Rift-Systeme an aktiven Kontinentalrändern: Eine Fazies- und Provenanzstudie der vulkanosedimentären Entwicklung der Mitu Group (Perm-Trias; zentrale Anden, Peru)
Zusammenfassung der Projektergebnisse
The Permian-Triassic transition from the Late Paleozoic arc regime of southwestern margin of Gondwana to the Andean accretionary orogen initiated in the Early Jurassic is marked in the Central Andes by the development of extensional basins, presumably formed in back-arc or riftrelated settings. In the Peruvian Andes, the basin fills consist of stratigraphically poorly controlled red beds and volcanosedimentary successions commonly known as the Mitu Group and equivalents. The Mitu succession is characterized by bi-modal alkaline to calc-alkaline lavas, ignimbrites and tuffs that are interbedded with thick continental successions deposited in fluvial, floodplain and alluvial environments. We present results of our analysis of the facies evolution and provenance of twelve Permian- Triassic stratigraphic sections along the Eastern Cordillera of Peru encompassing ~1200 km of the Mitu basin. Our study aims at constraining the sedimentology, chronology, spatial development and tectonic setting of evolving depocenters by single-grain studies of heavy minerals, LA-ICP-MS dating and Lu-Hf isotope analysis of detrital zircons. Previous studies indicate that the Upper Permian part of the Mitu Group overlies the limestones and subordinate sandstones of the Lower Permian? Copacabana Group above a hiatus, and that the timespan of the extensional tectonics and the depositional evolution of the basin fill is still unclear. However, our new results using facies analysis and U-Pb dating of detrital zircons indicate the absence of a significant hiatus in the Cusco region, exhibiting a mixed carbonate-siliciclastic transition from marine (Copacabana Group, maximum depositional age of 262.6±1.5 Ma) to continental conditions (Mitu Group, maximum depositional age of 260.3±3.7 Ma) during the Upper Guadalupian. A sandstone at the top of Mitu section in Cusco with a maximum depositional age of 197.3±2.7 Ma indicates that the Mitu sedimentation and extensional tectonics may have persisted until the Early Jurassic. Concordia ages on volcanic zircons from crystal-rich ignimbrites exhibit consistent ages, establishing, at least, four volcanic episodes during the basin filling: 260.2±1.9 Ma (Guadalupian to Lopingian, Upper Permian), 252.9±1.3 Ma (Transition Upper Permian-Lower Triassic), 236.0±0.94 Ma (Carnian, Upper Triassic) and 223.0±2.0 Ma (Norian, Upper Triassic). Upper Permian-Early Jurassic detrital and volcanic zircons extracted from sandstones and ignimbrites, respectively, yield a large εHf(t) variation between +5.54 and - 12.00, suggesting variable degrees of contamination of mantle-derived magmas with crustal components. The relative abundance of inherited zircons and the distribution of εHf(t) values indicates that older crustal rocks significantly contributed to the development of magmatism and volcanism in the Mitu basin. In view of the presence of arc magmatism at Mitu Group time, from the late Permian to the late Triassic, in both Ecuador and in northern Chile, that is N and S of the Mitu basin, one has to conclude that the Mitu Group basin also formed at an active margin. The volcanic arc of this active margin is unknown. In view of large-scale subduction erosion since the onset of the Andean orogenic cycle near the Triassic-Jurassic transition, it is highly likely that there originally was a Permian-Triassic magmatic arc which has been eroded since by subduction processes.
Projektbezogene Publikationen (Auswahl)
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(2017): Rift systems at continental margins: A case study of facies and provenance of the sedimentary-volcanic Mitu Group (Permotriassic; Central Andes, Peru).- GeoBremen 2017, DGGV Annual Meeting, abstracts
Panca, F., Bahlburg, H.
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(2018): Climate-tectonic interaction in the Chugach-St. Elias Mountains: insights from sediments Provenance and facies analysis evolution of extensional basins: a case study of the Permotriassic Mitu Group (Central Andes, Peru). 4th Workshop of the Working Group on Sediment Generation (WGSG), Dublin, abstracts
Panca, F., Bahlburg, H., Berndt, J.
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(2018): Provenance, chronostratigraphic framework and volcanosedimentary facies architecture of the Permotriassic Mitu Group in southern Peru, central Andes. XIX Congreso Peruano de Geología, Lima, abstracts
Panca, F., Bahlburg, H.
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(2018): Provenance, chronostratigraphic framework and volcanosedimentary facies architecture of the Permotriassic Mitu Group in southern Peru, central Andes.- 11th South American Symposium on Isotope Geology, Cochabamba, Bolivia, abstracts
Panca, F., Bahlburg, H.
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(2018): Rift systems at continental margins: A case study of facies and provenance of the volcanosedimentary Permotriassic Mitu Group (Central Andes, Peru).- 11th South American Symposium on Isotope Geology, Cochabamba, Bolivia, abstracts
Panca, F., Bahlburg, H.
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(2019): Provenance, facies, geochronology and tectonic evolution of continental extensional basins: a case study of the Permotriassic Mitu Group (Central Andes, Peru).- GeoMünster 2019, DGGV-DMG Annual Meeting, abstracts
Panca, F., Bahlburg, H.
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(2021): Paleozoic and Triassic crustal evolution of the proto-Andes from detrital heavy minerals.- Australian Earth Science Convention 2021, Hobart, Tasmania, Australia, abstracts
Bahlburg, H., Panca, F.
