Ferrand Thomas P, Manea Elena F
Institut des Sciences de la Terre d'Orléans, CNRS UMR 7327, Université d'Orléans, Orléans, France.
National Institute for Earth Physics, Calugareni, 12, Măgurele, Ilfov, Romania.
Sci Rep. 2021 May 13;11(1):10315. doi: 10.1038/s41598-021-89601-w.
Vrancea, Eastern Romania, presents a significant intermediate-depth seismicity, between 60 and 170 km depth, i.e. pressures from 2 to 6.5 GPa. A debate has been lasting for decades regarding the nature of the seismic volume, which could correspond to the remnant of a subducted slab of Tethyan lithosphere or a delamination of the Carpathians lithosphere. Here we compile the entire seismicity dataset (≈ 10,000 events with 2 ≤ Mw ≤ 7.9) beneath Vrancea for P > 0.55 GPa (> 20 km) since 1940 and estimate the pressure and temperature associated with each hypocenter. We infer the pressure and temperature, respectively, from a depth-pressure conversion and from the most recent tomography-based thermal model. Pressure-temperature diagrams show to what extent these hypocentral conditions match the thermodynamic stability limits for minerals typical of the uppermost mantle, oceanic crust and lower continental crust. The stability limits of lawsonite, chloritoid, serpentine and talc minerals show particularly good correlations. Overall, the destabilization of both mantle and crustal minerals could participate in explaining the observed seismicity, but mantle minerals appear more likely with more convincing correlations. Most hypocentral conditions match relatively well antigorite dehydration between 2 and 4.5 GPa; at higher pressures, the dehydration of the 10-Å phase provides the best fit. We demonstrate that the Vrancea intermediate-depth seismicity is evidence of the current dehydration of an oceanic slab beneath Romania. Our results are consistent with a recent rollback of a W-dipping oceanic slab, whose current location is explained by limited delamination of the continental Moesian lithosphere between the Tethyan suture zone and Vrancea.
罗马尼亚东部的弗勒恰地区存在显著的中源地震活动，震源深度在60至170千米之间，即压力在2至6.5吉帕之间。关于该地震活动区域的性质，一场争论已经持续了数十年，它可能对应特提斯岩石圈俯冲板块的残余部分，或者是喀尔巴阡山脉岩石圈的拆沉作用。在此，我们汇总了自1940年以来弗勒恰地区下方深度P > 0.55吉帕（> 20千米）范围内的整个地震活动数据集（约10000次震级为2 ≤ Mw ≤ 7.9的地震事件），并估算了每个震源的压力和温度。我们分别从深度 - 压力转换以及最新的基于层析成像的热模型中推断压力和温度。压力 - 温度图展示了这些震源条件与上地幔、洋壳和下地壳典型矿物的热力学稳定极限的匹配程度。硬柱石、硬绿泥石、蛇纹石和滑石矿物的稳定极限显示出特别好的相关性。总体而言，地幔和地壳矿物的失稳都可能有助于解释观测到的地震活动，但地幔矿物似乎更有可能，其相关性更具说服力。大多数震源条件与2至4.5吉帕之间的叶蛇纹石脱水情况相对较好地匹配；在更高压力下，10埃相的脱水提供了最佳拟合。我们证明，弗勒恰地区的中源地震活动是罗马尼亚下方一个大洋板块当前脱水的证据。我们的结果与一个向西倾斜的大洋板块近期的后撤相一致，其当前位置可由特提斯缝合带和弗勒恰之间的莫埃西亚大陆岩石圈的有限拆沉作用来解释。
