Probing the mantle: The story from carbonatites

Abstract

One of the most exciting advances in Earth science in the last several decades has been our increased understanding of the structure and composition of the mantle. Seismic tomography and isotope geochemistry have been major players in those advances. The isotopic studies used basalts from ocean basins to minimize the problems of possible crustal contamination. Data from mid‐ocean ridge basalts (MORBs) and oceanic island basalts (OIBs) revealed a relatively detailed picture of the isotope geochemistry of the sub‐oceanic mantle [e.g. Hofmann, 1997] that led to the recognition of four principal magma components that define end‐member compositions. These are DMM, HIMU, EMI, and EM2 (see Table 1 for further details). All of these components except DMM have been attributed to subduction of different materials, such as oceanic and continental crust and lithosphere, down into the mantle. Several studies have indicated that the mantle is isotopically heterogeneous with heterogeneities that were probably established at least several billions of years ago.

Carbonatite-like dykes from the eastern Himalayan syntaxis: geochemical, isotopic, and petrogenetic evidence for melting of metasedimentary carbonate rocks within the orogenic crust

“…1a and b). Considering that the carbonate melts have low viscosities (perhaps the lowest of any terrestrial rock melts), low temperatures and low densities compared to silicate melts (see summery by Bell and Tilton, 2002), the remobilized carbonate melts could have even contributed to the exhumation of the Greater Himalayan Crystallines (GHC). This suggests that the Greater Himalayan Crystallines of the eastern Himalayan syntaxis exhumed during late Neogene based on the K-Ar and Ar-Ar geochronology data mentioned-above.…”

“…Recently, the argument has been brought up that recycling of sedimentary carbon via subduction of the oceanic crust into the mantle is necessary to sustain carbonatite magmatism (Barker, 1996;Achterbergh et al, 2002;Hoernle et al, 2002). Others have argued for the origin of carbonate melts by deep mantle-plumes (Bell and Tilton, 2002). The above kinds of petrogenesis of igneous carbonate rocks are exclusive because no other possibilities seem to exist.…”

U–Th–Pb geochronology of meta-carbonatites and meta-alkaline rocks in the southern Canadian Cordillera: A geodynamic perspective

“…Carbonatites are comparatively rare ultrabasic/alkaline magmatic rocks, composed of over 50 vol.% carbonate minerals (Woolley and Kempe, 1989), that are important in understanding the chemical evolution of the mantle over time (e.g., Bailey, 1983;Bell and Blenkinsop, 1989;Bell and Tilton, 2002;Bell et al, 1982Bell et al, , 1999Keppler, 2003) and assessing continental break-up (Burke et al, 2003;Rukhlov and Bell, 2010). However, for reconstructing processes of continental growth, break-up and evolution and deciphering their bearing on the underlying mantle, geochronology is one of the most important tools (Bailey, 1983;Kröner, 2010;Parrish, 2001;Rukhlov and Bell, 2010).…”

Evidence for the Multi-Stage Petrogenetic History of the Oka Carbonatite Complex (Québec, Canada) as Recorded by Perovskite and Apatite

“…Both HIMU and EMI are prevalent mantle components that underlie most of East Africa and also characterize the isotope compositions of ocean island basalts (OIBs) worldwide. Several previous investigations have advocated for the involvement of HIMU, EMI, and FOZO (Focus Zone) mantle components in the generation of most young (<200 Ma) carbonatites on a global scale [77][78][79][80][81]. On the basis of a compilation of both radiogenic and stable isotopic data from carbonatites worldwide, Bell and Simonetti [82] made the argument that parental carbonatitic magmas are derived from a sub-lithospheric source that is associated with either asthenospheric "upwellings" or more deep-seated, plume-related activity.…”