[Widdekind]

When new Oceanic Crust is created, at Mid-Ocean Ridges, it is hot, and, hence, light and comparatively buoyant. But, by the time that Oceanic Crust has migrated across its Oceanic Tectonic Plate, and at last reaches a deep Subduction Trench, many millions of years later, it is colder and denser, and so sinks down deeper. Indeed, the downward sinking of Oceanic Crusts at Subduction Trenches drives the movement of Oceanic Tectonic Plates, by pulling the rest of their Oceanic Tectonic Plates away from the Mid-Ocean Ridges, and allowing Mantle Magma to "passively rise up between the spreading plates"*.

* History Channel How the Earth was Made -- Deepest Trench (TV)

CONCLUSION: Planetary Crusts thicken as they age, and cool. For example, Mars' Crust is probably about twice as thick as Earth's*. Thus, the sinking of Oceanic Crusts conceivably comes about by Under-Plating, as more and more Mantle Magma accretes onto the underside of that Oceanic Crust.

* Thomas T. Arny. Explorations (1st. Ed.), pg. 479. Cf. http://www.astronomyforum.net/moon-...rigid-than-near-side.html

Moreover, Oceanic Crust "consists mostly of basaltic rock overlain by muddy sediments"*. So, assuming that Sedimentation Rates, from the overlying Oceans, are approximately constant, than the accumulating "Sedimentary Mud Load" burdening Oceanic Tectonic Plates may progressively produce enough pressure to increasingly sink the seafloor, as well.

* http://www.tiscali.co.uk/reference/.../hutchinson/m0006375.html

Under-Plating (from below) and Sedimentation (from above) could conceivably combine to push sea-floors deeper down into the Mantle.

[Geosciences-Forum.com]

Log dich ein, um die Werbung auszublenden und alle Funktionen nutzen zu können.

[Widdekind]

[Platzhalter für ein Bild]
Figure 1. Schematic Diagram of Oceanic Crustal Accretion Processes

[Geosciences-Forum.com]

Log dich ein, um die Werbung auszublenden und alle Funktionen nutzen zu können.

[Widdekind]

Revision -- Update:

When new Oceanic Crust is created, at Mid-Ocean Ridges, it is hot, and, hence, light and comparatively buoyant. But, by the time that Oceanic Crust has migrated across its Oceanic Tectonic Plate, and at last reaches a deep Subduction Trench, many millions of years later, it is colder and denser, and so sinks down deeper. Indeed, the downward sinking of Oceanic Crusts at Subduction Trenches drives the movement of Oceanic Tectonic Plates, by pulling the rest of their Oceanic Tectonic Plates away from the Mid-Ocean Ridges, and allowing Mantle Magma to "passively rise up between the spreading plates"*.

* History Channel How the Earth was Made -- Deepest Trench (TV)

CONCLUSION: Planetary Crusts thicken as they age, and cool. For example, Mars' Crust is probably about twice as thick as Earth's*. Thus, the sinking of Oceanic Crusts conceivably comes about by Under-Plating, as more and more Mantle Magma accretes onto the underside of that Oceanic Crust.

* Thomas T. Arny. Explorations (1st. Ed.), pg. 479. Cf. http://www.astronomyforum.net/moon-...rigid-than-near-side.html

Moreover, Oceanic Crust "consists mostly of basaltic rock overlain by muddy sediments"*. Indeed, these sediments are a "fine, light-colored silt" [paraphrase] which covers the oceans' Abyssal Plains, making them virtually featureless**. So, assuming that Sedimentation Rates, from the overlying Oceans, are approximately constant, than the accumulating "Sedimentary Mud Load" burdening Oceanic Tectonic Plates may progressively produce enough pressure to increasingly sink the seafloor, as well.

* http://www.tiscali.co.uk/reference/.../hutchinson/m0006375.html
** National Geographic Channel Naked Science -- Science of the Deep (TV)

Under-Plating (from below) and Sedimentation (from above) could conceivably combine to push sea-floors deeper down into the Mantle.