Quartzite–Schist Sequences of the Aktau–Mointy Massif (Central Kazakhstan): Structural Position, Provenance, and Formation Stages of the Earth Crust in the Precambrian.

Detrital zircons from quartzite–schist sequences of the Aktau–Mointy Massif (Central Kazakhstan), which occur in various structural positions relative to the Early Neoproterozoic felsic volcanics, were studied. The obtained U–Pb zircon dating results suggest similarity of detrital zircon age populations with a lower limiting depositional age of 1220 Ma in all quartzite–schist sequences. The different positions of quartzite–schist sequences relative to the felsic volcanics are due to subsequent deformations. The ages of detrital zircons studied fall mostly within the intervals of 1149–2105 and 2354–3159 Ma with major peaks at 1218, 1338, 1468, 1581, 1628, 1743, 1851, and 2520 Ma and minor peaks at 2016, 2619, 2696, 2791, 2823, and 3114 Ma. The structural features of quartzite–schist sequences and the presence of heavy minerals that are unstable during long-term transport indicate the predominance of local source areas, which either form the buried part of the basement of the Aktau–Mointy Massif or have been eroded completely. Within the Aktau–Mointy Massif, it enables us to use the U–Pb ages and Lu–Hf isotope compositions of detrital zircons from quartzite–schist sequences to reconstruct the history of Precambrian continental crust formation. Results suggest that the production of juvenile continental crust prevailed only during Middle Mesoproterozoic, while formation during the Mesoarchean–Neoproterozoic time accompanied magmatic reworking of the older crustal complexes. [ABSTRACT FROM AUTHOR]