A type of amphibolite rock that originated from basic igneous rocks like basalt or gabbro, rather than sedimentary rocks. It is primarily composed of amphibole and plagioclase feldspar, often with traces of epidote and quartz. Geologists distinguish it from para-amphibolite by analyzing its trace element geochemistry, which helps reconstruct the tectonic history of a region.
Heard on the job
The drill core shows a sharp transition from the metasediments into a massive orthoamphibolite unit.