Hostname: page-component-cd9895bd7-jkksz Total loading time: 0 Render date: 2024-12-23T15:40:13.707Z Has data issue: false hasContentIssue false
  • English
  • Français

Significance of 40Ar–39Ar encapsulation ages of metapelites from late Palaeozoic metamorphic complexes of Aysén, Chile

Published online by Cambridge University Press:  17 December 2007

ELISA RAMÍREZ-SÁNCHEZ ,
KATJA DECKART  and
FRANCISCO HERVÉ
ELISA RAMÍREZ-SÁNCHEZ*
Affiliation:
Departamento de Geología, Universidad de Chile, Plaza Ercilla 803, Casilla 13518, Santiago, Chile
KATJA DECKART
Affiliation:
Departamento de Geología, Universidad de Chile, Plaza Ercilla 803, Casilla 13518, Santiago, Chile
FRANCISCO HERVÉ
Affiliation:
Departamento de Geología, Universidad de Chile, Plaza Ercilla 803, Casilla 13518, Santiago, Chile
*
*Author for correspondence: [email protected]
Get access Rights & Permissions [Opens in a new window]

Abstract

The ages obtained by the 40Ar–39Ar encapsulation technique (retention and total gas ages) on <2 μm fractions of five metapelites from the Eastern Andean Metamorphic Complex and two from the Chonos Metamorphic Complex allow discussion of the latest recorded metamorphic event in each zone. The Kübler Index (KI) of illite/muscovite (principal component of the metapelites) varies between 0.15° and 0.45° Δ°2θ, indicating regional variation from diagenetic to epizonal metamorphic grade. The 40Ar–39Ar encapsulation analyses reveal 39Ar loss varying between 21 and 25%, which shows a limited positive correlation with KI values. The obtained retention and total gas metapelite ages reflect distinct metamorphic conditions. Retention ages most probably indicate burial or regional metamorphic events without plutonic influence in the southern Eastern Andean Metamorphic Complex. Total gas ages reflect contact ages for metapelites close to intrusions in the northern and southern Eastern Andean Metamorphic Complex and in the Chonos Metamorphic Complex. The thermal overprinting of metapelites occurred in Early Cretaceous times at 130 Ma and 145 Ma and is related to the contact metamorphism of an emplacement pulse of the North Patagonian Batholith. Total gas metapelite ages obtained from the western belt of the Chonos Metamorphic Complex suggest a thermal event related to a distinct pulse of the North Patagonian Batholith.

Keywords

40Ar–39Ar encapsulationmetapelitemetamorphic complexes of AysénChile
Type
Original Article
Information
Geological Magazine , Volume 145 , Issue 3 , May 2008 , pp. 389 - 396
Copyright
Copyright © Cambridge University Press 2007

