A clearer view of crustal evolution: U-Pb, Sm-Nd, and Lu-Hf isotope systematics in five detrital minerals unravel the tectonothermal history of northern China
Authors: Zhou Guangyan , Fisher Christopher M. , Luo Yan , Pearson D. Graham , Li Long , He Yu , Wu Yuanbao 
Published: April 2020

Much of the global picture of crustal evolution has been constructed using zircon. While this has revealed a rich and complex history, this view is necessarily incomplete because of the lithology-specific affinity of zircon and the high temperatures needed to reset the U-Pb and Lu-Hf systems inherent within it. Here we use a five mineral, multi-isotope system approach to compare the record of crustal evolution recorded by zircon versus the picture provided by monazite, titanite, apatite, and rutile from the Yong-Ding and Luan rivers, northern China. These other minerals sample more diverse lithologies and temperature-pressure conditions that reflect additional tectonothermal events to those recorded solely by zircon. Zircon from both studied rivers predominantly reflects magmatic features, yielding age peaks at 2.6–2.3, 2.0–1.8, and 0.38–0.13 Ga, corresponding to the major magmatic events in their catchments. However, the detrital zircon record from both catchments fails to record and detail several important tectonothermal events. Specifically, the detrital monazite U-Pb ages cluster into two Paleoproterozoic peaks of ca. 1.95 and 1.85 Ga, while detrital apatite and rutile ages document unimodal and protracted U-Pb age peaks at 1.9–1.6 Ga. The different U-Pb closure temperatures of monazite, apatite, and rutile likely record two metamorphic events and the subsequent cooling history—key details that are absent from or obscured in the zircon record. The Phanerozoic mineral U-Th-Pb ages correspond to multiple magmatic events between 0.40 and 0.24 Ga and subsequent 0.24–0.20 Ga metamorphism. The 0.60–0.25 Ga rutile U-Pb ages along with 0.33–0.24 Ga U-Pb ages in some zircon grains with radiogenic Hf isotope compositions from the Luan River do not match the geological records in the North China Craton, but instead reflect the protracted subduction-accretionary history of the Central Asian Orogenic Belt. In addition to their U-Th-Pb ages, Nd model ages of monazite, titanite, and apatite, plus zircon Hf model ages provide additional constraints on regional crustal evolution. The Nd model age information is blurred by the fact that the relationship between the Sm/Nd of these minerals and their former host rocks is not precisely known. Taken at face value, the monazite Nd model ages have two Neoarchean peaks at 2.9–2.7 and ca. 2.5 Ga, that may correspond to two crustal growth episodes, while the titanite Nd model ages with predominant peaks at 2.2–1.8 and 1.5–1.3 Ga broadly correspond with those derived from the whole-rock analyses of the wide spread Phanerozoic granitoids, and hence record extensive crustal reworking. In contrast, the zircon Hf model ages are strongly skewed to a 2.9–2.7 Ga period and fail to record the post-Archean evolution of this region. These data highlight the power of integrating the U-Th-Pb age and Lu-Hf/Sm-Nd isotope compositions of multiple detrital minerals, with a broad range in geochemical behavior and closure temperatures, to gain a more complete understanding of tectonothermal history and crustal evolution than zircon alone.