Paleomagnetism, geochemistry and 40Ar/39Ar dating of the North-eastern Parana Magmatic Province: tectonic implications

Seventy sites of sills, flows and dikes from Northeastern Parana Magmatic Province (PMP), were submitted to paleomagnetic, chemical and radiometric analyses. The rocks are high in TiO2 content, and similar in composition to the rocks from the northern region of PMP. The sills intrude mainly Paleozoic sediments, and can be subdivided into two domains; the northern being characterized by sills showing reversed polarities, and the southern essentially by sills of normal polarities. 40Ar/39Ar dating of three distinct sills gave plateau ages (129.9 +/- 0.1, 130.3 +/- 0.1 and 131.9 +/- 0.4 Ma) that are similar to surface-outcropping flows of the Northern Parana Basin, and the Ponta Grossa dikes. The new paleomagnetic data combined with existing data from the northern PMP allowed the calculation of a paleomagnetic pole at 71.4 degrees E and 83.0 degrees S (N = 92; alpha(95) = 2.4 degrees; k = 39). This pole is in good agreement with poles for central and southern PMP, which are slightly older than the northern PMP, as well as for the contemporaneous Central Alkaline Province (Paraguay) on the western side of PMP. In contrast, the coeval pole for the Ponta Grossa dikes (eastern border of PMP), however, is slightly displaced from that group of poles, suggesting that dikes in that area may have undergone some tectonic tilting. (C) 1999 Elsevier Science Ltd. All rights reserved.