First Measurements of the Magnetic Field within the Ocean Crust: Deep Sea Drilling Project Legs 68 and 69

Пономарев, В. Н.; Nekhoroshkov, V. L.

doi:10.2973/dsdp.proc.69.109.1983

Cited by 10 publications

(7 citation statements)

References 2 publications

(2 reference statements)

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“…The first borehole magnetic measurements of the Deep Sea Drilling Project were made on Legs 88, 89, and 78B in Holes 501, 504B, 505B, and 395A by a team of scientists from the U.S.S.R. using a three-component fluxgate magnetometer combined with a magnetic susceptibility meter (Ponomarev andNechoroshkov, 1983, 1984). Although these logs represent a first in ocean drilling research, they cannot be analyzed for magnetic declination because the probe lacked a means of orientation independent of the magnetic measurements themselves.…”

Section: Introductionmentioning

confidence: 99%

Interpretation of Magnetic Logs in Basalt, Hole 418A

Bosum¹,

Scott²

1988

Proceedings of the Ocean Drilling Program

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Borehole measurements of the Earth's magnetic field and the magnetic susceptibility of rocks penetrated by Hole 418A were made on Leg 102 with a gyroscope-oriented three-axis borehole magnetometer probe (Bundesanstalt fur Geowissenschaften und Rohstoffe, Federal Republic of Germany) and a magnetic susceptibility probe (U.S. Geological Survey). Measurements made with the two probes were analyzed together to obtain the in-situ magnetic properties of pillow and massive basalts, which compared favorably with laboratory-measured equivalent properties of basement cores recovered from Hole 418A on DSDP Leg 53. The logs provide a continuous record of the magnetic characteristics of basalts penetrated by the borehole, which makes them useful for locating boundaries of lithologic units, for detecting polarity reversals, and for delineating zones with different magnetic inclinations. In addition, estimates of paleomagnetic pole positions interpreted from the Leg 102 borehole magnetic data compare favorably with Apparent Polar Wander Paths from shore-based paleomagnetic studies of oriented cores.

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Section: Introductionmentioning

confidence: 99%

Interpretation of Magnetic Logs in Basalt, Hole 418A

Bosum¹,

Scott²

1988

Proceedings of the Ocean Drilling Program

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“…Before Leg 134 magnetic logging experiments were conducted during DSDP and ODP legs only for volcanic units characterized by strong magnetic anomalies. The first experiments were conducted on DSDP Legs 68 and 69 by Ponomarev and Nechoroshkov (1983) and later on DSDP Leg 78 (Ponomarev and Nechoroshkov, 1984). A gyroscope-oriented three-axis borehole magnetometer and a susceptibility tool were used in mid-Cretaceous basalts at Hole 418 A (ODP Leg 102; Bosum and Scott, 1988).…”

Section: Introductionmentioning

confidence: 99%

Magnetic Logging and In-Situ Magnetostratigraphy: A Field Test

Roperch¹,

Barthés²,

Pocachard³

et al. 1994

Proceedings of the Ocean Drilling Program

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During Ocean Drilling Program Leg 134 (Vanuatu), geological high sensitivity magnetic tools (GHMT) developed by CEA-LETI and TOTAL were used at two drill sites. GHMT combine two sensors, a proton magnetometer for total magnetic field measurements with an operational accuracy of 0.1 nanoteslas (nT), and a highly sensitive induction tool to measure the magnetic susceptibility with an operational accuracy of a few I0" 6 S1 units.Hole 829 A was drilled through an accretionary prism and the downhole measurements of susceptibility correlate well with other well-log physical properties. Sharp susceptibility contrasts between chalk and volcanic silt sediment provide complementary data that help define the lithostratigraphic units.At Hole 83 IB magnetic susceptibility and total field measurements were performed through a 700-m reef carbonate sequence of a guyot deposited on top of an andesitic volcano. The downhole magnetic susceptibility is very low and the amplitude of peak-to-peak anomalies is less than a few 10~5 S1 units. Based on the repeatability of the measurements, the accuracy of the magnetic logging measurements was demonstrated to be excellent. Total magnetic field data at Hole 83IB reveal low magnetic anomalies of 0.5 to 5 nT and the measurement of a complete repeat section indicates an accuracy of 0.1 to 0.2 nT. Due to the inclination of the earth's magnetic field in this area (~-40°) and the very low magnetic susceptibility of the carbonate, the contribution of the induced magnetization to the total field measured in the hole is negligible. Unfortunately, because the core recovery was extremely poor (<5%) no detailed comparison between the core measurements and the downhole magnetic data could be made. Most samples have a diamagnetic susceptibility and very low intensity of remanent magnetization (< I0" 4 A/m), but a few samples have a stable remanent magnetization up to 0.005 A/m. These variations of the intensity of the remanent magnetization suggest a very heterogeneous distribution of the magnetization in the carbonate sequence that could explain the magnetic field anomalies measured in these weakly magnetized rocks.

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“…Magnetic logging was attempted previously on DSDP Legs 68, 69, and 78B (Holes 501, 504B, 505B, and 395A) by a team of scientists from the U.S.S.R., using a three-component flux gate magnetometer without orientation sensors, combined with a magnetic susceptibility meter (Ponomarev andNechoroshkov, 1983, 1984). Because the holes were nearly vertical, the magne tometer probe was not stabilized by contact with the borehole wall.…”

Section: Introductionmentioning

confidence: 99%