Detrital remanent magnetization of single-crystal silicates with magnetic inclusions: constraints from deposition experiments

Abstract

SUMMARY Quasi-linear field-dependence of remanence provides the foundation for sedimentary relative palaeointensity studies that have been widely used to understand past geomagnetic field behaviour and to date sedimentary sequences. Flocculation models are often called upon to explain this field dependence and the lower palaeomagnetic recording efficiency of sediments. Several recent studies have demonstrated that magnetic-mineral inclusions embedded within larger non-magnetic host silicates are abundant in sedimentary records, and that they can potentially provide another simple explanation for the quasi-linear field dependence. In order to understand how magnetic inclusion-rich detrital particles acquire sedimentary remanence, we carried out depositional remanent magnetization (DRM) experiments on controlled magnetic inclusion-bearing silicate particles (10–50 μm in size) prepared from gabbro and mid-ocean ridge basalt samples. Deposition experiments confirm that the studied large silicate host particles with magnetic mineral inclusions can acquire a DRM with accurate recording of declination. We observe a silicate size-dependent inclination shallowing, whereby larger silicate grains exhibit less inclination shallowing. The studied sized silicate samples do not have distinct populations of spherical or platy particles, so the observed size-dependence inclination shallowing could be explained by a ‘rolling ball’ model whereby larger silicate particles rotate less after depositional settling. We also observe non-linear field-dependent DRM acquisition in Earth-like magnetic fields with DRM behaviour depending strongly on silicate particle size, which could be explained by variable magnetic moments and silicate sizes. Our results provide direct evidence for a potentially widespread mechanism that could contribute to the observed variable recording efficiency and inclination shallowing of sedimentary remanences.

Quantifying Contributions of Magnetic Inclusions Within Silicates to Marine Sediments: A Dissolution Approach to Isolating Volcanic Signals for Improved Paleoenvironmental Reconstruction

“…This implies that magnetic inclusions in marine sediments may represent one of the magnetic components of volcanic material. The morphology and distribution of magnetic inclusions within silicates also support this inference, which shows similar feature to those in gabber and mid‐ocean ridge basalts (Chang et al., 2021). Although, there are ion substitutions in the magnetic inclusions, a remarkable Verwey transition was observed.…”

“…Although noninclusion silicates may also show hole structures in natural and laboratory environments (e.g., Gerald & Harrison, 1993), these silicates could be magnetically extracted from residues, reflecting that there are magnetic inclusions in their interior. These hole structures were likely or at least fractionally occupied by magnetic particles before dissolution (Chang et al., 2021). In addition, TEM images show abundant opaque grains, where strong Si and O, as well as weak Fe signals, were detected by EDS (Figures 9d–9f) reflecting that magnetic inclusions were preserved within silicates upon dissolution.…”

“…Instead, chemical digestion techniques have been applied to characterize silicate‐hosted magnetic inclusions in marine sediments (Blatt et al., 1982; Stevens, 1991); however, these studies are mainly limited to quartz and feldspars (Usui et al., 2018). Most recently, hydrochloric acid (HCl) has been used to extract magnetic inclusions within silicates from gabbro and mid‐ocean ridge basalt samples (Chang et al., 2021), which provides a reference for obtaining silicate hosted magnetic inclusions from marine sediments.…”

Seafloor Magnetism Under Hydrothermal Alteration: Insights From Magnetomineralogy and Magnetic Properties of the Southwest Indian Ridge Basalts

“…Nano‐scale titanomagnetites generally have high and wide coercivity distributions, but their signals are often blanketed by micron‐scale titanomagnetites in MORBs. This was confirmed by chemically extracted nano‐scale titanomagnetites prepared for deposition experiments: coercivity distribution expands toward high fields after dissolving the micron‐scale titanomagnetites by hydrochloric acid (Chang et al., 2021).…”

Understanding the Role of Biogenic Magnetite in Geomagnetic Paleointensity Recording: Insights From Ontong Java Plateau Sediments

“…Silicate‐hosted magnetic‐mineral inclusions are another candidate for preserving paleomagnetic signals in sediments (Chang et al., 2021; Chang, Roberts, et al., 2016; Zhang et al., 2018). Host silicate minerals can protect magnetic‐mineral inclusions from iron‐ and sulfate‐reducing diagenesis, and the inclusions commonly occur as fine particles.…”