New evidence for the breakup of the Columbia supercontinent from the northeastern margin of Tarim Craton: rock geochemistry, zircon U-Pb geochronology and Hf-O isotopic compositions of the ca. 1.55 Ga diabase sills in the Kuruktag area

Abstract

The Mesoproterozoic diabase sills from Kuruktag along the northeastern margin of the Tarim Craton (TC) is of great significance for the understanding of the breakup of the Columbia supercontinent. In this contribution, we report new sensitive high-resolution ion microprobe (SHRIMP) zircon U-Pb ages and in-situ Hf-O isotopes, as well as whole-rock elemental and Sr-Nd isotopic data for the Astingbulake diabase sills. Zircons had high Th/U ratio and banded zoning in cathodoluminescence images, indicating their mafic magmatic origin, and yielded a weighted 207 Pb/ 206 Pb age of 1 551±8 Ma and elevated δ 18 O values of 5.52‰ to 6.53‰ (Gaussian distribution peak at 5.8‰) relative to mantle zircons. Geochemically, the diabase samples are characterized by high FeO T (11.4% -13.4%), low TiO 2 (1.51% -2.45%) and MgO (5.46% -7.11%) contents with Mg # ranging from 43 to 52. They contained relatively low REEs contents (90.1 -116)×10 -6 with slightly positive Eu anomalies (δEu=1.05 -1.27). Moreover, these samples are featured by enrichment in light rare earth elements (LREEs) and large ion lithophile elements (LILE) and depletion in heavy rare earth elements (HREEs) and Nb-Ta high field strength elements (HFSEs), consistent geochemical features with continental flood basalts (CFB). The coupled whole rock Nd and zircon Hf isotope compositions, with ε Nd (t) ranging from -3.8 to -1.8 and ε Hf (t) from -3.7 to 1.9, suggest that the Astingbulake diabase sills derived from enriched continental lithospheric mantle within intra-plate rifting or extensional setting, and the ca. 1.55 Ga diabase is closely related in time to the global early-Mesoproterozoic anorogenic magmatism associated with the breakup of Columbia supercontinent.