Hello everyone!
I have returned from my two week travel to Houston and Baltimore studying the micro-structures of zircons and learning about planetary radar. I wanted to talk about both Houston and Baltimore in this post, but to keep things short and to the point I will be dedicating this post to my trip to Houston. Baltimore will be the topic for the next one.
"HOW TO STAY ACTIVE AND EXERCISE AT UNIVERSITY" Before I jump into everything, I wanted to turn your attention to an article that I think you guys might find interesting. Most people, especially graduate students, struggle to balance work, health, fitness, and social life in their schedules, which often leads to stress, imposter syndrome, mental health issues, breakdowns, and unhealthy habits (e.g., ordering in most nights when you have a fridge full of food). More studies have been conducted in the past decade alone proving how a balanced work-health-social schedule can help improve your motivation, mental health, and relationships with friends, co-workers and loved ones. The article I want to introduce to is called by Exercise Right. The article interviews someone I know very well, Izzy Tolometti, my younger sister, who is studying sports and health sciences at Robert Gordon University in Aberdeen, UK. She answers questions about how someone can easily balance a fitness and healthier lifestyle with a busy work schedule. For some context, she trains for gymnastics at least 24 hours a week while having to work on her third year undergrad assignments, coach young gymnasts, and socialize with her friends. I highly recommend reading this article. I found it insightful since I am a graduate student who sometimes struggles to balance work, health, and a social life.
Right, now back to research. Before the new year, I was contacting Dr Timmons Erickson at the NASA Johnson Space Center in regards to my research seeking to determine the temperature conditions of impact melt produced during meteorite impact events. Timmons was a co-author on a 2017 research paper (Timms et al., 2017) where he and the team he was a part of discovered a zircon crystal (ZrSiO4) in a black impact glass sample from the Mistastin Lake impact structure (located in Northern Labrador, Canada) with an interior structure implying initial melt temperatures of <2370°C. This is currently the only impact melt temperature datum confirmed by planetary scientists. In September 2019, I discovered more zircon crystals with similar textures and structures to the crystal studied by Timms et al. (2017). After speaking to my supervisor's Dr Gordon Osinksi and Dr Catherine Neish, they recommended I reach out to Timmons and potentially work with him to study these samples and see if we can estimate more temperature data points. In short, I spoke to Timmons over the course of a couple of months, made arrangements to travel to the Johnson Space Center to study the interior of the zircon crystals I discovered in my samples, and analyze the data to present at future planetary science conferences.
I arrived at the Johnson Space Center (JSC) on the 18th of February. It was originally supposed to be the 17th but the badge office was closed on Presidents Day...you can read more about it in my short blog from a couple of weeks ago. For three days, Timmons and I worked in the JSC Secondary Electron Microscopy (SEM) laboratory. We were studying the interior structure of the zircons crystals, or to be more specific the micro-structures and crystallographic orientations. The zircon crystals in my samples have experienced a range of different pressure and temperature conditions. These conditions, cause the crystals to breakdown, recrystallize, polymerize (change structure but keep the same chemical composition), and fracture. By studying how the orientations of the crystals changed, we can determine what structures existed when the impact melt was at its hottest, estimate the temperatures of the impact, and what happened to the melt as it cooled from >2000 °C to <500 °C. To help explain all of this, let's break out some of the images I have analyzed and processed.
The images in the gallery above are zircon mineral phase and orientation maps generated from electron backscatter diffraction (EBSD) data. EBSD is a technique that maps and quantifies the crystallographic orientation of minerals, providing mineralogical and crystallographic information such as phase, unit cells, crystal axes, and space groups (if you want to learn more about these terms, click on the link here). I briefly explained EBSD in one of my previous short blogs, but for any new readers I will go over it again. EBSD (see image below) bombards the surface of a sample inclined at 70° using an incident electron beam. The the electrons diffract off the surface and travel to an electron diffraction detector. The intensity of the diffracted electrons changes depending on the orientations of the crystals in the sample. From this data, maps of the micro-structure and crystallographic orientations of the samples are generated.
From the data, Timmons and I created zircon mineral phase and orientation maps to illustrate how they have changed due to high pressure and temperature conditions. Below are the individual images shown in the image gallery above. The first image is a mineral phase map. What I mean by phase is a mineral with a fixed composition and uniform chemical and physical properties. The orientations are not shown in this image because we are only interested with telling which mineral is which. The image shows a zircon core (dark green) surrounded by a vermicular (spotted or spongy) corona (ring) of zirconia-monoclinic crystals (mustard yellow). Reidite (high-pressure polymorph of zircon) is also present (light blue), but is very scare and difficult to see in the image.
The second image is a map showing the orientations of the zircon crystals. You can see that two green colours dominate this sample. This is because this zircon was once subjected to extreme pressure conditions that converted the zircon to its high pressure polymorph reidite. Immediately afterwards, the temperature began to increase as the rocks struck by a meteorite decompressed. Reidite is only stable at temperature conditions <1200 °C, so the reidite broke back down to zircon when it became too hot. This can leave an irregular stripped pattern in the core.
The vermicular corona is made up of zirconia-monoclinic minerals. These are zircons but with a monoclinic crystal system instead of a tetragonal crystal system. Zirconia-monoclinic minerals are also referred to as baddeleyite, and these can form from two processes: (1) zircon ➔ ZrO2-tet ➔ ZrO2-mon (1690–2350 °C), or (2) zircon ➔ ZrO2-tet ➔ ZrO2-cubic ➔ ZrO2-tet ➔ ZrO2-mon (>2350 °C). I am still in the early stages of processing and interpreting the EBSD data, but I have an initial thought. While the reidite reverted back to tetragonal zircon, the core also dissociated (material separating; in this case, ZrO2 and SiO2) to form the baddeleyite corona (tetragonal to monoclinic, or tetragonal to cubic to monoclinic).
The next stage is to quantify the crystallographic orientations. To do this, I need to plot the orientations onto pole figures. I have an example of a pole figure below. I am still figuring out how to filter out unnecessary orientation points and produce plot figures similar to the ones reported in Timms et al. (2017). I am hoping to get access to a more sophisticated program later this week, which will allow me to create the pole figures I want for this research a lot easier than the freely available online programs.
I will be updating you guys as more process is made. Subscribe to my blog (home page on website) to get notifications about new releases and research updates :D
Oh! This is not research related, but if anyone lives in or is planning on visiting Ontario Canada in the near future you should check out SAMY's Alpaca Farm and Fibre Studio! I went with my girlfriend on the 1st of March and we had an amazing time! You get to pet, feed, and walk alpaca's!!!
See you guys next time!