COMPARATIVE APPRAISAL OF DETRITAL MONAZITE-ZIRCON U-TH-PB AGE SPECTRA IN PAGANZO BASIN (ARGENTINA): A STEP TOWARDS SINGLE GRAIN DOUBLE DATING OF MONAZITE FOR BASIN ANALYSIS.

Documented biases in zircon U-Pb age distributions necessitate a multi-proxy approach for more accurate basin analysis. Monazite is the ideal candidate for this as it has proven to be a reliable U-Th-Pb geochronometer for basement rocks, though its detrital applications are relatively rare. Due to its petrogenetic characteristics, it is especially useful in analyzing orogenic basins where polyphase metamorphism and sediment recycling are expected.

We present novel detrital zircon (N=8) and monazite (N=6) U-Th-Pb data from the Cerro Guandacol section of the Carboniferous-Permian Paganzo Basin (Sierras Pampeanas). This basin was chosen for this study because it is a long-lived basin with well-characterized potential sources that were recycled during the basin evolution. However, its sediment routing and tectonic context are under debate. The basin succession starts with diamictite-bearing sandstones of the Guandacol Fm. and transitions into conglomerate-bearing fluvial sandstone units of the Tupe Fm. The fluvial Patquía Formation overlies these, and the sequence ends with thin aeolian deposits. Zircon ages reveal a strong presence of Grenvillian/Sunsás (1.3-1 Ga) and Famatinian (500-420 Ma) influences throughout the section, except in the uppermost sample. The older samples also have strong Pampean/Wichita (590-520 Ma) peaks, but these ages are less abundant in the younger samples. The uppermost sample has a dominant Choiyoi (290-270 Ma) peak, although Famatinian and Pampean/Wichita influences are present. Limited number of Carboniferous arc-related zircons are present throughout the section. A consistent feature of the monazite age spectra is the absence of Grenvillian/Sunsás peaks, likely due to overprinting. Apart from this, the monazite Th-Pb age spectra do not show any systematic differences from those of zircon. Samples with prominent Famatinian zircon peaks show significant correlation between monazite and zircon age spectra. However, two samples dominated by Pampean/Wichita and Choiyoi zircons show a weaker correlation between zircon and monazite ages. These results highlight the advantage of monazite for detecting first-order sediment contributions compared to the inherited/recycled distribution of zircon ages. This study is coupled with ongoing monazite (U-Th)/He dating efforts to fully leverage this mineral for basin analysis.