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Detrital zircon U–Pb ages of Paleo- to Neoproterozoic black shales of the Baikal-Patom Highlands in Siberia with implications to timing of metamorphism and gold mineralization

2018; Elsevier BV; Volume: 174; Linguagem: Inglês

10.1016/j.jseaes.2018.10.022

1878-5786

Ekaterina E. Palenova, Marina A. Yudovskaya, Dirk Frei, Nikolai V. Rodionov,

earthquake and tectonic studies

A U–Pb isotope system of detrital zircons was used to determine the provenance and maximum deposition age of the Paleoproterozoic Mikhailovka and the Ediacaran Khomolkho, Aunakit and Dogaldyn Formations in the Baikal-Patom Highlands, one of the most ancient components of the Central Asian Orogenic Belt (CAOB). The Baikal-Patom area hosts the world-class Lena orogenic gold province with total endowment of up to 6000 tons Au. The gold deposits are confined to the compressional syn- or post-metamorphic structures at various stratigraphic levels in Paleoproterozoic to Neoproterozoic black shale sequences deposited in the Bodaibo passive margin of the Siberian platform. Nine samples were collected from mineralized rocks to address possible detrital zircon recrystallization and transformation during superimposed metamorphic and hydrothermal events. Zircon was analyzed using laser ablation – single collector – magnetic sectorfield – inductively coupled plasma – mass spectrometry (LA-SF-ICP-MS). The Mikhailovka metasediments yielded three concordant isotopic age clusters: predominant Archean (2.45–3.25 Ga), Paleoproterozoic (1.96–2.10 Ga), and Cambrian-Ediacaran-Cryogenian (524–702 Ma), whereas most of the zircon grains yielded discordant isotopic ages. Multiple lines of evidence (i.e., grain morphologies, specific set of mineral inclusions, distinctly high U and Th in zircon, and several persistent Pb-loss arrays of discordant ages with lower intercepts of concordia line at closely the same point) suggest the youngest cluster combines formerly metamict zircon of different ancient ages recrystallized under the peak conditions of the regional metamorphic event synchronous with or slightly preceding mineralization. Therefore, the youngest detrital grain isotopic age of 1961 ± 20 Ma determines the maximum depositional age of the Mikhailovka sediments that predates the emplacement of the Paleoproterozoic collisional Chuya-Nechera granitoids. Zircon grains from these granitoids represent a major population in the overlying Ediacaran sequences that indicate the prevalence of supply from proximal local sources, such as the uplifts of the ancient Siberian basement within the Bodaibo paleobasin. The age span of the Neoproterozoic detrital zircon population (604–966 Ma) in the younger formations is in agreement with the events in the CAOB and Siberian platform.