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Augustsson, C., Münkers, C., Bahlburg, H., & Fanning, C. M. 2006. Provenance of late Palaeozoic metasediments of the SW South American Gondwana margin: a combined U–Pb and Hf-isotope study of single detrital zircons. Journal of the Geological Society, London 163, 983–95.CrossRefGoogle Scholar
Bell, C. & Suárez, M. 2000. The Río Lácteo Formation of southern Chile. Late paleozoic orogeny in the Andes of southernmost South America. Journal of South American Earth Sciences 13, 133–45.CrossRefGoogle Scholar
Dallmeyer, R. D., Reuter, A., Clauer, N. & Liewig, N. 1989. Chronology of Caledonian tectonothermal activity within the Gaissa and Lakefjord nappe complexes (Lower Allochthon), Finnmark, Norway. In The Caledonide Geology of Scandinavia (ed. Gayer, R. A.), pp. 9–26. London: Graham and Trotman.CrossRefGoogle Scholar
Dong, H., Hall, C., Peacor, D. & Halliday, A. 1995. Mechanisms of Argon retention in clays revealed by laser 40Ar–39Ar dating. Science 267, 355–9.CrossRefGoogle ScholarPubMed
Fang, Z., Boucot, A., Covacevich, V. & Hervé, F. 1998. Discovery of Late Triassic fossils in the Chonos Metamorphic Complex, Southern Chile. Revista Geológica de Chile 25, 165–73.Google Scholar
Faúndez, V., Hervé, F. & Lacassie, J. P. 2002. Provenance and depositional setting of pre-Late Jurassic turbidite complexes in Patagonia, Chile. New Zealand Journal of Geology and Geophysics 45, 411–25.Google Scholar
Gradstein, F. M., Ogg, J. G., Smith, A. G., Agterberg, F. P., Bleeker, W., Cooper, R. A., Davydov, V., Gibbard, P., Hinnov, L. A., House, M. R., Lourens, L., Luterbacher, H. P., McArthur, J., Melchin, M. J., Robb, L. J., Shergold, J., Villeneuve, M., Wardlaw, B. R., Ali, J., Brinkhuis, H., Hilgen, F. J., Hooker, J., Howarth, R. J., Knoll, A. H., Laskar, J., Monechi, S., Plumb, K. A., Powell, J., Raffi, I., Röhl, U., Sadler, P., Sanfilippo, A., Schmitz, B., Shackleton, N. J., Shields, G. A., Strauss, H., Van Dam, J., van Kolfschoten, T., Veizer, J. & Wilson, D. 2005. A Geologic Time Scale 2004. Cambridge University Press, 589 pages.Google Scholar
Hall, C., Higueras, P., Kesler, S., Lunar, R., Dong, H. & Halliday, A. 1997. Dating of alteration episodes related to mercury mineralization in the Almadén district, Spain. Earth and Planetary Science Letters 148, 287–98.Google Scholar
Hall, C., Kesler, S., Simon, G. & Fortuna, J. 2000. Overlapping Cretaceous and Eocene Alteration, Twin Creeks Carlin-Type Deposit, Nevada. Economic Geology 95, 1739–52.Google Scholar
Hervé, F., Mpodozis, C., Davidson, J. & Godoy, E. 1981. Observaciones estructurales y petrográficas en el basamento metamórfico del Archipiélago de los Chonos entre el Canal King y el Canal Ninualac, Aisén. Revista Geológica de Chile 13/41, 3–16.Google Scholar
Hervé, F., Fanning, C. M. & Pankhurst, R. 2003. Detrital zircon age patterns and provenance of the metamorphic complexes of southern Chile. Journal of South American Earth Science 16, 107–23.Google Scholar
Hunziker, J. C., Hurley, P. M., Clauer, N., Dallmeyer, R. D., Friedrichsen, H., Flehmig, W., Hochstrasser, K., Roggwiler, P. & Schwander, H. 1986. The evolution of illite to muscovite: mineralogical and isotopic data from the Glarus Alps, Switzerland. Contributions to Mineralogy and Petrology 92, 157–80.Google Scholar
Kligfield, R., Hunziker, J. C., Dallmeyer, R. D. & Schamel, S. 1986. Dating of deformation phases using K–Ar and 40Ar–39Ar techniques: Results from the Northern Apennines. Journal of Structural Geology 8, 781–98.Google Scholar
Lagally, U. 1975. Geologische Untersuchungen im Gebiet Lago General Carrera-Lago Cochrane, Prov. Aisén, Chile. Published Thesis, Ludwig Maximilians Universität 131 pp.Google Scholar
