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首页> 外文期刊>Geochemical Journal >Tectonics and mechanism of a spreading ridge subduction at the Chile Triple Junction based on new marine geophysical data
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Tectonics and mechanism of a spreading ridge subduction at the Chile Triple Junction based on new marine geophysical data

机译：基于新的海洋地球物理数据的智利三结交界处的扩展构造和伸展脊俯冲的机制

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摘要

The Chile Triple Junction (CTJ), an RTT-type triple junction located at 46° 13' S, 75°48' W off the western coast of Chile, is characterized by the subducting Chile Ridge, which is the constructive plate boundary that generates both the Nazca Plate and the Antarctic Plate. The ridge subduction mechanism and the regional tectonics around the CTJ were investigated primarily using marine geophysical data (topography, gravity, geomagnetic field and single-channel seismics) collected during the SORA2009 cruise (Cruise ID = MR08-06) by R/V MIRAI together with other cruise data from the National Geophysical Data Center. The segment of the ridge axis just before the subduction around the CTJ is associated with an axial deep covered with thick sediment unlike that seen in typical ridge crests. The profiles of both topography and the free air anomaly around the CTJ show quite different patterns from those of ordinary subduction zones. However, topographic features typical of a slow-spreading type ridge, including a median valley and both flanks, remain in the seaward side of the trench. Even after the subduction of the eastern flank, the topographic features of the western flank remain. A slight Outer Rise and an Outer Gravity High, which are common in the western Pacific area, were observed in an area far away from the CTJ on both Nazca and Antarctic plate sides. The geomagnetic anomaly pattern around the Chile Ridge near the CTJ shows that the estimated spreading rate decreases gradually towards the ridge crest. This suggests that volcanic activity diminishes gradually towards the subducting ridge axis. The lithosphere under the Chile Ridge might have amalgamated with the surrounding oceanic lithosphere due to heat loss after the cessation of volcanic activity. The oceanic lithosphere towards the trench also thickens rapidly due to heat loss. Consequently, shallow-angle subduction of the youngest and most immature oceanic plate occurs smoothly via slab-pull force without any resistance along the interface between the South American continental plates.
机译：智利三结（CTJ）是RTT型三结，位于智利西海岸外46°13'S，西经75°48'W，其特征是俯冲智利海岭，这是构造性板块边界，产生纳斯卡板块和南极板块。 R / V MIRAI主要使用SORA2009航行期间（巡航ID = MR08-06）收集的海洋地球物理数据（地形，重力，地磁场和单通道地震）研究了CTJ周围的脊俯冲机制和区域构造。以及来自国家地球物理数据中心的其他巡航数据。与典型的山脊峰不同，刚好在CTJ俯冲之前的山脊轴段与轴向深处覆盖着厚厚的沉积物。 CTJ周围的地形和自由空气异常的剖面显示出与普通俯冲带完全不同的模式。但是，典型的缓慢扩展型山脊地形特征（包括中间谷和两个侧面）仍保留在海沟的海侧。即使在俯冲东侧后，西侧的地形特征仍然存在。在纳斯卡和南极板块两侧远离CTJ的区域中都观察到了西太平洋地区常见的轻微外上升和外重力高。靠近CTJ的智利山脊周围的地磁异常模式表明，估计的扩散速率向山脊逐渐减小。这表明火山活动向俯冲岭轴线逐渐减小。火山活动停止后，由于热量散失，智利山脊下的岩石圈可能已与周围的海洋岩石圈合并。由于热量损失，通往海沟的岩石圈也迅速增厚。因此，最年轻和最不成熟的洋洋板的浅角俯冲通过板拉力顺利进行，而南美大陆板之间的界面没有任何阻力。

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