Search for Records of the Hadean Dynamo from Detrital Zircons

This is an INSPIRE award, which is being co-funded by programs in the Geoscience Directorate (Geophysics Program, Petrology and Geochemistry Program) and Math and Physical Sciences Directorate (Atomic, Molecular, and Optical Experimental Physics), as well as co-funding from OIA-INSPIRE and OISE. The Earth's magnetic field is generated by fluid motions in the metallic core, a process known as the geodynamo. The time of origin and intensity of the geodynamo during the first ~1 billion years of Earth history are essentially unknown. The geodynamo's early history has major implications for the thermal evolution of the planet, the physics of magnetic field generation, and the habitability of the early Earth. The only minerals of which we are aware that might record the field during this earliest epoch are zircon (ZrSiO4) crystals found in sedimentary rocks in Western Australia. Ranging up to 4.38 billion years in age, they are the oldest known terrestrial minerals. Here the investigating team has developed a project to measure the magnetization of these crystals, supported by the Integrated NSF Support Promoting Interdisciplinary Research and Education (INSPIRE) program, that could finally determine the geodynamo's time of origin and earliest evolution. This project is an international collaboration between geophysicists, geochemists, geologists, and physicists from seven institutions and includes leaders in ultrahigh sensitivity magnetometry, quantum science, radiometric dating, field geology, mineralogy, and stable isotope geochemistry. It supports the development of next-generation magnetometry techniques for the analysis of extremely weakly magnetic materials and geochemical techniques for determining the alteration histories of samples from the early Earth. It also funds the training of graduate students at three universities, who will participate in the international field work to collect samples, as well as in the interdisciplinary science.

The central challenge of this project is to determine the time of origin of the zircons' magnetization. Prior paleomagnetic, geochemical and mineralogical analyses have shown that the host rocks and many zircons have been pervasively remagnetized well after they formed. This team proposes to determine the thermal and alteration histories and study the remanent magnetization of numerous zircons older than 4 billion years from Western Australia. To achieve this, they will characterize the geology and stratigraphy of the zircon host rocks and determine zircon ages using U-Pb geochronometry. They will analyze the extremely weak magnetizations of the zircons using two new ultrahigh-sensitivity magnetometry techniques: superconducting quantum interference device (SQUID) microscopy (SM) and quantum diamond magnetometry (QDM)]. Finally, a variety of microanalytical techniques will be employed to establish which grains have primary ferromagnetic inclusions. So that others can independently test these results, the team will create an open archive of their key measurements and samples accessible by other researchers and make time available on their magnetometers to qualified researchers.