New palaeomagnetic results from Late Paleozoic volcanic units along the western Gondwana margin in La Pampa, Argentina

Renata Nela Tomezzoli,Teresa Saint Pierre,Claudia Valenzuela

doi:10.1186/bf03352898

Abstract

Abstract Preliminary palaeomagnetic results from the Paleozoic volcanic units along the Gondwana margin in Argentina are presented. Even though we are still working on the palaeomagnetic data of the sampled section, these data are consistent with data from former studies carried out in the area. More than 90 specimens were measured from the Sierra Chica locality (37°52′S; 65°27′W) computed in 11 sites (Sc1-Sc11). These rocks are carriers of a characteristic remanence magnetization with reverse polarity, acquired during the Early Permian and assigned to the Kiaman Superchron. The resulting palaeomagnetic pole (PP) is Lat.: 64°S; Long.: 017°E, A95 = 15°, K = 12, N = 10. Others interpretations are also possible if the directions of two sites (SC9 and SC10) are considered to have a different magnetic field record. In that case, the PP calculated for sites Sc1-Sc7 is Lat.: 65°S; Long.: 44°E, A95 = 8°, K = 54, N = 7, and the virtual geomagnetic pole (VGP) calculated for sites Sc9 and Sc10 is Lat.: 48.5°S; Long.: 315°E, A 95 = 8°, N = 2. The last possibility to consider Sc9 and Sc10 after structural correction, and the resulting PP position is Lat.: 66.5°S; Long.: 034°E, A 95 = 8°, K = 41, N = 9. This deformation episode could be related to the San Rafaelic orogenic phase, found for the first time in La Pampa province, but previously observed in other neighboring areas during Permian time. However, more detailed palaeomagnetic sampling, rock magnetism studies, and age dating are necessary to complete the palaeomagnetic study of this area.

Highlights

To improve upon our understanding of the evolution of the Western Gondwana during the Late Paleozoic to Early Mesozoic and to explore regional relationships between sedimentation, volcanism, and the age of the deformation, new palaeomagnetic studies are underway in the Gondwanides belt (Keidel, 1916) or “Samfrau Geosynclinal” (Du Toit, 1927) exposed in the central Argentina (Fig. 1)
Geological Setting The volcanic rocks of Sierra Chica (37◦52 S; 65◦27 W; Fig. 2) are located in the Southern part of the Chadileuvu Block (Llambıas et al, 1996), in La Pampa province, central Argentina (Fig. 1)
As the top of the Kiaman is approximately 266 Ma (Gradstein et al, 2004), this result implies an older age for these rocks

Summary

Introduction

To improve upon our understanding of the evolution of the Western Gondwana during the Late Paleozoic to Early Mesozoic and to explore regional relationships between sedimentation, volcanism, and the age of the deformation, new palaeomagnetic studies are underway in the Gondwanides belt (Keidel, 1916) or “Samfrau Geosynclinal” (Du Toit, 1927) exposed in the central Argentina (Fig. 1). 2. Geological Setting The volcanic rocks of Sierra Chica (37◦52 S; 65◦27 W; Fig. 2) are located in the Southern part of the Chadileuvu Block (Llambıas et al, 1996), in La Pampa province, central Argentina (Fig. 1). Geological Setting The volcanic rocks of Sierra Chica (37◦52 S; 65◦27 W; Fig. 2) are located in the Southern part of the Chadileuvu Block (Llambıas et al, 1996), in La Pampa province, central Argentina (Fig. 1) This volcanism is part of the Choiyoi Group, the Permian–Triassic igneous rocks, whose extension in Argentina exceeds 500,000 km (Llambıas et al, 2003). TOMEZZOLI et al.: NEW PALAEOMAGNETIC RESULTS FROM LATE PALEOZOIC IN ARGENTINA

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Discussion