(Peer-Reviewed) The onset of deep recycling of supracrustal materials at the Paleo-Mesoarchean boundary
Xiaolei Wang 王孝磊 ¹, Ming Tang 唐铭 ², Jeff Moyen ³, Di Wang 王迪 ¹, Alfred Kröner ⁴, Chris Hawkesworth ⁵, Xiaoping Xia 夏小平 ⁶, Hangqiang Xie 颉颃强 ⁷, Carl Anhaeusser ⁸, Axel Hofmann ⁹, Junyong Li 李军勇 ¹, Linsen Li 李林森 ¹
¹ State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China. 南京大学 地球科学与工程学院 内生金属矿床成矿机制研究国家重点实验室
² School of Earth and Space Sciences, Peking University, Beijing 100871, China 北京大学 地球与空间科学学院
³ Laboratoire Magmas et Volcans UMR6524, Université de Lyon, UJM-UCA-CNRS-IRD, 42023 Saint Etienne, France
⁴ Institut für Geowissenschaften, Universität Mainz, Mainz 55099, Germany
⁵ Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK
⁶ State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China 中国科学院 广州地球化学研究所 同位素地球化学国家重点实验室
⁷ SHRIMP Center, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China 中国地质科学院 地质研究所 离子探针中心
⁸ Economic Geology Research Unit, University of the Witwatersrand, Private Bag 3, Wits 2050, Johannesburg, South Africa
⁹ Department of Geology, University of Johannesburg, PO Box 524, Auckland Park 2006, Johannesburg, South Africa
Recycling of supracrustal materials, and in particular hydrated rocks, has profound impacts on mantle composition and thus on the formation of continental crust because water modifies the physical properties of lithological systems and the mechanisms of partial melting and fractional fractionation. On the modern Earth, plate tectonics offers an efficient mechanism for mass transport from the Earth's surface to its interior, but how far this mechanism dates back in the Earth's history is still uncertain.
Here, we use zircon O isotopes to track recycling of supracrustal materials into the magma sources of early Archean igneous suites from the Kaapvaal craton, southern Africa. The mean δ¹⁸O values of zircon from TTG (tonalite–trondhjemite–granodiorite) rocks abruptly increase at the Paleo-Mesoarchean boundary (ca. 3230 million years ago; Ma), from mantle zircon values of 5–6‰ to approaching 7.1‰, and this increase occurs in the ≤ 3230 Ma rocks with elevated Dy/Yb ratios.
The ¹⁸O enrichment is a unique signature of low temperature water-rock interaction on the Earth's surface. Because the later phase was emplaced into the same crustal level as the older one and TTG magmas would derive from melting processes in the garnet stability field (>40 km depth), we suggest that this evident shift in TTG zircon O isotopic compositions records the onset of recycling of the mafic oceanic crust that underwent the seawater hydrothermal alteration at low temperature.
The onset of enhanced recycling of the supracrustal materials may also develop elsewhere in other Archean cratons and reflects a significant change in tectonic realm during craton formation and stabilization, which may be important processes for the operation of plate tectonics on early Earth.