科研之友
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摘要
Thirty new high-precision U-Pb perovskite and zircon ages from kimberlites in central North America delineate a corridor of mid-Cretaceous (115-92 Ma) magmatism that extends approximate to 4000 km from Somerset Island in Arctic Canada through central Saskatchewan to Kansas, USA. The least contaminated whole rock Sr, Nd, and Hf isotopic data, coupled with Sr isotopic data from groundmass perovskite indicates an exceptionally limited range in Sr-Nd-Hf isotopic compositions, clustering at the low (Nd) end of the OIB array. These isotopic compositions are distinct from other studied North American kimberlites and point to a sublithospheric source region. This mid-Cretaceous kimberlite magmatism cannot be related to mantle plumes associated with the African or Pacific large low-shear wave velocity province (LLSVP). All three kimberlite fields are adjacent to strongly attenuated lithosphere at the edge of the North American craton. This facilitated edge-driven convection, a top-down driven processes that caused decompression melting of the transition zone or overlying asthenosphere. The inversion of ringwoodite and/or wadsleyite and release of H2O, with subsequent metasomatism and synchronous wet partial melting generates a hot CO2 and H2O-rich protokimberlite melt. Emplacement in the crust is controlled by local lithospheric factors; all three kimberlite fields have mid-Cretaceous age, reactivated major deep-seated structures that facilitated kimberlite melt transit through the lithosphere. Plain Language Summary A model is proposed in which molten rocks that are known to carry diamonds (kimberlites), are generated at great depth (>400 km) in the Earth, with the magma generation being facilitated by convection cells at the edge of the old North American craton
- 出版日期2017-7
