法国巴黎大学Nirmit Dhabaria和Satish C. Singh合作报道了大西洋赤道地区沿70Ma缓慢扩张地壳段极薄地壳的地震证据。相关论文发表在2024年10月8日出版的《地质学》杂志上。

据研究人员介绍，缓慢扩张海脊的洋壳是岩浆和构造共同作用的结果。通常用于确定地壳结构的地震层析成像研究表明，成熟的缓慢扩张地壳的平均厚度为6.1±0.9km，上下地壳厚度比为2.3。然而，层析成像方法是基于高频近似，只能提供有关大尺度晶体结构的信息。

研究人员利用海底地震仪资料的地震全波形反演，揭示了在赤道地壳大西洋缓慢扩张的大西洋中脊形成的约100km，70Ma的地壳段上，存在着几乎均匀且极薄的地壳(4±0.2km)，地壳上下厚度比为0.74。这一薄的地壳下面被1±0.5km厚的莫霍面过渡带所覆盖，因此地壳和莫霍面过渡带的总厚度为5±0.6km。

研究显示，地壳变薄主要是由于下地壳变薄，很大一部分的地壳是由熔岩流和岩脉侵入形成的。极薄地壳的存在表明，地幔温度至少下降了50°C，赤道地区大西洋上地幔热极小值的范围很广，并且没有受到来自70Ma的Siera Leone地幔柱的影响。

附：英文原文

Title: Seismic evidence of an extremely thin crust along a 70 Ma slow-spreading crustal segment in the equatorial Atlantic Ocean

Author: Nirmit Dhabaria, Satish C. Singh

Issue&Volume: 2024-10-08

Abstract: The oceanic crust at slow-spreading ridges is formed by a combination of magmatic and tectonic processes. Seismic tomographic studies, commonly used to determine crustal structures, indicate that mature slow-spreading crust has an average thickness of 6.1 ± 0.9 km, with a lower to upper crustal thickness ratio of 2.3. However, tomographic methods are based on high-frequency approximations and can only provide information about large-scale crustal structures. Using seismic full-waveform inversion applied to ocean bottom seismometer data, we report the presence of nearly uniform and extremely thin crust (4 ± 0.2 km) with a lower to upper crustal thickness ratio of 0.74 along an ～100 km, 70 Ma crustal segment formed at the slow-spreading Mid-Atlantic Ridge in the equatorial Atlantic Ocean. This thin crust is underlain by a Moho transition zone that is 1 ± 0.5 km thick, resulting in a combined crustal and Moho transition zone thickness of 5 ± 0.6 km. The crustal thinning is primarily due to the thinning of the lower crust, suggesting that a significant part of the crust is formed by lava flows and dike intrusions. The presence of an extremely thin crust indicates a decrease in mantle temperature by at least 50 °C, suggesting a vast extent of the upper mantle thermal minimum in the equatorial Atlantic Ocean, and the absence of influence of the mantle from the Siera Leone mantle plume 70 m.y. ago.

DOI: 10.1130/G52480.1

Source: https://pubs.geoscienceworld.org/gsa/geology/article-abstract/doi/10.1130/G52480.1/649070/Seismic-evidence-of-an-extremely-thin-crust-alongredirectedFrom=fulltext