Composiciones isotópicas y estudio de proveniencia en circones de las rocas magmáticas y sedimentarias del paleozoico tardío-jurásico de la península Antártica : implicancias para la evolución del margen occidental de Gondwana
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2021
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es
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Universidad Andrés Bello
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Resumen
Hasta la fecha no se han reportado datos de carácter concluyente sobre
si la Península Antártica (PA) evolucionó a través de un desarrollo autóctono del
margen sur occidental de Gondwana durante el Paleozoico y Mesozoico, o si solo
el Dominio Oriental (DO) era parte del proto-margen de Gondwana, y el Dominio
Central (DC) corresponde a un arco continental alóctono acrecionado al Dominio
Oriental y suturado a través de la Zona de Sutura de Tierra de Palmer Este
(ZCTPE) durante el Cretácico. En este trabajo se estudiaron las poblaciones de
edades U-Pb y las composiciones isotópicas de Hf de los circones de las rocas
magmáticas y sedimentarias del Paleozoico tardío – Mesozoico temprano de la
PA para tratar de obtener evidencia de su evolución geológica paleozoica y
mesozoica en el sur de Gondwana. Ambos domino de la PA se habrían
dispersado en su marque margen sur occidental a lo largo del margen de Terra
Australis de Cawood (2005). Las edades de concordia 206Pb/238U de bordes de
circón magmático del Jurásico abarca entre 151 ± 1 y 183 ± 8 Ma en la PA. Las
rocas magmáticas jurásicas, se encuentran presentes en ambos dominios de la
Península, y el magmatismo Jurásico se habría desarrollado a través de 3
periodos de mayor actividad magmática en; 183-179, 167-160, y 155-151 Ma. En
el Jurásico, la apertura del Mar de Weddell habría provocado transcurrencia en
la ZCTPE, acompañada de la depositación de circón detrítico en el DO. El circón
heredado habría sido conservado preferentemente en el DO. Las fuentes que
alimentaron al sistema detrítico del DO, no se habrían encontrado in-situ, y en el
Jurásico las rocas ígneas del DO no habían incorporado fuentes Devónicas ni
Ordovícicas. Durante el Jurásico el DC se habría alimentado de circón ígneo del
DO y detrítico no autóctono, provenientes desde fuentes distales a la PA,
apoyando una historia común para ambos dominios. Desde el Fanerozoico el DO
venía incorporando fuentes mixtas corticales. El sistema detrítico del DO no se
acopló con el magmatismo del mismo durante el Neoproterozoico–Cámbrico, y ambos sistemas habrían tenido fuentes diferentes. Las composiciones isotópicas
de Hf de los circones ígneos son similares en ambos dominios en el Paleozoico
tardío, y el magmatismo del DC también fue incorporando fuentes corticales
mixtas, pero en menor medida y en un periodo más restringido que DO.
Concluyendo que la ZCTPE corresponde a una zona de sutura en la corteza
continental Cretácica dado que las poblaciones de los circones de las rocas que
se encuentran a distintos lados de la ZCTPE registran poblaciones y
composiciones isotópicas distintas durante parte del Paleozoico y Mesozoico
temprano. No obstante las diferencias encontradas no apoyan conclusivamente
una historia separada para ambos dominios, dado que las composiciones
isotópicas de Hf se vuelven similares en el Paleozoico tardío y ya en el Triásico
se encuentran bastante bien acopladas, además los circones ígneos jurásicos se
encuentran en ambos dominios, y el DC debió estar en cercanía relativa con el
DO para poder alimentarse de sus componentes Paleozoicos, por lo que es más
probable que ambos dominios de la PA hallan evolucionado a través de
mecanismos similares desde su posible origen autóctono común en el margen
sur occidental de Gondwana, y probablemente mantuvieron su cercanía relativa
hasta su completo ensamblaje durante el Cretácico.
