Three‐dimensional interpretation of the KTB gravity and magnetic anomalies
Three‐dimensional interpretation of the KTB gravity and magnetic anomalies
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DOI：
10.1029/96jb03407
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发表时间：
1997-08
影响因子：
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通讯作者：
W. Bosum;U. Casten;F. C. Fieberg;I. Heyde;H. Soffel
中科院分区：
文献类型：
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作者：
W. Bosum;U. Casten;F. C. Fieberg;I. Heyde;H. Soffel
通过将近距离地面重力测量与高分辨率直升机航磁测量以及钻孔重力和磁力计测量相结合，可以对KTB钻井现场的异常进行详细的三维（3-D）建模。这些模型可以受到来自三维地震勘探的新证据以及来自岩心和岩屑的构造地质和岩石物理数据的约束。重力正异常的震源体为高密度变基性岩。布格异常的垂向导数并不像所有地区的航磁异常，表明部分变基性岩或多或少地被侵蚀。令人惊讶的是，磁黄铁矿是深度约300米以下的主要磁性矿物，这证实了大陆结晶基底岩石中其他深钻孔的观察结果。磁铁矿主要产于360-520 m和7300-7900 m深度段。较低的时间间隔导致60 nT/km的地磁场垂直梯度异常。钻孔中约3000米处的强磁性矿物的出现与岩性有关，而在更深的部分，它与化学过程（还原/氧化）活跃的裂缝和断层带更相关。
A combination of a closely spaced surface gravity survey with a high-resolution helicopter aeromagnetic survey as well as borehole gravity and magnetometer measurements allowed a detailed three-dimensional (3-D) modeling of the anomalies at the KTB drill site. The models could be constrained by new evidence from a 3-D seismic survey and by structural geology and petrophysical data from drill cores and cuttings. The source body for the positive gravity anomaly consist of high-density metabasite. The vertical derivative of the Bouguer anomaly does not resemble the aeromagnetic anomaly in all areas, indicating that parts of the metabasites are more or less nonmagnetic. Surprisingly and confirming the observation in other deep drill holes into continental crystalline basement rocks, pyrrhotite is the dominant magnetic mineral below a depth of about 300 m. Magnetite mainly occurs in the depth intervals 360–520 m and 7300–7900 m. The lower interval causes the anomalous vertical gradient of 60 nT/km for the geomagnetic field. The occurrence of strongly magnetic minerals in the borehole down to about 3000 m correlates with the lithology, while in the deeper parts it is more related to fissures and fault zones where chemical processes (reduction/oxidation) are active.