|Carbonatite from Jacupiranga, Brazil. This stone is chemical compound of calcite, magnetite as well as olivine|
Carbonatite is a unique type of intrusive igneous deposit which is rich inwards calcium carbonate (calcite, CaCO3) as well as minerals of the carbonate class. Calcium carbonate is typically burned out of igneous materials past times intense heat; the preponderance of calcite institute inwards carbonatite thence makes it a rattling odd type of igneous formation. Carbonatite deposits may cast equally plugs, dikes, sills, or veins when carbonatite magma intrudes into host stone formations. Carbonatites are solely observed to hap inwards continental plates as well as exercise non hap inwards oceanic plates or at plate boundaries.
Carbonatite magma differs greatly from the to a greater extent than prevalent silicate magma, as well as the 2 dissimilar types of magma are immiscible. Carbonatite rarely contains to a greater extent than than 10% silica past times volume as well as may contain much less. Such magmas possess a rattling depression viscosity because the lack of silica prevents extensive silicate polymerization. It has been shown experimentally that at a temperature of unopen to 600° Celsius a magma possessing a high carbon dioxide (CO2) content volition dissever into separate, immiscible silicate as well as carbonatite magmas.
One possible method of carbonatite formation is that a raise magma originating inwards the drape underneath a continental crust rises until it reaches the boundary betwixt crust as well as mantle. The magma may as well as so hold out of a higher density than the crustal plate as well as may hold out detained. Ferromagnesic silicates may crystallize out at these high temperatures although non ferromagnesic silicates stay liquid. Portions of the crustal plate, which contains plentiful carbonates, may too melt as well as hold out incorporated into the magma. When the ferromagnesic silicates are removed from the magma its density decreases due to the newly lessened relative concentration of atomic expose 26 as well as magnesium. The magma may as well as so rising into the crust until it reaches zones of lower temperature (around 600° Celsius) where it may separate into silicate as well as carbonatite magmas.
Carbonatites contain atypically high concentrations of globe elements such equally titanium (Ti), vanadium (V), manganese (Mn), atomic expose 26 (Fe), copper (Cu), zinc (Zn), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), barium (Ba), lanthanum (La), cesium (Ce), samarium (Sm), europium (Eu), Pb (Pb), thorium (Th), as well as uranium (U). The elements sulfur (S), phosphorous (P), as well as fluorine (F) are too oft present. High concentrations of magnetic materials may upshot inwards observations of odd magnetic phenomena; atypically high concentrations of radioactive elements may create odd levels of radioactive decay inwards the vicinity of a carbonatite.
Calcite (CaCO3), dolomite (CaMg(CO3)2), as well as ankerite (CaFe(CO3)2) are the well-nigh mutual minerals institute inwards carbonatites. The carbonates strontianite (SrCO3), as well as magnesite (MgCO3); the sulfides pyrite (FeS2), molybdenite (MoS2), galena (PbS), chalcopyrite (CuFeS2), as well as sphalerite (ZnS); the oxides ilmenite (FeTiO3), hematite (Fe2O3), rutile (TiO2), as well as zircon (ZrSiO4); the sulfate barite (BaSO4); the phosphates monazite ((Ce,La)PO4), as well as fluorapatite (Ca5F(PO4)3); as well as the halide fluorite (CaF2) are other species which are often present.
|Carbonatite lava at Ol Doinyo Lengai volcano, Tanzania.|
Carbonatites are rare, peculiar igneous rocks formed past times odd processes as well as from odd source rocks. Three models of their formation exist:
- direct generation past times rattling depression score partial melts inwards the drape as well as melt differentiation
- liquid immiscibility betwixt a carbonate melt as well as a silicate melt
- peculiar, extreme crystal fractionation
Evidence for each procedure exists, only the telephone commutation is that these are odd phenomena. Historically, carbonatites were idea to cast past times melting of limestone or marble past times intrusion of magma only geochemical as well as mineralogical information discount this.