New, high resolution swath bathymetry of Gettysburg and Ormonde Seamounts (Gorringe Bank, eastern Atlantic) and first geological results
New, high resolution swath bathymetry of Gettysburg and Ormonde Seamounts (Gorringe Bank, eastern Atlantic) and first geological results
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葛底斯堡和奥蒙德海山（东大西洋戈林滩）的新高分辨率条带测深和第一个地质结果
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发表时间：
2003
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通讯作者：
R. Tonielli
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作者：
G. Alteriis;S. Passaro;R. Tonielli
浅海（< 200米）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年在Gorringe岸（东大西洋）上空的巡航中，我们收集了岸的两个浅峰（葛底斯堡和奥蒙德）在-25/-400米深度范围内的多波束测深数据，其分辨率在海洋海山上很少达到。我们还在同一水深间隔内进行了海底取样和二次潜水。所采用的回声测深仪的采集参数和特性允许生成具有高达75-100米深度的度量空间分辨率的数字地形模型（DTM）。为确保正确的潮汐修正，在调查期间在海底部署了一个验潮仪。DTM揭示了葛底斯堡海山的一个几乎完美的圆形首脑会议所造成的毯子上的生物碎屑沉积物的火成岩的“核心”组成的剪切和叶理蛇纹岩。岩芯被N 10° W走向的隆起分割，隆起高度约为数十米，中间填充生物碎屑砂。叶理和山脊模式似乎有关的主要火成岩组构，而不是后来的构造变形。整体圆形证实海山起源于地幔蛇纹岩底辟，与小笠原海沟（西太平洋）观察到的类似但与俯冲有关的圆形海山类似。与此相反，Ormonde延长峰会遵循区域构造趋势，N60 ° E活跃（地震？）东南侧的断层。其基底形态与以辉长岩、火山岩和脉状侵入岩为主的火成岩露头相对应。两座海山的地形剖面图显示，“大陆架”区域有些凸起，而不是像“太平洋型”盖奥特那样平坦，其边界是一个沉积的、局部侵蚀的大陆架间断，位于-170米至-130米之间。各种阶状表面和一些地质证据证实了以前的观察，并表明相对海平面振荡与部分再现的两个高峰，似乎发生在最后一次冰期循环（过去120万年）。
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).