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

Seventy sites of sills, flows and dikes from Northeastern Parana Magmatic P rovince (PMP), were submitted to paleomagnetic, chemical and radiometric an alyses. The rocks are high in TiO2 content, and similar in composition to t he rocks from the northern region of PMP. The sills intrude mainly Paleozoi c sediments, and can be subdivided into two domains; the northern being cha racterized by sills showing reversed polarities, and the southern essential ly by sills of normal polarities. Ar-40/Ar-39 dating of three distinct sill s gave plateau ages (129.9 +/- 0.1, 130.3 +/- 0.1 and 131.9 +/- 0.4 Ma) tha t are similar to surface-outcropping flows of the Northern Parana Basin, an d 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 PM P, which are slightly older than the northern PMP, as well as for the conte mporaneous 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.