A global 1deg x 1deg thermal model for the continental lithosphere TC1 is an update of the 2001 model, it fills-in "white spots" with no heat flow measurements. |
THERMAL THICKNESS AND EVOLUTION OF
PRECAMBRIAN LITHOSPHERE:
A GLOBAL STUDY
The thermal thickness of Precambrian lithosphere is modeled and
compared with estimates from seismic tomography and xenolith data. We
use the steady-state thermal conductivity equation with the same
geothermal constraints for all of the Precambrian cratons (except
Antarctica) to calculate the temperature distribution in the stable continental
lithosphere. The modeling is based on the global compilation of heat flow
data by Pollack et al. (1993) and more recent data. The depth distribution
of heat-producing elements is estimated using regional models for about
300 blocks with sizes varying from 1deg x 1deg to about 5deg x 5deg in
latitude and longitude and is constrained by laboratory, seismic and
petrologic data and, where applicable, empirical heat flow/heat production
relationships.
Maps of the lateral temperature distribution at depths 50, 100 and 150 km
are presented for all continents except Antarctica. The thermal thickness of
the lithosphere is calculated assuming a conductive layer overlying the
mantle with an adiabat of 1300 oC. The Archean and early Proterozoic
lithosphere is found to have two typical thicknesses, 200-220 km and
300-350 km. In general, thin (~ 220 km) roots are found for Archean and
early Proterozoic cratons in the southern hemisphere (South Africa,
Western Australia, South America and India) and thicker (>300 km) roots
are found in the northern hemisphere (Baltic Shield, Siberian Platform,
West Africa, and possibly the Canadian Shield).
We find that the thickness of continental lithosphere generally decreases
with age, from >200 km beneath Archean cratons, to intermediate values
of 200+/-50 km in early Proterozoic lithosphere, to about 140+/-50 km in
middle and late Proterozoic cratons. Using known crustal thickness, our
calculated geotherms, and assuming that isostatic balance is achieved at the
base of the lithosphere, we find that Archean and early Proterozoic mantle
lithosphere is 1.5% less dense (chemically depleted) than the underlying
asthenosphere, while middle and late Proterozoic sub-crustal lithosphere
should be depleted by ~ 0.6-0.7 %. Our results suggest three contrasting
stages of lithosphere formation at the following ages: >2.5 Ga, 2.5-1.8 Ga,
and <1.8 Ga. Ages of komatiites, greenstone belts, and giant dike swarms
broadly define similar stages, and apparently reflect secular changes in
mantle temperature and, possibly, convection patterns.
PRECAMBRIAN LITHOSPHERE:
A GLOBAL STUDY
The thermal thickness of Precambrian lithosphere is modeled and
compared with estimates from seismic tomography and xenolith data. We
use the steady-state thermal conductivity equation with the same
geothermal constraints for all of the Precambrian cratons (except
Antarctica) to calculate the temperature distribution in the stable continental
lithosphere. The modeling is based on the global compilation of heat flow
data by Pollack et al. (1993) and more recent data. The depth distribution
of heat-producing elements is estimated using regional models for about
300 blocks with sizes varying from 1deg x 1deg to about 5deg x 5deg in
latitude and longitude and is constrained by laboratory, seismic and
petrologic data and, where applicable, empirical heat flow/heat production
relationships.
Maps of the lateral temperature distribution at depths 50, 100 and 150 km
are presented for all continents except Antarctica. The thermal thickness of
the lithosphere is calculated assuming a conductive layer overlying the
mantle with an adiabat of 1300 oC. The Archean and early Proterozoic
lithosphere is found to have two typical thicknesses, 200-220 km and
300-350 km. In general, thin (~ 220 km) roots are found for Archean and
early Proterozoic cratons in the southern hemisphere (South Africa,
Western Australia, South America and India) and thicker (>300 km) roots
are found in the northern hemisphere (Baltic Shield, Siberian Platform,
West Africa, and possibly the Canadian Shield).
We find that the thickness of continental lithosphere generally decreases
with age, from >200 km beneath Archean cratons, to intermediate values
of 200+/-50 km in early Proterozoic lithosphere, to about 140+/-50 km in
middle and late Proterozoic cratons. Using known crustal thickness, our
calculated geotherms, and assuming that isostatic balance is achieved at the
base of the lithosphere, we find that Archean and early Proterozoic mantle
lithosphere is 1.5% less dense (chemically depleted) than the underlying
asthenosphere, while middle and late Proterozoic sub-crustal lithosphere
should be depleted by ~ 0.6-0.7 %. Our results suggest three contrasting
stages of lithosphere formation at the following ages: >2.5 Ga, 2.5-1.8 Ga,
and <1.8 Ga. Ages of komatiites, greenstone belts, and giant dike swarms
broadly define similar stages, and apparently reflect secular changes in
mantle temperature and, possibly, convection patterns.
| Double-click to enlarge the maps |
| Map of Precambrian cratons |
| Temperature at 50 km depth |
| Locations of heat flow measurements |
| Temperature at 100 km depth |
| Surface heat flow |
| Mantle heat flow |
| Lithospheric thermal thickness versus geologic age |
| Last modified December, 2004; irina@swave.wr.usgs.gov |
| Temperature at 150 km depth |
| Artemieva I.M. and Mooney W.D., 2001. Journal Geophysical Research, v.106(B), 16387-16414 |
- THE CONTINENTAL LITHOSPHERE
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- THE CONTINENTAL LITHOSPHERE
| THERMAL REGIME, STRUCTURE, AND EVOLUTION OF |
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