< p >海洋岩石圈(地球物理定义壳+上地幔,作为“板”)主要是玄武岩组成,上层是辉长岩玄武岩和较低的水平。高层已被证明与水井,而低水平已经从转换断层抽样推断与蛇绿岩和比较。这个序列是由地幔橄榄岩的部分熔融速率控制的相当。以至于玄武岩形成于这种方式甚至有一个特定的组成“MORB”(大洋中脊玄武岩)。< / p > < p >相反,大陆岩石圈是更复杂的,往往是“花岗岩”组成。这包括花岗岩但还可以包括很多变质岩(如。片麻岩)和沉积物。沉积物较低密度(高孔隙空间),但也是quartz-rich花岗岩等岩石。建立大陆的各种过程倾向于硅成分丰富,导致批量“花岗岩”组成。例如,有限的部分熔融最初将生产高硅、高碱融化。侵蚀会分解前最常见的矿物石英——离开quartz-rich沉积物(因此砂岩主要是石英)。 Metamorphism of pelites (rocks rich in Al and Si) will tend from the initial mudstones & basalts through to gneisses & migmatites (which have a lot of quartz and feldspar). Migmatites are partially melted - and the melted bits are essentially granite. Basalt is denser than granite. On gravity surveys, basalts and gabbros will appear as positive anomalies, whilst granites and sedimentary basins will appear as negative anomalies.