Vaddineni Venkata A, Singh Satish C, Grevemeyer Ingo, Audhkhasi Pranav, Papenberg Cord
Université de Paris Institut de Physique du Globe de Paris CNRS Paris France.
GEOMAR Helmholtz Centre of Ocean Research Kiel RD4-Marine Geodynamics Kiel Germany.
J Geophys Res Solid Earth. 2021 Jun;126(6):e2020JB021390. doi: 10.1029/2020JB021390. Epub 2021 Jun 22.
We present seismic tomographic results from a unique seismic refraction and wide-angle survey along a 600 km long flow-line corridor of oceanic lithosphere ranging in age from 0 to 27 Ma in the equatorial Atlantic Ocean at 2° 43'S. The velocities in the crust near the ridge axis rapidly increase in the first 6 Myr and then change gradually with age. The upper crust (Layer 2) thickness varies between 2 and 2.4 km with an average thickness of 2.2 km and the crustal thickness varies from 5.6 to 6 km along the profile with an average crustal thickness of 5.8 km. At some locations, we observe negative velocity anomalies (∼-0.3 km/s) in the lower crust which could be either due to chemical heterogeneity in gabbroic rocks and/or the effects of fault related deformation zones leading to an increase in porosities up to 1.6% depending on the pore/crack geometry. The existence of a low velocity anomaly beneath the ridge axis suggests the presence of partial melt (∼1.3%) in the lower crust. Upper mantle velocities also remain low (∼7.8 km/s) from ridge axis up to 5 Ma, indicating a high temperature regime associated with mantle melting zone underneath. These results suggest that the evolution of the crust and uppermost mantle at this location occur in the first 10 Ma of its formation and then remains unchanged. Most of the structures in the older crust and upper mantle are fossilized structures and could provide information about past processes at ocean spreading centers.
我们展示了在赤道大西洋南纬2°43′处，沿着一条600公里长的、年龄从0到27百万年不等的大洋岩石圈流线走廊进行的独特地震折射和广角测量所得到的地震层析成像结果。洋中脊轴附近地壳中的速度在前6百万年迅速增加，然后随年龄逐渐变化。上地壳（第2层）厚度在2至2.4公里之间变化，平均厚度为2.2公里，地壳厚度沿剖面从5.6公里到6公里不等，平均地壳厚度为5.8公里。在某些位置，我们在下地壳中观测到负速度异常（约 -0.3公里/秒），这可能是由于辉长岩中的化学不均匀性和/或与断层相关的变形带的影响，导致孔隙率增加高达1.6%，具体取决于孔隙/裂缝的几何形状。洋中脊轴下方存在低速异常表明下地壳中存在部分熔体（约1.3%）。上地幔速度从洋中脊轴到5百万年也保持较低（约7.8公里/秒），表明其下方与地幔熔融带相关的高温状态。这些结果表明，该位置地壳和最上地幔的演化在其形成的前10百万年发生，然后保持不变。较老地壳和上地幔中的大多数结构都是化石结构，并且可以提供有关过去洋中扩张中心过程的信息。
