Crustal structure of the Carpathian Orogen in Romania from receiver functions and ambient noise tomography: how craton collision, subduction and detachment affect the crust
Crustal structure of the Carpathian Orogen in Romania from receiver functions and ambient noise tomography: how craton collision, subduction and detachment affect the crust
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DOI：
10.1093/gji/ggz140
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发表时间：
2019-07
影响因子：
2.8
通讯作者：
L. Petrescu;G. Stuart;D. Tataru;B. Grecu
中科院分区：
文献类型：
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作者：
L. Petrescu;G. Stuart;D. Tataru;B. Grecu
碰撞造山带边缘的结构和过程是复杂的，地壳受俯冲物质、板片断裂和碰撞后岩浆活动影响的程度受到很大限制。喀尔巴阡弧是一个阿尔卑斯造山系统，它涉及到东欧板块的碰撞、俯冲和特提斯洋的闭合。异常的新近纪弧后岩浆活动是在2.9Ma前俯冲结束后发展起来的，上地幔Mw>7级地震与Vrancea带的残余板片活动断裂有关。为了研究地壳和上地幔结构，我们分析了罗马尼亚和摩尔多瓦56个宽带地震台站记录的强震。利用接收函数的相位加权H − κ叠加，我们估计了地壳厚度和Vp/Vs比，这是一个很好的地壳成分判别式。所有台站都采用了这一技术，并假定地壳为单层，底部有不连续面。此外，通过联合反演接收器功能和环境噪声，我们获得剪切波速（Vs）模型到34个台站下方60公里的深度，并提供另一个独立的测量莫霍面深度和明显的地震锐度。在莫霍面呈渐变或壳内不连续性占主导地位的地区，用这两种方法估算的地壳厚度不一致。我们支持这一解释与一系列的合成测试。Vs剖面上，在Vrancea板片之上，存在多个壳内不连续面和莫霍面，高Vp/Vs（>1.83）与岩浆底侵作用相一致。在板片的弧后一侧，岩浆活动渗透的地壳具有低Vp/Vs特征（<1.73），这与长英质成分或水的存在相一致，而没有广泛的部分熔融。在弧后的Transcendian盆地和Apuseni山脉，上地幔具有异常低的Vs（<4 km s-1至60 km深度），地壳主要是长英质和薄的（<35 km），莫霍面可能继承自仰冲的新特提斯蛇绿岩。在弧前一侧，沉积盆地具有低Vs（<2.5 km s-1）和高Vp/Vs（>1.8）的特征，表明流体压力较高。最后，前陆的前寒武纪单元在地震上是不均匀的，莫霍面深度为30-50 km，并在南喀尔巴阡山脉和东南喀尔巴阡山脉下方延伸100 km，这意味着Vrancea板片位于前寒武纪地壳之下。
The structure and processes of collisional orogens at the edges of cratons are complex and the extent to which the crust is affected by subduction of cratonic material, slab break-off and post-collisional magmatism is poorly constrained. The Carpathian arc is an Alpine orogenic system, involving the collision and subduction of the East European Craton and the closure of the Tethys ocean. Unusual Neogene backarc magmatism developed after subduction ended ∼9 Ma ago and upper-mantleMw>7 earthquakes are associated with a relic slab actively breaking-off in the Vrancea Zone. To investigate the crustal and uppermost mantle structure, we analyse teleseismic earthquakes recorded at 56 broad-band seismic stations in Romania and Moldova. Using phase-weightedH− κ stacking of receiver functions, we estimate the bulk crustal thickness andVp/Vsratio, a good discriminant of crustal composition. This technique was used on all stations and assumes a single-layer crust with a discontinuity at its base. Additionally, by jointly inverting receiver functions and ambient noise we obtain shear wavespeed (Vs) models to ∼60 km depth beneath 34 stations and provide another independent measure of the Moho depth and its apparent seismic sharpness. Crustal thickness estimates from the two methods are inconsistent in regions where the Moho is gradational or an intracrustal discontinuity is more dominant. We support this interpretation with a range of synthetic tests. Above the actively detaching Vrancea slab, multiple intracrustal discontinuities and a gradational Moho are identified onVsprofiles, and highVp/Vs(>1.83) are consistent with magmatic underplating. On the backarc side of the slab, magmatism-pervaded crust has lowVp/Vssignature (<1.73), consistent with felsic composition or the presence of water without extensive partial melt. In the backarc Transylvanian Basin and Apuseni Mountains, the upper mantle has anomalously lowVs(<4 km s−1to 60 km depth), the crust is dominantly felsic and thin (<35 km), with a Moho probably inherited from the obducted Neo-Tethys ophiolites. On the forearc side, sedimentary basins have lowVs(<2.5 km s−1) and highVp/Vssignatures (>1.8), indicating a high fluid-pressure regime. Finally, Precambrian units in the foreland are seismically heterogenous, with Moho depths of 30–50 km, and extend ∼100 km beneath the South and Southeast Carpathians, implying that the Vrancea slab underlies Precambrian-aged crust.