Abstract

This study was focused on the estimation and geodynamic interpretation of the contents and character of distribution of highly siderophile and chalcophile elements in rock samples from mafic–ultramafic assemblage sampled at the Stalemate Ridge in the NW Pacific and the Shirshov Rise in the Bering Sea. All of the samples were collected during Cruise 249 of German R/V Sonne. These mafic–ultramafic rock complexes situated at the opposite sides of Aleutian Island Arc may carry important information on the structure and composition of the old Pacific lithosphere subducted under Aleutian Arc, as well as on the products of suprasubduction magmatism in back-arc basin of the Bering Sea. The newly acquired data presented in this paper indicate that the real structure of the northwestern segment of the Stalemate Ridge is inconsistent with the currently widely assumed model that the local lithosphere corresponds to the canonic oceanic type. The lithosphere in the area includes mafic–ultramafic complexes whose origin was not related to mantle reservoirs of the oceanic type (e.g., DM). At the same time, the tectonic remobilization of the lithosphere in this part of the NW Pacific suggested in (Lonsdale, 1988) is confirmed by results of dredging at sites on the northwestern flank of the Stalemate Ridge. Vertical tectonic motions in this region combined lithospheric blocks that might have been formed in contrasting geodynamic settings. These lithospheric blocks may have included fragments of magmatic complexes formed by suprasubduction magmatism and were identical in the their isotope geochemistry (⁸⁷Sr/⁸⁶Sr, ¹⁴³SNd/¹⁴⁴Nd) to the mafic–ultramafic assemblage occurring in the Shirshov Rise, which lies immediately north of the northwestern Stalemate Ridge segment and likely is a relic of a backarc spreading center.

中文翻译：

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北大西洋太平洋僵局岭和白令海希尔肖夫崛起的镁铁质-超镁铁质复合体：地球化学的异同

摘要

这项研究的重点是对西北太平洋Stalemate Ridge和白令海Shirshov Rise采样的镁铁质-超镁铁质组合岩石样品中高度嗜铁和嗜硫元素的含量和分布特征进行估算和动力学解释。所有样品都是在德国R / V Sonne的249巡游期间收集的。这些位于阿留申岛弧对侧的镁铁质-超镁铁质岩石复合体可能具有重要信息，包括在阿留申弧下俯冲的旧太平洋岩石圈的结构和组成，以及该盆地弧后盆地超俯冲岩浆作用的产物。白令海。本文提供的新获得的数据表明，僵局岭西北段的真实结构与当前被广泛假定的模型（当地岩石圈对应于典型的海洋类型）不一致。该地区的岩石圈包括镁铁质-超镁铁质复合体，其起源与海洋类型的地幔储集层（例如DM）无关。同时，在西北太平洋这一部分的岩石圈构造运动建议在（Lonsdale，1988年）在Stalemate Ridge西北侧面的挖泥结果得到证实。该区域的垂直构造运动组合了岩石圈块，这些岩石圈块可能是在相反的地球动力学环境下形成的。这些岩石圈块可能包括超俯冲岩浆作用形成的岩浆复合物的碎片，并且它们的同位素地球化学相同（⁸⁷ Sr / ⁸⁶ Sr，¹⁴³ SNd / ¹⁴⁴ Nd）到Shirshov Rise中发生的铁镁质-超音速组合，位于Stalemate Ridge西北段的正北，很可能是后弧扩散中心的遗迹。