Our knowledge on the behaviour of the geomagnetic field through time critically depends on how information of the past state of the field is recorded by, and stored in iron-bearing minerals such as magnetite. For small, single domain grains these processes are described by classical Néel theory, but the magnetic behaviour of larger, pseudo-single domain or multidomain grains, still is enigmatic. Here we present a chemical, crystallographic and magnetic characterisation of three to six individual, large (~3-10 μm) iron-oxide grains from eleven different flows sampled on the Big Island of Hawai'i.
View Article and Find Full Text PDFMajor earthquakes frequently nucleate near the base of the seismogenic zone, close to the brittle-ductile transition. Fault zone rupture at greater depths is inhibited by ductile flow of rock. However, the microphysical mechanisms responsible for the transition from ductile flow to seismogenic brittle/frictional behaviour at shallower depths remain unclear.
View Article and Find Full Text PDFThe controversial Younger Dryas impact hypothesis suggests that at the onset of the Younger Dryas an extraterrestrial impact over North America caused a global catastrophe. The main evidence for this impact--after the other markers proved to be neither reproducible nor consistent with an impact--is the alleged occurrence of several nanodiamond polymorphs, including the proposed presence of lonsdaleite, a shock polymorph of diamond. We examined the Usselo soil horizon at Geldrop-Aalsterhut (The Netherlands), which formed during the Allerød/Early Younger Dryas and would have captured such impact material.
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