Preliminary analysis of the Knipovich Ridge segmentation: influence of focused magmatism and ridge obliquity on an ultraslow spreading system
Preliminary analysis of the Knipovich Ridge segmentation: influence of focused magmatism and ridge obliquity on an ultraslow spreading system
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DOI：
10.1016/s0012-821x(02)00790-2
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发表时间：
2002-09
影响因子：
5.3
通讯作者：
K. Okino;D. Curewitz;M. Asada;K. Tamaki;P. Vogt;K. Crane
中科院分区：
文献类型：
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作者：
K. Okino;D. Curewitz;M. Asada;K. Tamaki;P. Vogt;K. Crane
利用水深测量、重力和深拖声纳图像数据，确定了东北大西洋挪威-格陵兰海400公里长的超低扩张Knipovich海脊的分段。离散的火山中心以大型火山构造为标志，并伴随着短波长的地幔布格异常(MBA)低，通常类似于Gakkel山脊和最东端的西南印度山脊。这些神奇的坚固的分段中心沿着山脊规则地间隔约85-100公里，其特点是堆积的丘陵地形、高起伏、离轴海山链和显著的MBA低。我们认为，这些喷发中心对应于岩浆流量增强的区域，它们的间距反映了下伏地幔上涌单元的几何形状。地幔的大尺度热结构主要控制着离散和集中的岩浆活动，这些段的相对较宽的间距可能反映了山脊下的冷地幔。Knipovich海脊南段的分段中心比海脊北段具有较低的起伏和较小的MBA异常。这表明，脊倾角是Knipovich山脊建造的次要控制因素，因为倾角从北到南分别从35°到49°变化，而扩展速率和轴向深度基本保持不变。倾角的增大可能导致有效扩散速率的降低，岩浆上升速度和熔体形成的降低，以及近地表水平岩脉的有限传播。我们还发现了微小的、神奇的弱节段，具有低起伏、很少或没有MBA异常，没有离轴表达。我们认为，这些地段要么是来自相邻岩浆强度更强的地段的横向熔体迁移，要么是代表了较小的、离散的地幔上升中心，熔体供应短暂。
Bathymetry, gravity and deep-tow sonar image data are used to define the segmentation of a 400 km long portion of the ultraslow-spreading Knipovich Ridge in the Norwegian–Greenland Sea, Northeast Atlantic Ocean. Discrete volcanic centers marked by large volcanic constructions and accompanying short wavelength mantle Bouguer anomaly (MBA) lows generally resemble those of the Gakkel Ridge and the easternmost Southwest Indian Ridge. These magmatically robust segment centers are regularly spaced about 85–100 km apart along the ridge, and are characterized by accumulated hummocky terrain, high relief, off-axis seamount chains and significant MBA lows. We suggest that these eruptive centers correspond to areas of enhanced magma flux, and that their spacing reflects the geometry of underlying mantle upwelling cells. The large-scale thermal structure of the mantle primarily controls discrete and focused magmatism, and the relatively wide spacing of these segments may reflect cool mantle beneath the ridge. Segment centers along the southern Knipovich Ridge are characterized by lower relief and smaller MBA anomalies than along the northern section of the ridge. This suggests that ridge obliquity is a secondary control on ridge construction on the Knipovich Ridge, as the obliquity changes from 35° to 49° from north to south, respectively, while spreading rate and axial depth remain approximately constant. The increased obliquity may contribute to decreased effective spreading rates, lower upwelling magma velocity and melt formation, and limited horizontal dike propagation near the surface. We also identify small, magmatically weaker segments with low relief, little or no MBA anomaly, and no off-axis expression. We suggest that these segments are either fed by lateral melt migration from adjacent magmatically stronger segments or represent smaller, discrete mantle upwelling centers with short-lived melt supply.