Continental Crusts

In contrast to the relatively simple volcanic seafloor crusts, continental crust is made up of a diverse range of present-day to ancient rocks dating back to the earliest Archaean times (some 4,000 million years ago).

On each of the small Earth models the continental rocks can be visualised as a mosaic of continental crustal domains which are broadly made up of three dominant crustal types. In geology, these crustal types are referred to as cratons, orogens, and basins. These terms are defined as:

• A craton is defined as a part of the Earth's crust that has attained relative crustal stability and the rocks have been little deformed for a prolonged period of time. By definition, these rocks must have reached crustal stability by about 2,400 million years ago (the end of the Archaean Eon) and since then have undergone little deformation compared to adjacent parts of the crust.

• An orogen refers to a belt of rocks characterised by regional folding, metamorphism, and intrusion of magmatic rocks. The rocks of an orogen can include deformed, eroded, and reworked parts of older, early-formed cratons, as well as young volcanic and sedimentary rocks. A distinct tectonic phase of Earth movement, over a relatively short period of time, first establishes an orogen. It is also possible for an orogen to become re-activated during subsequent tectonic events and the belt normally remains as a permanent zone of relative weakness within the Earth's crust.

• A basin refers to an area that is underlain by a substantial thickness of sedimentary rocks. These rocks possess unifying characteristics of both sediment type and deformation history. Within a basin, sediments are deposited during a regionally restricted period of time, often extending for tens to hundreds of millions of years, during crustal depression or a related sequence of such events. The term basin is usually synonymous with the term sedimentary basin and it represents a regional topographical down-warp of the Earth's surface, generally filled with water.

Construction of Palaeozoic and Precambrian Expansion Tectonic small Earth models involves the progressive removal of all younger basin sediments and magmatic rocks and simply returning these rocks to the ancient lands or back to the mantle where they came from. Each basin is then progressively restored to a pre-stretching or pre-rifting configuration on a smaller sized Earth model. By moving back in time, adopting this process enables the adjacent margins of each sedimentary basin to be moved closer together as part of one seamless ancient supercontinental crust, while still preserving the spatial integrity of the adjacent, more ancient, crusts.

•	A craton is defined as a part of the Earth's crust that has attained relative crustal stability and the rocks have been little deformed for a prolonged period of time. By definition, these rocks must have reached crustal stability by about 2,400 million years ago (the end of the Archaean Eon) and since then have undergone little deformation compared to adjacent parts of the crust.
•	An orogen refers to a belt of rocks characterised by regional folding, metamorphism, and intrusion of magmatic rocks. The rocks of an orogen can include deformed, eroded, and reworked parts of older, early-formed cratons, as well as young volcanic and sedimentary rocks. A distinct tectonic phase of Earth movement, over a relatively short period of time, first establishes an orogen. It is also possible for an orogen to become re-activated during subsequent tectonic events and the belt normally remains as a permanent zone of relative weakness within the Earth's crust.
•	A basin refers to an area that is underlain by a substantial thickness of sedimentary rocks. These rocks possess unifying characteristics of both sediment type and deformation history. Within a basin, sediments are deposited during a regionally restricted period of time, often extending for tens to hundreds of millions of years, during crustal depression or a related sequence of such events. The term basin is usually synonymous with the term sedimentary basin and it represents a regional topographical down-warp of the Earth's surface, generally filled with water.