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(2020) Lu–Hf Isotope Systematics of Carbonatites

Polák L, Ackerman L, Magna T, Bizimis M & Rapprich V


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03i: Room 1, Thursday 25th June 22:09 - 22:12

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Submitted by Anthony Lanati on Thursday 25th June 07:51
Interesting work! I was hoping you might be able to give more insight into what is causing the two groups in the EAR? Since the associated silicate phases are pyroxenites are their any clues to magmatic source given little recycled carbon and hydrothermal input based on your dC/dO18 plot?
Hi, In general, the HIMU and EMI reservoirs are considered as a source of EAR carbonatites. A plume is melting subcontinental lithosphere which is entering EMI and HIMU supply path with uplifting magma (recycled C is coming from here). Due to the repeated metasomatic and magmatic events in the past is an isotopic composition under East Africa highly variable and heterogeneous. I just quickly drawn an image (sorry for quality; https://ibb.co/3mGjbcM) comparing Tororo and Sukulu/Oldoinyo Dili and showing them in the relation of HIMU and EMI. It´s probable that the EAR grouping is a feature of source and depends on different mix composition of HIMU and EMI (and maybe recycled material). 207/204Pb and 206/204Pb data show that Sukulu/Oldoinyo Dili carbonatites fit HIMU related group more than Tororo.

Submitted by Kathryn Goodenough on Thursday 25th June 14:44
You have some really interesting data, and I'm very interested in the contrasting epsilon Nd values between groups A and B. What do you think this reflects in the mantle source of the carbonatites?
Hi, I think that in most cases different epsilon Ndi is reflecting heterogenity of mantle source. Source of group A have a higher content of crustal material in source, while group B is more less ,,clean" mantle. Carbonatites are usually enriched in Sr and Nd content and contaminate Sr-Nd isotopic system without noticeable changes in other systems is almost impossible. This can be clearly seen in Samalpatti carbonatites. Samalpatti carbonatites are extremely depleted in Sr and Nd isotopes so a highly radiogenic signature is a result of contamination of crustal material.

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