K-Ar ages, Sr-isotopic compositions and chemistry of late Cretaceous-Tertiary basalts from the Nubian Desert (northern Sudan)

Abstract

Major and trace element chemistry of basaltic rocks from the Nubian Desert in northern Sudan reveals characteristics typical of continental intraplate basalts. Chondrite normalized rare earth element patterns show enrichment in LREE and moderate depletion in HREE. K-Ar whole rock ages of the basalts range from 34 to 92 Ma. According to the K-Ar age data the basalts belong to the volcanic activity widespread in northern Sudan and in southern Egypt at the transition between Cretaceous and Tertiary times. Initial 87 Sr/ 86 Sr ratios vary from 0.7029 to 0.7035, indicating a depleted upper mantle source. 87 Sr/ 86 Sr vs. 1/Sr suggests that the isotopic variation is due to mantle heterogeneity rather than to crustal contamination. There is no correlation between 87 Sr/ 86 Sr isotopic values or K-Ar ages and any general trends of chemical composition. However, the alkali contents of the basalts appear to have decreased during the eruption period, whereas the K/Rb ratios increased