title: Origin of unusual HREE-Mo-rich carbonatites in the Qinling orogen, China.
abstract: Carbonatites, usually occurring within intra-continental rift-related settings, have strong light rare earth element (LREE) enrichment; they rarely contain economic heavy REE (HREE). Here, we report the identification of Late Triassic HREE-Mo-rich carbonatites in the northernmost Qinling orogen. The rocks contain abundant primary HREE minerals and molybdenite. Calcite-hosted fluid inclusions, inferred to represent a magmatic-derived aqueous fluid phase, contain significant concentrations of Mo (~17 ppm), reinforcing the inference that these carbonatitic magmas had high Mo concentrations. By contrast, Late Triassic carbonatites in southernmost Qinling have economic LREE concentrations, but are depleted in HREE and Mo. Both of these carbonatite types have low δ26Mg values (-1.89 to -1.07‰), similar to sedimentary carbonates, suggesting a recycled sediment contribution for REE enrichment in their mantle sources. We propose that the carbonatites in the Qinling orogen were formed, at least in part, by the melting of a subducted carbonate-bearing slab, and that 10 Ma younger carbonatite magmas in the northernmost Qinling metasomatized the thickened eclogitic lower crust to produce high levels of HREE and Mo.
authors.affiliation: Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing 100871, China.
authors.forename: Wenlei
authors.initials: W
authors.lastname: Song
authors.affiliation: Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing 100871, China.
authors.forename: Cheng
authors.initials: C
authors.lastname: Xu
authors.affiliation: School of Environment and Technology, University of Brighton, Brighton BN41 2HQ, United Kingdom.
authors.forename: Martin P
authors.initials: MP
authors.lastname: Smith
authors.affiliation: Department of Geology and Pedology, Mendel University, Brno 61300, Czech Republic.
authors.forename: Jindrich
authors.initials: J
authors.lastname: Kynicky
authors.affiliation: Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing 100871, China.
authors.forename: Kangjun
authors.initials: K
authors.lastname: Huang
authors.affiliation: Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing 100871, China.
authors.forename: Chunwan
authors.initials: C
authors.lastname: Wei
authors.affiliation: Key Laboratory of High-temperature and High-pressure Study of the Earth's Interior, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China.
authors.forename: Li
authors.initials: L
authors.lastname: Zhou
authors.affiliation: State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China.
authors.forename: Qihai
authors.initials: Q
authors.lastname: Shu