Authors: Claudia Banks, Scott Miller, Joseph Meert, George Kamenov, Paul Mueller, Anup Sinha, M.K Pandit
Faculty Mentor: Dr. Joseph Meert
College: College of Liberal Arts and Sciences
The Singhbhum craton is one of five Archean nuclei comprising Peninsular India. It is a composite Archean block that includes the Older Metamorphic Group, the Older Metamorphic Tonalite Gneisses, the Singhbhum Granite, and the Iron Ore Group as its major units. The ages of these components range from ~3.5 to ~3.1 Ga, although overlapping ages and similar rock types confound their genetic relationships. Plutonic felsic rocks from the southeastern Singhbhum craton (BK1: a foliated tonalite, KP1: a non-foliated granite, and SG14: a non-foliated granite) yield U-Pb (zircon) ages of 3321 ± 2 Ma (BK1), 3301 ± 1 Ma (KP1), and 3261 ± 1 Ma (SG14) that coincide with a pulse of Singhbhum Granite emplacement at 3.27 to 3.33 Ga. REE patterns and tectonic discrimination diagrams based on major and trace element ratios suggest a subduction zone setting for these rocks. We report major and trace element data for and compare them to previous works in order to characterize the Archean felsic plutonic history of the craton.
Not sure how this virtual symposium works, but I am curious if you can summarize in non-technical language, the significance of your work?
Hi! Thank you for checking it out. Essentially this is important because if we can match up a certain rock and its chemistry to the environment it formed in, it becomes easier to identify the environment of formation based on the rock and vice versa. Regarding this project and India, because the crust in the Singhbhum craton is so old, the environment that the crust formed in is not yet completely known so we are attempting to provide information to constrain when and how this crust formed based off the rocks.
Hi Claudia! This is an excellent presentation. Your poster is very aesthetically pleasing and I believe you presented your research well.
Thank you, Sam!
Great job Claudia! I was wondering if you could expand on why in particular we would expect to see this type of trace element pattern in subduction zones, and why it is specific to these environments and not something else (not requiring plate tectonics).
Thank you, Courtney. Since the Nb is a high field strength element (dense but small), it is immobile and remains in the solid even when water (which is present in subduction zone settings because oceanic crust is subducting under continental) is around, which explains the depletion. The enrichment in Pb is also common in subduction zones because when the oceanic crust subducts it dehydrates and Pb-rich fluids seep off of it (I think they are from sediments on the oceanic crust).
Hi Claudia, this is a great poster and presentation! I really like your geologic map and the methods by which you investigated the craton (modal min, major and trace elements). Seems like there’s more work to be done to see how plausible ‘subduction zone’ is. Thanks for sharing!
Thanks Syd!
Hi Claudia! This is really interesting work, thanks for sharing it! Since it sounds like your samples must have formed in a subduction zone, are there any continental reconstructions from this time period to help you explore more about this putative subduction zone?
Hi Amy!
Thank you! Well, a certain lab group in the geology department does focus on continental reconstructions of India but I had not thought about looking to see if they have a reconstruction from the exact time I’m looking at. Thank you for the idea!
Claudia,
Thanks for doing this work. I am curious if you can speculate on why so many rock types (including mafic dykes) seem to give an active plate margin signature? Might the discrimination methods be flawed?
I think because there’s a lot of variety in the processes that occur with active plate margins. For example, there’s continent-continent crust collision, continent-oceanic crust collision, and oceanic-oceanic crust collision and from that, we can get assimilation, magma mixing, flux melting and more; all of which can give us a different rock composition. I think the discrimination methods are fair, however, obviously, we may later find out that there are some flaws and that using a cookie-cutter method to distinguish these settings don’t work exactly how we thought.
Great job on the presentation Claudia! I am very curious to hear more about what you discover in regards to the presence of past subduction zones in this region.
Thank you, Chance!
Nice work, Claudia! I’m interested in what your take is on the subsequent history of these granites post emplacement. There’s been a fair amount of metamorphism and alteration in Singhbhum Craton; what effect has this had on the rocks you analyzed?
Hi Tony!
So the alteration and metamorphism were super apparent in the thin sections. Both BK1 and SG14 had sericitization of plagioclase which indicates some hydrothermal alteration. KP1 also had some chlorite present. Also, the zircons in all of the samples were pretty beat up and were rarely the prismatic shape zircons usually are.
Hey Claudia,
Great presentation and poster! It’s really interesting to see the evidence we have for an explanation of how a part of ancient Earth formed and to see it all laid out on the figures. I do have a question, though. I’m not really familiar with the KDE measurement, it said “Karmel distribution estimate” on the figure. What does that measure?
Great Presentation!
What other geological analytical tools could you use to expand this research?