Why is the remanent magnetic intensity of Cretaceous MORB so much higher than that of mid to late Cenozoic MORB?

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doi: 10.1130/GES00024.1
Author(s): Wang, Daming; Van der Voo, Rob; Peacor, Donald R.
Author Affiliation(s): Primary:
University of Michigan, Department of Geological Sciences, Ann Arbor, MI, United States
Volume Title: Geosphere (Boulder, CO)
Source: Geosphere (Boulder, CO), 1(3), p.138-146. Publisher: Geological Society of America, Boulder, CO, United States. ISSN: 1553-040X
Note: In English. 26 refs.; illus., incl. 4 tables, sketch map
Summary: The fact that the natural remanent magnetization (NRM) intensity of mid-oceanic-ridge basalt (MORB) samples shows systematic variations as a function of age has long been recognized: maximum as well as average intensities are generally high for very young samples, falling off rather rapidly to less than half the recent values in samples between 10 and 30 Ma, whereupon they slowly rise in the early Tertiary and Cretaceous to values that approach those of the very young samples. NRM intensities measured in this study follow the same trends as those observed in previous publications. In this study, we take a statistical approach and examine whether this pattern can be explained by variations in one or more of all previously proposed mechanisms: chemical composition of the magnetic minerals, abundance of these magnetization carriers, vectorial superposition of parallel or antiparallel components of magnetization, magnetic grain or domain size patterns, low-temperature oxidation to titanomaghemite, or geomagnetic field behavior. We find that the samples do not show any compositional, petrological, rock-magnetic, or paleomagnetic patterns that can explain the trends. Geomagnetic field intensity is the only effect that cannot be directly tested on the same samples, but it shows a similar pattern as our measured NRM intensities. We therefore conclude that the geomagnetic field strength was, on-average, significantly greater during the Cretaceous than during the Oligocene and Miocene.
Year of Publication: 2005
Research Program: DSDP Deep Sea Drilling Project
ODP Ocean Drilling Program
Key Words: 18 Geophysics, Solid-Earth; Basalts; Cenozoic; Cores; Cretaceous; Curie point; Deep Sea Drilling Project; Electron probe data; Global; Grain size; Igneous rocks; Magnetic field; Magnetic intensity; Magnetic properties; Magnetization; Mesozoic; Mid-ocean ridge basalts; Middle Cenozoic; Natural remanent magnetization; Ocean Drilling Program; Oxidation; Oxides; Paleomagnetism; Remanent magnetization; Temporal distribution; Titanomagnetite; Upper Cenozoic; Variations; Volcanic rocks
Record ID: 2006011268
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States

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