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Palaeozoic and Proterozoic zircons from the Mid-Atlantic Ridge

机译：大西洋中脊古生代和元古代锆石

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摘要

According to the theory of plate tectonics, rocks found in the vicinity of mid-ocean ridges—where oceanic plates are created— should be relatively young (at most several Myr old). Here we report the discovery of zircons with ages of about 330 and 1,600 Myr that were drilled from exposed gabbros beneath the Mid-Atlantic Ridge near the Kane fracture zone. Age determi- nations were made using the ~(207)Pb/~(206)Pb evaporation method and confirmed with conventional U-Pb dating and ion microprobe (SHRIMP) analysis. We suggest two plausible explanations for the origin of these unusually old zircons. During the opening of the Atlantic, sheared crustal material or delaminated continental lithosphere sank into small roll-like circulation cells that developed in the shallow mantle at each side of the ridge axis and the material was then transported through these cells to the ridge axis. Alternatively, material from the continental crust has been trapped within the Kane fracture zone since the opening of the Atlantic Ocean basin through a series of transform migrations and ridge jumps, with portions of this material subsequently migrating down the ridge axis.
机译：根据板块构造学说，在洋中脊附近（形成洋板的地方）发现的岩石应该相对年轻（至多为Myr老）。在这里，我们报道了从凯恩断裂带附近大西洋中脊下方裸露的辉长岩中钻出的锆石，年龄分别为330和1,600 Myr。使用〜（207）Pb /〜（206）Pb蒸发法确定年龄，并通过常规U-Pb测年和离子微探针（SHRIMP）分析进行确认。对于这些异常古老的锆石的起源，我们提出了两个合理的解释。在大西洋开放期间，剪切的地壳物质或分层的大陆岩石圈沉入了小的卷状循环池中，这些循环池在脊轴两侧的浅地幔中发育，然后通过这些单元将其运输到脊轴。或者，自大西洋海盆开放以来，来自大陆壳的材料已通过一系列转换迁移和山脊跳跃而被困在凯恩断裂带内，其中部分材料随后沿山脊轴线向下迁移。

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