什么是 Natural, thermal, detrital and chemical remanent magnetisation？

The natural remanent magnetisation (NRM) of a rock is the remanence it carries as it is collected, the sum of components acquired at different times. A thermoremanent magnetisation (TRM) is acquired by cooling through the blocking temperatures in a field, as in a lava flow or an intrusion. A detrital remanent magnetisation (DRM) is acquired when magnetic grains settling in water, or in the wet sediment just below its surface, rotate into the field before they are locked. A chemical remanent magnetisation (CRM) is acquired when a magnetic mineral grows, through a blocking volume, in a field, as haematite does when a red bed forms.