A large scale isotope anomaly in the southern hemisphere mantle
This presentation is the property of its rightful owner.
Sponsored Links
1 / 11

A Large-scale isotope anomaly in the Southern Hemisphere mantle PowerPoint PPT Presentation


  • 82 Views
  • Uploaded on
  • Presentation posted in: General

A Large-scale isotope anomaly in the Southern Hemisphere mantle. Stanley R. Hart. Figure 14-9. (Winter) From Hart (1984) Nature, 309, 753-756. Can Generate tholeiitic and alkaline basalts from a chemically uniform mantle. Variables Temperature Pressure.

Download Presentation

A Large-scale isotope anomaly in the Southern Hemisphere mantle

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


A large scale isotope anomaly in the southern hemisphere mantle

A Large-scale isotope anomaly in the Southern Hemisphere mantle

Stanley R. Hart


A large scale isotope anomaly in the southern hemisphere mantle

Figure 14-9. (Winter) From Hart (1984) Nature, 309, 753-756.


Can generate tholeiitic and alkaline basalts from a chemically uniform mantle

Can Generate tholeiitic and alkaline basalts from a chemically uniform mantle

Variables

  • Temperature

  • Pressure

Figure 10-2 (Winter) Phase diagram of aluminous lherzolite with melting interval (gray), sub-solidus reactions, and geothermal gradient. After Wyllie, P. J. (1981). Geol. Rundsch. 70, 128-153.


Trace elements rees

Trace Elements: REEs

Figure 14-2. (Winter) After Wilson (1989) Igneous Petrogenesis. Kluwer.


Isotope geochemistry

Isotope Geochemistry

  • Isotopes do not fractionate during partial melting of fractional melting processes, so will reflect the characteristics of the source

  • OIBs, which sample a great expanse of oceanic mantle in places where crustal contamination is minimal, provide incomparable evidence as to the nature of the mantle


Pb isotopes

Pb Isotopes

Pb produced by radioactive decay of U & Th

238U 234U 206Pb

235U 207Pb

232Th 208Pb


A large scale isotope anomaly in the southern hemisphere mantle

Pb is quite scarce in the mantle

  • Mantle-derived melts susceptible to contamination

  • U, Pb, and Th are concentrated in continental crust (high radiogenic daughter Pb isotopes)

  • 204Pb is non-radiogenic, so 208Pb/204Pb, 207Pb/204Pb, and 206Pb/204Pb increase as U and Th decay

  • Oceanic crust has elevated U and Th content (compared to the mantle) as will sediments derived from oceanic and continental crust

  • Pb is a sensitive measure of crustal (including sediment) components in mantle isotopic systems


A large scale isotope anomaly in the southern hemisphere mantle

Figure 14-8. After Wilson (1989) Igneous Petrogenesis. Kluwer. Data from Hamelin and Allègre (1985), Hart (1984), Vidal et al. (1984).


A large scale isotope anomaly in the southern hemisphere mantle

  • Can map the geographic distribution of the isotopic data

Figure 14-9. From Hart (1984) Nature, 309, 753-756.


A large scale isotope anomaly in the southern hemisphere mantle

  • Isotopically enriched reservoirs (EMI, EMII, and HIMU) are too enriched for any known mantle process, and they correspond to crustal rocks and/or sediments

  • EMI (slightly enriched) correlates with lower continental crust or oceanic crust

  • EMII is more enriched, especially in radiogenic Sr (indicating the Rb parent) and Pb (U/Th parents) correlates with the upper continental crust or ocean-island crust


A large scale isotope anomaly in the southern hemisphere mantle

A Model for Oceanic Magmatism

Continental

Reservoirs

DM

OIB

EM and HIMU from crustal sources (subducted OC + CC seds)

Figure 14-10. Nomenclature from Zindler and Hart (1986). After Wilson (1989) and Rollinson (1993).


  • Login