Velocity structure and radial anisotropy of the lithosphere in southern Madagascar from surface wave dispersion
Velocity structure and radial anisotropy of the lithosphere in southern Madagascar from surface wave dispersion
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表面波色散研究马达加斯加南部岩石圈的速度结构和径向各向异性
DOI：
10.1093/gji/ggaa550
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发表时间：
1944
影响因子：
2.8
通讯作者：
Rümpker
中科院分区：
文献类型：
--
作者：
Rindraharisaona;Tilmann;Dreiling;Priestley;Rümpker
我们研究了马达加斯加南部的上地幔地震结构，并推断了马达加斯加从非洲和印度分裂以及早期裂谷期以来地球动力学事件的印记。采用双站法对远震地震资料进行分析，确定了马达加斯加南部剖面上的瑞利波和洛夫波相速度。对于较短的周期（<20 s），这些数据由先前发表的由环境噪声相关性确定的色散曲线补充。首先，确定了相速度层析模型。第二步，基于层析模型提取的频散曲线反演SV和SH波速的一维模型。由于岩石圈地幔以高速为代表，我们用最强的负速度梯度来识别岩石圈-软流圈边界。最后，根据SV和SH速度模型的差异，推导出径向各向异性（RA）。对岩石圈厚度的另一个限制是接收函数中出现的负转换，这导致在马达加斯加大部分地区的估计值可比较。我们推断马达加斯加南部的岩石圈厚度为110 - 150公里，明显薄于东非的活动带（150 - 200公里），那里的地壳年龄相当，位于冈瓦纳兰，靠近马达加斯加。岩石圈厚度与地质域有关。最薄的岩石圈（约110公里）位于Morondava盆地下方。分裂前的卡鲁失败裂陷，冈瓦纳大陆的裂陷和分裂很可能使那里的岩石圈变薄。元古代地体（Androyen和Anosyen域）的岩石圈厚度为125 ~ 140 km，比坦桑尼亚的莫桑比克带薄约30 km。Ikalamavony域（元古代）和塔那那利佛域西部（太古代）的岩石圈最厚，厚度约为150 km。太古宙东部以下岩石圈厚度减小至~ 130 km。整个剖面下方的岩石圈以正RA为特征。在Morondava盆地下方的最上层地幔中观察到最强的RA（最大值为~ 9%），这是可以理解的，因为该盆地在Karoo和随后的裂谷期暴露于强烈的拉伸中。在元古代（最大值为~ 5%）和太古代（最大值为~ 6%）域以下，各向异性仍然显著为正，这可能是中生代和/或之后岩石圈扩张的结果。在软流圈中，在Morondava沉积盆地东部和元古宙域下方为正RA，表明软流圈为水平流。东部太古宙下方为负RA，提示存在小规模软流圈上升流，与前人研究一致。另外，该地区软流圈相对较高的横波速度表明，负RA可能与东部沿海的r<s:1>地幔柱有关，至少在火山地层之下。
We investigate the upper mantle seismic structure beneath southern Madagascar and infer the imprint of geodynamic events since Madagascar’s break-up from Africa and India and earlier rifting episodes. Rayleigh and Love wave phase velocities along a profile across southern Madagascar were determined by application of the two-station method to teleseismic earthquake data. For shorter periods (<20 s), these data were supplemented by previously published dispersion curves determined from ambient noise correlation. First, tomographic models of the phase velocities were determined. In a second step, 1-D models of SV and SH wave velocities were inverted based on the dispersion curves extracted from the tomographic models. As the lithospheric mantle is represented by high velocities we identify the lithosphere–asthenosphere boundary by the strongest negative velocity gradient. Finally, the radial anisotropy (RA) is derived from the difference between the SV and SH velocity models. An additional constraint on the lithospheric thickness is provided by the presence of a negative conversion seen inSreceiver functions, which results in comparable estimates under most of Madagascar. We infer a lithospheric thickness of 110−150 km beneath southern Madagascar, significantly thinner than beneath the mobile belts in East Africa (150−200 km), where the crust is of comparable age and which were located close to Madagascar in Gondwanaland. The lithospheric thickness is correlated with the geological domains. The thinnest lithosphere (∼110 km) is found beneath the Morondava basin. The pre-breakup Karoo failed rifting, the rifting and breakup of Gondwanaland have likely thinned the lithosphere there. The thickness of the lithosphere in the Proterozoic terranes (Androyen and Anosyen domains) ranges from 125 to 140 km, which is still ∼30 km thinner than in the Mozambique belt in Tanzania. The lithosphere is the thickest beneath Ikalamavony domain (Proterozoic) and the west part of the Antananarivo domain (Archean) with a thickness of ∼150 km. Below the eastern part of Archean domain the lithosphere thickness reduces to ∼130 km. The lithosphere below the entire profile is characterized by positive RA. The strongest RA is observed in the uppermost mantle beneath the Morondava basin (maximum value of ∼9 per cent), which is understandable from the strong stretching that the basin was exposed to during the Karoo and subsequent rifting episode. Anisotropy is still significantly positive below the Proterozoic (maximum value of ∼5 per cent) and Archean (maximum value of ∼6 per cent) domains, which may result from lithospheric extension during the Mesozoic and/or thereafter. In the asthenosphere, a positive RA is observed beneath the eastern part Morondava sedimentary basin and the Proterozoic domain, indicating a horizontal asthenospheric flow pattern. Negative RA is found beneath the Archean in the east, suggesting a small-scale asthenospheric upwelling, consistent with previous studies. Alternatively, the relatively high shear wave velocity in the asthenosphere in this region indicate that the negative RA could be associated to the Réunion mantle plume, at least beneath the volcanic formation, along the eastern coast.
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影响因子：
2.9
作者：
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影响因子：
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作者：
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影响因子：
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作者：
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影响因子：
2.8
作者：
Cristo Ramirez;A. Nyblade;M. Wysession;Martin Pratt;F. Andriampenomanana;T. Rakotondraibe
通讯作者：
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表面波层析成像得出的马达加斯加地壳和上地幔的剪切速度结构
影响因子：
5.3
作者：
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E. Rindraharisaona