地质历史中板块构造启动时间

When Did Plate Tectonic Start on Earth?

地质历史中板块构造是何时开始启动的长期存在着激烈的争论,最极端的一是认为板块构造在新元古代的800 Ma前开始,二是在冥古宙4.3 Ga就已启动,多数学者认为在太古宙末开始启动。确定板块构造启动时间主要依据以下几方面:(1)地球动力学特点,如地幔的热状态以及粘塑性地幔对流模拟表明,板块构造可能是在地球热和冷停滞状态之间演化的一个相。在太古宙较热的地球中,板片强度低,板片的频繁断离阻止了形成类似现代样式的长期俯冲体系,太古宙的板块构造是短期的、阵发性的;(2)代表俯冲的标志的蛇绿岩、蓝片岩和超高压(UHP)变质地体;(3)具有弧特征的岩石组合,如拉斑玄武岩-安山岩-英安岩-流纹岩及英云闪长岩-奥长花岗岩-花岗闪长岩(TTG)岩套;(4)增生楔中混杂岩和大洋板块地层、前陆盆地、大陆裂谷、双变质带、造山带;(5)与俯冲带关系密切的造山型Au矿、斑岩Cu矿和浅成热液矿床、火山岩型块状硫化物矿床(VHMS),它们最早出现的年龄一致在3.5~3.1 Ga,指示了板块构造的开始;(6)世界不同地区大陆的Ni/Co、Cr/Zn比值随沉积年龄变年轻而降低,陆壳从3.0 Ga前的镁铁质转变为2.5 Ga时的长英质,表明全球板块构造的启动应在3.0 Ga的古中太古代;(7)冥古宙锆石、太古宙金刚石中矿物包裹体及Hf、O、C、N同位素组成研究表明,冥古宙地球表面存在类似板块汇聚边缘,太古宙含有大陆沉积物的海洋岩石圈俯冲进入地幔。

It is controversial when Earth＇s modern tectonic regime began. Most scientists believe it operated in Late Archean, even thougth some researchers suggest it began late in Neoproterozoic ca. 800 Ma, and others argue that subduction began early in Hadean ca. 4.3 Ga. The following indicators can be tracked into the geologic past plate tectonics： （1） geodynamics, such as the mantle potential temperature have shown the interior of the early Earth was much hotter than it is today which resulted frequent slab break-off events prevented a modern-style long-lived subduction system, and plate tectonics may be a phase in the Earth＇s evolution based on viscoplastic mantle convection simulations; （2） petrotectonic assemblages such as ophiolites, blue schists, and ultrahigh-pressure metamorphic terranes are reliable indicators of plate tectonics, in addition the arc and back-arc rock assemblages--tholeiite-andesite- dacite-rhyolite and TTG suites are also evidence of subduction zones; （3） accretionary prisms and ocean plate stratigraphy, foreland basins, continental rifts, paired metamorphic belts and orogens are all important hallmarks. Other reliable indicators are from porphyry Cu-Au and epithermal-type Au-Ag deposits, orogenic gold deposits and VHMS and other types of mineral deposits. Ni/Co and Cr/Zn ratios of the Archean terrigenous sedimentary rocks and Archean igneous/metaigneous rocks showed that the crust evolved from a highly mafic bulk composition before 3.0 Ga ago to a felsic by 2.5 Ga ago. This compositional change suggests the onset of global plate tectonics at ca. 3.0 Ga ago. Archean subduction was recorded by Re-Os isotopes in sulfide inclusions in diamonds. Extreme crustal oxygen isotope signatures preserved in coesite inclusions in Archean diamond present compelling evidence for the subducted nature of the prototiths of the diamond eclogite suite.