Abstract Details
(2020) Petrogenesis of Middle Triassic Mafic Microgranular Enclaves and Host Granodiorite in the Eastern Kunlun Orogenic Belt, NW China: Record of Juvenile Lower Crustal Melting and Crust-Mantle Interactions at the Paleo-Tethys Ocean Subduction Terminating
Li G, Zhang D & Wei J
https://doi.org/10.46427/gold2020.1474
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04j: Room 1, Saturday 27th June 06:06 - 06:09
Guomeng Li
Daohan Zhang
Junhao Wei
Daohan Zhang
Junhao Wei
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Submitted by Changqian Ma on Wednesday 24th June 09:34
Thank you for showing an important result! How to distinguish the plagioclase in mafic microgranular enclaves from a xenocryst or a phenocryst?
First of all, Prof. Ma, thank you for your insightful question. Medium-coarse plagioclase in MMEs shows characteristic reverse zoning structure , which is obviously different from the plagioclase phenocryst in the host rock with normal zoning structure. In addition, this kind of plagioclase usually has eroded and rounded core. We proposed that this plagioclase was captured from the host felsic magma rather than crystallized in the mafic magma forming MMEs. After capture, the plagioclase was eroded by the high-temperature and Ca-rich mafic magma, and then underwent recrystallization or continued growth to form a reverse zoning structure with low An value at the core and high An value at the rim. Therefore, we tend to regard this plagioclase as xenocryst rather than phenocryst. MMEs in the granitoid in East Kunlun Orogenic Belt are generally considered as record of magma mixing (Ma et al., 2015). The mineralogical evidences of plagioclase xenocryst and quartz xenocryst (coarse quartz enclosed by amphibole rings) in MMEs reported here suggests that these enclaves were indeed formed by magma mixing.
Thank you for showing an important result! How to distinguish the plagioclase in mafic microgranular enclaves from a xenocryst or a phenocryst?
First of all, Prof. Ma, thank you for your insightful question. Medium-coarse plagioclase in MMEs shows characteristic reverse zoning structure , which is obviously different from the plagioclase phenocryst in the host rock with normal zoning structure. In addition, this kind of plagioclase usually has eroded and rounded core. We proposed that this plagioclase was captured from the host felsic magma rather than crystallized in the mafic magma forming MMEs. After capture, the plagioclase was eroded by the high-temperature and Ca-rich mafic magma, and then underwent recrystallization or continued growth to form a reverse zoning structure with low An value at the core and high An value at the rim. Therefore, we tend to regard this plagioclase as xenocryst rather than phenocryst. MMEs in the granitoid in East Kunlun Orogenic Belt are generally considered as record of magma mixing (Ma et al., 2015). The mineralogical evidences of plagioclase xenocryst and quartz xenocryst (coarse quartz enclosed by amphibole rings) in MMEs reported here suggests that these enclaves were indeed formed by magma mixing.
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