We use cookies to ensure that we give you the best experience on our website. You can change your cookie settings at any time. Otherwise, we'll assume you're OK to continue.

Durham University

Department of Earth Sciences


Publication details for Professor Yaoling Niu

Huang, Hui, Niu, Yaoling, Teng, Fang-Zhen & Wang, Shui-Jiong (2019). Discrepancy between bulk-rock and zircon Hf isotopes accompanying Nd-Hf isotope decoupling. Geochimica et Cosmochimica Acta 259: 17-36.

Author(s) from Durham


Zircon is an important accessory mineral for studying the crust-mantle interaction and crustal growth through time because zircon crystals not only allow precise dating but also record initial Hf isotope ratios of the host magmas. Our study on a suite of gabbronorite, mafic diorite cumulates, diorite and granite from the Kekeli Batholith in the North Qilian Orogenic Belt, northern Tibetan Plateau, shows (1) a significant Hf isotope discrepancy between zircons and their bulk rocks; and (2) bulk-rock Nd-Hf isotopic decoupling. These observations thus demonstrate that zircons do not always capture the full history of magmatic system. The significant positive correlation between bulk-rock Hf isotope ratios and TiO2 content (R2=0.94) indicates that Ti-rich minerals (e.g., ilmenite, amphibole) are likely important Hf hosts. The early-formed Ti-rich minerals possibly record different Hf isotopes from those of zircons crystallized subsequently, thus causing discrepancy between zircons and bulk-rocks and leading to bulk-rock Nd-Hf isotope decoupling. Correlations between bulk-rock TiO2 content, Mg isotopes and Hf isotopes indicate a mixing process, with granite and gabbronorite representing two compositional endmembers. Because Ti minerals have higher crystallization temperatures than zircons, when the mixing melts have contrasting isotopes (or from heterogeneous sources/ have a strong crustal contamination), the bulk-rock and zircon Hf isotope discrepancies reflect mineral crystallization sequence during mafic and felsic magma mixing. It is thus imperative to consider early formed minerals such as Ti-rich minerals and the bulk rock composition, not just zircons, when using Hf isotopes to track melt evolution and precisely constrain mantle contribution to granitoid petrogenesis.