Recently, Professor Wang Xiaolei's team from the School of Earth Science and Engineerings and Engineeringof Nanjing University and the State Key Laboratory for Mineral Deposits Research, Nanjing University has obtained new progress on the accretion and reconstruction process of the continental arc crust on the western margin of the Yangtze block approximately 800 million years ago.
In previous studies, a typical profile representing the mid upper crust of the Neoproterozoic continental arc (2021, Nature Commun. 12:3533) was discovered at the western margin of the Yangtze block, revealing the rapid process and mechanism of crustal material recycling in the continental arc. Recently, the team's further research work found that the seepage reaction flow played a prominent role in the arc crust differentiation, not only transforming the arc crust surrounding roc below the solidus (Li JY and Wang XL et al., 2024, EPSL) but also transforming the arc crystal congee reservoir that was not fully crystallized.
Two research papers have been published on Communications Earth & Environment (DOI：doi.org/10.1038/s43247-024-01279-w) and Earth and Planetary Science Letters (DOI doi.org/10.1016/j.epsl.2024.118678). Li Junyong, a postdoctoral fellow at Nanjing University, is the first author of the paper, and Professor Wang Xiaolei is the corresponding author. Professor Peter Cawood from Monash University in Australia, and Dr. Gu Zhidong from China Petroleum Exploration and Development Research Institute also participated in the related research.
The abstract of the article published on Communications Earth & Environment is following:
The reactive melt flow emerges as an important factor for diversification of basaltic magmatic reservoirs, but whether and how it influences continental arc basaltic mushes are enigmatic. Here, we used mineral and whole-rock geochemistry to examine the petrogenesis of a suit of mafic and intermediate plutons in western Yangtze Block, which were emplaced at continental arc crust and primarily had plagioclase and clinopyroxene as early cumulate mineral phases. We found the crystal mushes were infiltrated by externally-derived reactive melt with high δ18O and fertile crustal signatures, resulting in the changes of mineral phases (e.g., clinopyroxene transformed to hornblende) and bulk-rock geochemistry (including isotopes). Then, the reacted granitic melt was prone to either be extracted from or stall in the crystal mushes, generating quartz-poor (mafic) or quartz-rich (intermediate) plutons, respectively. This study supports the reactive melt infiltration may serve as an important engine for compositional diversity of basaltic mush system within continental arc settings.
Figure 1. Zircon isotope and trace element characteristics of two gneiss samples. The ages of the two samples are ca, respectively 1400 Ma and CA 830 Ma, all in CA Metamorphosis occurred at 830-820 Ma. Zircon has undergone transformation by foreign melts and related dissolution recrystallization, resulting in significant inconsistency in Hf and O isotopes. The Ti content of edge zircon is generally less than 2 ppm, indicating a low-temperature metamorphic and melt infiltration environment.
Figure 2. (A) Neoproterozoic Middle High Pressure Metamorphic Records of the Panxi Hannan Belt on the Western Margin of the Yangtze Block, with the peak metamorphic temperature and pressure of the studied samples marked by a pentagram. (B) The metamorphism of the sample is accompanied by the infiltration, remelting, and melt mineral rebalancing processes of external aqueous melts. This process occurs in the environment of the Neoproterozoic accretionary orogeny, and material migration is carried out through the reverse thrust process of subducting plates or intra arc faults.
Figure 3. (a-c) TIMA images of two types of samples, where alternative structures of amphibole pyroxene and plagioclase orientation are commonly seen in quartz poor and quartz rich intrusions. The (d-f) whole rock Nd isotopes, zircon Hf-O isotopes, and quartz O isotopes indicate that magma differentiation does not occur in a closed system, but is influenced by external melts.
Figure 4. Concept map: the influence of infiltration melt flow on the continental arc basic crystal Congee reservoir. The chemical exchange reaction takes place between the external melt of rich and high δ18O and the crystals in crystal Congee of different crustal scales. The amphibole equilibrium melt can be extracted from the crystal Congee or stayed, forming basic or neutral rocks, resulting in the composition stratification of the crystal Congee reservoir.
Writer: Guo Junlin
Editor: Shao Yihang
