Recognition of drilling-induced remanent magnetization by Q-factor analysis: a case study from the KTB-drillholes

摘要

Drilling-induced magnetizations (DIRM) have been detected in the rocks of the KTB (German Continental Deep Drilling Program) by determining the Konigsberger factor (Q-factor), the ratio of remanent to induced magnetization. Specimens from the outer part of the drillcores show significantly enhanced Q-factors (up to 10 times) compared to those from the internal part. Contamination by coating with abrasive material, for example from the drill bit, and grain size variations due to cutting action of the diamond coring system, can be excluded. The DIRM is interpreted to be caused by the magnetization of the core barrel and drill string, which produce higher fields dose to rim than in the interior of the drill core. After removing the DIRM contaminated samples from the database, the Q-factors for the main KTB rock units have mean values of 4.8 for the gneiss units and 1.6 for the metabasite units. The uncontaminated data set fits in the appropriated field of the susceptibility-Q plot of Henkel [J. Appl. Geophys. 32 (1994) 43-53] for metamorphic continental rocks. (C) 2001 Elsevier Science B.V. All rights reserved. [References: 20]