Geologica Acta: an international earth science journal ISSN: 1695-6133 [email protected] Universitat de Barcelona España GEUNA, S.E.; ESCOSTEGUY, L.D.; LIMARINO, C.O. Paleomagnetism of the Carboniferous-Permian Patquía Formation, Paganzo basin, Argentina: implications for the apparent polar wander path for South America and Gondwana during the Late Palaeozoic Geologica Acta: an international earth science journal, vol. 8, núm. 4, diciembre, 2010, pp. 373-397 Universitat de Barcelona Barcelona, España Available in: http://www.redalyc.org/articulo.oa?id=50515686003 How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative REFERENCES Geologica Acta, Vol.8, Nº 4, December 2010, 373-397 DOI: 10.1344/105.000001578 Available online at www.geologica-acta.com Paleomagnetism of the Carboniferous-Permian Patquía Formation, Paganzo basin, Argentina: implications for the apparent polar wander path for South America and Gondwana during the Late Palaeozoic 1 2 1 S.E. GEUNA L.D. ESCOSTEGUY C.O. LIMARINO 1 Departamento de Ciencias Geológicas, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires / CONICET Ciudad Universitaria Pab. 2, C1428EHA, Ciudad de Buenos Aires, Argentina. Geuna E-mail: [email protected]. Phone number: 54-11-47883439 2 Instituto de Geología y Recursos Minerales, Servicio Geológico Minero Argentino ABSTRACT The magnetic properties of the Carboniferous-Permian red beds of the Patquía Formation at Punta del Viento, Sierra de Umango and some previously reported localities, all in the Paganzo Basin (Argentina), have been stud- ied. Whereas all sites are characterized by hematite as the main magnetic carrier and a reversed-polarity magnetic remanence, we found a pattern of variation in magnetic properties along the integrated column for Patquía For- mation. The Lower Member (Late Carboniferous) showed higher intensity of natural and saturation isothermal remanent magnetisation (NRM and SIRM, respectively) than the Permian Upper Member. The fall in NRM in- tensity from the Lower to Upper Member of the Patquía Formation may be related to a change in quantity and/ or grain-size of the hematite pigment, which may reflect the change in environmental and/or depositional setting. As for directional values of NRM, paleomagnetic poles reported for both sections are clearly different. The lower section provided a pole position coincident with Late Carboniferous poles for Gondwana, while the upper section poles are departed from the Early Permian position. We cannot decide whether the Upper Member pole is due to a primary magnetisation at 290 Ma or to a remagnetisation at ~260-270 Ma; even so, the obtained paleomagnetic pole is robust and indicates a rapid apparent polar wander in a ~30o counter clockwise rotation of the region, after deposition of the Late Carboniferous lower section, and in coincidence with the San Rafael Orogenic Phase. KEYWORDS Red beds. Paleomagnetism. Magnetic remanence. Apparent polar wander. INTRODUCTION also owing to red beds have demonstrated to be particu- larly suitable for paleomagnetic studies. Red beds share in Continental red beds are of special significance in pale- common the red colour given by finely disseminated ferric omagnetism, not only because they were the first sedimen- oxides, usually in the form of haematite. They comprise a tary rocks to be studied in any detail (Turner, 1980) but wide range of sedimentary facies mainly deposited in con- 373 S.E. GEUNA et al. Paleomagnetism of the Carboniferous-Permian Paganzo basin, Argentina tinental environments, though some examples of marine haematite crystallisation and changes in the depositional red beds have been also quoted (McBride, 1974; Franke setting. and Paul, 1980; Limarino et al., 1987; Hu et al., 2005). Haematite is usually the main carrier of magnetic re- GEOLOGICAL SETTING manence in red beds, and hence the age of the remanence is given by the time of haematite crystallization. Haematite The Paganzo basin covers an area of 140.000 km2 in red beds may form by the oxidation of magnetite, the where mainly continental sedimentation took place from inversion of maghemite, or the dehydration of goethite, the latest Early Carboniferous to the Late Permian (Lima- the latter formed by breakdown of hydrous clay minerals rino et al., 1996; Tedesco et al., 2010; Fig. 1). The sedimen- and ferromagnesian silicates (McBride, 1974; McPherson, tary cover is thinner to the east, where it was deposited on 1980; Dunlop and Özdemir, 1997). All the reactions typi- Proterozoic igneous-metamorphic basement of the Sierras cally occur during burial in a sedimentary pile, through Pampeanas; in the western part, a narrow belt