Magma-hydrothermal interactions at the Costa Rica Rift from data collected in 1994 and 2015
Magma-hydrothermal interactions at the Costa Rica Rift from data collected in 1994 and 2015
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DOI：
10.1016/j.epsl.2019.115991
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发表时间：
2020-02
影响因子：
5.3
通讯作者：
R. Lowell;L. Zhang;M. Maqueda;D. Banyte;V. Tong;R. Johnston;R. Harris;R. Hobbs;C. Peirce;A. Robinson;K. Kolandaivelu
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文献类型：
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作者：
R. Lowell;L. Zhang;M. Maqueda;D. Banyte;V. Tong;R. Johnston;R. Harris;R. Hobbs;C. Peirce;A. Robinson;K. Kolandaivelu
我们使用同位CTD/透射仪铸件和多通道地震反射调查进行的哥斯达黎加裂谷（CRR），以提供一个更好的了解岩浆热液过程发生在一个中速扩张中心。水柱观测显示，在海底上方约650米处有一个200米厚的羽流头，相当于海脊轴线处热液热输出为200±100兆瓦。假设热液喷口温度为350° C，排放面积为10 4至10 5 m2，这一热量输出意味着排放区内的平均地壳渗透率在2× 10− 14至6× 10− 13 m2之间，导热边界层厚度为1.20 m。在过去的二十年中，维持当前热液热输出所需的岩浆体积应导致跨轴轴向岩浆透镜（AML）宽度在270和1300米之间，这取决于冷却和结晶的量。然而，1994年和2015年获得的地震反射图像显示，AML在两次调查之间从2.4公里到6.0公里明显沿轴增长，同时也表明，截至2015年，AML的表观横向宽度不超过300米，并且以中等扩张速率CRR的岩浆输送可能在数十年的时间尺度上是间歇性的。1994年和2015年在CRR收集的岩浆-热液相互作用的数据表明，热液系统可能已经显着冷却和结晶AML，主要是在横轴方向上，并且该热液系统也可能偶尔打开和关闭。目前的微震活动模式支持这一结论，事件不仅反映了AML的深度和脊轴下的位置，而且还具有随时间变化的焦点。
We use co-located CTD/transmissometry casts and multichannel seismic reflection surveys conducted at the Costa Rica Rift (CRR) to provide a better understanding of magma-hydrothermal processes occurring at an intermediate-rate spreading center. Water column observations reveal an∼ 200 m thick plume head∼ 650 m above the seafloor, which corresponds to a hydrothermal heat output of∼ 200±100 MW at the ridge axis. Assuming a hydrothermal vent temperature of 350° C and a discharge area between 10 4 and 10 5 m 2, this heat output implies a mean crustal permeability within the discharge zone of between 2× 10− 14 and 6× 10− 13 m 2, and a conductive thermal boundary layer thickness of∼ 20 m. The volume of magma required to maintain the current hydrothermal heat output over the past two decades should result in an across-axis axial magma lens (AML) width between 270 and 1300 m, depending on the amount of cooling and crystallization. However, seismic reflection images, acquired in 1994 and 2015, while showing an apparent along-axis growth of the AML from 2.4 to 6.0 km between surveys, also suggest that, as of 2015, the AML has an apparent across-axis width of no more than 300 m, and that magma delivery at the intermediate spreading rate CRR may be episodic on time scales of tens of years. The data on magma-hydrothermal interactions at the CRR collected in 1994 and 2015 suggest that the hydrothermal system may have significantly cooled and crystallized the AML, primarily in the across-axis direction, and that this hydrothermal system may also episodically turn on and off. The current pattern of microseismicity supports this conclusion, with events not only mirroring the AML depth and location beneath the ridge axis, but also having a temporally varying focus.