Pipes Formation Location Mines
Kimberlite Formation
Kimberlites are small volume, volatile rich, potassic, ultrabasic magmas that are formed at great depth in the Earth's mantle. During their ascent, kimberlite magmas entrain substantial mantle and crustal material, hence provide a unique window into the nature of the deep mantle and lower crust. Despite their importance, there is no consensus on their depth of origin or trigger mechanism responsible for their formation. Based on more than 200 precise and robust radiometric age determinations of North American Kimberlites and related rocks, kimberlite and related magmatism in North America was emplaced during the last1-billion-year period of Earth history.
The popular known kimberlite magmatism is Cenozoic to Mesozoic in age, and kimberlites intrude all known Archean cratons. Four distinct kimberlite emplacement patterns have been identified and that can be related to magma generation in a variety of tectonic environments. Kimberlites that bear diamonds occur in each domain.
The fact that kimberlites have enormous capacity for entraining and transporting mantle material to the Earth's surface provides a unique opportunity to study the nature and architecture of continental roots, including the primary mantle host rocks which contain diamond. As most diamond-friendly cratons worldwide, the kimberlites that intrude the Slave craton in northwest Canada have sampled two main diamond-bearing mantle lithologies; harzburgite and eclogite. Although some Slave craton harzburgitic diamonds are ancient , a compilation of Re-Os model ages from Slave Peridotites indicate a dominance of Neoarchean ages, implying that much of the continental lithospheric mantle formed significantly later than the formation of these ancient diamonds. The dominance of Neoarchean mantle peridotite ages coincides very closely with the dominant period of Slave juvenite crust formation between 2.75 and 2.58 Ga, indicating a coupled mantle/crust evolution for the Slave craton.
In contrast to the dominantly Archean history recorded by Slave CLM peridotites, the majority of Slave diamonds have eclogitic sources that are much younger. There are various geochemical varieties and ages of eclogite recovered from the Slave craton that reflect a diversity of origins including; 1) remnants of sub ducted oceanic crust, 2) magmatic high-pressure cumulates linked to Paleoproterozoic large igneous province formation, and 3) hybrid origins involving the interaction between basaltic melts and peridotite. In most cases, the origin of diamond in these eclogites is linked to one or more periods of mantle metasomatism.
