On The Extraterrestrial Impact and Plate Tectonic Dynamics: A Possible Interpretation

摘要

The plate tectonics theory arose in the sixties, and its geometry and kinematics have been rather well solved in recent years. However, the dynamics of plate tectonics remains still a controversial problem. According to recently discovered data, the stress orientation of the lithosphere plates varied remarkably in an interval of 10 million years in the Meso-Cenozoic. Sometimes the plates even show radial movements, and the tectonic stress (differential stress) decreases rapidly with the depth under the earth's surface. The mega-impact center and microtektite about 1 Ma ago was situated near the triple junction of the southern Indian plates, and those 34 Ma in age was near the triple junction of the eastern Pacific plates. The velocities of plate motion are well known as 2-12 cm/a, but the velocities of mantle convection are believed to be only several mm/a. Many data show that the hypothesis of mantle convection driving the lithosphere plate motions is difficult to be established., and the influence of extraterrestrial impact on piate motions should not be ignored. Depending on the limited data, we consider that the mega-impact and microtektite impact could produce craters with hundreds of kilometers in diameter and tens of kilometers in depth, thus forming partial debility in the upper part of the lithosphere, especially in the oceanic part. This would bring about the upward surge of the mantle material through isostatic compensation and lead to horizontal spreading of the oceanic plates, resulting in subduction, collision or shearing between them. It seems that in the Meso-Cenozoic the extraterrestrial mega-impacl may be the main inducing factor for plate motions and the partial upward surge of the mantle material may have driven the plates apart.