Age constraints on the Cambrian Mesón Group (NW Argentina) based on detrital zircons U–Pb geochronology and magnetic polarity bias

Abstract

The Cambrian Mes´on Group represents the first infill stages of the NW Argentina Paleozoic basin, given after the major orogenic event represented by the Tilcaric orogenic phase. This unit extends for several hundred kilometers along the Eastern Cordillera in the provinces of Salta and Jujuy, but its age is poorly constrained due to the paucity of fossil evidence and scarce geochronological data. U–Pb LA-ICP-MS geochronological studies were carried out on detrital zircons from the Lizoite, Campanario and Chalhualmayoc formations, that make up the Mes´on Group, in outcrops in the Santa Victoria sub-basin in northernmost Argentina. Maximum depositional ages of 524.8 ±4.1, 519.7 ±2.4 and 508.6 ±1.7 Ma were obtained for these formations, respectively. These new data, together with previous detrital zircon ages from southernmost outcrops of this Group, points to a possible diachronism in deposition, with younger ages towards the south. In our studied units, a dominant peak of Cambrian to late Ediacaran zircons is characteristic for the three formations, although a somewhat larger contribution from older crystals is observed in the Campanario and Chalhualmayoc formations. This pattern is similar to most other reported detrital zircon age spectra for the Mes´on Group along the basin. Published paleomagnetic data for the Campanario Formation indicates a very strong reverse magnetic polarity bias, which allows us to infer three more likely intervals for the deposition of this formation (roughly 512–510, 509–505 and 497-493 Ma). These three alternatives are analyzed with respect to either major diachronous or roughly synchronous deposition of the Mes´on Group sediments across the whole basin. Published magnetic fabric data for the Campanario Formation at three distant localities suggest possible paleocurrent directions from W to E.