBs to Tristan da Cunha and Gough. The ages range from 114 Ma at the northeastern end to 58–72 Ma for DSDP Sites 525A and 528 at the southwestern end of the Walvis Ridge, to 27–49 Ma for the Guyot Province and to 80–87 Ma for the Rio Grande Rise, which is believed to represent the counterpart of the Walvis Ridge on the South American Plate. We also found anomalously young (late-stage) volcanism on the Walvis Ridge (~ 55 Ma) and the Rio Grande Rise (~ 46 Ma), which, like late-stage volcanism on other hotspot tracks, represents more silica-undersaturated compositions than the main “shield stage” tholeiitic volcanism. Combining our new ages with published ages for the Etendeka CFBs yields a general volcanic migration rate of ~ 30 mm/a for the Tristan-Gough track assuming a constant velocity of the African Plate. Our new geochronological constraints for an age progression provide further support for a mantle plume origin of the Tristan-Gough track. Finally our new age data imply a faster volcanic migration rate for this hotspot track than previously published rates, which needs to be factored into plate tectonic reconstruction models.