U-Pb ZIRCON PROVENANCE ANALYSIS OF THE YACORAITE FORMATION, TRES CRUCES SUB- BASIN, SALTA GROUP, EASTERN CORDILLERA ARGENTINA

PAMELA ALEJANDRA APARICIO GONZÁLEZ; LUBIN ERIC CAYO; NATALIA HAUSER; IGNACIO GALLARDO; CARMEN MARTINEZ DOPICO

Santiago de Chile

Congreso; XII South American Symposium on Isotope Gology; 2022

Universidad del Desarrollo Chile

A U-Pb age provenance analysis on detrital zircons was carried out in the Cretaceous calcareous rocks of the Yacoraite Formation, the most relevant economic unit of the Northwest Argentina. The Yacoraite Formation is the oil-source rock and main reservoir of the Salta rift basin, as well as a host for relevant U, V, Cu mineralizations.This abstract proposes to establish the location of the source areas of the sedimentation of the clastic levels of the Yacoraite Formation (Balbuena Subgroup). The studied area is in Tres Cruces sub-basin in the northern part of the Eastern Cordillera. In this area, the Yacoraite Formation is composed of limestones, laminate pelites, calcareous sandstones and stromatolitic limestones with traces fossils and dinosaur tracks. It transitionally overlays the Lecho Formation (Maastrichtian). The deposits of the Balbuena Subgroup (Maastrichtian-Danian) are lying unconformably dipping towards to the west, above the quartz sandstones of the Mesón Group (middle-upper Cambrian). The thickness of Yacoraite Formation in the Maimará section is 55 m, where the base of the Lecho Formation is composed of a fining-upward succession of matrix supported conglomerates and coarse to fine sandstones. The conglomerates are composed of angular and poorly sorted fragments of rocks with a clear provenance from the Mesón Group. We present U-Pb detrital ages of two samples analyzed in the LA.TE. ANDES Laboratory. The first sample is from the base of the unit, a calcareous sandstone (Y1) and the second sample is a calcareous oolite (Y2) from the top of the Yacoraite Formation. Sample Y1: One hundred and seven (107) spots on single zircon grains of the base of the Yacoraite Formation (BM) were analyzed. Frequency data shows a unimodal zircon age distribution with a main mode Neoproterozoic, U-Pb age between 542 Ma to 891 Ma (77 %), and a second mode with Paleoproterozoic ages (11 %). The Cambrian ages were found, Lower Cambrian (6%), Middle Cambrian (3%) and a tail with Mesoproterozoic and Archean ages (2 %, 1 %).Sample Y2: Ninety-six (96) analyses were spotted on single zircon grains from a sample taken from the top of the unit. It shows a frequency data conforming a polymodal zircon distribution, with a main population of Cambrian (22% of grains) and Neoproterozoic (53 % of grains) ages. Others zircon ages were found: Paleoproterozoic (16 % of grains), and four (4) zircons of Mesoproteorozoic age and two zircons of Archean age were recognized. Finally, three (3) grains with Ordovician ages were found.Both datasets show that the main sources of detrital zircons in the Yacoraite Formation correspond with the Paleozoic rocks of the region. In the Maimará section, the main sources are Neoproterozoic and Cambrian rocks (i.e., Puncoviscana Complex and Meson Group). At the top of the sequence, ordovician zircons were found, suggesting a change of the provenance.The sedimentation of the Yacoraite Formation occurred near an active volcanic front. Different tuffaceous levels were identified with provenance from the chilean arch. The depositional ages of the tuffs vary between 60 to 68 Ma. However, in the provenance analysis of the Yacoraite Formation, these younger zircon ages are absent. Therefore, we conclude that the influence of the paleorelief (basement) in the sedimentation of Yacoraite Formation in the Tres Cruces sub-basin played a major role in the compositional variability of the unit.