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首页> 外文期刊>Journal of Volcanology and Geothermal Research2012V243-244NOCT,15 >Krysuvik high temperature geothermal area in SW Iceland: Geological setting and 3D inversion of magnetotelluric (MT) resistivity data
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Krysuvik high temperature geothermal area in SW Iceland: Geological setting and 3D inversion of magnetotelluric (MT) resistivity data

机译：冰岛西南部的Krysuvik高温地热区：大地电磁（MT）电阻率数据的地质背景和3D反演

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摘要

The Krysuvik area in SW Iceland is characterized by a 40 km long and around 6-8 km wide fissure swarm and two NE-SW trending tindars complexes. Associated with the fissure swarms are fumarole fields located primarily on parallel postglacial eruptive fissure segments. There are indications that Krysuvik hosts a buried caldera and an intrusion complex in its roots. The geothermal surface manifestations cover an area of around 50-60 km(2) and has potential for future exploitation. Faulting accompanies the ridges and postglacial volcanic fissures, with normal faults and open fissures with a maximum throw of 10 m.A 3D inversion was performed of the static shift corrected off-diagonal impedance tensor elements of 102 MagnetoTelluric (MT) resistivity soundings from the Greater Krysuvik geothermal area. In the inversion, 21 periods were used, evenly distributed from 0.01 to 100 son a logarithmic scale. The robustness of the inversion was tested by using three different initial models: A model compiled from a joint ID inversion of TEM and MT soundings, with a homogeneous Earth of resistivity 100 Omega m and a homogeneous Earth of resistivity 10 Omega. A flat topographic surface was assumed in the 3D inversion. The resulting models were later elevation corrected. The results of the 1D inversion and the 3D inversion are strikingly similar, where the 1D inversion reproduces the main resistivity structures while the 3D inversion shows considerably more details. An analysis of the electrical strike directions based on the vertical magnetic field data is in fairly good agreement with the final resistivity model.The subsurface resistivity structure in Krysuvik has the same main features as other high temperature areas in Iceland and in general where the host rocks are basaltic. Above a shallow conductive cap, a high resistivity zone is seen, reflecting unaltered rock. The conductive cap reflects smectite hydrothermal mineral alteration. Below the low-resistivity cap, a resistive core is found, reflecting chlorite-epidote alteration. Good correlation is observed in the Krysuvik field between the subsurface resistivity structure and the hydrothermal alteration revealed by boreholes cuttings. Parts of the field have cooled down and therefore the resistivity structure indicates alteration mineralogy but not necessarily the present rock temperature. The geothermal up-flow zones are therefore most likely where the hydrothermal alteration and the resistive core reach the highest elevation.The 3D inversion shows an indication of a relatively deep-seated conductive body below the central part of the high temperature area. This body coincides horizontally with the centre of the 2010-2011 inflation source at 4-5 km depth. It has been suggested that the 2007-2016 inflation/deflation periods are linked to gas flux, as no signs of S-wave attenuation have been found. It is therefore unlikely that the deep-seated conductive body resolved by our resistivity models comprises partial melt. The body is probably connected to the heat source of the geothermal field and could be due to emission of gas or dehydration. (C) 2018 Elsevier B.V. All rights reserved.
机译：冰岛西南部的Krysuvik地区的特征是40公里长，约6-8公里宽的裂隙群和两个NE-SW趋势锡达波群。与裂隙群相关的是喷气孔领域，其主要位于平行的冰川后喷发裂隙段。有迹象表明，Krysuvik的根部有一个埋藏的破火山口和一个侵入综合体。地热表面表现物覆盖约50-60 km（2）的面积，并具有未来开发的潜力。断裂伴随着山脊和冰川后火山裂缝，正常断层和开裂裂缝的最大投掷量为10 mA。对来自大克雷苏维克地热的102个磁电（MT）电阻率测深进行了静位移校正的非对角阻抗张量元素的3D反演。区。在反演中，使用了21个周期，从0.01到100个对数刻度均匀分布。通过使用三个不同的初始模型测试了反演的鲁棒性：一个由TEM和MT测深的联合ID反演编译而成的模型，其均匀的电阻率地球为100Ωm，均匀的电阻率地球为10Ω。在3D反演中假定地形平坦。最终对模型进行了高程校正。 1D反演和3D反演的结果非常相似，其中1D反演再现了主要的电阻率结构，而3D反演则显示了更多的细节。根据垂直磁场数据对电击方向的分析与最终电阻率模型非常吻合。Krysuvik的地下电阻率结构具有与冰岛其他高温地区相同的主要特征，并且通常在宿主岩中是玄武岩。在较浅的导电帽上方，可以看到高电阻率区域，反射了未改变的岩石。导电盖反映了蒙脱石热液矿物的变化。在低电阻率上限以下，发现了一个电阻芯，反映了亚氯酸盐-静电石的变化。在Krysuvik场中，地下电阻率结构与井眼钻屑揭示的热液变化之间存在良好的相关性。油田的某些部分已经冷却下来，因此电阻率结构表明矿物学发生了变化，但不一定代表当前的岩石温度。因此，地热向上流动区很可能是水热蚀变和电阻芯达到最高高度的地方.3D反演表明在高温区域的中心部分下方有相对较深的导电体。该机构与2010-2011年通胀源的中心在4-5公里深度处水平重合。由于没有发现S波衰减的迹象，因此有人认为2007-2016年的通货膨胀/通货紧缩时期与气体通量有关。因此，通过我们的电阻率模型解析的深层导电体不太可能包含部分熔体。机体可能与地热场的热源相连，可能是由于气体排放或脱水造成的。 （C）2018 Elsevier B.V.保留所有权利。

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