page_title: Lutetium–hafnium dating
section_title: ɛHf value implications
hierarchical_section_title: Lutetium–hafnium dating / Epsilon (ɛHf value) / ɛHf value implications
caption_attribution_description: English: ɛHf plot.
context_page_description: Lutetium–hafnium dating is a geochronological dating method utilizing the radioactive decay system of lutetium–176 to hafnium–176. With a commonly accepted half-life of 37.1 billion years, the long-living Lu–Hf decay pair survives through geological time scales, thus is useful in geological studies. Due to chemical properties of the two elements, namely their valences and ionic radii, Lu is usually found in trace amount in rare-earth element loving minerals, such as garnet and phosphates, while Hf is usually found in trace amount in zirconium-rich minerals, such as zircon, baddeleyite and zirkelite.
  The trace concentration of the Lu and Hf in earth materials posed some technological difficulties in using Lu–Hf dating extensively in the 1980s. With the use of inductively coupled plasma mass spectrometry with multi-collector in later years, the dating method is made applicable to date diverse earth materials. The Lu–Hf system is now a common tool in geological studies such as igneous and metamorphic rock petrogenesis, early earth mantle-crust differentiation, and provenance.
context_section_description: ɛHf values are closely related to the enrichment or depletion of Hf relative to the chondritic uniform reservoir. A positive ɛHf value means that ¹⁷⁶Hf concentration in sample is larger than that of chondritic uniform reservoir. This also means a higher Lu/Hf ratio in sample. Positive value would be found in the residue solid after melt extraction, as the liquid would be enriched in Hf. It is worth noting that the enrichment of Hf in melt would means removing the more abundant isotopes of Hf to a larger extent than ¹⁷⁶Hf, resulting in the observed ¹⁷⁶Hf/¹⁷⁷Hf enrichment in residue solid. Using the same logic, a negative ɛHf value would represent the extracted melt from reservoir, forming an evolved, juvenile material.
  The original figure 9 from Rehman et al. (2012) showed an intermedia, mixed ɛHf trend for the eclogites that was studied. The experimental result indicate that the eclogites were formed from ocean-island basalt with contamination from sediments to produce the intermediate ɛHf values.
caption: Original figure 9 from Rehman et al. (2012);[11] An example of ɛHf plot.
exif: {"Image XResolution": "200", "Image YResolution": "200", "Image ResolutionUnit": "Pixels/Inch", "Image ExifOffset": "78", "EXIF ExifImageWidth": "1028", "EXIF ExifImageLength": "672"}