Lynne J. Elkins
Date of this Version
Lyu, Y., 2019, Major and trace element analyses for studying oceanic crustal construction and ridge morphology along the Kane-Atlantis supersegment of the Mid-Atlantic Ridge [M.S. thesis]: University of Nebraska-Lincoln
Faulting style along slow-spreading ridge segments exerts a major control over oceanic crustal construction and ridge morphology. Seafloor spreading along slow-spreading ridges is classified into asymmetrical detachment faulting and symmetrical spreading styles. Magma supply variations may influence the formation of symmetric versus asymmetric segments, but the factors that derive such variations remain unclear. We present U and Th concentration data by isotope dilution for basalts from 24 to 30 oN MAR, of which 18 samples were retrieved from detachment faulted and 10 from symmetrical segments. The U-Th concentration results from this study are further compiled with prior published data from Gale et al. (2013) and data from Langmuir (personal communication). The compiled dataset provides robust combined major and trace element analyses of basalts from the study area.
Statistical analyses show that basalt samples from asymmetrical segments have higher mean MgO, but lower mean Na2O, Sr and Sr/Nd contents compared to samples from symmetrical segments (at the 95% confidence level). The differences in these major and trace elements may indicate a higher proportion of pyroxenites and/or a more trace element enriched peridotite in the source mantle beneath symmetrical segments, which increases the magma supply and prevents the formation of detachment faults beneath these segments. Furthermore, the larger amount of magma supply facilitates the crust to fully accommodate seafloor spreading and generate symmetrical accretion along the Kane-Atlantis segments. On the other hand, the detachment faults beneath asymmetrical segments may decrease the degrees of assimilation and fractional crystallization at shallow levels.
Advisor: Lynne J. Elkins