22-EPN3-038: Asteroidal source(s) of L chondrites and its collisional evolution – U,Pb geochemistry of phosphates in meteorite Antonin.
Visit by Monika Kusiak (Institute of Geophysics Polish Academy of Sciences (IG PAS), Poland) and Agata Krzesinska (University of Oslo) to TA2 Facility 26 – KBSI Sensitive High Resolution Ion MicroProbe / SHRIMP-IIe/MC (South Korea).
Dates of visit: 12-23 May 23
Report Summary: The main goal of the visit was to conduct in-situ U-Pb geochronological study of phosphate minerals in the Antonin L chondrite. Fall of the Antonin, on 15th July 2021, was recorded by European Fireball Network, and this recording led to reconstruction of the pre-atmospheric orbit of meteoroid. The orbital parameters of the Antonin differ from reconstructed orbits of other L chondrites, but suggest it was sourced from the inner asteroid belt. To track the orbit to the parent body, it is important to understand dynamic collisions experienced, which are recorded in minerals of the meteorite. U-Pb dating allows to decipher details on events that led to resetting of phosphates.
During the visit to KBSI facility, we collected SHRIMP (Sensitive High-Resolution Ion MicroProbe) analyses within multiple apatite and merrillite grains. Initial U-Pb results show minor discordance of ages of phosphates, indicating a mild collision after the crystallization of the minerals. The timing of reset event cannot be inferred with high precision, but it likely occurred between 500–100 Ma.
Additionally, formation of phosphates can be well constrained from collected data at ca. 4450 Ma. This age implies that phosphates formed/recrystallized in response to a collision as impacts were the only source of heat after cessation of accretional activity. Altogether, the results suggest two collisions in the evolution of parent body and will be combined with further data to pinpoint key events in dynamical evolution of parent body of L chondrites.
22-EPN3-008: U/Pb-Dating of the Youngest Eclogites on Earth.
Visit by Linus Streichers and Willem van Westrenen (Vrije Universiteit Amsterdam, Netherlands) to TA2 Facility 26 – KBSI Sensitive High Resolution Ion MicroProbe / SHRIMP-IIe/MC (South Korea).
Dates of visit: 05 April 2023 – 01 May 23
Report Summary: A total of 184 U-Pb-ages of zircon from eclogites from Sulu-Dabie UHP metamorphic belt (China), the D’Entrecasteaux Islands (Papua New Guinea) and the Western Gneiss Region (Norway) were successfully determined using the SHRIMP IIe/mc of the Korean Basic Science Institute.
Using the concordia method, we could identify a concordant age of the peak metamorphism of eclogite from Sulu-Dabie of ca. 240 Ma. In addition, a discordant age of around 720 Ma could be identified, which may reflect the age of inherited, magmatic zircon cores. The zircon from the D’Entrecasteaux Islands revealed ages below 8 Ma, which is younger than ages previously measured on the same sample in a previous study. This makes this sample one of the youngest eclogites ever discovered on Earth’s surface. Zircons from the Western Gneiss Region reveal ages of three distinct events. With 1.5 Ga, the oldest age determined probably reflects the Precambrian formation of the UHP region, while ages of around ca.
900 Ma correspond with the Sveconorwegian orogeny. The youngest age found in Norway reflects the Scandian orogeny at an age of ca. 415 Ma. The age information obtained will help us to develop improved evolutionary models for the formation of UHP rocks by combining these ages with trace element data.
20-EPN2-057: A Zircon Provenance Study of the Kanye Basin (Botswana) to Constrain Terrestrial Geodynamics Across the Archaean-Proterozoic Transition.
Virtual visit by Denice Borsten and Jochem Sikkes (Vrije Universiteit Amsterdam, Netherlands) to TA2 Facility 26 – KBSI Sensitive High Resolution Ion MicroProbe / SHRIMP-IIe/MC (South Korea).
Dates of visit: 23 September 2021 -17 February 2022
Report Summary: This study investigates the Neoarchaean to Paleoproterozoic Transvaal Supergroup sedimentary sequence in Botswana that formed in the centre of the Kaapvaal Craton during the early oxygenation of the atmosphere. We used U-Pb dating on magmatic and sedimentary zircons from throughout the sedimentary sequence to determine the tectono-magmatic evolution of the hinterland basement. This approach constrains regional crustal growth, uplift and erosion events and establishes if additional cratons were in the hinterland, e.g. Pilbara. Knowledge of zircon provenance will allow critical comparison to known tectonic scenarios, e.g. Alpine style molasse basin and any potential change in Neoarchaean tectonics by considering erosion and crustal growth-reworking. The geochronology results help evaluate spatial and temporal variations in depositional environments associated with oxygenation of the atmosphere. Results indicate that the age of the basement, Gaborone Granite and the Kanye volcanic are indistinguishable (2768.9 ± 6.0 Ma). Sediments deposited from 2.642 Ga to 2.550 Ga are also dominated (> 90%) by zircons of ~2.77 Ga. This implies that there was a major crustal growth event in the Kanye region at 2.77 Ga that included minimal crustal reworking. Erosion products to the Kanye Basin are derived from this juvenile crust throughout the Archaean and Proterozoic until > 2.0 Ga. Only then are older and younger basement rocks recorded in the sedimentary sequence. This region of the planet yields no evidence of a major tectono-magmatic event associated with the oxygenation of the atmosphere.