Liu Junlai

Timing, scale and mechanism of the destruction of the North China Craton

The North China Craton (NCC) is a classical example of ancient destroyed cratons. Since the initiation of the North China Craton Destruction Project by the National Natural Science Foundation of China, numerous studies have been conducted on the timing, scale, and mechanism of this destruction through combined interdisciplinary research. Available data suggest that the destruction occurred mainly in the eastern NCC, whereas the western NCC was only locally modified. The sedimentation, magmatic activities and structural deformation after cratonization at ∼1.8 Ga indicate that the NCC destruction took place in the Mesozoic with a peak age of ca 125 Ma. A global comparison suggests that most cratons on Earth are not destroyed, although they have commonly experienced lithospheric thinning; destruction is likely to occur only when the craton has been disturbed by oceanic subduction. The destruction of the NCC was coincident with globally active plate tectonics and high mantle temperatures during the Cretaceous. The subducted Pacific slab destabilized mantle convection beneath the eastern NCC, which resulted in cratonic destruction in the eastern NCC. Delamination and/or thermal-mechanical-chemical erosion resulted from the destabilization of mantle convection.

Late Mesozoic metamorphic core complexes: new constraints on lithosphere thinning in North China

Abstract Metamorphic core complexes (mccs) are among the most prominent structural styles of lithosphere extension and thinning during late Mesozoic in North China. In this paper, the geometrical, kinematic and age characteristics of some of the mccs, e.g. Liaonan, Waziyu (Yiwulushan), Yunmengshan, etc., are discussed. Some common characteristics, such as kinematic polarity, geometric asymmetry, occurrence over a time span, scattered and isolate distribution, and progressive development, can provide direct constraints on the regional lithosphere extension and thinning in North China, Which does not favor the prevailing plume model, a general delamination model or extensional collapse of overthickened orogenic crust. We are that several aspects, such as the kinematic polarity atdepths during lithosphere extension, gradual break-up of lithosphere plate, relationship between magmatism and regional extension, and coeval activity of mccs and Tan Lu fault, should be taken into consideration when constructing...

Micro- and submicrostructural evidence for high-temperature brittle-ductile transition deformation of hornblende: Case study of high-grade mylonites from Diancangshan, western Yunnan

OM (optical microscope)/TEM (transmission electron microscope) micro-and submicrostructural analysis of hornblende rocks sheared at high temperatures from the Diancangshan area, western Yunnan reveals evidence for deformation in the brittle-ductile transition of hornblende at middle crustal level (about 637°C and 0.653 GPa) and mechanisms of deformation in the transitional regime are further discussed. Sheared hornblende rocks at middle crustal level have typical mylonitic microstructures, shown by coarse porphyroclasts and fine matrix grains. Different mineral phases in the rocks show distinct deformation characteristics. Hornblende and feldspar grains are intensely deformed with obvious grainsize reduction, but quartz grains are recrystallized dominantly by grain growth. Hornblende grains show typical brittle-ductile transition nature. Initial crystallographic orientations of porphyroclasts have strong effects on the behavior of grains during deformation. There are mainly two types of porphyroclasts, type I “hard” porphyroclasts and type II “soft” porphyroclasts, with [001] perpendicular and parallel to external shear stresses respectively. “Hard” porphyroclasts generally occur as competent grains that are rarely deformed or sometimes deformed by fracturing and dislocation tangling. “Soft” porphyroclasts are highly deformed primarily by dislocation tangling (as shown in the cores of the porphyroclasts), but twinning, dislocation glide and climb probably due to hydrolytic weakening also contribute to dynamic recrystallization of the porphyroclasts into fine grains in the matrix. The micro-and submicrostructures of the two types of porphyroclasts and fine-grained matrix provide powerful evidence for the behavior of brittle-ductile transition of hornblende grains. It is concluded that twinning nucleation is one of the most important processes that operate during dynamic recrystallization of hornblende crystals at the brittle-ductile transition. (100) [001] twin gliding and dislocation creep (dislocation glide and climb) are mutually enhanced during twinning nucleation. As a newly discovered mechanism of dynamic recrystallization, it may have played more important roles than ever recognized during dynamic recrystallization of crystals with twins in the brittle-ductile transition.

Structure, evolution and regional tectonic implications of the Queshan metamorphic core complex in eastern Jiaodong Peninsula of China

The Queshan MCC is an important example of a crustal extensional structure in the eastern Jiaodong Peninsula along the southeastern margin of the NCC in the Early Cretaceous. The MCC is a typical Cordilleran-type core complex with a three-layered structure: (1) the upper plate is constituted by the Cretaceous supradetachment basin and Paleoproterozoic basement; (2) the lower plate comprises the Neoarchean high-grade metamorphic complexes and late Mesozoic granitic intrusions; and (3) the two plates are separated by a master detachment fault. A series of late NEN-oriented brittle faults superimposed on and destructed the early MCC. Petrology, geometry, kinematics, macro- and micro-structures and quartz c-axis fabrics imply that the MCC has a progressive exhumation history from middle-lower to subsurface level (via middle-upper crustal level) under the nearly WNW-ESE regional extensional regime. We present structural and geochronological evidence to constrain the exhumation of the Queshan MCC from ca. 135 to 113 Ma. Based on the comprehensive analysis of the different patterns of extensional structures in the Jiaodong and Liaodong Peninsula, we have defined the Jiao-Liao Early Cretaceou extensional province and further divided the crustal extension of it into two stages: the first stage was the intense flow of the middle-lower crust and the second stage was the extension of the middle-upper crust. Combining the tectonic setting, the lithosphere thinning in the Jiao-Liao Early Cretaceous extensional province can be considered a typical model for the response of crust-mantle detachment faulting under regional extension in East Asia.