Quasi‐continuous depth profiles of rock magnetization from magnetic logs in the HSDP‐2 borehole, Island of Hawaii
Quasi‐continuous depth profiles of rock magnetization from magnetic logs in the HSDP‐2 borehole, Island of Hawaii
复制标题
夏威夷岛 HSDP-2 钻孔中磁性测井的岩石磁化强度准连续深度剖面
DOI：
10.1029/2002gc000330
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发表时间：
2003
期刊：
影响因子：
3.7
通讯作者：
M. Leven
中科院分区：
文献类型：
--
作者：
E. Steveling;J. Stoll;M. Leven
在夏威夷科学钻探项目2 （HSDP‐2）中，在600 ~ 1800 m之间获得了准连续磁测井，对应的时间间隔约为350 ~ 480 ka。采用三轴井眼磁强计测量水平和垂直磁场。在井下和井下进行了测量，两者之间具有良好的相关性。首先，对日志进行低通滤波器传递函数的校正，然后对测井深度进行校正。为了从磁性成分中计算岩石的磁化强度，我们对穿透的岩石使用了多盘圆柱形模型。盘厚与测井采样率对应0.1 m。HSDP‐2井的磁井测井证实了以下情况：块状熔岩流可以与透明质岩流区分开来，使我们能够补充岩性，特别是在岩心采收率较低的深度层段。磁测井得到的岩石磁化倾斜度与HSDP‐2井岩心样品的测量结果吻合较好。这同样适用于测井的磁化强度，即感应磁化和剩余磁化的总和，以及岩心样品的剩余磁化的实验室测定。我们观察到当地现今的地心轴向偶极子（GAD）倾角为35.6°，与平均测井倾角22.7°之间存在明显差异。此外，还观察到系统的倾角随深度而减小。通过向下移动HSDP‐1 100 m的深度，可以使HSDP‐2的测井和岩心倾角与HSDP‐1先导井的岩心倾角一致。两个钻孔之间的倾角数据的相关性和HSDP - 1已知的年龄-深度关系被用来重新检验夏普等人的莫纳克亚山的“年龄-深度”模型曲线（手稿准备，2003年）。我们初步确定了两个随地磁场偏移而记录的倾角极小值，即360-370 ka的“Levantine”和400-420 ka的“Unknown”。
A quasi‐continuous magnetic log has been obtained in the Hawaii Scientific Drilling Project 2 (HSDP‐2) between 600 m and 1800 m, which corresponds to a time interval of approximately 350 ka to 480 ka. A tri‐axial borehole magnetometer was employed to measure the horizontal and vertical magnetic fields. Measurements were taken in downhole and uphole runs, with a good correlation between the two. In a first step the logs were corrected for the transfer function of the employed low‐pass filter and then for the logging depths. To calculate rock magnetizations from magnetic components, we used a multidisk cylindrical model for the penetrated rocks. The disk thickness corresponds with 0.1 m to the logging sampling rate. Magnetic borehole logging in the HSDP‐2 hole has established the following: Massive lava flows can be distinguished from those with prevailing hyaloclastites and enables us to supplement the lithology, especially in depth intervals with poor core recovery. The inclinations of rock magnetization derived from the magnetic log agree well with those measured in core samples from HSDP‐2 hole. The same applies to magnitudes of magnetizations from logging, as the sum of induced and remanent magnetizations, with laboratory determinations of the remanent magnetizations of core samples. We observe a distinct discrepancy between the local present‐day geocentric axial dipole (GAD) inclination of 35.6° and the mean logging inclination of 22.7°. Furthermore, a systematic inclination decrease with depth is observed. Logging and core inclinations in HSDP‐2 can be brought into agreement with core inclinations in the HSDP‐1 pilot hole by shifting depths of HSDP‐1 100 m downward. The correlation of inclination data between the two boreholes and the known age‐depth relation of HSDP‐1 is used to reexamine the “age versus depth” model curve for Mauna Kea of Sharp et al. (manuscript in preparation, 2003). We identify tentatively two logged inclination minima with excursion of the geomagnetic field in Brunhes, namely, “Levantine” at 360–370 ka and “Unknown” at 400–420 ka.