The uppermost mantle seismic velocity structure of West Antarctica from Rayleigh wave tomography: Insights into tectonic structure and geothermal heat flow
The uppermost mantle seismic velocity structure of West Antarctica from Rayleigh wave tomography: Insights into tectonic structure and geothermal heat flow
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DOI：
10.1016/j.epsl.2019.06.024
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发表时间：
2019-09
影响因子：
5.3
通讯作者：
J. O’Donnell;G. Stuart;A. Brisbourne;K. Selway;Yingjie Yang;G. Nield;P. Whitehouse;A. Nyblade;D. Wiens;R. Aster;S. Anandakrishnan;A. Huerta;T. Wilson;J. P. Winberry
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作者：
J. O’Donnell;G. Stuart;A. Brisbourne;K. Selway;Yingjie Yang;G. Nield;P. Whitehouse;A. Nyblade;D. Wiens;R. Aster;S. Anandakrishnan;A. Huerta;T. Wilson;J. P. Winberry
我们从2016-2018年英国南极地震网络中提出了一个西南极上地幔到200公里深度的剪切波模型，具有增强的区域分辨率。该模型是从环境噪声（周期8-25秒）和地震数据提取的基本模式瑞利波相速度的组合，通过双平面波分析（周期20-143秒）。我们试图（一）图像和解释构造对西南极洲的构造演化，和（ii）提取信息的地震模型，可以作为边界条件的冰盖和冰川均衡调整建模工作。上地幔低速异常的分布表明，西南极裂谷系（WARS）的现代构造活动主要集中在裂谷边缘之下，且主要局限于上地幔（< 180 km）。在WARS的北方边缘，一个明显的低速异常从玛丽伯德地穹丘下方向东延伸到思韦茨冰川下的松岛湾，但没有延伸到松岛冰川。如果是与羽流有关的热成因，则该异常与内部WARS之间的速度差为1.5%，这意味着温度差为1.25 -200摄氏度。然而，走向的异常平行古太平洋收敛边缘冈瓦纳，所以它可能反映俯冲相关的熔体和挥发物，而不是异常升高的温度，或两者的组合。出于捕虏体分析，我们推测，高速区成像南部的玛丽伯德地圆顶和东部罗斯海海湾可能反映了古代大陆碎片的成分签名。一个明显的低速异常下的南部跨南极山脉（TAM）是一致的岩石圈沉没假说。结合大地电磁研究，主张由厚而稳定的岩石圈对中部TAM进行弯曲支撑，这表明TAM的构造历史存在沿走向变化。位于南部威德尔海裂谷系的高速异常可能反映了与冈瓦纳大陆碎裂有关的大量熔体提取后的地幔岩石圈亏损。从代表西南极洲构造域的一维剪切波速度剖面中提取的岩石圈厚度估计值表明，WARS、玛丽伯德地和瑟斯顿岛地块的平均岩石圈厚度为1.85 km。在埃尔斯沃思山脉，这一距离增加到196公里。地表热流为1.60 mW/m 2，地热为1.60 mW/m 2，最能解释WARS中部和邻近松岛冰川的瑟斯顿岛地块的岩石圈地幔剪切波速度;地热为1.50 mW/m 2，最能解释埃尔斯沃思山脉的速度;地热为1.60 mW/m 2，最能解释南极半岛南部约束较弱的速度剖面。我们强调，这些都是区域平均（数百公里）热流估计地震数据的限制与有限的敏感性上地壳成分。
We present a shear wave model of the West Antarctic upper mantle to∼ 200 km depth with enhanced regional resolution from the 2016-2018 UK Antarctic Seismic Network. The model is constructed from the combination of fundamental mode Rayleigh wave phase velocities extracted from ambient noise (periods 8-25 s) and earthquake data by two-plane wave analysis (periods 20-143 s). We seek to (i) image and interpret structures against the tectonic evolution of West Antarctica, and (ii) extract information from the seismic model that can serve as boundary conditions in ice sheet and glacial isostatic adjustment modelling efforts. The distribution of low velocity anomalies in the uppermost mantle suggests that recent tectonism in the West Antarctic Rift System (WARS) is mainly concentrated beneath the rift margins and largely confined to the uppermost mantle (< 180 km). On the northern margin of the WARS, a pronounced low velocity anomaly extends eastward from beneath the Marie Byrd Land dome toward Pine Island Bay, underlying Thwaites Glacier, but not Pine Island Glacier. If of plume-related thermal origin, the velocity contrast of∼ 5% between this anomaly and the inner WARS translates to a temperature difference of∼ 125-200 C∘. However, the strike of the anomaly parallels the paleo-Pacific convergent margin of Gondwana, so it may reflect subduction-related melt and volatiles rather than anomalously elevated temperatures, or a combination thereof. Motivated by xenolith analyses, we speculate that high velocity zones imaged south of the Marie Byrd Land dome and in the eastern Ross Sea Embayment might reflect the compositional signature of ancient continental fragments. A pronounced low velocity anomaly underlying the southern Transantarctic Mountains (TAM) is consistent with a published lithospheric foundering hypothesis. Taken together with a magnetotelluric study advocating flexural support of the central TAM by thick, stable lithosphere, this points to along-strike variation in the tectonic history of the TAM. A high velocity anomaly located in the southern Weddell Sea Rift System might reflect depleted mantle lithosphere following the extraction of voluminous melt related to Gondwana fragmentation. Lithospheric thickness estimates extracted from 1D shear wave velocity profiles representative of tectonic domains in West Antarctica indicate an average lithospheric thickness of∼ 85 km for the WARS, Marie Byrd Land, and Thurston Island block. This increases to∼ 96 km in the Ellsworth Mountains. A surface heat flow of∼ 60 mW/m 2 and attendant geotherm best explains lithospheric mantle shear wave velocities in the central WARS and in the Thurston Island block adjacent to Pine Island Glacier; a∼ 50 mW/m 2 geotherm best explains the velocities in the Ellsworth Mountains, and a∼ 60 mW/m 2 geotherm best explains a less well-constrained velocity profile on the southern Antarctic Peninsula. We emphasise that these are regional average (many hundreds of km) heat flow estimates constrained by seismic data with limited sensitivity to upper crustal composition.