In-phase- and out-of-phase magnetic susceptibility fabrics in Ediacaran dykes from Jordan: insights into magma flow and emplacement processes

Dyke swarms are a widespread geological feature in Precambrian craton blocks. Such large magmatic plumbing system serve as exceptional recorders of the Earth’s magnetic field, offering valuable insights into paleogeography of these early geological periods and constrains on the intensity of the ancient magnetic field, as contributed to demonstrated in past work with J.P. Valet. But by using rock magnetism, especially the anisotropy of magnetic susceptibility (AMS), dykes are also excellent witnesses to provide a comprehensive picture of magmatic systems and the tectonic evolution of an area. While it has recently become easy to measure the out-of-phase susceptibility, its use for studying dyke’s emplacement mechanisms is relatively modest. In this study, we analyze the AMS in Ediacaran dykes from Jordan to investigate the potential of such out-of-phase signal on magma flow patterns. A total of 315 samples from 42 sites, including dolerites and rhyolites, were analyzed. Our results show that 47% of the doleritic dykes exhibit a clear difference between in-phase AMS (ipAMS) and out-of-phase AMS (opAMS) fabrics. This may reflect the presence of sub-fabrics, potentially linked to distinct grain populations crystallized under varying stress conditions (Hrouda et al., 2019). Magnetic mineralogy data (susceptibility as a function of temperatures and FORC measurements) suggests the presence of SD (single-domain) magnetite grains in dykes with differing fabrics, and MD (multi-domain) grains in cases with consistent fabrics. This distinction allows us to identify zones where magma flowed freely versus those dominated by forceful intrusion. Our findings emphasize the potential of opAMS measurements in deciphering emplacement processes in mafic dykes.