The North America mid‐Cretaceous kimberlite corridor: Wet, edge‐driven decompression melting of an OIB‐type deep mantle source. (27th July 2017)

• Record Type: Journal Article
• Authors: Kjarsgaard, B. A.; Heaman, L. M.; Sarkar, C.; Pearson, D. G.
• Is Part Of: Geochemistry, geophysics, geosystems. Volume 18:Number 7(2017)
• Page Start: 2727
• Page End: 2747
• Publication Date: 2017-07-27
• Subjects: kimberlite -- deep mantle source region -- U‐Pb geochronology -- Sr‐Nd‐Hf isotope -- edge‐driven convection; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 550.5
• DOI: 10.1002/2016GC006761
• Languages: English
• ISSNs: 1525-2027

Abstract

Abstract: 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 ∼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 ɛNd 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 H2 O, with subsequent metasomatism and synchronous wet partial melting generates a hot CO2 and H2 O‐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 Key Points: U‐Pb geochronology defines a 4, 000km kimberlite corridor in central North America with similar Sr‐Nd‐Hf low ɛNd OIB isotopic compositions Kimberlites all located at the highly attenuated lithospheric edge of the North American Craton, facilitating edge‐driven convection (EDC) Kimberlite melt generation in upper TZ and lower asthenosphere driven by wet decompression melting, EDC provides top down driver