developed the diagenetic stage (early diagenesis, mesodiagenesis, te- on more mobile areas, where thicker deposits lie upon lodiagenesis) in a process that strongly depends on basin metamorphic basement and Lower Palaeozoic sediments conditions. of the Precordillera (Azcuy et al., 1999). There is evidence of oblique convergence in the Late Palaeozoic subduction Continental red beds are extremely sensitive indicators zone to the west (Mpodozis and Kay, 1992; Kay, 1993); of the nature and extent or red bed diagenesis. The paleo- strike-slip faults have controlled the development of the magnetic study shows that diagenesis must be a rate proc- forearc basins (Fernández Seveso and Tankard, 1995). A ess in which the rate, including the rate of acquisition of N-S trending structural high, the Proto Precordillera, par- magnetization, is determined by a) the original mineralogy tially separated the Paganzo basin from its marine exten- of sediment, where immature sediments are susceptible to sions to the west: the Río Blanco and Calingasta-Uspallata more extensive alteration and prolonged magnetization; b) basins (Limarino et al., 1996; Fig. 1). the depositional conditions, finer grained sediments be- ing less susceptible to alteration; c) the prevailing climate, Terrigenous clastic fill of the Paganzo basin was origi- warm arid climates being favourable for the long-contin- nally subdivided into three “stages” referred to as Car- ued alteration (Turner, 1980). The age of the magnetization boniferous, Permian and Triassic by Bodenbenber (1911). in red beds is a direct result of the rate of acquisition of Azcuy and Morelli (1970) restricted the name Paganzo remanence, which is variable because it represents the sum Group to the Carboniferous-Permian sections, separating of several discrete diagenetic processes. The Paganzo Basin in western Argentina has been the + 28o + site of deposition for Carboniferous-Permian red beds + which provided several paleomagnetic poles, some of them + Western SOUTH + AMERICA domain controversial. Most of them were published before recent + + methodological advances in the paleomagnetic routine, and DLC + PV System up till now no study has considered the characterization of Famatina the magnetic mineralogy of these red beds. + ME Río Blanco Sub-basin La Rioja HU LC ? ? + PZO In this paper we present a preliminary study on a section CHILE CC in the Sierra de Umango in Paganzo Basin, where Carbon- + Paganzo iferous-Permian red beds can be compared with overlying + Basin red Cretaceous units. The comparison is extended to other + CH localities studied before by Embleton (1970b), Valencio et + San Juan Eastern al. (1977) and Sinito et al. (1979a). The magnetic proper- + 32o domain Sierras Precordillera ties were distinctive for the two members recognized in the + VOLCANICARC + Late Palaeozoic red beds: haematite is more abundant in the Pampeanas + lower fluviatile facies than in the upper desert association, + Mendoza and both sections provided different paleomagnetic poles. + 69o W 67o W Calingasta-Uspallata Sub-basin 0 100 200 km We compared the Paganzo basin paleomagnetic poles FIGURE 1 Sketch of Paganzo Basin, with localities referred in the to the paleomagnetic record from other Gondwana plates text (modified from Azcuy et al., 1999). Locality codes as in table 3; during the Late Palaeozoic. We inferred the timing for re- PV is the location of the present study in Punta del Viento, Sierra de manence acquisition and analysed it in terms of diagenesis, Umango. Geologica Acta, 8(4), 373-397 (2010) 374 DOI: 10.1344/105.000001578 S.E. GEUNA et al. Paleomagnetism of the Carboniferous-Permian Paganzo basin, Argentina the Triassic sequence (usually referred to as the Upper Pa- western basin, linked with active subduction during the ganzo Section or “Paganzo III” in former paleomagnetic Late Palaeozoic. Convergence culminates in the San Ra- contributions) as an independent cycle. The Triassic ex- fael Orogenic Phase (SROP) during the Early Permian tensional basins developed following a tectonic inversion (Kleiman and Japas, 2009), whose effects in the western marked by a major unconformity that truncates Permian margin of Gondwana are reflected in a major erosion sur- sequences, identified with the Amanaica Orogenic Phase face on which Choiyoi Magmatic Province (280-240 Ma) (Aceñolaza and Toselli, 1981; Limarino et al., 1988). developed. Lower Choiyoi magmatism is calc-alkaline with typical continental-subduction signatures, coeval with The infill of the Carboniferous-Permian basin com- transpression, followed by shoshonitic magmatism related prises the Paganzo Group, consisting