Recycling of Subducted Carbonates Generated the Tarim Carbonatites in Paleoproterozoic Orogenic Processes

Abstract

Carbonatites are critical carriers of carbon and potential reservoirs of rare earth elements, which provide valuable insights into probing Earth’s deep processes. Recent studies have identified carbonatitic melts derived from the partial melting of sedimentary carbonates in Phanerozoic subduction zones. However, whether such carbonatites could be formed in Precambrian settings remains unclear due to high mantle temperatures and uncertain Archean–Paleoproterozoic tectonic dynamics. In this study, we sampled Paleoproterozoic carbonatites from the southeastern Tarim craton, northwest China, and conducted geochemical, isotopic, and geochronological analyses to elucidate their petrogenesis. Zircon and apatite U–Pb ages indicate carbonatite crystallization occurred at ca. 1.87 to 1.83 Ga, and mineral chemistry points to mantle depths of melt generation. However, the Tarim carbonatites have trace element patterns comparable with sedimentary carbonates and Sr–Nd isotopes (⁸⁷Sr/⁸⁶Sr<inf>i</inf> = 0.704–0.706; ¹⁴³Nd/¹⁴⁴Nd<inf>i</inf> = 0.509895–0.510052) differing from those of mantle-derived carbonatites. In addition, their C–O isotopes (δ¹³CPDB = 11.78–14.32%; δ¹⁸O<inf>SMOW</inf> = 14.83–15.97%) resemble the extents of marine carbonates, which were deposited in the Lomagundi-Jatuli Event (ca. 2.3–2.0 Ga). Hence, we propose that the Tarim carbonatites originated from partial melting of subducted Lomagundi-Jatuli Event carbonates at mantle depths. Our findings provide the earliest evidence for carbonatites derived from subducted sedimentary carbon, hinting that carbon recycling at the crust–mantle scale has been operative as early as the Paleoproterozoic.