Evidence of South American lithosphere mantle beneath the Chile mid-ocean ridge
Evidence of South American lithosphere mantle beneath the Chile mid-ocean ridge
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DOI：
10.1016/j.epsl.2023.118320
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发表时间：
2023-10
影响因子：
5.3
通讯作者：
S. Mallick;Sophie E. Kuhl;A. Saal;E. Klein;W. Bach;B. Monteleone;J. Boesenberg
中科院分区：
文献类型：
--
作者：
S. Mallick;Sophie E. Kuhl;A. Saal;E. Klein;W. Bach;B. Monteleone;J. Boesenberg
对大洋中脊玄武岩的许多地球化学研究已经确定上地幔存在成分和岩石不均匀性。这些研究成功地限制了地球上地幔化学不均匀性的组成和年龄。然而，这些异质性的起源仍然存在很大争议。智利大洋中脊位于东南太平洋，远离任何热点，正在碰撞和俯冲到南美洲板块之下，促进板片窗的形成。综合地球化学数据（主要，微量，挥发性元素含量和Sr，Nd，Hf和Pb同位素比值）在智利海岭海底玻璃收集超过1000公里的海岭长度表现出显着的地幔成分的变化。主要地幔组分有：典型的太平洋MORB地幔、富集地幔（如，EM-1）、俯冲改造地幔和具有异常高Hf同位素比的古代亏损地幔。令人惊讶的是，尽管大的成分变化，所有的玻璃-包括那些与俯冲签名-挥发性耐火元素的比例范围内的太平洋正常MORB。我们建议，巴塔哥尼亚次大陆岩石圈地幔，早古生代以来的交代，被侵蚀，并纳入软流圈与南大西洋MORB地幔组成，是向西流动的板窗口从南美到智利脊。这种情况与一个广为接受的地球动力学模型相反，该模型预测地幔流动的方向相反。我们推测，从板块窗口向西的地幔流动可能是对1.30Ma以来德雷克通道开启和太平洋地幔东移的一种逆流响应。
Numerous geochemical studies on mid-ocean ridge basalts have established the presence of both compositional and lithological heterogeneities in the upper mantle. These studies have successfully constrained the composition and age of the chemical heterogeneities within the Earth's upper mantle. However, the origin of those heterogeneities remains highly debated. The Chile Mid-Ocean Ridge in the southeast Pacific Ocean, located far away from any hotspot, is colliding and subducting under the South America plate promoting the formation of a slab window. Comprehensive geochemical data (major, trace, volatile element contents and Sr, Nd, Hf and Pb isotope ratios) on Chile Ridge submarine glasses collected over the 1000 km ridge length demonstrate significant mantle compositional variability. Four main mantle components have been recognized: the typical Pacific MORB mantle, an enriched mantle (e.g., EM-1), a Subduction Modified mantle, and an anciently depleted mantle with unusually high Hf isotope ratios. Surprisingly, despite the large compositional variability, all glasses – including those with a subduction signature – have volatile-refractory element ratios within the range of the Pacific normal MORB. We propose that the Patagonia sub-continental lithospheric mantle, variably metasomatized since the Early Paleozoic, is eroded and incorporated into an asthenosphere with a south Atlantic MORB mantle composition that is flowing westward across the slab window from South America to the Chile Ridge. This scenario contrasts with a well-accepted geodynamic model that predicts the opposite direction of mantle flow. We speculate that the westward mantle flow across the slab window might be a counter-flow response to the opening of the Drake passage and the eastward movement of Pacific mantle since ∼30 Ma ago.