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The geodynamics of collision of a microplate (Chilenia) in Devonian times deduced by the pressure-temperature-time evolution within part of a collisional belt (Guarguaraz Complex, W-Argentina)

  • The Guarguaraz Complex in West Argentina formed during collision between the microplate Chilenia and South America. It is composed of neritic clastic metasediments with intercalations of metabasic and ultrabasic rocks of oceanic origin. Prograde garnet growth in metapelite and metabasite occurred between 1.2 GPa, 470 degrees C and 1.4 GPa, 530 degrees C, when the penetrative s(2)-foliation was formed. The average age of garnet crystallization of 390 +/- 2 Ma (2 sigma) was determined from three four-point Lu-Hf mineral isochrones from metapelite and metabasite samples and represents the time of collision. Peak pressure conditions are followed by a decompression path with slight heating at 0.5 GPa, 560 degrees C. Fluid release during decompression caused equilibration of mineral compositions at the rims and also aided Ar diffusion. An Ar-40/39 Ar plateau age of white mica at 353 +/- 1 Ma (1 sigma) indicates the time of cooling below 350-400 degrees C. These temperatures were attained at pressures of 0.2-0.3 GPa, indicative of an averageThe Guarguaraz Complex in West Argentina formed during collision between the microplate Chilenia and South America. It is composed of neritic clastic metasediments with intercalations of metabasic and ultrabasic rocks of oceanic origin. Prograde garnet growth in metapelite and metabasite occurred between 1.2 GPa, 470 degrees C and 1.4 GPa, 530 degrees C, when the penetrative s(2)-foliation was formed. The average age of garnet crystallization of 390 +/- 2 Ma (2 sigma) was determined from three four-point Lu-Hf mineral isochrones from metapelite and metabasite samples and represents the time of collision. Peak pressure conditions are followed by a decompression path with slight heating at 0.5 GPa, 560 degrees C. Fluid release during decompression caused equilibration of mineral compositions at the rims and also aided Ar diffusion. An Ar-40/39 Ar plateau age of white mica at 353 +/- 1 Ma (1 sigma) indicates the time of cooling below 350-400 degrees C. These temperatures were attained at pressures of 0.2-0.3 GPa, indicative of an average exhumation rate of >= 1 mm/a for the period 390-353 Ma. Late hydrous influx at 0.1-0.3 GPa caused pervasive growth of sericite and chlorite and reset the Ar/Ar ages of earlier coarse-grained white mica. At 284-295 Ma, the entire basement cooled below 280 degrees C (fission track ages of zircon) after abundant post-collisional granitoid intrusion. The deeply buried epicontinental sedimentary rocks, the high peak pressure referring to a low metamorphic geotherm of 10-12 degrees C/km, and the decompression/heating path are characteristics of material buried and exhumed within a (micro) continent-continent collisional setting.show moreshow less

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Metadaten
Author:Arne P. Willner, Axel Gerdes, Hans-Joachim Massonne, Alexander Schmidt, Masafumi Sudo, Stuart N. Thomson, Graciela Vujovich
DOI:https://doi.org/10.1007/s00410-010-0598-8
ISSN:0010-7999 (print)
Parent Title (English):Contributions to mineralogy and petrology
Publisher:Springer
Place of publication:New York
Document Type:Article
Language:English
Year of first Publication:2011
Year of Completion:2011
Release Date:2017/03/26
Tag:Albite-amphibolite facies; Collision zone; Fission track (zircon); Garnet; Geothermobarometry; K-Ar system; Lu-Hf system; Potassic white mica
Volume:162
Issue:2
Pagenumber:25
First Page:303
Last Page:327
Funder:Deutsche Forschungsgemeinschaft [Ma1160/24]; German-Chilean BMBF-CONICYT [CHL07/025]
Organizational units:Mathematisch-Naturwissenschaftliche Fakultät / Institut für Erd- und Umweltwissenschaften
Peer Review:Referiert