T61 Life and Death of a Craton: Implications of Archean Crust-Keel Systems for Crustal Growth, Crustal Preservation, and Mantle Evolution

Sunday, 22 September 2019
1:30 PM - 5:30 PM
Room 131ABC, North Building

DENSITY STRUCTURE OF CRATONIC LITHOSPHERE MANTLE: A TALE OF FOUR CRATONS

Paper number: T61-2
Program: Technical Sessions
Time: 1:35 PM – 1:55 PM

Authors

Abstract

Geochemical studies of mantle-derived xenoliths indicate that the cratonic lithospheric mantle has a unique depleted composition such that it has low bulk density at SPT (room pressure-temperature) conditions. However, the nature’s sampling is uneven, sparse, and possibly biased. Here we calculate and compare mantle density structure of four cratonic regions: the East European craton (including the Baltic and Ukrainian shields), the Siberian, the North China, and the Kaapvaal cratons. Our calculations are based on gravity and free-board modeling for in situ mantle density, which we then convert to SPT density by introducing a temperature correction and compare with global and regional xenolith data.

In all studied regions, the cratonic lithospheric mantle has a highly heterogeneous density structure. In Europe, a low density mantle (3.32 g/cm3) beneath the Archean-early Proterozoic shields of Baltica and Greenland corresponds to the known kimberlite provinces and we find a strong correlation between mantle density and the occurrence of diamondiferous kimberlites. In Siberia and Kaapvaal, kimberlites sample exclusively those parts of the mantle where the isopycnic condition is satisfied, while the pristine lithospheric mantle which has not been affected by magmatism has a significantly lower SPT density. In the North China craton, only a part of the Trans-North China Orogen retains the density structure typical of the Archean undisturbed cratonic lithosphere, while most of the craton has density values typical of fertile Proterozoic and Phanerozoic lithospheric mantle. Deep intracratonic basins have a very dense mantle (>3.40 g/cm3), which indicates that eclogitization may have played an important role in their formation. Our results indicate that most of the Archean lithospheric mantle has been significantly reworked by tectono-magmatic processes and kimberlite-hosted xenoliths provide deceptive basis for density of the Archean lithosphere mantle.

Geological Society of America Abstracts with Programs. Vol. 51, No. 5

doi: 10.1130/abs/2019AM-335680

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