Crustal and Upper Mantle Xenoliths Mantle xenoliths, pieces of rock carried to the surface by volcanoes, are the only way to see the deep rocky interior of the Earth, called the mantle, directly. The name means "strange stone" in scientific Greek. Nearly everything we know about the rocks of the deep crust, and the Earth's mantle beneath it, comes from xenoliths found in lava. Diamonds come from xenoliths that originated hundreds of kilometers below the ground. But xenoliths might also be bits of a volcano's throat at shallow levels. When limestone, for instance, is engulfed by lava, the results are spectacular metamorphic minerals.

Large Igneous Provinces. Mantle Melts. < A Large Igneous Province (LIP) is an extremely large accumulation of igneous rocks—intrusive, extrusive, or both—in the earth's crust. In 1992 researchers first used the term 'large igneous province' to describe very large accumulations—areas greater than 100,000 square kilometers (slightly larger than the area of Portugal)— of mafic igneous rocks that were erupted or emplaced at depth within an extremely short geological time interval—a few million years or less. The definition of 'LIP' is now used to describe voluminous areas of, not just mafic, but all types of igneous rocks. The source of many or all LIPs are variously attributed to mantle plumes or to processes associated with plate tectonics. Some LIPs are now intact, such the basaltic Deccan Traps in India, while others have been dismembered by plate tectonic motion, like the basaltic Central Atlantic Magmatic Province (CAMP)—parts of which are found in Brazil, eastern North America, and north-western Africa. Melting in the mantle is a complex process which produces variable amounts of melted material of different mineral composition depending on the conditions during the formation. Important points are: - The melting process itself. Three melting styles are usually considered: Batch, fractional, and assimilative melting. Since melts react with solids as they ascend, the time scale of melting becomes important. - The temperature needed to melt mantle rock increases with pressure and hence depth. - Volatiles (such as the best studied one, water) decrease the melting temperature.