Lin, L.-H., Onstott, T. & Dong, H. 2000. Backscattered 39Ar loss in fine–grained minerals: Implications for 40Ar/39Ar geochronology of clay. Geochimica et Cosmochimica Acta 64, 3965–74.Google Scholar
Onstott, T. C., Miller, M. & Ewing, R. C. 1994. Recoil refinements: Implications for the 40Ar/39Ar dating technique. Geochimica et Cosmochimica Acta 59, 1821–34.Google Scholar
Parada, M., Palacios, C. & Lahsen, A. 1997. Jurassic extensional tectono-magmatism and associated mineralization of the El Faldeo polymetallic district, Chilean Patagonia: geochemical and isotopic evidence of crustal contribution. Mineralium Deposita 32, 547–54.CrossRefGoogle Scholar
Pankhurst, R., Weaver, S. D., Hervé, F. & Larrondo, P. 1999. Mesozoic–Cenozoic evolution of the North Patagonian Batholith in Aysen, southern Chile. Journal of the Geological Society, London 156, 673–94.Google Scholar
Pankhurst, R. J., Riley, T. R., Fanning, C. M. & Kelley, S. P. 2000. Episodic silicic volcanism in Patagonia and the Antarctic Peninsula: chronology of magmatism associated with the break-up of Gondwana. Journal of Petrology 41, 605–25.Google Scholar
Ramírez, E. & Sassi, R. 2001. The baric character of the Patagonian basement as deduced from the muscovite d(060,33) spacing: a first contribution from Eastern Andean Metamorphic Complex (Andes, Chile). European Journal of Mineralogy 13, 1119–26.Google Scholar
Ramírez-Sánchez, E., Hervé, F., Kelm, U. & Sassi, R. 2005. P–T conditions from metamorphic complexes in Aysen, Chile. Journal of South American Earth Sciences 19, 373–86.Google Scholar
Reuter, A. & Dallmeyer, R. 1987. Significance of 40Ar/39Ar age spectra of whole-rock and constituent grain-size fractions from anchizonal slates. Chemical Geology (Isotope Geoscience Section) 66, 73–88.Google Scholar
Reuter, A. & Dallmeyer, R. D. 1989: K–Ar and 40Ar/39Ar dating of cleavage formed during very low-grade metamorphism: a review. In Evolution of metamorphic belts (eds Daly, J. S., Cliff, R. A. & Yardley, B. W. D.), pp. 161–71. Geological Society of London, Special Publication no. 43.Google Scholar
Samson, S. & Alexander, E. C. 1987. Calibration of the interlaboratory 40Ar–39Ar dating standard, MMhb-1. Chemical Geology (Isotope Geoscience Section) 66, 27–34.CrossRefGoogle Scholar
Suárez, M. & De La Cruz, R. 2001. Jurassic to Miocene K–Ar dates from eastern central Patagonian Cordillera plutons, Chile (45–48° S). Geological Magazine 138, 53–66.Google Scholar
Thomson, S., Hervé, F. & Fanning, C. 2000. Combining fission-track and U–Pb SHRIMP zircon ages to establish stratigraphic and metamorphic ages in basement sedimentary rocks in southern Chile. Actas IX Congreso Geólogico Chileno 2, 769–73.Google Scholar
Thomson, S. & Hervé, F. 2002. New time contraints for the age of metamorphism at the ancestral Pacific Gondwana margin of southern Chile (42–52°S). Revista Geologica de Chile 29, 255–71.Google Scholar
Turner, G. & Cadogan, P. 1974. Possible effects of 39Ar recoil in 40Ar–39Ar dating. Proceedings, 5th Lunar Science Conference, Geochimica et Cosmochima Acta 5, 1601–15.Google Scholar
Warr, L. & Rice, H. 1994. Interlaboratory standardization and calibration of clay mineral crystallinity and crystallite size data. Journal of Metamorphic Geology 12, 141–52.CrossRefGoogle Scholar
Willner, A., Hervé, F. & Massonne, H. J. 2000. Mineral Chemistry and Pressure–Temperature evolution of two constraining High pressure–Low temperature belts in the Chonos Archipelago, Southern Chile. Journal of Petrology 41, 309–30.CrossRefGoogle Scholar
York, D., Evensen, N. M. & Smith, P. E. 1992. Recoil. EOS, Transactions, American Geophysical Union 73, 363.Google Scholar