Zircon radiometric dating constraints on the pliocene fitzcarrald arch uplift (Western Amazonia)

ABSTRACT The Fitzcarrald Arch is a prominent geomorphic feature that plays a key role in the drainage and biodiversity patterns of Western Amazonia. However, the timing of its uplift is not precisely known. To address this issue, we utilize detrital zircon (DZ) U-Pb dating and trace elements to establish maximum depositional ages and sediment provenance for three samples from the Solimoes Formation (Acre Basin) and one modern sand sample deposited by a river draining the Fitzcarrald Arch. The DZ age distributions of the Solimoes samples are characterized by a dominant contribution of Paleozoic zircons and subordinate contributions of Meso-Cenozoic zircons sourced by the Eastern Cordillera and the Altiplano. The modern sands are characterized by the presence of a similar zircon population but with a dominant contribution of Grenville/Sunsas zircon and a higher percentage of rounded and subrounded zircons. The youngest zircons from the Solimoes Formation samples indicate a latest Miocene to early Pliocene maximum depositional ages (6.92±0.45 to 5.98±0.06 Ma), with zircons derived from mafic to intermediate volcanic rocks. The youngest zircon of the modern sands suggests that the connection with the Andes remained active in the Acre Basin until the early Pliocene (5.20±0.7 Ma), which indicates a similar maximum age for the uplift of the Fitzcarrald Arch. At that time, the Fitzcarrald Arch area ceased to be a subsiding area and became a source of sediment for the Amazon River.