宝石级原生金刚石的形成条件及成因

On the Forming Conditions and the Origin of Natural Diamond

金刚石有多种成因类型，但宝石级金刚石是在地壳最稳定区──克拉通之下的地慢中形成的，时间上比携带它们从地球深部至浅部的岩浆岩早得多（数亿年－数十亿年），它们在温度９９～１３００℃，压力４．５～６ＧＰａ和适当的氧化－还原条件下长期稳定地保存在地慢中，为形成高质量的宝石级金刚石，要求携带它们的岩浆从地慢向上喷发的速度大于７０ｋｍｈ－１也可以在具备沉积盖层并隐伏深断裂的条件下，通过底辟然后爆发的方式形成．

There are many genetic types of natural diamond. The diamond of gem - quality is formed in the mantle fluid under the old Cratons. The forming time of the diamond is much earier than the forming time of magmatic rocks that transported them from the deep part of the earth to the shallow part of the carth. A temperature of 900￣1 300℃, pressure of 4.5- 6GPa and moderate reduction-oxidation potential are the most important conditions to keep diamond stable in the mantle. The magma must erupt at a rate of more than 70km.h-1 to form gem diamond. They were also formed through diapiring and erupting under conditions of sedimentary cover overlying the deep faults.