Ferrodoleritic dykes in the Tarim Craton signal Neoproterozoic breakup of Rodinia supercontinent

摘要

Mafic dyke swarms are important bar codes for the rifting and breakup of supercontinents. Here we report a Neoproterozoic mafic (ferrodoleritic) dyke swarm from the Aksu area along the northern margin of the Tarim Craton, NW China. Zircon U-Pb analyses of two dyke samples yielded ages of 801 +/- 9 Ma and 804 +/- 13 Ma. The ferrodoleritic dykes show high total FeO (11.55-14.55 wt%) and TiO2 contents (2.84-3.26 wt%) and variable SiO2 (47.90-52.74 wt%). They display positive anomalies of Rb, Ba, K and negative anomalies of Nb, Ta, Ti and the enrichment of light rare earth elements relative to heavy rare earth elements. The whole-rock epsilon(Nd) (t) values (-5.4 to -7.2) indicate a relatively homogeneous and enriched magma source. Trace element mod elling suggests that the ferrodoleritic dykes were generated by low degree of partial melting (garnet lherzolite 3-5%, pyroxenite 5-10%) of a mixed mantle source (60% garnet lherzolite and 40% pyroxenite). The results from our study suggest two major mafic magma pulses at ca. 830-800 Ma and ca. 780-750 Ma during the Neoproterozoic, which we correlate to the onset of Rodinia supercontinent breakup.