ISSN: 2152-1972 The IRM Inside... Visiting Fellows' Reports 2 Report on Castle Meeting 4 Current Articles 6 QuarterlySpring 2018, Vol. 28 No.1 ... and more throughout! The 2018 Summer School in Rock Magnetism Panoramic of the mini-workshop on micromagnetic modeling using MERRILL. Wyn Williams (University of Edinburgh) is teaching the classroom the fundamentals of magnetic modeling, while Lesleis Nagy (left) supervises. Photo by Josh Feinberg. Dario Bilardello goals and an indication of how rock magnetic studies could help the applicant’s research. This year we were able to award every participant a partial reimbursement Institute for Rock Magnetism offered by the United States National Science Founda- [email protected] tion. Three students received scholarships thanks to The fifth IRM Summer School in Rock Magnetism funds provided by the Geomagnetism, Paleomagne- was held between June 4-13th at the Institute for Rock tism, and Electromagnetism section of the American Magnetism, University of Minnesota. This was the first Geophysical Union: Congratulations to Marie Troyano Summer School held in the newly renovated home of the (IPGP), Christina Verhagen (Rutgers University) and IRM, the Tate Laboratory of Physics: SSRM 2.0, if you Gabriel West (Stockholm University) for taking home will. the AGU Scholarships! Since the Summer School of 2013, registration has Students were also asked to describe their research been capped at 20 students per school to ensure a “hands interests for the purpose of creating suitable afternoon on” and personal experience for every participant. This laboratory projects. Based on interest, the students were year, the 20 spots filled up within three days of open- subdivided into four groups that worked on: A) Paleoin- ing the registration, a real record! Moreover, the 10-spot tensity; B) DRM; C) Environmental Magnetism; and D) wait list also filled up soon after, with a handful of peo- Magnetic Anisotropy. The groups were guided by Josh ple still enquiring about the possibility to register. We Feinberg, Dario Bilardello, Pete Solheid and Mike Jack- sympathize with all those who were not able to partici- son, respectively. A shout-out also goes to IRM students, pate and we are very glad that the interest in the Summer postdocs and alumni Janelle Ruth, Kathryn Hobart, Max School is so high. Longchamp, Mike Volk and Dan Maxbauer for their help Participants were of different nationalities. Six stu- creating the projects and/or their assistance during the dents (US and international) traveled from five United lab sessions. States institutions (California Institute of Technology, As always, the true hero of the Summer School was Rutgers University, University of Massachusetts, Uni- IRM director Bruce Moskowitz who unremittingly versity of Oregon, and University of Rochester). The taught the majority of the morning classes, 8:30 to 12:00 remaining fourteen students travelled from eight differ- (fifteen hours of lecturing over the first eight days!). ent countries (Canada, China, France, Mexico, Norway, The lectures covered the whole spectrum of topics in Sweden, Taiwan, and United Kingdom). rock-magnetism, from basics to applications. Lectures When applying for the Summer School, participants included: the physics of magnetism; the geomagnetic field; magnetism of solids I and II; magnetic mineralogy; cont’d. on were offered the possibility to apply for a scholarship, pg. 12... based on a short research statement, describing research fine particle magnetism; superparamagnetism to multi- 1 crons). All samples have a magnetite Verwey transition (Tv) Visiting Fellow Reports between 112 K and 127 K (average 120.5 K; Fig. 1a), and two samples have a pyrrhotite Besnus transition at ~30 K. Some samples also show significant unblocking Rock magnetic characterization of of the low-temperature remanence below ~50 K, which may be an ilmenite component. A few samples have FC in-situ oceanic gabbros from Atlantis and ZFC curves that do not converge at T > Tv (Fig. Bank 1b), a property consistent with goethite; Liu et al. (2006) attribute this to the high saturation field of goethite and in-field cooling through the blocking temperature(s). Julie Bowles FORC data clearly show the presence of at least Geosciences, three different populations: a “pseudo-single-domain” University of Wisconsin- Milwaukee population (Fig. 2a), a non-interacting single-domain [email protected] population (Fig. 2b), and a lower-coercivity, somewhat interacting SD population (Fig. 2c). We suggest that IODP Expedition 360 to Atlantis Bank on the South- the non-interacting SD population is largely confined to west Indian Ridge was the first step in a planned multi- silicate-hosted inclusions, and measurements on min- expedition project designed