Sind Zirkone für die Ewigkeit? Zum Problem ererbter Zirkone in juveniler Lithosphäre (ozeanische Gesteine) und im subkontinentalen Mantel
Zusammenfassung der Projektergebnisse
To our initial question: Are zircons forever? Our answer is yes! Even if we can not (100 %) demonstrate it and new scientific questions arise, our project has contributed to a better understanding of the problem of zircon inheritance in mantle-derived rocks. We also nicely show that by just sampling in a Pacific beach sand we are able to know what is underneath volcanic islands (with the tiny but mighty zircon) and unravel the history of a mantle plume. Zircon is stable down to 300 km depth, before it transforms into reidite, and it is expected to form after significant crystallization of primitive Zr-subsaturated basaltic liquids. This translates into the potential crystallization of zircons from near-solidus Zr-saturated evolved basaltic liquids at plume-head regions with limited melt fraction. Experimental work shows that zircon can survive in the presence of basic melt for long time as long as the volume of melt that interact with a crystal of zircon is limited in extent. This implies that, once formed, zircon can survive in a hot mantle provided that the plume region was not later affected by relatively large partial melting or by porous flow of significant amount of Zr-undersaturated basaltic liquid, even more if zircon is shielded within other minerals. If shielded in grains of Pb-free minerals, zircon grains can retain their U-Pb crystallization ages even at 1500 ºC, independently of how long they have remained in the mantle. Eventually, rapidly ascending liquids may pick zircon-bearing rock fragments and bring them to the surface. Likely processes may involve dissolution of (some) zircon, if not shielded and/or the liquid arrests in a magma chamber, but ultimately some survived in the crystallizing magmas that eventually reached Zr-saturation and formed new zircon in the lavas, as demonstrated in this study. Our findings of significantly old asthenospheric mantle zircons in Galapagos and Easter, challenge current ideas about asthenosphere convection and plume/lithosphere interaction. In our Galapagos paper we explore circulation processes in the head of the mantle plume and adjacent mantle that may have allowed some of the early crystallized material to remain in the asthenosphere over millions of years until eventually extracted by ascending Galápagos lavas.
Projektbezogene Publikationen (Auswahl)
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(2014). Detrital and igneous zircon ages for supracrustal rocks of the Kyrgyz Tianshan and palaeogeographic implications. Gondwana Research, 26(3-4), 957-974
Rojas-Agramonte, Y., Kröner, A., Alexeiev, D. V., Jeffreys, T., Khudoley, A. K., Wong, J., ... & Seltmann, R.
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(2016). Recycling and transport of continental material through the mantle wedge above subduction zones: A Caribbean example. Earth and Planetary Science Letters, 436, 93-107
Rojas-Agramonte, Y., Garcia-Casco, A., Kemp, A., Kröner, A., Proenza, J. A., Lázaro, C., & Liu, D.
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(2017). A geotraverse across two paleo-subduction zones in Tien Shan, Tajikistan. Gondwana Research, 47, 110-130
Konopelko, D., Seltmann, R., Mamadjanov, Y., Romer, R. L., Rojas-Agramonte, Y., Jeffries, T., ... & Niyozov, A.
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(2017). Ancient xenocrystic zircon in young volcanic rocks of the southern Lesser Antilles island arc. Lithos, 290, 228-252
Rojas-Agramonte, Y., Williams, I. S., Arculus, R., Kröner, A., García-Casco, A., Lázaro, C., ... & Mertz-Kraus, R.
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(2018). Cold plumes trigger contamination of oceanic mantle wedges with continental crust-derived sediments: Evidence from chromitite zircon grains of eastern Cuban ophiolites. Geoscience Frontiers, 9(6), 1921-1936
Proenza Fernández, Joaquín Antonio; González Jiménez, Jose María; Garcia Casco, Antonio; Belousova, Elena; Griffin, William L.; Talavera, Cristina; Rojas-Agramonte, Yamirka; Aiglsperger, Thomas Hans; Navarro Ciurana, Dídac; Pujol Solà, Núria; Gervilla, Fernando; O'Reilly, Suzanne Yvette; Jacob, Dorrit E.
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(2018). Recycling in the subduction factory: Archaean to Permian zircons in the oceanic Cretaceous Caribbean island-arc (Hispaniola). Gondwana Research, 54, 23-37
Torró, L., Proenza, J. A., Rojas-Agramonte, Y., Garcia-Casco, A., Yang, J. H., & Yang, Y. H.
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(2019). Detrital-zircon geochronology and provenance of the El Oro Metamorphic Complex, Ecuador: Geodynamic implications for the evolution of the western Gondwana margin. Journal of South American Earth Sciences, 90, 520-539
Suhr, N., Rojas-Agramonte, Y., Chew, D. M., Pinto, A. J., Villagómez-Díaz, D., Toulkeridis, T., & Mertz-Kraus, R.
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(2019). Evolution of Cambrian and Early Ordovician arcs in the Kyrgyz North Tianshan: Insights from U-Pb zircon ages and geochemical data. Gondwana Research, 66, 93-115
Alexeiev, D. V., Kröner, A., Kovach, V. P., Tretyakov, A. A., Rojas-Agramonte, Y., Degtyarev, K. E., ... & Kiselev, V. V.
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(2019). Evolution of the middle Paleozoic magmatism in the Chinese Altai: Constraints on the crustal differentiation at shallow depth in the accretionary orogen. Journal of Asian Earth Sciences, 175, 230-246
Yu, Y., Sun, M., Yuan, C., Zhao, G., Huang, X. L., Rojas-Agramonte, Y., & Chen, Q.
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(2020). Cryptic alkaline magmatism in the oceanic Caribbean arc (Camagüey area, Cuba). Lithos, 376, 105736
Torró, L., Cambeses, A., Rojas-Agramonte, Y., Butjosa, L., Iturralde-Vinent, M., Lázaro, C., ... & Garcia-Casco, A.
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(2020). Ediacaran, Early Ordovician and early Silurian arcs in the South Tianshan orogen of Kyrgyzstan. Journal of Asian Earth Sciences, 190, 104194
Alexeiev, D. V., Biske, G. S., Kröner, A., Tretyakov, A. A., Kovach, V. P., & Rojas- Agramonte, Y.
