Destruction of the North China Craton and its influence on surface geology and terrestrial biotas

Abstract

The North China Craton (NCC), a major geological element of East Asia, had hehaved as a stable craton untile late Mesozoic. The NCC experiencd multiple contraction and extension in late Mesozoic, evidened by three phases of shortening and two phases of stretching. The three shortening phases occurred in the late Middle Jurassic, earliest Early Cretaceous, and latest Early Cretaceous, respectively. Crustal stretching happened in Late Jurassic and Early Cretaceous times, and was marked by large-scale magmatism and development of rift basins and metamorphic core complexes. Widespread vigorous magmatism and extensive rifting indicate the loss of the NCC stability in the Early Cretaceous. Alternating crustal contraction and extension of the NCC are attributed to the change in subduction angles of the paleo-Pacific plate, with low-angle subduction resulting in shortening and high-angle subduction leading to stretching. However, magmatism, deformation and lithospheric thinning are merely the various expressions of the NCC destruction. It is shown that deep thermal processes must have strongly altered the properties of overlying lithosphere, resulting in a change from the continental into oceanic mantle. It was the transformation of physico-chemical properties of the lithospheric mantle that destabilized the NCC. Also noticeable are occurrences of the Yanliao and Jehol biotas that evolved in the Middle-Late Jurassic and Early Cretaceous, respectively, and just coincided with the initial and peak stages of the NCC destruction. Flourishing and vanishing of the biotas appeared closely related to volcanic intensity and rift basin development in space and time, implicating a profound control of deep dynamic processes on surface paleogeography and ecosystems. Implicitly, life should have been evolving in accord with surrounding environments. Volcanism might have exerted a strong influence on prosperity and disappearance of the Yanliao and Jehol biotas, with ash fallout leading to perfect preservation of a variety of precious fossils. Also noteworthy is that biotas thrived in the period when rift basins were developing, whereas biotas died out when basins were inverted. It is still a challenge to explore the linkage of terrestrial life evolution and tectonic processes. Recent developments in geodynamic studies reveal that subduction of the western paleo-Pacific plate might have produced a unique mantle profile in late Mesozoic, with the stagnant plates in mantle transition zone being sandwiched between the lower mantle and the big mantle wedge. Extensive dehydration and decarbonization of the stagnant plates resulted in melting and metasomatism of the upper and lower parts of mantle transition zone. These processes should have played a crucial role in altering the nature of lithospheric mantle and in triggering large-scale magmatism in the crust. A big mantle wedge is thought to have developed beneath the East Asia continent during the Early Cretaceous as a result of the slab rollback and the stagnation in the mantle transition zone. The combined tectonic processes must have exerted a profound influence on both the NCC destruction and Yanliao/Jehol biotal evolution. Interdisciplinary researches will help us understand the complicated interaction of deep and surface processes and comprehend the past, present and future of our habitable planet.