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Article

Rare Earth Element and Incompatible Trace Element Abundances in Emeralds Reveal Their Formation Environments

1
Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA
2
Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093, USA
*
Author to whom correspondence should be addressed.
Academic Editors: Paul Sylvester, Alexander R. Cruden, Sytle M. Antao, Huifang Xu, Nigel J. Cook, Theodore J. Bornhorst, Hanumantha Rao Kota and Anna H. Kaksonen
Minerals 2021, 11(5), 513; https://doi.org/10.3390/min11050513
Received: 29 April 2021 / Revised: 6 May 2021 / Accepted: 11 May 2021 / Published: 13 May 2021
(This article belongs to the Special Issue 10th Anniversary of Minerals: Frontiers of Mineral Science)
Emeralds require the unusual association of typically compatible elements (Cr, V), with incompatible Be to form, and occur in complex tectonic settings associated with sediments (type IIB; Colombia) or, more commonly, with magmatism and regional metamorphism (IA). Precise rare earth element (REE) and incompatible trace element abundances are reported for a global suite of emeralds, enabling the identification of the environments in which they formed. Type IIB emeralds have nearly flat continental crust normalized REE patterns (La/YbCC = ~2), consistent with a sedimentary source origin. Type IA emerald REE patterns have upturns in the heavy REE (La/YbCC = ~0.3), a feature also shared with South African emeralds occurring in Archaean host rocks. Modeling of type IA emerald compositions indicates that they form from magmatic fluids of sedimentary (S)-type granite melts interacting with Cr, V-rich mafic–ultramafic crustal protoliths. This geochemical signature links emerald formation with continental suture zones. Diamonds, rubies, and sapphires have been considered as ‘plate tectonic gemstones’ based on mineral inclusions within them, or associations with plate tectonic indicators. Emeralds are distinct plate tectonic gemstones, recording geochemical evidence for origin within their mineral structure, and indicating that plate tectonic processes have led to emerald deposit formation since at least the Archaean. View Full-Text
Keywords: emeralds; gemstones; trace elements; rare earth elements; plate tectonics; sediments; s-type granite emeralds; gemstones; trace elements; rare earth elements; plate tectonics; sediments; s-type granite
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MDPI and ACS Style

Alonso-Perez, R.; Day, J.M.D. Rare Earth Element and Incompatible Trace Element Abundances in Emeralds Reveal Their Formation Environments. Minerals 2021, 11, 513. https://doi.org/10.3390/min11050513

AMA Style

Alonso-Perez R, Day JMD. Rare Earth Element and Incompatible Trace Element Abundances in Emeralds Reveal Their Formation Environments. Minerals. 2021; 11(5):513. https://doi.org/10.3390/min11050513

Chicago/Turabian Style

Alonso-Perez, Raquel, and James M.D. Day 2021. "Rare Earth Element and Incompatible Trace Element Abundances in Emeralds Reveal Their Formation Environments" Minerals 11, no. 5: 513. https://doi.org/10.3390/min11050513

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