To date, no conclusive data has been reported on whether the Antarctic Peninsula (AP) evolved through autochthonous development of the southwestern margin of Gondwana during the Paleozoic and Mesozoic, or whether only the Eastern Domain (ED) was part of the proto-margin of Gondwana, and the Central Dominion (CD) corresponds to an allochthonous continental arc accreted to the Eastern Dominion and sutured through the Eastern Palmer Land Shear Zone (EPSZ) during the Cretaceous. In this work, the populations of U-Pb ages and the Hf isotopic compositions of the zircons of the late Paleozoic – early Mesozoic magmatic and sedimentary rocks of the AP were studied to try to obtain evidence of their Paleozoic and Mesozoic geological evolution in southern Gondwana. Both domains of the Antarctic Peninsula would have been dispersed in their far southwestern margin along the margin of Terra Australis from Cawood (2005). The 206Pb/238U concord ages of Jurassic magmatic zircon boundaries span between 151 ± 1 and 183 ± 8 Ma in the AP. Jurassic magmatic rocks are present in both domains of the Peninsula, and Jurassic magmatism developed through 3 periods of increased magmatic activity in; 183-179, 167-160, and 155-151 Ma. In the Jurassic, the opening of the Weddell Sea would have caused elapse in the EPSZ, accompanied by the deposition of detrital zircon in the ED. The inherited zircon would have been preferentially conserved in the ED. The sources that fed the ED detrital system were not found in-situ, and in the Jurassic ED igneous rocks had not incorporated Devonian or Ordovician sources. During the Jurassic, the CD would have fed on igneous zircon from the ED and non- autochthonous detrital, coming from sources distal to the PA, supporting a common history for both domains. Since the Phanerozoic, the ED had been incorporating mixed cortical sources. The ED detrital system did not couple with its magmatism during the Neoproterozoic–Cambrian, and both systems had different sources. The Hf isotopic compositions of the igneous zircons are similar in both domains in the late Paleozoic, and the CD magmatism was also incorporating mixed crustal sources, but to a lesser extent and in a more restricted period than ED. Concluding that the EPSZ corresponds to a suture zone in the Cretaceous continental crust since the zircon populations of the rocks that are found on different sides of the EPSZ record different populations and isotopic compositions during the Paleozoic and early Mesozoic. However, the differences found do not conclusively support a separate history for both domains, since the isotopic compositions of Hf become similar in the late Paleozoic and already in the Triassic they are quite well coupled, in addition, the Jurassic igneous zircons are found in both domains, and CD must have been in relative proximity to ED in order to feed on its Paleozoic components, so it is more likely that both domains of PA have evolved through similar mechanisms from their possible common autochthonous origin in the southwestern margin of Gondwana, and probably maintained their relative proximity until their complete assembly during the Cretaceous.
To date, no conclusive data has been reported on whether the Antarctic Peninsula (AP) evolved through autochthonous development of the southwestern margin of Gondwana during the Paleozoic and Mesozoic, or whether only the Eastern Domain (ED) was part of the proto-margin of Gondwana, and the Central Dominion (CD) corresponds to an allochthonous continental arc accreted to the Eastern Dominion and sutured through the Eastern Palmer Land Shear Zone (EPSZ) during the Cretaceous. In this work, the populations of U-Pb ages and the Hf isotopic compositions of the zircons of the late Paleozoic – early Mesozoic magmatic and sedimentary rocks of the AP were studied to try to obtain evidence of their Paleozoic and Mesozoic geological evolution in southern Gondwana. Both domains of the Antarctic Peninsula would have been dispersed in their far southwestern margin along the margin of Terra Australis from Cawood (2005). The 206Pb/238U concord ages of Jurassic magmatic zircon boundaries span between 151 ± 1 and 183 ± 8 Ma in the AP. Jurassic magmatic rocks are present in both domains of the Peninsula, and Jurassic magmatism developed through 3 periods of increased magmatic activity in; 183-179, 167-160, and 155-151 Ma. In the Jurassic, the opening of the Weddell Sea would have caused elapse in the EPSZ, accompanied by the deposition of detrital zircon in the ED. The inherited zircon would have been preferentially conserved in the ED. The sources that fed the ED detrital system were not found in-situ, and in the Jurassic ED igneous rocks had not incorporated Devonian or Ordovician sources. During the Jurassic, the CD would have fed on igneous zircon from the ED and non- autochthonous detrital, coming from sources distal to the PA, supporting a common history for both domains. Since the Phanerozoic, the ED had been incorporating mixed cortical sources. The ED detrital system did not couple with its magmatism during the Neoproterozoic–Cambrian, and both systems had different sources. The Hf isotopic compositions of the igneous zircons are similar in both domains in the late Paleozoic, and the CD magmatism was also incorporating mixed crustal sources, but to a lesser extent and in a more restricted period than ED. Concluding that the EPSZ corresponds to a suture zone in the Cretaceous continental crust since the zircon populations of the rocks that are found on different sides of the EPSZ record different populations and isotopic compositions during the Paleozoic and early Mesozoic. However, the differences found do not conclusively support a separate history for both domains, since the isotopic compositions of Hf become similar in the late Paleozoic and already in the Triassic they are quite well coupled, in addition, the Jurassic igneous zircons are found in both domains, and CD must have been in relative proximity to ED in order to feed on its Paleozoic components, so it is more likely that both domains of PA have evolved through similar mechanisms from their possible common autochthonous origin in the southwestern margin of Gondwana, and probably maintained their relative proximity until their complete assembly during the Cretaceous.
Notas
Memoria (Geólogo)
Palabras clave
Rocas Magmáticas, Rocas Sedimentarias, Circones, Antártica