Lithospheric Structure and Tectonic Processes Constrained by Microearthquake Activity at the Central Ultraslow‐Spreading Southwest Indian Ridge (49.2° to 50.8°E)
Lithospheric Structure and Tectonic Processes Constrained by Microearthquake Activity at the Central Ultraslow‐Spreading Southwest Indian Ridge (49.2° to 50.8°E)
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DOI：
10.1029/2017jb015367
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发表时间：
2018-08
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通讯作者：
Zhiteng Yu;Jiabiao Li;X. Niu;N. Rawlinson;A. Ruan;Wei Wang;Hao Hu;Xiaodong Wei;Jie Zhang;Yuyang Liang
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作者：
Zhiteng Yu;Jiabiao Li;X. Niu;N. Rawlinson;A. Ruan;Wei Wang;Hao Hu;Xiaodong Wei;Jie Zhang;Yuyang Liang
在超低速扩张脊之下，海洋岩石圈仍然知之甚少。利用海底地震仪临时阵列的记录，我们在这里报告了对超低速扩张的西南印度洋脊（49.2°至50.8°E）的两个部分（27和28）进行的为期约17天的微地震研究。共记录了214个可定位的微震;地震活动似乎集中在第28段的西中谷和邻近的非转换不连续面内。地震的最大深度在海底以下约20 km，主要发生在地幔中，这意味着岩石圈是冷而厚的。段28下方相对均匀的脆性/韧性边界表明，在该区域没有集中熔融。大多数地震位于莫霍界面以下，在28段和邻近的非转换不连续面下方存在5 km厚的抗震带。在龙旗热液喷口区沿着段28，拆离断层的存在已被推断从地貌特征和地震层析。我们的地震活动数据表明，这个拆离断层深深地穿透到地幔中，有一个陡倾角（~65°）的界面，它似乎在上地壳中旋转到一个较低的角度，有~55°的翻转。在岩浆段27下方有一个虚拟的地震空区，这可能与扩张中心下方的轴向岩浆房和集中熔融有关;在这种情况下，增加的岩浆供应产生了一个广泛的高温环境，这抑制了地震的发生。
Beneath ultraslow‐spreading ridges, the oceanic lithosphere remains poorly understood. Using recordings from a temporary array of ocean bottom seismometers, we here report an ~17‐days‐long microearthquake study on two segments (27 and 28) of the ultraslow‐spreading Southwest Indian Ridge (49.2° to 50.8°E). A total of 214 locatable microearthquakes are recorded; seismic activity appears to be concentrated within the west median valley at Segment 28 and adjacent nontransform discontinuities. Earthquakes reach a maximum depth of ~20 km beneath the seafloor, and they mainly occur in the mantle, implying a cold and thick brittle lithosphere. The relatively uniform brittle/ductile boundary beneath Segment 28 suggests that there is no focused melting in this region. The majority of earthquakes is located below the Moho interface, and a 5‐km‐thick aseismic zone is present beneath Segment 28 and adjacent nontransform discontinuities. At the Dragon Flag hydrothermal vent field along Segment 28, the presence of a detachment fault has been inferred from geomorphic features and seismic tomography. Our seismicity data show that this detachment fault deeply penetrates into the mantle with a steeply dipping (~65°) interface, and it appears to rotate to a lower angle in the upper crust, with ~55° of rollover. There is a virtual seismic gap beneath magmatic Segment 27, which may be connected to the presence of an axial magma chamber beneath the spreading center and focused melting; in this scenario, the increased magma supply produces a broad, elevated temperature environment, which suppresses earthquake generation.