Igneous Rocks and Processes (A2) Flashcards
What are four factors which control melting?
Temperature, Pressure, Volatile content, Mineral mix
Define Serpentinite
Chemically weathered gabbro or peridotite through the hydrothermal alteration of olivine
What is an example of a fast spreading ridge?
East Pacific Rise
What is an example of a slow spreading ridge?
Mid Atlantic Ridge
Define Ocean Core Complex
Uplifted footwalls of very large offset, low angle normal faults that exhume lower crust and mantle rocks onto the sea floor at slow spreading ridges
Define Hot Spot
Area of volcanism that is located far from plate boundaries. Produced by mantle plume
Define Mantle Plume
Zones of hot solid mantle rising to the surface
What are two characteristics of a mantle plume?
Hot and Solid
What are four characteristics of eruptions associated with hot spots?
Low silica content, Low viscosity, Thin lava flows, Effusive eruptions
Define Igneous Provinces
Huge outpourings of basalt from a fissure eruption e.g. Deccan Traps
Define Flux Melting
If something can be added to the mantle, it could cause the solidus and liquidus temperatures to be lowered to the extent that the solidus could become lower than the geothermal gradient and result in partial melting without having to raise the geothermal gradient
What is evidence of water being added to the mantle at subduction zones?
Volcanoes release water vapour when erupting
Why can’t melt be generated at subduction zones via decompressional melting?
Decompressional melting occurs at divergent plate boundaries where hotter material rises to lower pressure. At subduction zones pressure increases with depth
Define Crustal Anatexis
Partially melting of continental crust
What are three potential mechanisms for making granite?
Magmatic processes, Underplating, Orogenesis
What does 147Sm decay into?
143Nd
Define Lopolith
Saucer shaped igneous body e.g. Bushveld Complex
Define Laccolith
Forcible intrusion with flat bottom and rounded top
Why are the minerals closer to the bottom of Bowen’s Reaction Series less likely to weather?
Formed at lower temperatures so more stable at earth’s surface
Define Differentiation
The way in which you can change the composition of magma by separating it into two different fractions
Define Fractional Crystallisation
The removal and segregation from the melt of mineral precipitates. This leads to a change in composition of a magma (always more quartz rich)
Define Gravity Settling
Dense minerals fall to the bottom of the magma chamber or igneous body
Define Cumulates
Layer at the bottom of the magma chamber/igneous body formed by gravity settling
Define Assimilation
Addition of country rock to a magma will cause it to change composition. Rocks get incorporated via stoping
Define Stoping
Magma forces its way through cracks then rips off part of the country rock to incorporate into melt
Define Xenolith
Blocks of country rock not fully melted. Adds new elements into the magma when the xenolith is melted
Define Enclave
Blob of magma with a different composition to the main host that is left after incomplete melting
