Abstract Details
(2020) Genesis of Rare-Element Pegmatites at Kalu’an, the Chinese Altay: Insights from Columbite U-Pb Dating and Melt Inclusion Study
Feng Y, Liang T, Linnen R & Tan X
https://doi.org/10.46427/gold2020.707
The author has not provided any additional details.
08i: Plenary Hall, Friday 26th June 22:24 - 22:27
Yonggang Feng
View all 2 abstracts at Goldschmidt2020
View abstracts at 5 conferences in series
Ting Liang View all 2 abstracts at Goldschmidt2020 View abstracts at 3 conferences in series
Robert Linnen View all 2 abstracts at Goldschmidt2020 View abstracts at 13 conferences in series
Xijuan Tan View all 2 abstracts at Goldschmidt2020 View abstracts at 2 conferences in series
Ting Liang View all 2 abstracts at Goldschmidt2020 View abstracts at 3 conferences in series
Robert Linnen View all 2 abstracts at Goldschmidt2020 View abstracts at 13 conferences in series
Xijuan Tan View all 2 abstracts at Goldschmidt2020 View abstracts at 2 conferences in series
Listed below are questions that have been submitted by the community that the author will try and cover in their presentation. To submit a question, ensure you are signed in to the website. Authors or session conveners approve questions before they are displayed here.
Submitted by Bénédicte Cenki-Tok on Thursday 25th June 01:57
Thanks for this very interesting work. Have you considered a continuous emplacement of these pegmatites over 30 Ma instead of discrete events ? As these pegmatites are crustally-derived, it would'nt be surprising that the melting crust remained hot for this period of time. Any other possible interpretation for the source for the Ta-Nb pegmatite, like a refractory granulitic lower crust ?
The emplacement of pegmatite-forming melts could be continuous. What we have demonstrated is only that the formation of Li-rich pegmatites could be a very long process. It may also depend on how many Li-rich pegmatites we date. The more pegmatite dikes we date, the more accurate age distribution we can confirm. We are still investigating the source for the pegmatites, though we would think that a metasedimentary source in mid-crust could be more Li-rich rather than a refractory granulitic lower crust. Thanks for these inspiring questions.
Thanks for this very interesting work. Have you considered a continuous emplacement of these pegmatites over 30 Ma instead of discrete events ? As these pegmatites are crustally-derived, it would'nt be surprising that the melting crust remained hot for this period of time. Any other possible interpretation for the source for the Ta-Nb pegmatite, like a refractory granulitic lower crust ?
The emplacement of pegmatite-forming melts could be continuous. What we have demonstrated is only that the formation of Li-rich pegmatites could be a very long process. It may also depend on how many Li-rich pegmatites we date. The more pegmatite dikes we date, the more accurate age distribution we can confirm. We are still investigating the source for the pegmatites, though we would think that a metasedimentary source in mid-crust could be more Li-rich rather than a refractory granulitic lower crust. Thanks for these inspiring questions.
Submitted by Kathryn Goodenough on Friday 26th June 12:15
Thankyou, this is a really interesting presentation, and the pegmatites look fascinating, I would love to visit this area! In your slide 10, you suggest that there are two dykes, with the younger dyke being lepidolite-rich. Have you considered the possibility that the lepidolite zone actually represents late-stage metasomatism of the older dyke, rather than intrusion of new magmas? There is a lot of recent work suggesting that late-stage fluids in many Li pegmatites may redistribute the Li and also introduce metals such as Sn, Ta.
Hi Kathryn, thanks for the question. It is possible that the lepidolite zone actually represents late-stage metasomatism. Based on petrographic observations, lepidolite replaces spodumene and muscovite and is mainly a secondary phase.
Thankyou, this is a really interesting presentation, and the pegmatites look fascinating, I would love to visit this area! In your slide 10, you suggest that there are two dykes, with the younger dyke being lepidolite-rich. Have you considered the possibility that the lepidolite zone actually represents late-stage metasomatism of the older dyke, rather than intrusion of new magmas? There is a lot of recent work suggesting that late-stage fluids in many Li pegmatites may redistribute the Li and also introduce metals such as Sn, Ta.
Hi Kathryn, thanks for the question. It is possible that the lepidolite zone actually represents late-stage metasomatism. Based on petrographic observations, lepidolite replaces spodumene and muscovite and is mainly a secondary phase.
Submitted by Mona Sirbescu on Friday 26th June 20:37
If pegmatites are considered anatectic, how do you explain the regional zoning (I, II, III...) that seem to parallel the contact with the older granite, with barren pegmatite near the contact and Li-rich pegmatites more distal?
Hi Mona, the geological map was made in 1980s and the real regional zoning is actually not what it was speculated to be. We are now redrawing the map based on our new field observations. According to our field observations, the Li-rich pegmatites are mainly confined to the northern part of the region whereas Be-rich pegmatites are mainly in the southern part. The distribution pattern parallel to the boundary of the older granite was likely due to the influence of the magmatic fractionation model back in the early days. Geochronological studies show that the granite (~400 Ma old) is unlikely the parental granite to the rare-element pegmatites (~225 to 200 Ma) in the same region.
If pegmatites are considered anatectic, how do you explain the regional zoning (I, II, III...) that seem to parallel the contact with the older granite, with barren pegmatite near the contact and Li-rich pegmatites more distal?
Hi Mona, the geological map was made in 1980s and the real regional zoning is actually not what it was speculated to be. We are now redrawing the map based on our new field observations. According to our field observations, the Li-rich pegmatites are mainly confined to the northern part of the region whereas Be-rich pegmatites are mainly in the southern part. The distribution pattern parallel to the boundary of the older granite was likely due to the influence of the magmatic fractionation model back in the early days. Geochronological studies show that the granite (~400 Ma old) is unlikely the parental granite to the rare-element pegmatites (~225 to 200 Ma) in the same region.
Submitted by Mona Sirbescu on Friday 26th June 20:38
If pegmatites are considered anatectic, how do you explain the regional zoning (I, II, III; slide 7) that seem to parallel the contact with the older granite, with barren pegmatite near the contact and Li-rich pegmatites more distal?
Hi Mona, the geological map was made in 1980s and the real regional zoning is actually not what it was speculated to be. We are now redrawing the map based on our new field observations. According to our field observations, the Li-rich pegmatites are mainly confined to the northern part of the region whereas Be-rich pegmatites are mainly in the southern part. The distribution pattern parallel to the boundary of the older granite was likely due to the influence of the magmatic fractionation model back in the early days. Geochronological studies show that the granite (~400 Ma old) is unlikely the parental granite to the rare-element pegmatites (~225 to 200 Ma) in the same region.
If pegmatites are considered anatectic, how do you explain the regional zoning (I, II, III; slide 7) that seem to parallel the contact with the older granite, with barren pegmatite near the contact and Li-rich pegmatites more distal?
Hi Mona, the geological map was made in 1980s and the real regional zoning is actually not what it was speculated to be. We are now redrawing the map based on our new field observations. According to our field observations, the Li-rich pegmatites are mainly confined to the northern part of the region whereas Be-rich pegmatites are mainly in the southern part. The distribution pattern parallel to the boundary of the older granite was likely due to the influence of the magmatic fractionation model back in the early days. Geochronological studies show that the granite (~400 Ma old) is unlikely the parental granite to the rare-element pegmatites (~225 to 200 Ma) in the same region.
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