地球起源以及大陆的生长与破坏

早期的地球是45亿年前从太阳系星云中的较重元素所组成的星子非均匀吸积、增生而成的。陨击作用造成地表岩石撞碎,诱发地幔的超临界流体或岩浆上涌,造成剧烈的火山爆发,并使地幔上部硅酸盐中的气体挥发分在固体地球表面聚集,逐渐演化成水圈、大气圈。洋壳主要是由深部铁镁硅酸盐岩大面积喷出地表所形成的拉斑玄武岩所组成,可能是陨击作用所派生的片麻岩穹窿则造成了原始大陆地壳的核心。岩石圈板块在18~16亿年前开始形成。大洋与大陆板块间俯冲作用和陆陆板块间碰撞作用的应变速率都是极低的,它们可以造成岩石的局部破裂,但是韧性变形作用、变质作用,以及岩浆与超临界流体的贯入与冷凝却使岩石愈合,非但没有使大陆被破坏与撞碎,反而使大陆不断地增生。亚洲大陆板块就是从18亿年前或16亿年前到现代,由27个较大的古地块及上百个小地块,经过14次板块间的俯冲或碰撞而汇聚成的。至于大陆的破坏,则可能是地幔羽的隆升或巨大陨石撞击所诱发的。

Earth origin and continental growth

The Earth in the early period (4.5 billion years before)was produced by the accumulation and accretion of the planetesimals, composed largely of the heavier elements, which had previously condensed from the solar nebula. The meteorite impact caused that the earth surface rocks against and crushed, evoked the supercritical fluid or magma uplift from the mantle, formed the violent volcanic eruption and let the volatile component concentrat on the solid earth surface, then let them gradually evolve to the hydrosphere and atmosphere. The oceanic crust was mainly formed by tholeiitic basalt, which was caused by the violent eruption of iron magnesium silicate rocks. The original continental cores were formed by gneiss domes, which may be also caused by the meteorite impact. The lithosphere plates were developed in 1.8～1.6 billion years ago. The strain rates of subductions between oceanic and continental plates or collision between continent and continent plates are all very low, which could be formed the partial fractures. However, the ductile deformation, metamorphism, magmatism and the injection and cooling caused the continents accretion continually. The Asian continental lithosphere plate was formed by 14 subductions or collisions, caused by 27 bigger ancient blocks and about hundreds small blocks from the 1.8 or 1.6 billion years ago to the recent. As to the continent destroyed, it may be caused by mantle plume uplift or giant meteorite impact.