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SUMMARY:Effects of source heterogeneity on segmentation and melt productio
 n at mid-ocean ridges - Vincent Salters\, Florida State
DTSTART:20131029T163000Z
DTEND:20131029T173000Z
UID:TALK47483@talks.cam.ac.uk
CONTACT:John Maclennan
DESCRIPTION:New trace element abundances and isotope compositions (Sr\, Nd
 \, Hf and Pb) of mid-ocean ridge basalts from 5.5-19 degrees N East Pacifi
 c Rise show systematic variations along the ridge axis that coincide with 
 ridge discontinuities.  Two adjacent ridge segments are different in both 
 isotopic and trace element systematics and thus source. \nThe compositiona
 l variability along the northern EPR can be explained by three components:
  a depleted component\, an enriched one and a component similar to recycle
 d gabbro. Our high-resolution sampling indicates that on a segment-scale t
 wo “local” components are needed to explain the chemical variability w
 ithin the individual ridge segments and two adjacent segments have\, at mo
 st\, one “local” component in common. These segment-scale “local” 
 components are a combination of the three end members.  The coincidence of
  distinct source compositions in adjacent ridge segments indicates that so
 urce composition influences segmentation.  \nUltra depleted mantle is an o
 ften ignored component of the asthenosphere because\, by virtue of its nat
 ure\, it is hard to recognize.  Our isotope studies of abyssal peridotite 
 show that an ultra depleted component is present and sometimes abundant.  
 The Hf-Nd isotope variations in MORB also indicate the presence of an ultr
 a depleted component.  Such component will yield little or no melt during 
 ascent under a ridge and thus reduce overall melt productivity and allows 
 models where even for thin crust melting starts deep\, i.e. in the garnet 
 stability field.  \nOur data also allows calculation of the model age of d
 epletion of a abyssal peridotite.  Lu-Hf and Sm-Nd model ages on abyssal p
 eridotites are all relatively young (up to 2.4Ga) and are consistent with 
 multiple depletion and enrichment events.
LOCATION:Harker 1 seminar room\, Department of Earth Sciences
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