Vulkanoklastische Serien am Südrand des Transmexikanischen Vulkangürtels als Zeugen der miozänen Plattenreorganisation vor der mexikanischen Westküste
Final Report Abstract
The Tepoztlan Formation (TF) represents a remnant continental arc succession, made up of andesitic to rhyolithic volcaniclastic rocks, of the initial phase ofthe Transmexican Volcanic Belt, which has been rarely studied so far. For the first time we set-up a geochronology and an evolutionary model of the TF. Over an total area of 1000 km2, geological mapping, logging of six sedimentological sections up to 378 m long, paleocurrent analysis, and wall panel analysis has been carried out in key areas. Paleomagnetic sampling along the sections combined with K/Ar and Ar/Ar dating of lava flows revealed an age of Early Miocene (22.8-18.8 Ma) and let us correlate the sections. Based on this framework new lithostratigraphic members and a facies model have been developed. The Malinalco member (22.8 - 22.2 Ma) is dominanted by fluvial, epiclastic deposits. Pyroclastic material was mostly reworked by sheet floods and fluvial processes. In the San Andres member (22.2 - 21.3 Ma) coarsening-up and thick pyroclastic flows show increased production of volcanic material which temporarily overloaded and buried the fluvial system with debris. Continuous build-up of the volcanic centers accentuated further the topography, and in the Tepozteco member (21.3 - 18.8 Ma) mass flow deposits became dominant. Geochemical analyses, including Sr- and Nd isotopes, show a heterogenous mantle array as well as assimilation of lower crust and support a subduction model. Pollen findings in the volcaniclastic rocks let us estimate the mean annual temperature (MAT) at about 14.5°C (present MAT 20°C), and mean annual rainfall at around 1200 mm (present 770 mm). These surprisingly low temperatures and high humidity for the Lower Miocene (Upper Aquitanian - Lower Burdigalian) in this area give hints to an already highly elevated plateau in Central Mexico with volcanic edifices clearly exceeding 3000 m a.s.l.
Publications
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(2006): A new reference section from volcaniclastic rocks of Miocene terrestrial palynomorphs in Central Mexico. - EGU Geophysical Research Abstracts, Vol. 8: 03121
Lenhardt, N., Götz, A.E., Hinderer, M. & Hornung, J.
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(2006): Palaeoenvironmental Reconstruction of the Miocene Tepoztlan Formation (Central Mexico): Preliminary Results of Palynological Investigations. In: Espinasa-Perena, R. & Pint, J. (eds.): Proceedings of the X, XI, and XII International symposia on volcanospeleology. AMCS Bulletin, 19: 158-161
Lenhardt, N., Martinez-Hernandez, E., Götz, A.E., Hinderer, M., Hornung, J., Torres-Alvarado, I.S. & Kempe, S.
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(2006): Palaeoenvironmental reconstruction of the Miocene Tepoztlan Formation using palynology. XII International Symposium on Volcanospeleology, Tepoztlan, 02.-07.07.06, Programm and Abstracts: p. 6
Lenhardt, N., Martinez-Hernandez, E., Götz, A.E., Hinderer, M., Hornung, J. & Kempe, S.
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(2006): Palynomorph assemblages from a Miocene volcaniclastic section in Central Mexico (Tepoztlan Formation): evidence for palaeoenvironmental changes.- 7th European Paleobotany-Palynology Conference, Prague 6.-11.09.06, Program and abstracts, p. 80, ISBN 80-7036-198-0
Lenhardt, N., Martinez-Hernandez, E., Götz, A.E., Hinderer, M. & Hornung, J.
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(2007): Depositional processes of Miocene volcaniclastic series at the southern edge of the Transmexican Volcanic Belt.- 20th Colloquium on Latin American Earth Sciences, Kiel 11 .-13.07, Abstracts, SZ2P05, p. 290
Lenhardt, N., Trauth, N., Hornung, J., Hinderer, M., Torres-Alvarado, I.S. & Boehnel, H.
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(2007): The Miocene Tepoztlan Formation (Central Mexico) - Key to a better understanding of the initial phase of the Transmexican Volcanic Belt.- Eos Trans. AGU, 88(52), Fall Meet. Suppl., Abstract V41D-0805
Lenhardt, N., Hinderer, M., Hornung, J., Torres-Alvarado, I.S. & Boehnel, H.
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(2008): A facies model of a volcaniclastic apron: The Miocene Tepoztlan Formation (Central Mexico).- 26th IAS Regional Meeting/SEPM-CES Sediment 2008, Bochum, 1.-3.09., SDGG 58, Abstract volume, p. 167
Lenhardt, N., Hinderer, M., Hornung, J., Torres-Alvarado, I.S. & Boehnel, H.
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(2008): Facies model of the Miocene volcaniclastic Tepoztlan Formation: a step forward in deciphering the initial phase of the Transmexican Volcanic Belt.- IAVCEI General Assembly 2008, Reykjavik 17.-22.08.
Lenhardt, N., Hinderer, M., Hornung, J., Torres-Alvarado, I.S. & Boehnel, H.
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(2008): Palynology of the Tepoztlan Formation, Central Mexico - palaeoenvironmental and palaeoclimatological implications.- Terra Nostra 2008/2, 12th International Palynological Congress IPC-XII/IOPC-VIII, Bonn, Abstract Volume, p. 162
Lenhardt, N., Herrmann, M., Mosbrugger, V. & Hinderer, M.
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(2008): Reservoir characteristics of ash-flow deposits: a case study on the Tepoztlan Formation, Central Mexico.- IAVCEI General Assembly 2008, Abstracts: Poster Session IV, 2I-P04: p. 30
Lenhardt, N. & Götz, A.E.
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(2009): Volcaniclastic successions of the southern edge of the Transmexican Volcanic Belt: evidence for the Miocene plate reorganisation in Central America (Morelos, Mexico). Ph.D thesis, Institut für Angewandte Geowissenschaften, TU Darmstadt: 141 pp.
Lenhardt, N.
