K-U-Th systematics of Earth' igneous rocks for planetologic comparisons: Normal-type Mid-Ocean Ridge Basalt on Earth vs. tholeitic-basalt materials on Venus

Literature-derived computer data base for the Normal (nonhotspot) Mid-Ocean Ridge Basalt (N-MORB) samples was compiled as a first step in K-U-Th systematization of Earth' igneous rocks. The final set of 67 samples of N-MORB qualified as fresh for the K-U-Th systematics shows the average contents and standard deviations as following: K, O, 0.09±0.04 wt.%; Th, 0.16±0.08 ppm and U, 0.06±0.03 ppm. Four low-K Venus' materials measured in only K, U and Th contents and consistently interpreted earlier as tholeitic-basalt materials were compared with the set of Earth's N-MORB. The comparison relative to N-MORB. This result suggests the tectono-magnetic setting of the venusian tholeite formation was different of Earth' N-MORB and should provide conditions for enrichment of their magmas in incompatible elements. 73 refs.; 6 figs