Search ETDs:
Hafnium Isotope Geochemistry of the Gabbroic Crust Sampled Along the Mid-Atlantic Ridge: Constraints on the Nature of the Upper Mantle

2013, Master of Science (MS), Ohio University, Geological Sciences (Arts and Sciences).
I characterize εHf values in zircon hosted in gabbroic rocks from three sites along the Mid-Atlantic Ridge (ODP cores 1270D, 1275D and IODP core 1309D) in order to examine mechanisms for igneous construction of the lower oceanic crust, and characterize the isotopic heterogeneity of the underlying mantle source. The samples of intrusive oceanic crust display a broad range of εHfzircon values from 13.3 to 22.1 (n=134), and zircons from individual drill cores spanning <1400 mbsf differ by up to 7.4 epsilon units. The variation within these single cores is similar to published data for extrusive basalts sampled over scales of ~200 km. The distribution of εHf values within cores supports crustal construction from individual, discreet pulses of magma. Since isotopic variations cannot develop through igneous differentiation processes, the wide range in values indicates derivation from a locally heterogeneous mantle source. Based on these observations, we propose that small-scale regions (<1 km) exhibit varying degrees of isotopic depletion, resulting either from differential melt extraction or refertilization in the geologic past. Considering geologically reasonable 176Lu/177Hf ratios of natural magmas, the observed εHf range would requires the development of these compositionally distinct mantle parcels between 550 million to 2 billion years ago.
Craig Grimes, Dr. (Advisor)
Greg Nadon, Dr. (Committee Member)
Doug Green, Dr. (Committee Member)
112 p.

Recommended Citations

Hide/Show APA Citation

Thomas, C. (2013). Hafnium Isotope Geochemistry of the Gabbroic Crust Sampled Along the Mid-Atlantic Ridge: Constraints on the Nature of the Upper Mantle. (Electronic Thesis or Dissertation). Retrieved from https://etd.ohiolink.edu/

Hide/Show MLA Citation

Thomas, Christine. "Hafnium Isotope Geochemistry of the Gabbroic Crust Sampled Along the Mid-Atlantic Ridge: Constraints on the Nature of the Upper Mantle." Electronic Thesis or Dissertation. Ohio University, 2013. OhioLINK Electronic Theses and Dissertations Center. 17 Oct 2017.

Hide/Show Chicago Citation

Thomas, Christine "Hafnium Isotope Geochemistry of the Gabbroic Crust Sampled Along the Mid-Atlantic Ridge: Constraints on the Nature of the Upper Mantle." Electronic Thesis or Dissertation. Ohio University, 2013. https://etd.ohiolink.edu/

Files

Thomas, Christine accepted thesis 04-23-13 Su 13.pdf (10.74 MB) View|Download