THE CRUST-MANTLE TRANSITION LAYER AND TECTONIC EVOLUTION
LIN Ge; FAN Weiming; GUO Feng; WANG Yuejun(Changsha Institute of Geotectonics, Academia Sinica, Changsha 410013)
As an open system the crust-mantle transition layer is an important layer where materialand energy exchange between crust and mantle takes place. The different styles of transitionlayer observed in seismic reflection profiles, which are associated with different lock-mineralcompositions indicate different tectonic settings. The transition layer in Tibet, China, acomplex geological unit constituted by random and reticular high and lower seismic velocitylamellae with qrid shaped reflection layer and big thickness, the rock-mineral associationsbearing a dual nature of both mafic granulite factes and ultramafic factes rocks which are thetypical upper mantle rocks, indicates that the crust movement is very intense in this regionnow. The transition layer in North China is usually composed of a thinner strong positive velocity gradient layer, and its rock-mineral associations also bear a dual nature. This suggeststhat the crust is still active though the intense mobile period is over. The transition layer inthe remaining platform basin of China is characterized by a relatively sharp seismic discontinuity inferred the feature of the deep geological processes in the platform is more stable.