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首页> 外文期刊>Marine Geophysical Research >New, high resolution swath bathymetry of Gettysburg and Ormonde Seamounts (Gorringe Bank, eastern Atlantic) and first geological results
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New, high resolution swath bathymetry of Gettysburg and Ormonde Seamounts (Gorringe Bank, eastern Atlantic) and first geological results

机译：葛底斯堡和奥蒙德海山（戈林格银行，东大西洋）的新型高分辨率测深仪和初步地质结果

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High resolution swath bathymetry of shallow water (< 200 m) oceanic seamounts is a relatively rare issue. During the recent Gorringe_2003 cruise over the Gorringe Bank (Eastern Atlantic) we collected multibeam bathymetry on the bank’s two shallow summits, Gettysburg and Ormonde in the –25/–400m depth range at a resolution rarely achieved over an oceanic seamount. We also carried out bottom samplings and ROV dives in the same bathymetric interval. The acquisition parameters and the characteristics of the echosounder employed allowed to generate a Digital Terrain Model (DTM) with metric spatial resolution upto 75–100 m depths. To ensure proper tidal corrections a tide-gauge was deployed at sea-bottom during the survey. DTM reveals for the Gettysburg Seamount an almost perfectly circular summit resulting from the blanket of bioclastic sediments over an igneous ‘core’ consisting of sheared and foliated serpentinites. The core is dissecated by N 10° W trending ridges elevating some tens of metres and filled in between by bioclastic sands. Both foliation and ridge patterns seem related to primary igneous fabric rather than later structural deformation. The overall circular shape confirms the origin of the seamount as a mantle serpentinite diapir in analogy with similar, but subduction-related, circular seamounts observed in the Bonin Trench (western Pacific). In contrast the Ormonde elongated summit follows the regional tectonic trend with a N 60° E active (seismogenic?) fault on its southeastern flank. Its basement morphology corresponds to the outcrops of igneous rocks chiefly consisting of gabbros, volcanic rocks and dyke intrusions. On both seamounts topographic profiles show that the ‘shelf’ area is somewhat convex rather than flat like that of ‘Pacific type’ guyots and is bordered by a depositional, locally erosional shelf break, located between –170 and –130 m. Various terraced surfaces and some geological evidence confirm previous observations and indicate relative sea-level oscillations with partial emersion of the two summits that seem occurred during the last glacial cycle (past 120 ka).
机译：浅水区（<200 m）海洋海山的高分辨率条带测深是一个相对罕见的问题。在最近的Gorringe_2003航行于Gorringe银行（东大西洋）的航行中，我们收集了该银行两个浅顶山峰–25 / –400m范围内的葛底斯堡和奥蒙德的多波束测深图，其分辨率几乎没有在大洋海山上实现。我们还以相同的测深间隔进行了底部采样和ROV潜水。所使用的采集参数和回声测深仪的特征允许生成数字地形模型（DTM），其空间分辨率可达75–100 m深度。为了确保进行正确的潮汐校正，在调查期间在海底部署了一个潮汐仪。 DTM为葛底斯堡海山揭示了一个几乎完美的圆形峰顶，这是由于在由剪切和叶状蛇纹岩组成的火成岩“核心”上覆盖了生物碎屑沉积物所致。岩心被N 10°W趋势脊分开，该脊上升了几十米，并在其间被生物碎屑砂填充。叶面和脊状图案似乎都与主要火成的织物有关，而不是与后来的结构变形有关。整个圆形形状证实了海山的起源是地幔蛇纹岩底辟，类似于在波宁海沟（西太平洋）中观测到的类似但与俯冲有关的圆形海山。相比之下，奥蒙德拉长型山顶遵循区域构造趋势，其东南侧面有N 60°E活跃（地震成因）断层。它的基底形态与火成岩的露头相对应，主要由辉长岩，火山岩和堤坝侵入组成。在两个海山上，地形图都显示“架子”区域有些像凸凹，而不是像“太平洋型”古丘一样平坦，并且被沉积的局部侵蚀性的架子断裂所包围，位于–170至–130 m之间。各种阶地表面和一些地质证据证实了先前的观察结果，并表明了相对的海平面振荡以及似乎在最后一个冰川周期（过去120 ka）中发生的两个顶峰的部分出现。

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