Unraveling Precambrian cratonic roots beneath South America: A contribution from surface wave tomography

IF 2.7 3区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS
André V.S. Nascimento , George S. França , Carlos A.M. Chaves , Giuliano S. Marotta , Marcelo Assumpção
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Abstract

We examine some aspects of the tectonic evolution of Precambrian cratonic roots beneath South America based on lithospheric distribution of shear-wave velocities. We derive our model by inverting 26,984 fundamental mode Rayleigh wave group velocity dispersion curves, at periods of 9–180 s. We first regionalize our measurements and then invert the result for a 3D S-wave velocity model extending to 200 km depth. Fast velocities beneath the Amazonian and São Francisco cratons, and beneath buried cratonic units in the Parnaíba and Paraná basins, are long wavelength features consistent with previous tomography studies. For the Amazonian craton at 150 km depth, we find an increase of velocities with province age, except for the Maroni-Itacaiúnas province, where we hypothesize that K'Mudku intraplate tectono-thermal events at the middle-late Mesoproterozoic and emplacement of a large igneous province following the breakup of Pangea could have altered at least partially its lithosphere. Our results are consistent with a São Francisco paleocontinent whose borders extend beyond the surface limits of the present São Francisco craton into the neighboring Araçuaí and Brasília belts. Based on slow shear-wave velocities in the upper mantle beneath the Borborema province, consistent with lithospheric thinning, we argue that a possible cratonic root of the São Francisco Paleocontinent beneath this province has likely been eroded away. This analysis is further corroborated by tectonic events that led to the alteration of the Borborema mantle, including hydration in the Paleoproterozoic, rifting in the early-middle Tonian, reworking during Neoproterozoic Brasiliano events, and lithospheric stretching during the breakup of Pangea. Finally, we also image a fast shear-wave velocity structure in the region of the Río de la Plata craton, consistent with magnetotelluric studies.

揭开南美洲地下前寒武纪板块构造的根源:面波断层扫描的贡献
我们根据岩石圈的剪切波速度分布,研究了南美洲地下前寒武纪板块构造演化的某些方面。我们通过反演 26,984 条周期为 9-180 秒的基模雷利波群速度频散曲线得出了我们的模型。我们首先将测量结果区域化,然后将结果反演为延伸至 200 千米深度的三维 S 波速度模型。亚马孙和圣弗朗西斯科火山口下的快速速度,以及帕尔奈瓦和巴拉那盆地埋藏的火山口单元下的快速速度,都是长波长特征,与以前的层析成像研究结果一致。对于深度为 150 千米的亚马孙环形山,我们发现速度随岩层年龄的增加而增加,但马罗尼-伊塔卡尤纳斯岩层除外,我们假设 K'Mudku 板块内构造热事件发生在中新生代中晚期,以及潘加断裂后一个大型火成岩岩层的形成可能至少部分改变了其岩石圈。我们的研究结果与圣弗朗西斯科古大陆相吻合,其边界超出了目前圣弗朗西斯科克拉通的地表范围,延伸到了邻近的阿拉苏阿伊带和巴西利亚带。根据博博雷马省下方上地幔中缓慢的剪切波速度(与岩石圈减薄一致),我们认为该省下方圣弗朗西斯科古陆可能的板块根部很可能已被侵蚀殆尽。导致博博雷马地幔蚀变的构造事件进一步证实了这一分析,这些事件包括古新生代的水合作用、早中托尼安时期的断裂、新元古代巴西里亚诺事件期间的再加工以及潘加断裂期间的岩石圈拉伸。最后,我们还绘制了拉普拉塔河陨石坑地区的快速剪切波速度结构图,这与磁电研究结果一致。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Tectonophysics
Tectonophysics 地学-地球化学与地球物理
CiteScore
4.90
自引率
6.90%
发文量
300
审稿时长
6 months
期刊介绍: The prime focus of Tectonophysics will be high-impact original research and reviews in the fields of kinematics, structure, composition, and dynamics of the solid arth at all scales. Tectonophysics particularly encourages submission of papers based on the integration of a multitude of geophysical, geological, geochemical, geodynamic, and geotectonic methods
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