The Early Triassic magmatism of the Alto ParaguayProvince, Central South America: Paleomagneticand ASM data

Abstract

A paleomagnetic studystudywork was carriedout on the Alto Paraguay Province (APP), a belt of alkalinecomplexes that parallel the Paraguay river for morethan 40 km at the border of Brazil and Paraguay. Theprovince is well dated by 40Ar/39Ar method giving ages inthe range 240–250 Ma with a preferred age of 241 Ma. Intrusiverocks are predominant but the stocks may be toppedby lava flows and ignimbrites. Paleomagnetic work onstocks, dikes and flows of the APP identified normal andreversed magnetic components which are carried mainlyby titanomagnetites. The calculated paleomagnetic polelocated at 319ºE 78ºS (α95 = 6º; k = 23) is in agreementwith other South American poles of Permo-Triassic age.Most of the sampling sites showed large variations in rockmagnetization, but similar patterns in the variation of thewithin-site magnetizations, mainly in dikes, suggest geomagneticpolarity transition records. The magnetizationdata along with the anisotropy of magnetic susceptibilitydeterminations suggested that the South and North areasof the province have different evolution characteristics.

Keywords

• alkaline magmatism
• paleomagnetism
• magneticanisotropy
• alto paraguay province