With lots of discussions with Adam Dziewonski, Rick O’Oconnell

What do noble gases really say about mantle What do noble gases really say about mantle convection and the deep Earth volatile cyclesconvection and the deep Earth volatile cycles

Work done with Helge Gonnermann, Rice

After Barfod, 1999

MORBs: sample well-mixed degassed mantle with low 3He/U+Th

OIBs: sample heterogeneous, less degassed mantle with high 3He/U+Th

Preserving noble gases in a convecting mantleGonnermann and Mukhopadhyay, Nature 2009

UM concentrationfrom ocean He flux

~50% of slabs have gone into lower mantle over Earth history.

The upper mantle has passed through the ridge system 3-7 times.

Mass flux out of lower mantle = 0.5-1 times lower mantle mass. Very limited direct mixing between upper and lower mantle.

A toy model for the carbon cycle

qtfoeCtC )1()(

50% of slabs circulate in lower mantle and small degree of direct coupling between upper and lower mantle

For q=1 (lower mantle), C/3He increases by 1.8; ~50% of C in LM still primordial.

For q=5 (upper mantle), C/3He increases by 46; essentially no primordial C.

.Initial C/3He is ~0.7 -1 x 108, present day C/3He is ~1-2 x108 in LM and ~2-3 x 109 in UM.C content of BSE is 80-250 ppm. Zhang&Zindler (1993) ->100 ppm

Are there two distinct reservoirs in the mantle with 129Xe anomalies?

Are there two distinct reservoirs in the mantle with 129Xe anomalies?

The solid Earth volatile cycle

If we put strong constraints on production rates of tectonic plates and how the flux of subducted plates is partitioned between upper and lower mantle, we can start putting strong constraints on volatile cycles and the injection of oxidants into the mantle.

5 RA

50 RA

8 RA

3H

e/4

He

50 RA

5 RA

FOZO

HIMU EM1 EM2

DMM

Estimated CO2 contents in parental magmas

Based on measured noble gases in erupted lavas water depth