Igneous rocks found on the oceanic ridge cool quicker and are more compressed from the ocean’s pressure. rocks found at the oceanic ridge are the least ancient rocks on planet. (I hope that was what you were going for?)
Mount belts can form for different reasons. They can form through the subduction of a oceanic plate under a continental plate. In this type of mountain belt you can find some mafic(small silica) rock intermediate rock and felsic(more than 70% silica) rock. These contain basalt/gabbro in small amounts and mainly Andisite or maybe granite. An example would be the andes mountains in South America. the other form of mountian building is continent-continent collision and you really dont get new igneous rock.
In an oceanic ridge you have divergant plate motion(moving apart) which allows molten rock from the asthenosphere to surface. Since the asthenosphere contains ultramafic rock you get ultramafic-mafic rock(basalts, peridotites, and gabbros) at the ridge
Now in mountain building the molten rock is coming from the asthenosphere but as it moves up through the granite plate it goes through crystal fractionation(as it cools crystals form and change the chemistry) and melts the surounding rock. Both processes change the chemistry of the magma and thats why you get felsic and intermediate rock.
Igneous rocks found on the oceanic ridge cool quicker and are more compressed from the ocean’s pressure. rocks found at the oceanic ridge are the least ancient rocks on planet. (I hope that was what you were going for?)
Mount belts can form for different reasons. They can form through the subduction of a oceanic plate under a continental plate. In this type of mountain belt you can find some mafic(small silica) rock intermediate rock and felsic(more than 70% silica) rock. These contain basalt/gabbro in small amounts and mainly Andisite or maybe granite. An example would be the andes mountains in South America. the other form of mountian building is continent-continent collision and you really dont get new igneous rock.
In an oceanic ridge you have divergant plate motion(moving apart) which allows molten rock from the asthenosphere to surface. Since the asthenosphere contains ultramafic rock you get ultramafic-mafic rock(basalts, peridotites, and gabbros) at the ridge
Now in mountain building the molten rock is coming from the asthenosphere but as it moves up through the granite plate it goes through crystal fractionation(as it cools crystals form and change the chemistry) and melts the surounding rock. Both processes change the chemistry of the magma and thats why you get felsic and intermediate rock.