Science Olympiad Dynamic Planet Practice Test

What type of terrane is formed when a crustal fragment does not subduct but is instead accreted to an overriding plate?

1. Accreting terrane

2. Orogenic terrane

3. Tectonostratigraphic terrane

4. Stable terrane

The correct answer is: Accreting terrane

An accreting terrane is formed when a crustal fragment, which may be a piece of continental crust or island arc, is pushed against an overriding tectonic plate instead of being subducted beneath it. This process occurs along convergent plate boundaries where tectonic plates interact. When these fragments collide with a continental margin, they can become welded onto the existing crust through complex geological processes, thereby forming what is known as an accreting terrane. Accreting terranes are significant in understanding geological history and evolution, as they provide insights into the movement of tectonic plates and the assembly of continents over geological timescales. Each accreted terrane has a unique geological history and can include diverse rock types and structures, reflecting their origin and the conditions under which they were formed. In contrast, orogenic terranes are specifically associated with mountain-building processes and do not necessarily focus on the accretion aspect. Tectonostratigraphic terranes refer to geological units categorized based on their tectonic and stratigraphic characteristics, and stable terranes are regions that have not been significantly affected by tectonic forces for long periods.