Chemical remanent magnetization in oceanic sheeted dikes

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doi: 10.1029/96GL00771
Author(s): Worm, Horst-Ulrich; Bach, Wolfgang
Author Affiliation(s): Primary:
Universität Göttingen, Institut für Geophysik, Goettingen, Federal Republic of Germany
GeoForschungsZentrum, Federal Republic of Germany
Volume Title: Geophysical Research Letters
Source: Geophysical Research Letters, 23(10), p.1123-1126. Publisher: American Geophysical Union, Washington, DC, United States. ISSN: 0094-8276 CODEN: GPRLAJ
Note: In English. 29 refs.; illus., incl. 1 table, 2 plates
Summary: Marine lineated magnetic anomalies often exhibit anomalous skewness that indicates non-vertical boundaries between normally and reversely magnetized crust. The acquisition of secondary magnetization components well after formation of the crust has been suspected as one possible cause for anomalous skewness. A petrographic and rock magnetic study on sheeted dikes recovered from the lower part of the deepest drill hole in the oceanic crust, ODP (Ocean Drilling Program) Hole 504B, demonstrates that these rocks carry a secondary chemical remanent magnetization (CRM) and not a thermoremanent magnetization (TRM). Primary titanomagnetites have mostly been altered to non-magnetic phases while the remanent magnetization resides in secondary magnetite that formed below its Curie temperature (∼600°C at ambient pressure) mainly by the alteration of olivine. The natural remanent magnetization (NRM) has been compared with laboratory anhysteretic remanent magnetization (ARM) and TRM. The intensities relate NRM < ARM < TRM, each by a factor of ≈ two. Because previous studies have shown that CRMs are much lower in intensity than TRMs and because of the common presence of secondary magnetite we conclude that the NRMs of the lower Hole 504B dikes are CRMs. The dikes exhibit the same reversed magnetization as the overlying extrusive basalts, and, thus, the timing of CRM acquisition is most likely confined to the time span between the crustal age of Hole 504B and the next younger field reversal, i.e. 0.25 m.y. after emplacement. Copyright 1996 by the American Geophysical Union.
Year of Publication: 1996
Research Program: DSDP Deep Sea Drilling Project
IPOD International Phase of Ocean Drilling
ODP Ocean Drilling Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Cenozoic; Chemical remanent magnetization; Crust; DSDP Site 504; Deep Sea Drilling Project; Dikes; East Pacific; Equatorial Pacific; Hydrothermal alteration; IPOD; Intrusions; Leg 111; Leg 137; Leg 140; Leg 148; Leg 69; Leg 70; Leg 83; Leg 92; Magnetite; Magnetization; Metasomatism; Miocene; Natural remanent magnetization; Neogene; Nesosilicates; North Pacific; Northeast Pacific; Ocean Drilling Program; Oceanic crust; Olivine; Olivine group; Orthosilicates; Oxides; Pacific Ocean; Paleomagnetism; Remanent magnetization; Reversals; Secondary magnetization; Sheeted dikes; Silicates; Tertiary; Titanomagnetite; Upper Miocene
Coordinates: N011335 N011338 W0834348 W0834357
Record ID: 1996063771
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