Destruction of the North China Craton

Archean cartons are commonly underlain by a cold, thick (>200 km), isotopically enriched, and compositionally refractory lithospheric keel, and represent some of the most stable regions on our planet. However, the North China Craton (NCC), an old continental geological structure dating back 4.0 Ga, is underlain by a thin lithosphere (<100 km) and shows many signs of thermo-tectonic reactivation. This observation challenges the traditional view that the lithosphere beneath cratons has always been stable and supports the new concept of "craton destruction". This concept has now been widely accepted and has contributed to our understanding of the processes of intraplate magmatism generation and ore-forming, and of continental evolution in general. In 2006, Chinese earth scientists sponsored by the National Natural Science Foundation of China (NSFC) embarked on a major research program entitled "The Destruction of the North China Craton". Over the past six years, they have carried out a comprehensive study covering the geology, geophysics, and geochemistry of the NCC with a global perspective using the "natural laboratory research" scientific model. A summary of recent developments and outcomes, taking the same title of the NSFC's major research program, was published in Science China, Earth Sciences, 2012, Vol. 55(10).

The scientists focused on important scientific issues relating to NCC destruction including the spatio-temporal distribution of the NCC, the structure of the deep earth and thermal-tectonic-fluid processes, correlation between the surface geology and cratonic destruction, processes and mechanisms, and the role of cratonic destruction in global geological and continental evolution. Using mobile seismic stations and in-situ isotope tracer technology, they obtained high-resolution, large-scale and multi-attribute observations, and collected and analyzed a huge amount of data. Interdisciplinary approaches based on the observations and experimental data have resulted in new evidence and insights into the destruction of the NCC and its implications for near-surface resources and global continent evolution.

Mesozoic and Cenozoic mantle-derived rocks and the peridotite xenoliths entrained in them were sampled throughout the NCC for petrological and geochemical investigations that used newly developed tracers of radiogenic isotopes (Hf and Os) and non-traditional stable isotopes (Li, Mg and Fe). These studies led to new insights into the properties of the Phanerozoic lithospheric mantle beneath the craton and the processes that modified these properties. The sub-continental lithospheric mantle of the late Mezozoic was found to be rich in water while that of the Cenozoic was highly deficient in water. It was found that the lithosphere of the NCC had thinned substantially since the Mesozoic and had undergone a significant change in composition from a refractory cratonic lithospheric mantle before the thinning to a relatively fertile "oceanic" mantle after its thinning, while during the decratonization the composition of the lithospheric mantle was very heterogeneous. It has been demonstrated that this compositional change was caused by peridotite–melt interaction. This evidence and the results of Li-Fe-Mg isotope studies infer that the reactive melts are crustal melts originating from deep continental subduction or from recycled oceanic crust and mantle-derived silicate and carbonatite melts from the asthenosphere. The formation of these melts was related to the subduction of circum-craton plates, in particular the continental Yangtze plate and the Pacific plate.

Exploring the role of craton destruction within the framework of global continental evolution, it is necessary to understand not only the nature of the lithosphere and its modification processes, but also the dynamic and tectonic system that caused craton destruction. The crust and upper mantle structures pose important constraints on the tectonic elements affecting the NCC. Since 2000, a total of 975 stations equipped with portable broadband seismometers for recording temporal data have been deployed in the NCC with an average spacing of about 10