We present combined U-Pb, Sr, and Nd isotope data for small perovskite crystal fractions from kimberlites in West Greenland. Based on this high-precision TIMS data set, we revise the age range for kimberlite magma emplacement in the Sarfartoq and Tikiusaaq fields to 550-590. Ma and 158-166. Ma, respectively. These improved U-Pb perovskite age constraints reinforce the close temporal association of kimberlite and carbonatite magmatism across the North Atlantic craton. The new combined U-Pb, Sr, and Nd isotope data for perovskites provide evidence for kimberlite magma derivation from a moderately depleted mantle source region during both the Neoproterozoic and Mesozoic. Moreover, we demonstrate that the difference in initial Sr-Nd isotope compositions between the Neoproterozoic Sarfartoq ( 87Sr/ 86Sr=0.70278-0.70293; ε Nd=+1.6 to +3.6; n=13) and Mesozoic Tikiusaaq ( 87Sr/ 86Sr=0.70319-0.70346; ε Nd=+4.8 to +5.1; n=3) kimberlite fields can be readily explained by isotopic evolution of a common mantle reservoir. This mantle reservoir appears to have continuously participated in global crust-mantle differentiation and recycling, which points to the well-stirred convective upper mantle as the ultimate kimberlite magma source region beneath West Greenland. The apparent geographic shift of kimberlite and associated carbonatite magmatic activity from the craton margin during the Neoproterozoic toward the craton center during the Mesozoic is explained by changes in localized, small-scale mantle flow along the underside of progressively thinning cratonic lithosphere.
|Status||Udgivet - 6 aug. 2012|
- Programområde 4: Mineralske råstoffer