What is kimberlite? Ultramafic, incompatible-element and volatile rich igneous rock formed by melting and entrainment of deep mantle material Occur in volcanic and sub-volcanic settings Complex, hybrid rocks → wide range of characteristics Heterogeneous – “magma” includes the following components: solids - mantle-derived silicate melt - phenocrysts, groundmass volatiles - H2O / CO2 → segregations, deuteric alteration, eruption Complicated by: contamination with crustal material during emplacement / eruption and; considerable textural variation associated with different intrusion / eruption / reworking processes weathering

Commonly, they exhibit a distinctive inequigranular texture resulting from the presence of macrocrysts (and in some instances megacrysts) set in a fine grained matrix. The megacryst/macrocryst assemblage consists of rounded anhedral crystals of magnesian ilmenite, Cr-poor titanian pyrope, olivine, Cr-poor clinopyroxene, phlogopite, enstatite and Ti-poor chromite. Olivine is the dominant member of the macrocryst assemblage.

Morphology of Kimberlite Based on studies of numerous kimberlite deposits, geologists have divided kimberlites into 3 distinct units based on their morphology and petrology. These units are: 1) Crater Facies Kimberlite 2) Diatreme Facies Kimberlite 3) Hypabyssal Facies Kimberlite

1)Crater Facies Kimberlite: The surface morphology of an unweathered kimberlite is characterised by a crater, up to 2 kilometers in diameter, whose floor may be several hundred meters below ground level.

he crater is generally deepest in the middle. Around the crater is a tuff ring which is relatively small, generally less than 30 meters, when compared to the diameter of the crater. Two main categories of rocks are found in crater facies kimberlite: a.)pyroclastic, those deposited by eruptive forces; b.)epiclastic, which are rocks reworked by water.

2) Diatreme Facies Kimberlite Kimberlite diatremes are 1-2 kilometer deep, generally carrot-shaped bodies which are circular to elliptical at surface and taper with depth. The dip contact with the host rocks is usually degrees. The zone is characterized by fragmented volcaniclastic kimberlitic material and xenoliths plucked from various levels in the Earths crust during the kimberlites journey to surface.

Pelletal lapilli - appear to have formed by the rapid crystallization of a volatile poor magma containing phenocrysts. They are characterised by a crystal nucleus surrounded by microphenocrysts which align themselves tangentially to the central crystal.Pelletal lapilli

Nucleated autoliths - similar to pelletal lapilli but lacking microphenocryst orientation. Kernel grain usually country rock. Magmatic nucleation about a nucleating center. Matrix composed almost entirely of fine- grained diopside, serpentine and phlogopite.

3) Hypabyssal Facies Kimberlite These rocks are formed by the crystallization of hot, volatile-rich kimberlite magma. Generally, they lack fragmentation features and appear igneous.

i. Calcite-serpentine segregations in matrix. ii. Globular segregations of kimberlite in a carbonate-rich matrix. iii. Rock fragments have been metamorphosed or exhibit concentric zoning. iv. Inequigranular texture creates a pseudoporphyritic texture.

Facts: about Kimberlite It is named after the town of Kimberley in South Africa, where the discovery of an 83.5-carat (16.7 g) diamond in 1871 spawned a diamond rush, eventually creating the Big Hole.Kimberley South AfricaBig Hole Kimberlite occurs in the Earth's crust in vertical structures known as kimberlite pipes.crustkimberlite pipes