Hydrothermal alteration at high-temperature vents near mid-ocean ridge is thought to produce pervasive magnetization lows on basaltic ocean crust, but the detailed alteration process is insufficiently documented. Here, we performed microscopic and magnetic analyses on a large set of hydrothermal-related basaltic samples from the Southwest Indian Ridge. Fresh basalts were chloritized and brecciated during hydrothermal alteration, where titanomagnetite nanoparticle clusters hosted in interstitial glasses were dissolved in the first order, followed by large micron-scale dendritic particles. Natural remanent magnetization was reduced from 10 0 -10 1 A/m for fresh basalts to 10 −3 A/m for fully altered basalts. Hydrothermal deposits acquired a chemical remanent magnetization of 10 −2 A/m. Our results link direct magneto-mineralogical observations to geophysical interpretations, which is important in understanding seafloor hydrothermal circulation and mid-ocean ridge geodynamics.Plain Language Summary Seafloor hydrothermal vents, also known as black chimneys, produce valuable mineral resources through fluid-rock reactions beneath the seafloor-a process called hydrothermal alteration. On basaltic ocean crust, hydrothermally altered regions are generally found to be less magnetic, which provides a way to detect seafloor hydrothermal vents. To understand the cause of this phenomenon, we studied how fluid-rock reactions modify magnetic minerals on basaltic ocean crust in the Southwest Indian Ridge. We have established a detailed alteration pathway that the primary magnetic minerals were progressively replaced by nonmagnetic minerals with increasing alteration degree and the strongly magnetized nanoparticles were preferentially consumed at the very beginning of the reaction. This finding directly contributes to magnetic surveying the seafloor hydrothermal vents and establishes the value of rock magnetic proxies for quantifying the alteration degree to trace fluid-rock reactions.
Titanomagnetites in mid‐ocean ridge basalt (MORB) experience variable post crystallization alterations associated with seafloor tectonic and environmental processes. Compared to low‐temperature oxidation, seafloor hydrothermal alteration is thought to be more destructive but its magnetic aftermaths are insufficiently documented. Here we present comprehensive rock magnetic and electron microscopic analyses of fresh and hydrothermally‐altered MORBs dredged from the Longqi and Yuhuang hydrothermal fields, Southwest Indian Ridge. We observe large variations in magnetic properties of fresh MORBs, originated from relative proportions of nano‐scale single‐domain to vortex state and micron‐scale vortex to multi‐domain state dendritic titanomagnetites. Progressive hydrothermal alteration produces secondary magnetite through recrystallization of exsolved and dissolved Fe from primary titanomagnetite. Exsolution is evident by a dual Verwey transition signature and coexisting Ti‐poor titanomagnetites and sphenes in partially chloritized basalts. A schematic model is proposed to explain the variations in magnetomineralogy and magnetic properties with progressive hydrothermal alteration. Intermediate hydrothermal alteration products retain a secondary chemical remanent magnetization (CRM) which is related to the long‐term magnetization variations in oceanic basalts. The established framework allows characterizing MORB hydrothermal alteration and ultimately contributes to resolving the complexity of seafloor magnetism.
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.
Objective Recently, blueberry has been identified as a candidate for the treatment of liver fibrosis. Given the role of gut-liver axis in liver fibrosis and the importance of the gut microbiota homeostasis to the maintenance of the intestinal epithelial barrier, this study aimed to investigate whether blueberry could attenuate liver fibrosis and protect the intestinal epithelial barrier by maintaining the homeostasis of the gut microbiota. Method A CCl4-induced rat liver fibrosis model was used to detect the roles of blueberry in liver fibrosis and intestinal epithelial barrier. The liver weight and body weight were measured, the liver function was monitored by ALT and AST activity, protein and mRNA were determined by western blot and RT-qPCR, and the gut microbiome was detected by Miseq. Results The results showed that blueberry could reduce the rate of liver weight/body weight gain (p < 0.05), ALT (p < 0.01) and AST (p < 0.05) activity, and the expression of collagen I (p < 0.01), collagen IV (p < 0.01), and α-SMA (p < 0.01) expression in CCl4-induced rat liver. CCl4 impaired the intestinal epithelial barrier and decreased the expression of the tight junction protein. Blueberry restored the intestinal epithelial barrier and increased the expression of the tight junction protein. The gut microbiota homeostasis was impaired by CCl4, but after treatment with blueberry, the intestinal flora returned to normal. Conclusion Blueberry attenuated liver fibrosis, protected intestinal epithelial barrier, and maintained the homeostasis of the gut microbiota in a CCl4-induced injury rat model.
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