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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Crustal structures in the geothermal areas of southern Tuscany (Italy): Insights from the CROP 18 deep seismic reflection lines
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Crustal structures in the geothermal areas of southern Tuscany (Italy): Insights from the CROP 18 deep seismic reflection lines

机译：托斯卡纳南部（意大利）地热区的地壳结构：CROP 18深地震反射线的见解

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Two deep seismic reflection lines, named CROP 18A and 18B and roughly NNW-SSE-oriented, were acquired to investigate the crust between the Larderello and the Mt. Amiata geothermal areas, both located in southern Tuscany. Since the Early-Middle Miocene, southern Tuscany has been affected by extensional tectonics, and since the Pliocene, by widespread magmatism. Presently, extension is demonstrated by NE-dipping normal faults and brittle shear zones which affect the crust down to the brittle/ductile transition. In the Larderello area, these shear zones are seismically evidenced by NE-dipping weak reflections and by the loss of the K-horizon reflectivity, a regional mid-crustal high amplitude reflector, located at the top of the brittle/ductile transition. The CROP 18A and 18B lines were reprocessed down to 10 s TWT, down to the crust/mantle boundary. Their reflectivity results are closely related to the direction of the survey: a clear decrease in reflectivity occurs when the survey plane intersects the crustal shear zones along strike. Nevertheless, both lines display segments with low reflectivity and homogeneous acoustic impedance which indicate intrusive magmatic bodies at different crustal levels. A wide, partially crystallised granitoid may be sited at about 7-8 km depth underneath the Larderello geothermal field. In the lower part of the crust, the CROP 18A and 18B transects show group of bright reflections, mainly related to the occurrence of pressurised fluids and/or lithological differences. The base of the crust is located at about 20 km depth.
机译：采集了两条深地震反射线，分别称为CROP 18A和18B，大致面向NNW-SSE，以研究Larderello和Mt.之间的地壳。 Amiata地热区均位于托斯卡纳南部。自中新世中期以来，托斯卡纳南部一直受到伸展构造的影响，而上新世以来受到广泛岩浆作用的影响。目前，延伸是通过NE浸入正常断层和脆性剪切带来证明的，这些断层会影响地壳直至脆性/延性转变。在拉德雷洛地区，这些剪切带通过NE蘸微弱反射和位于脆性/延性转变顶部的区域性中地壳高振幅反射器K地平线反射率的损失而在地震中得到证明。将CROP 18A和18B线重新处理至10 s TWT，直至地壳/地幔边界。它们的反射率结果与测量方向密切相关：当测量平面沿走向与地壳剪切带相交时，反射率会明显下降。然而，两条线都显示了低反射率和均质声阻抗的线段，表明在不同地壳水平上的侵入岩浆体。宽的部分结晶的花岗岩可能位于Larderello地热田下约7-8公里的深度。在地壳的下部，CROP 18A和18B断面显示了一组明亮的反射，主要与加压流体的发生和/或岩性差异有关。地壳的底部位于约20 km的深度。

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