The Helium, Neon

1

• The Helium, Neon Carbon Footprints of the Mantle

2
Ratios gt 9 or 12 are conventionally attributed to
the deepest mantlethey could be the shallowest
W.Greenland
such materials have very low 3He
Concave up
plume or perisphere?
DM
continent
3
MORB has much higher helium contents than the
primitive component
High 3He/4He, low 3He
FOZO
sequence
Mixing lines
4He(FOZO)/4He(MORB)1
1/33
Juan Fernandez
EM
Variable LIL isotopes, converge on 8 Ra
Haleakala
Hanyu et al 2005
4
carbonatites
Iceland
DM
Natland 2004
5
In all variants of the standard model, OIB gases
are considered to be the residue of massive
degassing
Gonnermann Mukhopadhyay with additions
Degassed MORB has more 3He than OIB
mixing
Retained or residual gas
3He
MORB
Expelled gas
Loihi
3He/22Ne
MORB degassing
OIB
Popping rock
the gap paradox
W.Greenland Baffin Bay
Seawater, air, trapped exsolved gases, shallow
mantle
3He
In the Canonical Model OIB contains residual gas.
In the perisphere model OIB picks up old
exsolved gases plus air-like gas
6
Nucleogenic ingrowth or addition
Seawater addition
Air seawater
Louisville
radiogenic
7
(No Transcript)
8
(No Transcript)
9
Figure 5 Plot of 3He/22Ne vs. 4He/21Ne (from,
Dixon et al., 2001).
10
Louisville most OIB have orders of magnitude
less He Ne than MORB
Many MORB have values this high
11
Highest R/Ra

• 21/22 0.030-0.04
• 20/22 9.9-10.3
• 208/204 37.5-38.8
• 206/204 17.4-19.0
• 143/144 .5132-.5126
• 87/86 .703-.704
• Data defines curvilinear triangles between
  endmembers with curvature implying low 3He for
  high 3He/4He solar components

12
air
Definitions
Exsolved gas Expelled gas Trapped gas Secondary
gas Orphaned He Ne
Low 3He/22Ne Low 4He/21Ne Low 4He/40Ar Ancient
3He/4He
OIB
This step is not involved in Canonical Models for
LIL
Separation of He Ne from U Th
gas
MORB
magma
Residual gas, dissolved gas, high 3He/22Ne etc.
13
High 3He/4He (R/Ra) low 21/22 simply reflect
ancient separation of He U,Th (4He 21Ne
producers). U,Th-poor lithologies are buoyant
(perisphere)
350 300 250 200 150 100 50 0
300
Rapid decay in U,Th-rich and/or gas poor mantle
Slow decay in gas-rich or U,Th-poor mantle
R/Ra
The perisphere has very little in it that is of
interest to isotope geochemists
Shallow perisphere
MORB-mantle (popping rock based)
4 3 2
1 0
except the solution to the Pb, Os He paradoxes!
Age (Ga)
After Porcelli Pepin 2008
14
Mixing curves

• OIB MORB data define triangular regions with
  essentially no data beyond the linear sides
• This implies that He/Sr, He/Ne (high R/Ra) etc.
  is or lt He/Sr (MORB other OIB)
• Observed 3He concentrations in MORB are gtgt than
  in OIB
• MORB-like R/Ra is the floor of the triangle the
  terminus of OIB fields
• Mixing components are DM, PM/solar,
  seawater/air IDP in sediments