40Ar/39Ar Geochronology of the lithium-rich tuff in the Macusani Volcanic field, Oriental Cordillera, Peru
Date
2024-09-10
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Pontificia Universidad Católica del Perú
Abstract
Descubierto en 2017 en el Campo Volcánico Macusani, Puno, SE Perú, el Proyecto de Litio
Falchani contiene recursos inferidos e indicados de 5,53 Mt de carbonato de litio equivalentes.
El recurso de litio está alojado mayormente en una unidad llamada Lithium-rich Tuff. Esta
unidad comprende principalmente lodolitas tufáceas y ha sido correlacionada
estratigráficamente con la Formación Macusani, depositada entre ca. 10 y 6.5 Ma. En esta tesis
presento las primeras dataciones radiométricas en Lithium-rich Tuff y tobas brechificadas
coespaciales para evaluar su adscripción estratigráfica y contextualización de este evento
magmático dentro de la evolución Neógena de los Andes Centrales. Las edades, obtenidas
mediante el método 40Ar/39Ar en cristaloclastos de mica, están comprendidas entre 8.978 ± 73
ka y 8.717 ± 44 ka. Las muestras de toba brechificada arrojaron edades comprendidas en un
estrecho rango entre 8.823 ± 9 ka y 8.815 ± 16 ka, que se encuentra dentro del intervalo de
edad definido por las muestras de Lithium-rich Tuff. Las edades obtenidas representan edades
de cristalización o enfriamiento de las micas y reflejan edades máximas de sedimentación. De
acuerdo a estos datos, los cristaloclastos de mica se formaron o fueron expulsados durante un
breve periodo de ca. 261 kyr (entre 144 kyr y 379 kyr considerando errores analíticos). Las
edades obtenidas coinciden con el lapso de tiempo comprendido entre los dos ciclos eruptivos
a 10 ± 1 Ma y 7 ± 1 Ma registrados para la Formación Macusani. En base a una exhaustiva
recopilación de dataciones geocronológicas previas en la Cordillera Oriental de los Andes en
el SE de Perú se demuestra que no existen unidades intrusivas, volcánicas o volcaniclásticas
de edad equivalente. Por lo tanto, se concluye que el evento asociado a la formación o
enfriamiento de las micas en la Lithium-rich Tuff ocurrió durante un periodo de muy baja o
nula actividad magmática en la región.
The Falchani Lithium Project was discovered in 2017 in the Macusani Volcanic Field, Puno, SE Peru. The inferred and indicated resources of the project total 5.53 Mt of lithium carbonate equivalent. The lithium resource is hosted mostly in a unit called Lithium-rich Tuff. This unit is composed primarily of tuffaceous mudstone and has been stratigraphically correlated with the Macusani Formation, which was deposited between ca. 10 and 6.5 Ma. In this thesis, I present the first radiometric dating on Lithium-rich Tuff and cospatial brecciated tuff to evaluate their stratigraphic ascription and the contextualization of the associated magmatic event within the Neogene evolution of the Central Andes. The dates obtained by the 40Ar/39Ar method on mica crystal clasts in Lithium-rich Tuff range from 8,979 ± 73 ka to 8,717 ± 44 ka. The brecciated tuff samples yielded dates within a narrow range between 8,823 ± 9 ka and 8,815 ± 16 ka, which is within the age interval defined by the Lithium-rich Tuff samples. The dates obtained represent crystallization or cooling ages of the micas and reflect maximum sedimentation ages. The data indicate that the mica crystal clasts formed or were ejected during a relatively brief period of ca. 261 kyr (between 144 kyr and 379 kyr, considering analytical errors). The obtained dates align with the temporal span between the two eruptive cycles at 10 ± 1 Ma and 7 ± 1 Ma recorded by the Macusani Formation. A comprehensive review of previous geochronological studies in the Eastern Cordillera of the Andes in southeastern Peru reveals the absence of intrusive, volcanic, or volcaniclastic units of comparable age. This suggests that the event related to the formation or cooling of the mica crystal clasts in the Lithium-rich Tuff occurred during a period of very low or nil magmatic activity in the region.
The Falchani Lithium Project was discovered in 2017 in the Macusani Volcanic Field, Puno, SE Peru. The inferred and indicated resources of the project total 5.53 Mt of lithium carbonate equivalent. The lithium resource is hosted mostly in a unit called Lithium-rich Tuff. This unit is composed primarily of tuffaceous mudstone and has been stratigraphically correlated with the Macusani Formation, which was deposited between ca. 10 and 6.5 Ma. In this thesis, I present the first radiometric dating on Lithium-rich Tuff and cospatial brecciated tuff to evaluate their stratigraphic ascription and the contextualization of the associated magmatic event within the Neogene evolution of the Central Andes. The dates obtained by the 40Ar/39Ar method on mica crystal clasts in Lithium-rich Tuff range from 8,979 ± 73 ka to 8,717 ± 44 ka. The brecciated tuff samples yielded dates within a narrow range between 8,823 ± 9 ka and 8,815 ± 16 ka, which is within the age interval defined by the Lithium-rich Tuff samples. The dates obtained represent crystallization or cooling ages of the micas and reflect maximum sedimentation ages. The data indicate that the mica crystal clasts formed or were ejected during a relatively brief period of ca. 261 kyr (between 144 kyr and 379 kyr, considering analytical errors). The obtained dates align with the temporal span between the two eruptive cycles at 10 ± 1 Ma and 7 ± 1 Ma recorded by the Macusani Formation. A comprehensive review of previous geochronological studies in the Eastern Cordillera of the Andes in southeastern Peru reveals the absence of intrusive, volcanic, or volcaniclastic units of comparable age. This suggests that the event related to the formation or cooling of the mica crystal clasts in the Lithium-rich Tuff occurred during a period of very low or nil magmatic activity in the region.
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Litio--Perú--Carabaya (Puno : Provincia), Volcanes--Perú--Carabaya (Puno : Provincia), Datación radiactiva--Perú--Carabaya (Puno : Provincia), Estratigrafía--Perú--Carabaya (Puno : Provincia)
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