to better understand the eral separates confirm that some silicates display simi- nature of lower oceanic crust and the Moho at slower lar FORC behavior. The interacting SD population may spreading ridges. This includes understanding the in- be linked to olivine alteration, and a similar FORC was teraction between magmatism and tectonism in accom- measured by Usui (2013) on olivine separates. Final- modating seafloor spreading at slow spreading centers. ly, the PSD population may be discrete magnetite, but Paleomagnetic and magnetic anisotropy data will play we note that at least some multidomain structures were a key role in answering these questions, and a better un- found as silicate inclusions using MFM. The MFM data derstanding of the magnetic mineralogy is therefore in also show that magnetic structures consistent with a non- order to properly interpret these data. interacting SD population are found as exsolution fea- There is relatively little rock magnetic data from in- tures in larger, non-magnetic oxides. Conversely, non- situ oceanic gabbros, but Gee and Kent (2007) summa- magnetic exsolution features in larger magnetic oxides rize observations of magnetite present in three forms: produce magnetic structures consistent with an interact- discrete, primary magnetite; fine-grained silicate-hosted ing SD population. magnetite; and magnetite associated with alteration of olivine. Low-temperature data presented by Zhao and Acknowledgements Tominaga (2009) also suggest at least the occasional I thank the IRM for the Visiting Fellowship that al- presence of pyrrhotite. lowed me to collect this data, and Mike, Peat, and Dario At the IRM, we measured hysteresis loops and for all their skilled assistance! Many thanks to T. Mor- FORCs on samples from both oxide-rich and oxide- ris and M. Tivey, my co-magnetists on board Expedition poor samples that displayed a wide variety of NRM and 360, as well all of the Expedition 360 scientists and crew. thermal demagnetization behavior. On a subset of these Travel to the IRM was additionally supported by funds samples, we also measured a room-temperature 2.5 T from the U.S. Science Support Program. IRM (RTSIRM) on cooling to 10K and warming back to room temperature. A 2.5 T IRM was applied at 10 K References Gee, J. S., and Kent, D. V. (2007), Source of oceanic mag- and measured on warming, following zero-field cooling netic anomalies and the geomagnetic polarity timescale, in (ZFC) and cooling in a 2.5 T field (FC). Finally, three Treatise on Geophysics, v. 5, M. Kono (Ed.), pp. 455-507, samples were examined with the magnetic force micro- Elsevier, New York. scope (MFM) to investigate domain structures within Harrison, R. J., and Feinberg, J. M. (2008). FORCinel: An im- some of the very coarse oxides (tens to hundreds of mi- proved algorithm for calculating first-order reversal curve 360-U1473A- 360-U1473A- /kg) 2 31R-2,123 cm 21R-2,116 cm 8 Am 0.02 -3 6 0.01 AB4 M (x 10 100 200 300 100 200 300 Temperature (K) Temperature (K) Figure 1: Example FC (blue) and ZFC (red) data. 2 ABC ) (T u B 360-U1473A- 360-U1473A- 360-U1473A- 5R-1,12 cm 27R-3,112 cm 75R-4,127 cm Bc (T) Bc (T) Bc (T) Figure 2. Example FORC data. Processed with FORCinel (Harrison and Feinberg, 2008) distributions using locally weighted regression smooth- mental evidence for it remains scarce, in part due to the ing. Geochemistry Geophysics Geosystems, 9, https:// difficulty to obtain samples with well-known remag- doi:10.1029/2008GC001987 netization temperatures, and was sometimes negative Usui, Y. (2013). Paleointensity estimates from oceanic gab- (Kent, 1985). Related is the problem of cooling rates, bros: Effects of hydrothermal alteration and cooling rate. i.e. the ability to obtain insight into how fast a rock body Earth Planets Space, 65, 985-996. Zhao, X., and Tominaga, M. (2009). Paleomagnetic and rock cooled after its formation or emplacement by analyzing magnetic results from lower crustal rocks of IODP Site its blocking temperatures during stepwise thermal de- U1309: Implication for thermal and accretion history of the magnetization. Knowledge of cooling rates is essential Atlantis Massif. Tectonophysics, 474, 435-448. for paleointensity accurate estimates; as slower cooling rocks generally show higher magnetic intensities during thermal demagnetization. In a previous visit to the IRM, Blocking temperatures: Are they really we performed the first experimental study of this latter relation, between cooling rates and unblocking tempera- as we think they are? tures (Berndt et al., 2017), which yielded discrepancies to the theoretically predict temperatures that could only Thomas Berndt empirically be accounted for (Fig. 1). School of Earth and Space Sciences, In this second visit to the IRM, additional