Alteration and weartering processes in the early terrestrial crust

地壳物质自形成以来，不断受到水的风化和蚀变作用。这些现象是目前太阳系中地球上物质演化的最典型特征。然而，风化/蚀变的过程不能很容易地被跟踪，因为在地球上的火山，构造活动。在加拿大苏必利尔上级省太古代斜长岩杂岩中，可以看到一些元古宙蚀变/风化作用的产物。为了模拟元古界环境，我们对橄榄石、辉石和斜长石单晶进行了定向薄片溶解实验。改变实验条件（温度、ph值、时间和取向），测量溶解速率并精确观察反应晶体的表面。结果表明，孪晶、解理等微织构对溶解速率的影响很大，晶体结构的各向异性对溶解过程起着重要作用。

The materials of the terrestrial crust have contineously been weathered and altered by water since its formation. These phenomena are the most characteristic features of material evolution on the earth in the present solar system. However, the process of the weathering/alteration can not easily be traced because of the following volcanic, tectonic activities on the earth. We can see some products of the proteozoic alteration/weathering activities in the archean anorthosite complex in Superior Province, Canada. In order to simulate the proteozoic environment, we carried out the dissolution experiments on the single crystals of olivine, pyroxene and plagioclase, where the oriented thin specimens were used. Changing the experimental conditions (temperature, ph, time and orientation), the dissolution rate was measured and the surface of the reacted crystal was precisely observed. It can be concluded that the microtextures such as twinning or cleavage contribute very much on the dissolution rate and that the anisotropy of the crystal structure plays essential roll on the dissolution process.