How much does a tectonic plate weigh?

An estimate of the mass of an "average" continental lithospheric plate is 40.7x1021 kg or forty sextillion, seven hundred quintillion kilograms.

It should be noted that this can only ever be considered a rough approximation of the order of magnitude of the mass of a lithospheric continental plate as there are so many unknowns. For example the exact thickness of the lithospheric plates, and the horizontal and vertical variations of density which can't be known exactly and so require the use of assumed or average values.

For the assumptions and working required to arrive at this value, please see the following:

This question is impossible to give an exact answer to as all the Earth's tectonic plates are of varying size and thickness and are composed of material that has varying densities with increasing depth.

However it may be possible to make a very rough estimate of the order of magnitude of the mass / weight of a tectonic plate as follows:

There are 8 major tectonic plates and a number of smaller ones. If it can be assumed that the major plates cover the majority of the Earth's surface (and that the minor plates are of negligible area) then it can be assumed that an average major plate has a surface area equal to 1/8 of the surface area of the Earth.

Earth's surface area = 510,072,000 km2

Average plate = 510,072,000 / 8 = 63,759,000 km2

We have to make a further assumption here about the average density and thickness of a tectonic plate in order to make an estimate of its mass and weight.

According to the Wikipedia entry (see the related links), typical Oceanic Lithosphere is on average 100 km thick and typical continental lithosphere is on average 200 km thick (obviously this varies significantly depending on the presence of mountain ranges etc. but is a reasonable assumption for a rough estimate).

Further to this an estimate must be made of the average density of both the oceanic and continental crusts as well as the upper brittle mantle which is also part of a tectonic plate.

According to the Wikipedia entry for the oceanic and continental crust, their average density is 3300 kg/m3 and 2750 kg/m3 respectively. Further to this, the upper 200-300 km of the mantle can be assumed to also have an average density of 3300 kg/m3 A

As such it is possible to estimate the mass of an "average" continental plate and an "average" oceanic plate or at least to gain an estimate of the order of magnitude.

Mass of an "average" continental plate:Average thickness of continental crust = 40 km

Volume of continental crustal portion of plate:

63,759,000,000,000 x 40,000

= 2.55036 x 1018 m3

Mass of continental crustal portion of plate

= 2.55036 x 1018 x 2,750 =

7.01349 x 1021 kg

Volume of continental lithospheric portion of plate:

63,759,000,000,000 x 160,000

= 1.020144 x 1019 m3

Mass of continental lithospheric portion of plate:

1.020144 x 1019 x 3,300

3.3664752 x 1022 kg

Total estimated mass of a continental lithospheric plate:

7.01349 x 1021 + 3.3664752 x 1022

= 4.0678242 x 1022 kg

=40,678,242,000,000,000,000,000 kg.

or 40.7x1021 kg

or forty sextillion, six hundred and seventy eight quintillion, two hundred and forty quadrillionkilograms.

Please see the related links.