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M

Magma

A melt, generally containing suspended crystals and other volatiles, formed by total or partial melting of solid mantle or crustal material.

Mantle

The layer beneath the crust, but above the core in the interior of the Earth. It's composition is broadly that of ultrabasic rocks.

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Mare

Area of dark basaltic lava on the Moon (pl. Maria).

Melange

A melange is formed in the accretionary wedge as sediment and oceanic crust is scraped off the descending plate in a subduction zone. The melange comprises a strongly brecciated unit with large blocks of pre-existing rocks in a deformed fine grained matrix. Olistostromes are similar units but have a gravity sliding origin rather than a tectonic one. For a melange to be described as such it must be of mapable size, contain 'exotic' clasts (i.e. not derived from immediately adjacent units) and be matrix supported.

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Member

A division of a formation, generally of distinct lithologic character and of only local extent.

Mesozoic

Era comprising the Triassic, Jurassic and Cretaceous, spanning 245-65Ma.

Metamorphism

Metamorphosis require heat, pressure and time and is an extension of lithification, but it can occur on any rocks type (including metamorphic rocks). There is a continuum of type from heat dominated (marble) to pressure dominated (blueschist). Metamorphism is ranked in terms of a grade. A high grade metamorphic rock is a gneiss, which has undergone intense heat and pressure. It is important to note metamorphism occurs in the solid state - there is no melting. If the rock starts to melt it is called a migmatite (Mixed IGneous and metamorphic rock).

Micrite

Micro-crystalline carbonate mud.

Mineral

A naturally occurring homogeneous solid with a highly ordered lattice and of a defined chemical composition.

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