Thermal controls of crustal diapirism: implications for the earliest crust and sub-cratonic

lithosphere

Catherine Robin

&

Richard Bailey

Neutrino Geoscience

Sudbury, 2008

1028

1026

1024

1022

1020

1018

1016

Viscosity (Pa s)

Intermediate:H = 7 W/m3

qm = 25 mW/m2

Hot:H = 10 W/m3

qm = 40 mW/m2

Cold:H = 5 W/m3

qm = 20 mW/m2

Implications:• Predominantly vertical (diapiric) crustal tectonics in the Early Earth; but also:

• Supplies metabasalts to the lower crust to form TTGs (tonalites, trondhjemites and granodiorites)

• Leaves a depleted restite which can be harzburgitic to dunitic (for komatiitic volcanism), and which can accumulate from the top-down to form the SCLM (sub-cratonic lithospheric mantle), without calling on large plumes or strong horizontal plates (but doesn’t preclude some of these)

The plausibility of vertical tectonics (and the transition to modern-day tectonics) depends on the assumed heat source distribution and mode of volcanism of the early earth, and on its evolution with time.

Thanks!